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Biomedical subjects

Y Kotoura

Publications and source records attributed to Y Kotoura.

At least 55 records · Page 3Linked to original sources
PubMed1991

Poly(vinyl alcohol) hydrogel as an artificial articular cartilage: evaluation of biocompatibility.

We have developed a new poly(vinyl alcohol) hydrogel (PVA-H) of increased physical strength through a new manufacturing process. Its mechanical properties have been found to be preferable as a substitute for articular cartilage. To evaluate its biocompatibility as an artificial articular cartilage, a series of in vivo tests within the intraarticular, as well as the intramuscular, environment were conducted. Tissue reactions of cartilage, bone, synovium, and muscle to PVA-H were studied histologically. In the experimental group, in which PVA-H was implanted, inflammatory reactions of all of these tissues were very slight. In the control group, in which ultra-high molecular weight polyethylene (UHMWPE) was implanted, although tissue reactions of bone and muscle were as slight as in the experimental group, those of cartilage and synovium were somewhat more conspicuous. By way of these findings, the better biocompatibility of PVA-H was documented.

Animals↗
PubMed1991

A heat-generating bioactive glass-ceramic for hyperthermia.

Glass plates of the chemical composition: CaO (29.0), SiO 2 (31.0), Fe 2O 3 (40.0), B 2O 3 (3.0), P 2O 5 (3.0) in weight ratio were heated to 1050 degrees C at a rate of 5 degrees C/min and then cooled to laboratory temperature. The resulting glass-ceramic containing magnetite and wollastonite crystals showed high-saturation magnetization. The bonding ability of this new glass-ceramic to bone tissue was evaluated using rabbit tibiae, and compared with glass of the same composition. This glass-ceramic formed a Ca, P-rich layer on its surface and bonded tightly with bone within 8 weeks of implantation. However, the glass did not form this Ca, P-rich layer, nor had it bonded with bone at 25 weeks. The bone-heating ability of this glass-ceramic was investigated by applying a max. 300-Oe, 100-kHz magnetic field. The granules of the glass-ceramic filled in the rabbit tibiae heated the whole surrounding bone to more than 42 degrees C and maintained this temperature for 30 min. Bioactive ceramics reinforce the mechanical strength of bone tissue. Furthermore, this heat-generating bioactive glass-ceramic can be used for hyperthermic treatment of bone tumors.

Animals↗
PubMed1991

Bone-bonding ability of P2O5-free CaO.SiO2 glasses.

An apatite- and wollastonite-containing glass-ceramic (A.W-GC) has been reported to form a tight bond with living bone through an apatite layer formed on its surface. This layer is considered to be formed by dissolution of Ca2+ and HSiO3- ions from the glass-ceramic into the surrounding body fluids. In order to confirm this proposed mechanism for the surface reaction of A.W-GC, three kinds of glass in the systems CaO-SiO2, CaO-SiO2-CaF2, and CaO-SiO2-P2O5 were implanted into the tibiae of rabbits for 3 or 8 weeks. Contact microradiography and SEM-EPMA showed that all three kinds of glass formed a Ca,P-rich layer in combination with a Si-rich layer on their surfaces within 3 weeks and formed a direct bond with bone via these layers. The detaching test, performed 8 weeks after implantation, showed that the loads required to detach the implants from the bone were almost equal for the phosphorus-free and the phosphorus-containing glasses. It was concluded that even P2O5-free CaO.SiO2 glass formed a Ca,P-rich layer on its surface and bonded tightly with living bone. If glasses and glass-ceramics release at least Ca2+ and HSiO3- ions, this would be sufficient for them to form the Ca,P-rich layer on their surfaces in vivo, enabling them to bond directly with bone.

Animals↗
PubMed1991

Low wear rate of UHMWPE against zirconia ceramic (Y-PSZ) in comparison to alumina ceramic and SUS 316L alloy.

Partially stabilized zirconia ceramic is being recognized among ceramics for its high strength and toughness. With this ceramic, is possible to manufacture a 22-mm-size femoral head for low friction arthroplasty of the hip joint in association with an ultra-high-molecular-weight polyethylene socket. Wear-resistant properties of zirconia ceramic were screened on two principally different wear devices. Sterile calf bovine serum, physiological saline, and distilled water were chosen as the lubricant fluid media. Depending on the lubricant medium, the wear factor of polyethylene against zirconia ceramic counterfaces was 40 to 60% less than that against alumina ceramic counterfaces, and 5 to 10 times lower than with the SUS316L metal counterfaces. Polyethylene wear against metal was more susceptible in saline in which it had 2 to 3 times higher wear rate than with serum. On the other hand, different fluid media had little effect on polyethylene wear against ceramic counterfaces. In each set of tests, the wear factor obtained on an unidirectional wear device showed 10 to 15 times higher values, in comparison to the wear factor estimated on a reciprocating wear device.

