NOVEL HYDROGEL TISSUE EXPANDERS

Abstract

The present invention provides tissue expanders comprising biodegradable, chemically cross-linked hydrogels which are elastic in the dry state. These biocompatible tissue expanders are self-inflating and membrane-free. They swell slowly and elicit minimal negative tissue responses, while allowing for rapid and easy manipulation by the surgeon at the time of emplacement.

Claims

1. A hydrogel, chemically-cross-linked via ester-acrylate bonds, comprising: triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymers having molecular weights of 1,000 to 50,000 Da, wherein: the percent ratio of ((molecular weight of total PLGA)/(molecular weight of total copolymer)100%) for the copolymers is >60%; and each of x, y, and z is independently an integer from 1 to 500.

2. The hydrogel of claim 1, wherein the triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymers have molecular weights of 2,000 to 40,000 Da.

3. (canceled)

4. The hydrogel of claim 1, wherein the percent ratio of ((molecular weight of total PLGA)/(molecular weight of total copolymer)100%) for the copolymers is 95-75%.

5. (canceled)

6. The hydrogel of claim 1, wherein the triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymers comprise 1% to 80% (w/w) of the hydrogel.

7. (canceled)

8. (canceled)

9. The hydrogel of claim 1, wherein the lactide:glycolide ratio in the (PLGA)x copolymer ranges from about 50:50 to about 99:1.

10. (canceled)

11. (canceled)

12. (canceled)

13. The hydrogel of claim 1, wherein (PLGA).sub.x is about 1000 to about 7000 Da, (PEG).sub.y is about 200 to about 2000 Da, and (PLGA).sub.z is about 1000 to about 7000 Da.

14. (canceled)

15. (canceled)

16. (canceled)

17. The hydrogel of claim 1, wherein x=z.

18. The hydrogel of claim 1, further comprising (PLGA)- or (PLA)-diacrylates having molecular weights of 1,000 to 200,000 Da.

19. (canceled)

20. (canceled)

21. The hydrogel of claim 18, wherein the concentration of the (PLGA)- or (PLA)-diacrylates is 1% to 30% (w/w) of the hydrogel.

22. (canceled)

23. (canceled)

24. The hydrogel of claim 18, wherein the lactide:glycolide ratio in the (PLGA)-diacrylate copolymer ranges from about 50:50 to about 99:1.

25. (canceled)

26. The hydrogel of claim 1 to 25, further comprising poly(ethylene glycol) diacrylates having molecular weights of 100 to 10,000 Da.

27. (canceled)

28. (canceled)

29. The hydrogel of claim 26, wherein the concentration of the poly(ethylene glycol) diacrylates is 5% to 70% (w/w) of the hydrogel.

30. (canceled)

31. (canceled)

32. The hydrogel of claim 1, further comprising ethylene glycol dimethacrylate as a crosslinker.

33. The hydrogel of claim 32, wherein the ethylene glycol dimethacrylate has a concentration of 1% to 30% (w/w) of the hydrogel.

34. (canceled)

35. (canceled)

36. The hydrogel of claim 1, wherein the cross-linking density (trilinked chains/mg) is 0.1 to 5.0.

37. (canceled)

38. (canceled)

39. The hydrogel of claim 1, wherein the overall hydrophobicity (directly water insoluble content/water soluble content) is 35% to 90%.

40. (canceled)

41. (canceled)

42. The hydrogel of claim 1, wherein the hydrogel is impregnated with one or more drugs selected from: a growth factor, an antibiotic, a pain-relieving drug, a blood-coagulation modifying agent, and an immune-response modifying agent.

43. (canceled)

44. (canceled)

45. (canceled)

46. (canceled)

47. (canceled)

48. (canceled)

Description

DETAILED DESCRIPTION OF THE INVENTION

[0096] The present invention provides tissue expanders comprising novel hydrogels which elicit controlled expansion of mucosa or skin following surgical implantation. These expanders can be reshaped by the surgeon prior to emplantation without losing their characteristic of delayed expansion. For dental purposes, these hydrogel tissue expanders are typically placed in a resorbed alveolar ridge. FIG. 1 illustrates the use of a tissue expander in the mandibular posterior area, but it could also be used in the anterior and maxilla alveolar areas. Outside the oral cavity, the device can be used to expand the skin in a variety of locations.

[0097] The hydrogel expanders of the present invention add a very useful feature to tissue expanders: the ability to modify the size and shape of the implant. These devices are useful in many areas of reconstructive surgery, since they can assume a wide range of large to very small sizes and shapes. Beyond intraoral and plastic surgical procedures, these devices can be used for in utero closure of conditions such as spinae bifida (T. Kohl, Minimally invasive feloscopic interventions: An overview in 2010, Surg. Endosc., (2010) 24(8): pp. 2056-2067; N. S. Adzick, et al., A randomized trial of prenatal versus postnatal repair of myelomeningocele, N. Engl. J. Med., (2011) 364(11): pp. 993-1004; and M. A. Fichter, et al., Fetal spina bifida repaircurrent trends and prospects of intrauterine neurosurgery, Fetal Diagn. Ther., (2008) 23(4): pp. 271-286), cleft lips and palates, especially using conventional and feto-endoscopic surgery (N. A. Papadopulos, et al., Foetal surgery and cleft lip and palate: Current status and new perspectives, Br. J. Plast. Surg., (2005) 58(5): pp. 593-607), as well as other in utero surgical procedures (T. Kohl, Minimally invasive fetoscopic interventions: An overview in 2010, Surg. Endosc., (2010) 24(8): pp. 2056-2067).

[0098] As used herein:

[0099] AIBN means azobisisobutyronitrile;

[0100] -DA indicates that a material has been diacrylated;

[0101] DCM means dichloromethane;

[0102] DCS means differential scanning calorimetry;

[0103] -DMA indicates methacrylation of a material;

[0104] DMSO means dimethylsulfoxide;

[0105] EGDMA means ethylene glycol dimethacrylate;

[0106] Ether means diethyl ether;

[0107] ETO means ethylene oxide;

[0108] MW means molecular weight;

[0109] PEG means polyethylene glycol;

[0110] PLA means polylactic acid;

[0111] PLGA means poly(lactic-co-glycolic acid);

[0112] RG503-DA indicates the acrylated form of commercially-obtained PLGA;

[0113] RT means room temperature; and

[0114] TEA means triethylamine;

[0115] The following preparations, Examples and tests illustrate how to make and use specific embodiments of the invention, and are not intended to limit the scope thereof:

[0116] Preparations:

[0117] Triblock Copolymer Synthesis:

[0118] (PLGA).sub.x-(PEG).sub.v-(PLGA).sub.z triblock copolymers are synthesized by ring opening reaction, with PEG diol used as an initiator. A desired block size of PEG-diol is commercially purchased and purified by dissolution in DCM and precipitation in ether. Afterwards, a specific quantity is dried by heating to 150 C. under a deep vacuum in a 2-neck round-bottom flask for three hours. Commercially purchased lactide and glycolide monomers are recrystallized twice in ethyl acetate to further purify. Prior to use, stannous octoate (Sn(OCt).sub.2) is vacuum distilled to remove residual water, and stored over desiccant. A predetermined molar quantity of these monomers is added to the PEG and Sn(OCt).sub.2 catalyst dissolved in toluene (10% w/v). These are placed under a deep vacuum for 0.5 hour, and then heated to 150 C. for 8 hours. After synthesis, the (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z triblock polymer is dissolved in a small amount of DCM, filtered, and re-precipitated in ether.

