Bioadhesive

Proteins such as gelatin and carbohydrates such as starch have been used as general-purpose glues by man for many years, but typically their performance shortcomings have seen them replaced by synthetic alternatives.

][14] Organisms such as limpets and sea stars use suction and mucus-like slimes to create Stefan adhesion, which makes pull-off much harder than lateral drag; this allows both attachment and mobility.

Spores, embryos and juvenile forms may use temporary adhesives (often glycoproteins) to secure their initial attachment to surfaces favorable for colonization.

Tacky and elastic secretions that act as pressure-sensitive adhesives, forming immediate attachments on contact, are preferable in the context of self-defense and predation.

Many permanent bioadhesives (e.g., the oothecal foam of the mantis) are generated by a "mix to activate" process that involves hardening via covalent cross-linking.

The Fe(L-DOPA3) complex can itself account for much cross-linking and cohesion in mussel plaque,[16] but in addition the iron catalyses oxidation of the L-DOPA[17] to reactive quinone free radicals, which go on to form covalent bonds.

[24] Mucoadhesive agents are usually polymers containing hydrogen bonding groups that can be used in wet formulations or in dry powders for drug delivery purposes.

[25] In the case of a dry polymer powder, the initial adhesion is most likely achieved by water movement from the mucosa into the formulation, which has also been shown to lead to dehydration and strengthening of the mucus layer.