Formation and osteoblast behavior of HA nano-rod/fiber patterned coatings on tantalum in porous and compact forms

Abstract

The novel bilayered coatings, comprising hydroxyapatite (HA) nano-rods/fibers as an outer-layer and the CaTa₂O₆-based matrix as an inner-layer, were fabricated on Ta in porous and compact forms using microarc oxidation and hydrothermal treatment (HT). The formation mechanism and change in the topography of the HA nano-rods/fibers were investigated. Moreover, the evolution of structure and adhesive strength, apatite-inducing ability, and cytocompatibility of the nano-rod/fiber patterned coatings together with Ta were also explored. During HT, the HA nanorods directly nucleated on the CaTa₂O₆-based matrix and grew in length to nanofibers with HT time. Meanwhile, the orientation of the nano-rods/fibers on the resultant HT3h, HT6h and HT24h coatings also changed, appearing to be quasi-vertical, bent, and parallel to the underlying substrate, respectively, corresponding to the widening of inter-rod/fiber spacing. The coatings adhered firmly to Ta substrates with long-term adhesive strength stability, and exhibited a superior apatite-inducing ability. The survival and proliferation of osteoblasts were significantly enhanced on the quasi-upright HA nanorod patterned HT3h coating, however, greatly inhibited on the paralleled HA nanofiber patterned HT24h coating compared to Ta. The difference may have resulted from the stable cell adhesion on the HT3h coating and enhanced cell apoptosis caused by unstable cell adhesion on the HT24h coating, owing to the narrow interrod spacing for the former and the wide interfiber spacing for the latter.