Sustained delivery of antimicrobials from 3D printed calcium phosphate scaffolds in single-stage management of osteomyelitis

Thesis (Ph. D.)--University of Rochester. Department of Biomedical Engineering, 2019.Implant-associated osteomyelitis is a bacterial bone infection that is the bane of existence for orthopedic surgeons due to its relapsing nature. The gold standard for treating implant-associated osteomyelitis is a two-stage revision, where surgical debridement is performed, antibiotics are delivered locally from poly(methyl methacrylate) (PMMA) bone cement, and then the bone cement is removed in a subsequent surgery. Despite this, relapse rates remain high due to the poor drug release kinetics of the PMMA cement. Compounding these shortcomings are the abilities of the predominant pathogen, Staphylococcus aureus, to form an extracellular matrix, biofilm, and metabolically-deficient subpopulations, small colony variants (SCV). Both enable evasion of the immune response and reduced susceptibility to conventional antibiotics. Here, we address the limitations of PMMA bone cement and the persistence of S. aureus by first performing a high throughput screen of an FDA-approved drug library to identify antimicrobials that are effective against S. aureus SCV and biofilm. Sitafloxacin, a fluoroquinolone antibiotic, was identified and additionally displayed a high therapeutic ratio. Next, sitafloxacin was incorporated into 3D printed calcium phosphate scaffolds (CaPS) functioning as a local drug vehicle and biocompatible spacer. Rifampin was also incorporated to minimize the occurrence of bacterial resistance. Coating these scaffolds with poly(lactic co-glycolic) (PLGA) enhanced their mechanical strength and enabled a biphasic drug release profile at sustained concentrations above the minimum inhibitory concentration for 2 weeks after an initial burst release. To evaluate the efficacy of antibiotic-laden spacers, we developed a novel mouse model of implant-associated osteomyelitis, utilizing a single-stage revision to simulate clinical treatment. Implanting 3D printed CaPS with sitafloxacin and rifampin resulted in effective management of the infection with reduced bacterial colonization in comparison to mice treated with gentamicin-impregnated PMMA spacers. Furthermore, significant bone formation was observed 3- and 10-weeks post-revision indicating the osteoconductive nature of the CaPS. The improved management of the bacterial bioburden and bone regenerative potential establishes a foundation for treating implant-associated osteomyelitis in a single-stage procedure without additional revisions. These findings and the versatility of 3D printing will facilitate future research to achieve the eradication of infection with complete bone healing