Barnacles are notorious marine fouling organisms, whose life cycle initiates with the planktonic larva, followed by the free-swimming cyprid that voluntarily explores, and searches for an appropriate site to settle and metamorphoses into a sessile adult. Within this life cycle, both the cyprid and the adult barnacle deposit multi-protein adhesives for temporary or permanent underwater adhesion. Here, we present a comprehensive review of the biochemistries behind these different adhesion events in the life cycle of a barnacle. First, we introduce the multiple adhesion events and their corresponding adhesives from two complementary aspects: the in vivo synthesis, storage, and secretion as well as the in vitro morphology and biochemistry. The amino acid compositions, sequences, and structures of adult barnacle adhesive proteins are specifically highlighted. Second, we discuss the molecular mechanisms of adult barnacle underwater attachment in detail by analyzing the possible adhesive and cohesive roles of different adhesive proteins, and based on these analyses, we propose an update to the original barnacle underwater adhesion molecular model. We believe that this review can greatly promote the general understanding of the molecular mechanisms underlying the reversible and irreversible underwater adhesion of barnacles and their larvae. Such an understanding is the basis for the prevention of barnacle fouling on target surfaces as well as designing conceptually new barnacle-inspired artificial underwater adhesives.

HIGHLIGHTS • An overview of the formation mechanisms, fabrication methods, and applications of bioinspired wrinkling patterns on curved substrates is provided. • The effect of substrate curvature is described in detail to clarify the difference of wrinkling patterns between planar and curved substrates. • Opportunities and challenges of the surface wrinkling in the biofabrication, three-dimensional micro/nano fabrication, and fourdimensional printing are discussed.

Template‐free, highly efficient, and large‐area construction of complex multiscale architectures is still a great challenge for microfabrications. Inspired by the hierarchical micropapillae on the superhydrophobic surface of natural rose petals, here, a facile 3D shrinking method is reported to build a graphene oxide (GO) papillae array. Circular GO speckles with a gradient of thickness are deposited on an inflated latex balloon through the water‐evaporation‐driven assembly of GO nanosheets, which then shrink into hierarchical papillae under compressive stresses upon deflation. The fluoroalkylsilane modified GO papillae array exhibits a combined performance of strong superhydrophobicity (CA > 170°), tunable adhesive force (39.2–129.4 µN), and ultralarge liquid capacity (25 µL). The wetting states (Wenzel, Cassie‐I, and Cassie‐Baxter), the adhesive forces, and the liquid capacities all can be tuned by varying the buckling topography (microwrinkle or microfold), the papillae number (3, 4, 6, or 7), and the array arrangement (triangle, square, or hexagon). For one single papillae, the highest adhesive force and the highest liquid capacity incresed to a record breaking value of 26.5 µN and 4.2 µL, respectively, which are promising for programmable manipulations of microdroplets and relevant for multistep microreactions.

Developing adhesives that can function underwater remains a major challenge for bioengineering, yet many marine creatures, exemplified as mussels and barnacles, have evolved their unique proteinaceous adhesives for strong wet adhesion. The mechanisms underlying the strong adhesion of these natural adhesive proteins provide rich information for biomimetic efforts. Here, combining atomic force microscopy (AFM) imaging and force spectroscopy, we examine the effects of pH on the self-assembly and adhesive properties of cp19k, a key barnacle underwater adhesive protein. For the first time, we confirm that the bacterial recombinant Balanus albicostatus cp19k (rBalcp19k), which contains no 3,4-dihydroxyphenylalanine (DOPA) or any other amino acids with post-translational modifications, can self-assemble into aggregated nanofibers at acidic pHs. Under moderately acidic conditions, the adhesion strength of unassembled monomeric rBalcp19k on mica is only slightly lower than that of a commercially available mussel adhesive protein mixture, yet the adhesion ability of rBalcp19k monomers decreases significantly at increased pH. In contrast, upon preassembly at acidic and low-salinity conditions, rBalcp19k nanofibers keep stable in basic and high-salinity seawater and display much stronger adhesion and thus show resistance to its adverse impacts. Besides, we find that the adhesion ability of Balcp19k is not impaired when it is combined with an N-terminal Thioredoxin (Trx) tag, yet whether the self-assembly property will be disrupted is not determined. Collectively, the self-assembly-enhanced adhesion presents a previously unexplored mechanism for the strong wet adhesion of barnacle cement proteins and may lead to the design of barnacle-inspired adhesive materials.

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