Material Preparation And Structure Design Of Composite Gradient Osteochondral Repair Scaffold

Tissue engineering is an effective method to treat osteochondral defects,which overcomes the limitations of autograft and allograft.One of the main requirements of this new method is to prepare biocompatible scaffolds with geometric and mechanical properties.The development of3 D printing technology has made it possible to design multiple types of bone scaffolds in osteochondral tissue engineering,but the simultaneous incorporation of multiple types of gradients in the same structure remains a challenge.In this paper,screw extrusion 3D printing technology was used to design integrated scaffolds for osteochondral repair from three aspects of material preparation,structural design and porosity change strategy.The main contents of this paper were shown:1.Based on the microscopic composition of natural osteochondral tissue,the overall design scheme of osteochondral repair scaffold was determined as follows: PCL silk material for bone layer,PCL powder for cartilage layer,PCL/HA and PCL/MWCNT composite materials for calcified cartilage layer.2.By comparing the surface area to volume ratio,equivalent compressive stress distribution and flow performance of square pore cell structure,cylindrical pore cell structure and semi-arch pore cell structure,it is determined that the semi-arch pore structure has better mechanical properties and flow performance;The effect of porosity change mode on the equivalent stress distribution,elastic modulus and shear modulus of bone layer scaffold was studied.The results showed that 60%-80%porosity was not suitable for the bone layer porosity,and the bone scaffold with the porosity between 25%-40% and smooth transition met the requirements of elastic modulus of bone layer scaffold.3.The cartilage layer scaffold material was prepared by screw extrusion 3D printer.The optimal printing process was needle temperature120℃,hot bed temperature 60℃,extrusion ratio 5r/min,and the forming path was parallel to the X axis.Under these parameters,the mechanical properties of PCL powder are as follows: Young’s modulus 89.843 MPa,yield strength MPa.Based on the mechanical properties of PCL powder,the porosity of cartilage layer was determined as follows: superficial zone(80%)-transition zone(72.5%)-deep zone(65%).4.The calcified cartilage layer scaffold was prepared by screw extrusion 3D printer and the effects of HA content and MWCNT content on the properties of the composite were studied.The results showed that when HA content was 4wt%,the mechanical properties of PCL/HA composite were better.When the content of MWCNT is 0.2wt%,the mechanical properties of PCL/MWCNT composites are good.Based on the mechanical properties of the composites,the porosity of calcified cartilage layer was determined as 55%-50%-50%-45%.5.Compression experiments were carried out on the 3D printed scaffolds for osteochondral repair.The results showed that the experimental results were not different from the simulation results,and were all within the range of natural osteochondral tissue modulus.The results showed that PCL material and its composites were biodegradable and the environment in which the degradation products were formed was harmless to human body.