Effect of surface topography and chemistry on adhesion, orientation and growth of fibroblasts on nickel–titanium substrates

Nickel–titanium alloy (NiTi) is a metallic biomaterial known for its mechanical and shape memory properties. These properties suggest that it could be used for medical purposes such as surgical implants. To evaluate the effects of the chemical composition and microtexture of the metal surface on the cellular behaviour, the adhesion, orientation and proliferation of human gingival fibroblasts were studied with substrates having different surface roughnesses. To separate the effects of material roughness and composition on the fibroblast response, we have chosen to compare substrates of different surface roughnesses but of the same chemical composition (NiTi). Moreover, substrates of different surface compositions (Ti6Al4V, cp-Ti, 316L stainless steel) but of similar smooth surface topography were also tested. The texture, chemical state and composition of the surfaces were determined using a surface-tracing instrument for roughness characterisation and X-ray photoelectron spectroscopy (XPS) for chemical analysis. The effect of γ-sterilisation on the chemical composition was studied. Human gingival fibroblasts attached, spread and proliferated on all titanium-based surfaces. On samples exhibiting the highest roughness, the cells were oriented in a parallel order along the grooves caused by mechanical polishing, whereas on smooth surfaces, they appeared to grow with no specific orientation. We observed low cell proliferation on the NiTi surfaces of the highest roughness.