[0119] In a typical PLGA synthesis, the presence of small quantities of water, along with the Sn(Oct).sub.2, initiate the ring opening reaction. In this reaction, the Sn(Oct).sub.2 catalyst converts the alcohol endcaps of the polyethylene glycol to an activated RO-Sn+ form, which causes these sites to serve for initiation of the PLGA chain, thus leading to a block copolymer.

[0120] TABLE 1 describes several Examples of triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymers. Because these triblock copolymers are not commercially available at the listed molecular weights, they are custom synthesized. Of these triblocks, TB05 notably has biodegradable block lengths which are substantially higher in molecular weight than the original PEG block (10:1 ratio of PLGA: PEG). This renders the macromer inherently water insoluble even prior to cross-linking. The application of this macromer, and others like it, to the generation of hydrogels lends itself to surprising changes in the resultant gel properties.

TABLE-US-00001 TABLE 1 Triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymers PEG Block LA:GA PLGA Block Name (Nominal MW) Ratio (Nominal MW) TB01 1,500 1:1 333 TB02 1,500 4:1 246 TB03 2,000 1:0 750 TB04 2,000 1:1 666 TB05 1,000 1:1 5,000 TB06 1,500 4:1 492 TB07 1,500 1:1 340 TB08 400 1:1 717 TB09 1000 1:1 7500 TB10 1000 1:1 3500 TB11 1000 1:0 5000

[0121] Triblock Copolymer Acrylation:

[0122] Following synthesis and purification of the triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymer, the resultant polymer is activated with acrylate endcaps to allow cross-linking. A two-neck flask is purged with dry nitrogen for 20-30 min. The triblock (PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z copolymer is dissolved in 30 ml of benzene or DCM. TEA and acryloyl chloride are added to the reaction flask in a molar ratio of 3-times the (OH) groups, and the reaction mixture is stirred at 80 C. for 3 h under reflux conditions. The reaction mixture is then filtered to remove triethylamine hydrochloride, and the filtrate is dropped into excess n-hexane to precipitate the DA-(PLGA).sub.x-(PEG).sub.y-(PLGA).sub.z-DA product.

[0123] Subsequently, this product is re-dissolved in DMSO to a concentration of approximately 20% w/v, and reprecipitated in ethanol. This secondary process eliminates the excess acrylic acid formed from acryloyl chloride side reactions. Alternatively, the product is dissolved in ethyl acetate and mixed with activated carbon for 24 hours, followed by filtration, rotary evaporation (to remove ethyl acetate), re-dissolution in DCM, and precipitation in either ether or hexane:ethanol (80:20) mix. Finally, the precipitated product is dried at room temperature under reduced pressure for 24 h.

[0124] FIG. 2 shows the schematic chemical reaction process. FIG. 3 shows HNMR characterization results for TB05-DA, with the indicated peak assignments confirming successful triblock synthesis and diacrylation. The addition of the acrylate group renders the polymer vinylically-active, allowing it to participate in radical-chain, cross-linking reactions, thus converting the material to a macromer.

[0125] PLGA/PLA Acrylation:

[0126] A similar process as described for the triblock copolymer is utilized to acrylate PLGA. For this process, either a commercially-sourced PLGA may be utilized (e.g. Resomer RG503H MW 25,000 Da, Mn 12,000 Da acid end-capped), which results in single-end acrylation, or a custom-synthesized PLGA/PLA-diacrylate may be generated. For the synthesis of PLGA/PLA-diacrylate, the polyester is synthesized utilizing 1,10-decanediol as the precursor. The 1,10-decanediol is briefly purged at RT under deep vacuum to remove any surface moisture, and predetermined molar quantities of lactide, glycolide and Sn(Oct).sub.2 initiator are added to the decanediol, followed by vacuum purging and heating at 150 C. for 8 hours.

[0127] Prior to acrylation, the polyester is dissolved in dichloromethane and re-precipitated in hexane to purify it. The PLGA or PLA thus formed is di-alcohol end-capped, allowing for attachment of acrylate units on both termini of the polyester. After purification, the polyester is redissolved in DCM and reacted with 3 (OH) molar equivalent of TEA and acryloyl chloride, and purified, as described above.

[0128] For the custom synthesized materials, the compositions are named as in following example: PLGA(1:1, 10,000 Da)-DA. The di-alcohol end-capped polyester allows for not only additional hydrophobicity of the molecule, but also cross-linking, as the subsequent diacrylated polyester can conjugate two chains together.

[0129] Methacrylation:

[0130] The process of methacrylation is die same as that described for acrylation, with the exception that methacryloyl chloride is utilized during the reaction instead of acryloyl chloride.

[0131] Hydrogel Formation:

[0132] The components (PLGA).sub.x-(PEG).sub.y-(PLGA)z diacrylate, PLGA diacrylate, ethylene glycol dimethacrylate (EGDMA) and commercially-purchased PEG diacrylate, as well as other additives including commercial monomers and crosslinkers, are combined in DMSO (anhydrous) solvent to a total concentration of 10% to 30% w/v solid/DMSO. AIBN is recrystallized from methanol prior to use, while the other components are used as received, or as generated. AIBN is added to the DMSO at a concentration of 0.35% w/w solids, and the solution is briefly sparged with inert gas to remove dissolved oxygen. The solution is then placed in a 65 C. oven overnight. T. H. Tran, et al., Biodegradable Elastic Hydrogels for Tissue Expander Application, Handbook of Biodegradable Polymers, (2011) 9: p. 2.

[0133] The solution undergoes radical cross-linking reaction to form a three-dimensional hydrogel network. This is visually confirmed upon removal from the oven, as the solution solidifies due to cross-linking. The resultant hydrogels are immersed in alternating solutions of ethanol and ethyl acetate to remove unreacted residues and DMSO over the course of 1-2 weeks. The hydrogels are subsequently dried in a vacuum oven for more than 24 h.

