Modified Gelatin/Polyacrylamide Hybrid Hydrogel And For Cartilage Defect Repair

Articular cartilage defects are serious problems owing to the poor self-healing and regenerative capacity of cartilage of articular cartilage. It is essential to develop novel materials for cartilage repair for patients suffering from joint disease and arthritis trauma. Gelatin-based hydrogels are widely used in the field of tissue engineering due to their excellent biocompatibility, cell adhesion ability, and also good affinity of bioactive molecules. However, gelatin-based hydrogels have poor thermal stability, fast degradation rate and low mechanical strength, which limit their applications for cartilage repair. In this study, methacrylic anhydride (MA) was employed to modify gelatin in order to obtain photo-cross-linkable gelatin methacryloyl (GelMA). GelMA based hybrid hydrogels were prepared by co-polymerizing acrylamide (AM) and GelMA under ultraviolet radiation in the presence of a photo-initiator. The details of the study were described as followings.Preparation and characterization of GelMA and pure GelMA hydrogels. GelMA were obtained through an graft reaction method. Then three kinds of GelMA hydrogels (GelMA21, GelMA48 and GelMA62) were prepared by the UV-initiated free-radical polymerization of GelMA with different degree of methacrylation (21%,48% and 62%). GelMA hydrogels maintained good thermal stability at 37℃. Rheological tests showed that the elasticity of GelMA hydrogels increased with MA substitution degree. The swelling ratio and the degradation rate of GelMA hydrogels decreased with MA substitution degree. Compression tests showed that the GelMA hydrogel had the highest compression strength when the degree of methacrylation was 48%. GelMA48 was chosen for the following studies.Preparation and characterization of the GelMA/PAAM hybrid hydrogel. First, hybrid hydrogels with different mass ratio of GelMA and AM were prepared. Compression tests and showed that when the mass ratio of GelMA and AM is 1:0.5, the resulted GelMA/PAAM1-0.5 hybrid hydrogel performed better compression behaviors. The SEM micrographs also demonstrated that GelMA/PAAM1-0.5 hybrid hydrogel showed appropriate porous structure that is suitable for cell and tissue growth. Comparing with pure PAAM hydrogel and GelMA, the GelMA/PAAM1-0.5 hybrid hydrogel showed enhanced compression strength of 0.38 MPa and improved elasticity (storage modulus of 1000 Pa). The GelMA/PAAM1-0.5 hybrid hydrogel had a favorable degradation rate and realized sustain release of the growth factors for 20 days. These results indicated that the GelMA/PAAM hybrid hydrogel simultaneously possessed the advantages of the PAAM hydrogels and GelMA hydrogels.Biological evaluation of the hybrid hydrogels. In vitro cell culture tests showed the chondrocytes remained viable and proliferated on the hybrid hydrogel, demonstrating that the hybrid hydrogels had good cell adhesion and excellent biocompatibility. A rabbit knee cartilage defect model was used to evaluate the cartilage repair ability of the hybrid hydrogel in vivo. After six-month implantation, grossly observation showed that the defect treated by the hybrid hydrogel was filled with white and transparent tissues, and no inflammation response presented at the defect. The histology staining images showed that the group of GelMA/PAAM1-0.5 hybrid hydrogel loaded with TGF-β2 had better chondrocytes morphology, continuous subchondral bone, and much thicker newly formed cartilage, compared with GelMA groups and control blank groups. These results showed that GeIMA/PAAM1-0.5 hybrid hydrogel was a good candidate material to be applied in articular cartilage tissue engineering and may have great potential in various soft tissue engineering applications.