Biotemplate Biomimetic Synthesis Of Strontium-contained Calcium Phosphate Hollow Microspheres

Calcium phosphate bioceramic exhibits excellent biological activity, biocompatibilityand osteoconductivity, because of the similarity with the inorganic component of the naturalbone in the chemical composition and crystal structure. It is one of the important researchesand application categories in the study and development of bone regeneration materials.However, the traditional techniques can not be achieved on the precise control and biomimeticpreparation toward the product morphology, structure and composition at present. There arestill large differences between the artificial calcium phosphate and biological apatite in thecomposition, structure and properties, existed the problems such as the mechanical propertiesand biodegradation rate mismatching with the new bone formation, which greatly limits itsapplication in the regeneration and repair of bone defects. Besides to research the moreeffectively controllable biomimetic technology to prepare calcium phosphate bioceramic isrequired for developing the high-performance materials for bone regeneration and repair.In this study, biotemplate biomimetic technology was used. We innovatively used theyeast-based biotemplate to implement the effective control toward the porous hollowmicrosphere structure and the ionic content and ionic enriching position of the trace elements,and prepared the porous hollow storntium-contained calcium phospahte microspheres for thebone tissue regeneration and repair. The porous hollow microsphere structure has theadvantages, such as low density, high stability, good fluidity, good surface penetration abilityand accommodating a large number of guest molecules, etc. The structure makes the load andrelease with the functional molecules for the promotion of the new bone formation becomepossible. On this basis, we further researched on the ionic modification of the low dosesstorntium in calcium phospahte, which can significantly improve the biocompatibility,osteoconductivity and biodegradation, and effectively promote the new bone formation, aswell as increased the bone defect regeneration efficiency.The effect of the key parameters on the product component and structure was researched,such as the cell types, polyelectrolyte concentration, the self-assembly times, temperature, pHvalue, ion concentration, etc. We determined the optimal conditions for preparing the poroushollow calcium phospahte microspheres, and achieved on the precise control of the poroushollow microsphere structure. The biomimetic mechanism was discussed. The main phase ofthe finally product was β-TCP. The microsphere average diameter was about5.85μm. Theshell thickness was among0.5-1.0μm. There were numbers of micro-and nano-sized pore inthe shell wall （The pore diameter≤500nm）. Based on the use of the biotemplate for preparing porous calcium phosphate hollowmicrospheres, we further researched the ionic modification of the trace element on calciumphosphate and the problems of the component uneven and ion burst release. The specificadsorption of polyelectrolyte and microbial cells to the Sr²⁺was utilized to achieve on theeffective control of the ion content and ion enriching position. The porousstrontium-sbustituted calcium phosphate hollow microsphere/microcapsule （Sr-CPMC） wassuccessfully synthesized. The study was carried out for the effect of Sr²⁺on the hollowmicrosphere component and structure, as well as the infection of Sr²⁺content and Sr²⁺enriching position to the product’s ion release behavior, mineralization, protein adsorption andbiological performance.The results showed that the Sr-CPMC was obtained by using the polyelectrolyteadsorption. The Sr²⁺pre-substitued in the amorphous calcium phosphate, which became theSr-TCP after sintered. The Sr²⁺enriched in the outer layer of microspheres. The Sr²⁺contentand the initial Sr/（Sr+Ca） molar ratio was a proportional relationship. However, the theSr-CPMC prepared by using the yeast cells biosorption loaded the Sr²⁺on the innerbiotemplates. Sr²⁺incorporated in the TCP crystal lattice through the heat treatment, whichmainly enriched in the inner microspheres. The Sr²⁺content increased with the initial Sr²⁺concentration increased and then decreased. The biotemplate method can regulate the ionicmodification of the trace element in calcium phosphate and effectively control the Sr²⁺content, Sr²⁺enriching in outer/inner microsphere. Yeast cells as an intelligent primary devicefor the ion doping can achieve on the low dose ionic modification of the trace element.Sr-CPMC has the Sr²⁺slow release properties and good mineralization and proteinadsorption properties. The Sr²⁺content and Sr²⁺enriching location were the key parameters toaffect the Sr²⁺release behavior, mineralization and protein adsorption performance. Theporous hollow microsphere structure has the key function to control the Sr²⁺slow release.Sr-CPMC showed good compatibility during co-culturing wiht the human marrow stromalcells （hMSCs）. Sr-CPMC can promote the hMSCs proliferation and osteogenic differentiationdue to the synergies of the porous hollow microsphere structure and Sr-Ca component.Compared to the control, the cell proliferation rate of the Sr-CPMC sample increased about40%, when the Sr²⁺content was0.18±0.04at%and the Sr²⁺was enriching in the innermicrosphere. During co-culturing osteogenic process, the sample of the Sr²⁺enriching in theinner microsphere increased the hMSCs ALP activity about50%and significantly promotedthe hMSCs ALP, Collagen-I and Runx-2gene expression, as well as the ALP enzymesecretion and calcium nodule formation. Sr-CPMC and hMSCs were cultured to turn to be a powder-cells three-dimensional composite group after30days’ osteogenic process. HMSCsshowed good adhesion and proliferation condition both inside and outside of the compositegroup and produced a large number of Collagen-I after the osteogenic differentiation. Thethree-dimensional composite group has the potential of transforming to the bone tissue.In this work, the biotemplate method was used to prepare Sr-CPMC. The product hadgood ion slow release, mineralization, protein adsorption and cell biological properties. Weproposed the product could be made for the drug carrier, packing material, injectableself-setting calcium phosphate bone cement, or bone tissue engineering scaffold. The producthas broad prospects for the biomedical application.