Toshio Shinbo

Surface modification of poly(L-lactic acid) affects initial cell attachment, cell morphology, and cell growth

The object of this study was to develop a highly porous scaffold to be used in regeneration of blood vessels, nerves, and other hollow tissues with small openings. Using the phase-inversion method and a mixture of water and methanol as a coagulating agent, we prepared highly porous flat membranes from poly(l-lactic acid) (PLLA) with numerous pores both on the surface and in the interior of the membranes. Chinese hamster ovary (CHO) cells were cultured on the membranes to evaluate initial cell adhesion, cell proliferation, and cell morphology. Adhesion of CHO cells to PLLA was poor: the cells adhered at approximately half the rate observed with a tissue culture polystyrene dish (TCPS). In contrast, adhesion of cells to PLLA treated with a low-temperature oxygen plasma was good; the adhesion rate was the same as that on TCPS. The rate of cell proliferation on the treated membranes was no different from that on the nontreated membranes, but cell morphologies were quite different. The cells on the nontreated membranes were small and round and proliferated separately from one another. In contrast, the cells on the plasma-treated membranes proliferated in close contact with other cells, spreading out extensively in sheet-like formations. Since the plasma treatment not only accelerated cell adhesion but also enabled cells to proliferate in the form of sheets resembling biological tissue, we believe that oxygen-plasma treatment is extremely effective for modifying surfaces of materials used for tissue regeneration.

Fabrication of an asymmetric polyimide hollow fiber with a defect-free surface skin layer

Abstract An asymmetric polyimide hollow fiber with a completely defect-free thin surface skin layer has been fabricated by using a dry/wet phase inversion process. Effects of the composition of spinning solution and the air gap height on the formation of the skin layer were investigated in detail. The hollow fiber showed a microporous structure at the inner surface and a defect-free skin layer at the outer surface. The outer diameter (OD) of the fiber was 500xa0μm, with a wall thickness of 45xa0μm and the calculated apparent skin layer thickness was 470xa0nm. Permeance and selectivity of O 2 and N 2 for the hollow fibers at 35°C and 76xa0cmxa0Hg have been measured. The ( Q O 2 / Q N 2 ) selectivity of the hollow fiber was 5.4 and exhibited a larger value than that measured in the dense and asymmetric polyimide flat membranes.

Pervaporation of benzene/cyclohexane and benzene/n-hexane mixtures through PVA membranes

Poly(vinyl alcohol) (PVA) membranes (both homogeneous and asymmetric) were studied for the pervaporation separation of benzene/n-hexane and benzene/cyclohexane mixtures. The asymmetric PVA membrane with skin and porous layers was prepared through the phase inversion technique. Both asymmetric and homogeneous membranes were benzene-selective for all the feed compositions. The benzene separation factor of homogeneous PVA membrane was smaller than three, and the total permeation flux was several g/m2/h. The benzene selectivity of the asymmetric PVA membrane was much higher than that of the homogeneous membrane; weight fraction of benzene in the permeate side was larger than 90% for all the feed compositions. On the other hand, the total flux was almost unchanged compared with that of the homogeneous membrane. These results indicate that the density of the skin layer of the asymmetric membrane should be much higher than that of the homogeneous membrane.

Development of polyion complex membranes based on cellulose acetate modified by oxygen plasma treatment for pervaporation

Abstract Cellulose acetate (CA) membrane was modified with ultra-thin polyion complex (PIC) layers, and the pervaporation performance for water–ethanol mixture was investigated. Introduction of oxygen-containing anionic groups onto the surface of the CA membrane was attempted by the oxygen plasma treatment, and was confirmed by the electron spectroscopy for chemical analysis (ESCA). The formation of an ultra-thin PIC layer on the membrane surface by dipping of the plasma-treated membrane into an aqueous solution of polyallylamine (PALA) as the polycation was confirmed by the measurement of the attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra of the membrane. The results of the pervaporation of water–ethanol mixture showed that the PIC layer increased the selectivity of the CA membrane. The considerable increase in the selectivity was not accompanied by any large decrease in the water flux. Furthermore, it was observed that the applied energy for plasma treatment strongly affected the permeate flux and the selectivity of the CA/PIC membrane. Further improvement in the selectivity of the membrane was attained by the formation of multilayer PIC using polyacrylic acid (PAA) as the polyanion.

