Materials Science Forum Vols. 783-786

Abstract: Additive Manufacturing (AM) has solidly established itself not only in rapid prototyping but also in industrial manufacturing. Its success is mainly determined by a possibility of manufacturing components with extremely complex shapes with minimal material waste. Rapid development of AM technologies includes processes using unique new materials, which in some cases is very hard or impossible to process any other way. Along with traditional industrial applications AM methods are becoming quite successful in biomedical applications, in particular in implant and special tools manufacturing. Here the capacity of AM technologies in producing components with complex geometric shapes is often brought to extreme. Certain issues today are preventing the AM methods taking its deserved place in medical and biomedical applications. Present work reports on the advances in further developing of AM technology, as well as in related post-processing, necessary to address the challenges presented by biomedical applications. Particular examples used are from Electron Beam Melting (EBM), one of the methods from the AM family.

Abstract: Present paper describes early findings from the study of Ti-6Al-4V scaffolds additively manufactured using electron beam melting (EBM^®) technology and the influence of surface topography on the initial stages of cell acceptance. The surface topography of the components made by additive manufacturing (AM) processes including EBM^® are often hard to control within the desired feature size range without post-processing. Two groups of experiments studying the behavior of human osteoblast-like cells (MG63) on samples with different surface roughness were carried out in vitro: Ti-6Al-4V samples only powder-blasted, and Ti-6Al-4V samples additionally electrochemically polished. The cell migration into powder-blasted Ti-6Al-4V 3D scaffolds with different shapes and dimensions of the lattice structures were studied.

Abstract: Anti-corroded valve metals, such as Ti, Nb, Ta, and Zr have been used as metallic biomaterials. However, as untreated surfaces, they do not have high osteoconductivity, and surface coatings with bioactive substances are needed for the implantation into the bone. Surface property, especially hydrophilicity, is considered to have a strong influence on the biological reactions. However, the influence of a hydrophilic surface on osteoconductivity is not completely clear. In this study, we produced super-hydrophilic surface on valve metals (Ti, Nb, Ta and Zr) using a hydrothermal treatment at 180 °C for 180 min. in the distilled water, and then the treated samples were stored in 5PBS(-). This maintained water contact angle less than 10 (deg.) in an apparent. The osteoconducivity of super-hydrophilic treated metals was evaluated with in vivo tests. The hard tissue formation on the samples increased with decreasing the water contact angle. That is to say that super-hydrophilic valve metals without coating of bioactive substances had high osteoconductivity, and the surface properties strongly affected on the osteoconductivity.

Abstract: Constructing biomimetic tissue architecture in vitro holds the key to the realization of tissue engineering. To control the anisotropic microstructure of bone tissue which governs the mechanical properties of bone, especially, is imperative for the establishment of ideal bone regeneration process. In this study, highly aligned collagen scaffolds were fabricated to control osteoblast alignment. Collagen fibrillogenesis were regulated by an extrusion process, resulting in formation of biomimetic, hierarchically-aligned bony microstructure. Osteoblasts adhered to the fabricated scaffolds showed aligned morphology along the collagen orientation. In the present method, the degree of scaffold orientation is regulatable, which suggests that the designing of the appropriate scaffolds depending on the tissue anisotropy is possible. Interestingly, the bone matrix produced by the aligned osteoblasts exhibited anisotropic microstructure along the cell alignment. Our findings imply that controlling the osteoblast alignment by oriented collagen scaffolds could be an initiator to establish the anisotropic bone structural development or regeneration.

Abstract: In order to meet the requirements of the patients and surgeons simultaneously for spinal fixation applications, beta (β) -type Ti-Mo alloys with self-tunable Young’s modulus due to deformation have been developed to prevent the stress-shielding effect for patients and to suppress springback for surgeons. In this study, the effects of Mo on the deformation-induced omega-phase transformation were investigated and then the Mo content in binary Ti-Mo alloys was optimized in order to achieve a large increase in Young’s modulus via deformation-induced omega-phase transformation, leading to suppression of springback.

