FREEZE-DRIED POLYMER COMPOSITIONS FOR MIXING WITH PLATELET RICH PLASMA TO FORM IMPLANTS FOR TISSUE REPAIR AND/OR COMPOSITIONS FOR THERAPEUTIC INTRA-ARTICULAR INJECTIONS

Abstract

The present application relates to a freeze-dried polymer composition containing chitosan and at least one lyoprotectant, a process for preparing a freeze-dried composition containing chitosan and at least one lyoprotectant and the use of a reconstituted freeze-dried chitosan composition to prepare implants for tissue repair.

Claims

1. A freeze-dried homogeneous solid cake comprising chitosan having a molecular weight number of from about 4 kDa to about 250 kDa and a degree of deacetylation of from about 80% to about 85%, a clot activating amount of a clot activator, and at least one lyoprotectant, wherein said composition is without glycerol phosphate and said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution forming an injectable solution which upon injection: i) into tissue solidifies forming an implant for tissue repair; or ii) into an articular joint mixes with intra-articular fluids.

2. The freeze-dried homogeneous solid cake of claim 1 wherein the at least one lyoprotectant is selected from the group consisting of monosaccharide, polyol, disaccharide, trisaccharide, oligosaccharide/polysaccharide, high molecular weight excipient, amino acid, protein and a combination thereof.

3. The freeze-dried homogeneous solid cake of claim 1 wherein the chitosan has a molecular weight number from about 20 to about 250 kDa.

4. The freeze-dried homogeneous solid cake of claim 1 wherein the chitosan is present from about 0.25% to about 10% w/v.

5. The freeze-dried homogeneous solid cake of claim 1 wherein the at least one lyoprotectant is present from about 0.1% to about 30% w/v.

6. The freeze-dried homogeneous solid cake of claim 1 wherein the clot activator is selected from the group consisting of calcium chloride, calcium gluconate, calcium acetate, calcium carbonate, calcium glubionate, calcium gluceptate, calcium lactate, calcium lactobionate, calcium phosphate and combinations thereof.

7. A process for preparing a freeze-dried homogeneous solid cake comprising the steps of: a) contacting chitosan with water to form a chitosan/water aqueous mixture, b) contacting the aqueous mixture with at least one lyoprotectant, c) contacting the aqueous mixture with a clot activating amount of at least one clot activator forming a chitosan/water/clot activator mixture, d) sterilizing the chitosan, the at least one lyoprotectant and the at least one clot activator, individually, prior to mixing, or after addition of the at least one lyoprotectant and the at least one clot activator to said chitosan/water aqueous mixture; and e) freeze-drying the chitosan/water/clot activator mixture.

8. The process of claim 7 wherein the chitosan has a molecular weight number from about 4 to about 250 kDa.

9. The process of claim 7 wherein the chitosan is present from about 0.25% to about 10% w/v.

10. The process of claim 7 wherein the at least one lyoprotectant is selected from the group consisting of monosaccharide, polyol, disaccharide, trisaccharide, oligosaccharide/polysaccharide, high molecular weight excipient, amino acid, protein and a combination thereof.

11. The process of claim 7 wherein the at least one lyoprotectant is present from about 0.1% to about 30% w/v.

12. A freeze-dried homogeneous solid cake consisting of: chitosan at a concentration of no more than about 1% (w/v), having a molecular weight in the range of about M.sub.n 28 to about 56 kDa and at least one lyoprotectant at a concentration of no more than about 4% (w/v), wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution, wherein said freeze-dried homogenous solid cake further comprises a clot activating amount of a clot activator.

13. A freeze-dried homogeneous solid cake consisting of: chitosan at a concentration of no more than about 0.56% (w/v), having a molecular weight in the range of about M.sub.n 89 to about 108 kDa and at least one lyoprotectant at a concentration of no more than about 4% (w/v), wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution, wherein said freeze-dried homogenous solid cake further comprises a clot activating amount of a clot activator.

14. A freeze-dried homogeneous solid cake comprising: chitosan at a concentration range of about 0.42 and about 2% (w/v), having a molecular weight range of about M.sub.n 4 kDa to about 211 kDa and a degree of deacetylation of from about 80% to about 85%, at least one lyoprotectant at a concentration range between about 1 and about 10%, and a salt or a buffer, and being without glycerol phosphate, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution, wherein said salt is a clot activator present in a clot activating amount.

15. A freeze-dried homogeneous solid cake comprising chitosan having a molecular weight number of from about 4 kDa to about 250 kDa and a degree of deacetylation of from about 80% to about 85% and at least one lyoprotectant, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution forming an injectable solution, exhibiting at least one of the following: in situ coagulation achieved and not inhibited; able to withstand mechanical loading post-implantation; inhibition of platelet-mediated clot retraction to fill tissue defects; good mixing without phase separation of polymers and PRP, blood product and combinations thereof; viscous and paste-like formulations for tissue repair applications; close-to-physiological properties for in vivo application; and combinations thereof, wherein said freeze-dried homogenous solid cake further comprises a clot activating amount of a clot activator.

16. The freeze-dried homogeneous solid cake of claim 12 wherein said composition is without glycerol phosphate.

17. The freeze-dried homogeneous solid cake of claim 13 wherein said composition is without glycerol phosphate.

18. A freeze-dried homogeneous solid cake consisting of: chitosan at a concentration range of about 0.42 and about 2% (w/v), having a molecular weight range of about M.sub.n 4 to about 211 kDa and a degree of deacetylation of from about 80% to about 85%, at least one lyoprotectant at a concentration range between about 1 and about 10%, and a salt or a buffer, and being without glycerol phosphate, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution, wherein said salt is a clot activator present in a clot activating amount.

19. A freeze-dried homogeneous solid cake consisting of chitosan having a molecular weight number of from about 4 kDa to about 250 kDa and a degree of deacetylation of from about 80% to about 85%, a clot activating amount of a clot activator and at least one lyoprotectant, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution forming an injectable solution, exhibiting at least one of the following: in situ coagulation achieved and not inhibited; able to withstand mechanical loading post-implantation; inhibition of platelet-mediated clot retraction to fill tissue defects; good mixing without phase separation of polymers and PRP, blood product and combinations thereof; viscous and paste-like formulations for tissue repair applications; close-to-physiological properties for in vivo application; and combinations thereof.

20. The freeze-dried homogenous solid cake of claim 1 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

21. The freeze-dried homogeneous solid cake of claim 12 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

22. A freeze-dried homogeneous solid cake consisting of: chitosan at a concentration of no more than about 1% (w/v), having a molecular weight in the range of about M.sub.n 28 to about 56 kDa, at least one lyoprotectant at a concentration of no more than about 4% (w/v), and a clot activating amount of a clot activator, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution.

23. The freeze-dried homogeneous solid cake of claim 13 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

24. A freeze-dried homogeneous solid cake consisting of: chitosan at a concentration of no more than about 0.56% (w/v), having a molecular weight in the range of about M.sub.n 89 kDa to about 108 kDa and at least one lyoprotectant at a concentration of no more than about 4% (w/v), a clot activating amount of a clot activator, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution.

25. The freeze-dried homogeneous solid cake of claim 14 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

26. The freeze-dried homogeneous solid cake of claim 15 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

27. The freeze-dried homogeneous solid cake of claim 18 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

28. A freeze-dried homogeneous solid cake consisting of: chitosan at a concentration range of about 0.42 and about 2% (w/v), having a molecular weight range of about M.sub.n 4 kDa to about 211 kDa and a degree of deacetylation of from about 80% to about 85%, at least one lyoprotectant at a concentration range between about 1 and about 10%, and a salt or a buffer, and being without glycerol phosphate, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution, wherein said salt is a clot activating amount of a clot activator.

29. The freeze-dried homogeneous solid cake of claim 19 wherein said freeze-dried homogenous solid cake is soluble in said blood or blood product in 5 minutes or less.

30. A freeze-dried homogeneous solid cake consisting of chitosan having a molecular weight number of from about 4 kDa to about 250 kDa and a degree of deacetylation of from about 80% to about 85% and at least one lyoprotectant, a clot activating amount of a clot activator, wherein said freeze-dried homogeneous solid cake is soluble in blood or a blood product selected from the group consisting of platelet rich plasma (PRP), platelet-poor plasma (PPP), autologous conditioned plasma, platelet suspension, platelet lysate and combinations thereof for reconstitution of an injectable solution forming an injectable solution, exhibiting at least one of the following: in situ coagulation achieved and not inhibited; able to withstand mechanical loading post-implantation; inhibition of platelet-mediated clot retraction to fill tissue defects; good mixing without phase separation of polymers and PRP, blood product and combinations thereof; viscous and paste-like formulations for tissue repair applications; close-to-physiological properties for in vivo application; and combinations thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0045] FIGS. 1A and 1B depict various freeze-dried chitosan cakes and testing thereof of Example 1.

[0046] FIGS. 2A and 2B depict freeze-dried chitosan cakes and testing thereof of Example 2.

[0047] FIGS. 3A and 3B depict hybrid clots prepared with freeze-dried formulations and liquid solutions of Example 3.

[0048] FIGS. 4A and 4B depict freeze-dried chitosan cakes and hybrid clots of Example 4.

[0049] FIGS. 5A and 5B depict runniness test and TEG of varying chitosan formulations of Example 5.

[0050] FIG. 6A depicts various freeze-dried chitosan cakes and hybrid clots of Example 6.

[0051] FIG. 6B depicts TEG testing and liquid expression testing of various formulations under various testing conditions of Example 6.

[0052] FIG. 6C depicts runniness test and ex vivo implantation of chitosan formulations of Example 6.

[0053] FIG. 6D depicts mechanical strength test of hybrid clots of Example 6.

[0054] FIG. 7A depicts hybrid clots of Example 7.

[0055] FIG. 7B depicts hybrid clots undergoing various tests of Example 7.

[0056] FIG. 7C depicts Day 1 histological results of freeze-dried chitosan/PRP implants injected in NZW rabbits of Example 7.

[0057] FIG. 7D depicts Day 3 histological results of freeze-dried chitosan/PRP implants injected in NZW rabbits of Example 7.

[0058] FIG. 7E depicts macroscopic results of freeze-dried chitosan/PRP implants injected in NZW rabbits of Example 7.

[0059] FIG. 8A depicts cake appearance and solubility of various freeze-dried chitosan cakes of Example 8.

[0060] FIG. 8B depicts liquid expression testing of various freeze-dried chitosan cakes of Example 8.

[0061] FIG. 8C depicts TEG testing and clot histology of various freeze-dried chitosan cakes of Example 8.

[0062] FIG. 8D depicts the application of chitosan/PRP hybrids to surgical meniscal defects of Example 8.

[0063] FIG. 8E depicts day 1 and day 21 results following implantation of chitosan/PRP hybrids to meniscal defects of Example 8.

[0064] FIG. 9A depicts implantation of chitosan/PRP implants in chronic cartilage defects of Example 9.

[0065] FIG. 9B depicts day 21 results following implantation of chitosan/PRP hybrids in chronic cartilage defects of Example 9.

DETAILED DESCRIPTION OF THE FIGURES

[0066] Referring now to FIG. 1A, white arrows point to undissolved chitosan particles after reconstituting freeze-dried chitosan cakes with PRP using a swirling method (1A1) and by mixing with stainless steel beads (1A2). Chitosan dispersion in the PRP hybrid clots was not homogenous for any of the formulations (1A3 and 1A4 depict results of formulation #4). The rectangle in 1A3 underwent high magnification resulting in 1A4 and shows chitosan aggregates. Formulation #4: 0.56% (w/v) CS 80.6% DDA M.sub.w 380 kDa with 7% (w/v) trehalose and 45 mM CaCl.sub.2).

[0067] Referring now to FIG. 1B, liquid expression from the hybrid clots (formulations #2, 3, 4, 5, 6) was less than for PRP alone (1B1). Freeze-dried chitosan/PRP implant (formulation #3) was detected at the top of the microdrill holes 10 days post-treatment in a rabbit cartilage repair model (1B2). Formulation #2: 0.67% (w/v) CS 80.6% DDA M.sub.w 341 kDa with 201 mM NaCl activated post-reconstitution with liquid CaCl.sub.2); Formulation #3: 0.56% (w/v) CS 80.6% DDA M.sub.w 389 kDa with 6.3% (w/v) sucrose and 45 mM CaCl.sub.2); Formulation #4: 0.56% (w/v) CS 80.6% DDA M.sub.w 380 kDa with 7% (w/v) trehalose and 45 mM CaCl.sub.2; Formulation #5: 0.56% (w/v) CS 80.6% DDA M.sub.w 400 kDa with 5.2% (w/v) sucrose, 45 mM CaCl.sub.2 and 33 mM histidine; Formulation #6: 0.56% (w/v) CS 80.6% DDA M.sub.w 391 kDa with 5.8% (w/v) trehalose, 45 mM CaCl.sub.2 and 33 mM histidine.

[0068] Referring now to FIG. 2A, freeze-dried chitosan cakes obtained with formulation #1 (2A1) and formulation #14 (2A2) are depicted. Chitosan dispersion in the hybrid clots was not homogenous for any of the formulations (2A3 and 2A4 show formulation #1). The rectangle in 2A3 underwent high magnification resulting in 2A4 which depicts the presence of chitosan while the region above the rectangle in 2A3 did not. Formulation #1: 0.56% (w/v) CS 80.6% DDA M.sub.n 151 kDa with 42.2 mM CaCl.sub.2); Formulation #14: 0.56% (w/v) CS 80.6% DDA M.sub.n 148 kDa with 10% (w/v) trehalose and 42.2 mM CaCl.sub.2).

