3D Printing And Characterization Of A Novel Gradient Osteochondral Scaffold

Osteochondral defects are common diseases that affect people of all ages.However,blood vessels,nerves and lymphocytes are lack in the cartilage and the poor self-repairing ability is worse,some current clinical treatment methods have certain defects.The emergence of osteochondral tissue engineering brings hope for the repair and treatment of bone and cartilage defects,how to prepare the gradient engineering scaffold is the current research hotspot.In this study,a novel osteochondral gradient scaffold was prepared using 3D printing technology.The cartilage layer is a polycaprolactone scaffold,and the subchondral bone layer is a sintered hydroxyapatite scaffold.First,the PCL scaffold was prepared by fused deposition technology,then the influence of its relative molecular weight,nozzle movement speed,filament distance and lay-down angles on the mechanical properties of the scaffold was studied.The scaffold with low molecular weight is brittle and easy to break,while the scaffold with high molecular weight has a higher melting temperature;the filament distance increases,the mechanical strength of the scaffold will be weakened;when compressed in the Z direction,the lay-down angles has little effect on the compression mechanical properties of the scaffold,and compressed from the X and Y directions,the compression mechanical properties of the three structures of 0/45°,0/45/90135° and 0/60° are different,and the two structures of 0/60/120° and 0/90° closer.Secondly,two methods are used to prepare subchondral bone scaffolds.One method is to blend HAp and PCL,then prepare them by fused deposition technology and study the mechanical and biological properties of different content of HAp scaffolds.The other is to prepare HAp scaffold by direct ink writing then sinter and study the effect of filament spacing and lay-down angles on the mechanical properties of the scaffold.Since the mechanical strength of the sintered HAp scaffold is similar to that of actual joint bone,the subchondral bone layer is prepared by sintering HAp.Finally,the preparation of the osteochondral scaffold is to print the PCL cartilage layer on the sintered HAp bone layer.By heating the printing platform,the bonding strength between the two scaffolds is enhanced.Compression test results show that the yield strength of the gradient HAp/PCL scaffold is close to that of the PCL layer,and the fracture strength is close to that of the HAp layer.The compressive modulus,fracture strain and fracture energy are all between the HAp layer and the PCL layer.The finite element analysis results show that the main forced structure of the scaffold is adjacent filament nodes.The maximum equivalent stress of the HAp/PCL gradient scaffold is between the pure HAp and PCL scaffold,and the maximum equivalent elastic strain is much higher than that of the pure HAp and PCL and concentrated on the PCL layer.The compression test and the simulation results are highly consistent,and both show that the HAp/PCL scaffold combines the compression mechanical properties of HAp and PCL.In addition,the bone marrow mesenchymal stem cells seeded in the HAp layer and the PCL layer and grew well and proliferated rapidly.In summary,the osteochondral gradient scaffold designed in this study has mechanical properties similar to that of osteochondral.The PCL layer has elasticity similar to cartilage,and the sintered HAp layer has a compressive modulus and strength close to that of human bone,which is expected to be applied to osteochondral tissue engineering.