Precise Regulation Of Pore Size Of Calcium Phosphate Bioceramic Scaffolds And Its Effect On Bone Regeneration

Osteogenesis and angiogenesis are two important processes in bone regeneration,especially for repairing the segmental bone defects.Creating a good microenvironment of porous scaffold to rapidly promote osteogenesis and vascularization is an important research direction of bone repair materials,which has important scientific significance and clinical value.This study developed the key technologies of 3D printing for calcium phosphate bio-ceramic material through biomimetic preparation of calcium phosphate bioactive powder and controllable molding process.Bioceramic paste with high solid content and low addition of additives has been realized,with the dimensions and internal microstructure of scaffolds precisely controlled.Osteogenesis and vascular differentiation potential of cells seeded on the scaffolds with different pore sizes were investigated.In addition,different bone defect models were used to further reveal the bone regeneration capacity of the scaffolds and the underlying mechanism of bone formation mediated by the scaffolds with different porous structures.This study provide important scientific basis for the design of personalized bio-ceramics and research of the new bone regeneration materials.(1)3D printed calcium phosphate scaffolds with precise and controllable shape and pore sizeThe ceramic paste with high solid content(50 vt%)and good printability was prepared by post-processing the powder.A set of environmental control system was designed and developed through studying the relationship between printing paste and printing process parameters.?-TCP scaffolds with varied geometric shape,large scale and refined porous structure(pore size precisely controlled to 100 ?m)were fabricated by the 3D plotting technique,successfully solving the current challenges for bioceramic printing.(2)The behavior of mMSCs cells and HUVECs cells affected by calcium phosphate scaffolds with different pore sizes?-TCP scaffolds with 100,250,and 400 ?m pore size were targeted and well controlled by the 3D plotting technique.The scaffolds achieved excellent compressive strength(85.26 ± 2.71 MPa,71.81 ± 2.32 MPa,36.08 ± 5.86 MPa).Interacting with simulated body fluid(SBF)solution for 12 h,the 100 ?m and 250 ?m pore size groups showed good mineralization ability.In vitro results indicated that the ?-TCP scaffolds with 100 ?m pore size were more favoring the osteogenesis while the ?-TCP scaffolds with 400 ?m pore size performed better in promoting angiogenesis.(3)The vascularization capacity of calcium phosphate scaffolds with different pore sizes in subcutaneousSubcutaneous embedding experiment was carried out to investigate the vascularization mediated by the three pore size(100,250,and 400 ?m).The results showed that the connective tissue as well as abundant red blood cells had infiltrated the interconnected porous structure after implantation for 2 weeks.HE staining and immunohistochemistry of protein VEGF and CD31 staining results showed that 400 ?m pore size group was most efficient in inducing vessel formation.(4)Bone regeneration of different bone defects and the related mechanism affected by scaffolds with different pore sizesTypical long bone(tibia)defect model and flat bone(calvarial)defect model were applied to investigate their bone regeneration capacity and the underlying mechanism mediated by the pore sizes(100 ?m,250 ?m,and 400 ?m).Results showed that bone regeneration capability in vivo by these pore sizes was related to the defect models(rabbit tibial defects and calvarial defects).Among the three pore sizes being studied,100 ?m pore size was most efficient in inducing bone formation in repairing flat bone defects,which was owing to the enhanced osteoblast differentiation in the intramembranous ossification.Differently,the scaffolds with pore size of 400 ?m displayed the best ability of bone formation for repairing long bone defects,which was speculated to be related to the accelerated formation of cartilage templates and ossification centers in endochondral ossification.This study firstly solved the key technical problems of 3D printed calcium phosphate bioactive ceramic materials.Based on the porous scaffolds with precisely controlled pore size,the mechanism of the regulation of the pore size on cell behavior and the different bone defect regeneration was clarified.It provides a systematic theoretical guidance for the structural design of a new generation of personalized bone regeneration scaffolds.