[0069] Referring now to FIG. 2B, coagulation of freeze-dried chitosan/PRP hybrids was normal in the presence of 2% (w/v) lyoprotectant (Formulation #10 shown in 2B1) but was inhibited in the presence of 8% (w/v) or 10% (w/v) lyoprotectant (Formulations #13 and 14 shown in 2B2 and 2B3 respectively). Formulation #10: 0.56% (w/v) CS 80.6% DDA M.sub.n 162 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2); Formulation #13: 0.56% (w/v) CS 80.6% DDA with 8% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #14: 0.56% (w/v) CS 80.6% DDA M.sub.n 148 kDa with 10% (w/v) trehalose and 42.2 mM CaCl.sub.2).

[0070] Referring now to FIGS. 3A and 3B, chitosan aggregates were not dispersed throughout the freeze-dried hybrid clots prepared in glass tubes (Formulations #1&2 shown in 3A1 and 3A2 respectively) nor in meniscal defects (Formulations #1 &2 shown in 3B1 & and 3B2 respectively). Hybrid clots prepared with liquid solutions were homogenous whether prepared in glass tubes (Liquid formulations #3&4 shown in 3A3 and 3A4 respectively) or in meniscal defects (Liquid formulations #3&4 shown in 3B3 and 3B4 respectively). White dashed lines in 3A1 to 3A4 represent the bottom edge of the hybrid clots in glass tubes. White dashed lines in 3B1 to 3B4 represent the borders of the meniscal defects. Rhodamine-chitosan tracer appears white under epifluorescence. Formulation #1: 0.56% (w/v) CS 80.6% DDA M.sub.n 159 kDa with 130 mM NaCl and 42.2 mM CaCl.sub.2; Formulation #2: 0.56% (w/v) CS 80.6% DDA M.sub.n 162 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Liquid formulation #3: 0.56% (w/v) CS 80.6% DDA M.sub.n 163 kDa with 42 mM NaCl and 45 mM CaCl.sub.2 after mixing with PRP; Liquid formulation #4: 0.56% (w/v) CS 80.6% DDA M.sub.n 145 kDa with 2% (w/v) trehalose and 45 mM CaCl.sub.2 after mixing with PRP.

[0071] Referring now to FIG. 4A, freeze-dried chitosan cakes were obtained with formulation #6 (4A1) and formulation #10 (4A2). Formulation #6: 0.56% (w/v) CS 80.6% DDA M.sub.n 183 kDa with 6% (w/v) trehalose, 3.8 mM histidine and 42.2 mM CaCl.sub.2); Formulation #10: 0.56% (w/v) CS 80.6% DDA M.sub.n 167 kDa with 6% (w/v) mannitol, 3.8 mM histidine and 42.2 mM CaCl.sub.2);

[0072] Referring now to FIG. 4B, chitosan dispersion in the hybrid clots was homogenous when chitosan of medium M.sub.n was used to prepared the freeze-dried cakes (Formulation #18 with CS 82.5% DDA M.sub.n 38 kDa shown in 4B3 and 4B4), but not when chitosan of high M.sub.n (Formulation #3 with CS 80.6% DDA M.sub.n 131 kDa shown in 4B1 and 4B2) or of low M.sub.n were used (Formulation #23 with CS 84.4% DDA M.sub.n 11 kDa shown in 4B5 and 4B6). Rhodamine-chitosan tracer appears white under epifluorescence in the Figures. Formulation #3: 0.56% (w/v) CS 80.6% DDA M.sub.n 131 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2); Formulation #18: 0.56% (w/v) CS 82.5% DDA M.sub.n 38 kDa with 2% (w/v) mannitol, 3.8 mM histidine and 42.2 mM CaCl.sub.2); Formulation #23: 0.56% (w/v) CS 84.4% DDA M.sub.n 11 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2).

[0073] Referring now to FIG. 5A, increasing chitosan concentration from 0.56% (w/v) to 1% (w/v) or chitosan M.sub.n from 32 kDa to 56 kDa improved paste-like properties of freeze-dried formulations according to a runniness test on an inclined plastic plate (compare 5A1 to 5A2 and 5A1 to 5A3). Black arrows in 5A1 to 5A4 point out runniness of PRP without chitosan. Black ovals in 5A1 to 5A4 point out the runniness of different chitosan-PRP formulations.

[0074] Referring now to FIG. 5B, formulations containing 0.56% (w/v) chitosan M.sub.n 32 kDa clotted in 1-phase fashion similar to PRP only controls (5B1). Increasing chitosan M.sub.n or concentration induced a 2-phase coagulation mechanism as revealed by TEG tracings (5B2 to 5B4). Formulation #1: 0.56% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #2: 0.56% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #3: 0.56% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #4: 0.56% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #5: 1% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #6: 1% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2); Formulation #7: 1% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #8: 1% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #13: 0.56% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #14: 0.56% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #15: 0.56% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #16: 0.56% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #17: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #18: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #19:1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #20: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2).

[0075] Referring now to FIG. 6A, freeze-dried chitosan cakes were obtained with formulation #9 (6A1) and formulation #11 (6A2). Chitosan dispersion in the hybrid clots was found to be mostly homogenous whether chitosan M.sub.n 28 kDa (6A3) or chitosan M.sub.n 56 kDa (6A4) was used (Formulations #12 and 16 shown in 6A3 and 6A4 respectively). Formulation #9: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #11: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #12: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #16: 1% (w/v) CS 81.8% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2).

[0076] Referring now to FIG. 6B, TEG tracings showed a 2-phase coagulation mechanism (6B1 & 6B2). Liquid expression from the hybrid clots was mostly absent (0% liquid expression) with freeze dried chitosan/PRP versus about 80% volume loss with PRP alone (6B3). Formulation #9: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #10: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #11: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #12: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #13: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #14: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2); Formulation #15: 1% (w/v) CS 81.8% DDA M.sub.n 56 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #16: 1% (w/v) CS 81.8% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2).

[0077] Referring now to FIG. 6C, all formulations (#1 to 16) were paste-like compared to PRP (Formulations #9 to 16 shown in 6C1). Black arrows in 6C1 point out runniness of PRP without chitosan. Black ovals in 6C1 point out the runniness of different chitosan-PRP formulations. Hybrid clots were delivered ex vivo to cartilage defects created in pig joints using a syringe equipped with a 20-gauge needle where they solidified (Formulations #9, 10, 11, 12, 15 and 16 shown in 6C2). Formulation #9: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2); Formulation #10: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2); Formulation #11: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2); Formulation #12: 1% (w/v) CS 80.5% DDA M.sub.n 28 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #13: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #14: 1% (w/v) CS 80.1% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #15: 1% (w/v) CS 81.8% DDA M.sub.n 56 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #16: 1% (w/v) CS 81.8% DDA M.sub.n 56 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2).

[0078] Referring now to FIG. 6D, hybrid clots containing 2% (w/v) lyoprotectant (Formulation #3 shown in 6D1 and 6D2) had greater mechanical strength compared to hybrid clots prepared with 6% (w/v) lyoprotectant (Formulation #4 shown in 6D3 and 6D4). Formulation #3: 1% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #4: 1% (w/v) CS 81.2% DDA M.sub.n 32 kDa with 6% (w/v) mannitol and 42.2 mM CaCl.sub.2. Referring now to FIG. 7A, hybrid clots were prepared without the aid of stainless steel beads (7A1 to 7A4) and by mixing with three 0.39 g stainless steel beads (7A5 to 7A8). Formulation #15: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #19: 1% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #23: 0.56% (w/v) .sub.CS 80.6% DDA M.sub.n 89 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #27: 1% (w/v) CS 80.6% DDA M.sub.n 108 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2).

[0079] Referring now to FIG. 7B, results for crush test, % liquid expression, runniness and maximal amplitude for formulations reconstituted without and with steel beads and for PRP control from 2 different donors are depicted in 7B. Formulation #15: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #19: 1% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2); Formulation #23: 0.56% (w/v) .sub.CS 80.6% DDA M.sub.n 89 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2; Formulation #27: 1% (w/v) CS 80.6% DDA M.sub.n 108 kDa with 2% (w/v) mannitol and 42.2 mM CaCl.sub.2).

[0080] Referring now to FIG. 7C, subcutaneous freeze-dried chitosan/PRP implants injected into the backs of NZW rabbits showed leukocyte chemotaxis towards the implants at 1 day (7C1, 7C2, 7C3 and 7C4) post-injection. PRP-only controls attracted much less leukocytes at 1 day (7C5 and 7C6) post-injection. Formulation #13: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2); Formulation #14: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2).

[0081] Referring now to FIG. 7D, subcutaneous freeze-dried chitosan/PRP implants injected into the backs of NZW rabbits showed leukocyte chemotaxis towards the implants at 3 days (7D1, 7D2, 7D3 and 7D4) post-injection. PRP-only controls attracted much less leukocytes at 3 days (7D5 and 7D6) post-injection. Formulation #13: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #14: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2).

[0082] Referring now to FIG. 7E, freeze-dried chitosan/PRP hybrids were retained in vivo for at least 14 days post-implantation (7E1, 7E2 and 7E3) while recalcified PRP controls are present only until 3 days post-implantation (7E4 shows PRP control at day 1). Formulation #13: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 2% (w/v) trehalose and 42.2 mM CaCl.sub.2; Formulation #14: 0.56% (w/v) CS 80.6% DDA M.sub.n 41 kDa with 6% (w/v) trehalose and 42.2 mM CaCl.sub.2).

[0083] Referring now to FIG. 8A, freeze-dried chitosan cakes were obtained with CS M.sub.n 43 kDa and 85% DDA (8A1) and CS M.sub.n 36 kDa and 80% DDA (8A2) with 1% (w/v) CS concentration and 1% (w/v) trehalose concentration. Freeze dried chitosan cakes were completely soluble when mixed (8A3 & 8A4).

[0084] Referring now to FIG. 8B, chitosan/PRP hybrids expressed no liquid, while PRP only controls expressed more than 80% their weight in serum (8B1, 8B2, 8B3 and 8B4).

[0085] Referring now to FIG. 8C, chitosan/PRP hybrids had decreased clot reaction time and clot maximal amplitude as measured by thromboelastography (8C1 and 8C2). CS dispersion in hybrid clots was homogenous (8C3 and 8C4).

[0086] Referring now to FIG. 8D, surgical defects were created in the anterior portion of the medial meniscus in sheep using a scalpel blade (8D1). The defects were elongated to 10-mm length (8D2). The defects were rasped (8D3). The defects were sutured without tightening and 18-gauge needles were pre-placed to create trephination channels from the periphery of the meniscus to the tear (8D4 and 8D5). Chitosan/PRP hybrids were delivered to the meniscus tear through the trephination channels (8D6).

[0087] Referring now to FIG. 8E, chitosan/PRP hybrids were resident in the tears for at least 24 hours post-surgery (8E1 and 8E2). At 21 days, post-surgery the edges of the meniscus tears treated with chitosan/PRP hybrids were well apposed (8E3 and 8E4).

[0088] Referring now to FIG. 9A, cartilage-only defects of 4 mm×4 mm were created on the trochlea of NZW rabbits (9A1). The knees were closed and the defects were allowed to develop to chronic stage for 1 month (9A2). The defects were debrided and 4 microdrill holes of 0.9 mm diameter were pierce through the subchondral bone to a depth of ˜4 mm. One knee was treated by injecting the Chitosan/PRP implant (CS M.sub.n 40 kDa and 80% DDA with 1% (w/v) CS concentration and 2% (w/v) trehalose concentration) on top of the microdrilled defect (9A4). The contralateral knee was treated by injecting recalcified PRP as control on top of the microdrilled defect (9A3).

[0089] Referring now to FIG. 9B, evaluation of the macroscopic appearance of the defects (9B1 and 9B2) and histological assessment (9B3 and 9B4) were done after 21 days of healing. Black dashed squares in 9B1 and 9B2 show the borders of the chronic cartilage defect.

DETAILED DESCRIPTION

[0090] In a preferred embodiment, in one procedure, room temperature chitosan was weighed into 15 mL Falcon tubes and ddH.sub.2O and HCl 1N were added to each tube. Chitosan concentration ranged between 0.42% to 2% (w/v). HCl concentration ranged between 12 and 57 mM. The tubes were placed on a rotator and stirred overnight at room temperature to ensure complete dissolution.

[0091] Two sterilization methods were used for sterilization of the chitosan solution: 1) Autoclave for 10 minutes for chitosan M.sub.n>100 kDa or 2) Filtration for chitosan M.sub.n<100 kDa.

[0092] Under a laminar flow hood, filter-sterilised 270 mM CaCl.sub.2) was added to the chitosan solution to a final concentration of 45 mM or of 42.2 mM. Filter-sterilised 15% (w/v) trehalose, mannitol or autoclaved 20% (w/v) sucrose, trehalose were added as required resulting in a lyoprotectant concentration ranging between 0 to 10% (w/v). Autoclaved 5 M NaCl was added as required to achieve a final concentration between 130 and 201 mM. Filter-sterilised histidine was added as required to achieve a final concentration of 3.8, 33 or 39 mM. A filter-sterilised rhodamine-chitosan tracer was added to a final ratio of 0.01% (vol tracer/vol solution) for imaging purposes.

[0093] After mixing well with a vortex until a homogeneous solution was achieved, 1 mL aliquots were distributed into 3 mL or 10 mL glass vials for freeze-drying using a membrane on top of the vials to maintain sterility. Alternatively, smaller 300 μL aliquots were distributed into 2 mL glass vials for freeze-drying. The freeze-drying cycle consisted of: 1) Ramped freezing to −40° C. in 1 hour then isothermal 2 hours at −40° C., 2) −40° C. for 48 hours and 3) Ramped heating to 30° C. in 12 hours then isothermal 6 hours at 30° C., at 300 or 100 millitorrs. Cakes were visually assessed post-lyophilization. As per Criteria 1 above, freeze-dried cakes should be homogenous, solid and present good mechanical properties for storage and shipping.

[0094] Anti-coagulated whole blood was collected from rabbit, sheep and human donors and placed in Vacutainer tubes. The anti-coagulant was either acid citrate dextrose (13 mM trisodium citrate dihydrate; 7 mM citric acid; 24 mM dextrose in blood) or sodium citrate (12.9 mM trisodium citrate dihydrate in blood).

