Porous Titanium for Biomedical Applications: Evaluation of the Conventional Powder Metallurgy Frontier and Space-Holder Technique

Titanium and its alloys are reference materials in biomedical applications because of their desirable properties. However, one of the most important concerns in long-term prostheses is bone resorption as a result of the stress-shielding phenomena. Development of porous titanium for implants with a low Young’s modulus has accomplished increasing scientific and technological attention. The aim of this study is to evaluate the viability, industrial implementation and potential technology transfer of different powder-metallurgy techniques to obtain porous titanium with stiffness values similar to that exhibited by cortical bone. Porous samples of commercial pure titanium grade-4 were obtained by following both conventional powder metallurgy (PM) and space-holder technique. The conventional PM frontier (Loose-Sintering) was evaluated. Additionally, the technical feasibility of two different space holders (NH4HCO3 and NaCl) was investigated. The microstructural and mechanical properties were assessed. Furthermore, the mechanical properties of titanium porous structures with porosities of 40% were studied by Finite Element Method (FEM) and compared with the experimental results. Some important findings are: (i) the optimal parameters for processing routes used to obtain low Young’s modulus values, retaining suitable mechanical strength; (ii) better mechanical response was obtained by using NH4HCO3 as space holder; and (iii) Ti matrix hardening when the interconnected porosity was 36–45% of total porosity. Finally, the advantages and limitations of the PM techniques employed, towards an industrial implementation, were discussed.