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Biomedical subjects

B Min

Publications and source records attributed to B Min.

53 records · Page 3Linked to original sources
PubMed1994

Fluid dynamic study of the moving actuator type total artificial heart by image-processing technique.

Flow velocity inside the artificial ventricle of a moving actuator type total artificial heart is investigated by the image-processing technique. Optical flow is estimated from two sequential images of flow patterns to find flow-velocity distribution. The region with high velocity inside the artificial ventricle is found from the estimated flow-velocity distribution. Fluid velocity in a simple glass conduit is analysed and can be estimated by calculating optical flow.

Blood Flow Velocity↗
PubMed1993

Different stroke volumes for the left and right ventricles in the moving-actuator type total artificial heart.

A new electromechanical moving-actuator type total artificial heart (TAH) has been developed to solve the imbalance problem without an extra compliance chamber. A different stroke volume was achieved by the large left sac size and the asymmetry of the actuator motion referred to the center position. The left ventricle consists of a double sac with the outer sac attached to the actuator providing active diastolic filling, while the double sac of the right ventricle being free from the actuator, and having sufficient suction produced due to the rigid pump housing. The stroke volume difference between the left and right sac is compensated through the air in the interventricular space of the variable volume (VV) space. Computer simulation based on the geometrical relationships between the blood sacs and the actuator was performed to simulate the physical mechanisms of the moving-actuator type TAH. Results were then compared with the measured pressure changes in various chambers of the pump and the stroke volume differences in mock circulation test. In two acute calf experiments, the balanced left and right atrial pressures were achieved in the moving-actuator type TAH without an extra compliance chamber.

Animals↗
PubMed1992

Positive and negative cis-acting regulatory elements mediate expression of the mouse vascular smooth muscle alpha-actin gene.

Segments of the 5'-flanking region of the mouse vascular smooth muscle alpha-actin gene were assayed for promoter activity in transfected mouse BC3H1 myogenic cells and AKR-2B embryonic fibroblasts. The region between -150 and -191 that functions as a positive transcriptional element in myogenic and fibroblastic cells contains a mammalian-specific inverted CC(A/T)6GG-type consensus sequence. Expression was restricted to fully differentiated myogenic cells when an additional sequence spanning -191 to -224 was included in reporter gene constructs. This 33-base pair (bp) negative regulatory element is 70% conserved between the mouse and human genes and contains a 10-bp motif at its 3' end that only partially resembles a CC(A/T)6GG element. Retention of a GGGA motif at the 3' boundary of the 33-bp region is sufficient to maintain full transcriptional repression in fibroblasts and is partly responsible for repression in undifferentiated myoblasts. Complete muscle tissue-restrictive expression requires an additional 8 bp from the CC(A/T)6GG-like element immediately 5' to the GGGA motif, since replacement of this region with an unrelated 10-bp sequence completely eliminated restrictive transcriptional behavior in undifferentiated myoblasts. The distal portion of the 5'-flanking region between -224 and -1074 contains six E-box motifs (CANNTG) and mediates high level transcription only in postconfluent BC3H1 myoblasts. Analysis of reporter gene constructs including either the proximal E-box at -240 or all six E-boxes indicate that the five distal E-boxes are not required for high level transcription. A 724-bp segment of the 5'-flanking region consisting of the proximal E-box flanked upstream by a mammalian-specific 352-bp region was sufficient for maximal transcriptional activation in postconfluent BC3H1 myoblasts. Deletion of the 352-bp region restricts the early transcriptional response to high cell density in temporal studies of promoter activity during BC3H1 myogenic cell differentiation.

Actins↗
PubMed1992

Density-dependent modulation of vascular smooth muscle alpha-actin biosynthetic processing in differentiated BC3H1 myogenic cells.

