Amyloid-Based Natural Adhesives and Cements - The Functional Fold: Amyloid Structures in Nature - page 132

β

generic amyloid intermolecular -sheet structure, while adhesive

strength was related to adhesive residues external to the amyloid
core. The mechanistic link of amyloid-based cohesive and adhesive
strength is now expected to be more widespread amongst natural
adhesives than previously thought. These remarkably robust and
highly ordered protein assemblies in biological adhesives provide
inspiration for the biomimetic development of a new generation of
adhesives for use in medicine, biotechnology, and a range of other
applications.

8.1 Introduction to Natural Adhesives

Nature has evolved extraordinary adhesive mechanisms to
promote the attachment of a wide diversity of organisms to many
materials. These strategies are essential for successful completion
of an organism's life cycle, thereby ensuring its survival in aquatic
or terrestrial habitats. Interest in natural adhesives has primarily
focused on organisms from aquatic environments, particularly marine,
to develop anti-fouling strategies, or to develop aqueous-based
biomimetic adhesives.

1,2

These marine adhesives are remarkably
effective in attaching to virtually any damp, wet, or submerged

surface, with strong, flexible bonds. Sessile marine organisms depend
upon tenacious permanent adhesion (e.g., barnacles, mussels, and
algae) to deal with shear forces in the ocean, or at the tidal interface,
while motile organisms rely instead on strong, but transitory, adhesion
to different surfaces (e.g., echinoderms, gastropods, gliding diatoms)
to readily enable locomotion.

3

Whether temporary or permanent,
nature provides many examples of successful attachment to various
materials in a moist environment

2

(Fig. 8.1).
Due to the chemical and structural complexity of biological
adhesives and cements, precise mechanisms have been clarified for
only a few systems. For example, the strong, permanent attachment
of the marine mussel has been found to be reliant

upon an adhesive with a high content of the modified amino acid
3,4-dihydroxy-l-phenylalanine,

Mytilus edulis

4,5

whereas barnacles adhere initially
in cyprid larval form via o-quinone cross-linking,

6

followed by an
adult cement comprising three groups of proteins that contain high
levels of serine, threonine, glycine, and alanine.

6,7