Shuzo Yamashita

Model polypeptide of mussel adhesive protein. I. Synthesis and adhesive studies of sequential polypeptides (X‐Tyr‐Lys)n and (Y‐Lys)n

The sequential polytripeptides and polydipeptides, (X-Tyr-Lys)n, (XGly, Ala, Pro, Ser, Leu, Ile, Phe), (Y-Lys)n, (YGly, Tyr), and (Gly-Tyr)n, which imitate a mussel adhesive protein, have been synthesized. The molecular weights of the polypeptides were estimated to be 7,200 ∼ 13,400 (19 ∼ 42 repeating units), and the polypeptides were found to have satisfactory amino acid sequences. The polypeptides were crosslinked by tyrosinase, and the optimal pH in the crosslinking reaction was 7.4 in the case of the polytripeptide, (Gly-Tyr-Lys)n. The optimal tyrosinase amount for the adhesive strength of (Gly-Tyr-Lys)n was 0.34 unit/mg (polypeptide) at pH 7.4. The shear adhesive strength of the polytripeptide increased with an increase in the polytripeptide concentration, and was not influenced by the third amino acid, X. The shear adhesive strengths of polytripeptides (X-Tyr-Lys)n were equal to one of the synthetic polydecapeptides, (Ala-Lys-Pro-Ser-Tyr-Pro-Pro-Thr-Tyr-Lys)n and (Gly-Pro-Lys-Thr-Tyr-Pro-Pro-Thr-Tyr-Lys)n which were the model polydecapeptides for blue mussel and Californian mussel, respectively.

Polyether-segmented nylon hemodialysis membranes. I. Preparation and permeability characteristics of polyether-segmented nylon 610 hemodialysis membrane

The effect of the coagulation condition in the phase inversion method on the permeability characteristics of poly(propylene oxide) or poly(tetramethylene oxide)-segmented nylon 610 (PPO-Ny610 or PTMO-Ny610) hemodialysis membranes, the stability of the membrane performance, and the mechanical strength were investigated. The polymers were dissolved in a solvent such as formic acid and methanol saturated with calcium chloride, and thus PPO-Ny610 and PTMO-Ny610 membranes were prepared using formic acid and a calcium chloride/methanol/water mixture as a polymer solvent and a coagulant, respectively. It is concluded that PPO-Ny610 membrane has better permeability characteristics than PTMO-Ny610 membrane, and possesses additional properties for hemodialysis membranes such as mechanical properties and permeability stability in the drying and sterilizing processes. Furthermore, the blood compatibilities of PPO-Ny610 and PTMO-Ny610 membranes were superior to regenerated cellulose membranes on the basis of the result of platelet adhesion test.

Laser‐irradiation‐induced surface graft polymerization method

A laser-induced surface graft polymerization method is reported in which surface radicals generated upon laser irradiation initiated radical polymerization. The radical concentrations generated upon excimer laser irradiation under vacuum on poly-(ethylene terephthalate) film surfaces were measured using a radical scavenger, 1,1-diphenyl-2-picrylhydrazyl. The density of surface radicals increased with laser fluence at low fluences but decreased at high fluences. Upon laser irradiation and subsequent treatment with gaseous N,N-dimethylacrylamide, surface graft polymerization occurred.

Characterization of surface‐charge‐mosaic‐modified ultrafiltration membranes prepared by laser‐induced surface graft polymerization

Surface-charge-mosaic-modified ultrafiltration membranes with charged domains of various sizes (500, 100, or 50 μm) were prepared by two-step laser-induced surface graft polymerization using a striped photomask. First, the surface of an ultrafiltration membrane was treated with 4-vinylpyridine after laser irradiation using a striped photomask. Subsequently, the striped photomask was shifted and the surface that was initially shaded from the laser beam by the photomask was exposed to laser irradiation and treated with acrylic acid. The surface element distribution, surface chemical structure, and ion-exchange capacities of the treated membrane were determined by scanning X-ray photoelectron spectroscopy (XPS) analysis, time-of-flight secondary ion mass spectrometry (TOF-SIMS) with imaging capacities, and acid-base titration, respectively. Oxygen and carbon distribution maps determined by the scanning XPS analysis and the TOF-SIMS maps for 16 O - and 25 CN - ions show that the surface of the treated membrane had striped domains composed of poly(4-vinylpyridine) and poly(acrylic acid). The anion- and cation-exchange capacities of the treated membranes were approximately 2.0 mEq/m 2 . The ultrafiltration rate of these membranes was markedly lower than that of a nontreated ultrafiltration membrane, but increased as the charge domain size decreased. The membrane flux of sodium ions also increased with decreasing charge domain size. This tendency was much stronger for sodium ions than for glucose.

