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C Nojiri

Publications and source records attributed to C Nojiri.

66 records · Page 4Linked to original sources
PubMedDate not supplied

Results of chronic animal experiments with a new version of a magnetically suspended centrifugal pump.

We have developed a magnetically suspended centrifugal pump (MSCP) for long-term ventricular support. This study reports results of chronic animal experiments using a new version of the MSCP. Three sheep weighing 50-70 kg were used in this study. A left heart assist system was established with cannulas into the descending aorta and the left ventricular apex. In two sheep the MSCP was positioned outside the body and in one sheep implanted on the chest wall. The pumping flow was estimated by the motor current and motor speed. The temperature of the pump and the muscle near the pump was recorded for 10 days after operation. The duration of continuous pumping was 60, 140, and 230 days+ (ongoing), respectively. The cause of termination was infection associated with thrombus formation in the first, and failure of magnetic suspension in the second sheep. No thrombus or embolus was observed after sacrifice of the second sheep. The third sheep has been going well despite skin necrosis around the pump pocket. The estimation of pumping flow was reliable even at 140 days. Temperature of the pump surface was 42 degrees C immediately after the operation and gradually reduced to 41 degrees C. The MSCP is a reliable pump for long-term circulatory assist.

Animals↗
PubMedDate not supplied

Recent progress in the development of Terumo implantable left ventricular assist system.

The research group of the Terumo Corporation, the NTN Corporation, and Setsunan University (T. Akamatsu) has been developing an implantable left ventricular assist system (ILVAS) featuring a centrifugal blood pump with a magnetically suspended impeller (MSCP). The impeller of the MSCP is suspended by a magnetic bearing, providing contact-free rotation of the impeller inside the pump housing. Thus the MSCP is expected to provide years of long-term durability. Ex vivo chronic sheep experiments using the extracorporeal model (Model I) demonstrated long-term durability, nonthrombogenicity, and a low hemolysis rate (plasma free Hb <6 mg/dl) for more than 2 years. The prototype implantable model (Model II; 196 ml, 400 g) was evaluated ex vivo in 2 sheep and intrathoracically implanted in a small sheep (45 kg). These experiments were terminated at 70, 79, and 17 days, respectively, because of blood leakage through the connector system within the housing of Model II. There was no thrombus formation on the retrieved pump surfaces. A new connector system was introduced to the Model II pump (modified Model II), and the pump was intrathoracically implanted in a sheep. Pump flow rate was maintained at 3-7 L/min at 1700-1800 rpm. The temperature elevation on the surfaces of the motor and the electromagnet inside the pump casing was kept less than 6 degrees C. The temperature of the tissue adjacent to the pump casing became normal 10 days postoperatively. The sheep survived for more than 5 months without any sign of mechanical failure or thromboembolic complication. In vitro real-time endurance tests of motor bearings made of stainless steel and silicone nitride have been conducted for more than 1 year without any sign of bearing wear. The next prototype system (Model III), with an implantable controller and a new MSCP with reduced input power, has been developed with a view toward a totally implantable LVAS.

Alanine Transaminase↗
PubMedDate not supplied

Improved blood compatibility of DLC coated polymeric material.

There is currently an increasing interest in the use of DLC (diamond like carbon) films in biomedical applications. These investigations making use of DLC in the biomedical area indicate its attractive properties. In this study, we succeeded in depositing DLC on polymer substrates and found the best conditions and method for this application. We evaluated the blood compatibility of polycarbonate substrates coated by DLC (PC-DLC) under different conditions by using epifluorescent video microscopy (EVM) combined with a parallel plate flow chamber. Segmented polyurethane (SPU), which has been used to fabricate medical devices including an artificial heart, and proven to have acceptable blood compatibility, was compared with polycarbonate substrates coated with DLC film. The EVM system measured platelet adhesion on the surface of the DLC, by using whole human blood containing Mepacrine labeled platelets perfuse at a wall shear rate of 100 s(-1) at 1 min intervals for a period of 20 min. PC-DLC demonstrated that Tecoflex showed higher complement activation than PC-DLC. There were significant differences between the PC-DLC substrates. On the basis of these results, it is recommended for use as a coating material in implantable blood contacting devices such as artificial hearts, pacemakers, and other devices. This DLC seems to be a promising candidate for biomaterials applications and merits further investigation.

Carbon↗
PubMedDate not supplied

In vivo nonthrombogenicity of heparin immobilized polymer surfaces.

The authors developed two different methods to immobilize heparin on polymer surfaces. One method involves in situ heparin immobilization on a segmented polyurethane urea (Biomer) surface via hydrophilic poly(ethylene oxide) (PEO, Mn = 4,000) spacers. The other method uses PEO/poly(dimethylsiloxane) (PDMS) block co-polymer and heparin covalently linked in a block co-polymer system (PEO-PDMS-Hep). These surfaces have demonstrated high heparin bioactivity in vitro and excellent blood compatibility in in vitro-ex vivo experiments. This report evaluates the long-term in vivo blood compatibility of these heparin immobilized surfaces. Vascular grafts (6 mm ID, 7 cm in length) were fabricated with Biomer, and heparin was immobilized in situ with PEO spacers (B-PEO4K) and coated on their luminal surfaces with PEO-PDMS-Hep. Biomer and PEO (Mn = 4,000) grafted Biomer (B-PEO4K) were used as controls. The grafts were implanted in the abdominal aorta of dogs and retrieved at 3 months or when graft occlusion was suspected. Retrieved grafts were evaluated with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM measured the thickness of the adsorbed protein layer on the surface and the protein distribution (albumin, fibrinogen, and IgG) visualized by an immunogold method. All heparin immobilized grafts were patent at 3 months, whereas Biomer and B-PEO4K grafts occluded within 1 month. SEM pictures of heparin immobilized surfaces after 3 months demonstrated minimal platelet adhesion and activation without detectable fibrin formation. Heparin immobilized surfaces showed a thin protein layer (300-600 A) even after 3 months, with high concentrations of albumin and IgG and less fibrinogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Suppression mechanisms for thrombus formation on heparin-immobilized segmented polyurethane-ureas.

Heparin-immobilized segmented polyurethane-ureas (Biomer, Ethicon Co., Somerville, NJ) containing long poly(ethylene oxide) spacers (Mn = 4,000) have shown excellent nonthrombogenic properties through enhanced heparin bioactivity in vitro. In this study, three different surfaces, Biomer (B), PEO-grafted Biomer (B-PEO) and heparin-immobilized Biomer with PEO spacers (B-PEO-Hep), were investigated, using a rabbit A-A shunt model. Occlusion times, at various flow rates (2.5, 5.0, 7.5, and 15.0 ml/min) were measured using surface modified tubings (1.5 mm ID, 30 cm length) inserted into rabbit carotid arteries. Platelet count, aggregability, and activated partial thromboplastin time (aPTT) were measured with whole blood to observe systemic effects in ex vivo experiments. For Biomer and B-PEO, occlusion times were prolonged with an increasing flow rate, while platelet count and aggregability decreased. B-PEO showed prominent prolongation of occlusion time at flow rates over 5.0 ml/min with decreased platelet count and aggregability, indicating surface-induced platelet activation and systemic thromboembolization possibly caused by the presence of PEO. In contrast, B-PEO-Hep surfaces showed the longest and relatively flow-rate-independent occlusion times without detectable platelet activation. We concluded that the improved ex vivo blood compatibility of B-PEO-Hep, compared with Biomer and B-PEO, is due to the prevention of fibrin net formation by immobilized heparin, resulting in a reduction in fibrin related platelet aggregation and subsequent thrombus formation.

Animals↗
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↗