Macroporous titanium implants for biomedical applications: synthesis, surface nano-texturing and characterisation

Titanium and its alloys are currently the most widely used materials in dental and orthopaedic implantology. However, they present a number of problems that have clinical consequences. These include the incompatibility between the rigidity of the bone tissue to be replaced and the implant (stress shielding, which causes bone resorption) and the low capacity for osseointegration. The aim of this research work is to propose a solution to both these problems. The first proposal is the realisation of substrates in Ti c.p grade IV through an already consolidated technique, the space holder. Different sizes (100-200 μm and 355-500 μm) of spacer particles (ammonium bicarbonate) are exploited to obtain porosity of different sizes and in different % (30/40/50/60). Complete characterization of the porosity and the evaluation of the Young's modulus and yield stress allow to conclude respectively that the technique allows to produce samples of the desired porosity and that this has a beneficial impact on the resulting mechanical properties. Samples with 50 % of porosity and 100-200 μm pore size present the best combinations of mechanical properties and are therefore used as substrates for the subsequent surface treatment. The innovative proposal for the second problem is, in fact, to apply a thermochemical treatment, already established for dense titanium, to porous substrates. Surface topography, chemical composition charge and bioactivity were evaluated on bare and modified titanium macroporous structures. The optimisation of the treatment resulted in a nano-textured titanium oxide uniformly developed on the external and internal surfaces of the macroporous structure.