Preparation, Structure And Performance Of Self-setting Porous Microsphere Based On Calcium Phosphate Cement

The current replacement procedures for bone defect therapy mainly depended onautologous tissue which is the golden standard. Unfortunately, the origination of autologousbone is often limited in supply, and the allogenous bone takes an increased risk of diseasetransmission. Microparticulate forms have been widely used to treat defective bones. Asmicrospheres were good at flowability, the defect of bone can be filled well by them.Completely-connected hole among microspheres is good for bone repair.Calcium phosphate cement (CPC) is highly promising for wide clinical applicationsbecause of its good biocompatibility, excellent bioactivity, low heat release during theself-setting reaction, adequate stiffness, and easy shaping for any complicated geometry. Inrecent years, new strategies that exploit the intrinsic properties of CPCs have been envisaged,and pre-set CPC scaffolds or granules by various processing techniques have been extensivelyput forward.In order to improve the cytocompatibility of microspheres, the surface modification ofhardened calcium phosphate cement has been study first. After immersed inpolyethyleneglycol solution the surface of modified sample was covered by regular blade-likecrystalline structure. The results of cell experiments exhibited that the samples with regularblade-like crystalline structure had better cell response (cell attachment, viability, proliferationand differentiation) compared to those with irregular blade-like crystalline structure.In this study, calcium phosphate microspheres(0.3-3mm) with apparent porosity of47%or more were prepared by dripping-freezing procedure. The mechanical strength, resistance todisintegration, resorbability, and bioactivity of the microspheres has been improvedsignificantly as calcium silicate added.No remarkably disintegration has been found duringtwo weeks because of the addition of calcium silicate. The microspheres with differentcontent of calcium silicate were implante in femoral bone defects and sarcotheca of back ofrabbits. New bone can be seen not only in the gaps between microspheres but also internal ofmicrospheres at8weeks. The microspheres contain40%calcium silicate have been degradedmost part at16weeks. The number of osteoblasts, osteocytes and multinuclear cells wasdecreased as time extension. Blood vessels can be found around new bones. These results indicated that calcium silicate improved the degradation and osteogenic capability ofmicrospheres. The pore structure among microspheres was good for vascularization.Another method used to produce porous calcium phosphate microspheres(0.3-3mm) isextrusion–spheronisation. Different with the microspheres which were prepared bydripping-freezing procedure, the main crystal structure is rodlike, no disintegration was foundmore than two weeks. After immersed in the polyethyleneglycol solution, the surface ofmicrospheres was covered by regular blade-like structure. The result of MTT showed that theregular blade-like structure is good for cell proliferation.The microspherical scaffolds were prepared by vacuum impregnation, PLGA was usedas binder. The porosity(35.36%±1.18%) of scaffold was tested by micro-CT. The strength ofscaffolds improved as the content of PLGA increased, but the porosity decreased as manypores were filled by PLGA. Process based simulation was used to simulation the process ofmicrospheres accumulation. The result indicated the pores among microspheres are fullconnected. This structure is good for transportation of nutrition and elimination of metabolin.