Yuichi Mori

A Synthetic Hydrogel with Thermoreversible Gelation. I. Preparation and Rheological Properties

Abstract Block copolymers composed of poly(N-isopropylacrylamide-co-n-butyl methacrylate) [poly(NIPAAm-co-BMA)] and poly(ethylene glycol) (PEG) were prepared. Aqueous solutions of the block copolymers were characterized by dynamic viscoelastic measurement as a function of temperature. The fluid solutions turned into hydrogels upon heating while keeping their transparency and without syneresis. The hydrogels turned back into solutions upon cooling. The thermoreversible sol-gel transition was observed with no hysteresis. The sol-gel transition temperatures were closely correlated to the lower critical solution temperature of the poly(NIPAAm-co-BMA) in the block copolymers. Gelation is believed to be caused by thermoreversible crosslinkages between intermolecular poly(NIPAAm-co-BMA) blocks due to hydrophobic interaction.

A Synthetic Hydrogel with Thermoreversible Gelation. Ii. Effect of Added Salts

Abstract The sol-gel transition temperature of a thermoreversible hydrogel composed of poly (N-isopropylacrylamide)-b-poly(ethylene glycol) was determined from dynamic viscoelastic measurement. The sol-gel transition temperature was affected by the amount and sort of added salts. With increasing salt concentration, salts with a salting-out nature decreased the sol-gel transition temperature whereas salts with a salting-in nature increased the sol-gel transition temperature. The effect of various anions on the sol-gel transition temperature was interpreted by their influence on the hydrophobic effect.

Preparation of Poly(N-Msopropylacrylamide)-B-Poly(Ethylene Glycol) and Calorimetric Analysis of Its Aqueous Solution

Abstract A block copolymer composed of poly(N-isopropylacrylamide) [poly-(NIPAAm)] and a hydrophilic polymer such as poly(ethylene glycol) was prepared. The aqueous solution of the block copolymer exhibited a calorimetric endothermic peak on heating, similar to a poly(NIPAAm) homopolymer, although in a random copolymer composed of NIPAAm and a hydrophilic monomer such as acrylamide, no endothermic peak was observed. This result suggests that it is the NIPAAm sequence length which dominantly affects the LCST phenomenon of the copolymer rather than the content of hydrophilic comonomers.

Vascular Graft Materials and Their Structure

It is well-known that thromboresistance, compliant properties and good healing are 3 major requisites for vascular grafts. These are closely interrelated and correlated with both the bio-chemical properties and the details of structure, such as porosity, of vascular graft materials. In this study a hydrogel (HM) which ionically combines heparin and a hydrogel (H-PEO) with long polyethylene oxide (PEO) chains have been developed as thromboresistant materials. The effects of the heparin release profile and of the chain length of PEO on the thromboresistance were studied in both the HM and the H-PEO. A thromboresistant material for vascular grafts, a hydrogel (HMN) with PEO chains which releases heparin has been developed. A new vascular graft has also been developed using ultra fine polyester fibers. The effects of fineness of vascular graft fiber on mechanical properties and the healing process were investigated.