Novel amphiphilic, thermo-
responsive polyaspartamides which showed both LCST (lower critical solution
temperature), and sol-gel transition were prepared and characterized. The polyaspartamide derivatives were synthesized from polysuccinimide, the polycondensate of aspartic
acid monomer, via successive nucleophilic ring-opening reaction by using dodecylamine and N-isopropylethylenediamine (NIPEDA). At the intermediate composition ranges, the dilute aqueous solution exhibited a thermally responsive phase separation due to the presence of LCST. The phase transition temperature was controllable by changing the content of pendent groups. In addition, a physical gelation, i.e. the sol-gel transition was observed from the concentrated solutions, which was elucidated by dynamic viscoelastic measurements. These novel injectable and thermo-responsive
hydrogels have potential for various biomedical applications such as tissue engineering and current drug
delivery system.
Stimuli-responsive polymers have attracted great interestin the field of novel drug delivery, cell encapsulation, and tissue engineering due to their promising potential. Among them, temperature and pH responsive systems have widely been investigated.1,2Poly(N-isopropyl acrylamide), PNIPAAm,is one of the most typical thermosensitive polymers, which undergoes a rapid and reversible hydration-dehydration change through the LCST(lower critical solution temper- ature). PNIPAAm, NIPAAm-containing copolymers, and the hydrogels have been widely applied to controlled drug delivery and various bio-related applications. Recently injectable polymeric hydrogels are becomingvery attractive in their applications such as novel drug delivery and tissue engineering field. The polymers are loaded with bioactive molecules or cells in an aqueous solution and in-situ turn into physically crosslinked hydro- gels by external stimuli such as temperature, pH, and light. Among them, thermo-responsive hydrogels have been ex- tensively investigated which can undergo rapid transformation from a liquid form to a gel state at body temperature without any additives. Most of the reported injectable hydrogels, however, are non-
biodegradable, and this may limit their use in biomedical field.Polypeptides and related synthetic poly(amino acid)s havebecome important because of their desirable properties such as biocompatibility and biodegradability, which are useful for various bio-related industries. Poly(aspartic acid), PASP, is one of water-soluble and biodegradable polyamide, which can be produced from the hydrolysis of polysuccinimide (PSI), the polycondensate of L-aspartic acid monomer. Poly(N-2-hydroxyethyl-DL-aspartamide), PHEA, is another derivative polymer, obtained by coupling PSI with ethanol-amine, which has been proposed as a potential plasma ex- tender and material for drug delivery, such as macromole- cular prodrugs, polymeric micelles, and nanoparticles. The attachment and chemical modification of pendent groups either by the aminolysis reaction to PSI or by the secondary reaction through hydroxyl or carboxylic groups of the PASP and PHEA can provide a variety of biodegradable functional polymers with specific properties. Very extensive studies on this class of material have been carried out by Giammona et al. and other groups.3-8Also, Watanabe et al reported somethermosensitive systems based on polyaspartamide derivatives recently.9,10In this work, we prepared novel amphiphilic graft copoly-mers based on polyaspartamides containing N-isopropyl- amine moiety to identify materials which showed both LCST behavior and sol-gel transition in aqueous solution
Bull. Korean Chem. Soc. 2006, Vol. 27, No. 12 1981
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