Bioinspired Underwater Adhesion to Rough Substrates by Cavity Collapse of Cupped Microstructures

Abstract

Underwater or wet adhesion is highly desirable for numerous applications but is counteracted by the liquids in the contact which weaken intermolecular attraction. The problem is exacerbated in conjunction with surface roughness when liquids partially remain in grooves or dimples of the substrate. In the present study, a cupped microstructure with a cavity inspired by suction organs of aquatic animals is proposed. The microstructures (cup radius of 100 µm) are made from polyurethane using two‐photon lithography followed by replica molding. Adhesion to rough substrates is emulated experimentally by a micropatterned model substrate with varying channel widths. Pull‐off stresses are found to be about 200 kPa, i.e., twice atmospheric pressure. Evaluation of force–displacement curves together with in situ observations reveal the adhesion mechanism, which involves adaptation to surface roughness and an elastic force induced by the collapse of the cavity that holds sealed contact with the substrate during retraction. This new microarchitecture may pave the way for next generation microstructures applicable to real, rough surfaces under wet conditions.

Attachment of bioinspired microfibrils in fluids: transition from a hydrodynamic to hydrostatic mechanism

“…As retraction progresses, the hydrostatic tension in the cavity increases due to volume conservation, thereby maintaining the sealed contact. Overall, such self-sealing involves the transition from a hydrodynamic to a hydrostatic state, which has been previously reported [8,10,33].…”

“…equal to100 kPa), while wet suction is theoretically limited by the cohesive strength of water, which corresponds to negative hydrostatic pressures of the order of tens of megapascals [6,7]. Therefore, underwater adhesion of suction cups can be much larger than in air [8][9][10]. This effect is exploited in the suction organs of octopus and other aquatic animals [11,12].…”

Water as a “glue”: Elasticity-enhanced wet attachment of biomimetic microcup structures

“…The present paper proposes the first design of a miniaturized suction cup that sheds light on the nature of the attachment mechanism. Using advanced two-photon lithography and molding process at submillimeter scale ( 25 ), we fabricate polyurethane microcups consisting of a stalk and a conical lip ( Fig. 1B ).…”

Design of Double‐Network Click‐Gels for Self‐Contained Underwater Adhesion and Energy‐Wise Applications in Floating Photovoltaics

“…[ 11 ] The study of natural materials and biological structures in marine organisms has inspired the design of biomimetic underwater adhesives, which have mainly been derived from catechol chemistry and biomimetic microstructures in the past decades. [ 5,12–20 ] However, many bioinspired catechol derivatives (glue‐type underwater adhesives) require slow curing processes for gelation. In addition, their underwater adhesion is intrinsically susceptible to oxidation, pH changes, and pretreated surfaces, which undermine the robustness and reliability under realistic conditions.…”