Alloys↗
PubMed1991

Incorporation of cortical bone autografts following intraoperative extracorporeal irradiation in rabbits.

In an experimental study using 60 rabbits, a cortical bone segment of the unilateral tibial diaphysis was resected, irradiated extracorporeally, and reimplanted immediately as an autograft. The subsequent process of graft incorporation was examined over a 26-week period by roentgenography, histology, and histomorphometry. The irradiation doses were 0 (control), 50, 100, and 200 Gy. Roentgenographic and histologic examinations revealed that cortical bone autografts irradiated at 50 to 200 Gy were incorporated in the same manner as non-irradiated controls. By histomorphometry, the mean unresorbed fraction of the grafts at 6 weeks post-implantation was estimated to be 88.4% for the control group and 89.4% for the 200 Gy group. That of 26 weeks postimplantation was 17.5% for the control and 28.5%, 26.1%, and 27.8% for the 50, 100, and 200 Gy groups, respectively. Cumulative new bone formation showed a similar but inverse pattern of difference between the control and irradiated groups at 26 weeks. However, these differences were not statistically significant and were considered to be slight when compared with the overall similarity of the process. The total cross-sectional area of cortical bone at 26 weeks was similar to that of the contralateral side in all groups. In none of the adopted evaluation methods was any difference detected among the three irradiated groups with different doses. The results of this study suggest that extracorporeal irradiation of autografts at the specified doses impairs possible cellular contribution of the grafted marrow to the incorporation process, but does not interfere with the contribution of the matrices. The results provide useful information concerning the method of limb salvage surgery using intraoperatively-irradiated autografts.

Animals↗
PubMed1991

A bioabsorbable delivery system for antibiotic treatment of osteomyelitis. The use of lactic acid oligomer as a carrier.

We prepared a composite of D,L-lactic acid oligomer and dideoxykanamycin B for use as a biodegradable antibiotic delivery system with sustained effect. The composite was implanted in the distal portion of the rabbit femur, and the effective concentration of the antibiotic was measured in the cortex, the cancellous bone, and the bone marrow. In all bone tissues around the implant, the concentration of antibiotic exceeded the minimum inhibitory concentration for the common causative organisms of osteomyelitis for six weeks. Most of the implant material had been absorbed and the bone marrow had been repaired to a nearly normal state within nine weeks of implantation. The implant caused no systemic side effects, and it is likely to prove clinically useful as a drug delivery system for treating chronic osteomyelitis.

Absorption↗
PubMed1991

Changes in bone after high-dose irradiation. Biomechanics and histomorphology.

We studied the effects of high-dose irradiation on the mechanical properties and morphology of cortical bone in rabbits for 52 weeks after a single dose of 50 Gy of electron-beam to the tibia. After four weeks, the bending strength of the irradiated bone was unchanged, but at 12 weeks, the strength had decreased significantly. At 24 weeks after irradiation mean strength was less than half of controls but by 52 weeks there was a tendency toward recovery. Similar, synchronous changes of damage and recovery were seen in cortical porosity, haematopoietic cells in the bone marrow and endosteal new bone formation.

Animals↗
PubMed1990

Elevated frequency of a specific allele of the L-myc gene in male patients with bone and soft-tissue sarcomas.

Restriction fragment length polymorphisms (RFLPs) of 2 oncogenes, c-Ha-ras and L-myc, have been analyzed in 101 patients with bone and soft-tissue sarcoma and in 98 normal individuals. The c-Ha-ras gene was highly polymorphic both in sarcoma patients and in normal individuals. In contrast to our previous observation in breast cancer patients (Honda et al., 1988), no significant difference in allele frequencies between normal and sarcoma populations was observed. The L-myc locus revealed 2-allele polymorphism, allele L (10-kb) and S (6.6-kb), after digestion with Eco RI. The allele frequencies of L and S in sarcoma patients were 0.381 and 0.619, respectively, and those in normal individuals were 0.485 and 0.515, respectively. While the distributions of alleles in both populations fitted well with the Hardy-Weinberg equilibrium, the frequency of the S allele was significantly higher in sarcoma patients than in normal individuals (p less than 0.05). When sarcoma patients were divided into male and female subpopulations, this difference was highly significant only in males (p less than 0.01) but not in females. Our results suggest that males carrying the S allele may be prone to develop sarcoma.

