Jun Komotori

Adhesion of osteoblast-like cells on nanostructured hydroxyapatite

The response of osteoblast-like cells seeded on hydroxyapatite (HAp) substrates consisting of nanosized crystals was investigated. Various types of HAp nanocrystals, such as nanofibers, nanoneedles and nanosheets, were selectively prepared as substrate through the hydrolysis of a solid precursor crystal of CaHPO(4) in alkaline solutions by varying the pH and ion concentrations. Although all the substrates were macroscopically flat and smooth, the nanoscale topography influenced cell activity, including the adhesion, proliferation, elongation and formation of actin stress fibers. The presence of fine nanoneedles and nanofibers on the surface restricted the cellular activities, while the cells steadily proliferated on a nanoscopically smooth surface of large grains and on a substrate consisting of wide nanosheets. These results suggest that the adhesion and subsequent responses of osteoblast-like cells were affected by the contact domain size between the cell and the substrate. Isolated small domains of the nanostructured HAp limited focal adhesion formation in the cells associated with the formation of stress fibers. Stable adhesion with contact domains larger than 100nm in width was suggested to be required for cell survival. On the other hand, insufficient adhesion on the fine nanoneedles was found to lead to apoptosis.

Preparation of hierarchically organized calcium phosphate?organic polymer composites by calcification of hydrogel

Abstract A novel type of calcium phosphate–organic polymer composite having a hierarchical structure was prepared by calcification of a poly(acrylic acid) hydrogel. Macroscopically, an organic gel containing phosphate ions was transformed into an opaque solid material by diffusion of calcium ions. We observed the formation of micrometer-scale layered structures consisting of nanoscale crystals of hydroxylapatite (HAp) in the opaque products. The laminated architecture resulting from the periodic precipitation of calcium phosphate varied with the reaction conditions, such as the concentrations of the precursor ions and the density of the gel. The nanoscopic structure of HAp crystals was modified by the addition of gelatin to the polymer matrix.

Improvement of corrosion resistance in metallic biomaterials using a new electrical grinding technique

Abstract A new electrical grinding method for the fabrication of machined surfaces with desirable characteristics for biomaterials and other engineering applications is presented. Conventional biomaterials, such as stainless steel and titanium alloy, require enhanced chemical stability and wear resistance, which are dependent on the quality of the surface oxide layer. However, it is difficult to produce sufficiently homogenous oxide layers by alumina polish finishing alone. The electrical grinding method proposed in this study, in which electric current is applied to the grinding fluid in the machining process, improves oxide formation on the finished surfaces, thereby realizing finished surfaces with extremely thick and stable oxide layers. Compared with alumina polishing, electrical grinding yields machined surfaces having excellent corrosion resistance.

Investigation on grinding characteristics and surface- modifying effects of biocompatible Co-Cr alloy

Co-Cr alloy used as a biomaterial is required to possess excellent resistance to corrosion, wear, and biocompatibility. In the present work, we performed Electrolytic In-Process Dressing grinding on Co-Cr alloy, and evaluated the processing characteristics and resulting surface properties. Final finishing using a #8000 wheel produced an extremely smooth ground surface with a roughness Ra of 7 nm. In addition, as compared with the conventionally polished samples, the ground samples demonstrated superior surface hardness and biocompatibility. These advantages can be attributed to the diffusion of several kinds of elements during the grinding process and the effect of grinding fluid compositions.

Th2 Immune Response Plays a Critical Role in the Development of Nickel-Induced Allergic Contact Dermatitis

Background:The precise roles of T helper (Th)1-type and Th2-type cytokine responses in nickel (Ni)-induced allergic contact dermatitis have not yet been clearly defined. We investigated the involvement of Th2 cytokines in Ni-induced contact hypersensitivity reaction using GATA-3 transgenic (Tg) mice. Methods: A Ni-titanium (Ti) alloy was implanted under the skin of GATA-3 Tg mice. A Ni solution was then injected 1 month after sensitization. The ear swelling response was measured at several time points after the injection; the cytokine levels in the skin were measured at 48 h after injection, and the serum levels of IgE were measured 1 month after injection. In addition, purified CD4+ splenic cells obtained from the GATA-3 Tg mice sensitized with the Ni-Ti alloy were infused into Rag-2–/– mice, and the ear swelling response of these mice after a further challenge with Ni solution was also measured. Results:Marked ear swelling and elevated serum IgE levels and skin tissue levels of IL-4 were observed in Ni-Ti-sensitized GATA-3 Tg mice. The Rag-2–/– mice transfused with the CD4+ splenic cells from the Ni-Ti alloy sensitized GATA-3 Tg mice showed a significantly more pronounced ear swelling response than the control mice. Conclusion: We confirmed the participation of Th2-type immune reactions in Ni-induced allergy using GATA-3 Tg mice.

