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Biomedical subjects

A Takahara

Publications and source records attributed to A Takahara.

15 recordsLinked to original sources
PubMed1992

Effect of soft segment chemistry on the biostability of segmented polyurethanes. II. In vitro hydrolytic degradation and lipid sorption.

A series of segmented polyurethanes (SPUs) with various polyol soft segments was prepared and their hydrolytic degradation and degradation due to lipid sorption was investigated. The hydrolytic degradation of the SPUs was investigated in a papain solution, where it was shown that the SPU based on poly(ethyleneoxide) (PEO) soft segment was susceptible to hydrolytic degradation. X-ray photoelectron spectroscopic (XPS) data suggest dissociation of the urethane linkage by enzymatic degradation. Degradation by lipid sorption was observed for the SPU based on a poly(dimethylsiloxane) (PDMS) soft segment. This is ascribed to the high solubility of lipid in the PDMS segment of the SPU.

Absorption↗
PubMed1991

Effect of soft segment chemistry on the biostability of segmented polyurethanes. I. In vitro oxidation.

A series of segmented polyurethanes (SPUs) containing various polyol soft segments was prepared and their resistance to oxidative degradation was investigated after aging in AgNO3 solution. The SPU with the polyether soft segment showed a large reduction in mechanical strength after exposure to the oxidative environment. Surface cracking was often observed for these specimens. XPS measurements revealed that scission of the ether linkage occurs upon oxidation. The oxidative resistance of SPUs containing aliphatic hydrocarbon soft segments was significantly improved over the poly(tetramethylene oxide) (PTMO) based polyurethane.

Calorimetry, Differential Scanning↗
PubMed1991

Effect of hydrophilic soft segment side chains on the surface properties and blood compatibility of segmented poly(urethaneureas).

Segmented poly(urethaneureas) with hydrophilic side chains were prepared from poly(tetramethylene oxide) (PTMO), 4,4'-diphenylmethane diisocyanate (MDI), ethylene diamine (ED) and a diol with a long hydrophilic side chain comprised of an ethylene oxide-proplene oxide copolymer. The end groups of the hydrophilic chains were either sodium sulfonate or methoxy groups. The state of microphase separation showed a small dependence on the fraction of long-chain hydrophilic diol. Surface analysis by means of static underwater contact angle and dynamic contact angle measurements revealed that the graft chains were at the aqueous interface in the hydrated state. An ex vivo A-V shunt experiment revealed that a more thrombogenic blood-material response was correlated with an increase in the concentration of polymeric hydrophilic side chain incorporation. The polyurethane containing a long chain diol with methoxy end groups exhibited a higher level of thrombogenicity than the similar polymers possessing a sulfonate terminated side chain.

Animals↗
PubMed1991

Effect of surface hydrophilicity on ex vivo blood compatibility of segmented polyurethanes.

The relationship between surface, bulk and ex vivo blood-contacting properties of segmented polyurethanes with various polyol soft segment was investigated. The polyols used in this study were poly(ethylene oxide), poly(tetramethylene oxide), hydrogenated poly(butadiene), poly(butadiene) and poly(dimethylsiloxane). The hard segment of these segmented polyurethanes was composed of 4,4' diphenylmethane diisocyanate and 1,4 butanediol, present at 50 wt%. An experimental polyurethane, Biostable PUR, which has shown excellent biostability, was used in this study. The segmented polyurethanes based on the hydrophobic polyols such as poly(dimethylsiloxane) and hydrogenated poly(butadiene) showed distinct microphase separation between hard and soft segments. X-ray photoelectron spectroscopy revealed the surface enrichment of the hydrophobic component at the air-solid interface. Dynamic contact angle measurements indicated that the poly(dimethylsiloxane)-based segmented polyurethane possessed a hydrophobic surface in water. The poly(dimethylsiloxane)-based segmented polyurethane had the lowest platelet adhesion among the segmented polyurethanes investigated in this study, whilst the platelet deposition on the poly(ethylene oxide)-based polymer increased with time.

Animals↗
PubMed1991

Natriuretic effect of TMB-8 in anaesthetized dogs.

