The amorphous to anatase transformation of anodized nanotubular titania surfaces has been studied by x-ray diffraction and transmission electron microscopy (TEM). A more rapid heat treatment for conversion of amorphous to crystalline anatase favorable for orthopedic implant applications was demonstrated. Nanotube titania surfaces were fabricated by electrochemical anodization of Ti6Al4V in an electrolyte containing 0.2 wt% NHF, 60% ethylene glycol and 40% deionized water. The resulting surfaces were systematically heat treated in air with isochronal and isothermal experiments to study the temperature and time dependent transformation respectively. Energy dispersive spectroscopy shows that the anatase phase transformation of TiO in the as-anodized amorphous nanotube layer can be achieved in as little as 5 min at 350 °C in contrast to reports of higher temperature and much longer time. Crystallinity analysis at different temperatures and times yield transformation rate coefficients and activation energy for crystalline anatase coalescence. TEM confirms the (101) TiO presence within the nanotubes. These results confirm that for applications where amorphous titania nanotube surfaces are converted to crystalline anatase, a 5 min production flow-through heating process could be used instead of a 3 h batch process, reducing time, cost, and complexity.
Electrochemical etching of titanium alloy in a fluoride-containing electrolyte results in ordered nanotextured surfaces. The reproducibility of nanotextured surfaces depends on several process parameters, most notably the fluoride ion concentration in the electrolyte. In the present work, electrochemical etching of Ti6Al4V alloy foils in ethylene glycol containing 0.66 wt% NH 4 F and 2% deionized water was carried out at 60 V for 45 minutes. This paper describes the depletion of fluoride ion concentration and contamination of electrolyte upon reuse. Inductively coupled plasma-optical emission spectroscopy was used to measure the dissolution of metal oxides in the electrolyte during etching. We found increasing concentration of the alloy elements Ti, Al, V contaminated the electrolyte due to repeated reuse of the electrolyte. The results show an appreciable log-linear depletion of fluoride ion concentration resulting in a changed surface morphology, chemical composition and etched volume. This paper provides an important insight to changes in surface morphology and surface chemistry with extended reuse of the etching electrolyte, useful for regulatory approvals.
Solid biologic fixation at the bone-implant interface provides long-term stability of orthopaedic implants. Historically, coatings and surface treatments on implant surfaces have been used to promote osseointegration of orthopaedic implants. The purpose of this research study is to evaluate two morphologies of titania nanotube (TiNT) surfaces via in vitro experiments as well as an in vivo model of femoral intramedullary fixation, in order to assess the influence of TiNT structure on de novo bone formation and bone-implant stability. Methods: TiNT structures were grown from Ti-6Al-4V materials via an established electrochemical anodization process. Samples were either sonicated then annealed (Aligned TiNT) or annealed without prior sonication (Trabecular TiNT), to produce different morphologies. As-received titanium alloy was the control. Marrow-derived stem cells were isolated from long bones of Sprague Dawley rats and cultured on samples. Alkaline phosphatase (ALP) and osteocalcin (OC) expression by stem cells were assessed via ELISA. Cells were lysed and subjected to quantitative polymerase chain reaction (qPCR) to assess Col1a1, osteonectin, and IGF-1 expression. An in vivo study evaluated bone formation at 4-and 12-week endpoints. Eight female Sprague Dawley rats per group per endpoint received bilateral Ti-6Al-4V K-wires as femoral implants. Left femur received control, while right femur received Aligned/Trabecular TiNT K-wire. Bone formation was assessed via microCT, backscatter electron imaging (BEI), and nondecalcified histologic analyses. Results: Aligned and Trabecular TiNT groups demonstrated higher ALP activity than control at 2 and 3 weeks. The in vivo study demonstrated increased bone volume fractions (BV/TV) and total bone volume (TBV) for TiNT surfaces (microCT). The ratio of both BV/TV and TBV in the distal VOI were nearly equivalent for both TiNT surfaces, indicating similar bone formation between both TiNT surfaces and control. In the midshaft VOI, the ratios between TiNT surfaces and control were 1.5 or greater, indicating increased bone formation. At 12 weeks, the bone-implant contact fraction ratio (BEI) showed Aligned TiNT and Trabecular TiNT were 1.3 and 1.4 times greater than control, respectively. Histologic analysis showed both TiNT surfaces had 1.5 times the bone-implant contact as control. Conclusion: In vitro studies demonstrated improved support for osteogenic functions of cultured marrow-derived stem cells on TiNT surfaces compared to controls. μCT, BEI, and histologic analyses associated with the in vivo study demonstrated increased bone formation in the TiNT femora, at specific timepoints and VOIs.
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