[0134] Successful synthesis of the hydrogel is further confirmed by FTIR. Upon triblock formation a peak, additional to the spectra of the PEG precursor, arises around 1750 cm.sup.1, corresponding to the formation of the ester carbonyl bonds (CO). After acrylation, a relatively weak peak is observed at 650 cmcm.sup.1 due to CH bending. Upon hydrogel formation, this peak disappears, indicating radical chain polymerization, which consumes the alkene bonds as part of the reaction.

[0135] Further confirmation is obtained by DSC. The PEG precursor exhibits a melting endotherm, typically in the range of 50-60 C., with the resultant triblock showing a melting endotherm slightly lower than the original PEG block, due to block copolymerization. After cross-linking, no melting endotherm is observed below 100 C. (maximum tested temperature), indicating successful formation of a cross-linked polymer, which is thermoset and does not melt upon increasing temperature. The Examples subsequently listed are hydrogels formed by this method. FIG. 4 shows a schematic example of this cross-linking reaction.

[0136] In-Vitro Analysis of Hydrogels

[0137] Mechanical:

[0138] Cylindrical portions of formed hydrogels are cut and their cross-sectional area measured. These hydrogel portions are then loaded onto a mechanical testing device (The TA XTPlus Texture Analyzer from Texture Technologies Corp., Algonquin, Ill.), compressed with a -inch radius Dacron tip at a crosshead speed of 0.5 mm/sec to 20% strain, and held there for 60 seconds before the tip is withdrawn. The slope of the stress-strain curve for 2% strain is measured as the elasticity modulus. The compression force at 20% strain after holding for 60 seconds is divided by the initial compressive force at 20% strain and converted to a percent, to yield stress relaxation.

[0139] The post-degradation mechanical strength of the degraded hydrogels is determined by compressing a sample with a -inch steel ball at a crosshead speed of 0.5 mm/sec. The force at which the hydrogel fails is divided by the height of the hydrogel to obtain mechanical strength in N/mm. The higher this number, the stronger the post-degraded hydrogel.

[0140] Swelling Rate:

[0141] Swelling studies are performed by measuring the swelling ratio, which is the weight of a swollen gel (W.sub.s) divided by the weight of a dry gel (W.sub.d). Sample hydrogels are placed in phosphate buffered saline, and the increase in weight due to swelling in water is measured at pre-determined time points after removing excess water with a KIMWIPE paper.

[0142] Swelling Pressure:

[0143] The swelling pressure of a hydrogel is measured by placing a cylindrical sample in a mechanical-testing texture analyzer with a specially modified stage. The standard texture analyzer base is replaced with a 37 C. hot plate to allow incubation during measurements. A 22-ml scintillation vial is placed on the base and the dry hydrogel introduced in this vial. The texture analyzer tip ( inch Dacron) is lowered until it touched the hydrogel. The tip is held still at this position while 10 ml of 0.154 M hydrochloric acid (HCl) is added to the vial, and the tip is held in place for 24 hours while the hydrogel is allowed to swell. HCl is used in the same ionic concentration as bodily fluids, so that PLGA degradation can be expedited with minimal impact on swelling properties. The maximum force exerted by the hydrogel during this time (for all samples this occurred prior to 24 hours) is recorded and divided by the contact area of the swollen hydrogel. This indicates the maximum possible force that the hydrogels can generate by their own swelling power.

Examples 1-19

[0144] TABLE 2 lists the compositions of hydrogel Examples 1-16. The formulas include the components listed as % w/v in DMSO. Unless otherwise specified, the PEG-DA has a molecular weight of 700 Da, and the reaction is initiated with 0.35% (w/w solids) AIBN.

TABLE-US-00002 TABLE 2 Formulas of hydrogel Examples 1-16 Example Formula (% w/v in DMSO) 1 10% TB01DA 2 7.5% TB01DA; 2.5% PEGDA 3 5% TB01DA; 5% PEGDA 4 2.5% TB01DA; 7.5% PEGDA 5 7.5% TB02DA; 2.5% PEGDA 6 5% TB02DA; 5% PEGDA 7 2.5% TB02DA; 7.5% PEGDA 5% TB05DA; 5% PEGDA; 0.01% acrylic acid 9 10% TB02DA; 5% PEGDA 10 10% TB04DA; 5% PEGDA 11 7.5% TB04DA; 7.5% PEGDA 12 10% TB04DA; 5% PEGDA; 0.45% acrylic acid 13 7.5% TB05DA; 7.5% PEGDA; 0.15% acrylic acid 14 7.5% TB02DA; 7.5% PEGDA; 0.15% methylene bisacrylamide; 0.3% acrylic acid 15 10% TB06DA; 5% PEGDA; 0.01% ethylene glycol dimethacrylate 16 7.5% TB01DA; 7.5% PEGDA; 0.15% PLGADA

[0145] Examples 1-16 are analyzed as described above and their properties listed in TABLE 3. The columns indicate values as shown:

[0146] (1) Initial swelling is the swelling ratio after the first 24 hours of incubation.

[0147] (2) Maximum swelling is the highest swelling ratio obtained over the course of the entire experiment (typically 60 days).

[0148] (3) Max time is the time in days it took to reach the maximum swelling.

[0149] (4) Elasticity and stress relaxation of dry hydrogels indicate their ability to be reshaped.

[0150] (5) Swelling pressure is in mm Hg and tested as indicated previously.

[0151] (6) Post condition describes the hydrogel morphology with failure strength in N/mm listed in parenthesis. ND indicates that no data is available for the sample for this category.

