Abstract
We present a two-step surface modification process to tailor the micro and nano morphology of niobium oxide layers. Niobium was firstly anodized in spark regime in a Ca- and P-containing solution and subsequently treated by acid etching. The effects of anodizing time and applied potential on the surface morphology is investigated with SEM and AFM, complemented by XPS compositional analysis. Anodizing with a limiting potential of 250 V results in the fast growth of oxide layers with a homogeneous distribution of micro-sized pores. Cracks are, however, observed on 250 V grown layers. Limiting the anodizing potential to 200 V slows down the oxide growth, increasing the anodizing time needed to achieve a uniform pore coverage but produces fracture-free oxide layers. The surface nano morphology is further tuned by a subsequent acid etching process that leads to the formation of nano-sized pits on the anodically grown oxide surface. In vitro tests show that the etching-induced nanostructure effectively promotes cell adhesion and spreading onto the niobium oxide surface.
Highlights
A major concern in the design of orthopedic and dental implants is the integration of the implant in the bone tissue
We present a two-step surface modification process to tailor the micro and nano morphology of niobium oxide layers
Alongside the most widely used titanium and its alloys [4,5,6], many studies have been conducted on other bio-metals, employing anodic oxidation to grow porous oxide layers enriched in osteoconductive ionic inclusions [7,8,9,10,11,12,13,14,15,16,17,18]
Summary
A major concern in the design of orthopedic and dental implants is the integration of the implant in the bone tissue. Attention has been focused on the oxide enrichment in Ca and P compounds for osteointegration purposes using various electrolytes: a porous oxide layer structure has been reported, with morphology and composition depending on electrolyte, applied potential, limiting current and process time [19,20,21,22,23,24]. Together with macro roughness, which can help to mimic the bone trabecular structure, micro/nano roughness has been reported to play a key role to stimulate osteoblast adhesion and proliferation [2,3,25,26,27,28,29,30]. The submicrometer morphology can help in preventing the adhesion of bacteria, limiting adhesion points on the material surface and causing mechanical rupture of bacterial cell membranes [31,32,33,34,35]
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