[0095] The Vacutainer tubes containing anti-coagulated whole blood were centrifuged in an ACE E-Z PRP™ centrifuge at 160 g for 10 minutes at room temperature. The supernatant was collected along with the first about 2 mm of erythrocytes and centrifuged again at 400 g for 10 minutes at room temperature in order to separate the platelet-rich plasma (bottom 1.5 mL in the tube, classified as a Leukocyte-PRP, also containing a fraction of erythrocytes) and platelet-poor plasma (clear plasma).

[0096] To test cake reconstitution and chitosan solubilisation, 1 mL of PRP or PPP (preferable for visual assessment because it is clear versus PRP which contains erythrocytes) was pipetted into each vial containing freeze-dried cake. Mixing was done by swirling or by shaking vigorously for 10 seconds in the presence or absence of three 0.39 g stainless steel balls. The ease of cake solubilisation was recorded. As per Criteria 2 above, cakes should be rapidly and easily reconstituted in PRP, PPP, blood or water, as required. pH and osmolality of reconstituted mixtures were also recorded to determine whether they are close to physiological. As per Criteria 8 above, the reconstituted mixtures should have close-to-physiological properties for in vivo implantation or intra-articular injections

[0097] To test cake performance, 1 mL of PRP was pipetted into each vial containing freeze-dried cake. Mixing was done by swirling or by shaking vigorously for 10 seconds in the presence or absence of three 0.39 g stainless steel balls.

[0098] Coagulation properties were measured by loading 360 μL of each formulation into a TEG cup immediately after reconstitution and recording TEG tracings for 1 hour. As per Criteria 3 above, coagulation should not be inhibited when gelation in situ is required.

[0099] Mechanical properties of the formulations were assessed with a manual crush test. After 1 hour of clotting, each hybrid clot was subjected to manual crushing and mechanical strength scored on a scale of 0 (weak) to 4+(strong). As per Criteria 4 above, the chitosan/PRP hybrid implants should be mechanically stable to withstand loading at implantation sites.

[0100] Hybrid clot volume retention was assessed by dispensing the reconstituted formulations into glass tubes at 37° C. After 60 minutes, liquid expression from the hybrid clots was quantified by weight measurement. As per Criteria 5 above, the chitosan/PRP hybrid implants should be able to fill tissue defects without undergoing platelet-mediated retraction.

[0101] Chitosan dispersion versus aggregation in hybrid clots was assessed by histology. For example, hybrid clots containing the rhodamine-chitosan tracer were fixed in 10% Neutral Buffered Formalin (NBF) and thick razor blade sections were observed with epifluorescence microscopy. Hybrid clots were fixed in 10% NBF (neutral buffered formalin) and 5 μm paraffin sections were collected for Safranin O/Fast Green staining. As par Criteria 6 above, good mixing must be achieved without phase separation of the polymer and blood components to ensure optimal in vivo responses and timely biodegradability.

[0102] Paste-like properties of the formulations were assessed with a runniness test. Runniness was assessed by placing a 30 μL drop of each formulation onto a rigid piece of plastic fixed at a certain angle (38 degrees) immediately after reconstitution and taking pictures at fixed times. As per Criteria 7 above, the mixtures should have appropriate handling properties which would be viscous and paste-like for tissue repair applications or a viscous suspension in the case of intra-articular viscosupplementation.

[0103] Handling properties of the formulations were tested ex vivo in a meniscal defect model. For example, a straight razor blade was used to take ˜0.5 mm cross-sections from pig meniscus and a horizontal flap was created towards the femoral (top) surface of the meniscus. A 4 mm biopsy punch was used to create a partial thickness defect towards the tibial (bottom) surface of the meniscus. The menisci were wrapped in humid plastic film and were placed at 37° C. for at least 30 min before the start of the experiment. Freeze-dried chitosan formulations reconstituted with PRP were injected into the partial-thickness meniscus defects using a syringe fitted with a 20-gauge needle and the flap was closed immediately. The menisci were immediately re-wrapped and sealed with humid plastic film and were placed at 37° C. for 1 hour. The menisci were fixed in 10% NBF and thick razor blade sections were observed with epifluorescence microscopy. Paraffin sections were stained with Safranin O/Fast Green.

[0104] Handling properties of the formulations were tested ex vivo in a cartilage defect model. Biopsy punches (8 mm dia.) and flat surgical blades were used to create cartilage defects in pig condyles and trochlea. The joints were placed in a humid chamber at 37° C. for at least 30 min before the start of the experiment. Freeze-dried chitosan formulations reconstituted in PRP were injected into the cartilage defects using a syringe and 20-gauge needle. The joints were immediately sealed in the humid chamber and were placed at 37° C. for 1 hour. The joints were then inspected to determine whether clotting occurred in situ.

[0105] In another embodiment, to test in vivo clearing of the freeze-dried formulations, chondral defects of 3.5 mm×4.5 mm were created bi-laterally in the trochlea of two 19-month old NZW rabbits. Four microdrill holes were pierced through the subchondral bone with a 0.9 mm drill bit to a depth of about 4 mm. Autologous PRP was prepared from rabbit blood extracted immediately prior to surgery. After creation of the defect, the freeze-dried chitosan cake was reconstituted with 1 mL PRP using the bead mixing method and the implant (1 hanging drop) was delivered over the defect site and allowed to solidify in situ for ˜5 min before closing the knee. On the contralateral knee, the freeze-dried chitosan was mixed with 1 mL fresh blood collected immediately prior to reconstitution and delivery. Implant residency was assessed at 10 days and at 21 days.

[0106] In another embodiment, a second rabbit model allowing for the simultaneous testing of several different chitosan formulations was used to test in vivo biodegradability. Autologous PRP was prepared from rabbit blood extracted immediately prior to surgery. Each freeze-dried cake was reconstituted in 300 μL PRP without the aid the bead mixing and injected subcutaneously in the back of the rabbits using a syringe fitted with a SubQ needle. Controls were recalcified PRP without chitosan. Implant residency and cell recruitment were assessed at 1, 3, 7 and 14 days post-injection.

[0107] In another embodiment, a sheep meniscus repair model was used to test hybrid implant retention and effect of implants on meniscal tissue repair. Hybrid implants of freeze-dried chitosan, a clot activator, a lyoprotectant and autologous PRP were injected into surgically created meniscus defects. Implant retention was assessed at 1 day and tissue repair was assessed at 21 days post-surgery.

[0108] In another embodiment, a chronic cartilage repair model was developed in the rabbit and used to test the effect of hybrid implants of osteochondral repair. Surgical defects were created on the trochlea of NZW rabbits and allowed to progress to chonic stage. The cartilage defects were treated with hybrid implants composed of freeze-dried chitosan, a clot activator, a lyoprotectant and autologous PRP. Healing was assessed at 21 days post-surgery.

Example 1

1—Preparation of Chitosan Formulations

[0109] Formulations without lyoprotectants or buffer: Chitosan weight average molecular weight M.sub.w 500 kDa, measured by GPC as described in [Nguyen, S., F. M. Winnik, and M. D. Buschmann, Improved reproducibility in the determination of the molecular weight of chitosan by analytical size exclusion chromatography. Carbohydrate Polymers, 2009. 75(3): p. 528-533], and 80.6% DDA was dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56% or 0.67% (w/v). The solutions were autoclaved for 10 minutes and cooled on ice. Post-autoclave chitosan M.sub.w was between 319-403 kDa. Autoclaved 5M NaCl and filter-sterilised 270 mM CaCl.sub.2 were added as required before dispensing in 10 mL individual vials for freeze-drying.

[0110] Formulations with lyoprotectants and buffer: Chitosan (M.sub.w 500 kDa, 80.6% DDA) was dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56% or 0.67% (w/v). Autoclaved 20% (w/v) sucrose or 20% (w/v) trehalose was added, as required. The solutions were autoclaved for 10 minutes and cooled on ice. Post-autoclave chitosan M.sub.w was between 342-421 kDa. Filter-sterilised 270 mM CaCl.sub.2 and stock L-histidine 200 mM were added as required before dispensing in 10 mL individual vials for freeze-drying.

[0111] As per Tables 1&2, the HCl concentration was adjusted so that all formulations had theoretical target pH 6.6. The histidine buffer concentration was adjusted to match the overall monomer content in the cakes. The lyoprotectant concentrations were adjusted so that all formulations had theoretical osmolality 350 mOsm.

2—Freeze-Drying Cycle

[0112] The freeze-drying cycle consisted of: 1) Ramped freezing to −40° C. in 1 hour then isothermal 2 hours at −40° C., 2) −40° C. for 48 hours and 3) Ramped heating to 30° C. in 12 hours then isothermal 6 hours at 30° C., at 300 millitorrs.

TABLE-US-00001 TABLE 1 Formulations containing the clot activator (CaCl.sub.2) to be reconstituted directly with PRP. Total Aliquot volume Chitosan HCl NaCl Sucrose Trehalose Histidine CaCl.sub.2 volume Rehydration Formulation Group prepared (w/v) (mM) (mM) (mM) (mM) (mM) (mM) for F/D volume 1 Chitosan- 5 mL 0.56% 12 130 — — — 45 1 mL 1 mL NaCl PRP .sup.1 3 Chitosan- 5 mL 0.56% 12 — 184 — — 45 1 mL 1 mL 6.3% PRP .sup.2 Sucrose 4 Chitosan- 5 mL 0.56% 12 — — 185 — 45 1 mL 1 mL 7.0% PRP .sup.3 Trehalose 5 Chitosan- 5 mL 0.56% 12 — 152 — 33 45 1 mL 1 mL 5.2% PRP .sup.4 Sucrose- Histidine 6 Chitosan- 5 mL 0.56% 12 — — 153 33 45 1 mL 1 mL 5.8% PRP .sup.5 Trehalose- Histidine .sup.1 Final hybrid: Chitosan (0.56%)-HCl(12 mM)-NaCl(130 mM)-CaCl.sub.2(45 mM)-PRP .sup.2 Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Sucrose (184 mM)-CaCl.sub.2(45 mM)-PRP .sup.3 Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Trehalose (185 mM)-CaCl.sub.2(45 mM)-PRP .sup.4 Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Sucrose (152 mM)-Histidine (33 mM)-CaCl.sub.2(45 mM)-PRP .sup.5 Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Trehalose (183 mM)-Histidine (33 mM)-CaCl.sub.2(45 mM)-PRP

TABLE-US-00002 TABLE 2 Formulations to be activated with CaCl.sub.2 after reconstitution with PRP. Total Aliquot 3% volume Chitosan HCl NaCl Sucrose Trehalose Histidine volume Rehydration CaCl.sub.2 Formulation Group prepared (w/v) (mM) (mM) (mM) (mM) (mM) for F/D volume volume 2 Chitosan- 5 mL 0.67% 15 201 — — — 1 mL 1 mL 200 μL.sup.1 NaCl PRP 7 Chitosan- 5 mL 0.67% 15 — 293 — — 1 mL 1 mL 200 μL.sup.2 10.0% PRP Sucrose 8 Chitosan- 5 mL 0.67% 15 — — 296 — 1 mL 1 mL 200 μL.sup.3 11.2% PRP Trehalose 9 Chitosan- 5 mL 0.67% 15 — 250 — 39 1 mL 1 mL 200 μL.sup.4 8.6% PRP Sucrose- Histidine 10 Chitosan- 5 mL 0.67% 15 — — 251 39 1 mL 1 mL 200 μL.sup.5 9.5% PRP Trehalose- Histidine .sup.1Final hybrid: Chitosan (0.56%)-HCl(12 mM)-NaCl(167 mM)-CaCl.sub.2(45 mM)-PRP .sup.2Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Sucrose (244 mM)-CaCl.sub.2(45 mM)-PRP .sup.3Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Trehalose (247 mM)-CaCl.sub.2(45 mM)-PRP .sup.4Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Sucrose (208 mM)-Histidine (39 mM)-CaCl.sub.2(45 mM)-PRP .sup.5Final hybrid: Chitosan (0.56%)-HCl(12 mM)-Trehalose (209 mM)-Histidine (39 mM)-CaCl.sub.2(45 mM)-PRP

3—Cake Appearance

[0113] Cake appearance was scored on a scale of—(shrunken, sheet-like or cracked) to 3+ (homogenous solid bulky form). Cakes that scored 2+ or 3+ were deemed acceptable.

[0114] Formulations containing NaCl had uneven surfaces and formulation #1 shrunk significantly during freeze-drying. Formulations containing histidine buffer (33 to 39 mM) had cracked and uneven surfaces.

[0115] Formulations containing sucrose or trehalose with and without CaCl.sub.2) had a smooth even white surface and were slightly depressed at the top. The presence of a lyoprotectant aids in obtaining mechanically stable cakes.

4—Isolation of Rabbit PRP

[0116] Whole blood was extracted from NZW rabbits and mixed with acid citrate dextrose (ACD) anti-coagulant (8.5 mL blood to 1.5 mL ACD).

[0117] The blood was centrifuged in an ACE E-Z PRP™ centrifuge at 160 g for 10 minutes at room temperature.

[0118] The supernatant fractions containing plasma and the buffy coat as well as the first 1-2 mm of the erythrocyte layer was removed using a 2½ inch (18-gauge) blunt needle attached to a 10 mL syringe.

[0119] The plasma and buffy coat were further centrifuged at 400 g for 10 minutes at room temperature in order to separate platelet-rich plasma (PRP) from platelet poor plasma (PPP).

5—Cake Reconstitution

[0120] Cakes were reconstituted with 1 mL PRP only (Formulations #3 to 6) or with 1 mL PRP and then activated with 200 μL 3% (w/v) CaCl.sub.2) (Formulations #2, 7 and 8).

