Medical implant

Abstract

The present invention relates to a cell-free, multi-layered medical device having bespoke, multifunctional bioactivity for the purpose of regeneration of skeletal tissues. The medical device may actively promote homing of stem cells into the medical device and promote their differentiation into the required cell type and promote de-novo tissue formation. The invention includes methods of making the medical device, uses of the medical device in promoting regeneration of the articular cartilage of a joint surface and in promoting healing and regeneration of skeletal tissues, for example, meniscal cartilage, tendon and ligament tissues and also healing of bone tissue indications such as fractures.

Claims

1. An acellular biomimetic medical device comprising a scaffold coated in or adsorbed on its surfaces with a first layer comprising a cationic agent, the first layer being covered or coated with a second layer comprising an anionic oligosaccharide or polysulphated moiety, which is non-covalently bound to a mixture of a plurality of bioactive factors, wherein the plurality of bioactive factors comprises: (i) an agent that can stimulate stem cell differentiation and/or promote appropriate extracellular matrix formation for the tissue to be regenerated selected from the transforming growth factor group; and (ii) a stem cell homing or migratory factor which is a chemokines and optionally (iii) an agent that inhibits enzymes associated with the breakdown or catabolism of extracellular matrix.

2. The device according to claim 1, wherein the first and second layers are non-covalently bound together.

3. The device according to claim 1, wherein the scaffold is synthetic, natural, and/or selected from the group comprising polyester compositions, polylactic acid, polylactic acid-glycolic acid copolymer compositions, polycaprolactone, polyester-polyallylamine copolymers, collagens, peptides, silks, chitosan, hyaluronan-based polymers, decellularized tissue, calcium phosphate-based materials, hydroxyapatite and ceramic based biomaterials and combinations and compositions of the foregoing scaffold materials with ceramic based biomaterials.

4. The device according to claim 1, wherein the cationic agent is a stable unsaturated amine or is allylamine.

5. The device according to claim 1, wherein the second layer comprises an anionic oligosaccharide or a sulphated moiety.

6. The device according to claim 5, wherein the anionic oligosaccharide is selected from the group comprising heparin and heparan sulphate, dermatan sulphate, chondroitin-4-sulphate, chondroitin-6-sulphate, hyaluronic acid, hyaluronan, keratan sulphate and pentosan polysulphate and oligosaccharides derived from any of the above.

7. The device according to claim 1, wherein the bioactive factor is bound to the anionic material either directly, indirectly, or indirectly via a linker moiety.

8. The device according to claim 7, wherein the linker moiety is selected from the group comprising fibronectin, insulin-growth factor binding protein, vitronectin and laminin and peptide derivatives thereof.

9. The device according claim 1, wherein the chemokine is selected from the group consisting of CXCL12, SDF1, CCL2 (MCP-1), CCL21, CXCL1, and CXCL8 (IL8), and optionally wherein the agent that inhibits enzymes associated with the breakdown or catabolism of extracellular matrix is selected from the group consisting of tissue inhibitor of metalloproteinase-3, osteoprotegerin, Wnt proteins such as Wnt 3a, DNA complexes, DNA plasmid/viral complexes, complexes of RNA, microRNA and derivatives or biologically active fragments thereof.

10. The device according to claim 1, wherein the stem cell homing or migratory factor is CXCL12.

11. The device according to claim 1, wherein the plurality of bioactive factors are sequestered at levels in the nanogram/picomole range.

12. The device according to claim 1, further including a surface modification to include a bioactive agent that enhances osteogenic function-or a treatment which promotes deposition of hydroxyapatite particles to create an osseous region on the device.

13. The device according to claim 1, further which is an osteochondral device purposed to aid implant fixation for the regeneration of articular cartilage and underlying subchondral bone which may be fabricated of different biomaterials composing the chondral and osseous regions.

14. A method of making the device of claim 13, comprising electrospinning a chondral scaffold onto an osseous scaffold or by physically attaching a chondral portion to an osseous region.

15. A method of constructing the acellular biomimetic medical device of claim 1, comprising: (i) providing a scaffold core; (ii) coating a surface of the scaffold core or impregnating the surface of the scaffold core with a first layer comprising a cationic agent; (iii) covering the first layer of with a second layer comprising an anionic oligosaccharide or polysulphated moiety; and (iv) attaching a mixture of a plurality of bioactive factors non-covalently either directly to said second layer or indirectly via a linker moiety to said second layer, wherein the plurality of bioactive factors comprises: a) an agent that can stimulate stem cell differentiation and/or promote appropriate extracellular matrix formation for the tissue to be regenerated selected from the transforming growth factor group; and b) a stem cell homing or migratory factor which is a chemokine; and optionally c) an agent that inhibits enzymes associated with the breakdown or catabolism of extracellular matrix.

16. The method according to claim 15, wherein the scaffold comprises a non-woven porous material.

17. The method according to claim 15, wherein the surface of the scaffold core is coated or covered with the first layer comprising the cationic agent by plasma polymerisation.

18. A method of promoting mesenchymal stem cell differentiation into an appropriate cell type for tissue regeneration and/or promoting appropriate extracellular matrix formation and/or inhibiting enzymes associated with the breakdown or catabolism of extracellular matrix or the cartilage matrix and/or encouraging stem cell homing into a tissue defect to promote tissue regeneration and/or treating or promoting healing of an injured joint surface, or an early osteoarthritic lesion, and promoting healing of bone, meniscal cartilage, tendon and/or ligament injuries in a subject in need thereof, the method comprising implanting the device according to claim 1 into an area of a joint or other area of the subject.

19. The method according to claim 18, wherein the joint is a synovial joint.

20. The method according to claim 16, wherein the material is electrospun poly-L-lactic acid or polyglycolic acid-poly-L-lactic acid co-polymers or polycaprolactone polymers.

21. The device according to claim 1, wherein the agent that can stimulate stem cell differentiation and/or promote appropriate extracellular matrix formation for the tissue to be regenerated is TGF3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

(2) FIGS. 1A and 1B are scanning electron microscope images of the electrospun PLLA. Scale bar in 1A=100 m. Scale bar in 1B=10 m. FIGS. 1C and 1D are X-ray photon spectroscopy images of the PLLA scaffolds before (1C) and after (1D) cold plasma treatment with allylamine using the described methods.

(3) FIG. 2A shows a graph of the X-ray photon spectroscopy image of the allylamine-coated PLLA scaffold. FIG. 2B shows the X-ray photon spectroscopy image of the heparin-treated, allylamine coated PLLA scaffold.

(4) FIG. 3 shows a graph of the amount of [H.sup.3]-radiolabelled heparin bound to the allylamine-treated scaffold vs the amount added.

(5) FIG. 4A shows the binding of TGF3 and FIG. 4B the binding of TGF1 to an allylamine and heparin-functionalised surface. Detection was by anti-TGF1 or anti-TGF3 antibodies.

(6) FIG. 5 shows various examples of bioactive factors binding to several example sulphated glycosaminoglycan oligosaccharides immobilised on an allylamine functionalised surface. Bioactive factors shown are TGF1 (FIG. 5A), TGF3 (FIG. 5B), CXCL12 (FIG. 5C), SDF1 (FIG. 5D), MIA (FIG. 5E), Wnt 3a (FIG. 5G) and BMP2 (FIG. 5H). FIG. 5 also shows an example of a biological factor (MIA) (FIG. 5F) binding to a specific binding protein or an extracellular matrix protein (fibronectin) which will bind to glycosaminoglycans. Results are the means+/standard error of the mean.

(7) FIG. 6 shows an example of the attachment of mesenchymal stem cells to control (PLLA) and scaffolds functionalised with the example chondrogenic BF, TGF3. FIG. 6 are scanning electron micrographs of bovine synovial fluid mesenchymal stem cells 48 hr after seeding the cells onto PLLA (FIG. 6A), and PLLA scaffolds functionalised with allylamine (FIG. 6B), heparin (FIG. 6C) and TGF3 (FIG. 6D). Scale bars on the micrographs=50 m.

