Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: innovation, surface technology and biomechanics: 174. Surface topography and chemistry effects on PEEK and titanium osseointegration

BACKGROUND CONTEXT Nearly 500,000 spinal fusion surgeries are performed each year in the U.S. Interbody fusion devices have been used for decades to facilitate fusion across the disc space, yet debate continues over the optimal material and structure used for these devices. Current cages are primarily made from PEEK due to its radiolucency and bone-like stiffness. However, current smooth PEEK cages are often associated with fibrous encapsulation and implant migration. This poor response is often attributed to inherent material properties of PEEK. However, the smooth surface of conventional PEEK surfaces may equally impede osseointegration, particularly when considering that rough and porous surfaces of various non-PEEK materials elicit more favorable osseointegration compared to smooth surfaces. PURPOSE The current study aimed to assess the relative influence of surface topography and chemistry on PEEK osseointegration by investigating the osseous response to smooth, rough, and porous surface topographies possessing a PEEK or titanium surface chemistry. STUDY DESIGN/SETTING Preclinical implant osseointegration model in the proximal tibial metaphysis of the rat. OUTCOME MEASURES Osseointegration was assessed by calculating bone ingrowth percentage, histological tissue evaluation, and biomechanical pullout testing. METHODS Porous PEEK implants were created as described previously. Rough surfaces were created by soda-blasting PEEK surfaces and smooth surfaces maintained an as-machined surface finish. Half of each group was coated with a ∼30nm thick layer of TiO2 using atomic layer deposition (ALD) while the other half maintained their native PEEK chemistry. Sterile implants were implanted into the proximal tibial metaphyses of skeletally mature male Sprague Dawley rats. At 8 weeks, animals were euthanized and bone-implant interfaces were subjected to µCT analysis (n=12), histology (n=4), and biomechanical pullout testing (n=8). All data were reported as mean±SE. Comparisons between groups were calculated using a 2-way ANOVA followed by a Tukey multiple comparisons test. RESULTS Quantitative µCT analysis demonstrated that mineralized tissue ingrowth was 38.9±2.8% for porous PEEK and 30.7±3.3% for porous titanium (p=0.07). µCT tomograms and matching histological sections showed bone ingrowth in porous titanium surfaces primarily consisted of thin bone shells that conformed to the pore walls, leaving the center of pores devoid of bone. In contrast, bone ingrowth within porous PEEK was greater in the center of pores with periodic contact with pore walls. Greater bone-implant contact was observed for titanium compared to PEEK surfaces. Histological and µCT observations were corroborated by biomechanics outcomes. Across all groups both surface chemistry and topography had a significant overall effect on pullout force (p CONCLUSIONS The poor osseointegration of conventional PEEK implants may be linked more to their smooth surface topography rather than their material composition. The effect of surface topography (specifically porosity) dominated the effect of surface chemistry in this study and could lead to further improvements in orthopaedic device design.