[0121] Two different mixing methods were tested: Swirling the vial for 10 seconds and aspirating-ejecting twice with a syringe equipped with a needle or mixing with three 0.39 g steel beads for 10 seconds.

[0122] Undissolved chitosan particles were observed post-reconstitution with both mixing methods tested (FIGS. 1A1 and 1A2).

6—Liquid Expression

[0123] Formulations reconstituted in PRP were dispensed into glass tubes at 37° C. After 60 minutes, liquid expression and volume loss from the hybrid clots was quantified by weight measurement.

[0124] All tested formulations clotted. The clot activator can be added directly to the freeze-dried cake.

[0125] All hybrid clots expressed less liquid than PRP alone (FIG. 1B1).

7—Clot Homogeneity

[0126] Hybrid clots were fixed in 10% NBF and paraffin sections stained with Safranin O/Fast Green to evaluate chitosan dispersion in the clots.

[0127] Chitosan aggregates were not dispersed throughout the hybrid clots for any of the formulations (FIGS. 1A3 and 1A4).

8—In Vivo Cartilage Repair Model

[0128] Two formulations (#3 and #4) were tested in vivo in a rabbit cartilage repair model.

[0129] Chondral defects of 3.5 mm×4.5 mm were created bi-laterally in the trochlea of two 19-month old NZW rabbits. Four microdrill holes were pierced through the subchondral bone with a 0.9 mm drill bit to a depth of ˜4 mm.

[0130] Autologous PRP was prepared from rabbit blood extracted immediately prior to surgery, as described above in section 4—Isolation of rabbit PRP. After creation of the defect, the freeze-dried chitosan cake was reconstituted with 1 mL PRP using the bead mixing method and the implant (1 hanging drop) was delivered over the defect site and allowed to solidify in situ for ˜5 min before closing the knee.

[0131] On the contralateral knee, the freeze-dried chitosan was mixed with 1 mL fresh blood collected immediately prior to reconstitution and delivery.

[0132] At 10 days post-surgery, freeze-dried chitosan/PRP hybrid implants were observed at the surface of the microdrill holes, along with inflammatory infiltrate (FIG. 1B2). Hybrid implants were cleared by 21 days post-surgery.

TABLE-US-00003 TABLE 3 Performance of the 10 different formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good Four met mechanical properties for shipping criteria 1 (Assessed with cake appearance) (#3-6) 2 Rapid and complete reconstitution None met (Assessed with visual inspection criteria 2 post-mixing) 3 The mixture should not inhibit coagulation Not checked (Assessed with thromboelastography) 4 The coagulated mixtures (implants) Not checked should be mechanically stable (Assessed with manual crushing test) 5 The coagulated mixtures (implants) Five met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression (#2, 3, 4, 5, 6) measurements) 6 Good mixing without phase separation None met of the polymer and blood components criteria 6 (Assessed with histology) 7 The mixtures should have appropriate Not checked handling properties (Assessed with runniness test) 8 The mixtures should have close to Not checked physiological properties (Assessed with pH and osmolality measurements)

[0133] In Example 1, lyoprotectants are required to obtain cakes that are mechanically stable for storage and shipping, but that adding buffer to the cakes induces surface cracking. The clot activator may be added directly to the freeze-dried cakes to induce coagulation of the chitosan/PRP mixtures in situ. Freeze-dried cakes prepared with high molecular weight chitosan however did not dissolve easily and completely in PRP. Freeze-dried chitosan/PRP hybrids did not induce chronic inflammation upon implantation in an acute rabbit chondral defect model and were cleared by 21 days in vivo.

Example 2

1—Preparation of Chitosan Formulations

[0134] Chitosan number average molecular weight M.sub.n 211 kDa, measured by GPC as described in [Nguyen, S., F. M. Winnik, and M. D. Buschmann, Improved reproducibility in the determination of the molecular weight of chitosan by analytical size exclusion chromatography. Carbohydrate Polymers, 2009. 75(3): p. 528-533] and 80.6% DDA was dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56% or 0.42% (w/v). The solutions were autoclaved for 10 minutes and cooled on ice. Post-autoclave chitosan M.sub.n was between 112-160 kDa. Autoclaved 20% (w/v) sucrose, 20% (w/v) trehalose and 5M NaCl as well as filter-sterilised 270 mM CaCl.sub.2) and were added, as required. A filter-sterilised Rhodamine-chitosan tracer (M.sub.n 143 kDa, 80.0% DDA) was added before dispensing in 10 mL individual vials for freeze-drying.

[0135] As per Table 4, the HCl concentration was adjusted so that all formulations had theoretical target pH 6.45. The NaCl concentration was adjusted so that all formulations had theoretical osmolality 350 mOsm. Lyoprotectant concentration was adjusted to be between 1 and 10% (w/v).

2—Freeze-Drying Cycle

[0136] The freeze-drying cycle consisted of: 1) Ramped freezing to −40° C. in 1 hour then isothermal 2 hours at −40° C., 2) −40° C. for 48 hours and 3) Ramped heating to 30° C. in 12 hours then isothermal 6 hours at 30° C., at 100 millitorrs.

TABLE-US-00004 TABLE 4 Formulations containing the clot activator (CaCl.sub.2) to be reconstituted directly with PRP. Volume Total of Aliquot volume tracer Chitosan HCl NaCl Sucrose Trehalose CaCl.sub.2 volume for Rehydration Formulation Group prepared added (w/v) (mM) (mM) (mM) (mM) (mM) F/D volume 1 Chitosan 10 mL 0.1 mL 0.56% 14 mM — — — 42.2 mM 1 mL 1 mL only PRP 2 Chitosan- 10 mL 0.1 mL 0.56% 14 mM 130 — — 42.2 mM 1 mL 1 mL NaCl mM PRP 3 Chitosan 1% 10 mL 0.1 mL 0.56% 14 mM —  29 mM — 42.2 1 mL 1 mL Sucrose mM PRP 4 Chitosan 2% 10 mL 0.1 mL 0.56% 14 mM —  58 mM — 42.2 1 mL 1 mL Sucrose mM PRP 5 Chitosan 4% 10 mL 0.1 mL 0.56% 14 mM — 117 mM — 42.2 1 mL 1 mL Sucrose mM PRP 6 Chitosan 6% 10 mL 0.1 mL 0.56% 14 mM — 175 mM — 42.2 1 mL 1 mL Sucrose mM PRP 7 Chitosan 8% 10 mL 0.1 mL 0.56% 14 mM — 234 mM — 42.2 1 mL 1 mL Sucrose mM PRP 8 Chitosan 10 mL 0.1 mL 0.56% 14 mM — 292 mM — 42.2 1 mL 1 mL 10% Sucrose mM PRP 9 Chitosan 1% 10 mL 0.1 mL 0.56% 14 mM — —  24 mM 42.2 1 mL 1 mL Trehalose mM PRP 10 Chitosan 2% 10 mL 0.1 mL 0.56% 14 mM — —  48 mM 42.2 1 mL 1 mL Trehalose mM PRP 11 Chitosan 4% 10 mL 0.1 mL 0.56% 14 mM — —  96 mM 42.2 1 mL 1 mL Trehalose mM PRP 12 Chitosan 6% 10 mL 0.1 mL 0.56% 14 mM — — 144 mM 42.2 1 mL 1 mL Trehalose mM PRP 13 Chitosan 8% 10 mL 0.1 mL 0.56% 14 mM — — 191 mM 42.2 1 mL 1 mL Trehalose mM PRP 14 Chitosan 10 mL 0.1 mL 0.56% 14 mM — — 239 mM 42.2 1 mL 1 mL 10% mM PRP Trehalose 15 Chitosan 10 mL 0.1 mL 0.42% 10 mM — — — 42.2 1 mL 1 mL only mM PRP 16 Chitosan- 10 mL 0.1 mL 0.42% 10 mM 133 — — 42.2 1 mL 1 mL NaCl mM mM PRP 17 Chitosan 1% 10 mL 0.1 mL 0.42% 10 mM —  29 mM — 42.2 1 mL 1 mL Sucrose mM PRP 18 Chitosan 2% 10 mL 0.1 mL 0.42% 10 mM —  58 mM — 42.2 1 mL 1 mL Sucrose mM PRP 19 Chitosan 4% 10 mL 0.1 mL 0.42% 10 mM — 117 mM — 42.2 1 mL 1 mL Sucrose mM PRP 20 Chitosan 6% 10 mL 0.1 mL 0.42% 10 mM — 175 mM — 42.2 1 mL 1 mL Sucrose mM PRP 21 Chitosan 8% 10 mL 0.1 mL 0.42% 10 mM — 234 mM — 42.2 1 mL 1 mL Sucrose mM PRP 22 Chitosan 10 mL 0.1 mL 0.42% 10 mM — 292 mM — 42.2 1 mL 1 mL 10% Sucrose mM PRP 23 Chitosan 1% 10 mL 0.1 mL 0.42% 10 mM — —  24 mM 42.2 1 mL 1 mL Trehalose mM PRP 24 Chitosan 2% 10 mL 0.1 mL 0.42% 10 mM — —  48 mM 42.2 1 mL 1 mL Trehalose mM PRP 25 Chitosan 4% 10 mL 0.1 mL 0.42% 10 mM — —  96 mM 42.2 1 mL 1 mL Trehalose mM PRP 26 Chitosan 6% 10 mL 0.1 mL 0.42% 10 mM — — 144 mM 42.2 1 mL 1 mL Trehalose mM PRP 27 Chitosan 8% 10 mL 0.1 mL 0.42% 10 mM — — 191 mM 42.2 1 mL 1 mL Trehalose mM PRP 28 Chitosan 10 mL 0.1 mL 0.42% 10 mM — — 239 mM 42.2 1 mL 1 mL 10% mM PRP Trehalose

3—Cake Appearance

[0137] Formulations containing chitosan-only were sheet-like (FIG. 2A1). Formulations containing NaCl only shrunk significantly during freeze-drying.

[0138] Formulations containing 2% (w/v) or more of sucrose or trehalose were bulkier, confirming that lyoprotectants are required to obtain mechanically stable clots. Cakes were bulkiest when increasing lyoprotectant concentrations were used (FIG. 2A2).

4—Isolation of Sheep PRP

[0139] Whole blood was extracted from Arcott cross sheep and mixed with acid citrate dextrose (ACID) anti-coagulant (8.5 mL blood to 1.5 mL ACID).

[0140] The blood was centrifuged in an ACE E-Z PRP™ centrifuge at 160 g for 10 minutes at room temperature.

[0141] The supernatant fractions containing plasma and the buffy coat as well as the first 1-2 mm of the erythrocyte layer was removed using a 2½ inch (18-gauge) blunt needle attached to a 10 mL syringe.

[0142] The plasma and buffy coat were further centrifuged at 400 g for 10 minutes at room temperature in order to separate platelet-rich plasma (PRP) from platelet poor plasma (PPP).

5—Cake Reconstitution

[0143] Cakes were reconstituted with 1 mL PRP and mixed with three 0.39 g steel beads for 10 seconds. Two different sheep donors were used to test each cake.

[0144] Undissolved chitosan particles were observed post-reconstitution.

6—Thromboelastography (TEG)

[0145] 360 μL of each formulation was loaded into a TEG cup immediately after mixing and TEG tracings were recorded for 1 hour.

[0146] Formulations containing chitosan only did not clot reproducibly.

[0147] Clotting was inhibited for the formulations containing NaCl only.

[0148] Formulations containing 2% (w/v) sucrose or trehalose coagulated normally and had clot reaction time (R) ranging between 9-18 minutes and maximal amplitude (MA) between 55 and 75 mm (FIG. 2B1).

[0149] Clotting was inhibited in 3 cases out of 8 for formulations containing 8% (w/v) sucrose or trehalose. For the other 5 cases, decreased maximal amplitude (MA) between 14 and 20 mm was observed (FIG. 2B2).

[0150] Clotting was inhibited in 5 cases out of 8 for formulations containing 10% (w/v) sucrose or trehalose (FIG. 2B3). For the other 3 cases, decreased maximal amplitude (MA) between 9 and 24 mm was observed.

6—Liquid Expression

[0151] Formulations reconstituted in PRP were dispensed into glass tubes at 37° C. After 60 minutes, liquid expression and volume loss from the hybrid clots was quantified by weight measurement.

[0152] All hybrid clots tested expressed less liquid than PRP alone.

7—Clot Homogeneity

[0153] Hybrid clots were fixed in 10% NBF and thick razor blade sections were observed with epifluorescence microscopy to evaluate chitosan dispersion in the clots.

[0154] Chitosan aggregates were not dispersed throughout the hybrid clots containing sucrose or trehalose (FIGS. 2A3 & 2A4). Dispersion was better in the formulations devoid of lyoprotectants.

TABLE-US-00005 TABLE 5 Performance of the 28 different formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good Sixteen met mechanical properties for shipping criteria 1 (Assessed with cake appearance) (#5-8, 11-14, 19-22, 25-28) 2 Rapid and complete reconstitution None met (Assessed with visual inspection criteria 2 post-mixing) 3 The mixture should not inhibit coagulation Four met (Assessed with thromboelastography) criteria 3 (#4, 10, 18, 24) 4 The coagulated mixtures (implants) Not checked should be mechanically stable (Assessed with manual crushing test) 5 The coagulated mixtures (implants) Sixteen met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression (#1, 2, 4, 7, measurements) 8, 10, 13, 14, 15, 16, 18, 21, 22, 24, 27, 28) 6 Good mixing without phase separation Four met of the polymer and blood components criteria 6 (Assessed with histology) (#1, 2, 15, 16) 7 The mixtures should have appropriate Not checked handling properties (Assessed with runniness test) 8 The mixtures should have close to Not checked physiological properties (Assessed with pH and osmolality measurements)

[0155] In Example 2, increasing lyoprotectant concentrations improves mechanical stability of cakes but also inhibits coagulation of chitosan/PRP mixtures. Freeze-dried cakes containing high molecular weight chitosan do not dissolve easily and completely in PRP.