TABLE-US-00003 TABLE 3 Properties of hydrogel Examples 1-16 Max Elasticity Swelling Post Initial Maximum Time (kPa)/Stress Pressure Condition Example Swelling Swelling (Days) Relaxation (%) (mmHg) (N/mm) 1 5 60 6 5.2/95 700 Liquid 2 8 138 5 2.6/92 471 Liquid 3 8 130 14 2.0/94 450 Liquid 4 11 248 9 2.6/95 411 Liquid 5 11 81 13 2.0/96 419 Liquid 6 12 65 24 3.0/95 433 Liquid 7 12 88 35 2.3/93 491 Liquid 8 4 11 16 ND/ND 87 Liquid 9 4 8 16 2.3/94 >1,000 Solid (0.05) 10 7 11 8 1.04/89 ND Solid (ND) 11 6 9 57 1.5/90 ND Solid (0.04) 12 7 13 16 0.68/80 728 Liquid 13 2 6 31 0.8/32 ND Solid (0.11) 14 4 5 35 0.3/47 ND Solid (0.49) 15 4 8 17 2.0/95 1,614 Solid (0.05) 16 1.9 2.1 17 3.1/8.8 ND Solid (0.33)

[0152] This series of tests indicates some common results. Generally, hydrogels prepared using these method and materials have the ability to be reshaped using common sharp surgical instruments. Also, these hydrogels have sufficient pressure to expand tissue. Previous researchers had suggested required pressures in the range of 25 to 235 mm Hg. S. J. Berg, et al., Tissue expansion using osmotically active hydrogel systems for direct closure of the donor defect of the radial forearm flap, Plast. Reconstr. Surg. (2001) 108(1): pp. 1-5, discussion pp. 6-7; K. G. Wiese, Tissue expander inflating due to osmotic driving forces of a shaped body of hydrogel and an aqueous solution, U.S. Pat. No. 5,496,368; and H. S. Z. Min and P. Svedman, On expander pressure and skin blood flow during tissue expansion in the pig, Annals of Plastic Surgery (1988) 21(2): p. 6. Since the expansion of the hydrogels of the present invention is controlled by time instead of pressure, having a maximal obtainable pressure within this range is not an issue. The important point of measuring the maximal pressure is to ensure that the hydrogels have sufficient pressure to expand skin. Adjusting the recipe has its most dramatic impact on the swelling profile of the expander and the strength of the material when expansion is completed. This information led to the preparation of improved device materials in Examples in 17-19.

Example 17

[0153] This hydrogel is prepared by reacting a 10% TB05-DA, 5% PEGDA, and 0.75% RG503-DA (w/v) solution in DMSO.

Example 18

[0154] This hydrogel is prepared by reacting a 10%, 4 TB05-DA, 5% PEGDA, 0.75% RG503-DA (w/v), and 0.15% ethylene glycol dimethacrylate solution in DMSO.

Example 19

[0155] This hydrogel is prepared by reacting a 10% TB05-DA, 5% PEGDA, and 1.5% RG503-DA (w/v) solution in DMSO.

[0156] Analysis of Examples 17-19 is focused on the swelling profiles of these hydrogels, both as made and after sterilization via ethylene oxide at 54 C. for a 16 hour cycle. Sterilization by ETO increases the speed of expansion, likely due to some damage of the PLGA chains. This is despite the fact that generally ETO is acknowledged as one of the least damaging methods of sterilization. S. E. Moioli, et al., Sustained release of TGFbeta3 from PLGA microspheres and its effect on early osteogenic differentiation of human mesenchymal stem cells. Tissue Engineering (2006) 12(3): pp. 537-546. The addition of PLGA slows the expansion back down to a reasonable rate.

[0157] FIG. 5 shows two example expansion profiles to highlight a surprising result. Use of water-soluble triblocks creates hydrogels with a built-in-delay time prior to extremely rapid swelling and dissolution (see FIG. 5A for hydrogels synthesized from 333-1500-333 PLGA-PEG-PLGA-diacrylate and PEG-diacrylate (700 Da) at the indicated ratios). The scale on the vertical axis is in 100's of expansion ratio. This result is due to the fact that the hydrogel, completely comprised of water soluble components, is under extreme stress to expand during the entire period. Upon degradation, the chains are set free to expand rapidly. Generally, this property is well suited for situations wherein rapid, relatively large expansion is required. For the tissue expansion application, however, this is not necessarily desirable.

[0158] The use of non-water-soluble, triblock copolymers (e.g., PLGA-PEG-PLGA, in which the PLGA block size is substantially larger than the PEG block size) creates expanders which have lower initial swelling, as well as almost zero-order continuous swelling. This is due to the moderate increase in hydrophilicity of the entire expander as degradation removes hydrophobic PLGA components. This feature is valuable for the tissue expander application, as it allows for continuous expansion instead of the stepwise manner of the current injectable-saline expanders Continuous expansion generates less trauma to the tissue as pressure is maintained at an almost constant level.

[0159] In Vivo Testing: Rat Model

[0160] Hydrogels of the present invention were tested in an in-vivo setting. All animal testing was performed at the Laboratory Animal Resource Center (LARC) at Indiana University Medical School (IUMed) in accordance with the Institutional Animal Care and Use Committee (IACUC) of this university. All procedures were performed under anesthesia as appropriate for the animal and procedure.

[0161] Based on in-vitro results described above, Examples 20-24 were prepared and used in animal studies. For the following preparations, the concentration of 20-25% w/v macromers in DMSO is fixed. As such, the formulations are described as % w/w of constituents.

Example 20

[0162] This hydrogel is prepared by reacting a (20% w/v solids) DMSO solution containing 70.2% TB05-DA, 3.5% RG503 Ac, and 26.3% PEGDA (% w/w) components.

Example 21

[0163] This hydrogel is prepared by reacting a (20% w/v solids) DMSO solution containing 45.1% TB05-DA, 6.4% RG503 Ac, 48.4% PEGDA, and 0.1% EGDiMAC (% w/w) components.

Example 22

[0164] This hydrogel is prepared by reacting a (20% w/v solids) DMSO solution containing 60.5% TB05-DA, 9.1% RG503 Ac, 30.3% PEGDA, and 0.1% EGDiMAC (% w/w) components.

Example 23

[0165] This hydrogel is prepared by reacting a (20% w/v solids) DMSO solution containing 63.2% TB05-DA, 4.8% RG503DA, 31.6% PEGDA, and 0.5% EGDiMAC (% w/w) components.

Example 24

[0166] This hydrogel has the same formulation as Example 17, but is coated with PVP (55 kDa) by briefly dipping the hydrogel in an aqueous solution of PVP and drying.

[0167] All hydrogels for animal studies were sterilized by ETO and handled asceptically prior to usage in the animal model. The pilot animal studies were performed on rats. Briefly, a section of tissue above the rats' skull was reflected, the implant was placed in beneath the tissue, and the wound was reclosed with stitches. The rats were then scanned with a 3D surface scanning FaroArm laser device to precisely calculate the expansion area and volume three times per week. The rats were also observed for any signs of tissue reaction. An initial 18 rat pilot study was performed on 6 prototypes, and no tissue reactions such as necrosis or dehiscence were observed. One rat displayed light ulceration caused by rubbing of the head on the top of the cage, which was remedied by placing the food on the bottom of the cage. After 6 weeks of expansion, the rats were sacrificed and histology was performed on the harvested tissue sections. TABLE 5 shows initial expansion results from the pilot study. Several of the hydrogels expanded successfully, yet crumbled upon removal due to insufficient hydrophobic content and cross-linking.

