Ultrafine surface features are commonly used to modulate the cellular activity of a variety of materials including ceramics, [1,2] composites, [3,4] nanofibers, [5,6] and polymers. [7,8] However, the main challenge for materials in contact with bone remains the development of a material with both favorable surface and bulk properties to modulate not only cell-substrate interactions but also to ensure the long-term stability of the implant. This challenge has motivated researchers to develop bulk nanostructured materials while applying different surface treatments to improve cellular adhesion and metabolic activities. Here, in a combined approach involving materials science and cell and molecular biology, the responses of pre-osteoblast and fibroblast cell lines to novel nanostructured titanium substrates produced by high-pressure torsion (HPT) is assessed and compared with the cellular activity on coarse-grained, annealed titanium substrates. The degree of osteoblast attachment is notably increased on the HPT-processed titanium substrates. The improved cellular response is attributed to the nanostructured features of the samples, which are characterized by an ultrafine grain size (< 50 nm), and a high degree of surface wettability associated with a distinctive oxide layer formed on the surface. This finding provides a valuable advantage for HPT-processed titanium over conventional and coated titanium implants, as both the mechanical and physical properties, along with biological activities, are improved. The most developed severe plastic deformation (SPD) techniques for producing bulk nonporous samples are equal-channel angular pressing (ECAP) and HPT. [9,10] Recent studies indicate that high pressure during SPD significantly affects the development of the crystal structure and consequently enables the production of materials composed of sub-micrometer-or nanometer-sized metal crystals, both on the surface and in the bulk, that have reduced porosity, cracks, and other macroscopic defects. [11,12] These characteristics make the material very attractive for advanced applications in the aerospace, sport, transportation, and, in particular, medical industries.[13] Along with nanostructured surface features, material processed by HPT has a good combination of high strength and high ductility at room temperature. These are two desirable but rarely co-existing properties important for the longterm stability of metallic implants. [14,15] Although many reports are available on the bulk characterization of these materials, reports detailing the effects of high pressure on the surface properties of nanostructured titanium are mostly fragmented, and its significance with regards to cell-substrate interactions has not been addressed. In this work, commercially pure titanium was used to fabricate substrates with different nano/microstructures through HPT and annealing processes. After fabrication of the substrates, surface characterization was performed by orientation image microscopy (OIM), transmission electron microscopy (T...
