Biomedical subjects

Junzo Tanaka

Publications and source records attributed to Junzo Tanaka.

65 records · Page 4Linked to original sources

PubMed2002

Novel hydroxyapatite ceramics with an interconnective porous structure exhibit superior osteoconduction in vivo.

Calcium hydroxyapatite ceramics (CHA) are nontoxic materials, provoke little reaction from tissues, and by virtue of these properties represent a good starting point for creating bone substitutes. Although several porous CHAs have been used clinically, there have been few reports that CHA is fully replaced by newly formed bone, which may be due to its structure and the limited connectivity between pores. We recently developed a fully interconnected porous CHA (IP-CHA) by adopting a "foam-gel" technique. Structural analysis by scanning electron microscopy revealed that IP-CHA had spherical pores of uniform size that were interconnected by window-like holes. The surface of the wall structure was smooth, and hydroxyapatite particles were bound tightly to one another. Most of the interpore connections of IP-CHA ranged from 10 to 80 microm in diameter (average, 40 microm). When the cylindrical IP-CHA (diameter, 6 mm; height, 15 mm) was implanted into a rabbit femoral condyle, bone, and bone marrow with abundant vessels formed deep in the pores through the interpore connections. Within a period of 6 weeks, new bone had formed and penetrated to a distance of 3 mm from the surface of the IP-CHA implant. Furthermore, a compression test at 9 weeks revealed that the implanted IP-CHA steadily increased in strength to more than double the value of the initial test. These results indicate that the IP-CHA may have clinical utility as a superior bone substitute.

Animals↗

PubMed2002

Development of an artificial vertebral body using a novel biomaterial, hydroxyapatite/collagen composite.

Hydroxyapatite/collagen (HAp/Col) composites having a bone-like nanostructure were synthesized and shaped into implants. This study was designed to develop an artificial vertebra system using this novel implant for anterior fusion of the cervical spine. Anterior fusion was carried out on 6 beagle dogs with the implants adsorbing rhBMP-2 (400 microg/ml). and 9 dogs with the implants without rhBMP-2. In 3 dogs of the rhBMP-treated group, as well as 6 dogs of the non-rhBMP-treated group, the implant was fixed with a poly-L-lactide plate and 2 titanium screws. Implants were taken out after 13 weeks from each 3 dogs in the rhBMP(-):plate(-). rhBMP(-):plate(+) and rhBMP(+):plate(+) groups. Also, the implants were removed from each 3 dogs in the rhBMP(-):plate(+) and rhBMP(+):plate(+) groups after 24 weeks. Histological and radiographical analysis suggested that since the larger part of the composite material was absorbed within 13 weeks, reduction of the intervertebral distance was caused, and that enhancement of callus formation and bone bridging by rhBMP-treatment was effective to prevent collapse of the implant, even though an effect of anterior plate-fixation was not obvious. The HAp/Col implant adsorbing rhBMP-2 may be a suitable replacement for the existing ceramics in anterior interbody fusion of the cervical spine.

Animals↗

PubMed2002

XPS study for the microstructure development of hydroxyapatite-collagen nanocomposites cross-linked using glutaraldehyde.

X-ray photoelectron spectroscopy (XPS) was measured for the dry body of hydroxyapatite (HAP)-collagen (COL) nanocomposites cross-linked using glutaraldehyde (GA). Survey scan XPS showed the elemental spectra of N, C, O, Ca and P, which came from HAP and COL. The covalent bond formation between Ca2+ of HAP and RCOO- of COL molecule was confirmed by XPS. The bridge formation between COL fibers could be assessed from C1s and N1s band spectrum. The dehydration of swelling water during drying led to the reduction of linking distance for pendant GA between COL fibrils and contributed to further cross-linkage reaction. Cross-linkage induced the enlargement of length scale unit of COL. The modification of length scale was doing the key role of structure manipulation in the cross-linked HAP-COL nanocomposites.

Anisotropy↗

PubMed2002

FT-IR study for hydroxyapatite/collagen nanocomposite cross-linked by glutaraldehyde.

