Introduction. Periprosthetic infections are leading causes of revision surgery resulting in significant increased patient comorbidities and costs. Considerable research has targeted development of biomaterials that may eliminate implant-related infections. 1. This in vitro study was developed to compare biofilm formation on three materials used in spinal fusion surgery – silicon nitride, PEEK, and titanium – using one gram-positive and one gram-negative bacterial species. Materials and Methods. Several surface treated silicon nitride (Si. 3. N. 4. , MC2. ®. , Amedica Corporation, Salt Lake City, UT), poly-ether-ether-ketone (PEEK, ASTM D6262), and medical grade titanium (Ti6Al4V, ASTM F136) discs Ø12.7 × 1mm were prepared or acquired for use in this well-plate study. Each group of discs (n=3) were ultrasonically cleaned, UV-sterilized, inoculated with 10. 5. Staphylococcus epidermidis (ATCC. ®. 25922™) or Escherichia coli (ATCC. ®. 14990™) and placed in a culture medium of phosphate buffered saline (PBS) containing 7% glucose and 10% human plasma on a shaking incubator at 37°C and 120 rpm for 24 or 48 hrs. Coupons were retrieved, rinsed in PBS to remove planktonic bacteria, placed in a centrifuge with fresh PBS, and vortexed. The bacterial solutions were serially diluted, plated, and incubated at 37°C for 24 to 48 hrs. Colony forming units (CFU/mm. 2. ) were counted using applicable dilution factors and surface areas. A two-tailed, heteroscedastic Student's t-test (95% confidence) was used to determine statistical significance. Results. Biofilm adhesion results are provided in Figures 1 and 2 for S. epi. and E. coli, respectively. For S. epi. at 24 hrs, biofilm growth on PEEK was about three orders of magnitude greater than on Ti6Al4V or any Si. 3. N. 4. material (all p<0.005). Ti6Al4V also had more bacteria than the Si. 3. N. 4. samples, but was only significant for as-fired and nitrogen-annealed
