Structure And Properties Of Three-dimensional Interconnected Porous Self-setting Calcium Phosphate Scaffolds Prepared By Indirect 3D Printing

Porous calcium phosphate scaffolds have been widely studied and applied to bone tissue regeneration due to their good biocompatibility,osteoconductivity,and degradable absorbability.In this study,we selected self-setting calcium phosphate cement(CPC)for its self-setting and easy-shaping characteristics to fabricate porous CPC scaffolds by an indirect three-dimensional(3D)printing technique.And on this basis,gelatin microspheres/CPC porous scaffolds were prepared by incorporating gelatin microspheres into CPC.Subsequently,physicochemical properties and cell biological properties of porous scaffolds were analyzed.The relationship between pore structure parameters(pore size,preformed 3D interconnected macropores,and in situ formation of hierarchical pore structure by combining gelatin microspheres)and properties of materials were investigated.Polycaprolactone(PCL)molds with good biocompatibility and mechanical properties were prepared by using the fused deposition modeling technique with 3D-bioplotter.CPC slurry was squeezed into the PCL molds and hardened,then the molds were eliminated by organic solvents to obtain 3D interconnected porous CPC scaffolds.Using the indirect 3D printing technique described above,we had fabricated porous CPC scaffolds with different pore sizes at room temperature.The results showed that the main phase of hydrated products of scaffolds was poorly crystalline hydroxyapatite.The scaffolds consisted of 3D interconnected macropores by elimination of PCL and plentiful micro/nano-pores by hydration of CPC.With the same macroporosity(25%),the scaffolds with smaller pore size(300-500 ?m)had higher compressive strength,lower total porosity and faster in vitro degradation.Porous CPC scaffolds had good biocompatibility,and cells could continuously penetrate into the interior of the scaffold.The porous structure of the scaffolds created a favorable microenvironment and promoted cell proliferation and differentiation.The scaffolds with smaller pores had better cell differentiation.The PLGA meshes were also prepared by using 3D printing.And the PLGA meshes and CPC were combined to obtain PLGA/CPC composite materials.Compared with CPC scaffolds prepared by sacrificial mold method,the influence of preformed 3D interconnected macropores on the properties of materials was discussed.Although both eventually had the same 3D interconnected macroporous structure,PLGA/CPC composites had higher compressive strength due to the lack of macropores at the initial stage.The PLGA meshes of PLGA/CPC degraded rapidly in situ within 14 days to form 3D interconnected macropores during degradation in Tris-HCl buffer solution.Compared with the CPC scaffold,the PLGA/CPC composite has slightly weaker adsorption ability of protein,weaker cell proliferation and weaker osteogenic differentiation,owing to their difference in composition and pore structure.The CPC scaffolds were modified with gelatin microspheres with good bioactivity and fast degradation to promote the degradation and improve the biological properties.Gelatin microspheres were prepared using inverse emulsion method.Then the gelatin microspheres/CPC composite scaffolds using indirect 3D printing by mixing gelatin microspheres with CPC powder.The gelatin microspheres were evenly distributed in CPC and did not significantly affect the phase and microstructure of the hydration products of CPC.As the amount of gelatin microspheres increased,the compressive strength of the scaffolds decreased,the porosity increased,and the degradation rate in vitro accelerated.Degradation of gelatin microspheres can make composite scaffolds have hierarchical pore structure(3D interconnected macropores,dispersed spherical macropores,micro/nano-pores).The cells tended to attach and grow around the gelatin microspheres and gradually grow into the center of the scaffolds over time.The incorporation of gelatin microspheres into CPC scaffolds promoted cell adhesion,proliferation,and osteogenic differentiation.