Diversified Material Designs in Biological Underwater Adhesives - Structural Interfaces and Attachments in Biology - page 181

What learned
from nature

Functional group Sequence Specific

conformation

Processing

DOPA in polymer,
recombinant, peptide,
extracts from animal

Type of
material

Peptide Recombinant Polymer,

recombinant

Form of
product

Adhesive
in humid
environments

Gel-like material Self-assembly Functional coating

Fig. 9.7 Impacts to artificial material designs

troublesome reaction [ 73 , 74 ]. Recently, metal-coordination bonding via DOPA is a
further trend to form intermolecular cross-linking [ 75 , 76 ]. The bonding is possibly
reversible, thus self-healing and tough mechanical properties are expected. In the
case of metal-coordination bonding, the free catechol group instead of the quinone is
essential. The chemical incorporation of DOPA seems to have priority in those cases
of metal-coordination bonding due to easy control of the chemistry. The gel-like
materials formed by DOPA cross-linkage may be available for tissue sealants and
drug delivery systems inmedical applications, although it is not known how good the
properties of the materials will be. Moreover, the addition of tyrosinase or harmful
oxidants and metals to form the gel may be unwelcome for medical applications. The
current process for using the material is also not yet practical.
Great impacts of DOPA/catechol have been found in the area of coating/surface
functionalization of materials. Incorporation of DOPA into a polyethylene glycol
(PEG) backbone was the first applicable case of a coating material [ 77 ]. The
material, adsorbed onto titanium, prevented the fouling of the surface by mammalian
cells for 6 months. DOPA-structure in the material was employed as the anchor and
the anti-fouling property was given by the PEG-structure. After the initial report,
adaptation of DOPA/catechol as a surface anchoring structure was investigated
extensively and is now a platform for materials design. Materials with DOPA/
catechol-anchor structure include anti-fouling coatings against proteins [ 78 ],
cells [ 79 ], and animals [ 80 ], functionalizing surfaces [ 81 , 82 ], and gels [ 83 ].
Apart from DOPA, protein-based materials are another choice to anchor foreign
functional proteins to material surfaces. Two barnacle proteins with surface