Example 3

1—Preparation of Chitosan Formulations

[0156] Chitosan (M.sub.n 211 kDa, 80.6% DDA) was dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56% (w/v). The solutions were autoclaved for 10 minutes and cooled on ice. Post-autoclave chitosan M.sub.n was 151 and 162 kDa. Autoclaved 20% (w/v) trehalose and 5M NaCl, as well as filter-sterilised 270 mM CaCl.sub.2) and were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 143 kDa, 80.0% DDA) was added before dispensing in 10 mL individual vials for freeze-drying.

[0157] As per Table 6, the HCl concentration was adjusted so that all formulations had theoretical target pH 6.45. The NaCl concentration was adjusted so that the formulation had theoretical osmolality 350 mOsm. Lyoprotectant concentration was set at 2% (w/v) for formulation #2.

[0158] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00006 TABLE 6 Freeze-dried formulation containing the clot activator (CaCl.sub.2) to be reconstituted directly with PRP. Total Volume Aliquot volume of tracer Chitosan HCl NaCl Trehalose CaCl.sub.2 volume for Rehydration Formulation Group prepared added (w/v) (mM) (mM) (mM) (mM) F/D volume 1.sup.1 Chitosan- 10 mL 0.1 mL 0.56% 14 130 mM — 42.2 1 mL 1 mL PRP NaCl mM mM 2.sup.2 Chitosan 10 mL 0.1 mL 0.56% 14 — 48 mM 42.2 1 mL 1 mL PRP 2% mM mM Trehalose .sup.1Final hybrid: Chitosan (0.56%)-HCl(14 mM)-NaCl(130 mM)-CaCl.sub.2(42.2 mM)-PRP .sup.2Final hybrid: Chitosan (0.56%)-HCl(14 mM)-Trehalose (48 mM)-CaCl.sub.2(42.2 mM)-PRP

2—Isolation of Human PRP

[0159] Whole blood was extracted from a human donor and mixed with 3.8% (w/v) tri sodium citrate dihydrate solution (9 mL blood to 1 mL sodium citrate).

[0160] The blood was centrifuged in an ACE E-Z PRP™ centrifuge at 160 g for 10 minutes at room temperature.

[0161] The supernatant fractions containing plasma and the buffy coat as well as the first 1-2 mm of the erythrocyte layer was removed using a 2½ inch (18-gauge) blunt needle attached to a 10 mL syringe.

[0162] The plasma and buffy coat were further centrifuged at 400 g for 10 minutes at room temperature in order to separate platelet-rich plasma (PRP) from platelet poor plasma (PPP).

3—Cake Appearance

[0163] The formulation containing NaCl only shrunk significantly during freeze-drying.

[0164] The formulation containing 2% (w/v) trehalose was mechanically stable and met performance criteria 1.

4—Cake Reconstitution

[0165] Cakes were reconstituted with 1 mL PRP and mixed with three 0.39 g steel beads for 10 seconds.

[0166] Undissolved chitosan particles were observed post-reconstitution.

5—Preparation and Mixing of Liquid Formulations

[0167] Liquid chitosan formulations were also prepared to test in parallel with the freeze-dried formulations (Table 7). The solutions were autoclaved for 10 minutes and cooled on ice. Post autoclave chitosan M.sub.n was 145 and 163 kDa.

[0168] 400 μL of liquid chitosan formulation was mixed with 800 μL PRP and activated using 240 μL of 3% (w/v) CaCl.sub.2).

TABLE-US-00007 TABLE 7 Liquid formulations to be mixed with PRP and activated with the clot activator (CaCl.sub.2). Volume of Total volume tracer Chito-san HCl NaCl Trehalose Sol Group prepared added (w/v) (mM) (mM) (mM) 3.sup.1 Chitosan-NaCl 10 mL 0.1 mL 2% 50 mM 150 mM — 4.sup.2 Chitosan 2% 10 mL 0.1 mL 2% 50 mM — 171 mM Trehalose .sup.1Final hybrid: Chitosan (0.56%)-HCl(14 mM)-NaCl(42 mM)-CaCl.sub.2(45 mM)-PRP .sup.2Final hybrid: Chitosan (0.56%)-HCl(14 mM)-Trehalose (48 mM)-CaCl.sub.2(45 mM)-PRP

6—Clot Homogeneity

[0169] Reconstituted freeze-dried formulations and liquid formulations were dispensed into glass tubes at 37° C. and left to clot for 1 hour.

[0170] Hybrid clots were fixed in 10% NBF and thick razor blade sections were observed with epifluorescence microscopy to evaluate chitosan dispersion in the clots.

[0171] Chitosan aggregates were not dispersed throughout the freeze-dried hybrid clots (FIGS. 3A1 & 3A2).

[0172] Chitosan was well dispersed within the hybrid clots prepared with liquid solutions (FIGS. 3A3 & 3A4).

7—Ex Vivo Implantation in Meniscal Defects

[0173] A straight razor blade was used to take ˜0.5 mm cross-sections from pig meniscus and a horizontal flap was created towards the femoral (top) surface of the meniscus.

[0174] A 4 mm biopsy punch was used to create a partial thickness defect towards the tibial (bottom) surface of the meniscus.

[0175] The menisci were wrapped in humid plastic film and were placed at 37° C. for at least 30 min before the start of the experiment.

[0176] Reconstituted freeze-dried formulations and liquid formulations were injected into the partial-thickness meniscus defects using a syringe fitted with a 20-gauge needle and the flap was closed immediately.

[0177] The menisci were immediately re-wrapped and sealed with humid plastic film and were placed at 37° C. for 1 hour.

[0178] Freeze-dried chitosan/PRP and liquid formulations were successfully implanted ex vivo in meniscal defects where they coagulated in situ.

[0179] Pig menisci were fixed in 10% NBF and thick razor blade sections were observed with epifluorescence microscopy to evaluate chitosan dispersion in the clots.

[0180] Chitosan was aggregated and not dispersed throughout the meniscal defects for the freeze-dried formulations (FIGS. 3B1 & 3B2).

[0181] Chitosan was well dispersed within the meniscal defects for the liquid formulations (FIGS. 3B3 & 3B4).

TABLE-US-00008 TABLE 8 Performance of the 2 different freeze-dried formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good One met mechanical properties for shipping criteria 1 (Assessed with cake appearance) (#2) 2 Rapid and complete reconstitution None met (Assessed with visual inspection criteria 2 post-mixing) 3 The mixture should not inhibit coagulation Not checked (Assessed with thromboelastography) 4 The coagulated mixtures (implants) Not checked should be mechanically stable (Assessed with manual crushing test) 5 The coagulated mixtures (implants) All met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression (#1, 2) measurements) 6 Good mixing without phase separation None met of the polymer and blood components criteria 6 (Assessed with histology) 7 The mixtures should have appropriate Not checked handling properties (Assessed with runniness test) 8 The mixtures should have close to Not checked physiological properties (Assessed with pH and osmolality measurements)

[0182] In Example 3, although liquid formulations of chitosan can be easily mixed with PRP, reconstitution of freeze-dried chitosan formulations in PRP is much more challenging. Freeze-dried cakes containing high molecular weight chitosan did not dissolve easily and completely in PRP but could still be implanted ex vivo in a meniscal defect model using a standard operating room apparatus.

Example 4

1—Preparation of Chitosan Formulations

[0183] Formulations with Chitosan M.sub.n>100 kDa: Chitosans (M.sub.n 211 kDa, 80.6% DDA and M.sub.n 105 kDa, 81.2% DDA) were dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56% (w/v). The solutions were autoclaved for 10 minutes and cooled on ice. Filter-sterilised 15% (w/v) trehalose, 15% (w/v) mannitol, 270 mM CaCl.sub.2), stock L-histidine buffer 55 mM pH 6.5 (prepared by mixing 10 mL of 0.017% w/v L-histidine and 10 mL of HCl 30 mM) and autoclaved 5M NaCl were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 110 kDa, 80.2% DDA) was added before dispensing in 3 mL individual vials for freeze-drying.

[0184] Formulations with Chitosan M.sub.n<100 kDa: Chitosans (M.sub.n 38 kDa, 82.5% DDA, M.sub.n 11 kDa, 84.4% DDA and M.sub.n 4 kDa, 80.2% DDA) were dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56% (w/v). The solutions were filter-sterilised. Filter-sterilised 15% (w/v) trehalose, 15% (w/v) mannitol, 270 mM CaCl.sub.2), 5M NaCl and stock histidine buffer 55 mM pH 6.5 (prepared by mixing 10 mL of 0.017% w/v L-histidine and 10 mL of HCl 30 mM) were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 40 kDa, 80.0% DDA or M.sub.n 10 kDa, 81.9% DDA) was added before dispensing in 3 mL individual vials for freeze-drying.

[0185] As per Table 9, the HCl concentration was adjusted so that all formulations had a HCl:glucosamine ratio of 0.6. The NaCl concentration was adjusted so that the formulation had theoretical osmolality 350 mOsm. A lower concentration of histidine (3.8 mM vs 33-39 mM in previous examples) was chosen to prevent cake cracking. Lyoprotectant concentration was set at 2% or 6% (w/v) enough to provide a stable cake but not impede coagulation.

[0186] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00009 TABLE 9 Freeze-dried formulations containing the clot activator (CaCl.sub.2) to be reconstituted directly with PRP. Chitosan HCl NaCl Trehalose Mannitol Histidine CaCl.sub.2 M.sub.n Type of Formulation Group (w/v) (mM) (mM) (mM) (mM) (mM) (mM) (kDa) chitosan 1 CS-NaCl 0.56% 16 150 0 0 0 42.2 126 High M.sub.n 2 CS-NaCl- 0.56% 16 150 0 0 3.8 42.2 130 Chitosan Hist 3 CS-2% 0.56% 16 0 53 0 0 42.2 131 Trehalose 4 CS-2% 0.56% 16 0 53 0 3.8 42.2 129 Trehalose- Hist 5 CS-6% 0.56% 16 0 159 0 0 42.2 N/D Trehalose 6 CS-6% 0.56% 16 0 159 0 3.8 42.2 183 Trehalose-Hist 7 CS-2% 0.56% 16 0 0 110 0 42.2 150 Mannitol 8 CS-2% 0.56% 16 0 0 110 3.8 42.2 148 Mannitol-Hist 9 CS-6% 0.56% 16 0 0 329 0 42.2 154 Mannitol 10 CS-6% 0.56% 16 0 0 329 3.8 42.2 167 Mannitol-Hist 11 CS-NaCl 0.56% 16.4 150 0 0 0 42.2 38 Medium M.sub.n 12 CS-NaCl-Hist 0.56% 16.4 150 0 0 3.8 42.2 38 Chitosan 13 CS-2% 0.56% 16.4 0 53 0 0 42.2 38 Trehalose 14 CS-2% 0.56% 16.4 0 53 0 3.8 42.2 38 Trehalose-Hist 15 CS-6% 0.56% 16.1 0 159 0 0 42.2 79 Trehalose 16 CS-6% 0.56% 16.1 0 159 0 3.8 42.2 102 Trehalose-Hist 17 CS-2% 0.56% 16.4 0 0 110 0 42.2 38 Mannitol 18 CS-2% 0.56% 16.4 0 0 110 3.8 42.2 38 Mannitol-Hist 19 CS-6% 0.56% 16.1 0 0 329 0 42.2 88 Mannitol 20 CS-6% 0.56% 16.1 0 0 329 3.8 42.2 89 Mannitol-Hist 21 CS-NaCl 0.56% 17 150 0 0 0 42.2 11 Low M.sub.n 22 CS-NaCl-Hist 0.56% 17 150 0 0 3.8 42.2 11 Chitosan 23 CS-2% 0.56% 17 0 53 0 0 42.2 11 Trehalose 24 CS-2% 0.56% 17 0 53 0 3.8 42.2 11 Trehalose-Hist 25 CS-6% 0.56% 16 0 159 0 0 42.2 4 Trehalose 26 CS-6% 0.56% 16 0 159 0 3.8 42.2 4 Trehalose-Hist 27 CS-2% 0.56% 17 0 0 110 0 42.2 11 Mannitol 28 CS-2% 0.56% 17 0 0 110 3.8 42.2 11 Mannitol-Hist 29 CS-6% 0.56% 16 0 0 329 0 42.2 4 Mannitol 30 CS-6% 0.56% 16 0 0 329 3.8 42.2 4 Mannitol-Hist

2—Cake Appearance

[0187] Formulations without lyoprotectant shrunk significantly during freeze-drying.

[0188] Histidine buffer used at a 3.8 mM concentration did not induced cake cracking as seen previously in Example 1 with higher concentrations of 33-39 mM.

[0189] Cakes were bulkiest when increased lyoprotectant concentrations were used. Cakes containing mannitol were bulkier than cakes containing trehalose (FIGS. 4A1 & 4A2).

3—Cake Reconstitution

[0190] Human PRP and PPP were extracted as described above in Example 3, Section 2-Isolation of human PRP.

[0191] Cakes were reconstituted with 1 mL PRP or 1 mL PPP and mixed with three 0.39 g steel beads for 10 seconds.

[0192] Medium and low M.sub.n chitosans dissolved better than higher M.sub.n chitosans, especially in the presence of lyoprotectants.

4—Liquid Expression

[0193] Formulations reconstituted in PRP were dispensed into glass tubes at 37° C. After 60 minutes, liquid expression from the hybrid clots was quantified by weight measurement.

[0194] All hybrid clots expressed less liquid than PRP alone.

5—Clot Homogeneity

[0195] Hybrid clots were fixed in 10% NBF and thick razor blade sections were observed with epifluorescence microscopy to evaluate chitosan dispersion in the clots.

[0196] Chitosan aggregated in most hybrid clots prepared with high M.sub.n chitosan (FIGS. 4B1 & 4B2).