1. Effects of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an inhibitor of intracellular calcium release, on renal function were examined in anaesthetized dogs. 2. Intrarenal arterial infusion of TMB-8 (0.03 and 0.1 mg/kg per min) increased urine flow rate, urinary sodium excretion and fractional excretion of sodium without affecting blood pressure, renal blood flow or glomerular filtration rate. 3. The results suggest that TMB-8 inhibits tubular sodium reabsorption to induce natriuresis.

Animals↗
PubMed1991

Surface properties and platelet reactivity of segmented poly(etherurethanes) and poly(etherurethaneureas).

Segmented poly(etherurethanes) (SPUs) and segmented poly(etherurethaneureas) (SPUUs) with various hard and soft segment components were prepared. The surface characterization of SPUs and SPUUs in the air-equilibrated state and in the hydrated-state was carried out by means of X-ray photoelectron spectroscopic (XPS) and dynamic contact angle measurements. XPS revealed that in the air-equilibrated state, lower surface free energy components were enriched at the air-solid interface, whereas in the hydrated-state higher surface free energy components were enriched at the water-solid interface. The change in environment from air to water induced the surface reorganization in order to minimize interfacial free energy. The large contact angle hysteresis was observed for SPUs and SPUUs. This hysteresis can be mainly ascribed to the surface reorganization process. Platelet adhesion tests on SPU and SPUU surfaces indicated that the existence of surface microphase separated structure played an important role in the attainment of blood compatibility.

Adsorption↗
PubMed1991

[A case of left coronary ostial obstruction due to syphilitic aortitis].

Coronary ostial stenosis is a rare lesion, which is a complication of syphilitic aortitis, Takayasu's aortitis, aortic valve disease, and familial hypercholesterolemia. We present a case of left coronary ostial obstruction due to syphilitic aortitis. A 67 years old man was admitted to our hospital for evaluation of a ten year history of angina on exertion. On physical examination, the only abnormal finding was a grade 2/6 high-pitched diastolic murmur. Coronary risk factor was not detected from biochemical results, but both the TPHA and FTA-ABS test were positive. Treadmill stress test showed more than 2 mm ST segment depression associated with chest pain. Coronary angiography revealed complete obstruction of left coronary ostium with good collaterals from the right coronary artery. The coronary arterial tree was otherwise normal. Furthermore, aortagraphy showed a moderate degree of aortic regurgitation. From the examination of previous reports including our own case, we think that the angiographic features of syphilitic coronary ostial stenosis can be summarized as below. 1. Coronary artery stenosis is generally limited to the ostium. 2. The grade of stenosis almost always shows more than 90% stenosis, and sometimes bilateral coronary ostium can be affected. 3. Aortic regurgitation is frequently noted, associated with coronary ostial stenosis.

Aged↗
PubMed1990

Effects of a novel Ca2+ entry blocker, CD-349, and TMB-8 on renal vasoconstriction induced by angiotensin II and vasopressin in dogs.

The effects of a Ca2+ entry blocker CD-349 and an intracellular Ca2+ release inhibitor TMB-8 on renal vasoconstriction induced by angiotensin II (ANG II) and arg-vasopressin (AVP) were examined in anesthetized dogs. Intrarenal bolus injection of ANG II (3-10 ng/kg), AVP (5-20 ng/kg) or a Ca2+ entry promotor Bay K 8644 (0.1-0.4 micrograms/kg) produced a dose-dependent decrease in renal blood flow (RBF). Intrarenal infusion of CD-349 (0.03-0.3 micrograms/kg/min) suppressed the RBF responses to ANG II, AVP, and Bay K 8644. The RBF responses to ANG II and AVP were augmented slightly by intrarenal infusion of Bay K 8644 (0.3 micrograms/kg/min). Intrarenal infusion of TMB-8 (0.03-0.1 mg/kg/min) also suppressed the RBF responses to ANG II and AVP, whereas it did not affect the RBF response to Bay K 8644. These results suggest that vasoconstriction induced by ANG II or AVP is mediated both by the influx of Ca2+ through dihydropyridine-sensitive Ca2+ channels and the release of Ca2+ from TMB-8-sensitive Ca2+ pools in the in vivo dog kidney.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

Surface molecular mobility and platelet reactivity of segmented poly(etherurethaneureas) with hydrophilic and hydrophobic soft segment components.

