4 years ago

Surface Topography of Silicon Nitride Affects Antimicrobial and Osseosintegrative Properties of Tibial Implants in a Murine Model

Chao Xie, Edward M. Schwarz, Karen L. de Mesy Bentley, B. Sonny Bal, Masahiro Ishikawa, Bryan J. McEntire
While silicon nitride (Si3N4) is an antimicrobial and osseosintegrative orthopaedic biomaterial, the contribution of surface topography to these properties is unknown. Using a methicillin-resistant strain of Staphylococcus aureus (MSRA), this study evaluated Si3N4 implants in vitro via scanning electron microscopy (SEM) and colony forming unit (CFU) assays, and later in an established in vivo murine tibia model of implant-associated osteomyelitis. In vitro, the “as-fired” Si3N4 implants displayed significant reductions in adherent bacteria versus machined Si3N4 (2.6x104 vs. 8.7x104 CFU, respectively; p< 0.0002). Moreover, SEM demonstrated that MRSA cannot directly adhere to native “as fired” Si3N4. Subsequently, a cross-sectional study was completed in which sterile or MRSA contaminated “as-fired” and machined Si3N4 implants were inserted into the tibiae of 8-week old female Balb/c mice, and harvested on day 1, 3, 5, 7, 10, or 14 post-op for SEM. The findings demonstrated that the antimicrobial activity of the “as-fired” implants resulted from macrophage clearance of the bacteria during biofilm formation on day 1, followed by osseointegration via the apparent recruitment of mesenchymal stem cells (MSC) on days 3-5, which differentiated into osteoblasts on days 7-14. In contrast, the antimicrobial behavior of the machined Si3N4 was due to repulsion of the bacteria, a phenomenon that also limited osteogenesis, as host cells were also unable to adhere to the machined surface. Taken together, these results suggest that the in vivo biological behavior of Si3N4 orthopaedic implants is driven by critical features of their surface nanotopography. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jbm.a.36189

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