[0197] Chitosan was well dispersed within most hybrid clots when medium M.sub.n chitosan was used (FIGS. 4B3 & 4B4).

[0198] Erythrocytes present in the PRP sedimented towards the bottom of the clots leaving a band of chitosan at the surface of the clot when the lowest M.sub.n chitosans were used (FIGS. 4B5 & 4B6).

6—Ex Vivo Implantation in Meniscal Defects

[0199] Freeze-dried chitosan/PRP formulations were successfully implanted ex vivo in meniscal defects where they coagulated in situ as described in Example 3, Section 7—Ex vivo implantation in meniscal defects.

TABLE-US-00010 TABLE 10 Performance of the 30 different formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good Sixteen met mechanical properties for shipping criteria 1 (Assessed with cake appearance) (#5-10, 15-20, 27-30) 2 Rapid and complete reconstitution Eighteen met (Assessed with visual inspection criteria 2 post-mixing) (#9-10, 13-20, 23-30) 3 The mixture should not inhibit coagulation Not checked (Assessed with thromboelastography) 4 The coagulated mixtures (implants) Not checked should be mechanically stable (Assessed with manual crushing test) 5 The coagulated mixtures (implants) Twenty-two met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression (#1-10, 13-20, measurements) 23, 25, 27, 29) 6 Good mixing without phase separation Six met of the polymer and blood components criteria 6 (Assessed with histology) (#13-18) 7 The mixtures should have appropriate Not checked handling properties (Assessed with runniness test) 8 The mixtures should have close to Ten met physiological properties (pH 6.6-7.0 criteria 8 and osmolality 400-600 mOsm) (#3-4, 7-8, (Assessed with pH and osmolality 13-14, 17-18, measurements) 23, 27)

[0200] In Example 4, decreasing chitosan molecular weight improves cake solubility in PRP, but that only chitosan of medium molecular weight (M.sub.n 38 kDa) produced chitosan/PRP hybrid clots that were homogenous without any phase separation that occurs at lower molecular weight or aggregation that occurs at higher molecular weight.

Example 5

1—Preparation of Chitosan Formulations

[0201] Medium M.sub.n Chitosans (M.sub.n 56 kDa, 80.1% DDA and MC 32 kDa, 81.2% DDA) were dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 0.56%, 1% or 2% (w/v). The solutions were filter-sterilised. Filter-sterilised 15% (w/v) trehalose, 15% (w/v) mannitol and 270 mM CaCl.sub.2 were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 40 kDa, 80.0% DDA) was added before dispensing in 3 mL individual vials for freeze-drying.

[0202] As per Table 11, the HCl concentration was adjusted so that all formulations had a HCl:glucosamine ratio of 0.6. Lyoprotectant concentration was set at 2% or 6% (w/v) enough to provide a stable cake but not impede coagulation.

[0203] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00011 TABLE 11 Freeze-dried formulations containing the clot activator (CaCl.sub.2) to be reconstituted directly with PRP. Chitosan HCl Trehalose Mannitol CaCl.sub.2 Aliquot Rehydrated CS Formulation Group (w/v) (mM) (mM) (mM) (mM) into in Chitosan 1 0.56% CS-2% 0.56% 16 mM  53 mM — 42.2 mM 1 mL 1 mL PRP 81.2% DDA Trehalose M.sub.n 32 kDa 2 0.56% CS-6% 0.56% 16 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 3 0.56% CS-2% 0.56% 16 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 4 0.56% CS-6% 0.56% 16 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol 5 1% CS-2%   1% 29 mM  53 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 6 1% CS-6%   1% 29 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 7 1% CS-2%   1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 8 1% CS-6%   1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol 9 2% CS-2%   2% 57 mM  53 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 10 2% CS-6%   2% 57 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 11 2% CS-2%   2% 57 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 12 2% CS-6%   2% 57 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol Chitosan 13 0.56% CS-2% 0.56% 16 mM  53 mM — 42.2 mM 1 mL 1 mL PRP 80.1% Trehalose 14 0.56% CS-6% 0.56% 16 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 15 0.56% CS-2% 0.56% 16 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 16 0.56% CS-6% 0.56% 16 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol 17 1% CS-2%   1% 29 mM  53 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 18 1% CS-6%   1% 29 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 19 1% CS-2%   1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 20 1% CS-6%   1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol 21 2% CS-2%   2% 57 mM  53 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 22 2% CS-6%   2% 57 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 23 2% CS-2%   2% 57 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 24 2% CS-6%   2% 57 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol indicates data missing or illegible when filed

2—Cake Appearance

[0204] Cakes were bulkiest when increased lyoprotectant concentrations were used. Cakes containing mannitol were bulkier than cakes containing trehalose.

3—Cake Reconstitution

[0205] Human PRP and PPP were extracted from 2 different human donors as described above in Example 3, Section 2-Isolation of human PRP.

[0206] Cakes were reconstituted with 1 mL PRP or 1 mL PPP and mixed with three 0.39 g steel beads for 10 seconds.

[0207] Formulations containing 2% (w/v) chitosan did not solubilise well.

[0208] Cakes containing lower M.sub.n chitosan 32 kDa were easier to reconstitute compared to cakes containing higher M.sub.n chitosan 56 kDa at both 0.56% and 1% (w/v) chitosan concentration.

4—Thromboelastography (TEG)

[0209] 360 μL of each formulation was loaded into a TEG cup immediately after mixing and TEG tracings were recorded for 1 hour.

[0210] Formulations containing 0.56% (w/v) chitosan M.sub.n 32 kDa clotted in 1-phase manner similar to PRP only controls (FIG. 5B1).

[0211] Increasing chitosan M.sub.n or concentration induced a 2-phase coagulation mechanism as revealed by TEG tracings (FIGS. 5B2 & 5B3).

[0212] In all cases, adding 6% (w/v) lyoprotectant gave softer clots with lower maximal amplitude (MA between 24-61 mm) than adding 2% (w/v) lyoprotectant (MA between 51-84 mm).

5—Runniness Test

[0213] Runniness was assessed by placing a 30 μL drop of each formulation onto a rigid piece of plastic fixed at a certain angle (38 degrees) immediately after reconstitution and taking pictures at fixed times.

[0214] Increasing chitosan concentration improved paste-like properties of formulations (Compare FIGS. 5A1 & 5A2). Increasing chitosan M.sub.n improved paste-like properties of formulations (Compare FIGS. 5A1 & 5A3).

TABLE-US-00012 TABLE 12 Performance of the 24 different formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good Twenty met mechanical properties for shipping criteria 1 (Assessed with cake appearance) (#3-12, 15-24) 2 Rapid and complete reconstitution Fourteen met (Assessed with visual inspection criteria 2 post-mixing) (#1-8, 13-16, 19-20) 3 The mixture should not inhibit coagulation Thirteen met (Assessed with thromboelastography) criteria 3 Note that #20 was not tested due to (#1-8, 13-16, 19) insufficient PRP extraction 4 The coagulated mixtures (implants) Not checked should be mechanically stable (Assessed with manual crushing test) 5 The coagulated mixtures (implants) Fourteen met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression (#2-8, 13-19) measurements) 6 Good mixing without phase separation Five met of the polymer and blood components criteria 6 (Assessed with histology) (#6, 7, 8, 9, 16) 7 The mixtures should have appropriate Twelve met handling properties criteria 7 (Assessed with runniness test) (#5-8, 13-20) 8 The mixtures should have close to Eleven met physiological properties (pH 6.6-7.0 criteria 8 and osmolality 400-600 mOsm) (#1-3, 5-7, 13-15, (Assessed with pH and osmolality 17, 19) measurements)

[0215] In Example 5, paste-like properties of formulations can be improved by increasing chitosan concentration or chitosan M.sub.n. Freeze-dried cakes containing medium molecular weight chitosan can be easily reconstituted in PRP as long as the chitosan concentration is below 2% (w/v).

Example 6

1—Preparation of Chitosan Formulations

[0216] Five different medium M.sub.n Chitosans (M.sub.n 56 kDa, 80.1% DDA, M.sub.n 56 kDa, 81.8% DDA, M.sub.n 32 kDa, 81.2% DDA, M.sub.n 30 kDa, 81.0% DDA and M.sub.n 28 kDa, 80.5% DDA) were dissolved in HCl overnight at room temperature to obtain a final chitosan concentration of 1% (w/v). The solutions were filter-sterilised. Filter-sterilised 15% (w/v) trehalose, 15% (w/v) mannitol and 270 mM CaCl.sub.2 were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 40 kDa, 80.0% DDA or M 110 kDa, 80.2% DDA) was added before dispensing in 3 mL individual vials for freeze-drying.

[0217] As per Table 13, the HCl concentration was adjusted so that all formulations had a HCl:glucosamine ratio of 0.6. Lyoprotectant concentration was set at 2% or 6% (w/v) enough to provide a stable cake but not impede coagulation.

[0218] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00013 TABLE 13 Formulations with CaCl.sub.2 reconstituted directly with PRP Chitosan HCl Trehalose Mannitol CaCl.sub.2 Aliquot Rehydrated CS Formulation Group (w/v) (mM) (mM) (mM) (mM) into in DDA 1 1% CS-2% 1% 29 mM  53 mM — 42.2 mM 1 mL 1 mL PRP 81.2% Trehalose M.sub.n 2 1% CS-6% 1% 29 mM 159 mM — 42.2 mM 1 mL 1 mL PRP 32 kDa Trehalose 3 1% CS-2% 1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 4 1% CS-6% 1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol DDA 5 1% CS-2% 1% 29 mM  53 mM — 42.2 mM 1 mL 1 mL PRP 81.0% M.sub.n Trehalose 30 kDa 6 1% CS-6% 1% 29 mM 159 mM — 42.2 mM 1 mL 1 mL PRP Trehalose 7 1% CS-2% 1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 8 1% CS-6% 1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol DDA 9 1% CS-2% 1% 29 mM  53 mM — 42.2 mM 1 mL 1 mL PRP 80.5% Trehalose M.sub.n 10 1% CS-6% 1% 29 mM 159 mM — 42.2 mM 1 mL 1 mL PRP 28 kDa Trehalose 11 1% CS-2% 1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol 12 1% CS-6% 1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP Mannitol DDA 13 1% CS-2% 1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP 80.1% Mannitol M.sub.n 14 1% CS-6% 1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP 56 kDa Mannitol 15 1% CS-2% 1% 29 mM — 110 mM 42.2 mM 1 mL 1 mL PRP Mannitol DDA 16 1% CS-6% 1% 29 mM — 329 mM 42.2 mM 1 mL 1 mL PRP 81.8%, Mannitol M.sub.n 56 kDa

2—Cake Appearance

[0219] Cakes were bulkiest when increased lyoprotectant concentrations were used. Cakes containing mannitol were bulkier than cakes containing trehalose (FIGS. 6A1 and 6A2).

3—Cake Reconstitution

[0220] Human PRP and PPP were extracted as described above in Example 3, Section 2-Isolation of human PRP.

[0221] Cakes were reconstituted with 1 mL PRP or 1 mL PPP and mixed with three 0.39 g steel beads for 10 seconds.

[0222] All formulations dissolved well and met performance criteria 2.

4—Thromboelastography (TEG)

[0223] 360 μL of each formulation was loaded into a TEG cup immediately after mixing and TEG tracings were recorded for 1 hour.

[0224] All formulations induced a 2-phase coagulation mechanism as revealed by TEG tracings (FIGS. 6B1 and 6B2).

[0225] In all cases, adding 6% (w/v) lyoprotectant gave softer clots with lower maximal amplitude (MA between 37-67 mm) than adding 2% (w/v) lyoprotectant (MA between 68-79 mm).

5—Runniness Test

[0226] Runniness was assessed by placing a 30 μL drop of each formulation onto a rigid piece of plastic fixed at a certain angle (38 degrees) immediately after reconstitution and taking pictures at fixed times.

[0227] All formulations had paste-like properties compared to PRP alone (FIG. 6C1).

6—Liquid Expression

[0228] Formulations reconstituted in PRP were dispensed into glass tubes at 37° C. After 60 minutes, liquid expression from the hybrid clots was quantified by weight measurement.

[0229] All hybrid clots expressed less liquid than PRP alone (FIG. 6B3).

7—Clot Homogeneity

[0230] Hybrid clots were fixed in 10% NBF and thick razor blade sections were observed with epifluorescence microscopy to evaluate chitosan dispersion in the clots.

[0231] Chitosan was dispersed throughout the hybrid clots for all the formulations (FIGS. 6A3 and 6A4)

8—Crushing Test

[0232] After 1 hour of clotting, each hybrid clot was subjected to a crushing test and mechanical strength scored.

[0233] 0=Clot could not be handled without disintegrating.

[0234] +=Clot was easily broken and crushed appearance was multiple fragments (more than 5 fragments).

[0235] ++=Clot was relatively firm and crushed appearance was multiple fragments (3-5 fragments).

[0236] +++=Clot was firm and elastic, crushed appearance was 2-3 fragments.

[0237] ++++=Clot was firm and elastic, crushed appearance was 2 fragments (sometimes still connected) or there was just a hole in the center of clot.

[0238] Adding 6% (w/v) lyoprotectant decreased clot mechanical strength compared to 2% (w/v) lyoprotectant (Compare FIGS. 6D1 and 6D2 to 6D3 and 6D4).

9—Ex Vivo Implantation in Cartilage Defects

[0239] Biopsy punches of 8 mm and flat surgical blades were used to create cartilage defects in pig condyle and trochlea.

[0240] The joints were placed in a humid chamber at 37° C. for at least 30 min before the start of the experiment.

[0241] Reconstituted freeze-dried chitosan/PRP formulations were injected into the cartilage defects.

[0242] The joints were immediately sealed in the humid chamber and were placed at 37° C. for 1 hour.

[0243] Freeze-dried chitosan/PRP formulations were successfully implanted ex vivo in cartilage defects using a syringe and 20-gauge needle where they coagulated in situ (FIG. 6C2).

