Materials Science Forum Vols. 706-709

Abstract: In this paper the in vitro degradation of ultrafine grained (UFG) Mg-Zn-Ca alloy produced by HPT was investigated by electrochemical measurements and immersion tests in SBF. It was found that UFG Mg alloy had better degradation properties and also higher microhardness value than as-cast Mg alloy. The corrosion current density of UFG Mg alloy decreased by about two orders of magnitude, compared with that of as-cast alloy. Through electrochemical impedance spectroscopy (EIS) test，UFG Mg alloy showed a higher charge transfer resistance value. In immersion test, UFG Mg alloy in SBF exhibited more uniform corrosion and lower degradation rate (0.0763 mm/yr) than as-cast alloy. The degradation properties were related with the microstructure evolution, namely the grain refinement and redistribution of second phase. Keywords: Mg-Zn-Ca alloy; High-pressure torsion (HPT); Degradation behavior; Simulated body fluid (SBF); Microhardness

Abstract: It was reported that one-dimensionally elongated pores in implants promote the production of new bone tissue possessing both high bone density and the preferential alignment of biological apatite (BAp) c-axis/collagen as a bone quality parameter. This finding indicates that the anisotropic orientation and/or migration of osteoblasts guided by the grooved-pore surface affected the establishment of the anisotropic microstructure of bone tissue. In this study, a grooved polytetrafluoroethylene (Teflon) implant, which may have a role in regulating osteoblast arrangement, was prepared to investigate the relationship between cell behavior and bone microstructure. A cylindrical Teflon implant with 8 grooves on its side was prepared. The width and depth of the groove cross-section were 0.5 and 0.75 mm, respectively. Each implant was inserted in a drill-hole defect created on a rabbit femur such that the groove direction was parallel or perpendicular to the long bone axis in which the BAp c-axis aligns one-dimensionally. The Young’s modulus of Teflon is approximately 0.5 GPa, much lower than that of bone; therefore, the effects of applied stress can be eliminated in this model. The oriented new bone was preferentially produced along the grooved surface. The alignment direction of the BAp c-axis was almost parallel to the grooved surface even near the surface vertically aligned to the long bone axis. The geometry of the implant surface can control the organization of BAp alignment through the arrangement of osteoblasts to orient and subsequently to migrate along the surface direction; hence, implant geometry, particularly the groove, is considered an important factor controlling the BAp orientation of regenerated bone tissues.

Abstract: Tooth movements in an orthodontic treatment are the result of an applied force system, wire-bracket-ligature, and the response of the bone tissue. Starting an orthodontic treatment, it is necessary to exercise a sufficient initial force and then to maintain to obtain a continuous tooth movement. Orthodontic wires, which generate the biomechanical forces, usually transfer forces through brackets to trigger tooth movement. In the case of excessive forces of friction, they are behaving as an opposing force with respect to the movement of the tooth, making it sometimes slower or incontrollable [1].

Abstract: The influence of discharged hydrogen from Pd-Ni based hydrogen storage alloys (HSAs) on cultured cells has been investigated. The susceptibility of cells to discharged hydrogen varied with the kind of cells. No influence was seen in the normal cells, while an effect of killing cancer cells was observed near the HAS and the region where the cell death was observed was limited to an extent of a few mm from the alloy surface. In order to examine the cause of the effects, the amount of gaseous hydrogen and hydrogen radicals released from the alloy surface and pH change of physiological saline aq. solution were measured. The amount of gaseous hydrogen and hydrogen radicals increased with time. The pH of physiological saline aq. solution decreased first and then recovered to the starting value after about 50h. The pH change behavior varied with alloy composition. It is inferred that the hydrogen radicals formed on alloy surface may bring a characteristic change in the cancer cells, leading to the effect of discharged hydrogen on cancer cell death.

Abstract: Formation of hydroxyapatite (HAp) in simulated body fluid (SBF) on heated nacre has been examined. Nacre is known as composite layer of aragonite platelets and organic materials. Nacre was obtained from the shell of Akoya pearl oyster after removing its prismatic layer. The nacre was heated up to 300°C in air and then soaked in SBF. Nacre heated at 300°C lost iridescent color and became brittle, implying that organic materials which plays a role as glue between aragonite platelets mostly disappeared by heating at 300°C. Formation of HAp particles on nacre in SBF was easier than that on pure Ti. Maximum formation rate of HAp particles was obtained on the nacre heated at 200°C. The amount of HAp particles formed on the nacre heated at 300°C is the smallest. The organic materials in nacre play a critical role for HAp formation on nacre in SBF.