Segmented poly(etherurethaneureas) (SPUUs) with hydrophilic and hydrophobic polyether components were prepared. The surface chemical composition of SPUUs in various environments was investigated by means of X-ray photoelectron spectroscopic and dynamic contact angle measurements. These measurements revealed that in a hydrated state, the higher surface free energy component is enriched on the surface of the SPUU in order to minimize the interfacial free energy between water and the solid surface. The surface molecular mobility showed a strong correlation with bulk molecular motion. Platelet adhesion tests and dynamic contact angle measurements after adsorption of bovine serum albumin revealed that the surface of SPUUs with hydrophilic soft segments has a non-adhesive nature. The platelet reactivity of hydrophobic SPUUs is influenced by microphase separation at the surface.

Biocompatible Materials↗
PubMed1985

Effect of aggregation state of hard segment in segmented poly(urethaneureas) on their fatigue behavior after interaction with blood components.

Characterization of microphase separated structure, interaction with blood components, such as lipids, and fatigue behavior after immersion in blood components were carried out for segmented poly(urethaneureas). The materials studied were Biomer and segmented poly(urethaneurea) (TU-Mn) composed of hard segment with 4,4'-diphenylmethane diisocyanate (MDI)-ethylenediamine (EDA) or 4,4'-diaminodiphenylmethane (DAM) and soft segment with MDI-polytetramethylene glycol (PTMG) [Mn of 856, 1350, and 2000]. Small-angle x-ray scattering, wide-angle x-ray diffraction, and dynamic viscoelastic measurements revealed that these materials showed the state of microphase separation. TU-Mn with PtMG of Mn = 856 shows the partial phase mixing between hard and soft segments, and phase separation was improved with an increase of Mn of PTMG. Biomer has the characteristics of stronger aggregation of hard segment than that of TU-Mn. All the specimen showed lipid absorption, but the amount of absorption decreased remarkably after precoating on the specimen surface with serum albumin. Lipid absorption of the specimen was confirmed by dynamic viscoelastic and IR measurements. In the case of segmented poly(urethaneurea) which did not immersed in lipids solution, their fatigue strength are sufficient for application to artificial heart systems. However, fatigue strength of the TU-Mn series was decreased drastically after absorption of lipids. On the other hand, Biomer did not show a decrease of fatigue strength after lipid absorption. The reduction of fatigue strength in the TU-Mn series after lipid absorption will be attributed to the weak aggregation of hard segment domain. This reduction of fatigue strength in the TU-Mn series is characterized by formation of microcrack and mirror zone in fatigue fractured specimen. As the precoating of the specimen surface with serum albumin inhibits the absorption of lipids, the reduction of fatigue strength was not observed for the specimen precoated with serum albumin even after immersing the TU-Mn series in lipids solution for 96 days.

Absorption↗
PubMed1985

Decrease of plasma sulfur amino acids in essential hypertension.

In order to evaluate the correlation between sulfur amino acids (derived mainly form animal protein in the diet) and blood pressure, free amino acids, including sulfur amino acids such as taurine and methionine, were determined in the plasma and cerebrospinal fluid (CSF) of twelve normotensive subjects and twelve patients with essential hypertension under nutritional control after at least 10 days of standard hospital diet (total calorie and protein content: 2100-2300 Cal per day and 78-83 g per day, respectively). The results obtained were as follows: plasma taurine, serine, methionine and threonine were significantly lower in patients with essential hypertension than in normotensive patients. The levels of plasma taurine, serine, methionine and total sulfur amino acids in individuals correlated inversely to systolic blood pressure. No difference was observed in the CSF levels of free amino acids in normotensive and hypertensive patients. As taurine, methionine and serine are involved in the metabolism of sulfur amino acids, these observations support the view that the decrease in plasma sulfur amino acids may be a factor contributing to elevated blood pressure.

Adult↗