In Vitro And Vivo Osteogenic Biophysical Properties Of 3D Printing Bone Tissue Engineering Scaffolds Based On Polycaprolactone

In clinical practice,the most urgent need for bone tissue engineering(BTE)scaffolds is the critical-sized bone defects(CSBD).3D printed BTE scaffolds have great potential of the application in the repair of bone defects.The selected preparation method,material and structure,which are interrelated,are the main factors that determine the performance of the scaffold.Through three study phases,this thesis has gradually studied the biophysical properties associated with osteogenesis of polycaprolactone(PCL)matrixed BTE scaffolds prepared by selective laser sintering(SLS)technique and what it studies applies into CSBD regeneration of rabbit radius.Stage Ⅰ:In the process of optimizing the SLS parameters of PCL scaffolds,previous researchers paid much attention to evaluating the mechanical properties and structural fidelity of scaffolds,and then made empirical adjustments according to the results in order to obtain the strongest and with least deformation scaffolds.However,these scaffolds are ultimately intended for biomedical applications,and their critical biological properties have not received enough attention.The change of SLS parameters will fundamentally affect the sintering state of PCL powder and the overall mechanical properties of the scaffold will be furtherly affected.Meanwhile,the surface properties of scaffolds,which is an important factor affecting biological activities were affected.In this part,the theoretical range of SLS parameter optimization was first determined by the energy density model(EDM)and the properties of raw PCL powder,and then different PCL scaffolds are prepared by systematically changing the laser power(W)and scanning speed(mm/s)in SLS process parameters.In addition to measuring the mechanical properties and structural accuracy of each scaffold,related to bioactivities,hydrophilicities and roughness of the scaffolds’ surface were studied.The enhanced green fluorescent protein(EGFP),expressed by the prokaryote,was used as a marker to test the protein adsorption performance of the scaffolds’ surface.Finally,by detecting the cell activity on the scaffold,it was demonstrated that different SLS processing parameters did affect the biocompatibility of the PCL scaffolds.Although the mechanical properties of scaffolds prepared by processing parameters with lower energy density was poor,the cells showed better survival conditions on their rough surface.This provides a new idea for the optimization of SLS process parameters of this kind of scaffolds in the future.Stage Ⅱ:Although pure PCL scaffolds have good biosafety,hydrophobic and slow degradation rate make it with low bioactivity.Borate bioactive glass(BBG)has good degradability so that it provides bioactive ingredients in vitro and vivo.However,BBG has poor mechanical properties due to its brittle texture,and its rapid degradation of BBG will result in overalkaline microenvironment and high B concentration leads to cytotoxicity.The preparation of BBG/PCL composite scaffolds is expected to complement the characteristics of the two materials.With the help of SLS technology,the amount of BBG in the composite scaffolds can be widely changed,which subsequently affects the biophysical properties of BBG/PCL composite scaffolds,including mechanical properties,porosity,degradation properties,hydrophilicity,biomineralization properties,protein adsorption properties,cytocompatibility and in vitro osteogenic alkaline phosphatase(ALP)activity.The results showed that the appropriate addition of BBG improved the mechanical properties and biological activities of PCL scaffolds,and the PCL matrix could achieve the slow degradation of BBG.The 20BBG/PCL scaffolds show the best performance and have the potential for bone defect repair.Stage Ⅲ:The repair of bone defects in large areas puts high requirements on the structure of BTE scaffolds,which not only needs the external contour matching with the defect area,but also needs the appropriate internal porous structure to promote bone integration.Further exploiting the advantages of SLS technology,a 20BBG/PCL with interconnecting body-centered cubic(BCC)unit structure was customized to regenerate the CSBD of radius in rabbits.After 6 and 12 weeks of surgery,samples were harvested and tested in terms of micro-CT,Masson and H&E tissue staining and qRT-PCR detection of osteogenic genes.The results showed that the addition of BBG(20wt%)significantly promoted the degradation of scaffolds and the osteogenic performance in vivo compared with pure PCL scaffolds.The overall structure of the scaffolds was stable in the process of repair,and the personalized structure well guided the direction of new bone formation.The internal reserved channels achieved the integration with the bone marrow cavities at both ends of the defect,and the appropriate porous structure allowed the growth of cells and blood vessels into the scaffold.Personalized 20BBG/PCL porous scaffolds prepared by SLS provide a new strategy for the treatment of CSBD.