European Polymer Journal
Melek Pamuk Algi, Oguz Okay
Poly(N,N-dimethylacrylamide) (PDMA) is a very useful hydrophilic biocompatible polymer with associative properties. Although there is a growing interest in PDMA hydrogels, they generally exhibit rather low mechanical strength and very low stretchability due to the lack of an efficient energy dissipation mechanism in the chemically crosslinked gel network. Highly stretchable PDMA hydrogels with self-healing properties are of great interest in tissue engineering and for biomedical applications. A promising strategy to design synthetic hydrogels with self-heal ability is to substitute the covalently crosslinked polymer chains by supramolecular ones. Here, we describe preparation of self-healing PDMA hydrogels by micellar copolymerization of N,N-dimethylacrylamide with 2 mol% stearyl methacrylate in aqueous sodium dodecyl sulfateNaCl solutions. The supramolecular PDMA hydrogels formed via hydrophobic interactions in micellar solutions can be compressed up to about 100% strain without any permanent failure, while during elongation, they rupture when stretched to 4200% strain. The hydrogels soften with increasing strain and exhibit liquid-like response at high strains, while they turn back to the initial gel state, if the force is removed. Loading and unloading mechanical cycles show a significant hysteresis and perfect superposition of the successive loading curves demonstrating damage done during loading is recoverable in nature. Tensile testing experiments performed using virgin and healed gel samples show that a healing time of 20 min suffices to recover all the initial mechanical properties of PDMA hydrogels.