Submicron/Nano-scale Surface Modification of Titanium-based Materials via Use of Gas/Solid Reactions

Titanium and its alloys are common industrial materials due to their attractive combination of properties, such as high strength to weight ratio, corrosion resistance, and biocompatibility. It is known that modifications of material structure at the nano and micro-scales can have a significant impact on chemical and biological performance of Ti and Ti alloys that affect the induction of osteogenic differentiation. Recently, additive manufacturing technologies for titanium alloys have been developed for the manufacturing of complex 3-D structures. However, current surface modification methods have limited capabilities for modifying the internal surfaces of such 3-D constructs. In this study, a gas/solid (non-line-of-sight) oxidation/reduction reaction-based surface modification technique using magnesium and calcium vapor as a reducing agent is introduced to add submicron/nano-scale roughness on dense titanium-based materials. Submicron/nano-scale roughness and pores were successfully incorporated on surfaces of the specimens and characterized by various measurement techniques such as SEM, EDX, TEM, AFM, XRD, and SAED analyses. Cell studies using human bone marrow stromal cells (MSCs) were also conducted, and substrates that underwent such novel surface modification technique significantly enhanced the production of osteopontin and osteocalcin, two potent markers of osteoblast differentiation and maturation. A kinetic study was also performed to determine the kinetic mechanism controlling the gas/solid calciothermic reduction of single crystal rutile at 800℃. Solid-state diffusion through product layers was found to be the rate-limiting step.