page_title: Self-healing hydrogels
section_title: Hydrogen bonding
hierarchical_section_title: Self-healing hydrogels / Interface chemistry of self-healing hydrogels / Hydrogen bonding
caption_attribution_description: English: An example of a dangling chain self healing hydrogel network. The carboxylic acid tail groups react with one another to crosslink the backbone carbon chain of the self healing hydrogel. In addition, the hydrophilic functional groups ensure the network readily absorbs water.
context_page_description: Self-healing hydrogels are a specialized type of polymer hydrogel. A hydrogel is a macromolecular polymer gel constructed of a network of crosslinked polymer chains. Hydrogels are synthesized from hydrophilic monomers by either chain or step growth, along with a functional crosslinker to promote network formation. A net-like structure along with void imperfections enhance the hydrogel's ability to absorb large amounts of water via hydrogen bonding. As a result, hydrogels, self-healing alike, develop characteristic firm yet elastic mechanical properties. Self-healing refers to the spontaneous formation of new bonds when old bonds are broken within a material. The structure of the hydrogel along with electrostatic attraction forces drive new bond formation through reconstructive covalent dangling side chain or non-covalent hydrogen bonding. These flesh-like properties have motivated the research and development of self-healing hydrogels in fields such as reconstructive tissue engineering as scaffolding, as well as use in passive and preventive applications.
context_section_description: Hydrogen bonding is a strong intermolecular force that forms a special type of dipole-dipole attraction. Hydrogen bonds form when a hydrogen atom bonded to a strongly electronegative atom is around another electronegative atom with a lone pair of electrons. Hydrogen bonds are stronger than normal dipole-dipole interactions and dispersion forces but they remain weaker than covalent and ionic bonds. In hydrogels, structure and stability of water molecules are highly affected by the bonds. The polar groups in the polymer strongly bind water molecules and form hydrogen bonds which also cause hydrophobic effects to occur. These hydrophobic effects can be exploited to design physically crosslinked hydrogels that exhibit self healing abilities. The hydrophobic effects combined with the hydrophilic effects within the hydrogel structure can be balanced through dangling side chains that mediates the hydrogen bonding that occurs between two separate hydrogel pieces or across a ruptured hydrogel.
caption: An example of a dangling chain self healing hydrogel network. The carboxylic acid tail groups react with one another to crosslink the backbone carbon chain of the self healing hydrogel. In addition, the hydrophilic functional groups ensure the network readily absorbs water.
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