Rapid pH/temperature-responsive cationic hydrogels with dual stimuli-sensitive grafted side chains

• Published in: Polymer (Guilford) 2009-05, Vol.50 (11), p.2516-2525
• Main Authors: Zhang, Jie, Xie, Rui, Zhang, Shi-Bo, Cheng, Chang-Jing, Ju, Xiao-Jie, Chu, Liang-Yin
• Format: Article
• Language: English
• Subjects: Applied sciences; Cationic hydrogels; Exact sciences and technology; Organic polymers; pH/temperature sensitivity; Physicochemistry of polymers; Properties and characterization; Rapid response; Solution and gel properties
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2009.03.044

Dual temperature- and pH-sensitive comb-type grafted cationic hydrogels are successfully synthesized by grafting polymeric chains with freely mobile ends, which are composed of both N-isopropylacrylamide (NIPAM) segments and N, N-dimethylamino ethyl methacrylate (DMAEMA) segments, onto the backbone of crosslinked poly(NIPAM- co-DMAEMA) networks. Equilibrium and dynamic swelling/deswelling properties of the prepared hydrogels responding to pH and/or temperature are investigated. The prepared hydrogels demonstrate a lower critical solution temperature (LCST) at about 34 °C and a p K a value at about pH 7.3. At lower pH and lower temperature, both the swelling degree and the swelling rate of the comb-type grafted hydrogel are larger than those of the normal-type crosslinked hydrogel. The comb-type grafted poly(NIPAM- co-DMAEMA) hydrogel exhibits a more rapid deswelling rate than that of the normal-type hydrogel in response to a pH jump from 2.0 to 11.0 at a fixed temperature. The volume changes of the poly(NIPAM- co-DMAEMA) hydrogels are acute in a series of fixed buffer solutions with an abrupt increase of environmental temperature from 18 °C to a temperature higher than the LCST. The comb-type grafted poly(NIPAM- co-DMAEMA) hydrogels show quite fast shrinking behaviors in response to simultaneous dual temperature and pH stimuli. Drug-release in vitro from the prepared poly(NIPAM- co-DMAEMA) hydrogels is carried out when the environmental temperature and pH are changed synchronously. The results show that the model drug Vitamin B 12 is released much more rapidly from the comb-type grafted hydrogel than that from the normal-type hydrogel. The proposed dual temperature/pH-sensitive comb-type grafted cationic poly(NIPAM- co-DMAEMA) hydrogel in this study may find various potential applications, e.g., for fabricating rapid-response smart sensors, actuators, and chemical/drug carriers and so on. [Display omitted]