Decreased bacteria activity on Si₃N₄ surfaces compared with PEEK or titanium

Abstract

A significant need exists for orthopedic implants that can intrinsically resist bacterial colonization. In this study, three biomaterials that are used in spinal implants – titanium (Ti), polyether-ether-ketone (PEEK), and silicon nitride (Si₃N₄) – were tested to understand their respective susceptibility to bacterial infection with Staphylococcus epidermidis, Staphlococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus. Specifically, the surface chemistry, wettability, and nanostructured topography of respective biomaterials, and the effects on bacterial biofilm formation, colonization, and growth were investigated. Ti and PEEK were received with as-machined surfaces; both materials are hydrophobic, with net negative surface charges. Two surface finishes of Si₃N₄ were examined: as-fired and polished. In contrast to Ti and PEEK, the surface of Si₃N₄ is hydrophilic, with a net positive charge. A decreased biofilm formation was found, as well as fewer live bacteria on both the as-fired and polished Si₃N₄. These differences may reflect differential surface chemistry and surface nanostructure properties between the biomaterials tested. Because protein adsorption on material surfaces affects bacterial adhesion, the adsorption of fibronectin, vitronectin, and laminin on Ti, PEEK, and Si₃N₄ were also examined. Significantly greater amounts of these proteins adhered to Si₃N₄ than to Ti or PEEK. The findings of this study suggest that surface properties of biomaterials lead to differential adsorption of physiologic proteins, and that this phenomenon could explain the observed in-vitro differences in bacterial affinity for the respective biomaterials. Intrinsic biomaterial properties as they relate to resistance to bacterial colonization may reflect a novel strategy toward designing future orthopedic implants.

Keywords:

• silicon nitride
• nanostructure
• anti-infective
• biofilm
• protein adsorption

Acknowledgments

The authors thank Khalid A Sethi, MD, FACS, and Christine Ann Snyder, PA, of the Southern New York NeuroSurgical Group, P.C., for their assistance in performing the studies, and David Bohrer for efforts in initiating this work. The authors also express their appreciation to Bryan McEntire, Chief Technology Officer, Alan Lakshminarayanan PhD, Senior Director of Research and Development, Ryan Bock PhD, Research Scientist, all of Amedica Corporation (Salt Lake City, UT); and Steven C Friedman, Senior Editor, Department of Orthopedic Surgery, University of Missouri, for their kind assistance with the manuscript.

Disclosure

B Sonny Bal is advisory surgeon to Amedica, developer of synthetic silicon nitride for orthopedic applications, and serves on the Board of Directors of Amedica, Salt Lake City, UT. Co-authors Deborah Gorth, Sabrina Puckett, Batur Ercan, Thomas J Webster, and Mohamed N Rahaman have no disclosures for this article.