Surface Microstructure on Hydroxyapatite Spherules and Its Regulation on Stem Cells

Abstract

HA spheres with different surface microstructures were prepared by a Sol-Gel route with various hydroxyapatite (HA)/chitin ratios. The surface morphologies, phase compositions, and biomimetic mineralization ability of samples were respectively analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), and biomimetic mineralization test. Furthermore, the influences of the surface microstructure on biological behavior of bone marrow-derived mesenchymal stem cells were examined by Alamar blue, SEM, alkaline phosphatase assay and flow cytometry. When the mass ratio of HA/Chitin was increased from 4/1 to 35/1, the surface microstructure of HA spheres changed substantially, as showed by a reduction of micro-porosity from (35%±0.8%) to (10.4%±0.7%), decrease of surface roughness, and gradual disappearance of micro-creases. The result of biomimetic mineralization test showed that the surface microstructure had important influence to the ability of biomimetic mineralization for HA spheres. In vitro culture of bone marrow-derived mesenchymal stem cells demonstrated that the rougher sphere surface, with abundant micro-creases and micro-pores, supported cell spreading and proliferation. In comparison, the smoother sphere surface with fewer micro-pores effectively induced cell elongation and up-regulated ALP expression, which suggested stem cells osteogenic differentiation. Meanwhile, the surface microstructure of spherules also modulated the expression of characteristic antigen makers on the surface of stem cells.