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To control the dynamics of dialysis-induced anisotropic gel formation, we have derived a theoretical expression for the development of the gel layer for a simple case where no cross-link sites for cross-linking agents exists and the inflow and the outflow of low molecular weight components through the dialysis membrane modify the state of polymer molecules to meet the gelation condition. A series of experiments using chitosan solution were done as a model case. The experimental results were compared with asymptotic expressions of the time development equation predicted by theory, and the compatibility of the theoretical picture was examined.

Re-entrant volume phase transition of hydrogel wall membrane of microcapsules (MC) was first observed using MC suspensions consisting of poly (L-lysine-alt-terephthalic acid) wall and aqueous inner and outer solutions with different pHs. To analyze the dynamics of the re-entrant phase transition, we extended the theory for the swelling and the shrinking dynamics of the microcapsule gel [T. Narita, T. Yamamoto, D. Suzuki, T. Dobashi, Langmuir 19 (2004) 4051]. In the theory, the microcapsule size and the force constant for the driving force which gives rise to the size relaxation were chosen as the thermodynamic variables. The time course of the cross-sectional area of the microcapsules fitted well to the theoretical equations, and the time constants determined as the fitting parameters were discussed in terms of the force constant relaxation and the size relaxation.

In order to obtain a gelatin hydrogel crosslinked by a reagent-free method, gamma-ray and electron beam radiation was applied to porcine, bovine and fish gelatin gels and the products were characterized by measuring the gel fraction, the swelling ratio and the enzymatic degradability. On increasing the radiation dose, the gel fraction increased and both the swelling ratio and the enzymatic degradability decreased. The transition temperature from gel to sol of the hydrogel containing more than 5% mammal gelatins increased up to more than 90 degrees C when gamma-ray or electron beam were irradiated by more than 10 kGy. The results show that the degree of crosslinking of irradiated gelatin hydrogels increases with increasing irradiation dose and with decreasing concentration. It is suggested that the radiation crosslinking occurs around the physical crosslinking point or multiple helix structure of gelatin gel.