Survivability of TiO₂nanotubes on the surface of bone screws

Abstract

Modifying surface chemistry and/or surface topography is considered to be a traditional way of optimizing bone-implant integration (osseointegration) for improved bone bonding. The previous results have shown enhanced in vitro osteoblast cell density on titania nanotube–covered surfaces compared with bare titanium surfaces. However, for titania nanotubes to be considered as a candidate surface modification for titanium implants, they must survive load-bearing conditions. The authors investigated the structural survivability of nanotubes on the surface of Ti-6Al-4V-ELI (extra low interstitials) cancellous bone screws subjected to insertion and removal using bone simulant. Measuring the torque during insertion in bone simulant was performed to provide input loads to a finite element model to predict the survivability of the titania nanotubes. Scanning electron microscopy was used to investigate the nanotube morphology before and after the insertion and removal tests. A finite element model using experimental insertion torque data estimated the maximum von-Mises stress in the titanium oxide nanotubes. The model predicted that the maximum von-Mises stress in the nanotubes due to combined compression and shear loading is well below the yield failure. Scanning electron microscopy observation confirmed the presence and survivability of the nanotubes after being subjected to multiple insertions and removals of the screws.

Electrochemical Evaluation of the Compact and Nanotubular Oxide Layer Destruction under Ex Vivo Ti6Al4V ELI Transpedicular Screw Implantation

“…Previous attempts to elaborate the mechanical degradation of TNT during implantation were carried out using flat foil [9,[14][15][16][17], on Ti, Ti6Al4V, and Ti6Al7Nb screws [19][20][21][22][23] using a nanoindenter test [37], wear test [6,36], or practical implantation of the screws to the bone. The implantation was carried out by inserting a screw into a bone and removing it, which caused double abrasion of the nanotube layer, and prevented TNT characterization inside the bone immediately after implantation.…”

“…The titania nanotubes (TNT) were successfully produced on Ti6Al7Nb screws [20], Ti CP2 screws [21], and Ti6Al4V ELI screws [19,22], etching to the Ti6Al4V screw [23]. Though the implantation process was not considered in this attempt, the formed nanotubular layer of TiO 2 was cracked [19] or produced exclusively in the α-phase [20][21][22][23]. This is extremely urgent for obtaining the homogenous layer of compact and nanotubular oxide on the surface of implantable devices and to ensure protection against microrupture, ion release, and corrosion that has not yet been done.…”

Engineering Nanotextured Titanium Surfaces

“…Electrochemical anodization produces a layer of nanotubes open at the top and closed at the bottom whose diameter and length can be controlled by using appropriate electrolyte concentration, anodization voltage and time. Over the years several research groups have focused on nanotube synthesis using electrochemical anodization with different nanotube diameters ranging from 65 nm to 150 nm and lengths ranging from 250 nm to 134 µm [7][8][9][10][11][12]. The nanoscale dimensions can change the ionic, electronic and bio-interface properties considerably, which may help to improve reaction/interaction between an implant and the surrounding tissue [13].…”

Local and Systemic In Vivo Responses to Osseointegrative Titanium Nanotube Surfaces

“…Two TiNT surface morphologies, termed aligned and trabecular, have been developed for orthopedic applications necessitating osseointegrative properties [17,[20][21][22]. The aligned TiNT morphology comprises arrays of vertically oriented nanotubes, while the trabecular TiNT morphology exhibits a random surface resembling the three-dimensional porous network of trabecular bone.…”