Design of a new plasma separation membrane by graft copolymerization

Abstract A new type of hydrophilic membrane for blood plasma separation has been successfully developed by vapor-phase glow discharge-initiated graft copolymerization. After exposing microporous polypropylene (PP) membrane to argon glow discharge, it was allowed to react with 2-methoxyethylacrylate (MEA) vapor to produce graft polymers. The polyMEA-grafted PP (PP-g-PMEA) membrane has the novel property of not causing hemolysis when blood first comes into contact with it in a dry state. It is thought that hydrophilic microporous membranes in a dry state cause hemolysis when they are initially exposed to blood, because plasma immediately penetrates into their pores by capillary attraction and erythrocytes are trapped rapidly on the micropores and lysed. Since PP-g-PMEA membranes have a weakly hydrophilic character, plasma penetrates into the micropores only slowly and hemolysis does not occur. Therefore, priming with physiological saline prior to use is not required, and consequently plasma separation procedures are simplified and shortened. A disk-type plasma separator equipped with a PP-g-PMEA membrane had good hemo-compatibility and an excellent separation capacity, enabling high recovery of plasma components. A decreased adsorption of plasma proteins due to the PMEA-grafted layer may be the reason for the performance of the membrane.

A new blood compatible and permselective hollow fiber membrane for hemodialysis.

&NA; The authors have prepared a blood compatible and highly permselective hemodialysis membrane composed of polyether segmented nylon. This block copolymer was synthesized by polycondensation of bis‐3‐aminopropyl‐poly(tetramethylene oxide) (PTMO) and poly(imino‐1,3‐bismethyl‐cyclohexyl‐iminoisophtharoyl) (NyBI) prepolymer obtained by polycondensation of 1,3‐bis(aminomethyl)cyclohexane (B) and isophthalic acid (I). The molecular weight (MW) calculated from the number of end‐groups was 16,000‐21,000. In vitro blood compatibility was evaluated in terms of platelet adhesion onto the surface. PTMO‐NyBI surfaces showed excellent platelet adhesion preventing properties. The PTMO‐NyBI hollow fiber membrane was obtained by a drywet spinning process. The membranes had higher permeability coefficients for macromolecules ranging from MW 10,000 to 20,000 than polysulfone hollow fiber membrane (PS membrane), and had acceptably low albumin permeability for use as a dialysis membrane. The ex vivo blood compatibilities of PTMO‐NyBI membrane and PS membrane were investigated by extracorporeal circulation in a pig model. The PTMO‐NyBI membrane gave excellent results when assessing hemodialysis leukopenia, oxidative burst, and free platelet count decrease. ASAIO Journal 1996;42:1019‐1026.

Anti-HIV-1 activity of an ionically modified porous polypropylene membrane determined by filtration of a viral suspension

We describe here a unique anti‐HIV‐1 membrane, derived from a chemically modified porous polypropylene (PP) membrane, which lowers viral infectivity upon the filtration of HIV‐1 suspension. A cationic polymer, polyethyleneimine (PEI) was graft‐polymerized onto the PP filter membrane (PP‐PEI), and infectious HIV‐1HTLV‐IIIB derived from MOLT‐4/HIV‐1HTLV‐IIIB cells (HIV‐1HTLV‐IIIB(MOLT‐4)) was applied. When a viral suspension of high titer (103.93 TCID50 ml 1) was filtered, efficient reduction (>99%) of gag p24 antigen levels and infectious titer resulted. In a viral suspension of medium titer (102.37 TCID50 ml 1), a significant decrease in the p24 antigen did not occur, although the titer was markedly reduced (>95%). Electron microscopic observation suggested that PEI induced viral aggregations under high titer conditions, and under medium titer conditions, PEI deprived HIV‐1HTLV‐IIIB of its infectivity alone to avoid virus adsorption. In contrast, HIV‐1 propagated in human peripheral blood mononuclear cells (PBMC) such as HIV‐1HTLV‐IIIB(PBMC) was more efficiently trapped by PP‐PEI at lower titers as compared with HIV‐1HTLV‐IIIB(MOLT‐4) from MOLT‐4/HIV‐1HTLV‐IIIB cells. These data suggest host cell modification in the interactions between PP‐PEI and HIV‐1 strains. Since HIV‐1HTLV‐IIIB(MOLT‐4) and HIV‐1HTLV‐IIIB(PBMC) were almost electrically neutral and negative, respectively, we concluded that the divergent effect of PEI on each HIV‐1HTLV‐IIIB resulted from their different electrical characteristics.

