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Decreased bacteria activity on Si3N4 surfaces compared with PEEK or titanium

Authors Gorth DJ, Puckett S, Ercan B, Webster TJ, Rahaman M, Bal BS

Published Date September 2012 Volume 2012:7 Pages 4829—4840

DOI http://dx.doi.org/10.2147/IJN.S35190

Received 20 June 2012, Accepted 24 July 2012, Published 7 September 2012

Deborah Gorth,1 Sabrina Puckett,1 Batur Ercan,1 Thomas J Webster,1 Mohamed Rahaman,2 B Sonny Bal3

1School of Engineering and Department of Orthopaedics, Brown University, Providence, RI, 2Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO, 3Department of Orthopaedic Surgery, School of Medicine, University of Missouri, Columbia, MO, USA

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), poly-ether-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

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