Lecture
Beta-titanium alloys, e.g. of the Ti-Nb system, become increasingly important mainly due to their significantly decreased Young’s modulus when compared to established implant materials [1]. A further reduction of stiffness can be achieved by the introduction of porosity into the material. In the present work a powder metallurgical process for the production of fine-grained porous samples by hot compaction of beta-Ti-45Nb powder with NaCl as space holder was developed. Moreover, the porous alloy bodies are utilized as substrates for bioactive and bioresorbable coatings that could foster bone bonding and thus, effectively support bone healing processes.
Gas-atomized Ti-45Nb powder with a spherical shape was employed. Marco-porous samples were produced using NaCl particles of 125 - 300 µm size as space holder material upon hot pressing. The space holders were afterwards removed by immersion in hot water (80 °C) for 6 hours.
Macro porous samples (45-50%) showed strength values of ~40 MPa which is close to the strength level of human cortical bone. The feasibility of electrodeposition techniques for coating Ti-Nb surfaces with hydroxyapatite [2] is demonstrated. Furthermore, the metallic scaffolds were coated with calcium phosphates (CaP) by the precipitation of CaP from apatite-forming bone cement [3] precursors. Bone cement precursors were suspended in organic solvent and allowed to infiltrate the pores of the metallic scaffolds under vacuum assistance. After drying, setting of the cement into Ca-deficient apatite was performed under humidity at 37°C. In summary, this approach resulted in a bioactivation of the surface and shows the high application potential of macro-porous coated Ti-45Nb bodies as load-bearing metallic scaffolds.
[1] M. Calin et al. “Elastic softening of beta-type Ti-Nb alloys by indium ( In ) additions,” J. Mech. Behav. Biomed. Mater., vol. 39, pp. 162–174, 2014.
[2] R. Schmidt, et al. “Electrochemical deposition of hydroxyapatite on beta-Ti-40Nb,” Surf. Coatings Technol., vol. 294, pp. 186–193, May 2016.
[3] M. Schumacher et al. “A novel and easy-to-prepare strontium(II) modified calcium phosphate bone cement with enhanced mechanical properties,” Acta Biomater., vol. 9, no. 7, pp. 7536–7544, 2013.
