Materials Science Forum Vols. 654-656

Abstract: Successful application of magnesium-based alloys as biodegradable biomaterials is critically dependent on controlling the degradation rate of the alloy. The present study suggests that electrochemical deposition of calcium phosphate on magnesium alloy at an optimal voltage enhances the degradation resistance of the alloy significantly.

Abstract: Hardness of Ag-20Pd-12Au-14.5Cu (mass%) subjected to a solution treatment (ST) at a temperature over 1073 K followed by water quenching increases drastically. This unique hardening behavior is not clarified becasue of their complex microsturucures. In this study, the relationship between the unique hardening behaviour and the microstructure of dental Ag-20Pd-12Au-xCu subjected to ST with different Cu/Ag ratios was investigated. The Vickers hardness of Ag-20Pd-12Au-14.5Cu increases remarkably from 192 to 286 Hv after ST whereas that of Ag-20Pd-12Au-6.5Cu decreases and that of Ag-20Pd-12Au-20Cu increases slightly after ST, respectively. The spotty regions are observed in only certain areas of Ag-20Pd-12Au-14.5Cu subject to ST. It is considered that the appearance of the spotty regions affects mainly to the unique hardening behaviour in Ag-20Pd-12Au-xCu.

Abstract: Thin films of diamond-like carbon (DLC) containing zirconium dioxide (DLC-ZrO2) have been deposited onto conducting (100) silicon wafer substrates using a pulsed direct-current metal–organic plasma activated chemical vapour deposition (MOPACVD) technique. DLC-ZrO2 thin films were immersed in simulated body fluid (SBF) at 37° C. The formation of apatite as a function of time was determined using a number of characterization techniques including XPS, FTIR, XRD, SEM and EDX. The XPS results confirmed the presence of calcium and phosphorus on the DLC-ZrO2 film surfaces after immersion in SBF. FTIR and XRD results confirmed that biomimetic apatite was formed on DLC-ZrO2 as an amorphous film. Ball-like particles composed of Ca and P were observed on the film surface. EDX results also confirmed that Ca and P were deposited on the film surface.

Abstract: The effect of grain boundary segregated dopant on phase stability of tetragonal zirconia polycrystal (TZP) is examined by accelerated exposure tests ageing in hot water. The materials used in this study are 3 mol%Y2O3 stabilized TZP (3Y-TZP) and 0.1mol%SiO2-doped 3Y-TZP. Accelerated exposure tests in an autoclave reveal that the tetragonal phase stability of 3Y-TZP in water is highly affected by the grain boundary segregated dopant and the grain size. When the grain size of TZP is about 0.55μm, the change in phase transformation behavior with dopant is explained from the change in grain boundary diffusivity of hydroxyl ion. Grain boundary diffusion of hydroxyl ion must be blocked by the presence of some segregated ion which reduces the effective area of grain boundary diffusion. On the other hand, when the grain size is about 0.35μm, the phase transformation behavior seems to be controlled by the grain boundary stress. Decreased grain boundary stress by the segregation of some dopant must enhance the phase transformation of 3Y-TZP.

Abstract: 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.

Abstract: The orientation of biological apatite (BAp) is one of the bone quality parameters dominating bone mechanical function. In the mandible, the preferential orientation of the BAp c-axis changes depending on alteration of the in vivo stress condition induced by a change in the biting stress. In this study, to clarify the functional adaptation of the preferential BAp orientation and bone mineral density (BMD), all beagle mandibular molars on one side were extracted to remove the biting stress, leading to changes in both BAp orientation and BMD. The BMD exhibited discontinuous distribution around the first molar, mainly responsible for mastication, on the normal side. However, the distribution was continuous along the mesiodistal axis of the edentulous side. The preferential BAp orientation was analyzed in mandibular cross-sections at the first molar root region. Molar extraction led to a change in the BAp orientation: immediately under the root region on the lingual sides, two-dimensional preferential alignment in the mesiodistal and biting directions of the normal side changed to one-dimensional alignment along the mesiodistal axis of the edentulous side. One-dimensional alignment was also observed on the buccal sides irrespective of molar extraction. These findings clarify the close relationship between in vivo biting stress and the preferential BAp orientation, and will be useful clinically for diagnosis, implant placement, and so on.

Abstract: To evaluate the material parameters of regenerated bone, it is important to clarify the mechanical performance of the regenerated portion. In general, the shape and size of regenerated bone tissue is heterogeneous. It is often difficult to elucidate material properties by means of conventional mechanical tests such as compressive and/or tensile tests and bending tests. The nanoindentation technique has been utilized to evaluate the material properties of small or microstructured materials because they do not necessarily require a large well-designed specimen. Thus, this technique may be useful for the evaluation of the material properties of regenerated bone tissue. In this study, this technique was applied for the assessment of the Young’s modulus and hardness of regenerated and intact long bones of a rabbit. The regenerated bone exhibited a significantly lower Young’s modulus and hardness than the intact bone. The regenerated long bone also exhibited impaired mechanical properties, which may have been caused by the difference in the nano-organization of its collagen fibers and mineral crystals (the main components of bone tissue), from that of the intact bone.

Abstract: Bone biopsy is a common procedure in bone disease diagnoses, therapies and research. In this procedure, bone biopsy needles are inserted into bone tissues. Although needle insertion into bone is often essential for the diagnosis of bone diseases, the hard tissue-needle interactions are not quantitatively understood. In this paper, we describe a quantitative assessment of forces involved in insertion of healthy trabecular bone using clinically applied Jamshidi CrownTM bone biopsy needles of gauge 8 (4-mm diameter). The measured forces were related to the insertion depths up to 25 mm and insertion rates of 1 mm/s to 5 mm/s. At the initial insertion stage, a clear linear force-depth relation was measured. With the increase of the insertion depth, the forces increased nonlinearly. In the final stage of insertion, the forces increased much more quickly at the lower insertion rate than that at the higher insertion rate. The maximum insertion force reached approximately 1000 N when the insertion depth reached 25 mm at the insertion rate of 1 mm/s.

Abstract: The microstructure of cuttlebone is investigated using Scanning Electron Microscopy (SEM). A graded aspect ratio of the base cells between layers is evident in some samples. A method for designing graded biomaterials mimicking this cuttlebone microstructure is developed. Simplified 3D biomaterial samples are created using CAD software. These biomaterials are fabricated using a stereolithographic apparatus (SLA). The homogenisation technique is used to evaluate the mechanical properties of the original cuttlebone sample and the fabricated biomaterial sample. Good agreement is found between the Young’s moduli of corresponding layers. However, it is inconclusive whether the Young’s moduli have a proportional relationship to the aspect ratio of the base cell at this stage of the study.

Abstract: In this work, we focused on the manufacture of artificial bone for medical replacement based on the combination of individual properties of ceramic and polymer. Here, periosteum was fabricated with a HAp (Hydroxylapatite) frame, while compact bone was fabricated from multi-layer electro-spun PS (polystyrene)/PCL (polycaprolactone) using biocompatible collagen glue. Spongy bone is formed from PCL/PLGA spongy loading BCP (Biphasic Calcium Phosphate) powder coated collagen. SEM images showed successful fabrication of the artificial bone scaffold through a combination of electro-spinning, extrusion, and use of the slurry method.