The expression of vascular smooth muscle (VSM) alpha-actin mRNA during BC3H1 myogenic cell differentiation is specifically stimulated by conditions of high cell density. Non-proteolytic dissociation of cell-cell and cell-matrix contacts in post-confluent cultures of BC3H1 myocytes using EDTA promotes loss of the differentiated morphological phenotype. EDTA-dispersed myocytes exhibit an undifferentiated fibroblastoid appearance and contained reduced levels of both VSM and skeletal alpha-actin mRNA. Muscle alpha-actin mRNA levels in EDTA-dispersed myocytes were not restored to that observed in confluent myocyte preparations by experimental manipulation of cell density conditions. Pulse-labeling techniques using L-[35S]cysteine to identify muscle actin biosynthetic intermediates revealed that EDTA-dispersed myocytes expressed nascent forms of both the VSM and skeletal muscle alpha-actin polypeptide chains. However EDTA-dispersed myocytes were less efficient in the post-translational processing of immature VSM alpha-actin compared to non-dispersed myocytes. Simple cell-to-cell contact may mediate VSM alpha-actin processing efficiency since high-density preparations of EDTA-dispersed myocytes processed more VSM alpha-actin intermediate than myocytes plated at low density. The actin isoform selectivity of the response to modulation of intercellular contacts suggests that actin biosynthesis in BC3H1 myogenic cells involves mechanisms capable of discriminating between different isoform classes of nascent actin polypeptide chains.

Actins↗
PubMed1992

Nucleotide sequence of the cDNA encoding the common alpha subunit of the chicken pituitary glycoprotein hormones.

Recombinant cDNA clones that encode the alpha subunit of the chicken pituitary glycoprotein hormones were isolated from a pituitary library. The longer of the two cDNA clones that were sequenced was 754 bp in length. It contained 81 nucleotides of the 5'-untranslated region (UTR), an open-reading frame of 360 bp that encoded a 24 amino acid leader polypeptide sequence as well as the 96 amino acid mature alpha subunit, and 268 nucleotides of the 3'-UTR, followed by a 45 bp poly(A) tract. There was 69-79% homology between the nucleotide sequence of the coding region for the chicken and mammalian alpha-subunit cDNAs. Northern blot analysis revealed that the steady-state levels of an approximately 800 bp alpha-subunit specific transcript increased quantitatively when dispersed chicken pituitary glands were treated in culture with chicken gonadotrophin-releasing hormone-I.

Amino Acid Sequence↗
PubMedDate not supplied

Effect of shear rates on protein adsorption in the total artificial heart.

Plasma protein adsorption is the first event in blood-material interaction and influences subsequent platelet adhesion and thrombus formation. Thromboembolic events are strongly influenced by surface characteristics of materials and fluid dynamics inside the blood pump. In vitro flow visualization, and an animal experiment with a moving actuator total artificial heart (TAH), were performed to investigate fluid dynamic effects on protein adsorption. The different levels of shear rate inside the ventricle were determined by considering the direction of opening of the four heart valves in the implanted TAH, and the visualized flow patterns as well. Each ventricle of the explanted TAH was cut into 12 segments according to the shear rate level. The adsorbed protein on each segment was quantified using an ELISA method after soaking in 2% (w/v) SDS/PBS for 2 days. Adsorbed protein layer thicknesses were measured by the immunogold method under transmission electron microscopy. Scanning electron microscopic observation showed that the right ventricle, immobilized with albumin, displayed different degrees of platelet adhesion on each segment, whereas the left ventricle, coated with polythyleneoxide-sulfonate, indicated nearly the same platelet adhesion behavior, regardless of shear rates. The surface concentrations of adsorbed proteins in the low shear rate region are higher than those in the high shear region, which was confirmed statistically.

Adsorption↗
PubMedDate not supplied

Albumin immobilized polyurethane and its blood compatibility.