(8) FIG. 7 shows an example of the attachment of bovine chondrocytes to PLLA and PLLA scaffolds functionalised with the example chondrogenic BF, TGF3. FIG. 7 are scanning electron micrographs of the chondrocytes 48 hr after seeding the cells onto PLLA (FIG. 7A), and functionalised PLLA scaffolds: allylamine (FIG. 7B), heparin (FIG. 7C) and TGF3 (FIG. 7D). Scale bars on the micrographs=100 m.

(9) FIGS. 8A-8E demonstrate the viability of various skeletal tissue cells cultured on scaffolds functionalised with one or more growth factors. The examples shown are mesenchymal stem cells derived from bone marrow (bone-marrow-derived mesenchymal stem cells, BM-MSCs) or joint fluid (synovial mesenchymal stem cells, SF-MSCs), ligament cells (ligamentocytes), chondrocytes and bone (MG 63 osteoblastic cells). FIG. 8A shows the cell viability of human bone-marrow mesenchymal stem cells cultured on control (PLLA) and examples of functionalised scaffolds 48 hr after seeding the scaffolds with the cells. The cells were cultured in basal medium in the absence of serum or additional growth factors. Results are the mean+/standard error of the mean (SEM). FIG. 8B shows the viability of synovial fluid-derived mesenchymal stem cells cultured on control (PLLA) and examples of functionalised scaffolds after seeding the cells onto the scaffolds. The cells were cultured in basal medium in the absence of serum or additional growth factors. Results are the mean+/SEM. FIG. 8C shows the cell viability of bovine articular chondrocytes cultured on control (PLLA) scaffolds and example functionalised scaffolds 48 h after seeding the scaffolds with the cells. The cells were cultured in basal medium in the absence of serum or additional growth factors. Results are the mean+/SEM. FIG. 8D shows the viability of human bone marrow-derived stem cells cultured on control (PLLA) and examples of the functionalised scaffolds 72 hr after seeding the scaffolds with the cells. The cells were cultured in basal medium or osteogenic medium in the absence of serum or additional growth factors. Results are the mean+/SEM. FIG. 8E shows the viability of human osteoblastic cells on examples of the functionalised scaffolds 48 hr after seeding the scaffolds with the cells. The cells were cultured in basal medium in the absence of serum or additional growth factors. Results are the mean+/SEM.

(10) FIG. 9 shows the individual experimental cell viability results for bone marrow mesenchymal stem cells cultured on the control (PLLA) and functionalised scaffolds. It is observed that the experimental variability in the results is reduced in the scaffolds functionalised with both CXCL12 and TGF3 which is an indication of a more even cell attachment to the scaffolds in this group. The cells were cultured in basal medium in the absence of serum or additional growth factors. Each bar represents a single experiment.

(11) FIGS. 10A and 10B shows the extracellular matrix (ECM) proteoglycan accumulation [measured as the amount of ECM glycosaminoglycans (GAG)] by constructs formed from human bone marrow-derived MSCs cultured on the control PLLA scaffolds and the functionalised scaffolds. The cells were cultured in basal medium in the absence of serum or additional growth factors. FIG. 10A shows the results for individual experimental scaffolds and the group means of the extracellular GAG accumulation in the absence of added serum or growth factors at 33 days. FIG. 10B shows the extracellular GAG accumulation in the absence of added serum or growth factors at 44 days. Results show the mean+/SEM.

(12) FIG. 11 shows the rate of glycosaminoglycan (GAG) accumulation in the culture medium which is a measure of proteoglycan synthesis indicative of chondrogenic differentiation of the mesenchymal stem cells, FIG. 11A shows the rate of accumulation of GAG between days 2-6 of culture of the cell-scaffold constructs, FIG. 11B shows the accumulation rate between days 6-9 of culture of the cell-scaffold constructs and FIG. 11C shows the rate of GAG accumulation between days 12-16 of the cell-scaffold constructs. It is seen that by day 9 of culture, cells cultured on the scaffolds functionalised with TGF3, TGF3+CXCL12 combination and TIMP3+TGF3+CXCL12 show an increase in GAG accumulation compared to PLLA. By day 16 cells cultured on all the functionalised scaffolds (with the exception of the heparin-only functionalised scaffold) showed greater GAG accumulation compared to cells on PLLA scaffolds. The cells were cultured in basal medium in the absence of serum or additional growth factors. Results are the mean+/SEM.

(13) FIG. 12 shows extracellular matrix (ECM) accumulation by constructs formed from bovine articular chondrocytes and cultured on the control PLLA scaffolds and the functionalised scaffolds. The cells were cultured in basal medium in the absence of serum or additional growth factors. Results are the mean+/standard deviation.

(14) FIG. 13 shows immunolocalisation of collagen II in constructs formed from bovine articular chondrocytes cultured on PLLA or functionalised scaffolds of PLLA for 35 days in basal medium in the absence of serum or additional growth factors. All images were taken at magnification of 20. Scale bars=100 m. FIG. 13A shows immunolocalisation of collagen II in chondrocytes cultured on PLLA and PLLA functionalised with allylamine only, heparin, TGF1 and TGF3. FIG. 13B shows immunolocalisation of collagen II in constructs formed from bovine articular chondrocytes and PLLA functionalised with TGF1, TGF3, CXCL12 or combinations of CXCL12 and TGF1 or CXCL12 and TGF3. All images are taken at magnification of 20.

(15) FIG. 14 shows the amount of alkaline phosphatase detected in cultures of MG 63 cells grown on Wnt 3a and BMP2-functionalised cell culture surface. The cells were cultured on the functionalised surfaces for 14 days in basal medium in the absence of serum or additional growth factors. Results are the means+/SEM.

(16) FIG. 15 shows the gross appearance of example tissues retrieved at post-mortum 28 days after surgery. FIG. 15A shows photographs of an example non-operated contralateral femoral condyle, a femoral condyle with empty chondral defect, and a femoral condyle with a chondral defect treated with a control implant (PLLA functionalised with heparin only), a femoral condyle with a chondral defect treated with an active implant (PLLA functionalised with CXCL12 and TGF3). FIG. 15B shows photographs of a mid-sagittal section taken through the chondral defects of the partially decalcified condyles. The defects treated with the active implant (PLLA functionalised with CXCL12 and TGF3) show a greater volume of cartilage-like tissue regeneration.

(17) FIG. 16 shows the components of an example osteochondral device. FIG. 16A is a diagram (not to scale) showing the basic components of an osteochondral implant. In this device, the chondral portion would be composed of a biological factor-functionalised scaffold as described herewithin. The osseous part could be formed by deposition of hydroxyapatite or brushite onto one end of an electrospun scaffold or by heat annealing or using a biological adhesive (for example, fibrin sealant) to attach an osseous scaffold onto a chondral portion. Alternatively, a chondral portion could be directly electrospun onto an osseous scaffold. This latter design is exemplified in FIGS. 16B and 16C which show photographs of an osteochondral medical device comprised of a hydroxyapatite disc osseous region onto which was electrospun a 1.8 mm random-fibre scaffold of polycaprolactone (PCL) to form the chondral portion. After fabrication the scaffold portions could be functionalised with bioactive factors as described herewithin. FIGS. 16D, 16E and 16F are scanning electron micrographs of the PCL chondral portion which was directly electrospun (depth 1.8 mm) onto the osseous scaffold (1 cm ceramic disc) of hydroxyapatite.

DETAILED DESCRIPTION

(18) Reference herein to a scaffold is intended to include a three dimensional structure that provides a matrix onto which the first, second and biological factor can be layered.

(19) Reference herein to biomimetic is the imitation of models, systems, and elements of nature for the purpose of solving complex problems associated with tissue repair and promotion of tissue healing.

(20) The terms surfaces and surface of a scaffold are interchangeable. Scaffolds comprise many surfaces (rather than just a top, bottom and sides) as they have many internal surfaces such as internal fibres and pores-which would be coated by the methodology of the present invention. The term surfaces include internal and external surfaces of the scaffold.

(21) Reference herein to layer is intended to include a coating, covering, film or an additional and different surface to the base surface onto which it is applied.

