Bisphosphonate coating on titanium screws increases mechanical fixation in rat tibia after two weeks

Recently published data indicate that immobilized N ‐bisphosphonate enhances the pullout force and energy uptake of implanted stainless steel screws at 2 weeks in rat tibia. This study compares titanium screws with and without a bisphosphonate coating in the same animal model. The screws were first coated with an ∼100‐nm thick crosslinked fibrinogen film. Pamidronate was subsequently immobilized into this film via EDC/NHS‐activated carboxyl groups within the fibrinogen matrix, and finally another N ‐bisphosphonate, ibandronate, was physically adsorbed. The release kinetics of immobilized 14 C‐alendronate was measured in buffer up to 724 h and showed a 60% release within 8 h. Mechanical tests demonstrated a 32% ( p = 0.04) and 48% ( p = 0.02) larger pullout force and energy until failure after 2 weeks of implantation, compared to uncoated titanium screws. A control study with physically adsorbed pamidronate showed no effect on mechanical fixation, probably due to a too small adsorbed amount. We conclude that the fixation of titanium implants in bone can be improved by fibrinogen matrix‐bound bisphosphonates. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008