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Biomedical subjects

Atsuro Yokoyama

Publications and source records attributed to Atsuro Yokoyama.

13 recordsLinked to original sources
PubMed2007

Mechanical properties and biological behavior of carbon nanotube/polycarbosilane composites for implant materials.

Multiwalled carbon nanotube/polycarbosilane (MWCNT/PCS) composites were fabricated by the spark plasma sintering (SPS) method. The MWCNT/PCS composites consisted of MWCNTs and nanosized SiC particles pyrolyzed from PCS and possessing good mechanical properties for bone tissue repair or dental implantation. The MWCNT/PCS composites were implanted in the subcutaneous tissue and femur of rats at 1 and 4 weeks after implantation. Histological investigations showed that there was little inflammatory response in the subcutaneous tissue, and newly formed bone tissue was observed in the femur. These results indicated that the MWCNT/PCS composite had little prophlogistic effect and good osteoconductivity. The study suggested the possibility that the MWCNT/PCS composite could be a candidate bone-substitute and dental-implant material in the future.

Animals↗
PubMed2005

Influence of length on cytotoxicity of multi-walled carbon nanotubes against human acute monocytic leukemia cell line THP-1 in vitro and subcutaneous tissue of rats in vivo.

Carbon nanotubes (CNTs) are single- or multi-cylindrical graphene structures that possess diameters of a few nanometers, while the length can be up to a few micrometers. These could have unusual toxicological properties, in that they share intermediate morphological characteristics of both fibers and nanoparticles. To date, no detailed study has been carried out to determine the effect of length on CNT cytotoxicity. In this paper, we investigated the activation of the human acute monocytic leukemia cell line THP-1 in vitro and the response in subcutaneous tissue in vivo to CNTs of different lengths. We used 220 nm and 825 nm-long CNT samples for testing, referred to as "220-CNTs" and "825-CNTs", respectively. 220-CNTs and 825-CNTs induced human monocytes in vitro, although the activity was significantly lower than that of microbial lipopeptide and lipopolysaccharide, and no activity appeared following variation in the length of CNTs. On the other hand, the degree of inflammatory response in subcutaneous tissue in rats around the 220-CNTs was slight in comparison with that around the 825-CNTs. These results indicated that the degree of inflammation around 825-CNTs was stronger than that around 220-CNTs since macrophages could envelop 220-CNTs more readily than 825-CNTs. However, no severe inflammatory response such as necrosis, degeneration or neutrophil infiltration in vivo was observed around both CNTs examined throughout the experimental period.

Animals↗
PubMed2005

Strict preparation and evaluation of water-soluble hat-stacked carbon nanofibers for biomedical application and their high biocompatibility: influence of nanofiber-surface functional groups on cytotoxicity.

Water-soluble H-CNFs modified with a carboxyl group possessed the ability to induce TNF-alpha, whereas CHAPS-treated H-CNFs possessed significantly greater activity and were also found to activate NF-kappaB reporter activity, to a significantly greater level than H-CNFs; furthermore the functional group modified or coated on the surface of H-CNFs was a significant cytotoxic factor that affected cell activation.

Carbon↗
PubMed2005

Biomimetic porous scaffolds with high elasticity made from mineralized collagen--an animal study.

Histological investigations of a new hydroxyapatite-collagen composite material were carried out to evaluate its possible suitability as a bone substitute. The three-dimensional scaffolds made from biomimetically mineralized collagen exhibit an interconnecting pore structure and elastic mechanical properties. They were implanted into the subcutaneous tissue and bone defects made in the femur of rats and harvested with the surrounding tissue at 1, 2, 4, 8, and 12 weeks after surgery. The materials implanted in the subcutaneous tissue were covered by fibrous connective tissue with a slight inflammatory response, and many foreign-body giant cells were observed on the surface of the scaffolds. Most of the material implanted in the subcutaneous tissue was resorbed at 8 weeks by phagocytosis. In the bone defects, new bone formation was observed on the surface of the material at 1 week. New bone increased with time, and osteoclasts were seen on the surface of the scaffolds at 2 weeks. Resorption and replacement by new bone of many parts of the materials implanted in the femur were observed by 12 weeks. These responses occurred faster than those of other hydroxyapatite-collagen composites. The results suggested that the new biomimetically mineralized collagen scaffolds were suitable as an implant material for bone-tissue reconstruction.

Animals↗
PubMed2005

Biological behavior of hat-stacked carbon nanofibers in the subcutaneous tissue in rats.