(22) Healthy ECM of tissues such as, articular cartilage contains stored biological/bioactive factors (BFs), which maintain the health and phenotype of the cells within the tissue and tissue integrity. These BFs are sequestered by their tight non-covalent binding to matrix sugar-based moieties [glycosaminoglycans (sGAG)] of ECM cartilage proteoglycans. This sequestration also prevents the BFs from rapidly leaching from the cartilage and protects them from degradation by proteolytic enzymes. Heparan sulphate GAGs are involved in BF-cell interactions, maintaining the BFs where they are required by the cells, thus reducing the concentration of BFs needed for biological activation. Therefore, the incorporation of growth factor-binding sGAG surfaces could be extremely useful in the generation of biofunctional, biomaterial implants that can present bioactive molecules such as growth factors in a structural and biochemical context using the same mechanisms as those found in native musculoskeletal tissues (for example, articular cartilage)

(23) The present invention is not directed towards tissue engineering of de novo tissues for subsequent implantation but rather the invention is a cell-free, multi-layered medical device having multifunctional bioactivity directed towards regeneration of joint tissues for subsequent use in vivo.

(24) The implants of the present invention mimic the natural biological factor(s)-sequestering mechanism in the ECM of tissues, for example cartilage, so that selected chondrogenic and stem cell migratory factors can be bound in the implant in a similar structural and biochemical context as found in native cartilage. Also low physiological concentrations of the BFs are required so reducing both cost and potential side-effects. Further modification of the bioactive implants can be made by deposition of hydroxyapatite particles into one end to create an osseous region to aid implant fixation by promoting early incorporation of this region with the subchondral bone. This technology permits fabrication of an off-the-shelf, innovative medical device with several bioactivities incorporated to both promote migration of repair cells (stem cells) and maturation of the stem cells into cartilage cells and so promote tissue regeneration at the site of injury. In addition, the technology is adaptable to allow fabrication of sophisticated biomimetic scaffolds containing differing BFs to optimise cartilage regeneration in cell therapy approaches to cartilage repair such as matrix-assisted chondrocyte implantation.

(25) A particular advantage of the device of the present invention is that, since the BFs are bound non-covalently in a potentially reversible manner, it allows for the possibility of conformational change to release in the vicinity of cells, and to allow optimal interaction with cell-surface receptors.

(26) Preparation of Poly-L-Lactic Acid and Poly-Caprolactone Scaffolds by Electrospinning

(27) A solution of poly-L-lactic acid (PLLA) or poly-caprolactone (PCL, Sigma) was prepared at 12% (w/v) in dichloromethane The polymer solution was placed in a 1 ml glass syringe fitted with a 2.5 cm 20-G needle (Fisnar). An 18 kV electric field was applied at a distance of 20 cm between an aluminium foil sheet covering a flat metal plate and the needle tip to form an electrospun PLLA mat composed of randomly oriented, 5 m microfibres on the aluminium foil. Alternatively, solutions of PLLA or PCL, were prepared in glass syringes as above and 18 kV was applied at 20 cm between needle and a rotating foil sheet collector. An electrospun mat was collected composed of randomly oriented microfibres with a diameter of 5 m and mat thickness of 1.8 mm. The electrospun mats were left overnight to allow the volatile solvent residues to escape. Heat annealing the microfibers was performed by heating the PLLA scaffolds at a melting temperature of 173 C. and heating PCL scaffolds at a melting temperature of 60 C.

(28) Preparation of Osteochondral Scaffolds

(29) PLLA and PCL fibres were also electrospun directly on to hydroxyapatite porous disks using the same processing parameters as above, to a 1.8 mm thickness. PLLA scaffolds were heat annealed onto the hydroxyapatite porous disks at a melting temperature of 173 C. PCL scaffolds were heat annealed on the hydroxyapatite porous disks at a melting temperature of 60 C.

(30) Scanning Electron Microscopy of Electrospun Matrices

(31) The architecture of the electrospun matrices was analysed by scanning electron microscopy (SEM Philips XL-20) at an accelerate voltage of 10 kV. Before SEM analysis, samples were coated with gold using a sputter coater. The SEM magnification (6000) was selected to have a squared analysis field of 50 m. The fibre diameters and distribution were quantified by analysing the SEM micrographs using ImageJ software. Three images of three different zones of three samples were analysed and the pore and fibre diameters were determined.

(32) Plasma Polymerisation

(33) Allylamine (Sigma Aldrich 99%) plasma polymerisation was conducted in a stainless steel vacuum reactor chamber. The flow of allylamine vapour into the chamber was adjusted using manual needle valves. The reactor was evacuated to less than 210.sup.3 mbar, using a vacuum pump. A liquid N.sub.2 cold alumina trap was used to protect the pump from monomers and their escape via the exhaust. The allylamine monomer was degassed using 3 freeze-thaw cycles. The plasma was ignited using a radio frequency generator at 13.56 MHz and the treatment was performed at a power of 10 W and a flow rate of 2 standard unit cm/min (sccm) for 20 min.

(34) Heparin Coating of Scaffolds

(35) For the preparation of heparin-functionalized scaffolds (PLLA-pAAm-HP), the allylamine-treated (pAAm) PLLA electrospun scaffold (200 m) was cut into circular discs with diameters of 5-6 mm. These were placed individually in wells of a 96 well culture plate, sterilized with 200 l of 2-Propanol (isopropanol) at ambient temperature for 15 minutes and, after 3 washes with PBS, incubated overnight in the dark at ambient temperature with 200 l of 50 g/ml heparin (Iduron, low molecular weight, porcine mucosa) solution in PBS. Unbound heparin was removed by washing 3 times with PBS.

(36) X-Ray Photon Spectroscopy

(37) PLLA, PLLA-pAAm and PLLA-pAAm-Hp scaffolds were analysed by X-ray photoelectron spectroscopy analysis (XPS) (K-alpha, Thermo Scientific). Amine derivate deposition on PLLA-pAAm membranes was checked by measuring the C1s and N1s signals, while the adsorption of the heparin on the PLLA-pAAm-Hp membrane was detected using the sulphur signal S2p.

(38) Quantitative Assessment of Bound Heparin

(39) [.sup.3H]-heparin (Hartmann, low molecular weight, 1 mCi/mg, 1 mg/ml) was diluted 1/10 with cold heparin (Iduron) to give 1 mg/ml heparin, 100 Ci/mg. PLLA-coated scaffolds were placed in minifuge tubes. The 1/10 hot/cold heparin stock solution was aliquoted onto the scaffolds to give final amounts of 0-70 g in 10 g (0.01 Ci) increments (2 replicates/dose) in 1 ml final volume of PBS. The tubes were gently vortexed then left overnight at 4 C. The next day the tubes were briefly centrifuged, the supernatant was poured off, 1 ml of PBS was added, the tubes were gently vortexed and kept at 4 C. for 20 min, before centrifugation and removal of supernatant. This washing step was repeated twice more. 100 l of 5M NaCl was added to each tube to dissociate the bound heparin from the scaffold. After 20 min at 4 C. the tubes were briefly centrifuged. The supernatants were dispensed into scintillation vials and replaced with another 100 l of 5M NaCl. After 60 min at 4 C. the tubes were centrifuged again and the supernatant was dispensed into the same scintillation vial. This was replaced with a third 100 l 5M NaCl which was left at 4 C. overnight. The following day the tubes were again centrifuged and the supernatant was added to the ones already present in the scintillation vial. 2 ml of scintillant (Ultima Gold) was added to the tubes which were placed in the scintillation counter (Beckman LS6500) and counted for 2 minutes. Disintegrations per minute (dpm) were provided automatically and converted to Ci from which the amount of bound heparin (g) was calculated.

(40) Quantitative Assessment of the Binding of Bioactive Factors to Sulphated Oligosaccharides.

