Promoting Infection Prevention and Biocompatibility of Magnesium for Orthopaedic Applications via Gallium-Strontium Phosphate Conversion Coatings

Device-associated bacterial infections remain a clinical challenge. Present strategies to prevent bacterial infection are either toxic to healthy mammalian cells and tissue or involve high doses of antibiotics that can prompt long-term negative consequences in terms of side effects or drug resistance. An antibiotic-free coating strategy to prevent bacterial attachment and biofilm formation is presented, which promotes bone cell growth and moderates the dissolution kinetics of resorbable magnesium (Mg) biomaterials. Herein pure Mg substrates were coated with gallium doped strontium-phosphate through a chemical conversion process. Gallium was distributed in a graduated manner throughout the strontium-phosphate coating, with a compact structure and a gallium-rich surface. It was demonstrated that the coating protected the underlying Mg from significant degradation in minimal essential media at physiological conditions over 9 days. In terms of bacteria culture, the liberated gallium ions from the coatings upon Mg specimens, even though minute quantities, reduced the viability and biofilm formation of Gram-negative P. aeruginosa and E. coli – two important clinical strains causing infections. More importantly, the gallium dopants displayed minimal interference with the strontium-phosphate based coating which boosted osteoblasts and undermined osteoclasts, in in vitro co-cultures. This work provides a new biocompatible strategy to prevent bacterial infection and control the degradation behaviour of Mg-based orthopaedic implants, while preserving osteogenic features of the devices.