Abstract
Prior work in the setting of MRSA (clinical isolate), showed that enhancement of Ti6Al4V with anodized nanotubes apparently disrupts the formation and adhesion of MRSA biofilm. The greater amount of cultured MRSA using effluent released from in vitro nanotube surfaces by sonication, compared with thermal plasma sprayed (TPS), indicated probable disruption of biofilm formation and adhesion. The use of nanosilver nanotubes in vivo in a rabbit model showed that after 1 week of infection followed by 1 week of vancomycin treatment, the nanotube MRSA level was 30% that of TPS, and the nanosilver nanotube MRSA level was only 5% of TPS. The implementation of the technology will enhance the remodeled bone locking ability of rough TPS, with surface nanotubes that provide antibacterial properties and increased bone adhesion.
Lap shear tests of the nanotubes were performed according to ASTM F1044. In multiple tests, circular adhesive films bonded Ti6Al4V bars containing nanotubes with plain Ti6Al4V. The assemblies were suitably arranged in a tensile tester and pulled to shear failure. There were three modes of failure; shear failure within the adhesive, failure of the adhesive from the plain titanium, and shear failure of the nanotubes from the bar. Tests determined the shear strength of the adhesive and its bonding strength to bare titanium. ImageJ software determined the area of each of the three failure modes. From this analysis, the shear strength of the nanotubes of each sample was calculated.
The analyses showed the shear strength of the nanotubes to be as high as 65MPa (9,500psi) with a more typical shear strength of 55MPa (8,000 psi), and several surfaces with 45MPa (6,000 psi). The literature presents models predicting the shear stress in bonded hip stems. Assuming the TPS with nanotubes performs similar to a bonded hip stem, owing to the locking of the bone with the TPS, a typical shear stress prediction for physiological loads is approximately 10 MPa. The nanotube shear strengths were 4–6 times higher than the expected stress during use.
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