text: A dangling side chain is a hydrocarbon chain side chains that branch off of the backbone of the polymer. Attached to the side chain are polar functional groups. The side chains "dangle" across the surface of the hydrogel, allowing it to interact with other functional groups and form new bonds. The ideal side chain would be long and flexible so it could reach across the surface to react, but short enough to minimize steric hindrance and collapse from the hydrophobic effect. The side chains need to keep both the hydrophobic and hydrophilic effects in balance. In a study performed by the University of California San Diego to compare healing ability, hydrogels of varying side chain lengths with similar crosslinking contents were compared and the results showed that healing ability of the hydrogels depends nonmonotonically on the side chain length. With shorter side chain lengths, there is limited reach of the carboxyl group which decreases the mediation of the hydrogen bonds across the interface. As the chain increases in length, the reach of the carboxyl group becomes more flexible and the hydrogen bonds can mediated. However, when a side chain length is too long, the interruption between the interaction of the carboxyl and amide groups that help to mediate the hydrogen bonds. It can also accumulate and collapse the hydrogel and prevent the healing from occurring.