Papers by Author: Toshiaki Dobashi

Abstract: We have prepared W/O/W-type microcapsules with polyureaurethane wall membrane and aqueous core containing methylene blue by means of the double emulsification method and the effect of the rate of agitation at the twice emulsification on the release of methylene blue to dispersing methanol was examined. The release curve was expressed fairly well by the streched exponential form: where C(t) and C_eq are the concentrations of methylene blue in the dispersing methanol at time t and at the equilibrium state, respectively. The time constant τ increased and the exponent α decreased with increasing the rate of agitation at the second emulsification, whereas τ decreased and α was constant with increasing the rate of agitation at the first emulsification. These differences are discussed from a viewpoint of inhomogeneity of the microcapsule wall membrane.

Abstract: Anisotropic gelation has been studied by immersing chitosan in aqueous acetic acid sandwiched by a pair of square cover glasses into aqueous sodium hydroxide. The shape of the gel front line initially remained a square, whereas it approached a circle with immersion time. The time course of the distance between the side of the cover glasses and the gel front line x_s was expressed initially as scaled proportional relationship (x_s/L)² =2K(t/L²), where t is the immersion time, L; the length of the side of the cover glasses and K; a constant. The characteristic behavior was independent of chitosan concentration.

Abstract: For efficient transcatheter arterial embolization therapy for hepatocellular carcinoma, we have developed microcapsules containing oil-based contrast medium, as obstructing materials. The microcapsules were prepared by means of the interfacial polymerization to make a wall membrane consisting of polyureaurethane with Lipiodol in the core. The average size of the particles was 80 μm, and the size distribution was fairly small. The extent of X-ray absorption of the microcapsules was controlled by the ratio of the amounts of triisocyanate monomer and Lipiodol in the oil phase on the interfacial polymerization.

Abstract: Different poly(N-isopropylacrylamide-co-hydroxyethyl methacrylate) copolymers (P(NIPAM-co-HEMA)) were synthesized from N-isopropylacrylamide (NIPA) and hydroxyethyl methacrylate (HEMA) comonomers by both radical and radiation polymerizations for comparison. PLLA-g-P(NIPAM-co-HEMA) graft copolymers were synthesized from L-lactide and respective P(NIPAM-co-HEMA) copolymers by ring opening polymerization. Both NMR and FTIR analyses demonstrated the PLLA chains have been grafted on to the P(NIPAM-co-HEMA) backbone. These graft copolymers revealed the cloud point temperature higher than that of PNIPAM homopolymer as determined by optical transmittance. The graft copolymers self-assembled into micelles with regularly spherical structures as observed by atomic force microscopy (AFM). The properties of these graft copolymers are interesting for the drug delivery system.

Abstract: We have prepared an anisotropic hydrogel with birefringence by means of dialysis method and analyzed the dynamics of the gel-forming process using purified chitosan with the degree of deacetylation at 100%. The dynamics was expressed well by a theory based on “moving boundary picture”(Nobe, Dobashi and Yamamoto, Langmuir 2005).