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Biomedical subjects

T Kokubo

Publications and source records attributed to T Kokubo.

At least 253 records · Page 14Linked to original sources
PubMed1990

A bioactive glass powder-ammonium hydrogen phosphate composite for repairing bone defects.

Bioactive glass powder (AW-G) was made into a rigid compound by mixing with ammonium hydrogen phosphate and was evaluated as a bone-defect filler. The proximal metaphysis of the rat tibia was drilled and packed with (a) polymethyl-methacrylate (PMMA) bone cement, (b) AW-G powder, (c) AW-G powder with ammonium hydrogen phosphate (AW-G)-(A-P), or (d) nothing, as a control. The animals, with different implantation periods up to 24 weeks, were sacrificed and the defective sites were histologically analyzed. The results revealed direct bonding between the bone tissue and the (AW-G)-(A-P). The general inflammatory reaction of (AW-G)-(A-P) was less than that of PMMA bone cement. The compressive strength of (AW-G)-(A-P) implanted subcutaneously into rats was measured chronologically and deterioration did not occur during a period of 24 weeks. The rigidity increased to 1.6 times 6 months after implantation as compared with the initial value. This compound can be used as paste and is transformed into a rigid compound in about 4 min without noticeable elevation of the temperature. Thus, this (AW-G)-(A-P) composite can be used as a bone defect filler, and there is a possibility that it can even be used as a bone cement if higher rigidity can be attained.

Animals↗
PubMed1990

Apatite--wollastonite containing glass ceramic granule-fibrin mixture as a bone graft filler: use with low granular density.

The purpose of this study was to investigate bone formation after implantation of a mixture of apatite--wollastonite containing glass ceramic granules (A-W.GC, 220-355 microns) and fibrin glue with a low A-W.GC granular density. The fibrinogen was prepared from rat blood plasma. A mixture of A-W.GC granules and fibrin glue 1:4 in volume ratio (1:4 mixture) was implanted in the proximal metaphysis of the rat tibia, and bone formation was evaluated quantitatively by histomorphometry in undecalcified specimens. Microangiography was performed in animals sacrificed 5 days after the operation. The results were compared with those of a previous study in which a 1:1 mixture of A-W.GC granules and fibrin glue was used. With the 1:4 mixture, the A-W.GC density was 39.7% because of concentration of fibrin at packing. Good early vascularization comparable to that after implantation of the 1:1 mixture was observed. Bone formation proceeded at the same rate as after implantation of 1:1 mixture, but the level of the plateau was higher than that for the 1:1 mixture. The osteoconductive potential of the 1:4 A-W.GC-fibrin mixture was similar to that of the 1:1 mixture, and was higher than that of A-W.GC without fibrin.

Animals↗
PubMed1990

Mechanical properties of bone after implantation of apatite-wollastonite containing glass ceramic-fibrin mixture.

Mechanical properties of bone implanted with a mixture of apatite-wollastonite containing glass ceramic (A-W.GC) granules and fibrin were examined by compression testing. A 1:1 mixture of A-W.GC granules and fibrin (Group 1), 1:4 mixture of A-W.GC granules and fibrin (Group 2), and 1:1 mixture of hydroxyapatite (HA) granules and fibrin (Group 3) were implanted in the distal femoral metaphyses of rabbits. Histomorphometric analysis suggested that A-W.GC has a greater osteoconductive potential than HA. Trabeculalike structures were observed 24 weeks after the operation in all groups but were most notable in Group 2. Twenty-four weeks after the operation, in Groups 1 and 3, the compressive strength and compressive stiffness were higher than that of normal cancellous bone, and the fracture toughness was comparable with that of normal cancellous bone. In Group 2, all three values were similar to those of normal cancellous bone. Implantation of A-W.GC granules at a low density induces the formation of bone tissue which is similar to normal bone in both mechanical properties and morphology.

Animals↗
PubMed1990

Analysis of A.W glass-ceramic surface by micro-beam x-ray diffraction.

