Gradient Scaffold/KGN Sustained-release Thermosensitive Hydrogel Composite System For Repair Of Osteochondral Defects

Objective:Self-repair of articular osteochondral defects presents considerable challenges due to the complexity of the tissue structure and the low proliferation rate of chondrocytes.Traditional clinical treatments that have not shown significant efficacy include microfractures,autologous/allogeneic osteochondral grafts and cell-based techniques.As a result,tissue engineering has been extensively explored in the repair of osteochondral defects with high efficacy by harnessing the natural regenerative potential to control cellular function.However,osteochondral tissue is a gradient structure with a smooth transition from cartilage to subchondral bone,involving changes in chondrocyte morphology and phenotype,extracellular matrixcomposition,collagen type and orientation,and cytokines.We attempted to prepare gradient scaffolds to alter the microenvironment for cell growth,induce osteochondrogenesis and promote the formation of an osteochondral interface to repair osteochondral defects.Methods:The PLGA scaffold was prepared by 3D printing and subsequently n HA was adsorbed onto the scaffold to form a gradient PLGA/n HA scaffold.PLGA-PEG-PLGA was subsequently synthesized and KGN was attached to the end of PLGA-PEG-PLGA to characterize the temperature sensitivity,degradability,and drug release properties of the hydrogel.After testing the biocompatibility of the scaffold and hydrogel,the composite system was implanted into rabbit knee osteochondral defects,and after reaching the time point,the material was removed and subjected to MicroCT,tissue section staining and key gene protein assays to evaluate the osteochondral repair ability of the gradient scaffold/KGN slow-release temperature-sensitive gel composite system.Results:The PLGA scaffold by 3D printing exhibits a good pore size gradient with a pore size of 200 μm in the cartilage layer,400 μm in the subchondral bone layer and a dense intermediate calcified cartilage layer.After gradient mineralization,different amounts of n HA attachment could be observed under SEM.The synthesized PLGA-PEG-PLGA has a good temperature sensitivity and can be achieved at 20% as a liquid at low temperature and as a gel at body temperature.Longer drug release periods were achieved after attaching KGN to PLGA-PEG-PLGA.The PLGA-PEG-PLGA-KGN composite PLGA/n HA scaffold group implanted in rabbit knee osteochondral defects showed the best osteochondral repair with the premise of ensuring the biocompatibility of the composite system.Conclusion:We have prepared a PLGA/n HA scaffold that mimics the natural structure of osteochondral bone by attaching KGN to the ends of PLGAPEG-PLGA to form a temperature-sensitive gel that can release KGN over time.We implanted the composite system in rabbit knee osteochondral defects for 24 weeks and successfully regenerated tissue resembling natural osteochondral bone.The developed gradient scaffold and KGN slowrelease temperature-sensitive gel system mimicked the gradient structure of osteochondral bone and successfully repaired the osteochondral defect.