The tissue response to hat-stacked carbon nanofibers (H-CNFs) was evaluated. H-CNFs were implanted in the subcutaneous tissue of rats. Histological and ultrastructural investigations were carried out by transmission electron microscopy. Although many macrophages and foreign body giant cells were seen around H-CNFs, no severe inflammatory response such as necrosis was observed. Some H-CNFs were observed in lysosomal vacuoles of phagocytes. These results showed that H-CNFs were not strong prophlogistic substances and were englobed in vivo.

Animals↗
PubMed2005

Novel bulk carbon nanotube materials for implant by spark plasma sintering.

Novel, bulk multiwall carbon nanotubes (MWCNTs) sintered with polycarbosilane (PCS) as a binder agent were fabricated by spark plasma sintering (SPS), and their microstructure and properties were investigated. Sintering was done with 20-60 MPa pressure at 1200 degrees C. SEM and TEM observations showed that the nanosized tube microstructure was preserved even after sintering, and tubes adhered to each other with the nanosized nodules of SiC pyrolyzed form PCS as revealed by X-ray diffraction. Bulk density and Vickers hardness were found to increase, whereas the specific surface area decreased, as PCS content and sintering pressure increased. Through animal experiments, the inflammatory reaction of CNTs/PCS material was found to be slightly increased with increasing PCS content. In conclusion, sintered CNTs had physical and mechanical properties close to bone, and their good biocompatibility based on tissue response served to pave their way as a suitable implant material in the future.

Animals↗
PubMed2004

Caged multiwalled carbon nanotubes as the adsorbents for affinity-based elimination of ionic dyes.

Multiwalled carbon nanotubes (MWCNTs) were used as the active elements for the first time for affinity-based elimination of ionic dyes. MWCNTs were encapsulated in cross-linked alginate (ALG) microvesicles using Ba2+ as the bridging ion. The Ba2+-alginate matrix constitutes a cage which holds the physically trapped MWCNTs. The cage carries negative charges on its surface. The cage restricts the access of anions of large molecular weight, such as humic acids, because of electrostatic repulsion. The cage also restricts the access of colloids of large size, because of size exclusion. Ionic dyes partition into the cage and then are captured by MWCNTs probably on the basis of van der Waals interactions occurring between the hexagonally arrayed carbon atoms in the graphite sheet of MWCNTs and the aromatic backbones of the dyes. As a result of these interactions the target species, namely, the ionic dyes, are eliminated efficiently by the MWCNTs of Ba2+-ALG/MWCNT composite adsorbents. The adsorptive capacities for elimination of acridine orange, ethidium bromide, eosin bluish, and orange G (the model species used for this study) were found as high as 0.44, 0.43, 0.33, and 0.31 micromol, respectively, for 1.0 mg of the caged MWCNTs. Adsorptive experiments with carbon nanofibers and activated carbons as the adsorbents were also performed. The MWCNT-based adsorbents provided the best capability for the affinity-based elimination of these targeted species. Biocompatibility experiments performed in vitro and in vivo provided promising results, suggesting potential applications of the caged MWCNTs in in situ environmental remediation.

Adsorption↗
PubMed2003

Tissue response to a newly developed calcium phosphate cement containing succinic acid and carboxymethyl-chitin.

We developed a new calcium phosphate cement containing succinic acid and carboxymethyl-chitin in the liquid component. In this study, the biocompatibility and osteoconductivity of this new cement were investigated. After mixing, cement in putty form was implanted immediately between the periosteum and parietal bone and in the subcutaneous tissues of rats. In control cement, distilled water was used instead of the liquid component. In addition to histological evaluations, analyses with X-ray diffraction and Fourier transform infrared were performed for the subcutaneously implanted cements. Histological examination showed slight inflammation around the new cement on the bone and in the subcutaneous tissue at 1 week after surgery. At 2 weeks, the cement was partially bound to the parietal bone. The extent of the surface of the new cement directly in contact with the bone increased with time, and most of the undersurface of the new cement bound to the host parietal bone by 8 weeks. Analysis by X-ray diffraction showed that the new cement in the subcutaneous tissue was transformed into hydroxyapatite by 8 weeks. These results indicate that this new calcium phosphate cement is useful as a bone substitute material.

Absorbable Implants↗
PubMed2003

Ultrastructure of ceramic-bone interface using hydroxyapatite and beta-tricalcium phosphate ceramics and replacement mechanism of beta-tricalcium phosphate in bone.

Hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) are useful for grafting and augmentation of bone tissue. Observation by transmission electron microscopy (TEM) was done to investigate the ultrastructures at the interfaces between the biomaterials and the adjacent tissue, and osteogenesis around the biomaterials in the present study. HA and beta-TCP ceramics were used in disk forms which had macropores and micropores, and were implanted between the parietal bone and the cranial periosteum of rats. Specimens were prepared for observation at 4 and 8 weeks postoperatively. The microscopic results indicated that an intervening layer was present on the surface of HA, whereas it was not present on the surface of beta-TCP. A characteristic fibrillar structure was observed in the intervening layer between HA and bone under decalcification by HCl. In beta-TCP, in reticular structures observed close to the bone tissue by optical microscopy, calcification and sparse collagen fibers were interspersed among the granules of beta-TCP. In addition, close to the interface between beta-TCP and bone, many osteocytes with numerous processes were present. Some processes were elongated towards the interface. These results revealed the difference in the ultrastructures of the interfaces between HA and beta-TCP, and the dissolution mechanism of beta-TCP in bone.

Animals↗
PubMed2003

Bone augmentation osteogenesis using hydroxyapatite and beta-tricalcium phosphate blocks.

PURPOSE: In this study, we investigated the differences in osteogenesis and resorption between hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) implanted on the parietal bone of rats. MATERIALS AND METHODS: HA and beta-TCP were used in blocks with macropores and micropores. They were implanted between the parietal bone and the cranial periosteum in rats. Osteogenesis around the implanted materials was investigated histopathologically and histomorphometrically at 1, 2, 4, 8, and 24 weeks after surgery. RESULTS: At 2 weeks, osteogenesis from the parietal bone was observed around both materials, and new bone had attached directly to the surfaces of both materials. New bone grew into the pores of the upper regions of both materials with time. The beta-TCP block had a characteristic basophilic reticular structure in which the dissolution of the materials was observed close to the new bone. The HA blocks were stable for 24 weeks, whereas parts of the beta-TCP blocks were fractured and resorbed at 24 weeks. Histomorphometrically, the volume of new bone around HA was larger than that around beta-TCP. There was no remarkable change in the amount of remaining HA, but that of beta-TCP was decreased. CONCLUSION: HA blocks in this model are suitable for onlay grafts because of its stability and osteogenesis, beta-TCP is not stable. Therefore, when beta-TCP blocks are used for onlay grafts, the mechanical stress on the recipient site should be taken into consideration because of resorption and fracture.

Absorbable Implants↗
PubMed2002

Development of calcium phosphate cement using chitosan and citric acid for bone substitute materials.

We developed a calcium phosphate cement that could be molded into any desired shape due to its chewing-gum-like consistency after mixing. The powder component of the cement consists of alpha-tricalcium phosphate and tetracalcium phosphate, which were made by decomposition of hydroxyapatite ceramic blocks. The liquid component consists of citric acid, chitosan and glucose solution. In this study, we used 20% citric acid (group 20) and 45% citric acid (group 45). The mechanical properties and biocompatibility of this new cement were investigated. The setting times of cements were 5.5 min, in group 20 and 6.4 min, in group 45. When incubated in physiological saline, the cements were transformed to hydroxyapatite at 3, and 6 weeks, the compressive strengths were 15.6 and 20.7 MPa, in group 45 and group 20, respectively. The inflammatory response around the cement implanted on the bone and in the subcutaneous tissue in rats was more prominent in group 45 than in group 20 at 1 week after surgery. After 4 weeks, the inflammation disappeared and the cement had bound to bone in both groups. These results indicate that this new calcium phosphate cement is a suitable bone substitute material and that the concentration of citric acid in the liquid component affects its mechanical properties and biocompatibility.

Animals↗
PubMed2002

Surface properties and biocompatibility of nitrided titanium for abrasion resistant implant materials.

Corrosion, other related properties and biocompatibility of surface nitrided titanium were investigated to examine its possible use as an abrasion resistant implant material. The nitrided layer about 2 microm thick composed of TiN and Ti2N was formed on titanium by a gas nitriding method. The dissolved amount of titanium ion in SBF was as low as the detection limit of ICP, and that in the 1% lactic acid showed no significant difference from titanium. The tissue reaction of the cylindrical implant in soft tissue of rats showed no inflammation, and fine particles of 1 microm induced phagocytosis, which was similar to titanium. The implantation in the femor showed the new bone formed in direct contact with implants. All the results suggested that the wettability, corrosion resistance, S. mutans adhesion and biocompatibility were nearly equivalent to those of titanium. The surface of nitrided titanium was promising, with biocompatibility comparable with titanium, as an implant material such as for an abutment part of a dental implant, which requires high abrasion resistance.

Animals↗