Efficient Wet Adhesion through Mussel‐Inspired Proto‐Coacervates

Abstract

threads was generated by secreting liquid mussel foot proteins (Mfps) from mussel foot. These Mfps are assembled and manufactured by glands by injection molding reaction. [3] The foot of a mussel presses against the surface to create a vacuum chamber, which propels the delivery of fluidic Mfps. It is believed that Mfps confined to plaques, such as Mfp-2, Mfp-3, Mfp-4, and Mfp-5, create coacervates when exposed to saltwater. All mfps include the post-translational amino acid DOPA, and mfp-5 contains the largest concentration of DOPA residues (30 mol%) and leads to strong adhesion. [4] It was reported that the coacervation of mfps, which occurs in a variety of ways, such as complex coacervation driven by electrostatic interaction, as revealed in polyions of Mfp-131 and Mfp-151, [5] and self-coacervation driven by electrostatic and/or hydrophobic forces as revealed in Mfp-3S. [6] An essential component in mussel adhesion is the special amino acid L-DOPA with its catechol group. [7] The catechols act as chemical jack-of-all-trades or Janus-like chemicals and allow attachment to almost all types of material surfaces using either covalent or noncovalent bonds. [8] Several research groups have suggested mussel-inspired materials to be used as bio-inspired adhesives, [9] with efforts being made by including features of the mussel foot proteins in synthetic polymers. [8a,b,10] Hence, catechols and analogues thereof are highly relevant in materials design. [8e,g] Great strides have been made in harnessing mussel-inspired chemistry in materials, however, many of previous efforts lack a simple and efficient way to deliver the materials to a surface underwater for efficient adhesion. [11] The blue mussel is thought to deliver its adhesive in the form of complex fluids that spread spontaneously and exhibit strong reversible interfacial bonding and tunable cross-linking. [4] The complex fluids are coacervates [12] -mainly composing mixtures of polyelectrolytes that form a separate phase from the aqueous medium. Thus, the mussel maintains its complex fluid glue that upon meeting the surface, spreads and presents DOPA residues to the target surface for attachment and subsequent curing (Figure 1A,B). Indeed, coacervates are used widely in biology (Figure 1A), including in sandcastle worm adhesives [13] and to infiltrate squid beak scaffold materials with proteins. [14] In the blue mussel, the whole gluing process takes only a few minutes and occurs within the spatial confines of the byssus Adhesion underwater is a major challenge. Mussel-inspired complex coacervates functionalized with L-3,4-dihydroxyphenylalanine (L-DOPA) are proposed for underwater adhesives through versatile chemistry of DOPA, however, simple, efficient, controllable, and nontoxic procedures to harness them are still under investigation. In this study, inspired from the mussel byssus formation process, coacervate adhesives are formed underwater by simple injection of an acidic proto-coacervate of DOPA functionalized polyelectrolytes on underwater surface...

Bioinspired Processing: Complex Coacervates as Versatile Inks for 3D Bioprinting

“…After successful printing in air, in this section, we use the unique ability that complex coacervates can transition from a viscoelastic fluid to a microporous solid upon an environmental trigger, for example, by switching from higher to lower salt concentration or a change in pH. [36,38,53] We investigate the possibility of broadening the range of printable HA-CHI materials, by printing directly in water the inks that showed poor shape fidelity in air. To this end, we use the HA-CHI L-L/pH6/0.15 m ink, with a composition that is close-to-physiological conditions, and which present good shear-thinning properties (Figure S3B,C, Supporting Information), but a poor shape fidelity upon printing in air (average Pr value of 0.8: see Figure 4A-i,ii).…”

“…Due to the complex coacervate nature of the adhesive, the material remained at the application site during solidification even when fully submerged in water. [35][36][37][38] 3) Nano-to microporous filtration membranes were prepared from polyelectrolyte complexes by first casting a homogeneous solution of oppositely charged polyelectrolytes with attractive interactions screened due to the high salt concentration, followed by immersion in salt-free water to induce aqueous phase separation through salt diffusion from the membrane into the bath. [39] In this work, we exploit the tunable properties of complex coacervates to establish a new class of biomaterial inks.…”

Bioinspired Injectable Polyurethane Underwater Adhesive with Fast Bonding and Hemostatic Properties

“…[16] Various approaches to developing tough adhesives have been inspired by plants and animals. [17] Marine organisms, such as mussels, [18] crustaceans, [19] and worms, [20] secrete mucins that enable them to firmly adhere to substrates in dynamic and turbulent environments. The protein-rich coacervate that diffuses freely, adapts to various forms, and solidifies quickly underwater, which is crucial for their attachment.…”

Underwater Fabrication of Carbon Nanotube/Coacervate Composites

“…38−40 Furthermore, an underwater injection− coacervation method from a protocoacervate was introduced by using L-3,4-dihydroxyphenylalanine functionalized chitosan (DOPA-chitosan) and PAA as the polyelectrolytes for the coacervate scaffold of the composites. 41 The mussel-inspired incorporation of the special amino acid L-DOPA with its catechol group provides efficient adhesion underwater. 42,43 Protocoacervates are high-concentration polyelectrolyte solutions formulated at a low pH.…”