Bridging Adhesion of Mussel-Inspired Peptides: Role of Charge, Chain Length, and Surface Type

Abstract

The 3,4-dihydroxyphenylalanine (Dopa)-containing proteins of marine mussels provide attractive design paradigms for engineering synthetic polymers that can serve as high performance wet adhesives and coatings. Although the role of Dopa in promoting adhesion between mussels and various substrates has been carefully studied, the context by which Dopa mediates a bridging or nonbridging macromolecular adhesion to surfaces is not understood. The distinction is an important one both for a mechanistic appreciation of bioadhesion and for an intelligent translation of bioadhesive concepts to engineered systems. On the basis of mussel foot protein-5 (Mfp-5; length 75 res), we designed three short, simplified peptides (15–17 res) and one relatively long peptide (30 res) into which Dopa was enzymatically incorporated. Peptide adhesion was tested using a surface forces apparatus. Our results show that the short peptides are capable of weak bridging adhesion between two mica surfaces, but this adhesion contrasts with that of full length Mfp-5, in that (1) while still dependent on Dopa, electrostatic contributions are much more prominent, and (2) whereas Dopa surface density remains similar in both, peptide adhesion is an order of magnitude weaker (adhesion energy Ead ∼ −0.5 mJ/m2) than full length Mfp-5 adhesion. Between two mica surfaces, the magnitude of bridging adhesion was approximately doubled (Ead ∼ −1 mJ/m2) upon doubling the peptide length. Notably, the short peptides mediate much stronger adhesion (Ead ∼ −3.0 mJ/m2) between mica and gold surfaces, indicating that a long chain length is less important when different interactions are involved on each of the two surfaces.

Mussel adhesion – essential footwork

“…Although comparatively weak, the bidentate H-bond of Dopa is notable for its bond lifetime, which is ∼10 6 times longer than that of the monodentate (Yu et al, 2011a), thus ensuring that once Dopa is 'on', the probability of protein desorption is low. Dopa-peptides are extensively H-bonded to titania and HAP surfaces at acidic pH (Wei et al, 2014. To better define how much Dopa contributes to H-bonding, researchers have attempted to 'knockout' Dopa of Mfp-3 and Mfp-5, by oxidation to Dopa-quinone (which can no longer H-bond to the surface) at acid pH.…”

“…In summary (Fig. 4A), interfacial interactions of the plaque with the substrate implicated at acidic pH include: bidentate H-bonding (Yu et al, 2011a), electrostatic attraction (Wei et al, 2013a,b) and hydrophobic interactions (Yu et al, 2014); coordination (see Glossary) is limited to pH≥5.…”

Siderophores and mussel foot proteins: the role of catechol, cations, and metal coordination in surface adhesion

“…[49,50]. Several catechol-containing adhesive materials have been compared to their phenol-containing analogs and the switch from the bidentate interaction of catechol to the monodentate interaction of phenol results in a significant decrease in measured adhesion forces [46,51]. According to Bell theory ( = !…”

Surface force measurements and simulations of mussel-derived peptide adhesives on wet organic surfaces

“…To facilitate the construction of nextgeneration underwater adhesives, we can mimic existing biological glues-such as those containing mussel foot proteins (MFPs)-and translate the glues' structures to create biologically inspired synthetic adhesives (6). Doing so requires detailed knowledge of the molecular interactions that take place, many of which occur on length and time scales that are, at present, too small to be accurately characterized by experiments.…”

“…With knowledge of Dopa's binding ability, an abundance of Dopa-containing polymers were synthesized that displayed impressive adhesive (8,9), coating (1,4), structural (10,11), and selfhealing (12,13) properties. The surface forces apparatus (SFA) has been used to measure the adhesion of MFP-containing glues (1,6,(14)(15)(16)(17); however, it remains difficult to unambiguously identify individual or cooperative interactions of amino acids that facilitate adhesion because few theoretical models are available for comparison (18,19).…”