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Biomedical subjects

Toshiyuki Ikoma

Publications and source records attributed to Toshiyuki Ikoma.

9 recordsLinked to original sources
PubMed2007

Fabrication and mechanical and tissue ingrowth properties of unidirectionally porous hydroxyapatite/collagen composite.

This study investigated the effects of the three-dimensional (3-D) pore structure of a porous hydroxyapatite/collagen (HAp/Col) composite on their mechanical properties and in vivo tissue ingrowth. The unique 3-D pore structure, comprising unidirectionally interconnected pores, was fabricated by the unidirectional growth of ice crystals by using a cooling stage and a subsequent freeze-drying process. The unidirectional pores had a spindle-shaped cross section, and their size gradually increased from the bottom to the upper face. The porous composite showed an elastic property and anisotropic compressive strength for the pore directions. While the strength and modulus parallel to the pore axis were 1.3- and twofold higher than those of the porous composite with spherical pores formed randomly, the strength and modulus perpendicular to the pore axis showed the lowest values. The subcutaneous implantations revealed that when compared with the random pores, the unidirectional pores promote the ingrowth of the surrounding tissues into the pores.

Absorbable Implants↗
PubMed2006

Fabrication of hydroxyapatite ultra-thin layer on gold surface and its application for quartz crystal microbalance technique.

We present a method for coating gold quartz crystal microbalance with dissipation (QCM-D) sensor with ultra-thin layer of hydroxyapatite nanocrystals evenly covering and tightly bound to the surface. The hydroxyapatite layer shows a plate-like morphology and less than 20 nm in thickness. The hydroxyapatite sensor operated in liquid with high stability and sensitivity. The in-situ adsorption mechanism and conformational change of fibrinogen on gold, titanium and hydroxyapatite surfaces were investigated by QCM-D technique and Fourier-transform infrared spectroscopy. The change of secondary structures of fibrinogen adsorbed on the surfaces depended on the adsorbed amounts of protein. The secondary structure of fibrinogen adsorbed on the surfaces changes with increasing coverage. This is explained by repulsion among fibrinogens, affecting water structure and thus the strength of fibrinogen interactions on the surface. The study indicates that the hydroxyapatite sensor is applicable for qualitative and conformational analysis of protein adsorption.

Adsorption↗
PubMed2006

Pre-adsorbed type-I collagen structure-dependent changes in osteoblastic phenotype.

Type-I collagen is the most abundant extracellular matrix in bones and modulates various functions of osteoblasts. We prepared two different structures of type-I collagen on tissue culture grade polystylene (TCPS) surfaces, one is feltwork structure of filamentous molecules from acid solutions (ACs) and the other is network structure of fibrils from neutral solutions (NCs), to examine effects of the structures on the maturation process of osteoblast-like cells. No significant differences of cell proliferation were observed between TCPS and ACs, but NCs delayed the proliferation. In initial cell attachment, the cells on ACs had tense lamellipodia with sharp tips, while those on NCs had loose lamellipodia. No detectable differences in levels of expressed integrin alpha2- and alpha5-subunits were observed between the structures. Although the matrix mineralization in NCs was also delayed in comparison with TCPS and ACs, fully mineralized levels in NCs were the same as those of TCPS and ACs. In addition, although we examined the effects of densities of pre-adsorbed collagen molecules on osteoblast maturation, the effects were less serious than those of the structures. This study suggests that the structures of collagen affect proliferation and mineralization of osteoblast-like cells.

Animals↗
PubMed2005

Injectable porous hydroxyapatite microparticles as a new carrier for protein and lipophilic drugs.

Hydroxyapatite (Ca10 (PO4)6(OH)2) is a biodegradable material that forms a major component of bones and teeth. We prepared injectable spherical porous hydroxyapatite microparticles (SP-HAp) as a drug carrier by the spray-drying method. We then examined the usefulness of SP-HAp as a carrier for drugs such as interferon alpha (IFNalpha), testosterone enanthate (TE), and cyclosporin A (CyA). SP-HAp had an average diameter of 5 mum and a porosity of approximately 58%. It could be injected subcutaneously through a 27-gauge needle. SP-HAp was observed to be biodegradable. The speed of degradation of SP-HAp could be regulated by altering the calcination temperature. IFNalpha was adsorbed well to SP-HAp particles, but INFalpha was released faster from the particles, than the particles could degrade in both in vitro and in vivo experiments. Addition of human serum albumin and zinc (reinforcement) to IFNalpha-adsorbed SP-HAp caused marked prolongation of release in vivo. The in vivo release of testosterone enanthate and CyA from SP-HAp preparation, which was easily injectable, was similarly prolonged to that from the oil preparation. In conclusion, the SP-HAp seems to be useful as a biodegradable and subcutaneously injectable drug carrier. It is suggested that the reinforcement of the SP-HAp is very effective on the sustained release of drugs.