Alleles↗
PubMed1990

Surface reactions of calcium phosphate ceramics to various solutions.

The surface reactions of calcium phosphate ceramics have been thought to play an important role in bonding with living bone. Hydroxyapatite (HA), tricalcium phosphate (TCP), and two kinds of apatite-containing glass ceramics were immersed in three types of solutions with different chemical constituents. The first solution was a physiological saline, the second contained phosphate (PO4), and the third was a balanced salt solution consisting of calcium (Ca), magnesium (Mg), and PO4. After serial incubation periods, changes in the solutions were assessed by measurement of total Ca, Mg, and PO4. The ceramic surfaces were studied using scanning electron spectroscopy, infrared reflection spectroscopy, and thin-film x-ray diffraction. The surface reactions of the ceramics were greatly affected by the chemical compositions of the surrounding media. In the complete solution with both Ca and PO4, a carbonated apatite layer was formed on the surfaces of HA, TCP, and the glass ceramics. In comparison to HA and TCP, the glass ceramics were characterized as Ca-releasing materials, the dissolved Ca creating an apatite layer on the surfaces in a few days, in conjunction with PO4 stock in the surrounding media. The immersion test with various solutions proved to be a simple and effective method of assessing surface conditions of ceramic materials.

Biocompatible Materials↗
PubMed1990

Better control of esophageal variceal bleeding by sclerotherapy followed by surgery.

This paper reports the clinical results of a retrospective study comparing endoscopic injection sclerotherapy (EIS) and back-up surgical treatment after EIS in the management of acute variceal bleeding. The 74 patients included in the study were divided into 2 groups. Group I consisted of 41 patients who received EIS over a mean period of 2.2 sessions and Group II consisted of 33 patients who underwent EIS and subsequent surgical intervention, in the form of 19 distal splenorenal shunts and 14 nonshunting procedures. The overall percentage of patients in whom initial control of variceal bleeding was achieved was 91.8 per cent. Four of the Group II patients were saved by emergency nonshunting operations. Rebleeding was experienced by 4 (28.6 per cent) of the 14 patients who underwent nonshunting surgery but by only 1 (5.3 per cent) of the 19 patients who underwent selective shunt surgery. The cumulative survival in Group II was significantly superior to that in Group I with 2 year survival being achieved in 66.7 per cent of the Group II patients but in only 23 per cent of Group I patients. Thus, the combination of initial EIS and back-up surgical intervention may be more beneficial than sclerotherapy alone for patients with acute variceal bleeding, while, the distal splenorenal shunt may be a more suitable surgical technique for patients having previously EIS.

Combined Modality Therapy↗
PubMed1990

Hepatobiliary and gastrointestinal imaging after pancreaticoduodenectomy--a comparative study on Billroth I and Billroth II reconstructions.

This study was conducted to compare the passage of bile and food through the remnant alimentary tract between 2 and 6 months following pancreaticoduodenectomy in patients undergoing Billroth I (Imanaga) and Billroth II (Child) reconstructions, using dual scintigraphy. In the patients who underwent Child's operation (n = 14), hepatobiliary scintigraphy showed a prominent stasis of bile tracer in the proximal jejunal loop and a significant time delay before the bile and food became mixed at the upper jejunum. On the other hand, in the patients who underwent Imanaga's operation (n = 9) no bile stasis in the proximal jejunal loop was found and the time taken before the two agents became mixed was similar to that of healthy controls (n = 7). The time taken for the two agents to mix at the upper jejunum was 65.8 +/- 7.9 min in the patients after Child's operation, 17.3 +/- 2.5 min in those after Imanaga's operation, and 18.5 +/- 2.8 min in the healthy controls, respectively. Continuous stasis of bile in the proximal loop and severe postcibal asynchronism in patients who undergo Child's operation can therefore cause reflux cholangitis and absorptive disturbances in the long postoperative term. The results of this study suggest that Imanaga's reconstruction is a more physiological procedure than Child's reconstruction following pancreaticoduodenectomy.

Anastomosis, Surgical↗
PubMed1990

Scintigraphic evaluation of aggressive fibromatosis.