Abstract: β-type titanium alloys such as a Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) are potential candidates for next-generation metallic biomaterials. However, the mechanical strength of β-type titanium alloys with a single β phase is not enough to be approved as materials for fabricating medical implant devices that are subjected to heavy loads, such as a spinal fixation device. Therefore, β-type titanium alloys are often subjected to aging treatments in order to improve their mechanical strength through precipitation hardening. However, β-type titanium alloys exhibit a heterogeneous microstructure because of microscale elemental segregation. In this study, the heterogeneous microstructure caused by the microsegregation of secondary phases was characterized by field emission scanning electron microscopy (FESEM) in TNTZ subjected to aging treatments. Furthermore, the influence of the heterogeneous distribution of secondary phases in TNTZ on mechanical properties was revealed by comparing its properties to the homogeneously structured TNTZ subjected to long-term homogenization.

Abstract: Cell-biomaterial interactions are strongly affected by topographical and chemical surface characteristics. We found out earlier that geometric titanium (Ti) pillar structures in the micrometer range induce the cells to rearrange their actin cytoskeleton in short fibers solely on the top of the pillars. As a result, cell physiology was hampered concerning collagen I synthesis and spreading capacity. Furthermore, the position-dependent initial cell adhesion strength was declined near the edges. We asked whether these observed cellular effects can be performed only in combination with Ti or occur independently of chemical surface features. In addition, the specific culture conditions, e.g. serum content or influence of gravity, were of interest. Human primary osteoblasts were cultured in Osteoblast Growth Medium with serum containing SupplementMix on pure silicon pillars (5x5x5 μm) or on samples additionally sputtered with Ti (as reference) or gold. To offer the cells ligands for their adhesion receptors, we coated the pillars with collagen I or alternatively with a plasma polymer layer from allylamine. Different from standard culture conditions, the cells were cultured against gravity as well as without serum. The actin cytoskeleton was stained with phalloidin-TRITC after 24 h and analyzed by confocal laser scanning microscopy. Interestingly, on all modifications tested the cell’s actin cytoskeleton was distinctly organized in short fibers on the top of the pillars. Thus, we were able to exclude the influence of (i) the material chemistry (gold, silicon, physical plasma vs. Ti), (ii) the protein deposition on the pillar top and edges, and (iii) the impression caused by gravity.

Abstract: In the present study, we demonstrated that antibacterial titanium can be simply fabricated by anodic oxidation technique, which involves connecting the Ti to the anode and then applying a direct current through the electrolyte. The substrate was soaked in 100−mM NH₄NO₃, 100−mM (NH₄)₂SO₄, and (NH₄)₃PO₄aqueous solutions, after which a constant current of 50 mA cm^-2 was galvanostatically applied for 30 min. The substrate was thereafter annealed at 723 K in air for 5 h, in order to improve the crystallinity. The XRD pattern showed the layer comprised TiO₂ with anatase and/or rutile type structures. All the anodized substrate could degrade methylene blue solution under ultraviolet (UV) and visible light illuminations. Antibacterial activities of the treated substrates were estimated using Escherichia coli (E. coli). The anodized Ti substrate showed sufficient antibacterial activity under weak UV light illumination with the intensity of 100 μW cm^-2. In conclusion, anodic oxidation is expected as one of the promising surface treatments, in order to improve the safety of Ti devices in human use.

Abstract: In this study, we conferred superhydrophilic properties on anodized TiO₂ coatings using a hydrothermal treatment, and developed a method to maintain this surface until implantation. The osteoconductivity of these coatings was evaluated with in vivo tests. A hydrothermal treatment made the surface of as-anodized samples more hydrophilic, up to a water contact angle of 13 deg. Storage in PBS(-) led to a reduction in the water contact angle, because of the adsorption of the inorganic ions in the solution, and the sample retained its high hydrophilicity for a long time. As the water contact angle decreased, the hard tissue formation ratio increased continuously up to 58 %, which was about four times higher than the hard tissue formation ratio on as-polished Ti.