Fibroblast growth factor-2-apatite composite layers on titanium screw to reduce pin tract infection rate

Fibroblast growth factor-2 (FGF-2)-apatite composite layers were formed on anodically oxidized titanium screws to improve bone-screw interface strength and to reduce pin tract infection rate through enhanced skin tissue healing in external fixation. A calcium-containing solution supplemented with FGF-2, a phosphate-containing solution, and a sodium bicarbonate solution were mixed at a Ca/P molar ratio of 2.0 to prepare a calcium phosphate solution supersaturated with respect to calcium phosphates. Screws were individually immersed in 10 mL of the calcium phosphate solution at 37 degrees C for 2 days. Low-crystalline apatite layers incorporating FGF-2 were formed on the screw surface at FGF-2 concentrations in the supersaturated calcium phosphate solution equal to or lower than 10 mug/mL. The amounts of FGF-2 immobilized on the screws ranged from 2.3- to 2.4-mug per screw. The immobilized FGF-2 retained biological activity, as demonstrated by NIH3T3 cell proliferation. Titanium screws with the composite layer were percutaneously implanted into the bilateral proximal tibial metaphyses in rabbits for 4 weeks. The titanium screws with the composite layer formed at the optimum FGF-2 concentration showed a significantly higher bone-screw interface strength and a lower pin tract infection rate than those without the composite layer: the extraction torque and infection rates were respectively 0.230 +/- 0.073 Nm and 43.8% for the screws with the composite layer, and 0.170 +/- 0.056 Nm and 93.8% for those without the composite layer. Therefore, titanium screws with the FGF-2-apatite composite layer are useful for improving bone-screw interface strength and infection resistance in external skeletal fixation.