Hidetsugu Fukuda

Fabrication and Characterization of Porous Implant Products with Aligned Pores by EBM Method for Biomedical Application

Recently, more attention has been devoted to porous implants to avoid stress-shielding effects and facilitate anchor effects. In addition, our previous research revealed that uniaxially aligned pores promoted early recovery of bone tissue with high bone quality similar to that of intact bone. In this study, Ti-based implant materials with uniaxially aligned pores were fabricated using the electron beam melting (EBM) method with 2 types of grid spacing, 0.5 and 1.0 mm. Although grid spacing was varied, the constituent phase and microstructure of the products were homogenous regardless of the grid spacing. Uniaxially aligned pores were created when the grid spacing was 1.0 mm, whereas almost solid structures with random pores were formed when the grid spacing was 0.5 mm. Young’s modulus of the products with the grid spacing of 1.0 mm was 34 GPa; this value is close to that of the bone. It is concluded that the porous material with aligned pores is suitable as a bone implant to reduce stress-shielding effects and to induce bone regeneration with good bone quality.

Effect of Energy Density of Incident Beam on Mechanical Property of Titanium Alloy Products Fabricated by Electron Beam Melting (EBM) Method

Electron beam melting (EBM) is a promising fabrication technique for directly producing metal products from powder as the starting material. Powders are provided as a thin layer (~100 μm) and melted layer by layer with an electron beam. In this study, the effects of the energy density of the incident beam on the mechanical properties of Ti–6 mass% Al–4 mass% V alloy products fabricated through EBM were examined. The products were fabricated using an electron beam at various energy densities depending on the electron beam current. The microstructures and crystallographic orientations were observed using optical microscopy and electron backscatter diffraction (EBSD), respectively. Compression tests were carried out in 2 loading directions using a mechanical testing machine equipped with strain gauges, one perpendicular (x–y direction) and the other parallel (z direction) to the stacking direction. In principle, the microstructure consisted of an acicular-shaped α phase (hcp lattice) and a small-volume β phase (bcc lattice). In addition, columnar grains elongated toward the z direction appeared during the repeated melting and solidification that occurred during the EBM process. An increase in the beam current of the incident beam enlarged the α grains and increased the relative density, resulting in the related Young’s modulus of the products. The energy density caused by the beam current also introduces anisotropy in the deformation behavior depending on the loading axis toward the stacking direction. This is closely related to the cast defect arranged along the stacking layers. It was concluded that the mechanical properties of the Ti–6 mass% Al–4 mass% V alloy products formed through EBM were very sensitive to the incident beam current and stacking direction, resulting in the exhibition of anisotropic deformation behavior within a limited range of energy density.

Development of a New Powder/Solid Composite for Biomimic Implant Materials by Electron-Beam Additive Manufacturing

We proposed a new biomaterial composed of solid and powder cubic compartments to exhibit isotropic or bone-mimic one-dimensional anisotropic mechanical properties. The raw material used was gas-atomized Ti-6Al-4V ELI powder comprising spherical particles with a diameter of approximately 80 μm. Cube-shaped products composed of 27 (3 × 3 × 3) unit cubic compartments occupied by solid or powder part were designed using three-dimensional CAD. The products were fabricated by electron beam melting (EBM) (Arcam AB, Sweden) according to the specifications shown in a CAD drawing. The residual unmelted powder in the products does not need to be removed to make the products more mechanically integrated. Moreover, the layout of the powder and solid compartments in the products were arranged to achieve isotropy resembling a face-centered cubic atomic arrangement or a long-bone-mimic mechanical anisotropy with square prismatic columns. The products demonstrate isotropic or anisotropic Young’s modulus, yield stress, and toughness, all of which can be changed by CAD design and EBM. In conclusion, novel powder/solid materials comprising solid cubic parts and functionalized powder particles between them were successfully developed, which could be useful in biomedical and industrial applications.

Hydrothermal Modification of Products Fabricated by Electron Beam Melting

Electron beam melting (EBM) method is one of the free-form fabrication techniques that enable near-net-shape manufacturing of complex three-dimensional, porous, and graded products, and is expected to facilitate the development of new methods for manufacturing biomaterials that could be used for hard-tissue substitutes. Titanium and its alloys have been used widely as biomaterials for hard-tissue substitutes because of their excellent mechanical properties and biocompatibility. However, the osteointegration of these materials is less than that of bioactive ceramics. Therefore, various surface-modification techniques have been developed to improve the osteointegration. The simplest way is to synthesize bioactive ceramic films on the surface of titanium or its alloys. The purpose of the present work was to synthesize a bioactive TiO2 film on Ti-6Al-4V (hereafter, abbreviated as Ti-64) substrates fabricated from powders using the EBM method and treated by a combination of chemical and hydrothermal treatment. Ti-64 plates fabricated by the EBM method were chemically treated with a H2O2/HNO3 aqueous solution under appropriate conditions. The plates were then hydrothermally treated with a NH3 aqueous solution. TiO2-gel films were produced by chemical treatment with a H2O2/HNO3 aqueous solution on the surface of a Ti-64 substrate. Anatase-type TiO2 films with high crystallinity were synthesized by the hydrothermal treatment of the TiO2-gel films.

Evaluation and Control of Crystallographic Alignment of Biological Apatite Crystallites in Bones

Our group focused on the preferential degree of biological apatite (BAp) c-axis, an important bone quality parameter based on the microstructural anisotropy in intact, pathological, and regenerated bones. The preferential degree of the BAp c-axis strongly depends on the bone position, in vivo stress distribution, bone growth, degree of pathology and regeneration, activity of bone cells, gene defect, etc. We attempted to challenge clarification of the BAp preferential alignment formation mechanism and control the degree of BAp orientation by using an anisotropic biomaterial design to develop suitable distribution of the BAp c-axis orientation.