TABLE-US-00004 TABLE 5 Expansion results from rat pilot study for Examples 19-24. Example Tissue (%).sup.1 End Condition 19 17/34/43 Broken/pieces 20 23/65/56 Broken/pieces 21 41/58/64 Broken/pieces 22 26/72/97 Broken/pieces 23 24/53/54 Broken/pieces 24 26/46/74 Broken/pieces .sup.1surface area increase (%) of tissue at 2 days, 2 weeks, and 6 weeks, respectively.

[0168] This rat pilot study demonstrates that hydrogels with an appropriate combination of swelling rate and higher density of permanent cross-links have improved removability. This may be due to higher strength after full swelling. Based on this information, an additional five hydrogels were prepared and tested in 6 rats per each expander. Three rats were sacrificed after 4 weeks and the remaining after 6 weeks. As a control, 3 commercially purchased OSMED expanders were implanted and tested in the same manner. The compositions of Examples 25-29 are as described in Table 6.

TABLE-US-00005 TABLE 6 Compositions of hydrogel Examples 25-29 and OSMED control Components (%, w/w) PEG Ethylene PLGA-PEG-PLGA PLGA- Diacrylate Glycol (mw-mw-mw) acrylate (600 Da) Dimethacrylate PEGDA + Example Triblock Diacrylate (20k Da) (PEGDA) (EGDMA) EGDMA 25 (7.5k-1k-7.5k) 8.7% 29.0% 4.3% 33.3% 58.0% 26 (7.5k-1k-7.5k) 0% 26.2% 3.8% 30.0% 70.0% 27 (5k-1k-5k) 78.6% 11.1% 4.9% 5.4% 10.3% 28 (5k-1k-5k) 40.0% 17.2% 42.8% 0.1% 42.9% 29 (5k-1k-5k) 39.3% 5.6% 42.1% 12.9% 55.0% OSMED Methylmethacrylate and N-vinylpyrrolidone copolymer (control) with outer silicone rubber shell

[0169] The resultant change in volume ratio (Volume(t)/Volume(i)) by expander was measured by analyzing the region of interest using the Faro arm scanner. TABLE 7 shows the resultant volume swelling at days 3-4 (initial burst) and -13-19 (delayed phase). Due to limitations on the number of animals handled on a single day, the timelines do not match exactly, but are very close to each other.

TABLE-US-00006 TABLE 7 Initial and delayed expansion volume of select Examples and OSMED control. Initial expansion ratio Delayed expansion ratio Example (days) (days) 21 (N = 6) 2.1 1.4 (4.5 days) 1.9 1.1 (14.0 days) 28 (N = 6) 1.2 0.6 (3.0 days) 1.9 1.5 (13.0 days) 29 (N = 6) 0.4 0.5 (3.2 days) 0.7 0.8 (13.2 days) OSMED 3.6 1.1 (2.0 days) 2.6 0.4 (19.0 days) control (N = 3)

[0170] The tissues surrounding the expanders were histologically examined with statistical analysis. Chi-square tests were performed to determine if there were any significant differences among groups for blebs, chronic inflammation, or acute inflammation. Mantel-Haenszel tests for ordered categorical responses were performed to determine if there were any significant differences among groups for fibrous capsule, vascularity, or foam cell scores.

[0171] The results indicate that there were no statistically significant differences among groups for blebs (p=0.17), fibrous capsule (p=0.30), chronic inflammation (p=0.30), foam cells (p=0.06) or acute inflammation (p=1.00). Example 29 had significantly higher vascularity scores than most other groups. The full histological scores are shown in TABLE 8. The best performer in terms of reduced initial expansion with slow expansion was Example 29. This expander also presented good clinical behavior in terms of ease of insertion and removal and had notably less crumbling than other expander prototypes. As noted in the last column of TABLE 6, Example 29 has the highest total concentration of non-degradable cross-linkers (55.0% of PEGDA+EGDMA). Thus, Example 29 was identified as a logical candidate for a dog study.

