Role of grain size in the regulation of osteoblast response to Ti-25Nb-3Mo-3Zr-2Sn alloy

Nano- and ultrafine-grained β-Ti layers were fabricated on Ti-25Nb-3Mo-3Zr-2Sn alloy by surface mechanical attrition treatment (SMAT). After being ground and polished, the two layers exhibited the same chemical composition, similar surface roughness and topography features to the coarse-grained surface, however, higher hardness values were exhibited on the ultrafine- and nano-grained surfaces, especially on nano-grained surface compared to coarse-grained surface. Hydrophilicity test, evaluated by measuring water contact angles, showed that the nano-grained surface was much more hydrophilic than the ultrafine- and coarse-grained surfaces. The adsorption of total protein and anchoring proteins such as vitronectin and fibronectin on the different surfaces from DMEM medium containing 10% fetal bovine serum was also examined. Employing hFOB1.19 cells, the behaviors of osteoblasts on the three kinds of grain-scaled surfaces, including adhesion, proliferation and differentiation, were evaluated by examining the morphology, the number of adherent cells, actin cytoskeleton reorganization, vinculin signals, expressions of steogenesis-related genes, alkaline phosphatase activity, contents of intracellular specific proteins and collagen type I, extracellular collagen secretion as well as matrix mineralization. The significant enhancements of osteoblast adhesion, proliferation, maturation and mineralization are exhibited on the nano-grained surface, while little improvements are found on the ultrafine-grained surface compared to the conventional coarse-grained surface. The differences in the cellular response to the three kinds of grain-scaled surfaces are related to grain size and degree of hydrophilicity. The improved cell functions together with mechanical properties make SMAT-processed nanograined β-Ti a promising biomaterial for surgical implants.