The purpose of this study is to examine the formation of hydroxyapatite on the surface of glass-ceramics (chemical composition: SiO2, 34.2; P2O5, 16.3; CaO, 44.9; MgO, 4.6; CaF2, 0.5 in weight ratio). Two experiments were performed. In the first experiment, plates (2 x 25 x 25 mm) of glass-ceramics containing apatite-wollastonite (designated A.W-GC) were used. In the second experiment, plates (15 x 10 x 2 mm) of A.W-GC and its parent glass (designated G) were used. In each experiment, two paired specimens of identical material, one tied with silk thread, the other not tied, were implanted subcutaneously into rats. In both experiments, bonding to each other of both tied and untied specimens was observed one month after implantation. A pattern resembling hydroxyapatite was identified on the detached surface of the bonded A.W-GC by micro-beam x-ray diffraction. The weak crystalline pattern was also observed on the detached surface of bonded G samples. Analysis of the interface by SEM-EPMA showed that a calcium-phosphorus rich layer formed between the two bonded surfaces in both experiments. It is suggested that the bonding between the two materials was formed by the calcium-phosphorus rich layer, and that the calcium-phosphorus rich layer is virtually identical to hydroxyapatite.

Animals↗
PubMed1990

Ca,P-rich layer formed on high-strength bioactive glass-ceramic A-W.

Glass-ceramic A-W, containing crystalline apatite and wollastonite in a MgO-CaO-SiO2 glassy matrix shows high bioactivity as well as high mechanical strength, but other ceramics containing the same kinds of crystalline phases in different glassy matrices do not show the same bioactivity. In order to investigate the bone-bonding mechanism of this type of glass-ceramic, surface structural changes of the glass-ceramics after exposure to simulated body fluid were analyzed with various techniques. A solution with ion concentrations which are almost equal to those of the human blood plasma was used as the simulated body fluid, instead of Tris-buffer solution hitherto used. For analyzing the surface structural changes, thin-film x-ray diffraction was used in addition to conventional techniques. It was found that a bioactive glass-ceramic forms a Ca, P-rich layer on its surface in the fluid but nonbioactive ones do not, and that the Ca, P-rich layer consists of carbonate-containing hydroxyapatite of small crystallites and/or defective structure. These findings were common to those of Bioglass-type glasses. So, we conclude that the essential condition for glass and glass-ceramic to bond to bone is the formation of the surface apatite layer in the body environment but it is not essential to contain apatite within the material. Bioactivity of glass and glass-ceramic can be evaluated in vitro by examining the formation of the surface apatite layer in the simulated body fluid described above.

Apatites↗
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

Solutions able to reproduce in vivo surface-structure changes in bioactive glass-ceramic A-W.

High-strength bioactive glass-ceramic A-W was soaked in various acellular aqueous solutions different in ion concentrations and pH. After soaking for 7 and 30 days, surface structural changes of the glass-ceramic were investigated by means of Fourier transform infrared reflection spectroscopy, thin-film x-ray diffraction, and scanning electronmicroscopic observations, in comparison with in vivo surface structural changes. So-called Tris buffer solution, pure water buffered with trishydroxymethyl-aminomethane, which had been used by various workers as a "simulated body fluid," did not reproduce the in vivo surface structural changes, i.e., apatite formation on the surface. A solution, ion concentrations and pH of which are almost equal to those of the human blood plasma--i.e., Na+ 142.0, K+ 5.0, Mg2+ 1.5, Ca2+ 2.5, Cl- 148.8, HCO3- 4.2 and PO4(2-) 1.0 mM and buffered at pH 7.25 with the trishydroxymethyl-aminomethane--most precisely reproduced in vivo surface structure change. This shows that careful selection of simulated body fluid is required for in vitro experiments. The results also support the concept that the apatite phase on the surface of glass-ceramic A-W is formed by a chemical reaction of the glass-ceramic with the Ca2+, HPO4(2-), and OH- ions in the body fluid.

Biocompatible Materials↗
PubMed1990

Quantitative study on osteoconduction of apatite-wollastonite containing glass ceramic granules, hydroxyapatite granules, and alumina granules.