TABLE-US-00007 TABLE 8 Histological scores for select hydrogel expander Examples. Example-weeks Scores (%) Category at necropsy 0 1 2 3 4 p-Value Blebs Example 21-4 0 (0%) 3 (100%) 0.17 Example 21-6 1 (33%) 2 (67%) Example 22-4 1 (33%) 2 (67%) Example 22-6 1 (33%) 2 (67%) Example 23-4 0 (0%) 3 (100%) Example 22-6 2 (67%) 1 (33%) Example 25-4 1 (33%) 2 (67%) Example 25-6 0 (0%) 3 (100%) Example 26-4 3 (33%) 2 (67%) Example 26-6 0 (0%) 3 (100%) Example 27-4 3 (50%) 1 (50%) Example 27-6 3 (33%) 2 (67%) Example 28-6 0 (0%) 3 (100%) Example 28-4 2 (67%) 1 (33%) Example 29-4 1 (33%) 2 (67%) Example 29-6 0 (0%) 3 (100%) Example 18-4 0 (0%) 3 (100%) Example 18-6 0 (0%) 3 (100%) OSMED-0611 3 (100%) 0 (0%) Fibrous Example 21-4 0 (0%) 0 (0%) 3 (100%) 0 (0%) 0.30 Capsule Example 21-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 22-4 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 22-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 23-4 0 (0%) 0 (0%) 2 (67%) 1 (33%) Example 23-6 1 (33%) 1 (33%) 1 (33%) 0 (0%) Example 25-4 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 25-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 26-4 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 26-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 27-4 1 (33%) 2 (67%) 0 (0%) 0 (0%) Example 27-6 0 (0%) 3 (100%) 0 (0%) 0 (0%) Example 28-6 0 (0%) 2 (67%) 0 (0%) 1 (33%) Example 28-4 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 29-4 0 (0%) 1 (33%) 1 (33%) 1 (33%) Example 29-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 18-4 0 (0%) 0 (0%) 1 (33%) 2 (67%) Example 18-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) OSMED-0611 0 (0%) 1 (33%) 2 (67%) 0 (0%) Chronic Example 21-4 2 (67%) 1 (33%) 0.30 Inflammation Example 21-6 3 (100%) 0 (0%) Example 22-4 2 (67%) 1 (33%) Example 22-6 3 (100%) 0 (0%) Example 23-4 2 (67%) 1 (33%) Example 23-6 2 (67%) 1 (33%) Example 25-4 2 (67%) 1 (33%) Example 25-6 3 (100%) 0 (0%) Example 26-4 3 (100%) 0 (0%) Example 26-6 3 (100%) 0 (0%) Example 27-4 1 (33%) 2 (67%) Example 27-6 2 (67%) 1 (33%) Example 28-6 2 (67%) 1 (33%) Example 28-4 2 (67%) 1 (33%) Example 29-4 0 (0%) 3 (100%) Example 29-6 3 (100%) 0 (0%) Example 18-4 2 (67%) 1 (33%) Example 18-6 3 (100%) 0 (0%) OSMED-0611 2 (67%) 1 (33%) Vascularity Example 21-4 0 (0%) 0 (0%) 3 (100%) 0 (0%) 0.0327 Example 21-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 22-4 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 22-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 23-4 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 23-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 25-4 1 (33%) 2 (67%) 0 (0%) 0 (0%) Example 25-6 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 26-4 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 26-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 27-4 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 27-6 0 (0%) 3 (100%) 0 (0%) 0 (0%) Example 28-6 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 28-4 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 29-4 0 (0%) 0 (0%) 0 (0%) 3 (100%) Example 29-6 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 18-4 0 (0%) 1 (33%) 2 (67%) 0 (0%) Example 18-6 0 (0%) 1 (33%) 2 (67%) 0 (0%) OSMED-0611 0 (0%) 1 (33%) 2 (67%) 0 (0%) Foam Cells Example 21-4 1 (33%) 1 (33%) 0 (0%) 1 (33%) 0 (0%) 0.06 Example 21-6 1 (33%) 1 (33%) 1 (33%) 0 (0%) 0 (0%) Example 22-4 0 (0%) 0 (0%) 2 (67%) 1 (33%) 0 (0%) Example 22-6 0 (0%) 0 (0%) 2 (67%) 0 (0%) 1 (33%) Example 23-4 0 (0%) 1 (33%) 1 (33%) 1 (33%) 0 (0%) Example 23-6 1 (33%) 2 (67%) 0 (0%) 0 (0%) 0 (0%) Example 25-4 0 (0%) 3 (100%) 0 (0%) 0 (0%) 0 (0%) Example 25-6 0 (0%) 1 (33%) 1 (33%) 1 (33%) 0 (0%) Example 26-4 1 (33%) 2 (67%) 0 (0%) 0 (0%) 0 (0%) Example 26-6 0 (0%) 3 (100%) 0 (0%) 0 (0%) 0 (0%) Example 27-4 1 (33%) 2 (67%) 0 (0%) 0 (0%) 0 (0%) Example 27-6 1 (33%) 2 (67%) 0 (0%) 0 (0%) 0 (0%) Example 28-6 0 (0%) 2 (67%) 1 (33%) 0 (0%) 0 (0%) Example 28-4 3 (100%) 0 (0%) 0 (0%) 0 (0%) 0 (0%) Example 29-4 2 (67%) 1 (33%) 0 (0%) 0 (0%) 0 (0%) Example 29-6 0 (0%) 3 (100%) 0 (0%) 0 (0%) 0 (0%) Example 18-4 1 (33%) 1 (33%) 1 (33%) 0 (0%) 0 (0%) Example 18-6 0 (0%) 2 (67%) 0 (0%) 1 (33%) 0 (0%) OSMED-0611 0 (0%) 1 (33%) 1 (33%) 1 (33%) 0 (0%) Acute Example 21-4 3 (100%) 1.00 Inflammation Example 21-6 3 (100%) Example 22-4 3 (100%) Example 22-6 3 (100%) Example 23-4 3 (100%) Example 23-6 3 (100%) Example 25-4 3 (100%) Example 25-6 3 (100%) Example 26-4 3 (100%) Example 26-6 3 (100%) Example 27-4 3 (100%) Example 27-6 3 (100%) Example 28-6 3 (100%) Example 28-4 3 (100%) Example 29-4 3 (100%) Example 29-6 3 (100%) Example 18-4 3 (100%) Example 18-6 3 (100%) OSMED-0611 3 (100%)

[0172] In-Vivo Testing: Dog Model

[0173] For this initial study, the molar teeth of both the maxillary and mandibular section from both sides of 2 beagle dogs were extracted, and the ridge ground down to model the natural process of bone resorption in humans. After 3 months of healing, the dogs had 6 Example 29 expanders and 2 OSMED.sup.gmbh control expanders surgically placed in either the left or right mandible or maxillary section of the jaw in a random block pattern. Example 29 expanders were reshaped by the surgeon at time of emplacement. The OSMED type 400-1070 expanders were inserted with a screw mounting to the bone as per manufacturer's directions.

[0174] The expanders were allowed to expand in the mucosa tissue for four weeks, or until secondary endpoint of tissue expander self-removal (popping out). At predetermined time points, dental impression and casts were made over the expanded tissue, and removed for future use in assaying expansion. After the 4-week time frame, a biopsy of the expanded mucosa was taken and the mucosa re-sutured to allow healing without sacrificing the dogs.

[0175] The OSMED control expanders both self-removed from the mucosa within 12 days of emplacement. This occurred via expulsion directly through the mucosa. One of the Example 29 hydrogels also underwent expulsion via a very similar pattern after 19 days of emplacement. In each case, expulsion occurred directly through the tissue rather than at the sutured point, indicating that time to suture healing was not the mechanism/problem that leads to these expanders being lost through the mucosa. Of the 5 remaining expander prototypes at the end of the study, only 2 were found and recovered in a maxilla of one of the dogs. The remaining 3 broke down and could not be recovered. Of the expanders that could be removed, all were observed to be fractured but remained in large enough pieces to allow traditional surgical removal using forceps and conventional surgical tools.

[0176] The initial results of the dog study are surprising. The expansion of mucosal tissue apparently requires a substantially-altered hydrogel relative to the Example 29 design. This requires further understanding on the relationship between hydrogel properties and in vivo results. The expulsion of the expander indicates higher expansion pressure than the tissue can bear, and the fractured expander indicates the weak/brittle nature of the expanded hydrogel.