Surface pretreatment with albumin on a blood contacting material inhibits platelet adhesion, activation, and subsequent thrombus formation. Although adsorbed albumin improves blood compatibility, rapid desorption occurs when this surface is exposed to circulating blood. In this study, human serum albumin was immobilized on a polyurethane (PU) surface to investigate its blood compatibility and extended effects on a blood-material interface. The PU surface was treated with hexamethylene diisocyanate (HMDI), and the PU-HMDI was further grafted with albumin to produce an albumin immobilized PU surface (PU-albumin). The PU-albumin surface was characterized by attenuated total reflection infrared electron spectroscopy for chemical analysis, scanning electron microscopy, and dynamic contact angle. Blood compatibility was evaluated by in vitro protein adsorption, platelet adhesion, and occlusion time in an ex vivo rabbit arterio-arterial shunt. Immobilization of albumin was confirmed by the disappearance of the -NCO peak observed at 2,250 cm-1 on the PU-HMDI surface by infrared spectroscopy and the existence of sulfur atomic percent by electron spectroscopy for chemical analysis. The concentration of PU-albumin was approximately 5.8 micrograms/cm2. The PU-albumin also showed a slight increase in hydrophilicity on the Wilhelmy plate method, and there was less fibrinogen adsorption than a PU control. In addition, PU-albumin had less platelet adhesion, platelet activation, and thrombogenicity. The ex vivo occlusion time of untreated PU was 50 min, that of PU-albumin was extended to 150 min, indicating that a PU-albumin surface has better blood compatibility than PU alone.

Adsorption↗
PubMedDate not supplied

Anti-infection treatment of a transcutaneous device by a collagen-rifampicine composite.

The polyurethane surface of a transcutaneous energy transmitter, which is implanted into a subcutaneous pouch for a total artificial heart, was coated with a Type I atelocollagen and rifampicine composite to prevent the infection that frequently occurs in the interfacial space between the tissue and the device. The specimen obtained after 7 weeks from a transcutaneous energy transmitter placed in a dorsal subcutaneous pouch of a dog revealed noninfected but well-attached dermal tissue without specific epithelial down-growth around the transcutaneous energy transmitter surface at the pouch-orifice area. The transcutaneous energy transmitter implanted in the pouch adhered well to the subcutaneous tissues. The collagen matrix seemed to have provided a favorable environment for the regenerating dermal tissue to obstruct the interfacial space. The coated collagen-antibiotic composite was degraded.

Animals↗
PubMedDate not supplied

Antithrombotic activity of a lumbrokinase immobilized polyurethane surface.

Six fractions of strong and novel fibrinolytic enzymes (lumbrokinase, LK) were extracted from the earthworm Lumbricus rubellus. The enzymes in these fractions appeared to be very stable and showed greater antithrombotic activity than other currently used antithrombotics. The authors immobilized an LK fraction that shows the most potent fibrinolytic activity on a polyurethane (PU) surface to investigate its enzymatic and antithrombotic activity. The methanol extracted PU surface was treated with a 3% (wt/vol) maleic anhydride methylvinyl ether copolymer (MAMEC) solution and finally incubated in an LK solution in PBS (pH 7.4). The immobilized LK activity was estimated by the fibrin plate method and caseinolytic activity assay. The antithrombotic activity was evaluated by in vitro 125I-fibrinogen adsorption in fresh whole blood and 99mTc platelet adhesion tests. In addition, the occlusion time was determined through ex vivo rabbit A-A shunt experiments. The content and unit activity of immobilized LK were found to be 24 micrograms/cm2 and 18 IU/cm2, respectively. The relative activity ratio of immobilized LK to soluble LK was found to be approximately 34%. Immobilized LK was stable within a various pH range and resistant to inhibitors and thermal inactivation. Less fibrinogen was adsorbed and fewer platelets adhered on an LK-immobilized surface than on PU and PU-MAMEC controls. The ex vivo occlusion time of untreated PU and PU-MAMEC surfaces were only 32 and 42 minutes, respectively. But that of LK-immobilized PU was extended to 140 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