Formulation of Inherently Antimicrobial Magnesium Oxychloride Cement and Effect of Supplementation with Silver Phosphate

The growing threat of bacterial resistance to antibiotics is driving an increasing need for new antimicrobial strategies. This work demonstrates the potential of magnesium oxychloride cements (MOC) to be used as inorganic antimicrobial biomaterials for bone augmentation. An injectable formulation was identified at a powder to liquid ratio of 1.4 g mL-1, with initial setting time below 30 mins and compressive strength of 35 MPa. Supplementation with Ag3PO4 to enhance antimicrobial efficacy of MOC was considered, and shown via real-time X-ray diffraction to retard formation of hydrated oxychloride phases by up to 30%. The antimicrobial efficacy of MOC was demonstrated in vitro against Staphylococcus aureus, with cement extracts after 72 hours of aging reducing the concentration of viable bacteria by a factor 107 CFU mL-1 after 24 hours culture. Enhanced efficacy was seen for silver doped formulations, with complete eradication of detectable viable colonies within 3 hours. Investigating the antimicrobial mode of action revealed that Mg and Ag release and elevated pH contributed to efficacy. Interestingly, sustained silver release was demonstrated over 14 days, suggesting the Ag3PO4 modified formulation offers two mechanisms of infection treatment, combining the inherent antimicrobial properties of MOC with controlled release of inorganic antimicrobials.