The osteoconductive potential of apatite-wollastonite containing glass ceramic (A-W.GC), hydroxyapatite (HA), and alumina (AL) was quantitatively evaluated by implanting them as granules into rat tibiae. The amount of mature bone formed in contact with the ceramics varied depending on the ceramic materials; it reached a plateau earliest in A-W.GC and latest in AL. The bone mass at the interface showed the same results. The osteoconductive potential was suggested to be higher in bioactive ceramics than in bioinert ceramics, and to be related to the formation rate of the surface apatite layer of the bioactive ceramics.

Aluminum Oxide↗
PubMed1990

Prominent meningeal enhancement adjacent to meningioma on Gd-DTPA-enhanced MR images: histopathologic correlation.

To assess tissue changes responsible for enhancement of the meninges adjacent to meningiomas on magnetic resonance (MR) images, the authors correlated the MR imaging characteristics of meningeal lesions seen before and after administration of gadolinium diethylenetriamine-pentaacetic acid (DTPA) with the appearance of these lesions on contrast material-enhanced computed tomographic (CT) images and with histopathologic findings in four patients. Histopathologic examination of meninges showed increased loose connective tissue, hypervascularity, and dilated vessels. There was neoplastic infiltration of the dura mater in two patients but it was restricted to the immediate junction of neoplasm and dura mater, with maximum peripheral extension within 1 mm of the tumor margin. In both patients the meninges were enhanced far beyond the neoplastic infiltration. The other two patients showed no infiltration of dura mater. These findings suggest that pathologic enhancement of meninges adjacent to meningioma after administration of Gd-DTPA mainly represents reactive changes to the neoplasm and does not necessarily indicate neoplastic involvement.

Female↗
PubMed1990

Replacement of the lumbar vertebrae of sheep with ceramic prostheses.

We prepared a prosthesis for the replacement of the lumbar vertebrae of sheep, using apatite- and wollastonite-containing glass-ceramic. The material is stronger than human cortical bone and has the special feature of chemical bonding to bone. Ten sheep underwent replacement of L3 and L4 vertebrae, without bone grafting. The animals were killed at intervals from three months to 27 months after operation, and the interface between the prosthesis and bone was examined radiologically, histologically and crystallographically. Bone bonding with the prosthesis had occurred in half the implants. It took at least one year for bonding to be complete, but an apatite layer on the surface of the prosthesis was observed as early as three months after the operation, suggesting the possibility of much earlier bone bonding if more rigid fixation of the prosthesis had been provided.

Animals↗
PubMed1990

[Transarterial embolization of metastatic pheochromocytoma].

We successfully controlled hypertension of a 48-year-old female by embolizing metastatic pheochromocytoma of the liver. Although transarterial embolization of the hepatic artery was uneventful, the patient soon developed severe hypertension and tachycardia which were controlled medically. Symptoms subsided within 10-20 days. Follow-up CT showed reduction of the liver mass.

Adrenal Gland Neoplasms↗
PubMed1990

[Difference between T1 and T2 weighted MR images in avascular necrosis of the femoral head].

T1 and T2 weighted MR images were compared in 32 hips with avascular necrosis, and the difference between them was discussed. In 27 of 32 hips, abnormal low intensity area in the affected femoral head is smaller in T2 weighted images than in T1 weighted images. The area of low intensity on T1 weighted image and high on T2 weighted image might be granuloma in reactive tissue and surrounding hyperemia. The difference between T1 and T2 weighted images must be taken into consideration especially in determination of the border of affected bone.

Adult↗
PubMed1990

[MR imaging of idiopathic transient osteoporosis of the hip].

Four patients with idiopathic transient osteoporosis of the hip were examined by magnetic resonance imaging (MRI). MRI clearly showed low signal intensity in the affected femoral head on T1-weighted images and high signal intensity on T2-weighted images. After regression of hip pain, MR images became normal. MRI was a useful method for diagnosis and follow-up study of idiopathic transient osteoporosis of the hip.

Adult↗
PubMed1989

Bone bonding behavior of MgO-CaO-SiO2-P2O5-CaF2 glass (mother glass of A.W-glass-ceramics).

