Figure 6. A novel antibiotic-impregnated implant coating results in reduced S. aureus infection, decreased inflammation and prevention of biofilm formation.

Orthopaedic-grade stainless steel K-wires were machine cut and coated with increasing concentrations of a tyrosine-based biodegradable antibiotic implant coating, which contained rifampin and minocycline or vehicle alone (coating without any antibiotic). The rifampin/minocycline concentrations for each of the coatings were: Coating A: 32.5/36.1 µg/mm³; Coating B: 46.1/47.7 µg/mm³ and Coating C: 97.4/104.2 µg/mm³. Furthermore, Coatings A and B were the same thickness (∼40–45 µm) and would elute at the same rate whereas Coating C would elute slower because it had double the coating thickness (∼80–90 µm). These coating implants were surgically placed into the distal femur and 5×10² CFUs/2 µl of S. aureus was inoculated into the knee joint in the area of the cut end of the implant. (A) Representative photograph of an uncoated stainless steel implant and an antibiotic-impregnated coated implant. (B) Bacterial counts as measured by in vivo S. aureus bioluminescence (mean maximum flux [p/s/cm²/sr] ± sem) (logarithmic scale) (n = 5 mice per group). (C) Neutrophil infiltration as measured by in vivo fluorescence (total flux [photons/sec] ± sem) (n = 5 mice per group). (D) Representative VP-SEM images of the cut ends of the implants are shown (1 of 2 mice per group, with similar results). Top panels represent a low power magnification (120x) and the bottom panels show a higher magnification (600x) of the area boxed in red. *p<0.05 †p<0.01 ‡p<0.001 coatings A, B, or C vs. vehicle coating (Student's t-test).