Human fibroblast reactions to standard and electropolished titanium and Ti-6Al-7Nb, and electropolished stainless steel

Stainless steel (SS), titanium (cpTi), and Ti-6Al-7Nb (TAN) are frequently used metals in orthopedic internal fracture fixation. Although reactivity to SS and cpTi are noted in reference, the soft tissue compatibility of TAN has not been comprehensively studied. This study focuses on the in vitro soft tissue compatibility of TAN in comparison to SS and cpTi using a human fibroblast model. The industrial standard surface finishes of these three materials vary considerably in view of their use in similar applications. To distinguish between material parameters of topography and chemistry, we have included electropolished (e.p) counterparts of the standard preparations of cpTi and TAN in the study (standard SS is e.p). All materials were characterized using atomic force microscopy, profilometry, and scanning electron microscopy. Our findings demonstrate that cell morphology and growth rate was similar for SS, and e.p. cpTi and TAN, with cells well spread and forming a confluent monolayer by 10 days. Cell growth on standard cpTi was similar to the electropolished samples; however, they showed a less spread morphology with more filopodia and surface ruffling present. Cell morphology on standard TAN was rounded or elongated and proliferation was inhibited at all time points, with possible cell necrosis by day 10. We found evidence of endocytosis of beta-phase particles originating from the standard TAN surface. We believe that the particle uptake coupled with the characteristic surface topography contribute to the noncytocompatibility of fibroblasts on standard TAN.