Gas transfer and blood compatibility of asymmetric polyimide hollow fiber

We have fabricated an asymmetric polyimide hollow fiber for use as a membrane oxygenator. A dry/wet phase inversion process has been applied to a spinning process to prepare the hollow fiber. The fiber structure consisted of a complete defect-free skin layer and a porous substructure characterized by the presence of an open-cell structure and macrovoids. The outer diameter was 480 μm with a wall thickness of 50 μm. Transfer rates of O2 and CO2 in the asymmetric polyimide fiber were 2.3 × 10-5 and 1.1 × 10-4 (cm3(STP)/(cm2s cmHg)), respectively, which were four times higher than those measured in the polydimethylsiloxane (PDMS) fiber of the presentlyavailable membrane oxygenator. The (QO2 /QN2)selectivity of the polyimide fiber was 4.9, indicating that the surface skin layer is essentially defect-free. The blood compatibility of the polyimide hollow fiber has been evaluated in vitro and in vivo. The polyimide had an excellent blood compatibility when compared with PDMS.

Effective cell separation utilizing poly(N-isopropylacrylamide)-grafted polypropylene membrane containing adsorbed antibody.

We previously developed a cell separation method using a poly(N-isopropylacrylamide)-grafted polypropylene (PNIPAAm-g-PP) membrane containing an adsorbed monoclonal antibody (mAb). The purpose of this study is to elucidate the cell separation mechanism in detail and to design an optimal method. As the grafting yield of PNIPAAm increased, the level of the adsorption of IgG(1) and cell adhesion to the membrane decreased. After BSA was adsorbed to a PNIPAAm-g-PP membrane at 6 degrees C, where PNIPAAm was hydrophilic, a small amount of IgG(1) was adsorbed to the membrane at 37 degrees C, where PNIPAAm was hydrophobic. The desorption of the adsorbed IgG(1) was not enhanced even though temperature was reduced to 10 degrees C, where PNIPAAm was hydrophilic. These results indicate that the antibody adsorbed to the intact PP surface of the membrane predominantly contributes to the capture of target cells through the antigen-antibody reaction and that a thermoresponsive transition of PNIPAAm contributes to the detachment of the captured cells. The total number of cells recovered from a PNIPAAm-g-PP membrane containing the adsorbed mAb decreased as the grafting yield increased. A PNIPAAm-g-PP membrane with a 1.7% grafting yield containing adsorbed anti-human CD34 mAb enriched CD34-positive KG-1a cells to 85% from a 1:1 cell suspension of KG-1a cells and CD34-negative Jurkat cells.

Size of polymeric particles forming hemodialysis membranes determined from water and solute permeabilities

Regarding hemodialysis membranes as layers packed with uniform polymeric particles, the size of the particles is determined using the Kozeny–Carman equation. Diameter of the spheres forming cellulosic membranes is the same order as the size of primary polymeric particles determined by electron microscopy in a previous article. Pore radii of the membranes calculated by the Kozeny–Carman equation are in agreement with those determined by the tortuous capillary pore model. The result suggests that an estimate of a pore radius of a membrane is feasible by the Kozeny–Carman equation only with water permeability of the membrane. Intramembrane diffusion coefficients of vitamin B12 calculated from an equation derived from the analogy of heat conduction in heterogeneous media consisting of a continuous phase and particles are larger than the experimental values. The result suggests the failure of the analogy between heat conduction and diffusion of vitamin B12 in a heterogeneous medium.

Simple thermodynamics of macroscopic phase separation in shrinking gels

The shrinking process induced in spherical gels by an abrupt change in temperature has been investigated qualitatively. The phase diagram of the gel system has been found to be helpful in classifying a variety of shrinking processes. When the solvent quality is lowered within the region between the volume transition and coexistence temperatures, the local swelling ratio of the inner portion, which is divided by a moving interface from the outer shrunk phase, declines in the course of the shrinking process. On the contrary, the local swelling ratio of the inner portion of the shrinking gel is enlarged when the solvent quality is lowered into the region between the coexistence and spinodal temperatures. In this latter case, owing to large local swelling of the inner portion in the vicinity of the interface, spherical symmetry will imply mechanical instability. This instability will be the origin of transient spatial patterns on the surfaces of shrinking gels.

Preparation of asymmetric hollow‐fiber membrane with ultrathin dense skin layer on the outer surface using dry/wet phase inversion process

The authors have developed an asymmetric hollow-fiber membrane with a skin layer on the outer surface using a dry/wet phase inversion process with a newly synthesized aromatic fluorinated polyamide. Because the skin layer is ultrathin and has no defects, the membrane has gas selectivity in addition to higher gas flux. The membrane has excellent hemocompatibility, which is probably related to packing density of the skin layer. Authors are now clarifying the mechanism of the microstructure formation of the membrane relating to spinning conditions by the standing point of polymer physics. Generally, the microstructure of a polymeric membrane prepared by a phase inversion process is discussed using the phase diagram of the system. However, the process is so dynamic that conventional discussion based on the start and end points is not sufficient, but which path is to be chosen on the phase diagram is more important.