(41) Oligosaccharides were incubated for 18 h at ambient temperature with allylamine-functionalised 96-well plates. Each well contained 10 ng of oligosaccharide in 200 l of PBS. After incubation, the wells were drained and washed 3 times with PBS. 300 l of PBS containing 5 mg/ml ELISA grade BSA (Sigma) was added/well and the plates incubated for 1 h at ambient temperature to block non-specific protein binding to the well surfaces. The plates were then drained of their contents and the wells washed 3 times with PBS/0.05% Tween 20. Bioactive factors were diluted in PBS containing 1 mg/ml BSA and 200 l added per well (10 ng/well TGF1 or TGF3, 25 ng/well CXCL12 or SDF1, 50 ng/well MIA, 20 ng/ml Wnt 3a, or 20 ng/ml BMP2) The plates were incubated with the bioactive factors for 5 h at ambient temperature after which the growth factors were removed and the plates washed with 3 changes of PBS/0.05% Tween 20. Specific rabbit polyclonal antibodies for each biological factor (PreproTech), were added at appropriate dilutions in PBS/BSA (200 l/well) and the plates were incubated overnight at 4 C. After incubation, the plates were drained, washed three times with PBS/0.05% Tween 20 and 200 l of a goat-anti-rabbit alkaline-phosphatase-labelled antibody in PBS/1 mg/ml BSA was added/well and incubated for 1 h at ambient temperature. The plates were then washed three times in PBS/0.05% Tween 20 followed by addition of 1 mM p-nitrophenol phosphate in a 100 mM glycine-NaOH buffer pH 9.4 containing 1 mM MgCl.sub.2. The rate of cleavage of the p-nitrophenol was followed spectrophotometrically at 405 nm using a TECAN Infinite M200 plate reader. For binding experiments where MIA was added to fibronectin-bound wells. The methodology was carried out as described above except that after blocking the plates with PBS/BSA and washing the wells with PBS, 250 ng/well of human fibronectin (R&D Systems) in PBS containing 1 mg/ml BSA was added. The plates were incubated for 3 h at ambient temperature and then unbound fibronectin removed by aspiration and draining the plates on paper towel. 50 ng well of MIA was then added and the assay completed as described above for the other BFs.

(42) Coating of Oligosaccharide-Functionalised Scaffolds with Bioactive Factors

(43) Oligosaccharide-functionalised scaffolds (5-6 mm) were incubated with 200 l of PBS containing 1 mg/ml bovine serum albumin (BSA) containing the required concentrations of bioactive factors, for example TGF and CXCL12 (PeproTech) and incubated for 4-5 h (ambient temperature) or 18 h (4 C.). Scaffolds were then washed three times with PBS containing 1 mg/ml BSA.

(44) In Vitro Cell Seeding of Scaffolds

(45) Bovine synovial fluid mesenchymal stem cells (SF-MSCs) and articular chondrocytes (BAC) were isolated and monolayer cultures established as described previously.sup.54,25. Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) were purchased from Promocell and monolayer cultures established as described for SF-MSCs. Cell culture reagents were purchased from Sigma or Promocell. Cells were removed from the culture dishes by trypsinisation, pelleted by centrifuging at 190g for 5 min and then re-suspended in medium [Chondrocytes: Dulbecco's Modified Eagle's Medium (4,500 mg/l glucose), containing 10 mM HEPES buffer pH 7.4, 100 units/ml penicillin/100 g/ml streptomycin, MEM nonessential amino acids, and 5% (v/v) foetal calf serum. MSCs: Dulbecco's Modified Eagle's Medium (1,000 mg/l glucose), 100 units/ml penicillin/100 g/ml streptomycin, MEM nonessential amino acids, and 5% (v/v) MSC qualified foetal calf serum].

(46) Sterile 5-6 mm diameter scaffolds were placed individually into wells of 24-well plates (suspension culture grade). 510.sup.5-110.sup.6 cells were added per scaffold in a total volume of 1 ml of culture medium and incubated for 24-48 h at 37 C. on an orbital shaker (75 rpm). The chondrocytes/scaffold constructs were transferred to 12 wells (1 construct/well) and cultured in the above DMEM containing 1 mg/ml BSA, ITS (10 g/ml insulin, 5.5 g/ml transferrin, 0.5 g/ml selenium and 4.7 g/ml each of linoleic and oleic acids) and 25 g/ml L-ascorbic acid (plus 10.sup.7M dexamethasone for MSCs). The constructs were cultured at 37 C. on an orbital shaker (30 rpm) for the required time with replacement of the culture medium every 3-4 days.

(47) Assessment of Cell Viability

(48) Prestoblue assay: Cell activity of the cell/scaffold constructs was determined by measuring the rate of conversion of resazurin dye to the fluorescent resorufin using the commercial resazurin dye preparation Prestoblue. The assay was performed according to the manufacturer's instructions and resorufin formation followed by determining fluorescence with a plate reader (TECAN Infinite M200) with an excitation wavelength of 535 nm and emission wavelength of 590 nm.

(49) Scanning Electron Microscopy

(50) Constructs were washed with PBS and fixed with 3% (v/v) glutaraldehyde. Fixation was performed at 4 C. for 45 minutes. Samples were washed twice in 100 mM cacodylate buffer, pH 7.4, for 10 min at ambient temperature. The constructs were washed with PBS, and 1% (w/v) osmium tetroxide, buffered in 100 mM cacodylate, pH 7.4, was added for 1 h. Finally, the samples were dehydrated by exposure to increasing concentrations of ethanol (from 10% to 100%) and then left to air dry. The samples were gold-coated using a sputter coater at 15 mA for 1.5 min. Coated samples were then examined by scanning electron microscopy (SEM) (Philips XL-20).

(51) Histology of Cell/Scaffold Constructs

(52) At the end of culture, the constructs were blotted with tissue, weighed and either frozen at 20 C. for biochemical analyses or mounted in cryoprotectant (OCT compound, BDH, Gurr) and 8-m frozen sections were cut and fixed for 30 min at 4 C. in 4% paraformaldehyde (Sigma P-6148) solution in PBS. The tissue sections were washed twice in distilled water, air-dried overnight and stored at 4 C. until they were used for staining procedures.

(53) Collagen II localisation: Immunolocalisation of type II collagen was performed in fixed sections. Sections were washed in PBS and pre-treated with 10 mg/ml hyaluronidase (Sigma H-3506) in PBS for 30 minutes at 37 C. followed by 2 mg/ml pronase (Sigma P-5147), for 30 minutes, at 37 C. The sections were washed in PBS and endogenous peroxidase activity was quenched with 3% hydrogen peroxide in 50% methanol (BDH 101586 6B) for 5 minutes. Sections were washed in Tris-buffered saline (TBS) solution and blocked with 3% BSA (Sigma A-2153) in TBS/Tween 20 (Sigma Ultra P-7949) for 1 hour to avoid non-specific staining. Sections were then incubated with primary antibody goat anti-type II collagen UNLB 1320-01 (Southern Biotech) overnight at 4 C. The next day, sections were washed once with high salt wash solution and twice in TBS/Tween 20, 10 minutes each and then incubated with biotinylated anti-goat IgG for 1 hour at room temperature. The tissue sections were washed with PBS and incubated for 30 min with ABC reagent from the Vectastain Elite ABC Kit PK-6105 (Vector Laboratories Ltd, UK) according to the manufacturer's instructions. Diaminobenzidine tetrahydrochloride (DAB, Vector DAB Kit, Vector Laboratories Ltd, UK) was prepared according to the manufacturer's instructions and incubated with the tissue sections for 2-10 min until a brown colour developed.

(54) Quantitation of Extracellular Matrix in Cell/Scaffold Constructs

(55) Proteoglycan content of the constructs was assessed by measuring the glycosaminoglycan (GAG) content.sup.61. Constructs were digested overnight at 60 C. in a papain digestion buffer [0.05% papain (from papaya latex), 6 mM n-acetyl cysteine in 200 mM phosphate buffer pH 6.8 containing 1 mM EDTA]. After digestion, scaffold fragments were pelleted by centrifugation (7,450g for 10 minutes) and the GAG concentration of the supernatants was analysed using 1,9-dimethylmethylene blue (DMB, Sigma 341088). 50 l of sample was then mixed with 250 l of DMB solution (0.0016% DMB in 40 mM glycine-HCL buffer pH 3.0 containing 40 mM NaCl) and the optical density measured at 525 nm using a TECAN infinite M200.

