54. Optimization Of Antimicrobial Efficacy and Biocompatibility In Fluorapatite Bone Scaffolds Through Low-dose Copper Doping For Advanced Bone Graft Applications

PURPOSE: Post-surgical infections pose a major challenge to bone graft survival, increasing patient morbidity and healthcare costs. The growing prevalence of antibiotic-resistant bacteria highlights the need for bone scaffolds with inherent antimicrobial properties that maintain biocompatibility. Osteogenic fluorapatite (FA) is a promising bone substitute, and previous studies demonstrated that 1-5 mol% copper-doped FA significantly reduced bacterial adhesion by 2- to 3-log folds compared to undoped FA. However, higher copper concentrations can lead to cytotoxicity. This study investigates the bacteriostatic efficacy and cytotoxicity of FA doped with 0-1 mol% copper. METHODS: FA doped with 0, 0.25, 0.50, 0.75, and 1 mol% copper was synthesized via the wet chemical precipitation method. Reagents used include calcium nitrate tetrahydrate, sodium phosphate dibasic, sodium fluoride, and copper nitrate trihydrate, with the latter serving as the doping agent. The dopants were gradually introduced to 12 L of water at 96°C and maintained at pH 9.2 by automated titration with sodium hydroxide. The synthesized materials were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, and inductively coupled plasma mass spectrometry. The morphology and topography of the sintered disks (1150ºC) were analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Disks were subjected to in vitro bacteria adhesion studies using Staphylococcus aureus and AlamarBlue-based cell viability assays using osteoblast cells. For bacteriostatic property evaluation, a known number of bacteria were placed on the disks (n=4/group), incubated for 2 hours, and then enumerated using serial dilution techniques. Undoped FA was used as the control. Group comparisons were conducted using an Analysis of Variance with a Tukey’s post hoc test, with p-value set at <0.05. RESULTS: The physical and chemical characterization of Cu-doped FA revealed that copper ions incorporated well within the FA crystal structure up to the 1 mol% substitution level. There was no evidence of a secondary tricalcium phosphate phase. The calculated Ca:P ratios of 1.67-1.7 were within the acceptable ranges reported in the literature. Preliminary findings indicate that all copper doped FA groups significantly reduced bacterial adhesion (p<0.01). CONCLUSION: The 0.25 and 0.5 mol% Cu-doped FA groups exhibited a 3 log-fold reduction in bacterial adhesion compared to FA. At lower copper doping, sintering at 1150°C resulted in smaller mean grain sizes. This may contribute to the micro-topographical features associated with the reduction of bacterial adhesions reported in the literature, but further studies are warranted. More importantly, the osteoblast cells were equally viable on all test surfaces, suggesting doping with copper below 1 mol% did not impact the biocompatibility of the FA disks. The 0.25 and 0.5 mol% Cu-doped FA surfaces appeared to balance antimicrobial efficacy and biocompatibility. It is therefore concluded that low percent copper-doped FA could serve as dual-purpose bone scaffolds for limiting infection-related graft failures in highly contaminated clinical environments. Still, efficacies need to be confirmed in animal studies.