Enhancement of Human Immunodeficiency Virus Type 1 (HIV‐1) Infection via Increased Membrane Fluidity by a Cationic Polymer

Cationic polymers are known to have potent activity against bacteria, but their effects on viral activity have been little studied. We investigated the effect of one such polymer, polyethyleneimine (PEI), on HIV‐1 infection. Although virus‐cell binding was significantly inhibited by PEI, HIV‐1 infection in human T‐cell lines such as MT‐4 and MOLT‐4 was accelerated conversely when the drug treatment was carried out, after the virus had attached to the cells or PEI was simultaneously added to the virus and cell culture system. This paradoxical effect of PEI on HIV‐1 infection was examined using HIV‐1 chronically infected cells (MOLT‐4/HIV‐1). Dissociation of the glycoprotein gp120 (as revealed by exposure of transmembrane protein gp41) from MOLT‐4/HIV‐1 cells and the resultant fusion of these cells was shown to be induced by the addition of PEI. Accordingly, it was suggested that the binding inhibition of HIV‐1 to CD4‐positive cells by PEI was due to the shedding of gp120 from HIV‐1 particles, and this PEI rather promoted membrane fusion between the virus and cells leading to the enhancement of HIV‐1 infection. Similarly, dissociation of gp120 from MOLT‐4/HIV‐1 was also induced by sCD4. The effect of these reagents on changes in membrane fluidity was evaluated by polarization (p) measurements, and it was observed that the acceleration of membrane fluidity occurred only in the PEI system. Therefore, it is likely that PEI accelerates HIV‐1 infection by facilitating virus entry into the host cells through an increase in membrane fluidity.

Polyether‐segmented nylon hemodialysis membrane. V. Evaluation of blood compatibility of polyether‐segmented nylons

The biocompatibility of poly(propylene oxide)-segmented nylon610 (PPO-Ny610), poly(ethylene oxide)-segmented nylon610 (PEO-Ny610), poly(ethylene oxide)-segmented nylonM10 (PEO-NyM10), and poly(ethylene oxide)-segmented nylon69/M10 (PEO-Ny69/M10) hollow fibers were investigated in terms of the transient leukopenia by the extracorporeal circulation in a rabbit. PPO-Ny610 and PEO-Ny610 hollow fibers showed that the minimum leukocyte counts during the circulations were > 80% against the initial count of leukocyte. These results indicate that these polymers have good blood compatibility. In PEO-NyM10 and PEO-Ny69/M10, the remarkable decreases of the leukocyte count were observed and the minimum counts were in the range of 45–50%. From the evaluation results of homo nylons (Ny610 and NyM10) hollow fibers, the low blood compatibilities observed in PEO-NyM10 and PEO-Ny69/M10 are not attributed to the chemical structure of the nylon blocks.

Polyether-segmented nylon hemodialysis membrane. VI. Effect of polyether segment on morphology and surface structure of membrane

Amorphous nylon, poly(iminoisophthaloyliminomethylene-1,3-cyclohexylenemethylene) (NyBI) and poly(ethylene oxide) (PEO)-segmented NyBI (PEO–NyBI) membranes were prepared by a phase-inversion method using water/dimethyl sulfoxide (DMSO) mixtures as coagulants. The influence of the PEO segment and coagulant compositions on the morphology of the membranes was investigated. The cloud-point curves in the polymer/DMSO/water ternary system showed that PEO–NyBI and NyBI had the same coagulation processes, that is, instantaneous liquid–liquid phase separation occurred, resulting in a fingerlike structure in the cross section of the membranes. The membrane morphologies observed under a scanning electron microscope (SEM) agreed with the prediction. The PEO segment had little or no effect on the membrane morphologies which were prepared in the coagulants with a low DMSO concentration, and it promoted the change of the phase-separation style from the instantaneous to the delayed one in the case of the DMSO-rich coagulant. The PEO segment, however, significantly influenced the ultrafiltration rate. Additionally, the relationship between the surface composition of the PEO–NyBI membrane and the coagulation condition was also investigated by use of electron spectroscopy for chemical analysis (ESCA) and static secondary ion mass spectrometry (SSIMS). A small enrichment of the PEO segment at the top surface of the membranes was observed with the increase of the DMSO concentration in the coagulant.