Abstract: This paper presents some results achieved in the biomedical applications of the EBM^® technology, and describes the resolved and unresolved challenges presented by modern medical implant manufacturing. In particular it outlines the issues related to the cellular structure design and metal surface modification. Moving to precision control of the metal surface at a micro-and sub-micrometer scale is a serious challenge to the EBM^® processing, because it uses the powder with average grain size of about 0.04 to 0.1 mm. Though manufacturing of components with solid-mesh geometry and porous surfaces using EBM^® is quite possible, post-processing (for example chemical or electrochemical) is needed to achieve desired control of the surface at smaller scales to realize full potential of the technology for biomedical applications.

Abstract: In this study, anodizing of Ti in the various concentration of H₃PO₄ aqueous solutions gave TiO₂ films, and the osteoconductivity was examined using in vivo testing. In the anodizing treatment, anodizing potential of < 200 V was applied to the Ti substrate in H₃PO₄ aqueous solutions with the concentration of 0.1 to 14 M at 298 K. The coatings were evaluated using SEM, XRD, FT-IR and XPS. In in vivo testing, the coated samples were implanted in the rats’ tibia for 14 d to evaluate the osteoconductivity. In H₃PO₄ aqueous solutions with any concentration, anatase-type TiO₂ films were obtained on the Ti substrate by anodizing. The crystallinity of anodized TiO₂ films depended on the concentration of H₃PO₄ and sparking. In less than 2 M H₃PO₄, anatase with high crystallinity was formed. On the other hand, anodizing with sparking in more than 4 M H₃PO₄, gave low crystallinity anatase film. In in vivo testing, osteoconductivity of the coatings with low crystallinity anatase was much higher than that with high crystallinity.

Abstract: In tissue engineering, topographical modification of implants has been used as a powerful tool for the development of biorelevant implant designs. However, there is still a lack of knowledge about the fundamental principles of the cell–material interaction and quantitative correlations between cell biological parameters and physicochemical surface characteristics. The focus of our studies on cell architecture–cell function dependencies on regular micro-scaled surface structures was to investigate and further quantify the cell phenotype obtained from images of confocal microscopy and scanning electron microscopy. We used periodically structured titanium surfaces with regular cubic pillar geometry (dimension 3x3x5 µm and 5x5x5 µm) in comparison to planar samples. Confocal microscopy revealed a considerable rearrangement of the actin cytoskeleton on the top of the pillars with a reduced filament length. The quantification of different actin filament networks of cells grown on structured surfaces was carried out with a novel software for automatic filament recognition, covering the majority of filaments and their branching in noisy data. The quantitative analysis of cell phenotype changes on surfaces with regular geometry opens new possibilities for the data correlation cell vs. material.

Abstract: Cells are known to sense the topographic features of the substrate and align along the direction of the surface pattern, and this is believed to be an important aspect in the formation and regeneration of anisotropic biological tissues. In this study, a unique and anisotropic stepped pattern was produced on single crystals of α-Ti with the h.c.p. lattice by plastic deformation in compression to demonstrate the effect of the pattern on cell behavior. Because the Schmid factor for the operative slip system of prismatic (100)[110] was set to be 0.5, the slip traces with an acute angle of 45° appeared on the surface. A smooth substrate without plastic deformation was used as a control. MC3T3-E1 osteoblastic cells were cultured on the substrate for 24 h, followed by observation of the morphology and alignment of the cells by Giemsa staining. On stepped substrates, cells aligned along the slip traces, and the filopodia of the aligned cells were found to extend parallel to the slip traces. The slip traces induced by plastic deformation of a single crystal was successfully proven to be a potent substrate to control the alignment of cells.

Abstract: This work investigates the mechanical properties of Ti-Cr-Sn-Zr alloys containing large amount of Zr. We focuses on the effect of the varying alloy composition on the microstructure, the Young’s modulus, the deformation mechanism and the deformation behavior. Ti-Cr-Sn-Zr alloys show much low Young’s modulus in the narrow composition range for Cr but wide for Zr. The Young’s modulus of Ti-2Cr-6Sn-xZr (x=5~60mass%) alloy decreases with increasing Zr and shows the minimum value of 41GPa in Ti-2Cr-6Sn-45Zr alloy. The alloys with low Young’s modulus consist in meta-stable β phase. The composition of the meta-stable β phase is close to the transition where the quenched microstructure transits from martensite to meta-stable β phase. Ti-2Cr-6Sn-45Zr alloy with lowest Young’s modulus show the super-elastic property.