Mussel-inspired Gelatin-based Double-layer Hydrogel And Its Application In Osteochondral Regeneration

The Incentive of joint trauma are very common and seriously affected people's health.The structure of articular cartilage is very special.Its self-repair ability is extremely limited.It is particularly important to study the repair materials for joint damage.However,the traditional cartilage defect repair have their own limitations and can not restore the function of cartilage tissue.Gelatin-based hydrogels are widely used in the field of tissue engineering due to their excellent biocompatibility,cell adhesion ability and excellent affinity to bioactive molecules.However,its high degradation rate,low thermal stability and mechanical strength limit their applications for cartilage repair.In this study,methacrylic anhydride(MA)was employed to modify gelatin in order to obtain photo-cross-linkable methacryloyl gelatin(MAGel).Then,mussel inspired double-layer composites hydrogels for osteochondral regeneration were prepared by incorporation dopamine(DA)and calcium phosphate(CaP)into MAGel-based hydrgrol.The details of this study were described as followings.First,three kinds of GelMA-based hydrogels(MAGel-PDA,MAGel-CaP and MAGel-PDA/CaP)were prepared by the free-radical polymerization of GelMA with incorporation of dopamine and calcium phosphate.By adjusting the content of dopamine and calcium phosphate,the hydrogels had the highest compression strength when the content of dopamine was 2%,and the content of phosphate calcium was 3%.The SEM micrographs also demonstrated that MAGel-based hydrogels showed appropriate porous structure that is suitable for cell and tissue growth.Also the swelling,degradation and release properties of these hydrogels were studied.Second,the biocompatibility of the three kinds of hydrogels was evaluated by studying the proliferation and differentiation of BMSCs and chondrocytes on the hydrogels.The results demonstrated that the dopamine-containing sample groups showed excellent cell affinity.Under the effect of dopamine and calcium phosphorus,MAGel-PDA/CaP hydrogel showed the potential of stem cell differentiation.After adding the growth factor BMP-2,it showed the good differentiation ability.Third,a double layer composite hydrogel for osteochondral repiring was prepared by simultaneously polymerized two layers.The upper MAGel-PDA hydrogel was used as the cartilage repair layer,and lower MAGel-PDA/CaP hydrogel as the subchondral bone repair layer.In order to improve the tissue-inducibility of hydrogels,the TGF-?2 was immobilized in the upper layer to induce cartilage regeneration and the BMP-2 was immobilized in the lower layer to induce bone regeneration.The bone/cartilage repair performance of the double layer hydrogel was studied by implanting the hydrogel into the full-thickness defect of rabbit knee joint cartilage.The results showed that the double-layer composite hydrogel with immobilized growth factors could promote the repair and regeneration of cartilage and subconchondral bone tissue.Histological results indicated that newborn cartilage and subchondral bone converge closely.Also the nascent tissue is well integrated with the surrounding host organization.In summary,the double-layer composite hydrogel for osteochondral repairing was designed.The upper and lower layers of the double-layer hydrogel have a good fusion at the interface,which is superior than the traditional double-layer hydrogel with poor bonding problem.This new type of the double-layer composite hydrogel provide a new route for repairing osteochondral defects.