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The morphological effect of nanostructured hydroxyapatite coatings on the osteoinduction and osteogenic capacity of porous titanium.

Weak osteogenic activity affects the long-term fixation and lifespan of titanium (Ti) implants. Surface modification along with a built-in porous structure is a highly considerable approach to improve the osteoinduction and osseointegration capacity of Ti. Herein, the osteoinduction and osteogenic activities of electrochemically deposited (ED) nanoplate-like, nanorod-like and nanoneedle-like hydroxyapatite (HA) coatings (named EDHA-P, EDHA-R, and EDHA-N, respectively) were evaluated in vitro and in vivo by comparison with those of acid/alkali (AA) treatment. The results revealed that the apatite forming ability of all nanostructured EDHA coatings was excellent, and only 12 h of soaking in SBF was needed to induce a complete layer of apatite. More serum proteins adsorbed on EDHA-P than others. In cellular experiments, different from those on EDHA-R and EDHA-N, the cells on EDHA-P presented a polygonal shape with lamellipodia extension, and thus exhibited a relatively larger spreading area. Furthermore, EDHA-P was more favorable for the enhancement of the proliferation and ALP activity of BMSCs, and the up-regulation of OPN gene expression. Based on the good biological performance in vitro, EDHA-P was selected to further evaluate its osteoinduction and osteogenic activities in vivo by comparison with AA treatment. Interestingly, a greater ability of ectopic osteoinduction was observed in the EDHA-P group compared to that in the AA group. At the osseous site, EDHA-P promoted more bone on/ingrowth, and had a higher area percentage of newly formed bone in the bone-implant interface and inner pores of the implants than in the AA group. Thus, a nanoplate-like HA coating has good potential in improving the osteoinductivity and osteogenic activity of porous Ti implants in clinical applications.