Antimicrobial PLA and Calcium Phosphate Coatings and Thin Film Composites for Implants Applications

Abstract

Implant-related infections after the insertion of biomedical implants are still prevalent, and the current treatment methodology requires the use of large doses of antibiotics systemically. Large doses can lead to a number of side effects including antibiotic resistance and adverse effects on the other organs. These infections delay healing, worsen functional outcome and incur significant socioeconomic costs. Bone implant related infections, surgery site infections (SSI), and osteomyelitis remain the most challenging clinical problems faced. This thesis aimed to develop a novel implant coating system based on a ‘Local and Controlled Antibiotic Delivery System with Biodegradable Polymeric Thin Film Composite Coating’ for metallic bone implants.

The specific aim of this study was to design a novel multi-functional and antibacterial coating for implants as the drug delivery systems to prevent post-operative complications and osteomyelitis. The main challenge was to obtain the perfect design and the selection of appropriate biomaterials; implantable device with antibacterial, biocompatible and bioactive properties. Therefore, gentamicin antibiotic (Gm) and Gm loaded coralline hydroxyapatite (HAp) particles were incorporated into a poly-lactic acid (PLA) matrix as the main biocomposite. A number of systems were produced, characterized and tested, which included PLA, PLA-Gm mixture, and a PLA-Gm-(HApGm) biocomposite.

The coral skeleton (CaCO₃) was converted to HAp by using the hydrothermal conversion method. These microspheres were loaded with Gm and HAp-Gm particles and incorporated within the PLA thin film composites. Coralline-HAp possesses a unique nano- and meso-porous structure and can be used as a drug carrier for the sustained release of antibiotics on metallic bone implants. While the physiochemical characterizations of the PLA biocomposite coating were evaluated, their Gm release profile were analyzed by the continuous dissolution method. The bioactivity and biocompatibility of the design was tested on Adipose-derived stem cells using in vitro studies. The antibacterial activity and biofilm formation behaviour were also analyzed with S. aureus and S. epidemidis.

Different Gm concentrations (5%, 10%, 15%, 20% and 30% [w/w]) were incorporated into the PLA biocomposites and were found to be highly effective on the inhibition of S. aureus and S. epidermidis growth at the planktonic stage. At the biofilm formation stage of S. aureus, the significant reduction of bacterial attachment and the increasing of dead microcolonies were observed for even the lowest 5% (w/w) PLA-Gm-(HAp-Gm) coated samples. This research showed that the biodegradable and antibacterial PLA biocomposite coatings design has high potential as a viable alternative method for existing clinical applications on many metallic orthopedic and maxillofacial bone implants.