In this study, variation of coating parameters was performed to determine a suitable condition for a vancomycin-coated Schanz pins in poly(lactic acid) (PLA) for prolonged antibacterial activity. Herein, the solvent used to dissolve the polymer (DCM vs. CHCl3), the concentration of the polymer in the solvent (2 vs. 5 w/v%), the vertical withdrawing speed of the implant from the solution (0.4 vs. 2.4 cm/s), and the number of dip-coating cycles denoted in layers (1 L vs. 3 L) were investigated for its drug loading. Results showed that the optimal parameters were at 2 w/v% PLA in DCM at 0.4 cm/s withdrawing speed and at 3 cycles for a high vancomycin loading with low deviation in result. Another experiment was performed by varying the concentration (1, 2, 4 w/v%) and number of dip-coating cycles (10 L, 20 L, 30 L) which finalized 2 w/v% PLA at 10 cycles as the optimal drug loading at 2.04 ± 0.09 mg. When observing the drug-release profile, the prior formulation released 2.21 ± 0.01 mg or 92.88 ± 0.44% of drug in one week. To reduce the amount of drug release in the first week, the method was further improved by spray-coating with PLA nanospheres (PLA-NS) for multiple cycles (10-, 20-, and 30-NS) to prolong drug release. After one, two, and three weeks, the drug-release were around 76%, 80%, and 88%, respectively. However, more drugs were lost as the number of cycles increases which suggests that lower (10-NS) coating cycle is better. Therefore, the final process was selected to be 2% PLA dip-coated for 10 cycles then spray-coated with PLA nanosphere for 10 cycles. Results showed that this method can help prolong release for at least 24 days. A short-term bacterial and cytotoxicity tests were done for 3 days with no S.aureus formed nor cytotoxicity. These results supported that the coating was successful in inhibiting the growth of S.aureus.

                                                         Reference: P. Chinavinijkul, K. Riansuwan, P. Kiratisin, S. Srisang, and N. Nasongkla, "Dip- and Spray-coating of Schanz pin with PLA and PLA nanosphere for prolonged antibacterial activity," Journal of Drug Delivery Science and Technology, vol. 65, 2021, doi: 10.1016/j.jddst.2021.102667.