Effects of the fiber content on the longitudinal tensile fracture behavior of uni-directional carbon/epoxy composites

Abstract This study is concerned with the effects of the fiber content on the macroscopic and macroscopic fracture mode of unidirectional carbon/epoxy composite. Necked-on-thickness specimens having a fiber volume fraction (Vf) ranging from 30 to 70% were tested in tension in the fiber direction. The effects of the fiber volume fraction on the fracture appearance were then examined. The results show that a transition in fracture mode occurred, from tensile fracture at the necked region at low Vf to interlaminar shear failure at high Vf. Fracture-mode transition also occurs at the microscopic level. Examination of SEM photomicrograph of the specimen surface shows that, at low Vf, the specimen fractured in fiber-break dominated fracture, whilst, at high Vf, interfacial-damage dominated fracture was observed. An analysis to determine the conditions for the occurrence of each fracture mode is presented.

Control of cellular activity of fibroblasts on size-tuned fibrous hydroxyapatite nanocrystals

We controlled the performance of L929 mouse fibroblasts using various hydroxyapatite (HA) nanocrystals, such as nanofibers, nanoneedles, and nanosheets, to better understand the effects of size and shape of the HA nanocrystals on the cells. The cellular activity on nanofibers with a diameter of 50-100 nm was significantly enhanced relative to that on a flat HA surface because large amounts of the proteins needed for adhesion and proliferation could be stored in the substrate. On the other hand, initial adhesion and subsequent proliferation were inhibited on surfaces consisting of fine nanoneedles and nanosheets with a diameter/thickness of less than 30 nm due to the limited area available for the formation of focal adhesions. These facts indicate that fibroblast activity is highly sensitive to the surface topography. Therefore, size tuning of the nanoscale units composing the substrate is essential to enhance cellular performance.

A new fracture mechanics model for multiple matrix cracks of SiC fiber reinforced brittle-matrix composites

A new model is proposed for multiple matrix cracking in order to take into account the role of matrix-rich regions in the cross section in initiating crack growth. The model is used to predict the matrix cracking stress and the total number of matrix cracks. The model converts the matrix-rich regions into equivalent penny shape crack sizes and predicts the matrix cracking stress with a fracture mechanics crack-bridging model. The estimated distribution of matrix cracking stresses is used as statistical input to predict the number of matrix cracks. The results show good agreement with the experimental results by replica observations. Therefore, it is found that the matrix cracking behavior mainly depends on the distribution of matrix-rich regions in the composite.

Investigation of substrate finishing conditions to improve adhesive strength of DLC films

Abstract This study investigated the effects of grinding wheels on the surface modification properties in Electrolytic In-process Dressing grinding. Three specimens were ground with different abrasive grinding wheels: diamond wheel, SiO2 wheel, and diamond + SiO2 wheel. These three different grinding wheels produced surfaces modified by the diffusion of the abrasive elements. Adhesive strength evaluation tests between the substrate surface and the DLC film were performed using micro-scratch testing. The finished surface ground by the diamond + SiO2 wheel showed the highest adhesive strength due to the physical and chemical properties of the diffused elements. As a result, application of this proposed grinding method to mold fabrication shows considerable promise.

Investigation on color-finishing process conditions for titanium alloy applying a new electrical grinding process

Abstract Titanium alloy is usually colored by coating or painting after finishing. Beyond that, however, if a stable oxide film can be successfully and efficiently generated on the surface at the time of grinding and polishing as part of surface processing, the surface properties of the processed workpiece will be greatly improved. This will also streamline surface treatment and allow for significant savings in energy and procedures. This study proposes an electrochemical processing system that organizes the thickness and structure of an oxide film generated on the processed surface by applying a direct current of extremely short pulses to the workpiece being ground. The authors focused specifically on the color of the oxide film generated on the processed surface as a result of optical interference, and studied closely the mechanism and control of this color finishing process conditions.