Structure And Properties Of Honeycomb-type Porous Calcium Phosphate Bioceramics Prepared By Combination Of Extrusion Moulding And Porogen

As porous calcium phosphate bioceramics have good biocompatibility,osteoconduction and degradability,they are widely applied in hard tissue repairing materials.Many fabrication methods can prepare porous bioceramics with high porosity.But they badly balanced the relationship between mechanical strength and porosity,interconnectivity.Based on this,tricalcium phosphate(?-TCP)powders prepared by solid reaction method were used in this study to construct honeycomb-type porous calcium phosphate bioceramics with big size and different pore structures by combination of extrusion moulding and porogen.Furthermore,improvement of mechanical and biological properties of three-dimensionally interconnected tricalcium phosphate(ITCP)bioceramic was obtained through polymer coating and element doping.The system of calcium phosphate pug with good plasticity was studied through an orthogonal experiment.The results showed that the ceramic pug had the best plasticity without obvious solid-liquid migration,when it mixed ?-TCP powders(3.03 ?m in average particle size)with 10 wt.% methyl cellulose(as the binder),35 wt.% deionized water,12 wt.% glycerol(as the plasticizer)and 6 wt.% paraffin liquid(as the release agent).The pressure in the extrusion process was predicted by a theoretical model(cited by Blackburn)combined with intrinsic parameters of the pug.The predicted pressure was basically consistent with the practical pressure under higher extruding velocity.Impact of sintering temperature on phase composition,microstructure,physic-chemical properties and cytobiological properties of unidirectional tricalcium phosphate(UTCP)bioceramics was studied.The results showed that the fabricated bioceramics had irregularly arrayed unidirectional pores(about 400 ?m in pore size)and a large quantity of micropores(about 1 ?m in pore size),while the total porosity was among 62%-72% and compressive strength was among 5-16 MPa.With the increasing of sintering temperature from 1050 to 1200 oC,the grain size and linear shrinkage of calcium phosphate bioceramics were increased,the pore size and wall thickness became smaller,the densification of pore walls was increased,the porosity was decreased and the compressive strength was enhanced.The cell experiments indicated that mouse bone mesenchymal stem cells(mBMSCs)had good cell attachment,proliferation and differentiation on these UTCP bioceramics.The UTCP bioceramic sintered at 1200 oC had good neovascularization.The effect of unidirectional pore structure on the mechanical strength,degradation and cytobological properties of UTCP bioceramics was investigated.Under the same porosity,the UTCP bioceramic with smaller pore size(in the range of 400-800 ?m)had higher compressive strength,faster in vitro degradation and better cell differentiation.Under the same pore size,the UTCP bioceramic with bigger wall thickness(in the range of 200-500 ?m)had higher compressive strength and better cell proliferation.The UTCP bioceramics with the same macroporosity but different pore shapes(square,triangle and circle)were further prepared.The bioceramic with circle pores had the highest compressive strength and the fastest in vitro degradation.Cytobiological tests showed that there was no significant difference on cell proliferation.But the bioceramic with angled(square and triangle)pores had better cell differentiation than the bioceramic with circle pores.Three-dimensionally interconnected tricalcium phosphate(ITCP)bioceramic was fabricated with gelatin microspheres(212-250 ?m in diameter)as soft porogens.When gelatin microspheres were 20 vol.%,the mechanical strength and connectivity of the bioceramic could be balanced.On the basis of ITCP bioceramic,hierarchically porous tricalcium phosphate(HTCP)bioceramic with good physic-chemical properties was prepared by introducing additional 70 vol.% PMMA powders as porogens.The physic-chemical properties,in vitro degradation and cytobiological properties of solid TCP bioceramic,UTCP,ITCP and HTCP were compared.It showed that ITCP bioceramic had the best comprehensive properties.The in vivo experiments showed that the osteogenesis of ITCP and HTCP was better than UTCP.To improve the mechanical property of ITCP bioceramic,a layer of gelatin film(3-5 ?m in thickness)was coated on the surface of ITCP bioceramic by a vacuum infiltration and freeze drying method.Though the open porosity decreased by about 10% compared with ITCP bioceramic,the compressive strength increased by 20%-80% and the initial cell seeding efficiency increased by 18%-35% in the gelatin coated ITCP scaffolds.Especially,the hybrid materials fabricated from 5 wt.% gelatin solution had good mechanical properties,in vitro degradation and cytobological properties.Improvement of mechanical strength and osteogenic activity of ITCP bioceramic was obtained through doping Zinc into ?-TCP powders.The results showed that Zn was successfully doped into the crystallize lattices of ?-TCP.Because Zn could inhibit the phase transition from ?-TCP(low-temperature phase)to ?-TCP(high-temperature phase),the Zn doped ITCP bioceramic could be prepared at higher temperature(1300oC)with the absence of ?-TCP.Compared to the undoped bioceramic,Zn doped ITCP bioceramic decreased the open porosity(4%-16%)but markedly increased the compressive strength(17%-45%).Meanwhile,cell proliferation and differentiation were improved.In this study,ITCP bioceramic was prepared by combination of extrusion moulding and porogen.Mechanical and biological properties were further improved on the basis of ITCP bioceramic through gelatin coating and Zn doping.In conclusion,considering the future of application in industrial production,this method is an effective method to fabricate macroporous bioceramcis with big size and three-dimensional interconnection.