(56) In Vivo Sheep Study

(57) An in vivo proof of concept study of the biomimetic implant design was carried out using a sheep model of a surgicallycreated, 6 mm diameter, full cartilage defect (2 mm) in the medial, femoral condyle articular cartilage of the knee. The sheep model is the most appropriate robust, weight-bearing model for assessing efficacy of medical devices and is used for pre-clinical confidence in concept before translation into man. Twenty four ewes (Mules, weight 58-73 kg, 2-3 years of age) were randomly allocated into three treatment groups: 1) control group which had a surgical defect only, no implant insertion, 2) surgical defect treated with control implant (heparin only-functionalised), or surgical defects with the active implant inserted (TGF3 and CXCL12-functionalised implant). A 1.8 mm thick electrospun PLLA scaffold was prepared from clinical grade PLLA under clean room conditions (Electrospinning Company). The scaffold was then surface modified by cold plasma treatment with allylamine. Prior to each surgery, 6 mm diameter scaffolds were sterilised with isopropanol, washed three times with PBS and incubated overnight at ambient temperature with 100 g/ml low molecular weight heparin (Iduron). The scaffolds were then washed three times with PBS. For control implants, the heparinfunctionalised scaffolds were incubated overnight at 4 C. in PBS/0.1% ovine serum album (OSA, Sigma). The active implants were prepared by incubating the heparinfunctionalised scaffolds overnight at 4 C. with TGF3 and CXCL12 [100 g/ml (PreproTech) in PBS/0.1% OSA]. The scaffolds were then washed in PBS/0.1% OSA, drained and kept on ice. The implants were warmed to ambient temperature before insertion into the cartilage defects. 6 mm defects were surgically created in the centrodistal region of the medial femoral condyle of anaesthetised animals using a 6 mm biopsy punch and scalpel to remove articular cartilage down to the subchondral bone. A full thickness cartilage defect was created and the subchondral plate micropicked to mimic microfracture used in the human. The implants were sutured in placed with uninterrupted sutures and the wound closed. For the group with the surgical defect only, the defect was left empty and the wound closed and treated as for the experimental groups. Elastic bandages were applied to the joint and joint motion reduced by using an external splint for 14 days. Topical anaesthesia was administered by analgesic patches 24 h before surgery and for 60 h after surgery. The animals were kept under observation and standard husbandry in a barn for the duration of the study. All procedures were carried out with the required ethical approvals

(58) The animals from each group were euthanased at 28 days or 4 months after surgery. At post mortem the treated joints were opened and examined macroscopically and the end of the femur removed and taken for photographic record and decalcification in preparation for histology. At the time of submission of this patent document the samples were still undergoing decalcification.

Example 1

(59) A PLLA scaffold was subjected to cold plasma treatment with allylamine as hereinbefore described and a coating of allylamine was confirmed by the presence of a nitrogen peak (FIG. 1D). FIG. 2B shows the X-ray photon spectroscopy image of the heparin-treated, allylamine coated PLLA scaffold. The small peak occurring at 168.1ev shows the presence of sulphur groups confirming binding of heparin to the allylamine-treated PLLA. FIG. 3 shows a linear relationship of the amount of [H.sup.3]-radiolabelled heparin bound to the allylamine-treated scaffold vs the amount added The scaffold thus provides a positive surface coating of allylamine to which heparin binds non-covalently. Once the heparin has bound further experiments were conducted to show that heparin-binding bioactive factors such as for example TGF1, TGF3 and CXCl12 applied singularly or in combination will bind directly to the heparin layer by a tight non-covalent interaction. FIG. 4 shows the binding of TGF1 and TGF3 to an allylamine and heparin-functionalised surface. The presence of these bioactive factors was determined using immunolocalisation using rabbit polyclonal antibodies to TGF1 (ab92486, Abcam) and TGF3 (ab15537, Abcam). Bound anti-TGF antibodies were detected using a goat alkaline-phosphatase-labelled, polyclonal, secondary antibody to rabbit IgG (ab97072, Abcam). Results are the means+/SD.

Example 2

(60) FIG. 5 shows the binding of several example heparin-binding bioactive factors to various allylamine and glycosaminoglycan functionalised surface. The results show the means+/standard error of the mean. We have demonstrated that TGF3 and TGF1, CXCL12, SDF1, MIA, Wnt 3a and BMP2 bind to a selection of oligosaccharides directly. MIA is considered to bind to heparin via binding to fibronectin which will bind to heparin.sup.41. Here we have shown that MIA will bind directly to immobilised sulphated oligosaccharides as well as via binding to sulphated oligosaccharides via binding to fibronectin which then binds to the oligosaccharides. There are literature reports which state that TGF3 does not bind to sulphated oligosaccharides.sup.56,58. However, we have clearly demonstrated that TGF3 does bind directly to various sulphated glycosaminoglycans.

(61) Binding of bioactive factors (BFs) which bind to GAG-binding proteins such as fibronectin or laminin, can be bound to the oligosaccharide-functionalised surface by first binding them to their oligosaccharide-binding protein partner (OBPP) such as fibronectin and then applying the biological factorOBPP combination to the oligosaccharide-functionalised surface. An example of this type of BF-binding to oligosaccharides is demonstrated in FIG. 5F which shows the binding of MIA to fibronectin immobilised on a surface functionalised with sulphated oligosaccharides

Example 3

(62) Studies were undertaken with bovine synovial fluid mesenchymal stem cells (SF-MSCs) or chondrocytes to investigate the attachment of the cells to an example of PLLA scaffolds functionalised with an example chondrogenic BF. Results for the SF-MSCs are shown in FIG. 6 and results for chondrocytes in FIG. 7. Cells were seeded onto the scaffolds as described herewithin and 48 hr after seeding the cell-scaffold constructs were fixed and examined by scanning electron microscopy. FIGS. 6 and 7 show scanning electron micrographs of SF-MSCs and chondrocytes attached to PLLA. (FIGSS. 6A 7A) and PLLA scaffolds functionalised with allylamine (FIGS. 6B and 7B), heparin (FIGS. 6C and 7C) and TGF3 (FIGS. 6D and 7D). For both cell types, TGF3-functionalised PLLA scaffolds showed a greater density of cells bound than allylamine or heparin functionalised PLLA scaffolds or unmodified PLLA. In summary, this data shows that MScs and chondrocytes can attach to PLLA scaffolds in higher cell densities on PLLA functionalised with TGF3 compared to non-functionalised PLLA or PLLA functionalised with heparin-only or allylamine-only.

Example 4

(63) FIGS. 8A to 8E show the cell viability of human bone-marrow derived mesenchymal stem cells (BM-MSCs, FIG. 8A), synovial fluid-derived mesenchymal stem cells (SF-MSCs, FIG. 8B), bovine articular chondrocytes (FIG. 8C), human MG63 osteoblastic cells (8D) and human ligamentocytes (FIG. 8E) cultured on various biological factor-functionalised PLLA scaffolds. These scaffolds were functionalised with examples of classical chondrogenic and collagen-stimulating BFs (e.g. TGF), chemotactic (e.g. CXCL12), protease inhibitor (e.g. TIMP3) and osteoblastic factors (e.g. Wnt 3a). FIGS. 8D, 8E and 8F show respectively BM-MSCs, ligamentocytes and MG63 osteoblastic cells cultured on Wnt 3A and BMP2-functionalised scaffolds under basal culture conditions. These bioactive factors are example osteogenic factors. All scaffolds showed good biocompatibility; all the cell types used showed viable cells on the various biological factor-functionalised scaffolds (determined using the vital dye PrestoBlue described herein) which were maintained throughout the culture period (from 0-42 days) without exogenous addition of growth factors or serum. Cell viability on PLLA functionalised with allylamine only or heparin or BFs was not statistically different from the PLLA control or enhanced above that of the PLLA controls FIG. 8 demonstrates that mesenchymal stem cells, cartilage, bone and ligament-derived cell types can successfully be cultured on the functionalised scaffolds and remain viable. We have also demonstrated (FIG. 9) that mesenchymal stem cells (MSCs) can bind to PLLA scaffolds functionalised with a combination of the growth factor TGF3 and chemokine CXCL12 in nanogram amounts provided less variability in seeding efficacies (as indicated by the PrestoBlue assay described herewithin) than when the cells were seeded onto PLLA or PLLA functionalised with just allylamine, or heparin, or TGF1 or TGF3 alone. FIG. 9 shows cell viability of individual cell/scaffold constructs 48 hr after seeding the scaffolds with human mesenchymal stem cells. Cell viability was assessed by the Prestoblue assay described hereinbefore. All scaffolds were biocompatible. The scaffolds functionalised with a combination of CXCL12 and TGF3 showed less variability in the cellular activity of the MSC/scaffold constructs (FIG. 9) compared to the PLLA and the other functionalised scaffolds (allylamine, heparin, CXCL12, TGF3). This is an indication of the more even seeding of MSCs observed on the scaffolds functionalised with the combination of CXCL12 and TGF3.