[0177] To aid in visualizing and tracking the expanders, a fluorescent fluorescein diacrylate dye was incorporated into the hydrogel structure. Thus, a new set of expander prototypes was synthesized. Of more than 80 new prototypes generated, two fluorescein-labeled versions (Example 30 and Example 31) were selected based on the in vitro properties for the dog study. Additionally, Example 32 was selected as a prototype that has similar expansion properties but has substantially improved end strength. (see Table

TABLE-US-00008 TABLE 9 Hydrogel expander Examples 30-32, with Example 29 shown for comparison. Components (%, w/w) PLGA-PEG- PLGA In vitro Properties (5k-1k-5k) PEG Ethylene Initial Overall End Triblock Polyester Diacrylate glycol Fluoroscein Swelling Swelling Strength Ex. Diacrylate Acrylates * (600 Da) dimethacrylate Diacrylate (Day 1-3) (Day 42) (N/mm) 29 39.3% (PLG1) 42.1% 12.9% .sup.0% 170% 246% 0.49 5.6% 30 45.8% (PLG2) 32.7% 9.8% 1.6% 168% 340% 1.61 9.8% 31 41.0% (PL2) 41.0% 12.6% 1.0% 173% 269% 0.57 4.1% 32 41.4% (PL2) 41.5% 12.8% .sup.0% 187% 250% 2.12 4.1% * (PLG1: RG503DA; PLG2: PLGA-diacrylate (8.7 kDa); PL2: PLA-diacrylate (8.7 kDa))

[0178] In addition to modifying in-vitro properties of the hydrogel, the initial shape of the expanders was adjusted to be substantially a half-moon. This is clinically beneficial based on its capacity to expand without exposing tissue to an expander's corners or sharp edges. Additionally, the half-moon, cross-section of a cylinder-shaped expander has a rounded point on the terminal end to aid in implantation. This was accomplished by carrying out the reactions in a half-cylinder mold, as shown in FIG. 6.

[0179] Six Example 30 expanders were placed in right maxillary and mandibular positions, while six of Example 31 were placed in left maxillary and mandibular positions. Since the expanders were already semi-cylindrical, reshaping the expander at time of emplacement was limited to adjusting the length of the hydrogel for insertion. The expanders were allowed to expand in the mucosa tissue for approximately 6 weeks. The results showed that four of the Example 30 expanders were expelled by necropsy day (44 days after implantation), while all of Example 31 expanders remained intact at the implantation sites. The data clearly demonstrates that Example 31 expanders performed better than Example 30 expanders. Furthermore, Example 31 expanders were observed to generate clinically useful flaps of tissue after 6 weeks of expansion, and remained intact even after recovery from the dog.

[0180] In vivo expansion of the inserted expanders was measured using a 3D scanning Faro-arm device. FIG. 7 shows expansion kinetics for Example 31. The increase in the expanded area volume matches with formation of new tissue. The kinetic data in FIG. 7 indicates that the expansion reaches plateau in about 4-6 weeks.

[0181] The histology and clinical notations ascertained from the animal studies indicate that the novel hydrogel expander materials of the invention are highly biocompatible and non-toxic and further investigated by biocompatibility testing of Example 32. This hydrogel was selected as it is chemically similar to Example 31, but does not contain fluorescein diacrylate that is intended only for tracking purposes, and not for inclusion in a clinical material. Cytotoxicity and biocompatibility testing of Example 32 were performed by Toxikon Corporation (Bedford, Mass.). The tests/regulatory # performed include: L929-MEM elution/ISO10993-5, Intracutaneous injection/ISO10993-10, Systemic injection/ISO10993-11, Rabbit pyrogen test/ISO10993-11, Muscle implant 7-Day/USP 34, NF-29, Reverse mutation assay/ISO10993-3, and Particulate matter by light obscuration/USP 34, NF-29. The results of the tests indicate that there is no cytotoxicity, no intracutaneous toxicity, no system toxicity, no sign of pyrogenic response, no significant biological response, same colonies as compared to negative controls, and average of 18.9 particles/ml (>10 m) and 3.7 particles/ml (>25 m). Overall, these tests indicate an extremely well-tolerated material with minimal biological toxicity. Thus, this material is considered to be highly biocompatible.

[0182] Despite the success of some Examples in the in-vivo dog model, in some situations failure still occurred Thus, Example 33 was prepared for in-vivo dog testing.

Example 33

[0183] This hydrogel was synthesized as previously described, containing (% w/w) 37.6% PLGA-PEG-PLGA, 37.6% PEGDA (600), 11.6% Ethylene glycol dimethacrylate, and 13.2% PLA-diacrylate (8.7 kDa) with total concentration w/v solids of 27% in DMSO. The initial 1.sup.st day swelling for this example was 171%, with final swelling of 242%.

[0184] Examples 32 and 33 were tested in the dog jawbone model as previously described. Of 4 expanders tested, Example 32 had 2 which were not found at necropsy, and 2 which were removed as crumbled pieces. Example 33 had 2 removed as one piece and 2 removed as crumbled pieces, indicating that this example is improved over Example 32.

[0185] Examples 34-39 were prepared to validate a material meeting the required in-vitro properties of Examples 30 and 31, without the addition of fluorescein diacrylate, as this is undesirable from a regulatory perspective. For this work, the % w/v solvents in DMSO was varied, as indicated in TABLE 10.

TABLE-US-00009 TABLE 10 Compositions of hydrogel Examples 34-39. Component (% w/w) PEG Ethylene Tribiock Polyester Diacrylate Glycol Lauryl Solids Example diacrylate Diacrylate (600 Da) dimethacrylate methacrylate (% w/v) 34 41.4% 4.7% PLG- 41.4% 12.4% 0.0% 24% TB11DA DMA 35 38.5% 5.1% PL- 38.5% 11.5% 6.4% 25% TB11DA DA 36 51.9% 5.2% PL- 26.0% 10.40% 6.5% 22% TB10DA DA 37 48.2% 14.5% PLG- 24.1% 7.20% 6.0% 24% TB10DA DMA 38 56.3% 5.6% PL- 28.2% 9.90% 0.0% 21% TB10DA DA 39 51.9% 15.6% PLG- 26.0% 6.50% 0.0% 22% TB10DA DMA Table 10 acronym key: PLG-DMA: PLGA-DMA (1:1, 9000 Da); PL-DA: P(DL)La-DA (70,000)

[0186] Examples 34-39 were assayed in-vitro as described above, with the resulting characteristics shown in TABLE 11.

TABLE-US-00010 TABLE 11 In-vitro characterization of Examples 34-39. End Initial swelling Full swelling Strength Example (Day 1) (Day 42-60) (N/mm) 34 272% 310% 2.50 35 226% 277% 2.68 36 128% 230% 2.48 37 135% 256% 1.41 38 137% 223% 1.76 39 145% 346% 0.45

[0187] Example 34, which is similar to Example 31 in composition except with use of PLA-PEG-PLA triblock instead of PLGA-PEG-PLGA triblock, had unfavorable initial swelling. Similarly, Example 35, which is similar with the addition of hydrophobicizing-agent laural methacrylate, also has unfavorable initial swelling. These results demonstrate that desirable compositions of the prototype expanders is unobvious, as the addition of the more highly hydrophobic PLA chains and lauryl methacrylate should logically lead to lower initial swelling. The compositions comprising PLA-PEG-PLA were observed to be opaque and cloudy, indicating phase transition within the matrix. This result indicates that for medical expander use, a PLGA-PEG-PLGA polymer is desirable. Examples 36-39 show that expanders with superior in-vitro properties can be obtained utilizing PLGA-PEG-PLGA (TB10) along with lauryl methacrylate or without it.

