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Novel thermo‐ and pH‐responsive hydrogels based on amphiphilic polyaspartamides possessing a lower critical solution temperature (LCST) and a volume‐phase transition were prepared and characterized. The polyaspartamide derivatives were synthesized from polysuccinimide, which is the polycondensate of L‐aspartic acid monomer, through successive ring‐opening reactions using hydrophobic 2‐diisopropylaminoethylamine and hydrophilic ethanolamine. The amphiphilic copolymer was then crosslinked with hexamethylene diisocyanate to afford the corresponding gel. The LCST of the copolymer in an aqueous solution was varied by changing both the graft composition and pH of the medium. The crosslinked gels showed stimuli‐responsive behavior, with their degree of swelling and porous structure morphology changing with temperature and pH. In addition, hydrolytic degradation depending on the crosslinking density of the hydrogel was examined. Copyright © 2009 Society of Chemical Industry

A series of amphiphilic graft copolymers based on polyaspartamide were synthesized by successive aminolysis reactions of polysuccinimide using 2‐diisopropylaminoethyl (DIP), O‐(2‐aminoethyl)‐O′‐methylpolyethylene glycol (PEG) and lauryl amine as pH‐sensitive, hydrophilic and hydrophobic groups, respectively. The pH‐dependent self‐assembly behavior of the aqueous copolymer solution was investigated. Nano‐aggregation, which was induced by a hydrophilic/hydrophobic shift of the DIP group in solution, occurred at a pH in the vicinity of the pKa of the DIP group. The mean diameter of the nano‐aggregate could be modulated by changing the compositions of both pendants. The mean diameter of the nanoparticles increased with increasing solution pH from 6.5 to 8. The dissolution of paclitaxel into these amphiphilic nanoparticles was attempted and the pH‐dependent release behavior was examined using a solvent‐casting method. The results showed a significantly faster release of paclitaxel at pH = 6.5, which is a tumoral acidic pH, than at neutral physiological pH. These pH‐sensitive PEGylated polyaspartamide derivatives have potential use as a tumor‐targeting delivery system.

Novel amphiphilic, thermo-and pH-responsive polyaspartamides showing both double-responsive (pH and temperature) behavior and a sol-gel transition were prepared and characterized. The polyaspartamide derivatives were synthesized by the successive aminolysis reactions of polysuccinimide using both hydrophobic N-alkylamine (laurylamine, octylamine, hexylamine) and hydrophilic N-isopropylethylenediamine. The composition of each component was analyzed by 1 H NMR. At the intermediate composition range, the system showed a lower critical solution temperature behavior in water. The transition temperature (pH dependent) could be modulated by changing the alkyl chain length and graft composition. The temperature dependence of the nanoparticle size distribution of the polyaspartamide derivatives was also examined. The critical micelle concentration of the copolymers in a phosphate-buffered saline (pH 7.4) solution ranged from 6 to 20 lg/L. In addition, physical gelation, i.e., a sol-gel transition, was observed in a concentrated solution. These novel doubleresponsive and injectable hydrogels have potential biomedical applications such as drug delivery systems and tissue engineering.