Example 5

(64) Extracellular matrix (ECM) accumulation by constructs formed from human bone marrow-derived MSCs cultured on the functionalised scaffolds compared to constructs formed from the cells cultured on PLLA was examined. The cell/scaffold constructs were incubated for 33 days in a basic, growth factor-free medium of DMEM containing 1 mg/ml BSA, 10.sup.7M dexamethasone, ITS (10 g/ml insulin, 5.5 g/ml transferrin, 0.5 g/ml selenium, 4.7 g/ml each of linoleic and oleic acids) and 25 g/ml L-ascorbic acid. The proteoglycan content of the ECM was determined by quantifying the glycosaminoglycan (GAG) content of the constructs using 1,9-dimethylmethylene blue as described above. Results (FIG. 10A) show the GAG content of individual constructs and the mean value for each experimental group. A combination of CXCL12 and TGF3 gave the highest level of GAG accumulation (P0.05 against all scaffolds, P0.01 against PLLA) compared to constructs formed on scaffolds functionalised with TGF or CXCL12 alone or with just allylamine or heparin-functionalisation. Constructs formed on PLLA functionalised with a combination of CXCL12 and TGF3 also showed the least variability in GAG accumulation per construct reflecting a more uniform cell seeding compared to all other scaffold groups.

(65) FIG. 10B shows the GAG content of human BM-MSCs cultured for 44 days on BF-functionalised scaffolds compared to PLLA. The constructs were incubated in the absence of serum or added growth factors using the basic medium described above. The scaffold groups of TGF3, TGF3+CXCL12 and the group TGF3+CXCL12+TIMP3, gave significantly greater levels of ECM GAG content compared to the controls (*p0.05. **p3.01) Therefore even after over a 6 week extended culture period in the absence of added growth factors, some BFs and BF combinations show enhanced ECM accumulation over PLLA or PLLA functionalised with heparin only.

(66) Measurement of GAGs in the culture media from MSCs grown on the functionalised scaffolds was carried out to monitor likely chondrogenic differentiation of the stem cells. FIG. 11 shows the rate of production of GAG into the culture media at day 6 (FIG. 11A), day 9 (FIG. 11B) and 16 (FIG. 11C) after seeding the cells on the scaffolds. By day 9 (FIG. 11B) a significant increase in the rate of GAG secretion was observed only for MSCs cultured on TGF3 functionalised scaffolds, or combinations of TGF3 and CXCL12 or TGF3 and CXCL12 and TIMP3, By day 16 after seeding FIG. 11C) all the functionalised groups (except those with heparin-functionalised scaffolds) showed increased GAG production compared to the PLLA control. Therefore, these results demonstrate that MSCs cultured on TGF3 functionalised scaffolds, or combinations of TGF3 and CXCL12 or TGF3 and CXCL12, had undergone chondrogenic differentiation earlier (by day 9), even in the presence of 10.sup.7M dexamethasone, compared to the PLLA controls or heparin-only functionalised scaffold.

(67) In summary these data show that the BF-functionalised scaffolds have biological activity and support MSC attachment, viability, chondrogenic differentiation and extracellular matrix formation.

Example 6

(68) Scaffolds were functionalised with example chondrogenic (for example TGF1 and TGF3) and cell homing (for example CXCL12) BFs. Extracellular matrix (ECM) accumulation by constructs formed from bovine articular chondrocytes seeded onto functionalised scaffolds were compared to constructs formed from chondrocytes seeded onto PLLA. The cell/scaffold constructs were incubated for 28 days in a basic, growth factor-free medium of DMEM containing 1 mg/ml BSA, 10.sup.7M dexamethasone, ITS (10 g/ml insulin, 5.5 g/ml transferrin, 0.5 g/ml selenium, 4.7 g/ml each of linoleic and oleic acids) and 25 g/ml L-ascorbic acid. The proteoglycan content of the ECM was determined by quantifying the glycosaminoglycan (GAG) content of the constructs using 1,9-dimethylmethylene blue as described above. Results shown in FIG. 12 are the means+/standard deviation. TGF1- and TGF3-functionalised scaffolds gave constructs with significantly greater levels of ECM GAGs than PLLA scaffolds (p0.01 and p0.001 respectively. CXCL12-functionalised scaffolds were found to significantly inhibit ECM GAG incorporation (P0.01). Scaffolds functionalised with a combination of CXCL12 and TGF1 did not yield constructs with ECM GAG levels greater than PLLA-based constructs. In contrast, TGF3 could overcome inhibition of ECM formation caused by CXCL12. TGF1 and TGF3 are often assumed to have very similar activities in the scientific literature. However, it is clear that TGF1 and TGF3 in combination with CXCL12 have differing effects on chondrocytes. Scaffolds functionalised with a combination of CXCL12 and TGF3 showed significant ECM GAG accumulation over PLLA-based constructs (P0.05). FIG. 12A shows that after 44 days of culture in basal medium without added growth factors or serum, the effect of the functionalised scaffolds in terms of extracellular matrix GAG incorporation, still remained significantly greater than the PLLA control or the heparin-only functionalised scaffold.

(69) The effect of the functionalised scaffolds on chondrocyte phenotype was investigated. Collagen II deposition in the ECM is a well-known chondrogenic marker indicative a differentiated chondrocyte phenotype. FIG. 13 shows histological sections of constructs and immunolocalisation of collagen II in the constructs formed from bovine articular chondrocytes and PLLA or chondrocytes and functionalised scaffolds of PLLA. Functionalisation of the PLLA with TGF1 or TGF3 resulted in a greater density of chondrocytes distributed throughout the scaffold and extensive formation of collagen II as shown in FIG. 13A. FIG. 13B shows immunolocalisation of collagen II in constructs formed from bovine articular chondrocytes and PLLA functionalised with TGF1, TGF3, CXCL12 or combinations of CXCL12 and TGF1 or CXCL12 and TGF3. Alone, CXCL12 functionalised scaffolds yielded little volume of extracellular matrix and less collagen II deposition. Also, scaffolds functionalised with CXCL12 in combination with TGF1 gave much less volume of ECM and collagen II deposition compared to that observed with TGF1 alone. However, in contrast, scaffolds functionalised with a combination of CXCL12 and TGF3 when seeded with chondrocytes, gave cell/scaffold constructs with good extracellular matrix formation and extensive collagen II deposition compared to that seen with chondrocytes cultured on unmodified PLLA or PLLA functionalised with only allylamine or heparin. These results were not expected and show that the composition of BFs used for functionalisation is important. Scaffolds functionalised with TGF1 and CXCL12 could potentially lead to temporary inhibition of cartilage matrix synthesis in the medical device. In contrast, scaffolds functionalised with a combination of TGF3 and CXCL12 should promote good cartilage matrix within the medical device. This example also demonstrates that members of the TGF group of BFs may give different biological effects in different tissues. This is rarely considered in the scientific literature.

(70) In summary, these data show that BF-functionalised scaffolds can support chondrocyte attachment and cell viability, and chondrocyte differentiation/maintenance of the chondrogenic phenotype

Example 7

(71) Scaffolds were functionalised with example osteogenic bioactive factors Wnt3a, BMP2 and a combination of both growth factors. FIG. 14 shows the effect of the functionalised scaffolds on alkaline phosphatase in MG 63 cells. Scaffolds functionalised with BMP2 showed a statistically significant increase in alkaline phosphatase levels. Wnt 3a showed some increase in alkaline phosphatase which did not reach statistical significance. Together with the cell viability data, scaffolds functionalised with osteogenic factors supported the survival of ligamentocytes, MSCs and MG 63 osteoblastic cells. Therefore, in summary, scaffolds functionalised with appropriate osteogenic factors could have utility in promoting regeneration of bone, ligament and related tendon tissues. In particular, use of appropriate bioactive factors could promote regeneration of the bone-ligament or bone-tendon insertion points (entheses) at which a tendon or ligament are often damaged by trauma.

