Controlled Release Mechanism of Vancomycin from Double-Layer Poly-L-Lactic Acid-Coated Implants for Prevention of Bacterial Infection

Implantation failure due to bacterial infection incurs significant medical expenditure

annually, and treatment tends to be complicated. This study proposes a method to prevent bacterial

infection in implants using an antibiotic delivery system consisting of vancomycin loaded into

poly-L-lactic acid (PLLA) matrices. A thin layer of this antibiotic-containing polymer was formed

on stainless steel surfaces using a simple dip-coating method. SEM images of the polymeric layer

revealed a honeycomb structure of the PLLA network with the entrapment of vancomycin molecules

inside. In the in vitro release study, a rapid burst release was observed, followed by a sustained

release of vancomycin for approximately 3 days. To extend the release time, a drug-free topcoat of

PLLA was introduced to provide a diffusion resistance layer. As expected, the formulation with

the drug-free topcoat exhibited a significant extension of the release time to approximately three

weeks. Furthermore, the bonding strength between the double-layer polymer and the stainless

steel substrate, which was an important property reflecting the quality of the coating, significantly

increased compared to that of the single layer to the level that met the requirement for medical

coating applications. The release profile of vancomycin from the double-layer PLLA film was best

fitted with the Korsmeyer–Peppas model, indicating a combination of Fickian diffusion-controlled

release and a polymer relaxation mechanism. More importantly, the double-layer vancomycin-PLLA

coating exhibited antibacterial activity against S. aureus, as confirmed by the agar diffusion assay,

the bacterial survival assay, and the inhibition of bacterial surface colonization without being toxic

to normal cells (L929). Our results showed that the proposed antibiotic delivery system using the

double-layer PLLA coating is a promising solution to prevent bacterial infection that may occur after

orthopedic implantation.