Animals↗
PubMed2003

Physical properties of type I collagen extracted from fish scales of Pagrus major and Oreochromis niloticas.

Type I collagens were extracted from fish scales of Pagrus major and Oreochromis niloticas as a possible underutilized resource for medical materials. The fish scales were demineralized with EDTA and digested by pepsin. The resultant type I collagens contained more than 33.6% of glycine as the most abundant amino acid. The denaturation temperatures of the collagens from P. major and O. niloticas were 303 and 308K, respectively, both of which were relatively lower than that of porcine dermis collagen (314K). CD spectra indicated that the denaturation temperatures were dependent on the amount of hydroxyproline, rather than proline residues. Raman spectra also indicated that the relative intensities of Raman lines at 879 and 855cm(-1) assigned to Hyp and Pro rings were changed due to the contents of the imino acids. Significantly, the content of sulphur-containing methionine was higher in the fish scales than in porcine dermis. The enthalpy and entropy estimated from thermal analyses could be correlated to amino acid sequences (Gly-Pro-Hyp) of type I collagens and the number of methionine amino acid residues.

Animals↗
PubMed2003

Microstructure, mechanical, and biomimetic properties of fish scales from Pagrus major.

The fish scale of Pagrus major has an orthogonal plywood structure of stratified lamellae, 1-2 microm in thickness, consisting of closely packed 70- to 80-nm-diameter collagen fibers. X-ray diffraction, energy-dispersive X-ray analysis, and infrared spectroscopy indicate that the mineral phase in the scale is calcium-deficient hydroxyapatite containing a small amount of sodium and magnesium ions, as well as carbonate anions in phosphate sites of the apatite lattice. The tensile strength of the scale is high (approximately 90 MPa) because of the hierarchically ordered structure of mineralized collagen fibers. Mechanical failure occurs by sliding of the lamellae and associated pulling out and fracture of the collagen fibers. In contrast, demineralized scales have significantly lower tensile strength (36 MPa), indicating that interactions between the apatite crystals and collagen fibers are of fundamental importance in determining the mechanical properties. Thermal treatment of fish scales to remove the organic components produces remarkable inorganic replicas of the native orthogonal plywood structure of the fibrillary plate. The biomimetic replica produced by heating to 873 K consists of stratified porous lamellae of c-axis-aligned apatite crystals that are long, narrow plates, 0.5-0.6 microm in length and 0.1-0.2 microm in width. The textured inorganic material remains intact when heated to 1473 K, although the size of the constituent crystals increases as a result of thermal sintering.

Animals↗
PubMed2003

Dextran templating for the synthesis of metallic and metal oxide sponges.

Silver or gold-containing porous frameworks have been used extensively in catalysis, electrochemistry, heat dissipation and biofiltration. These materials are often prepared by thermal reduction of metal-ion-impregnated porous insoluble supports (such as alumina and pumice), and have surface areas of about 1 m(2) g(-1), which is typically higher than that obtained for pure metal powders or foils prepared electrolytically or by infiltration and thermal decomposition of insoluble cellulose supports. Starch gels have been used in association with zeolite nanoparticles to produce porous inorganic materials with structural hierarchy, but the use of soft sacrificial templates in the synthesis of metallic sponges has not been investigated. Here we demonstrate that self-supporting macroporous frameworks of silver, gold and copper oxide, as well as composites of silver/copper oxide or silver/titania can be routinely prepared by heating metal-salt-containing pastes of the polysaccharide, dextran, to temperatures between 500 and 900 degrees C. Magnetic sponges were similarly prepared by replacing the metal salt precursor with preformed iron oxide (magnetite) nanoparticles. The use of dextran as a sacrificial template for the fabrication of metallic and metal oxide sponges should have significant benefits over existing technologies because the method is facile, inexpensive, environmentally benign, and amenable to scale-up and processing.

Copper↗
PubMed2002

An improved method to prepare hyaluronic acid and type II collagen composite matrices.

An improved method to prepare hyaluronic acid (HyA) and type II collagen composite matrices was developed. HyA and type II collagen formed polyion complex (PIC) in aqueous solution due to their opposite electrostatic charges. Therefore, optimal conditions at which PIC was not formed between HyA and type II collagen were determined in order to directly crosslink using a water-soluble carbodiimide [WSC; 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride]. HyA-collagen composite matrices were successfully obtained using WSC in the presence of 0.4M NaCl, which was found the optimal concentration to suppress PIC formation. Fourier transformed infrared spectra of the obtained matrices showed ester bond formation, indicating that the crosslinking reaction between HyA molecules, HyA and collagen molecules, and collagen molecules proceeded. The swelling ratio of a HyA-collagen composite matrix depended on the WSC concentration and HyA content. From scanning electron microscopy observations, the lyophilized matrices possess multi pore structures. The HyA-collagen composite matrices using this improved method will be useful in the preparation of cartilage regenerative scaffolds, and this methodology may be applied to other polyanion-polycation combinations as well.

Biocompatible Materials↗