Example 8

(72) FIG. 15 shows examples of gross morphology of example sheep femoral condyles retrieved at post-mortum 28 days after surgery. FIG. 15A shows photographs of an example non-operated contralateral femoral condyle, a femoral condyle left with an unfilled/empty chondral defect, and a femoral condyle with a chondral defect treated with a control implant (PLLA functionalised with heparin only) and a femoral condyle with a chondral defect treated with an active implant (PLLA functionalised with CXCL12 and TGF3). FIG. 15B shows the sagittal sections taken through the defects to show the volume of articular tissue regeneration. It can be seen that there is greater regeneration of the cartilage layer in the defects treated with the active (CXCL12 and TGF3-functionalised PLLA) implants vs the empty defects or defects treated with the control (heparin-functionalised) implant. This cartilage tissue regeneration was greater in area (FIG. 15A) and volume (FIG. 15B) with the active implants We have demonstrated that PLLA functionalised with CXCL12 and TGF3 can regenerate articular cartilage to a greater degree than leaving the defect empty/unfilled or implanting a scaffold functionalised with heparin only. In summary, these results show that appropriate bioactive factorfunctionalised scaffolds (such as CXCL12 and TGF3-functionalised PLLA) can have in vivo functionality to promote articular cartilage regeneration.

Example 9

(73) FIG. 16 shows the general design principles of an osteochondral implant. The diagram (not to scale) shown in FIG. 16A shows the basic components of an osteochondral implant. In this device, the chondral portion would be composed of a biological factor-functionalised scaffold as described herewithin. The osseous part could be formed by deposition of hydroxyapatite or brushite onto one end of an electrospun scaffold by for example, an alternative soaking technique.sup.62. Or a chondral scaffold could be attached to a suitable osseous scaffold or by heat annealing or using a biological adhesive (for example, fibrin sealant) Alternatively, a chondral portion could be directly electrospun onto an osseous scaffold as exemplified in FIGS. 16B and 16C which show photographs of an osteochondral medical device comprised of a hydroxyapatite disc osseous region onto which was electrospun a 1.8 mm random-fibre scaffold of polycaprolactone (PCL) to form the chondral portion. After fabrication the scaffold portions could be functionalised with appropriate bioactive factors as described herewithin. FIGS. 16D, 16E and 16F are scanning electron micrographs of the PCL chondral portion which was directly electrospun (depth 1.8 mm) onto the osseous scaffold (1 cm ceramic disc) of hydroxyapatite. Use of the osteochondral implant should enable better fixation and stabilisation of the implant in some clinical indications (e.g. large osteoarthritic lesions, or large full-depth lesions extending into the subchondral bone caused by trauma) compared to using just the functionalised chondral scaffold.

(74) Additionally, the results of the biological factor-functionalised scaffolds on chondrocyte function would suggest that scaffolds functionalised with suitable BFs could have utility as the biomaterial support used for matrix-assisted autologous chondrocyte implantation (MACI) which is a procedure which is used clinically although not currently available on the NHS.

(75) Throughout the description and claims of this specification, the words comprise and contain and variations of them mean including but not limited to, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

