Development of multifunctional materials (MFM):: Bioabsorbable drug-releasing hard tissue fixation screws

To develop a successful bone fixation device that can also release therapeutic agents such as antibiotics one has to consider mechanical, drug release, and biocompatibility properties. We have used bioabsorbable polymers (PLGA 80/20 or PLDLA 70/30) as the matrix and ciprofloxacin (CF) as antibiotic to develop such an implant. Initial shear strengths of the studied ciprofloxacin-releasing screws were 152 MPa (P/L/DL)LA) and 172 MPa (PLGA). Studied screws retained their mechanical properties for least 12 weeks (P(L/DL)LA) and 9 weeks (PLGA) in vitro at the level that ensures their fixation properties. Pull-out tests indicated that the early version of screws have lower values as compared to controls. CF was found to be released after 44 weeks (P/L/DL)LA) and 23 weeks (PLGA) in vitro. It remained in the range of 0.06 - 8.7 mu g/ml/day (for P(L/DL)LA) and 0.6 - 11.6 mu g/ml/day (for PLGA) after the jump start. Release CF was demonstrated to significantly inhibit S. epidermides growth, attachment and biofilm formation different than controls. Histology showed no difference from plain polymer screws, except for increased giant cells at the implantation site. Accordingly, SR-P(L/DL)LA and SR-PLGA MF implants were considered appropriate to proceed to pilot clinical application.