Despite its benign microscopic appearance, aggressive fibromatosis has potential to recur and infiltrate neighboring tissues. Therefore, it is necessary to determine the exact extent before therapy. In the present study, 11 cases of aggressive fibromatosis were examined scintigraphically using [99mTc(V)]dimercaptosuccinic acid (11 cases) and 67Ga-citrate (7 cases). Technetium-99m-(V)-dimercaptosuccinic acid demonstrated all lesions, while 67Ga-citrate detected 57% of the cases.

Adult↗
PubMed1989

Assignment of common allele loss in osteosarcoma to the subregion 17p13.

Human osteosarcomas frequently show loss of alleles on chromosome 17 as well as those on chromosome 13 that harbors the retinoblastoma gene, indicating concerted operation of another tumor-suppressing gene on chromosome 17. To assign the affected gene to a defined region of chromosome 17, we performed mitotic recombination/deletion mapping by the use of 10 polymorphic loci on chromosome 17. Of 37 tumors studied, 28 (75.7%) showed loss of heterozygosity on chromosome 17. The affected regions varied among tumors, ranging in extent from a whole chromosome to a distal segment of the short arm. However, allele loss in one region, notably in 17p13 between D17S1 and D17S30, was common to all 28 tumors, suggesting the presence of a tumor-suppressing gene in this defined region.

Alleles↗
PubMed1989

Preferential mutation of paternally derived RB gene as the initial event in sporadic osteosarcoma.

Successive loss of function of both alleles of the retinoblastoma susceptibility gene (RB) on human chromosome 13 seems to be critical in the development of retinoblastoma and osteosarcoma. In cases where the tumour is familial and susceptibility is inherited, a mutation in one of the alleles is carried in the germline. We have recently shown that cytogenetically visible germline mutations are usually in the paternally derived gene. Such a bias would not be expected for sporadic (non-familial) tumours, where both mutations occur in somatic tissue, but there has been some indication of a bias towards initial somatic mutation in the paternally derived gene on chromosome 11 in sporadic Wilms tumour. We have now examined 13 sporadic osteosarcomas and find evidence which indicates that in 12 cases the initial mutation was in the paternal gene, suggesting the involvement of germinal imprinting in producing the differential susceptibility of the two genes to mutation.

Blotting, Southern↗
PubMed1989

Strengthening of bone-implant interface by the use of granule coatings on alumina ceramics.

Three different granule coatings (a granular alumina ceramic coating, a granular hydroxyapatite coating, and a polished granular hydroxyapatite coating) applied to alumina ceramic substrate were evaluated for their strengthening effects of the bone-implant interface in rabbit tibiae. For a comparison, noncoated alumina ceramics, and dense hydroxyapatite were assessed in the same way. The granular alumina ceramic coating, creating a bioinert, porous surface, was most effective due to a strong mechanical bond between the bone and implant. The interface strength was even higher than that of the dense hydroxyapatite. The granular hydroxyapatite coating, creating a bioactive, porous surface, was less effective than the granular alumina ceramic coating because of the brittleness of the hydroxyapatite granules, although it formed a direct and mechanical bond with bone tissue. The polished granular hydroxyapatite coating, creating a bioactive, smooth surface, was least effective because of the brittleness of the hydroxyapatite granules, though it presented an improved interface strength compared with that of the noncoated alumina ceramics due to a direct bond between the bone and hydroxyapatite granules.

Aluminum↗
PubMed1989

The influence of calcium phosphate ceramics and glass-ceramics on cultured cells and their surrounding media.

The cytotoxicity of hydroxyapatite (HA), tricalcium phosphate (TCP), and two types of apatite-containing glass-ceramics designated A.W-GC and A.W.CP-GC was evaluated by the direct contact method using V79 cells. Compatibility of the cells was assessed as a function of cellular attachment and subsequent growth using scanning electron microscopy. Although all of the tested materials have surfaces available for cellular attachment, cell growth was markedly inhibited by HA sintered at 600 degrees C and 900 degrees C, and slightly inhibited by HA sintered at 1200 degrees C, TCP and the glass-ceramics. In attempts to clarify the cause of this toxicity, the interactions of the ceramics with culture medium was assessed by measurement of calcium (Ca), inorganic phosphate (P), magnesium (Mg), pH and albumin content in the medium. The grade of toxicity corresponded to the degree of reduction of Ca, P, and albumin in the medium. Furthermore, surface reactions of the ceramics were demonstrated to vary in both mode and degree depending on their chemical structure and level of microporosity. Thus, the surface reactivity of ceramic materials should be always taken into account in discussing their biocompatibility in vivo.

Animals↗