In this study, it was found that a Ca-P layer and a Si layer were formed on the interface of the mother glass of apatite-wollastonite containing glass-ceramics (designated AW) and bone tissue. The dissolution of Si, Ca, and P from glass (MgO-CaO-SiO2-P2O5-CaF2) is necessary to form a chemical film (a Si layer and a Ca-P layer). The three kinds of glasses used were 1) a mirror surface of the mother glass (MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, CaF 0.5 weight ratio) of AW (designated G-AW (mirror], 2) an abraded surface of G-AW (designated G-AW (#2000)), 3) a mirror surface SiO2 glass (designated G-Si, 100% SiO2). The glass plates (15 mm x 10 mm x 2 mm) were implanted into the metaphysis of tibia of mature male rabbits for 10 and 25 weeks. The failure load, when an implant detached from the bone or when the bone itself broke, was measured by a detaching test and the interface of glass/bone was observed by SEM-EPMA. Failure loads in G-Si, G-AW (mirror), and G-AW (#2000) 10 weeks after implantation were 0.18 +/- 0.24, 3.06 +/- 1.29, and 2.94 +/- 1.77 kg, respectively. Those in G-Si, G-AW (mirror), and G-AW (#2000) 25 weeks after implantation were 1.30 +/- 1.18, 3.88 +/- 1.06, and 3.55 +/- 1.51, respectively. The failure loads in G-Si vs. G-AW (mirror) and those in G-Si vs. G-AW (#2000) differed significantly (P less than 0.01). There were no significant differences in the failure load according to the surface roughness of G-AW. As shown by SEM-EPMA observation, a Si layer next to G was adjacent to a Ca-P layer next to the bone. The chemical film showed no increase in thickness as time passed. A Ca-P layer did not form on the interface of Si-G and bone.

Biocompatible Materials↗
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↗
PubMed1989

The bonding of glass ceramics to bone.

In this study the bonding behaviour of glass ceramics, containing apatite and wollastonite, to bone tissue is shown to vary depending on the amount of alumina they contain. We have experimented with three types of material: A.W-GC, AW-6 and AW-AL. Rectangular plates were implanted into the tibiae of rabbits. Ten weeks later a segment of bone around the plate was removed for examination, and the load of breaking by traction (failure load) was measured by an autograph. This was lowest for AW-AL and highest for A.W-GC (with AW-6 in between), and the figures differed significantly from each other (P less than 0.01). The interface was examined by a scanning electron micro-analyser and an energy dispersive X-ray micro-analyser (SEM-EPMA) and the reactive zone, the calcium-phosphorus rich layer, was assessed. Silicon and magnesium decreased, the calcium did not change, and the phosphorus increased. The reactive zone of A.W-GC was wider than that of AW-6. A Ca-P rich layer was not present between AW-AL and the bone. It is suggested that the strong bonding between glass-ceramics and bone was made through the formation of the Ca-P rich layer.

Animals↗
PubMed1989

Well-defined, dense and continuously spreading enhancement on single level dynamic CT of the liver: a characteristic sign of hepatic cavernous haemangioma.

The findings of single-level dynamic CT were reviewed in 83 lesions of cavernous haemangioma, 90 lesions of hepatocellular carcinoma, 29 lesions of metastatic tumour and 10 lesions of other hepatic masses in order to see the validity of characteristic findings of hepatic cavernous haemangioma. Well-defined, dense and continuously spreading enhancement (WDCSE) being defined as follows: 1. well-defined contour of enhanced area, 2. the density of maximally enhanced area almost same as that of enhanced vessel and 3. continuously spreading enhancement continuing over 20 seconds, WDCSE was noted definitely in 47 lesions of cavernous haemangioma alone (57%; 77% over 3 cm, 64% between 2 and 3 cm, and 19% under 2 cm in diameter) and, suggestively in 16 lesions of cavernous haemangioma and 4 lesions of hepatocellular carcinoma, but in no lesions of other tumours. WDCSE did not show a high sensitivity for cavernous haemangioma but it had a 100% positive predictive value for the disease. If WDCSE is noticed even in oncology patients with hepatic mass, no further examination may be necessary.

Carcinoma, Hepatocellular↗