Complex coacervates as a foundation for synthetic underwater adhesives

Abstract

Complex coacervation was proposed to play a role in the formation of the underwater bioadhesive of the Sandcastle worm (Phragmatopoma californica) based on the polyacidic and polybasic nature of the glue proteins and the balance of opposite charges at physiological pH. Morphological studies of the secretory system suggested the natural process does not involve complex coacervation as commonly defined. The distinction may not be important because electrostatic interactions likely play an important role in formation of the sandcastle glue. Complex coacervation has also been invoked in the formation of adhesive underwater silk fibers of caddisfly larvae and the adhesive plaques of mussels. A process similar to complex coacervation, that is, condensation and dehydration of biopolyelectrolytes through electrostatic associations, seems plausible for the caddisfly silk. This much is clear, the sandcastle glue complex coacervation model provided a valuable blueprint for the synthesis of a biomimetic, waterborne, underwater adhesive with demonstrated potential for repair of wet tissue.

The Effect of Salt on the Complex Coacervation of Vinyl Polyelectrolytes

“…Consideration of these variables is critical in the design of self-assembled materials. For instance, electrostatic complexation between oppositely-charged polyelectrolytes has been used in drug and gene delivery [7,[14][15][16][17][18], thin film coatings [19][20][21], processed food [22], and underwater adhesives [23][24][25][26]. Clearly, the functionality of the material must be considered in the context of the operational environment.…”

PRISM-Based Theory of Complex Coacervation: Excluded Volume versus Chain Correlation

“…[27][28][29][30] This recent activity in the field is concomitant with a desire to emulate the molecular features observed in a number of biological materials, such as underwater adhesives in mussels and the matrix adhesive holding together the dwelling of a sandcastle worm. 2,[31][32][33] The novelty of these materials is their extreme stability (yet responsiveness) with respect to environmental ionic conditions, even at high salt concentrations, as well as their reversible assembly behavior. [34][35][36][37][38] Complex coacervates are used for microencapsulation, drug delivery, 3,19 biomaterials, [39][40][41] and underwater adhesives, 2,31,32 where their self assembly and functionality relies 19,[23][24][25][26] on the relationship between charged species.…”

“…Furthermore, the nature of the charged species must allow for the formation of a 'coacervate', which represents a subset of complexes that undergo a liquid-liquid phase separation rather than forming solid precipitates. [1][2][3][4][5][6] Historical and current investigations into complex coacervates have studied the formation of such phases in natural polymers, such as proteins or polysaccharides, which are currently widely used as food additives. [7][8][9][10][11][12][13][14][15][16][17][18] Despite the utility of these systems, there has only recently been a resurgence of interest in their molecular behavior, in particular for its promise as a powerful route to self-assembled materials such as micelles, 3,[19][20][21][22] block copolymers, [23][24][25][26] and layer-bylayer assembly.…”

Investigation of the interfacial tension of complex coacervates using field-theoretic simulations

“…Such association can take the form of layer-bylayer assembly of polymers on a charged substrate, 1,2 or it could involve charge complexation in solution. [3][4][5] Examples of emerging technologies that rely on these and related phenomena include wet adhesives for medical, construction, consumer, and military use, 6,7 advanced biosensors, drug and gene delivery vehicles, [8][9][10] and responsive and switchable surfaces. 11,12 When the association takes place in solution, depending on the strength of the polyelectrolyte and the solvent conditions, the resulting polyelectrolyte complex can either be a solid precipitate or a polyelectrolyte-rich liquid phase termed a "complex coacervate."…”