FT-IR analysis was performed for the hydroxyapatite (HAp)/collagen (COL) nanocomposite cross-linked by glutaraldehyde (GA). The amide bands I, II and III from COL matrix, and phosphate and carbonate bands from HAp were identified. The amide B band arising from C-H stretching mode showed a sensitive conformation by the degree of cross-linking. The amide I band showed a complicate conformational change by the degree of cross-linking. The characteristic amide I band at 1685 cm(-1), which is known as an aging parameter in the biological bone, did not show a monotonous tendency by the degree of cross-linking. The relative contents of the organics in the cross-linked HAp/COL nanocomposite were evaluated as an integration ratio between the amide I band at 1600-1700 cm(-1) and PO(4)(3-) band at 900-1200 cm(-1). The increase of the organics content by the cross-linking is enabled by the further organization of Ca(2+) ions of HAp crystals in HAp/COL nanocomposite. The complicate conformational behavior in the amide I, II and III bands seems to be affected by the cross-linking induced directional arrangement of HAp/COL nanocomposite fibrils.

Amides↗

PubMed2002

Self-assembly phenomenon of hydroxyapatite nanocrystals on chondroitin sulfate.

Self-assembly phenomenon of hydroxyapatite (HAp) nanocrystals on chondroitin sulfate (ChS) templates was investigated. A HAp/ChS hybrid was synthesized through a precipitation method with a calcium hydroxide suspension and phosphoric acid solution containing the ChS. The preferential alignment of the crystallographic c-axis of the HAp crystals parallel to the long axis direction of the ChS templates was observed to occur with the chemical interactions between the HAp crystals and the functional groups of the ChS. This phenomenon was interpreted by the crystallochemical specific nucleation and growth of the HAp crystals regulated by the pre-organized functional groups of the ChS template. Practical implication may involve a biomimetic artificial bone or cartilage can be made through a precipitation method with suitable bio-organics.

Journal Article↗

PubMed2002

Crystal growth and structure analysis of twin-free monoclinic hydroxyapatite.

Single crystals of hydroxyapatite were grown by a flux method using Ca(3)(PO(4))(2) and Ca(OH)(2) under 100 MPa of Ar gas. The crystals obtained had stoichiometric composition of Ca(10)(PO(4))(6)(OH)(2) and some of them were twin-free single crystals. From X-ray diffraction analyses, the space group was confirmed to be monoclinic P2(1)/b with cell parameters a=0.9419(3) nm, b=1.8848(6) nm, c=0.6884(2) nm, and gamma=119.98(2) degrees. The detailed crystal structure was determined with a reliability factor R(w)=0.033; the O atoms of OH were located just on the 2(1) axis while the H atoms of OH occupied the positions a little deviated from the 2(1) axis. The origin of this structure was ascribed to the formation of hydrogen bonds between the H atoms of the OH ions and the specific O atoms of the PO(4) ions.

Journal Article↗

PubMed2002

Effect of anti-CD14 antibody on experimental periodontitis induced by Porphyromonas gingivalis lipopolysaccharide.

The lipopolysaccharide (LPS) released by Porphyromonas gingivalis, a Gram-negative bacterium found in the periodontal pockets of patients with periodontitis, induces bone resorbing activity in vivo. We previously showed that a receptor for LPS on human gingival fibroblasts and gingival epithelial cells is CD14. In this study, we established a mouse model of experimental periodontitis by applying a P. gingivalis LPS solution to the buccal region of mice. P. gingivalis LPS-induced bone resorption and interleukin-6 production in the gingival tissues were significantly inhibited by pretreatment with anti-CD14 antibody for 5 weeks prior to LPS treatment. This result suggests that anti-CD14 antibody may be usable as a prototype for the development of drugs for the treatment of periodontal disease.

Animals↗

PubMed2002

Long-term durability of porous hydroxyapatite with low-pressure system to support osteogenesis of mesenchymal stem cells.