TABLE-US-00014 TABLE 14 Performance of the 16 different formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good All met mechanical properties for shipping criteria 1 (Assessed with cake appearance) (#1-16) 2 Rapid and complete reconstitution All met (Assessed with visual inspection criteria 2 post-mixing) (#1-16) 3 The mixture should not inhibit coagulation All met (Assessed with thromboelastography) criteria 3 (#1-16) 4 The coagulated mixtures (implants) Eight met should be mechanically stable criteria 4 (Assessed with manual crushing test) (#1, 3, 5, 7, 9, 11, 13, 15) 5 The coagulated mixtures (implants) All met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression (#1-16) measurements) 6 Good mixing without phase separation Six met of the polymer and blood components criteria 6 (Assessed with histology) (#6, 8, 10, 12, 14, 16) 7 The mixtures should have appropriate All met handling properties criteria 7 (Assessed with runniness test) (#1-16) 8 The mixtures should have close to Eleven met physiological properties (pH 6.6-7.0 criteria 8 and osmolality 400-600 mOsm) (#1-3, 5-7, (Assessed with pH and osmolality 9-11, 13, 15) measurements)

[0244] In Example 6, different batches of chitosan powder with similar M.sub.n can be used to prepare cakes that will have equivalent performance characteristics. Chitosan cakes with high concentrations of lyoprotectant produce chitosan/PRP hybrids that are undesirably soft.

Example 7

1—Preparation of Chitosan Formulations

[0245] Four different M.sub.n Chitosans (M.sub.n 10 kDa, 80.6% DDA, M.sub.n 41 kDa, 80.6% DDA, M.sub.n 89 kDa, 80.6% DDA and M.sub.n 108 kDa, 80.6% DDA) were dissolved in Hof overnight at room temperature to obtain final chitosan concentrations of 0.56% (w/v), 1% (w/v) and 2% (w/v), the latter concentration only prepared for the chitosan M.sub.n 10 kDa. The solutions were filter-sterilised. Filter-sterilised 15% (w/v) trehalose, 15% (w/v) mannitol and 270 mM CaCl.sub.2 were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 10 kDa, 81.9% DDA, M.sub.n 40 kDa, 80.0% DDA or M.sub.n 110 kDa, 80.2% DDA) was added before dispensing in 3 mL or 2 mL individual vials for freeze-drying.

[0246] As per Table 15, the H5m concentration was adjusted so that all formulations had a HCl:glucosamine ratio of 0.6. Lyoprotectant concentration was set at 2%, 4% or 6% (w/v) enough to provide a stable cake but not impede coagulation.

[0247] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00015 TABLE 15 Formulations with CaCl.sub.2 reconstituted directly with PRP. HCl for 60% Rehydrated in Chitosan protonated Trehalose Mannitol CaCl.sub.2 (volume) of CS Sol Formulation (w/vol) (mM) (mM) (mM) (mM) Aliquot into PRP M.sub.n 10 kDa, 1 0.56% CS-2% 0.56% 16 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 2 0.56% CS-6% 0.56% 16 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 3 0.56% CS-2% 0.56% 16 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 4 0.56% CS-6% 0.56% 16 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 5 1% CS-2%   1% 29 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 6 1% CS-6%   1% 29 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 7 1% CS-2%   1% 29 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 8 1% CS-6%   1% 29 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 9 2% CS-2%   2% 57 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 10 2% CS-6%   2% 57 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 11 2% CS-2%   2% 57 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 12 2% CS-6%   2% 57 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol M.sub.n 41 kDa, 13 0.56% CS-2% 0.56% 16 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 14 0.56% CS-6% 0.56% 16 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 15 0.56% CS-2% 0.56% 16 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 16 0.56% CS-6% 0.56% 16 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 17 1% CS-2%   1% 29 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 18 1% CS-6%   1% 29 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 19 1% CS-2%   1% 29 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 20 1% CS-6%   1% 29 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol M.sub.n 89 kDa, 21 0.56% CS-2% 0.56% 16 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 22 0.56% CS-6% 0.56% 16 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 23 0.56% CS-2% 0.56% 16 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 24 0.56% CS-6% 0.56% 16 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol M.sub.n 108 kDa, 25 1% CS-2%   1% 29 mM  53 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 26 1% CS-6%   1% 29 mM 159 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 27 1% CS-2%   1% 29 mM — 110 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 28 1% CS-6%   1% 29 mM — 329 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol M.sub.n 10 kDa, 29 0.56% CS-4% 0.56% 16 mM 106 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 30 0.56% CS-4% 0.56% 16 mM — 220 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 31 1% CS-4%   1% 29 mM 106 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 32 1% CS-4%   1% 29 mM — 220 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol M.sub.n 41 kDa, 33 0.56% CS-4% 0.56% 16 mM 106 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 34 0.56% CS-4% 0.56% 16 mM — 220 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 35 1% CS-4%   1% 29 mM 106 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 36 1% CS-4%   1% 29 mM — 220 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol M.sub.n 89 kDa, 37 0.56% CS-4% 0.56% 16 mM 106 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL 80.6% DDA Trehalose 38 0.56% CS-4% 0.56% 16 mM — 220 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol 39 1% CS-4%   1% 29 mM 106 mM — 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Trehalose 40 1% CS-4%   1% 29 mM — 220 mM 42.2 mM 1 mL or 300 μL 1 mL or 300 μL Mannitol

2—Cake Appearance

[0248] Cakes were bulkiest when increased lyoprotectant concentrations were used. Cakes containing mannitol were bulkier than cakes containing trehalose.

3—Cake Reconstitution

[0249] Human PRP and PPP were extracted as described above in Example 3, Section 2-Isolation of human PRP.

[0250] Cakes were reconstituted with 1 mL PRP or 1 mL PPP and mixed by hand without the aid steel beads for 10 seconds. For four of the formulations (#15, 19, 23, 27), three 0.39 g steel beads were used to reconstitute the cakes as well to compare with previously obtained results.

[0251] The formulations prepared with chitosan M.sub.n 10 kDa at 0.56% (w/v) and at 1% (w/vol) dissolved completely. Formulations prepared with chitosan M.sub.n 10 kDa at 2% (w/vol) and with chitosan M.sub.n 41 kDa at 0.56% and 1% (w/vol) dissolved well. Formulations prepared with chitosan M.sub.n 89 kDa and 108 kDa were thicker and more difficult to handle.

4—Thromboelastography (TEG)

[0252] 360 μL of each formulation was loaded into a TEG cup immediately after mixing and TEG tracings were recorded for 1 hour.

[0253] Formulations containing chitosan M.sub.n 10 kDa at 0.56% (w/v) induced a 1-phase coagulation tracing. Increasing chitosan concentration and M.sub.n induced a 2-phase coagulation mechanism as revealed by TEG tracings.

[0254] Clot reaction time was high for formulations containing chitosan M.sub.n 10 kDa and short for formulations containing chitosan M.sub.n 108 kDa, with the 40 kDa formulations falling in between.

[0255] Maximal amplitude was greater for hybrid clots containing 2% (w/v) lyoprotectant compared to hybrid clots containing 4% or 6% (w/v) lyoprotectant.

5—Runniness Test

[0256] Runniness was assessed by placing a 30 μL drop of each formulation onto a rigid piece of plastic fixed at a certain angle (38 degrees) immediately after reconstitution and taking pictures at fixed times.

[0257] The formulations containing chitosan M.sub.n 10 kDa at 0.56% (w/vol) and 1% (w/vol) were runny.

[0258] All other formulations had paste-like properties compared to PRP alone.

6—Liquid Expression

[0259] Formulations reconstituted in PRP were dispensed into glass tubes at 37° C. After 60 minutes, liquid expression from the hybrid clots was quantified by weight measurement.

[0260] All hybrid clots expressed less liquid than PRP alone.

7—Clot Homogeneity

[0261] Large chitosan aggregates were observed in most hybrid clots prepared with chitosan M.sub.n 89 kDa and 108 kDa (FIGS. 7A3, 7A4, 7A7 and 7A8). Chitosan was well dispersed within most hybrid clots when chitosan M.sub.n 41 kDa was used (FIGS. 7A1, 7A2, 7A5 and 7A6). Erythrocytes present in the PRP sedimented towards the bottom of the clots leaving a band of chitosan at the surface of the clot when the chitosan M.sub.n 10 kDa was used.

8—Crushing Test

[0262] After 1 hour of clotting, each hybrid clot was subjected to a crushing test and mechanical strength scored.

[0263] 0=Clot could not be handled without disintegrating.

[0264] +=Clot was easily broken and crushed appearance was multiple fragments (more than 5 fragments).

[0265] ++=Clot was relatively firm and crushed appearance was multiple fragments (3-5 fragments).

[0266] +++=Clot was firm and elastic, crushed appearance was 2-3 fragments.

[0267] ++++=Clot was firm and elastic, crushed appearance was 2 fragments (sometimes still connected) or there was just a hole in the center of clot.

[0268] Adding 6% (w/v) lyoprotectant decreased clot mechanical strength.

9—Ex Vivo Implantation in Cartilage Defects

[0269] Biopsy punches of 8 mm and flat surgical blades were used to create cartilage defects in pig condyle, trochlea and tibial plateau.

[0270] The joints were placed in a humid chamber at 37° C. for at least 30 min before the start of the experiment.

[0271] Reconstituted freeze-dried chitosan/PRP formulations were injected into the cartilage defects.

[0272] The joints were immediately sealed in the humid chamber and were placed at 37° C. for 1 hour.

[0273] Freeze-dried chitosan/PRP formulations were successfully implanted ex vivo in cartilage defects using a syringe and 20-gauge needle where they coagulated in situ.

10—Reconstituting the Freeze-Dried Formulations without Beads Versus Mixing with Beads

[0274] Histological appearance of hybrid clots was similar whether the freeze-dried cakes were reconstituted without the aid of stainless steel beads or by mixing with three 0.39g stainless steel beads (compare FIGS. 7A1, 7A2, 7A3 and 7A4 with 7A5, 7A6, 7A7 and 7A8).

[0275] Performance characteristics of freeze-dried formulations were similar for hybrid clots prepared without the aid the without the aid of stainless steel beads or by mixing with three 0.39g stainless steel beads (see Table of FIG. 7B).

11—Osmolality of Formulations Reconstituted with PRP

[0276] Freeze-dried chitosan formulations containing mannitol had higher osmolality than freeze-dried formulations containing trehalose. Osmolality increased with lyoprotectant concentration. Formulations containing 2% (w/vol) trehalose had osmolality between 443-495 mOsm. Formulations containing 2% (w/vol) mannitol had osmolality between 526-582 mOsm. Formulations containing 4% (w/vol) trehalose had osmolality between 516-564 mOsm. Formulations containing 4% (w/vol) mannitol had osmolality between 608-665 mOsm. Formulations containing 6% (w/vol) trehalose had osmolality between 595-631 mOsm. Formulations containing 6% (w/vol) mannitol had osmolality between 759-823 mOsm.

12—Subcutaneous Implantation of Freeze-Dried Chitosan Formulations

[0277] Several formulations with low and high osmolality were tested in vivo in a rabbit subcutaneous implant model (Table 16).

TABLE-US-00016 TABLE 16 Formulations tested in vivo in a rabbit subcutaneous implant model. CS CS CS CS HCl Trehalose Mannitol CaCl.sub.2 No Formulation DDA.sup.1 M.sub.n CS M.sub.w PD conc conc conc conc conc pH.sup.3 mOsm.sup.3 13 0.56% CS- 80.6% 41 75 kDa 1.837 0.56% 16 mM  53 mM — 42.2 mM 6.913 477 2% kDa Trehalose 33 0.56% CS- 80.6% 41 75 kDa 1.837 0.56% 16 mM 106 mM — 42.2 mM 6.995 564 4% kDa Trehalose 14 0.56% CS- 80.6% 41 75 kDa 1.837 0.56% 16 mM 159 mM — 42.2 mM 6.962 593 6% kDa Trehalose 17 1% CS-2% 80.6% 41 75 kDa 1.837   1% 29 mM  53 mM — 42.2 mM 6.870 483 Trehalose kDa 35 1% CS-4% 80.6% 41 75 kDa 1.837   1% 29 mM 106 mM — 42.2 mM 6.794 527 Trehalose kDa 18 1% CS-6% 80.6% 41 75 kDa 1.837   1% 29 mM 159 mM — 42.2 mM 6.861 628 Trehalose kDa 21 0.56% CS- 80.6% 89 156 1.757 0.56% 16 mM  53 mM — 42.2 mM 6.970 461 2% kDa kDa Trehalose 22 0.56% CS- 80.6% 89 156 1.757 0.56% 16 mM 159 mM — 42.2 mM 6.950 629 6% kDa kDa Trehalose 25 1% CS-2% 80.6% 108 173 1.544   1% 29 mM  53 mM — 42.2 mM 6.957 443 Trehalose kDa kDa 27.sup.1 1% CS-2% 80.6% 108 173 1.544   1% 29 mM — 110 mM 42.2 mM 6.915 582 Mannitol kDa kDa .sup.1DDA of source chitosan depolymerised to M.sub.n 41, 89 and 108 kDa. 2 Note that formulation #27 was chosen because there were no mores cakes available containing the formulation 1% CS (M.sub.n 108 kDa) with 6% Trehalose. .sup.3pH and osmolality values obtained after reconstitution in human PRP.

[0278] The hair on the back of NZW rabbits was shaved and the skin was disinfected with 3 passages of Baxedin®, then with 3 alternating passages of proviodine and isopropanol 70%.

[0279] Autologous PRP was prepared from rabbit blood extracted immediately prior to surgery, as described above in Example 1 section 4—Isolation of rabbit PRP. Each 300 μL freeze-dried chitosan cake was reconstituted with 300 μL PRP without the aid of beads for mixing.

