Immobilized bioactive antibacterial ionic groups modulate titanium osteointegration

Objectives: The present study evaluated in vivo new bone formation around titanium implants modified with immobilized ionic sulfonate and/or carboxylate groups. These chemical compounds were chosen because they inhibit bacterial adhesion.

Methods: The curved surfaces of Ti-6Al-4V cylinders (5 mm in diameter ; 6 mm in length) were coated with immobilized ionic carboxylate (C) and/or sulfonate (S) groups by radical polymerization following established procedures. Unmodified (controls) and modified Ti-6Al-4V containing either 100% C, or 50% C and 50% S, or 80% C and 20% S, or 100% S (test groups) were bilaterally implanted in femoral lateral condyle defects in rabbits. New bone formation was evaluated qualitatively (using micro-X-ray and histological analyses) and quantitatively (using histomorphomertry) after 4 and 12 weeks post-implantation.

Results: Neither toxicity nor inflammation was observed for all implants tested for the duration of the study. After 4 weeks, peri-implant new bone formation varied as a function of the ionic composition of the titanium surfaces; for example, the percentage of bone implant contact (BIC) was the lowest (13.4% ± 6.3%) for the implants modified with immobilized carboxylate only. During this time interval, the percent BIC on implants with 20% sulfonate (24.6 ± 5.2%) was significantly (p<0.05) lower than that observed on 100% sulfonate (38.2+13.2%), the latter BIC value was similar to that of controls. The BIC of implants with more than 50% sulfonate content was similar to the unmodified titanium alloy (controls) after both 4 and 12 weeks.

Conclusions: Ti-6Al-4V implants modified with up to 50% sulfonate are both less vulnerable to bacterial adhesion and promote bone regeneration. Such materials are of clinical interest because they prevent peri-implant infections.