Structural, mechanical and in vitro characterization of individually structured Ti-6Al-4V produced by direct laser forming.

Direct laser forming (DLF) is a rapid prototyping technique which enables prompt modelling of metal parts with high bulk density on the base of individual three-dimensional data, including computer tomography models of anatomical structures. In our project, we tested DLF-produced material on the basis of the titanium alloy Ti-6Al-4V for its applicability as hard tissue biomaterial. To this end, we investigated mechanical and structural properties of DLF-Ti-6Al-4V. While the tensile and yield strengths of untreated DLF alloy ranged beyond 1000 MPa, a breaking elongation of 6.5+/-0.6% was determined for this material. After an additional post-DLF annealing treatment, this parameter was increased two-fold to 13.0+/-0.6%, while tensile and yield strengths were reduced by approx. 8%. A Young's modulus of 118.000+/-2.300 MPa was determined for post-DLF annealed Ti-6Al-4V. All data gained from tensile testing of post-DLF annealed Ti-6Al-4V matched American Society of Testing and Materials (ASTM) specifications for the usage of this alloy as medical material. Rotating bending tests revealed that the fatigue profile of post-DLF annealed Ti-6Al-4V was comparable to casted/hot isostatic pressed alloy. We characterized the structure of non-finished DLF-Ti-6Al-4V by scanning electron microscopy and observed a surface-associated layer of particles, which was removable by sandblasting as a finishing step. We manufactured porous specimens with nominal pore diameters of 500, 700 and 1000 microm. The diameters were reduced by the used DLF processing by approx. 300 microm. In an in vitro investigation, we cultured human osteoblasts on non-porous and porous blasted DLF-Ti-6Al-4V specimens to study morphology, vitality, proliferation and differentiation of the cells. The cells spreaded and proliferated on DLF-Ti-6Al-4V over a culture time of 14 days. On porous specimens, osteoblasts grew along the rims of the pores and formed circle-shaped structures, as visualized by live/dead staining as well as scanning electron microscopy. Overall, the DLF-Ti-6Al-4V approach proved to be efficient and could be further advanced in the field of hard tissue biomaterials.