Biomedical subjects

Y Umakoshi

Publications and source records attributed to Y Umakoshi.

6 recordsLinked to original sources

PubMed2006

Bioactive ceramic composites sintered from hydroxyapatite and silica at 1,200 degrees C: preparation, microstructures and in vitro bone-like layer growth.

Bioceramic composites were synthesized by sintering the powders of hydroxyapatite (HAp) mixed directly with additive of 0.5, 1.0, 2.0, 5.0 and 10 wt.%SiO(2), respectively, at 1,200( composite function)C. X-ray diffraction (XRD) analysis indicated that the phase transformation from HAp to tricalcium phosphate (TCP) comprising alpha-TCP and Si-TCP occurred and became more prominent with the addition of SiO(2) and the increase in SiO(2) content. The observations of their surface microstructures showed that the addition of SiO(2) suppressed the grain growth and promoted the formation of crystalline-glassy composites denoted HAp + TCP/Bioglass. As the SiO(2) content is as high as 5 wt.%, the composite made a feature of crystalline clusters with different sizes consisting of HAp and TCP grains surrounded by the matrix of glassy phase. Furthermore, the dependence of in vitro bioactivity of these composites on the SiO(2) content was biomimetically assessed by determining the changes in surface morphology, i.e., bone-like apatite layer growth, after soaking in an acellular stimulated body fluid (SBF) for 3 days at 36.5( composite function)C. It was found that the HAp-SiO(2) composites showed a much faster bone-like layer growth than pure HAp, and the propensity of composites to exhibit a better bioactivity was getting more notable with increasing SiO(2) content, except for the case of the highest content of 10 wt.%. It was believed that the formation of the bone-like layer on the surfaces of these bio-composites is closely related to the increasingly provided silanol groups and transformed TCP phase in materials associated with the content of SiO(2) added.

Biocompatible Materials↗

PubMed2002

Unique alignment and texture of biological apatite crystallites in typical calcified tissues analyzed by microbeam X-ray diffractometer system.

Preferential orientation of biological apatite (Ap) crystallites in typical calcified tissues of rabbit ulna, rabbit skull, and monkey dentulous mandible was investigated using a microbeam X-ray diffractometer, with a beam spot of 100 microm in diameter, to clarify relationship between the Ap orientation and mechanical function. Preferential alignment of the c-axis of the biological Ap was evaluated by the relative intensity between (002) and (310) diffraction peaks. Preferential alignment of biological Ap in each calcified tissue varied depending on the shape and stress condition in vivo; that is, the c-axes of biological Ap in the rabbit ulna and the rabbit skull bone were preferentially observed as a one-dimensional orientation along the longitudinal axis and a two-dimensional orientation along the surface, respectively. Precise analysis of the preferential alignment along the skull surface showed an elliptical distribution of the c-axis of biological Ap elongating along the suture inside the skull surface of both lamina exterior and interior. The c-axis of biological Ap in a monkey dentulous mandible basically aligned along the mesiodistal direction in the flat bone, but this alignment changed along the normal direction to the flat bone surface parallel to the biting direction near the tooth, due to the force of mastication. It was concluded that the microscale measurement of biological Ap texture is one of the useful new methods for evaluating mechanical function and stress distribution in vivo in calcified tissues.

Animals↗

PubMed2001

Control of hydroxyapatite crystallinity by mechanical grinding method.

Crystallinity of hydroxyapatite reflecting crystal size and crystal elastic strain was controlled by the mechanical grinding (MG) technique using a set of container and balls made of SUS304 stainless steel or agate. Variation in the crystallinity through MG was monitored by the XRD method and represented by the broadening of the diffraction peak. Effect of changes in crystallite size and strain on the crystallinity was also examined using the Hall-plot method. Crystallinity rapidly decreased with milling time. Significant crystallographic diffraction peaks disappeared and a broad diffraction around 2theta=32 degrees was observed after MG for 72 h. The broadening was dominantly due to an increase in crystal strain in addition to fine crystallite size. Contamination from the container and balls during MG was more suppressed using agate than SUS304 stainless steel. The recovery process of crystallinity during heating between 300 degrees C and 1200 degrees C was examined focusing on the decrease in residual elastic strain. Low crystallinity was maintained at annealing temperatures below 800 degrees C but lattice defects were recovered above 1000 degrees C.

Journal Article↗

PubMed2000

Microstructure and mechanical property of synthesized hydroxyapatite prepared by colloidal process.

Synthesized hydroxyapatite (HAp) was prepared by the colloidal process. Mixed slurry composed of 25 vol% HAp powder and 75 vol% aqueous solution containing a small amount of polycarboxylic acid ammonium as dispersant was produced. Viscosity of the HAp slurry, microstructure and mechanical property of the synthesized HAp prepared by this process depends on the quantity of dispersant. A mainly uniform microstructure was obtained in both green and sintered HAp with 2 wt% dispersant by preventing the agglomeration of powder in the slurry. A homogeneous microstructure was maintained even after annealing at temperatures between 1200 and 1400 degrees C. Maximum bending strength of 88.5 MPa was also obtained at an optimum dispersant concentration.

Colloids↗

PubMed1989

[A case of synchronous double primary malignant neoplasms (malignant astrocytoma, and lung cancer) diagnosed by autopsy].

Discussed is a deceased patient, a 54-year-old male, who was admitted to hospital with the chief complaint of motor aphasia. Computed assisted tomography in the cranium showed a massive lesion in the left brain. Further, chest X-ray showed an abnormal tumorous shadow with a pleural indentation in the left middle lung field. In spite of a negativity of cancer cells in a bronchial biopsy and a brushing, we decided that this case reflected a lung cancer with brain metastasis. However, on autopsy, the tumor in the lung histologically was determined as being an (adenocarcinoma alveolar cell type) and the brain tumor was found to be a malignant astrocytoma. We have reported on this case because a double primary neoplasm, a malignant astrocytoma and lung cancer, is rare in the literature.

Adenocarcinoma, Bronchiolo-Alveolar↗

PubMed1989

[Complement-mediated solubilization of immune complexes in immune complex nephritis].

In order to examine the ability of complement to solubilize the immune complexes (IC) in vivo, we made acute or chronic serum sickness nephritis in 10 rabbits or 12 rats with injection of BSA as antigen (Ag). Animals were divided into two groups. The 500 mu or 50 mu/week of cobra venom factor (CVF) for rabbits or rats was administered intraperitoneally in one group of animals to reduce the serum complement levels and complement-mediated solubilization of immune complex. On the other hand, the 2 ml or 0.2 ml/week of turpentine oil (TO) was injected intramuscularly in another group of animals to elevate the serum complement levels. The renal biopsy was performed with weekly intervals in each animals, and the specimens were stained for antigen (BSA), antibody (IgG) and C3 by immunofluorescence techniques. The result in this experiments showed the significant difference between TO-, and CVF-treated animals in the degree of disappearance of IC in the kidney lesions. The undetectable amount of IC (especially BSA) was remained in the renal tissue of TO-treated animals. This fact indicated that complement might act to solubilize the IC deposited in the tissue in vivo also.

Animals↗