Effects Of Sr-HA On The Behaviors Of Osteoblast

Strontium-containing hydroxyapatite(Sr-HA) has higher solubility and better mechanical properties because of the incorporation of strontium comparing to the pure HA and pure titanium. Additionally, low doses strontium can stimulate bone formation and reduce bone resorption .We developed Sr-HA coatings with different doses of strontium on titanium substrates by micro-arc oxidation (MAO) method, and chose three MAO time length to developing different surface topography. The aim of this study is to observe the properties of the films and investigate the cytotoxicity and osteoblast biocompatibility of the coatings.Methods:The surface morphology of the coatings was analyzed by scanning electron microscope (SEM).The element composition and phase component were analyzed with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Surface roughness and contact angle were measured using a surface profilometer and a contact angle measuring system.According to the GB and YY-T, L929 fibroblasts of mouse were used in MTT assay to examine the cytotoxicity of Sr-HA containing different strontium concentrations. Osteoblast cell adhesion and proliferation were examined by the MTT method and alkaline phosphatase (ALP) activity was assessed using test kits. The gene expression of several osteogenesis-related genes was surveyed by Realtime-PCR method.Results:1. Sr-HA coatings with different doses of strontium on titanium substrates can be developed by changing the proportion of [Sr/(Sr+Ca)] in the MAO electrolytes. HA was substituted by Sr-HA with the incorporation of strontium. The water contact angles had no significant deviation (P>0.05).2. The toxicity gradation of all groups was 0—1. Strontium incorporation did not induce obvious cytotoxicity, but the relative growth ratio slightly declined with the increase of strontium concentration.3. Samples containing 15.15% and 23.78% strontium enhanced osteoblast adhesion and proliferation while 7.24% Sr-HA increased the values of ALP activity after 7 d culture (P<0.05).After 3-d culture, on the Sr-HA coatings osteoblasts exhibited a good spreading and proliferation morghology.4. After 72h culture, the gene expression of BMP and Runx2 were increased on the Sr-HA coatings containing 7.24% strontium, while the expression of OCN was enhanced on the coating containing 23.78% strontium. No obvious variations in gene expression of OPN was observed on different strontium doses coatings.5. After prolonging the MAO time length, the coatings'surface morghology became more irregular, surface roughness was enhanced and water contact angles became smaller. Ca and P in the MAO electrolytes were incorporated into the oxidized coatings.6. MAO 10min and 15min coatings enhanced osteoblast adhesion after 60min and 90min-culture(P<0.05). Osteoblast exhibited fastest proliferation rate on the 5min surface, while lowest on the 15min surface. MAO 10min and 15min surface increased the values of ALP activity after 72h culture (P<0.05).7. After 3-d culture, osteoblast on MAO surfaces exhibited the typical osteoblast phenotype, the cells displayed lamellipodia and filopodia extensions, while on the Ti6Al4V surface cells were relatively flatter and displayed less functional morghology.8. After 72h culture, the gene expression of BMP and OCN were increased on the Sr-HA coatings after 15min MAO treatment. No obvious variations in gene expression of OPN and Runx2 were observed on different MAO time length treatments.Conclusions:Sr-HA coatings containing 15.15%—23.78% strontium after 10min—15min MAO treatment have better surface properties which favor the cell adhesion, proliferation, ALP activity and gene expression of osteoblast.