[0280] A 1-cc syringe equipped with a Sub Q needle was used to deliver 150 μL of each implant under the skin of the back of the rabbit

[0281] PRP controls were recalcified with 42.2 mM CaCl.sub.2) prior to injection.

[0282] The injection sites were systematically varied on each animal to avoid site-dependent outcomes.

[0283] Animals were euthanized at 1 (FIGS. 7C1 to 7C6), 3 (FIGS. 7D1 to 7D6), 7 and 14 days post-injection (FIGS. 7E2 and 7E3).

[0284] At day 1, the chitosan implants appeared largely intact. In some instances the erythrocytes present in the PRP were visible within the implants. White blood cells were attracted to the implants and were found mostly at the periphery of the implants (FIGS. 7C1, 7C2, 7C3 and 7C4).

[0285] By day 3, the chitosan/PRP implants were partly degraded and white blood cells were invading the implants (FIGS. 7D1, 7D2, 7D3 and 7D4).

[0286] There was an effect of time as white blood cell recruitment was increased at day 3 compared to day 1 (Compare FIGS. 7D1-7D4 to FIGS. 7C1-7C4).

[0287] The chitosan/PRP hybrids were resident in vivo until 14 days post-injection (FIGS. 7E1, 7E2 and 7E3).

[0288] The recalcified PRP controls were only visible until 3 days post-injection (FIG. 7E4 shows PRP control at 1 day) and did not induce much cell recruitment (FIGS. 7C5, 7C6, 7D5, 7D6 and 7E4).

TABLE-US-00017 TABLE 17 Performance of the 40 different formulations. Criteria Performance of number Criteria description formulations 1 Homogenous solid form with good All met mechanical properties for shipping criteria 1 (Assessed with cake appearance) 2 Rapid and complete reconstitution 30 met (Assessed with visual inspection criteria 2 post-mixing) (#1-20; 29-38) 3 The mixture should not inhibit coagulation All met (Assessed with thromboelastography) criteria 3 4 The coagulated mixtures (implants) 27 met should be mechanically stable criteria 4 (Assessed with manual crushing test) 5 The coagulated mixtures (implants) All met should largely inhibit clot retraction criteria 5 (Assessed with liquid expression measurements) 6 Good mixing without phase separation 12 met of the polymer and blood components criteria 6 (Assessed with histology) (#13-20; 35-38) 7 The mixtures should have appropriate All met handling properties criteria 7 (Assessed with runniness test) 8 The mixtures should have close to Seven did not physiological properties (pH 6.6-7.0 meet criteria 8 and osmolality 400-600 mOsm) (#4, 8, 12, 16, (Assessed with pH and osmolality 20, 24, 27) measurements)

[0289] In Example 7, mixing with stainless steel beads is not required for reconstitution of freeze-dried chitosan cakes with PRP. Formulations containing high concentrations of lyoprotectant have high osmolality and attract more leukocytes upon implantation in vivo. Chitosan/PRP hybrids were also found to be retained longer than recalcified PRP only controls in vivo. 8 specific formulations (#13, 15, 17, 19, 35-38) met all of the pre-defined performance characteristics.

Example 8

1—Preparation of Chitosan Formulations

[0290] Two different Chitosans (M.sub.n 43 kDa, 85% DDA and M.sub.n 36 kDa, 80% DDA) were dissolved in HCl overnight at room temperature to obtain final chitosan concentrations of 1% (w/v). The solutions were filter-sterilised. Filter-sterilised 15% (w/v) trehalose and 270 mM CaCl.sub.2) were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 40 kDa, 80.0% DDA) was added to some of the vials before dispensing in 3 mL individual vials for freeze-drying.

[0291] As per Table 18, the HCl concentration was adjusted so that all formulations had a HCl:glucosamine ratio of 0.6. Lyoprotectant concentration was set at 1% (w/v) in order to have osmolality close to physiological, provide a stable cake but not impede coagulation.

[0292] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00018 TABLE 18 Formulations with CaCl.sub.2 reconstituted directly with PRP. HCl for Rehydrated 60% in CS CS Chitosan protonated Trehalose Mannitol CaCl.sub.2 Aliquot (volume) of Sol Mn DDA Formulation (w/vol) (mM) (mM) (mM) (mM) into PRP 1 43 85% 1% CS-1% 1% 31 mM 26 mM — 42.2 mM 1 mL 1 mL kDa Trehalose 2 36 80% 1% CS-1% 1% 28 mM 26 mM — 42.2 mM 1 mL 1 mL kDa Trehalose

2—Cake Appearance

[0293] Cakes had a smooth surface and nice appearance without any collapse. There was a slight retraction of all the cakes in the glass vials upon freeze-drying (FIGS. 8A1 and 8A2).

3—Cake Reconstitution

[0294] Human PRP and PPP were extracted as described above in Example 3, Section 2-Isolation of human PRP.

[0295] Cakes were reconstituted with 1 mL PRP or 1 mL PPP and mixed by hand without the aid steel beads for 10 seconds.

[0296] The formulations had good solubility and dissolved completely (FIGS. 8A3 and 8A4).

4—Thromboelastography (TEG)

[0297] 360 μL of each formulation was loaded into a TEG cup immediately after mixing and TEG tracings were recorded for 1 hour.

[0298] Clot reaction time and maximal amplitude were lower for chitosan/PRP formulations compared to the PRP control (FIGS. 8C1 and 8C2).

5—Runniness Test

[0299] Runniness was assessed by placing a 30 μL drop of each formulation onto a rigid piece of plastic fixed at a certain angle (38 degrees) immediately after reconstitution and taking pictures at fixed times.

[0300] Formulations had paste-like properties compared to PRP control.

6—Liquid Expression

[0301] Formulations reconstituted in PRP were dispensed into glass tubes at 37° C. After 60 minutes, liquid expression from the hybrid clots was quantified by weight measurement.

[0302] Hybrid clots expressed no liquid while PRP controls expressed more than 80% of their weight in serum (FIGS. 8B1, 8B2, 8B3 and 8B4).

7—Clot Homogeneity

[0303] Hybrid clots were fixed in 10% NBF and chitosan dispersion observed using epifluorescent microscopy.

[0304] Chitosan was well dispersed within the hybrid clots (FIGS. 8C3 and 8C4).

8—Crushing Test

[0305] After 1 hour of clotting, each hybrid clot was subjected to a crushing test and mechanical strength scored as described in Example 7, Section 8-Crushing test.

[0306] Hybrid clots had good mechanical strength.

11—Osmolality of Formulations Reconstituted with PRP

[0307] The formulation containing Chitosan M.sub.n 43 kDa, 85% DDA had osmolality of 457 mOsm upon reconstitution. The formulation containing Chitosan M.sub.n 36 kDa, 80% DDA had osmolality of 444 mOsm upon reconstitution.

12—In Vivo Implantation in Meniscus Defects

[0308] The two above described formulations as well as PRP-only controls were tested in a sheep meniscus repair model.

[0309] On the morning of surgery, PRP was extracted from the sheep blood as described in Example 2, Section 4-Isolation of sheep PRP.

[0310] A 1.5 cm long arthrotomy was made to access the medial femorotibial joint space and a horizontal incision was made in the medial joint capsule to access the anterior ⅓.sup.rd of the meniscus.

[0311] A 10 mm tear was creasted at ⅓.sup.rd the length between the capsular and free borders (closer to the capsule) using a #11 scalpel blade to create a stab wound (FIG. 8D1) which was lengthened by a meniscus push knife (FIG. 8D2).

[0312] The tear and synovium were rasped to create some 3D space for the FD chitosan/PRP implant to adhere to without disrupting circumferential fibres that impart hoop strains (FIG. 8D3).

[0313] Two 3-0 polypropylene sutures were placed in a horizontal mattress pattern around the meniscus tear (FIG. 8D4).

[0314] Two trephination channels were created from the periphery of the meniscus to the tear with by placing two 18 gauge needles ˜2 mm apart (FIG. 8D5).

[0315] The chitosan cakes were reconstituted with 1 mL of autologous PRP and mixed vigorously for 10 seconds.

[0316] The chitosan/PRP mixture was aspirated using a 1-cc syringe.

[0317] The chitosan/PRP hybrid material was extruded into the channels and into the tear while pulling out the 18 gauge needles (FIG. 8D6).

[0318] The sutures were tightened 5 minutes after delivery with sufficient tension to appose the meniscal tear edges.

[0319] The joint capsule was sutured and the procedure repeated with the other knee as per study design.

[0320] The PRP-only controls were recalcified with 42.2 mM CaCl.sub.2) immediately prior to injection.

[0321] Animals were euthanized at 1 and 21 days post-injection surgery.

[0322] At day 1, chitosan/PRP was resident in the tears (FIGS. 8E1 and 8E2).

[0323] At day 21, the edges of the tears treated with chitosan/PRP were well apposed (FIGS. 8E3 and 8E4).

[0324] Example 8, exhibited that chitosan/PRP formulations may be injected into meniscus defects in vivo using standard surgical instrumentation, that chitosan/PRP hybrids are resident in the meniscus tears and that tears treated with chitosan/PRP hybrids have well apposed edges after 21 days of healing.

Example 9

1—Preparation of Chitosan Formulation

[0325] Chitosan (M.sub.n 40 kDa, 80% DDA) was dissolved in HCl overnight at room temperature to obtain final chitosan concentrations of 1% (w/v). The solution was filter-sterilised. Filter-sterilised 15% (w/v) trehalose and 270 mM CaCl.sub.2) were added, as required. Filter-sterilised Rhodamine-chitosan tracer (M.sub.n 40 kDa, 80.0% DDA) was added to the vials before dispensing in 2 mL individual vials for freeze-drying.

[0326] As per Table 19, the HCl concentration was adjusted so that the formulations had a HCl:glucosamine ratio of 0.6. Lyoprotectant concentration was set at 2% (w/v).

[0327] The freeze-drying cycle was identical to the one described in Example 2, Section 2-Freeze-drying cycle.

TABLE-US-00019 TABLE 19 Formulation with CaCl.sub.2 reconstituted directly with PRP. HCl for Rehydrated 60% in CS CS Chitosan protonated Trehalose Mannitol CaCl.sub.2 Aliquot (volume) of Sol Mn DDA Formulation (w/vol) (mM) (mM) (mM) (mM) into PRP 1 40 80% 1% CS-2% 1% 28 mM 53 mM — 42.2 mM 300 μL 300 μL kDa Trehalose

8—In Vivo Chronic Cartilage Repair Model

[0328] Chondral-only defects of 4 mm×4 mm were created bi-laterally in the trochlea of three 9-month old NZW rabbits (FIG. 9A1), the knees sutured and the defects were allowed to develop to chronic stage for 1 month (FIG. 9A2).

[0329] The knees were reopened, the defects debrided and four microdrill holes were pierced through the subchondral bone with a 0.9 mm drill bit to a depth of ˜4 mm.

[0330] Autologous PRP was prepared from rabbit blood extracted immediately prior to surgery, as described above in Example 1, section 4—Isolation of rabbit PRP. After creation of the defect, the freeze-dried chitosan cake was reconstituted with 300 μL PRP, mixed vigorously for 10 seconds and the implant (1 hanging drop) was delivered over the defect site and allowed to solidify in situ for ˜5 min before closing the knee (FIG. 9A4).

[0331] Recalcified PRP was delivered to the contralateral knee as control (FIG. 9A3).

[0332] At 21 days post-surgery, the repair tissues on the treated and control sides had a different appearance (FIGS. 9B1 and 9B2).

[0333] Increased cell recruitment and extensive bone remodeling were observed in the chitosan/PRP treated knee (FIG. 9B4), which was absent in the control knee (FIG. 9B3).

[0334] Example 9, provided that chitosan/PRP hybrid implants may be delivered in vivo to chronic cartilage defects, where they stimulate cell recruitment and bone remodeling, features previously associated with improved repair.

[0335] Based on the above, we were able to determine which chitosan compositions fulfilled at least one, in some instances more than one, and in some instances all of our pre-defined performance characteristics. The criteria that were met include: 1) Mechanically stable cakes for storage and shipping (FIGS. 6A1 and 6A2); 2) Rapid, easy and complete reconstitution in PRP (FIGS. 6A1 and 6A2); 3) In situ coagulation achieved and not inhibited (FIGS. 6B1 and 6B2); 4) Chitosan/PRP hybrid implants able to withstand mechanical loading post-implantation (FIGS. 6D1 and 6D2); 5) Inhibition of platelet-mediated clot retraction to fill tissue defects (FIG. 6B3); 6) Good mixing without phase separation of polymers and blood components (FIGS. 6A3 and 6A4); 7) Viscous and paste-like formulations for tissue repair applications (FIG. 6C1) and 8) Close-to-physiological properties for in vivo application (Example 7). Chitosan/PRP hybrids are resident for at least 14 days in order to successfully stimulate tissue repair in vivo in contrast recalcified PRP only which was cleared within 3 days (FIGS. 7C, 7D and 7E). In addition, chitosan/PRP hybrids were used in vivo in animal models to treat meniscus defects (FIGS. 8D and 8E), acute cartilage defects (FIG. 1B) and chronic cartilage defects (FIGS. 9A and 9B). Examples of preferred embodiments for tissue implantation and in situ gelation are: 1) Chitosan of a molecular weight between about M.sub.n 28 and about 56 kDa at a concentration of no more than about 1% (w/v) and no more than about 4% (w/v) lyoprotectant or 2) Chitosan of a molecular weight between about M.sub.n 89 and about 108 kDa at a concentration no more than about 0.56% (w/v) and no more than about 4% (w/v) lyoprotectant. Other formulations tested that met some of the pre-defined criteria contained chitosan of a molecular weight between about M.sub.n 4 and about 211 kDa at a concentration range of about 0.42 and about 2% (w/v), between about 1 to about 10% lyoprotectant (sucrose, trehalose, mannitol), a salt (NaCl) or a buffer (histidine).

[0336] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.