Biomedical subjects

Yoshiro Kitamura

Publications and source records attributed to Yoshiro Kitamura.

7 recordsLinked to original sources

PubMed2005

Preparation and interfacial properties of a novel biodegradable polymer surfactant: poly(ethylene oxide monooleate-block-DL-lactide).

In this paper, we report a novel synthesis of poly(ethylene oxide monooleate-block-DL-lactide) (MOPEO-PLA) in the presence of stannous 2-ethylhexanoate catalyst. By utilizing the surfactant property and the reactive double bond of the amphiphilic MOPEO-PLA, various characteristics of PLA microspheres, such as surface and internal structure, surface morphology, release property, and so on, may potentially be controlled. MOPEO-PLA was found to be hydrophobic enough to prevent loss by dissolution into aqueous solution, which is often a problem for MOPEO. Furthermore, the interfacial tension measurements of a MOPEO-PLA/toluene/water system revealed that MOPEO-PLA had a good surface activity almost equal to that of MOPEO. The MOPEO-PLA/PLA blend films were prepared by solvent casting on a water layer. Contact-angle measurements of MOPEO-PLA/PLA blend films confirmed that the hydrophilic PEO segments were selectivity accumulated at the oil/water interface. Moreover, the surface free energy on the 'water side' of the MOPEO-PLA/PLA blend films was increased because of the increase in polar components as a result of the ether bonds of the PEO segments. Schematic illustration of the adsorption property of a) MOPEO-PLA with a high-molecular-weight PLA segment and b) MOPEO-PLA with a low-molecular-weight PLA segment at an ethyl acetate/water interface.

Biodegradation, Environmental↗

PubMed2005

Surface morphology control of polylactide microspheres enclosing irinotecan hydrochloride.

In order to reduce the initial burst from polylactide (PLA) microspheres enclosing an antitumor agent, we prepared the microspheres with a smooth surface by varying solvent evaporation conditions such as operating temperature and pressure. PLA microspheres enclosing irinotecan hydrochloride (CPT) were prepared using the O/O emulsion system for solvent evaporation. The mean diameter and enclosing efficiency were almost constant because they were independent of solvent evaporation conditions. Scanning electron microscopic (SEM) observation verified the smooth surface of the PLA microspheres produced by varying the preparation conditions. In vitro release experiments show that the initial burst of microspheres with a smooth surface was less than that of those with a rough surface.

Camptothecin↗

PubMed2004

Reconstruction of a high-resolution image on a compound-eye image-capturing system.

The authors have proposed an architecture for a compact image-capturing system called TOMBO (thin observation module by bound optics), which uses compound-eye imaging for a compact hardware configuration [Appl. Opt. 40, 1806 (2001)]. The captured compound image is decomposed into a set of unit images, then the pixels in the unit images are processed with digital processing to retrieve the target image. A new method for high-resolution image reconstruction, called a pixel rearrange method, is proposed. The relation between the target object and the captured signals is estimated and utilized to rearrange the original pixel information. Experimental results show the effectiveness of the proposed method. In the experimental TOMBO system, the resolution obtained is four times higher than that of the unit image that did not undergo reconstruction processing.

Journal Article↗

PubMed2004

Bimodal fingerprint capturing system based on compound-eye imaging module.

A compact imaging system called TOMBO (Thin Observation Module by Bound Optics) is proposed in which a microlens array is used for thin hardware configuration. This paper describes a fingerprint-capturing module as an application of the TOMBO. Experimental results by the TOMBO prototype system are shown to clarify the applicability of the TOMBO to the fingerprint capturing. Different types of biometrics, i.e., fingerprint and face images, are captured by the same hardware, which shows the extendability of the system for multimodal identification.

Journal Article↗

PubMed2002

Mechanical properties and osteoconductivity of new bioactive composites consisting of partially crystallized glass beads and poly(methyl methacrylate).

