Department: Bioengineering
Faculty Advisor(s): Shyni Varghese
Award(s): Honorable Mention

Primary Student
Name: Ameya M Phadke
Email: aphadke@ucsd.edu
Phone: 858-822-7986
Grad Year: 2012

Materials capable of undergoing spontaneous self-healing are of great interest due to their ability to repair structural damage. While such materials typically utilize reversible weak interactions or embedded healing agents, the healing of permanently cross-linked hydrogels has remained elusive due to the presence of water as well as the irreversibility of the cross-links. We have developed for the first time, permanently cross-linked hydrogels capable of undergoing self-healing in an aqueous milieu via reversible hydrogen bonding across a crack. This self-healing takes place within 2-3 seconds of initial contact and is reversible in that it can also be switched on and off via changes in ambient pH. We determined that the healing requires the hydrogel network to contain moieties having an optimal balance of hydrophilic and hydrophobic functional groups. Specifically, hydrogels armed with N-acryloyl-6-aminocaproic acid-derived pendant side chains were found to undergo optimal healing; we found that even minute changes in the hydrophobicity of the pendant side chains dramatically reduced the ability of the networks to heal. This study demonstrates a mechanism through which secondary interactions can be used to impart novel properties to cross-linked polymer networks in aqueous systems. Furthermore, we demonstrate potential applications for these hydrogels for the rapid assembly of soft complex structures, as smart sealants for containers containing corrosive acids, as well as in regenerative medicine as potential gastric tissue adhesives.

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