In this study, we hypothesize that loading more marrow-derived mesenchymal stem cells (MSCs) into porous material by using a low-pressure system during subculture, creating a composite which combines MSCs and a novel mechanical reinforced porous hydroxyapatite, can result in more bone tissue formation in vivo. Within 26 weeks postimplantation, we examined in vivo bone formation of the experimental group with 100 mmHg pressure applied to porous HA blocks loaded with MSCs. For in vivo testing, the 2-week subcultured HA/MSC composites were implanted into subcutaneous sites of syngeneic rats. These implants were harvested at 13 and 26 weeks after implantation. SEM showed that the pore surface is covered by osteoblasts as well as collagenous extracellular matrix at 13 weeks. Light microscopy revealed the quantity of bone at 26 weeks was greater than at 13 weeks. These results showed that the novel mechanical reinforced porous HA combined with MSC has more potential for bone formation at 100 mmHg, making this method very efficient for bone reconstruction.

Animals↗

PubMed2001

Crystal Orientation of Hydroxyapatite Induced by Ordered Carboxyl Groups.

Hydroxyapatite (HAp) crystals were grown from simulated body fluid (SBF) onto the arachidic acid monolayers with carboxyl groups, which were prepared by the Langmuir-Blodgett (LB) method on substrates. From X-ray diffraction patterns, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and infrared spectra, it was concluded that the crystalline phase nucleated on the LB monolayers was HAp, which was induced by the monolayer because no crystalline materials were grown on substrates without a monolayer. According to SEM and TEM observations, HAp precipitates were hemispherical aggregates consisting of the plate-like crystallites whose specific {100} surfaces were well developed. The HAp crystallites were preferentially oriented with their c-axes in a specific direction parallel to the substrate near the inorganic/organic interface, which suggests the control of the crystallographic orientation in HAp by the aligned carboxyl groups in the LB monolayer. Copyright 2001 Academic Press.

Journal Article↗

PubMedDate not supplied

Improved synthesis with high yield and increased molecular weight of poly(alpha,beta-malic acid) by direct polycondensation.

The development of synthetic biodegradable polymers, such as poly(alpha-hydroxy acid), is particularly important for constructing medical devices, including scaffolds and sutures, and has attracted growing interest in the biomedical field. Here, we report a novel approach to preparing high molecular weight poly(malic acid) (HMW--PMA) as a biodegradable and bioabsorbable water-soluble polymer. We investigated in detail the reaction conditions for the simple direct polycondensation of l-malic acid, including the reaction times, temperatures, and catalysts. The molecular weight of synthesized alpha,beta-PMA is dependent on both the reaction temperature and time. The optimum reaction condition to obtain alpha,beta-PMA by direct polycondensation using tin(II) chloride as a catalyst was thus determined to be 110 degrees C for 45 h with a molecular weight of 5300. The method for alpha,beta-PMA synthesis established here will facilitate production of alpha,beta-PMA of various molecular weights, which may have a potential utility as biomaterials.

Malates↗

PubMedDate not supplied

L-Phe end-capped poly(L-lactide) as macroinitiator for the synthesis of poly(L-lactide)-B-poly(L-lysine) block copolymer.

A poly(L-lactide)-b-poly(Nepsilon-(Z)-L-lysine) (PLLA-b-PZLys) block copolymer was synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydride using L-Phe-terminated PLLA as a macroinitiator. The L-Phe-terminated PLLA was prepared through a novel three-step process. First, the hydroxyl-terminated PLLA was synthesized through the ring-opening polymerization of L-lactide initiated by n-butanol under the existence of tin(II) ethylhexanoate. Subsequently, the complete capping of the hydroxyl end group of PLLA with BOC-L-Phe was achieved by using a mixed anhydride of BOC-L-Phe under the catalysis of 4-(1-pyrrolidinyl) pyridine. Finally, the free amino end group was obtained by removal of the t-butoxycarbonyl group through trifluoroacetic acid treatment under anhydrous condition. All these treatments were conducted under mild conditions, thus avoiding the breakdown of the PLLA backbone. Poly(L-lactide)-b-poly(L-lysine) block copolymer was produced after deprotection treatment of PLLA-b-PZLys. The structure of the block copolymer was confirmed by 1H NMR, IR, and GPC. Adjustment of the ratio of the NCA monomer to the macroinitiator could control the chain length of the PLys block.

Biocompatible Materials↗