Study On An Injectable Continuous Stratified Biomimetic Construct For Enhancing Osteochondral Regeneration

Articular cartilage consisting of chondrocytes and matrix secreted by chondrocytes possess smooth surfaces and proper elasticity.Articular cartilage has the function of weight-bearing and lubrication.Almost no vascular,lymph-vessel or nerve are inside the natural articular cartilage.When being hurt,it is difficult for articular cartilage to achieve complete regeneration due to the absence cartilage regeneration-related cells.Moreover,the damage happens not only in the cartilage,but also in the subchondral bone.The subchondral bone provides a suitable mechanical environment for articular cartilage,which is important for the cartilage to maintain its structure and function.Therefore,it is pivotal for the perfect repair of articular cartilage to facilitate articular cartilage regeneration simultaneously promoting subchondral bone regeneration.Current treatments can hardly achieve satisfied results in the regeneration of both articular cartilage and subchondral bone.Osteochondral regeneration with the formation of hyaline cartilage and subchondral bone as well as the integration between the newly formed tissues with the host tissue still remains a great challenge.In this study,a construct containing an injectable continuous stratified scaffold and multiple cell systems was designed for enhancing osteochondral regeneration.Briefly,an injectable sodium alginate(SA)/bioglass(BG)composite hydrogel containing bone marrow stem cells(BMSCs)(SA/BG+BMSCs)was used for subchondral bone regeneration and an injectable thermosensitive SA/agarose(AG)composite hydrogel with co-culture of BMSCs and articular chondrocytes(ACs)(SA/AG+ACs/BMSCs)was applied for articular cartilage regeneration.The continuous SA phase and the stratified structure enabled the scaffold to mimic the natural osteochondral structure.In addition,the SA/BG+BMSCs hydrogel could enhance the osteoblast differentiation of BMSCs by upregulating their alkaline phosphatase and collagen I gene expressions,and the SA/AG+ACs/BMSCs hydrogel could promote the chondrocyte differentiation of BMSCs by upregulating their Acan and collagen II gene expressions,which indicated that this stratified scaffold could mimic the natural osteochondral function.Furthermore,after the stratified construct was injected into a rat osteochondral defect model,obvious neonatal articular cartilage tissues and subchondral bone tissues with regular surface and highly integration with normal tissues could be observed.This structural and functional biomimetic construct,together with its proper swelling ratio,could not only stimulate the hyaline cartilage and subchondral bone regeneration in an entire osteochondral unit but also promote the integration between the newly formed tissues and the host tissue.