Inspiration from the natural world: from bio-adhesives to bio-inspired adhesives

Abstract

Advances in materials science and engineering through bio-inspiration, at both the micro-and nanoscales, have flourished over recent years. By understanding principles used in nature to produce adhesives and other substances of interest, the field of bio-inspired engineering has emerged as an important area of innovation. In this review, we will focus on bio-adhesives based on three main mechanisms of generating attachment: dry, wet, and chemical adhesion. Dry adhesion, involving micro-to nanoscale filamentous structures, is used by many insects and reptiles to rapidly climb surfaces. Tree frogs and some insects make use of wet adhesion by leveraging capillary forces through the design of attaching structures that increases liquid drainage, and hence increases frictional contact. Finally, chemical adhesion is used by many plants and mollusks, which secrete adhesives composed of proteins, polysaccharides and carbohydrates to generate the strong forces necessary for adhesion. This paper reviews recent discoveries in animal and plant bio-adhesives, and details the mechanisms used in several representative biological systems. We extend the review to include the fundamental principles functioning in each form of adhesion at the micro-and nanoscales. This fast emerging research area has significant implications in the future design of bio-inspired adhesives, and offers further potential for a variety of applications.

Complex coacervate‐based materials for biomedicine

“…The scope of coacervation has expanded from proteins and polysaccharides to include polynucleotides, synthetic polymers, surfactants, nanoparticles, and other hierarchical assemblies . Furthermore, the utility of coacervates has extended into fields such as adhesives, drug delivery, nano/bioreactors, and cellular biology …”

Sticky mucilages and exudates of plants: putative microenvironmental design elements with biotechnological value

“…Some molecules within mucilages have bioadhesive properties, making them sought-after materials for biotechnological, biomedical or agricultural applications (Favi et al, 2014;George & Suchitra, 2019). Important breakthroughs have been made in the last few years in investigations of the sticky adhesives used by English ivy and by sundew (Zhang et al, 2010;Lenaghan & Zhang, 2012), and a current focus on molecular genetic investigations of seed coats (Golz et al, 2018;Sechet et al, 2018) and the rhizosheath (Sasse et al, 2018) underpins the potential of this field.…”

Linear viscoelasticity of complex coacervates

“…The self-assembly of these materials is driven by entropy, where the initial electrostatic attraction between oppositely-charged macro-ions results in the release of small, bound counter-ions and the restructuring of water molecules [1][2][3][4]. Complex coacervates have a long history of use in the food [5][6][7][8][9][10][11][12][13] and personal care [14,15] industries, and have found increasing utility as a platform for drug and gene delivery [1][2][3][4], as well as underwater adhesives [5][6][7][8][9][10][11][12][13][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62]. Coacervation has also recently been implicated in the formation of various biological assemblies [1,[14][15][16]55,…”