| Cartilage defect is hard to regenerate spontaneously due to the limited proliferation and migration of mature chondrocytes as well as the lack of vasculature and lymphatics.The present clinical treatment can not realize the structural and functional regeneration of cartilage defects.Cartilage tissue engineering is a promising way for cartilage regeneration.However,constructs containing cells and bioactive molecules are faced with the problems such as time consuming processes,shortage of cell sources,uncertain regulation of stem cells’differentiation,possible host immune reactions,and most importantly,difficult storage and transportation of the constructs,leading to the low possibility of clinic translation.Homing of endogenous cells for inductive cartilage regeneration would be a promising new therapeutic option to bypass the controversy of using exogenous cells and bioactive molecules.Fabrication of structured scaffolds with an ability to support and adapt to the regeneration-inductive nature of native tissues is under urgent need to realize the inductive cartilage regeneration.The bioactive scaffold with desired microstructure is of great importance to induce infiltration of somatic and stem cells,and thereby to achieve the in situ inductive tissue regeneration.Macro-porous fibrin scaffolds with regular and adjustable inter-connective pores were fabricated through a porogen-leaching method for the in situ inductive regeneration of full thickness cartilage defects in vivo.In vitro tests proved the survival and proliferation of BMSCs in the scaffolds.In vivo repair experiment was conducted by implantation of the cell-free macro-porous fibrin scaffolds into full thickness cartilage defects(4 mm in diameter and 4 mm in depth with bone marrow blood effusion)of New Zealand white rabbits for 6 and 12 w.The neo cartilage integrated well with the surrounding cartilage as well as the subchondral bone.Immunochemical and glycosaminoglycans(GAGs)staining revealed the high deposition of type Ⅱ collagen and GAGs in the neo cartilage after regeneration for 12 w.The quantitative reverse transcription-polymerase chain reaction(qRT-PCR)and western blotting(WB)revealed that the osteochondral-specific genes and proteins were significantly up-regulated compared with those of the normal cartilage.With the cell-free advantage and positive restoration of osteochondral defect in vivo,the fibrin scaffold is shelf-ready,and is expected to be conveniently used in clinics.A scaffold with an oriented porous architecture to facilitate cell infiltration and bioactive interflow between neo-host tissues is of great importance for in situ inductive osteochondral regeneration.Poly(lactide-co-glycolide)(PLGA)has been used widely in tissue engineering with the characteristics of satisfactory biocompatibility,low immunogenicity,good mechanical property,absolute biodegradability and controlled biodegradation rate.Unlike the scaffolds based on natural polymers such as collagen,ECMs,hyaluronic acid(HA)that usually have lower mechanical strength,the scaffolds based on PLGA could offer sustained support for tissue formation,and could be applied in both load-and non-load-bearing defects.A scaffold with oriented pores in radial direction was fabricated by using PLGA via controlled directional cooling of PLGA solution,following with lyophilization.Culture of bone marrow stem cells(BMSCs)in vitro revealed fast migration and regular distribution of cells in the scaffold.Implantation of the cell-free scaffold in rabbit osteochondral defect in vivo for 12 w regenerated simultaneously both cartilage and subchondral bone.With the positive restoration of osteochondral defect in vivo,the oriented macro-porous PLGA scaffold deserves further functionalization,and is promising for the convenient clinical application in the in situ inductive osteochondral regeneration without pre-seeded cells.HA is a kind of natural polysaccharide,resembling the extracellular matrices of cartilage composed of GAGs.Meanwhile,it possesses excellent bioactivities to promote cell proliferation,spontaneous accumulation of bone marrow stem cells(BMSCs),and differentiation of BMSCs into chondrocytes.A scaffold with oriented pores in radial direction was prepared by using methacrylated HA(HA-MA)via controlled directional cooling of HA-MA solution,and followed with photo-crosslinking to stabilize the structure.PLGA was further infiltrated to enhance the mechanical strength,resulting in a compressive modulus of 120 kPa.In vitro culture of BMSCs revealed spontaneous cell aggregation with a spherical morphology.In vivo transplantation of the cell-free scaffold in rabbit knees for 12 w regenerated simultaneously both cartilage and subchondral bone.Moreover,the expression of inflammatory factor interleukin-1β(IL-1β)was down regulated,although tumor necrosis factor-α(TNF-α)was remarkably up regulated.With the anti-inflammatory,bioactive properties and good enough restoration of full thickness cartilage defect in vivo,the oriented macro-porous HA-MA/PLGA hybrid scaffold has a great potential for the practical application in the in situ cartilage regeneration. |
