Highly stretchable and tough hydrogels

http://www.nature.com/nature/journal/v489/n7414/full/nature11409.html

Jeong-Yun Sun1,2, Xuanhe Zhao3, Widusha R. K. Illeperuma1, Ovijit Chaudhuri1, Kyu Hwan Oh2, David J. Mooney, Joost J. Vlassak & Zhigang Suo

The authors of this communications reported the synthesis of a hybrid hydrogel consisting of ionically crosslinked alginate and physically crosslinked polyacrylamide. The ionic interactions of the alginate based hydrogels occur between the carboxylic groups of mannuronic acid or guluronic acid and a divalent cation, which in their case was calcium. The acrylamide was polymerized with ammonium persulfate as the initiator, N,N-methylenebisacrylamide as the crosslinker, and N,N,N',N'-tetramethylethylenediamine as a crosslinker accelerator.  By mixing the alginate acrylamide together with initiators, crosslinkers, and calcium sulfate slurry, the authors were able to make a hybrid hydrogel. This gel could be stretched 20x their initial length, even with 90% water. The deformation was shown to be recoverable, and a notch cut into it was stable up until a critical stretch limit at which the notch started to tear. The hybrid gel was also shown to have a higher elastic modulus (29 kPa), which higher than the elastic modulus of each of the components (17 kPa for alginate and 8 kPa for polyacrylamide). The authors also probed the mechanism of deformation and recovery, and believe it to involve unzipping and re-zipping of the ionic crosslinks.