M. Shirtliff, S. Sankar, J. Crudden, P. Whang
Keywords: antibiofilm, osteoconductive, PEEK-Silver Zeolite, spine fusion
Summary:Background: CleanFuze (CF), a bioactive PEEK- silver zeolite composite has received european approval as a spine biomaterial,is expected to possess infection resistive and osteoblast stimulative effects due to silver ions and ceramic zeolite particles respectively. Aim: Evaluate the efficacy of CleanFuze in preventing biofilm formation and in promoting osteoblast growth relative to PEEK; without compromising PEEK’s biomechanics Methods: In vitro peri-operative contamination model: Competitive colonization between a GFP induced MRSA strain and human MG-63 osteoblast-like cells (ATCC CRL-1427 TM) was studied for CleanFuze and PEEK disks (~1.23 sq.cm)and were compared to their respective un-inoculated controls. Bacteria was seeded onto the implants for 4hrs to initiate adhesion,to mimic an infection,before the introduction of the osteoblasts. Osteoblast proliferation and bacterial viability were quantified at Day 3 and Day 7. In vivo Antibiofilm Testing using a Rabbit Spine infection Model: 12 NZW female rabbits- 2.5-3 kg. • Rabbits 1, 5, 9- PEEK; Rabbits 2,6,10 - Ag eluting CF; Rabbits 3,7,11,12- Surface Modified Ag eluting CF; Rabbits 4, 8 Ag-Zn surface modified CF. •Implant screw placed across mammillary spinous process. L3- control site with defect but no implant/inoculum. L6- site with implant and infected with 500 cfu’s of MRSA. •Equivalent implant sections and tissue at the implant site was explanted after a week and analysed for biofilm formation and histological parameters qualitatively via crystal violet(CV) biofilm and H&E staining. Dynamic Biomechanical Testing: 22x8 PLIF CleanFuze and PEEK cages were tested for dynamic compression and torsion (ASTM F2267-03, F2267-04) in PBS at 37 ± 3°C.Testing was done to ensure conformance to biomechanical requirements from a FDA clearance standpoint. Results: In vitro peri-operative contamination model: CleanFuze being antimicrobial is able to protect osteoblasts from attack, infiltration and destruction by MRSA. Infected CleanFuze shows ~ 46 times greater osteoblast proliferation compared to infected PEEK & three times greater proliferation compared to even uninfected PEEK In vivo Antibiofilm Testing using a Rabbit Spine infection Model Explanted PEEK implants show pick of CV dye and intense purple color indicative of biofilm formation while CleanFuze displays no purple coloration, i.e. absence of biofilm.Also, histological examination of the implant site proved that PEEK suffered from a suppurative and infected environment as shown by markers for tissue degradation/destruction while CleanFuze demonstrated a normal wound healing environment free of infection. Dynamic Biomechanical Testing CleanFuze was able to withstand a load of 4000N at 5 million cycles under compression and 5N.m at 5 million cycles under torsion. PEEK failed at 3750N after 925,018 cycles under compression and under torsion, failed at 5N.m after 502,794 cycles. CleanFuze implants surpass the minimum criteria set by the FDA for implant approval and possess superior biomechanical properties relative to PEEK cages for the exact same implant design. Conclusions: CleanFuze demonstrates enhanced anti-biofilm,osteoconductive and improved biomechanical properties relative to PEEK, thereby allowing for an alternative biomaterial in spine and orthopaedics with improved characteristics.