Hydrogels are semi-solid, gummy-bear-like squishy materials made of chains of hydrophilic polymer molecules. Hydrophilic polymers contain polar functional groups which makes them water soluble. The hydrophilic quality makes them a good analog for natural tissues so they often have medical applications.
The team at the University of California realized that the key to making the hydrogels self heal was giving the polymer chains a way to latch back on to each other if ripped apart or damaged. The solution is what they call "dangling side chains". They are finger like structures of hydrophilic polymer that reach off the main structure of polymers and act as something to grab on to. Another posotive trait of the self healing gel is that when pH of the solution it is in is lower, the bond becomes stronger between polymers. This will be ideal for suturing in the stomach, or creating containers for holding acidic materials.
The video below shows and explains how two pieces of the gel, when split apart, can put themselves back together with a little help. Enjoy.