Figure 2. Native “as fired” Si₃N₄ implant surfaces are highly resistant to MRSA adherence in vitro.

SS, Ti, PEEK, “as fired” Si₃N₄ and machined Si₃N₄ implants (n=4) were submerged in an overnight culture (O.D. = 0.7 at 630nm) of USA300LAC, air dried, and processed for SEM. Representative low power images of the L-shaped implants are shown at ×30 (A-E; scale bar in A = 200μm), and higher power images of regions containing adherent MSRA are shown at ×5,000 (F-J; scale bar in F = 1μm). Of note is that we failed to identify bacteria that were directly adhering to native “as fired” Si₃N₄ implant surfaces (I). However, bacteria were only observed on foreign material and culture debris (TSB precipitate and lysed bacteria) that adhered to the “as fired” Si₃N₄ implant surfaces (K ×2,000; scale bar = 5μm; inset image (L) ×5,000 scale bar = 1μm) and (M ×1,000 ; scale bar = 10μm; inset image (N) ×5,000 scale bar = 1μm). In contrast, bacteria were readily found on machined Si₃N₄ implant surfaces (O ×1,000 scale bar = 10μm). High power images of non-uniformly machined areas demonstrated preferential bacterial adhesion to the flatter surfaces, and lack of bacterial adhesion to incompletely machined surface structures (P-R ×5,000 scale bar = 1μm).