Biomedical subjects

T Akutsu

Publications and source records attributed to T Akutsu.

184 records · Page 11Linked to original sources

PubMedDate not supplied

A new amphiphilic block co-polymer with improved elastomeric properties for application in various medical devices.

The authors have demonstrated that an amphiphilic block co-polymer composed of 2-hydroxyethyl methacrylate (HEMA) and styrene (HEMA-st) showed excellent blood compatibility in in vitro, ex vivo, and in vivo experiments. The poor elastomeric properties of HEMA-st, however, have been an obstacle to its wider application in medical devices. To improve the mechanical properties of HEMA-st, the authors have developed a new amphiphilic block co-polymer composed of HEMA and octylstyrene (HEMA-oct). The size and morphology of the microdomain structures of HEMA-oct observed by transmission electron microscopy were similar to those of HEMA-st. Kink resistance tests showed improved elastomeric properties of HEMA-oct over HEMA-st. The blood compatibility of HEMA-oct was evaluated using an in vitro flow cell system combined with an epifluorescent video microscope, in which real time platelet adhesion and activation in whole blood can be observed and quantified, and ex vivo rabbit A-A shunt experiments. HEMA-st and a polyurethane (Pellethane 2363-80AE) were used for comparison. In a flow cell system, both HEMA-st and HEMA-oct showed minimal platelet coverage on the surfaces and less platelet activation as measured by beta-thromboglobulin (beta-TG), whereas Pellethane showed a considerable amount of platelet coverage with high beta-TG production. A-A shunt occlusion times were 309 +/- 31.2 min for HEMA-st, 251 +/- 47.7 min for HEMA-oct, and 30 +/- 3.4 min for Pellethane.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

Comparative blood compatibility of polyether vs polycarbonate urethanes by epifluorescent video microscopy.

The segmented polyether urethanes (PEUs) have been used in implantable medical devices due to excellent mechanical properties, acceptable blood compatibility, and good biostability. However, recent studies demonstrate that the polyether soft segment of PEU is susceptible to oxidative degradation in vivo due to scission of the polyether group. Recently, polycarbonate urethanes (PCUs) having no ether linkage in the soft segment have been developed, and show improved stability against oxidative degradation over PEUs. The current study evaluates blood compatibility of these PCUs in comparison with PEUs using epifluorescent video microscopy (EVM) combined with a parallel plate flow cell. The authors selected two PCUs, Corethane 80A (Corvita Corporation, Miami, FL) and PCU(1560), and two PEUs, Pellethene 2363-80AE (Dow Chemical Japan, Tokyo, Japan) and Tecoflex EG80A (Thermedics, Inc., Woburn, MA), all of which have similar hard segment compositions (MDI or HMDI:1,4-butanediol(BD)) and the same hardness of 80A. The EVM measured the amount of platelet coverage on the surfaces using human whole blood perfused at a wall shear rate of 100/sec for 20 min. Complement activation (C3a) also was measured. Both PEUs, especially Pellethane, showed significantly higher platelet adhesion than the PCUs (p < 0.05). There were no significant differences in platelet adhesion between the two PCUs. As for C3a measurements, Tecoflex showed higher complement activation than the others. Based on these results, it is recommended that PEUs should be replaced by ether free PCUs for use in implantable blood contacting devices such as artificial hearts and pacemaker lead insulators.

Biocompatible Materials↗

PubMedDate not supplied

More than 1 year continuous operation of a centrifugal pump with a magnetically suspended impeller.

The authors have been developing a centrifugal pump with a magnetically suspended impeller (MSCP) designed for total artificial heart and long-term ventricular support. The MSCP consists of a magnetic bearing, an impeller and housing, and a driving motor. The impeller is suspended by a magnetic bearing, therefore providing contact free rotation of the impeller inside the pump. This study was designed to evaluate long-term durability and nonthrombogenicity of the MSCP in a chronic sheep model. The blood contacting surfaces of the pump and conduits were completely modified by a heparin immobilization technique (Hepaface). The MSCP was placed paracorporeally as a left heart bypass between left ventricle and descending aorta in three adult sheep. Coumadin was given orally to maintain prothrombin time at 15-20 sec. The coagulation and hematologic parameters, including plasma free hemoglobin, were periodically monitored throughout the experiment. Under daily movement in the cage, the pump could produce average flow rates of 3-6 L/min (50-100 ml/kg) at 1,700-2,000 rpm. Although the arterial pulse contour decreased, there was no physiologic deterioration. The axial impeller excursion monitored by a position sensor was < 25 microns. Plasma free hemoglobin level remained at < 5 mg/dl throughout the experiment. There was no increase in the motor current, which indicates no massive thrombus formation around the impeller. One experiment was terminated at 70 days due to Hall sensor dysfunction of the motor. The retrieved pump was entirely free from thrombus formation. There was no detectable thrombus formation inside the pump or the inflow and outflow conduits. Hematologic, renal, and hepatic parameters remained within the normal range throughout the experiment. The other two sheep have survived for more than 395 and 41 days without major complication. These studies demonstrated that the MSCP has significant potential for long-term use.

Animals↗

PubMedDate not supplied

Modification of measurement of effective renal plasma flow from blood pool clearance curve of I-123-orthoiodohippurate using single blood sampling.

The methods of measuring effective renal plasma flow (ERPF) based on the two-compartment analysis of plasma clearance of I-123-orthoiodohippurate (OIH) disregard the distribution of I-123-OIH to erythrocytes, resulting in over-estimation of ERPF. In this study, a new simple modification was established to obtain accurate ERPF. Intercompartmental clearance rates among plasma, erythrocytes, and extracellular fluid were determined through in vitro and in vivo experiments to enable the three-compartment analysis of plasma clearance curves of I-123-OIH using multiple blood samplings in comparison with the two-compartment analysis. Multiplying renal blood flow derived from two-compartment analysis of the whole blood clearance curve by (1-hematocrit/100) was a new modification for measuring ERPF to reduce the complexity of three-compartment analysis and to supplement the distribution of I-123-OIH to erythrocytes. Comparing ERPF derived from the modified two-compartment analysis with that from three-compartment analysis demonstrated good agreement (r = 0.883, p = 0.001) between the two methods. ERPF derived by this new method was also compared with the clearance of paraaminohippurate (PAH), resulting in a regression line which was much closer to unity and a better correlation between them (r = 0.926) than that between PAH clearance and ERPF (r = 0.909) derived from conventional two-compartment analysis.

Erythrocytes↗