[0188] Example 40 further demonstrates the non-obvious nature of the hydrogel properties. It is similar to Example 38, with the exception of slightly more ethylene glycol dimethacrylate and PEG (256 Da) diacrylate, rather than PEG (600 Da) diacrylate.

Example 40

[0189] This hydrogel is synthesized as previously described using 55.6% TB11-DA, 5.6% P(DL)La-DA (70,000), 27.8% PEG-DA (256 Da), and 11.1% ethylene glycol dimethacrylate (21% w/v solids).

[0190] Notably, Example 40 is observed to be hard and crystalline, similar to chalk in texture. Despite the slight changes in ingredients, this prototype could not be cut or modified due to its brittle nature. Similarly, Example 41 demonstrates issues associated with too low of cross-linking. This hydrogel is synthesized by reacting 20% w/v TB11DA directly. The gelling observed is inconsistent, and an unsuitable quantity of solid is obtained, with a majority of material remaining substantially liquid.

[0191] The nature of the novel hydrogels described herein is that their mechanical and swelling properties are determined by a complex interplay of various components. Unlike typical hydrogels, which are primarily mixtures of monomers with a relatively low quantity of cross-linkers, the hydrogels of the invention are substantially comprised of cross-linker components. The cross-linking density of these new hydrogels is not controlled so much by the molar ratio of multi-vinyl components to monomeric units, but rather by the molecular weight of the multivinyl units. For this reason, traditional methods of calculating cross-linking density (i.e., moles cross-linker/moles monomer) are unsuitable for describing the cross-linking of these hydrogels. Instead, the cross-linking density can be considered based on relative number of vinyl units as compared to chain length of the macromer. On a per mole basis, TB05-DA contains 2 vinyl active units per 11 kDa of polymer chain, equivalent to 0.18 VI/kDa (number vinyl units/kilodalton macromer). Respectively, other cross-linkers could be ranked with their relative VI/kDa, as shown in TABLE 12

TABLE-US-00011 TABLE 12 Relative VI/kDa for Select Example macromers Macromer VI/kDa Macromer VI/kDa TB05-DA 0.18 Poly(ethylene glycol) 3.33 diacrylate (600 Da) PLGA-DMA (1:1, 0.22 Ethylene glycol 10.09 9000 Da) dimethacrylate PL-DA: P(DL)La- 0.03 PLGA-diacrylate (8.7 kDa) 0.23 DA (70,000) TB10-DA 0.25 TB09-DA 0.13 Fluorescein 4.54 TB01-DA 0.92 diacrylate

[0192] It should be noted that monomers do not contribute to cross-linking density. Multiplying the mass % content of the Example hydrogel's components by its respective VI/kDa can give the relative molar contribution of each macromer to the cross-linking density. Adding these together gives the cross-linking density of the example in #cross-links/mg or Q, as cross-linking density is commonly referred to.

[0193] The relative cross-linking density is shown for a series of Examples in TABLE 13. Cross-linking density is important to controlling the swelling as well as the mechanical properties. In situations where the cross-linking density is too high, the material is brittle and cannot be cut or properly emplaced. If the cross-linking density is too low, the resultant material is too soft and swells rapidly to a large size.

TABLE-US-00012 TABLE 13 Initial calculated cross-linking density for select Examples Calculated crosslink Example density (links/mg) Q 29 2.79 30 2.26 31 2.77 32 2.76 34 2.71 35 2.51 36 2.05 37 1.68 38 2.08 39 1.69 40 (too high 3.39 crosslinking) 41 (too low 0.18 crosslinking)

[0194] In addition to cross-linking density, the expansion properties of the hydrogels are controlled by the relative hydrophobic/hydrophilic contributions of the various components. Although this is a complex system and hydrophobic/hydrophilic are relative terms, generally it can be understood that the polyester chains, which are not normally water soluble, are considerably more hydrophobic than the poly(ethylene glycol) chains and the polyacrylate backbones.

[0195] Additionally, additives such as lauryl methacrylate and ethylene glycol dimethacrylate increase the overall hydrophobicity, even though ethylene glycol dimethacrylate has a greater impact on cross-linking. For the triblock copolymers, the hydrophobic/hydrophilic contribution can be calculated as the ratio of their total PLGA MW to their total MW. For instance, TB05-DA can be calculated to have a hydrophobic contribution of 10,000 Da (PLGA)/11,000 Da (total)=0.91.

[0196] Purely hydrophobic components (PLGA diacrylate and ethylene glycol dimethacrylate) can be considered to contribute 1 to hydrophobicity, and hydrophilic items (PEG diacrylate) can be considered to contribute 1 to hydrophilicity. Multiplying the hydrophic contributions of each component (PEGDA=0) by the % w/w content in the expander allows for the overall hydrophobicity of the expander to be calculated in terms of % hydrophobic. TABLE 14 shows initial hydrophobicity of select Examples. Example 1 is included to show an expander with substantially unsuitable initial hydrophobicity.

TABLE-US-00013 TABLE 14 Select expanders calculated initial hydrophobicity. Hydrophobic Hydrophobic Example content (%) Example # content (%) Example 1 (too low 31% 39 68% hydrophobicity) 36 68% 29 54% 37 70% 32 55% 38 65% 22 59%

[0197] It should be noted that die cross-linking density and the hydrophobic/hydrophilic contributions all play a role in defining the swelling of the hydrogel. This quantity is dynamic, however, as upon hydrolysis the decrease in PLGA/PLA content relative to hydrolytically-stable hydrophilic components, such as PEG and polyacrylic acid, decreases the overall hydrophobicity of the material and severs cross-links, thereby increasing the swelling.

[0198] The mechanical properties of materials are also important for tissue expanders. They must allow the expander to be trimmed to size and placed under the tissue by tunneling or similar surgical techniques. For this reason the material must not be too hard or too soft. A series of prototypes displaying good mechanical properties for implantation are shown in TABLE 15.

TABLE-US-00014 TABLE 15 Mechanical properties of select Examples Modulus of Elasticity Example (kPa, 2% strain) Stress Relaxation (%) 25 2.1 23.1 29 9.5 51.6 30 3.0 36.4 31 5.5 51.2 32 9 55 32 6.6 48.9 33 8.5 51.2 36 10.6 27.0 37 3.5 28.2 38 2.6 27.8 39 3.7 28.9