New bioactive composites consisting of partially crystallized glass beads as inorganic fillers and poly(methyl methacrylate) (PMMA) as an organic matrix were developed. Two kinds of partially crystallized glass beads, designated Cry820 and Cry850, were newly prepared by the heating of MgO-CaO-SiO(2)-P(2)O(5) glass at 820 and 850 degrees C, respectively. The glass beads were mixed with PMMA to form two new composites designated Cry820C and Cry850C, respectively. The goal of this study was to produce a highly osteoconductive and mechanically strong composite cement with these new fillers. A previously reported composite cement designated AWC, which was composed of apatite- and wollastonite-containing glass ceramic (AW-GC) as a powder filler and the same PMMA polymer used in the new composites, was used as a reference material. The quantity of filler added to each composite was 70 wt %. The bending strength of Cry820C was significantly higher than that of Cry850C. Composites were packed into intramedullary canals of rat tibiae to evaluate their osteoconductivity, as determined by an affinity index. The affinity index, which equaled the length of bone in direct contact with the composite surface expressed as a percentage of the total length of the composite surface, was calculated for each composite. The rats were euthanized at 4, 8, and 25 weeks after implantation. At each time interval studied, Cry820C showed a significantly higher affinity index than AWC up to 25 weeks after implantation. Cry850C showed a significantly higher affinity index than AWC up to 8 weeks and a higher affinity index than AWC at 25 weeks, although the difference was not significant. The values for each composite increased significantly with time up to 25 weeks. Our study revealed that the higher osteoconductivity of the new composites was due to the larger quantity of the glassy phase of the crystallized glass beads at the composite surface and the lower solubility of the PMMA powder to methyl methacrylate monomer. In addition, the spherical shape of the crystallized glass beads gave the new composites strong enough mechanical properties to be useful under weight-bearing conditions. The new composites show promise as alternatives, with improved properties, to conventional PMMA bone cement.

Animals↗

PubMed2002

Composites consisting of poly(methyl methacrylate) and alumina powder: an evaluation of their mechanical and biological properties.

We developed new composites consisting of comparatively high molecular weight poly(methyl methacrylate) (hPMMA) and delta-alumina powder or alpha-alumina powder (designated delta-APC and alpha-APC, respectively) that allowed direct bone formation on their surfaces in vivo. delta-Alumina powder was manufactured by the fusing and quenching of pulverized alumina powder. It was composed mainly of delta-crystal phases of alumina. The purpose of this study was to evaluate the static mechanical properties and biological properties of these composites. The hPMMA itself was used as a reference material. The bending strength and Young's modulus of both delta-APC and alpha-APC were significantly higher than those of hPMMA, and the alumina composites are believed to be strong enough for use under weight-bearing conditions. The three types of composites were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index. Rats were sacrificed 4 and 8 weeks after surgery. The affinity index, equal to the length of bone in direct contact with the composite surface and expressed as a percentage of the total length of the composite surface, was calculated for each composite at each interval. Histologically, new bone had formed along the surfaces of both delta-APC and alpha-APC within 4 weeks. The affinity indices for both delta-APC and alpha-APC increased significantly with time up to 8 weeks. At 8 weeks, the affinity index for delta-APC was significantly higher than the indices for alpha-APC and hPMMA. This study revealed that the excellent osteoconductivity of delta-APC was due to the delta-crystal phases of alumina and the high molecular weight of hPMMA. delta-APC shows promise as a base for developing a highly osteoconductive and mechanically strong biomaterial.

Aluminum Oxide↗

PubMed2002

PMMA-based bioactive cement: effect of glass bead filler content and histological change with time.

A new bioactive bone cement (designated GBC), which is a polymethyl methacrylate (PMMA)-based composite consisting of bioactive glass beads as an inorganic filler and high molecular-weight PMMA as an organic matrix, has been developed. The purpose of the present study was to evaluate the effect of the filler content on the mechanical properties and osteoconductivity of GBC, to decide the most suitable filler proportion, and to evaluate the degree of cement degradation with time. The bioactive beads, consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass, were added to the cement in various proportions (40-70 wt %). The bending strength of GBC did not differ among the proportions (approximately 136 MPa), but the elastic modulus of bending of GBC increased as the glass bead filler content increased (approximately 4.1-7.2 GPa). The all types of GBC were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface. Rats were sacrificed at 4, 8, 25, and 39 weeks after implantation, and the affinity index was calculated for each type of GBC at each time point. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks, even in GBC containing only 40 wt % of glass beads. The affinity indices of GBC tended to increase as the proportion of glass bead filler increased and as the implantation period increased. In GBC containing 60 or 70 wt % of glass beads, significant rapid increases in the affinity indices were found from 4 to 8 weeks, and the high values (approximately 70%) were maintained up to 39 weeks. A sign of glass bead degradation was observed at the bone-cement interface in the rat tibiae at 39 weeks. We conclude that, when mechanical properties and osteoconductivity are both taken into consideration, GBC containing 60 or 70 wt % of glass beads is the most suitable formulation, but that further studies are needed to investigate and overcome the degradation.

Animals↗