(76) Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

(77) The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

REFERENCES

(78) 1. Abramson S B, Attur M and Yazici Y, Prospects for disease modification in osteoarthritis. (2006). Nat. Clin. Pract. Rhematol. 2: 304-312. 2. Goldring M B and Goldring S R. Osteoarthritis. (2007). J Cellular Physiol. 213:626-634. 3. Abramson S B and Attur M. Developments in the scientific understanding of osteoarthritis. (2009). Arthritis Res. & Therapy 11: 227-236. 4. Leardini G, Salaffi F, Caporali R, Canesi B, Rovati L, Montanelli R. Direct and Indirect costs of osteoarthritis. (2004). Clin. Exp Rheumatol. 22: 699-706. 5. National Institute for Health and Clinical Excellence (NICE). (2008). Osteoarthritis: The care and management of osteoarthritis in adults. Clinical Guideline. 59. 6. Simon T M and Jackson, T W. Articular cartilage injury pathways and treatment options. (2006). Sports Med Arthrosc. 14: 146-154. 7. Laurpattarakasem W, Laopaiboon M, Laurpattarakasem P, Sumananont C. Arthroscopic debridement for knee osteoarthritis. (2008). Cochrane Database of Systematic Reviews. DOI:10.1002/14651858.CD005118.pub2. 8. Simon T M and Jackson, T W. Articular cartilage injury pathways and treatment options. (2006). Sports Med Arthrosc. 14: 146-154. 9. Messner K, Gillquist J. Cartilage repair: a critical review. (1996). Acta Orthop Scand 67:532-539. 10. Gidwani S and Fairbank A. The orthopedic approach to managing osteoarthritis of the knee. (2004). Br Med J 329: 1220-1224. 11. Sampson S, Botto-van Bemden A, Aufiero D. Autologous bone marrow concentrate: review and application of a novel intra-articular orthobiologic for cartilage disease. (2013). Phys Sports Med 41 (3): 7-18. 12. Roos E M. Joint injury causes knee osteoarthritis in young adults. (2005). Current Opinion Rheumatol. 17: 195-200. 13. National Institute for Health and Clinical Excellence (NICE). (2005). The use of autologous implantation for the treatment of cartilage defects in knee joints. Review of Technology Appraisal 16. www.nice.org.uk 14. Guidance on the selection of prostheses for primary total hip replacement. (2000). Technology Appraisal GuidanceNo. 2. National Institute for Clinical Excellence. www.nice.org.uk 15. Fisher J. Surgery for arthritis: total hip and knee joint replacement. (2004). Reports on the Rheumatic Diseases Series 5: Topical Reviews. Arthritis Research UK. www.aruk.org.uk. 16. Kim K T, Lee S, Ko D O, et al. Causes of failure after total knee arthroplasty in osteoarthritis patients 55 years of age or younger. (2014) Knee Surg Relat Res 26: 13-19. 17. Aggarwal V K, Goyal N, Deirmengian G, et al. Revision total knee arthroplasty in the young patient: is there trouble on the horizon? (2014) J Bone Joint Surg Am 96: 536-542. 18. Steadman J R, Rodkey W G, Rodrigo J J. Microfracture: surgical technique and rehabilitation to treat chondral defects. (2001). Clin OrthopRel Res 391(suppl):5362-S369. 19. Peterson L, Minas T, Brittberg M, Nilsson A, Sjorgenson-Jansson E. and Lindahl A. Two to 9-year outcome after autologous chondrocyte transplantation. (2000). Clin Orthop Relat Res 374: 212-234. 20. Minas T. and Peterson L. Advanced techniques in autologous chondrocytes transplantation. (1999) Clin Sports Med. 18: 13-44. 21. Trattnig S, Ba-Salamah A, Pinker K, Plank C, Vecsei V and Marlovits S. Matrix-based autologous chondrocytes implantation for cartilage repair: non-invaisive monitoring by high resolution magnetic resonance imaging. (2005). Man Reson Imaging 23: 779-787. 22. Clar C, Cummins E, McIntyre L, Thomas S, Lamb J, Bain L, Jobanputra P and Waugh N. Clinical and cost effectiveness of autologous chondrocyte implantation for cartilage defects in knee joints: systematic review and economic evaluation. (2005). Health Technology Assessment 9: no 47. 23. Waisiak J, Clar C and Villanueva E. Autologous cartilage implantation for full thickness cartilage defects of the knee. (2006). Cochrane Database of Systemic Reviews. Issue 3, article no: CD003323. 24. Ruano-Ravina, A and Diaz M J. Autologous chondrocyte implantation: a systemic review. (2006). Osteoarthritis & Cartilage 14: 47-51. 25. Jones E A, Crawford A, English A, Henshaw K, Mundy J, Corscadden D, Chapman T, Emery P, Hatton P V, McGonagle, D. Synovial Fluid mesenchymal stem cells in health and early osteoarthritis: Detection and functional evaluation at the single-cell level. (2008). Arthritis & Rheumatism. 58: 1731-1740. 26. Van der Kraan P M, Buma P, van Kuppevelt, van den Berg W. Interaction of chondrocytes, growth factors: relevance for tissue engineering. (2002). Osteoarthritis and Cartilage 10: 631-637. 27. Lotolf M P and Hubbell J A. Synthetic biomaterials as instructive microenvironments for morphogenesis in tissue engineering. (2005). Nature Biotech. 23: 47-55. 28. Kim S-H, Turnbull J, Guimond S. Extracellular matrix and cell signalling: the dynamic cooperation of integrin, proteoglycan and growth factor receptor. (2011). J. Endocrinol. 209: 130-151. 29. Knox S M, Whitelock J M. Perlecan: How does one molecule do so many things? (2006). Cell Mol Life Sci. 63(21): 2435-2445. 30. Rapraeger A C., Syndecan-regulated receptor signalling. (2000). J Cell Biol. 149(5): 995-997. 31. Lortat-Jacob H. The molecular and functional implications of chemokine interactions with heparin sulphate. (2009). Current Opin. Structural Biol. 19: 543-548. 32. Kufareva I, Salanga C L, Handel T M. Chemokine and chemokine receptor structure and interactions: implications for therapeutic strategies. (2015). Immun Cell Biol 93:372-383. 33. Raman R, Sasisekharan V, Sasisekharan R. Structural insights into biological roles of protein-glycosaminoglycan interactions. (2005). Chemistry and Biology 12(3): 267-277. 34. Zern B J, Chu Hh and Wang Y D. Control growth factor release using self-assembly [polycation:heparin] complex. (2010). Plos One 5(6): e11017. 35. Brown A, Robinson C J, Gallagher J T, Blundell I L, Co-operative heparin-mediated oligomerisation of fibroblast growth factor-1 (FGF-1) precedes recruitment of FGR2 to ternary complexes. (2013). Biophys. J 104: 1720-1730. 36. Chen G, Gulbranson D R, Yua P, Houa Z, Thomson J A. Thermal stability of fibroblast growth factor protein is a determinant factor in regulating self-renewal, differentiation and reprogramming in human pluripotent stem cells. (2012). Stem Cells 30(4): 623-630. 37. Laguri C, Arenzana-Seisdedos F, Lortat-Jacob H. Relationships between glycosaminoglycan and receptor binding sites in chemokinesthe CXCL12 example. (2008). Carbohydrate Research 343: 2018-2023. 38. Pomin V H, Mulloy B. Current structural biology of the heparin interactome. (2015). Current Opinion in Structural Biology 34:17-25 39. Proudfoot A E, Handel T M, Johnson Z, Lau E K, LiWang, P, Clark-Lewis I, Borlat F, Wells T N, Kosco-Vilbois M H. Glycosaminoglycan binding and oligomerization are essential for the in vivo activity of certain chemokines. (2003). Proc. Natl. Acad. Sci. 100: 1885-1890 40. Tscheudschilsuren G, Bosserhoff A K, Schlegel J, Vollmer D, Anton A, Alt V, Schnettler, R, Brandt J, Proetzel G. Regulation of stem cell and chondrocyte differentiation by MIA. (2006). Exp. Cell. Res. 312: 63-72. 41. Stoll R, Renner C, Zweckstetter M, Brggert M, Ambrosius D, PALme S, Engh R A, Golob M, Breibach I, Buettner R, Voelter W, Holak T A, Bosserhoff A-K. The extracellular human melanoma inhibitory activity (MIA) protein adopts an SH3 domain-like fold. The EMBO J. 20: 340-349 42. Hileman R E, Fromm J R, Weiler J M, Lindhardt R J. Glycosaminoglycan-protein interactions: definition of consensus sites in glycosaminoglycan binding proteins. (1998). Bioassays 20(2): 156-157. 43. Sun T, Mai S M, Norton D, Haycock J W, Ryan A J, MacNeil S. Self-organisation of skin cells in three-dimensional electrospun polystyrene scaffolds. (2005). Tissue Engineering 11: 1023-1033. 44. Xu X, Jha A K, Duncan R L. Heparin-decorated, hyaluronic acid-based hydrogel particles for the controlled release of bone morphogenic protein 2. (2011). Acta Biomater. 7: 3050-3059. 45. Vulic K, Shoichet M S. Tunable growth factor delivery from injectable hydrogels for tissue engineering. (2011). J. Am. Chem. Soc. 134: 882-885. 46. Volpato F Z, Almodovar J, Erickson K, Popat K, Migliaresi, C, Kipper M J. Preservation of FGF-2 bioactivity using heparin-based nanoparticles, and their delivery from electrospun chitosan fibers. (2012). Acta Biomater. 8: 1551-1559. 47. Chen M X, Li B K, Yin D K, Liang J, Peng D Y. Layer-by-layer assembly of chitosan stabilized multilayered liposomes for paclitaxel delivery. (2014). Carbohydrate Polymers 111: 298-304. 48. Manakhov A, Neas D, echal J, Pavlik D, EliM, Zajikov L. Deposition of stable amine coating onto polycaprolactone nanofibers by low pressure cyclopropylamine plasma polymerization. (2015). Thin Solid Films 581: 7-13. 49. Yasuda H and Gazicki M. Biomedical applications of plasma polymerization and plasma treatment of polymer surfaces. (1982). Biomaterials 3: 68-77. 50. Mahoney D J, Whittle J D, Milner C M, Clark S J, Mulloy B, Buttle D J, Jones G C, Day A J. Short R D. A method for the immobilization of heparin to surfaces. (2004). Anal. Biochem. 330: 123-129. 51. Short R, Buttle D, and Day A. Sugar binding surface. (2002) PCT/GB2003/004653 (WO/2004/040308). 52. Robinson D E, Marson A, Short R D, Buttle D J, Day A J, Parry K, Wiles M, Highfield P, Mistry A. Whittle J. Surface gradient of functional heparin. (2008). Advanced Materials, 20: 1166-1169 53. Robinson D E, Buttle D J, Short R D, McArthur S L, Steele D A, Whittle J D. Glycosaminoglycan (GAG) surfaces for characterising GAG-protein interactions. (2012). Biomaterials 334:1007-1016. 54. CN 101269240 Artificial crystalline lens with transforming growth factor resistant beta 2 antibody membrane on surface manufacturing method thereof 55. Crawford A, Dickinson S C. Chondrocyte isolation, expansion and culture on polymer scaffolds. (2004). Methods in Molecular Biology 238:147-158. 56. Rider C C. Heparin/heparan sulphate binding in the TGF-beta cytokine superfamily. (2006). Biochem Soc Trans. 34(Pt 3):458-60. 57. Lyon M, Rushton G, Gallagher J T. The interactions of transforming growth factor with heparin/heparin sulphate. (1997). J Biol Chem. 272:18000-18006. 58. McCaffrey T A, Falcone D J, Viicente D, Du B. Transforming growth factor-beta 1 is a heparin-binding protein: identification of putative heparin-binding regions and isolation of heparins with varying affinity for TGF-beta 1. (1992). J Cell Physiol. 152:430-440. 59. Freeman I, Cohen S. The influence of sequential delivery of angiogenic factors from affinity-binding alginate scaffolds on vascularisation. (2009). Biomaterials 30: 2122-2131. 60. US 2013/0251683 A1. Prolonged Delivery of Heparin-binding Growth Factors from Heparin-Derivatized Collagen. (2013). 61. Ferndale R W, Buttle D J, Barrett A J. Improved quantitation and improved discrimination of sulphated glycosaminoglycans by use of dimethylmethylene blue. (1986). Biochimia et Biphysica Acta 883: 173-177. 62. Tagushi T, Kishida A, Akashi M. Apatite formation on/in hydrogel matrices using an alternative soaking process: II Effect of swelling ratios of poly(vinyl alcohol) hydrogel matrices on apatite formation. (1999) J Biomaterials Polymer Science-Polymer Edition, 10: 331-339.