From Dry to Wet, the Nature Inspired Strong Attachment Surfaces and Their Medical Applications

Abstract

Strong attachment in complicated human body environments is of great importance for precision medicine especially with the rapid growth of minimal invasive surgery and flexible electronics. Natural organisms with highly evolved feet or claws can easily climb in complex environments from dry to wet and even underwater, providing significant inspiration for strong attachment research. This review summarizes the strong attachment behaviors of natural creatures in varied environments such as the gecko, tree frog, and octopus. Their attachment surfaces' complex micronano structures and material properties exhibit evolutionary adaptations that enable them to transition across dry, wet, and underwater environments, highlighting the intricate mechanism of interfacial micronano dynamic behaviors. The interfacial liquid/air media regulation and contact stress adjustment from the coupling effects of surface structures and materials have been concluded as key factors in natural strong attachments. With the bioinspired strong attachment surface design, manufacturing methods including mold-assisted replication, nano 3D printing, self-assembly and field induced molding have been discussed. Finally, applications of bioinspired surfaces in low damage surgical instruments, tissue repair and flexible electronics have been demonstrated.

Keywords: attachment mechanisms; bioinspired surfaces; biomimetic; interfacial dynamic behaviors; precision medicine; strong adhesion; strong friction; wearable electronics.

Figure 1

Schematic diagram illustrating the review of nature-inspired strong attachment surfaces. Nature has evolved a variety of organisms with exceptional adhesive properties, adapted to diverse humidity conditions ranging from dry to underwater environments. Examples include geckos, tree frogs, and octopuses, which display an evolutionary pattern in biological attachment systems. These organisms rely on delicate micro and nanostructures and materials to achieve robust adhesion through various attachment mechanisms, providing inspiration for the design and fabrication of artificial attachment surfaces. Bioinspired surfaces leverage the coupling effects of surface structures and materials to enable strong adhesion by regulating interfacial media behaviors and optimizing contact stress distribution, with broad applications in the precision medicine. [Pictures of Gecko were reprinted with permission from ref (6). Copyright 2006 The National Academy of Sciences of the USA. SEM of tree frog toe pads was reprinted with permission from ref (7). Copyright 2006 The Royal Society. Photographs of an octopus and its sucker were reprinted with permission from ref (9). Copyright 2017 Springer Nature. Diagram of negative pressure was reprinted with permission from ref (8). Copyright 2013 Authors, licensed under a Creative Commons Attribution (CC BY) license, published by PLoS One. The tree frog-inspired structure was reprinted with permission from ref (11). Copyright 2020 The Authors under a Creative Commons Attribution 4.0 International License, published by Wiley-VCH. The octopus-inspired architecture was reprinted with permission from ref (9). Copyright 2017 Springer Nature. The photograph of tissue adhesives was reprinted with permission from ref (30). Copyright 2019 Springer Nature. The photograph of drug delivery was reprinted with permission from ref (31). Copyright 2019 American Association for the Advancement of Science. The photograph of biosignal monitoring was reprinted with permission from ref (32). Copyright 2019 Wiley-VCH.]

Figure 2

Overview of strong attachment organisms and their adhesive structures across terrestrial to aquatic environments. Organisms have evolved a variety of attachment structures to adapt to changing humidity conditions, from dry to wet environments. These range from the hierarchical seta arrays of geckos for dry adhesion, to the patterned pillar arrays of tree frogs for wet adhesion, to the suction structures of octopuses and the chemically adhesive structures of mussels. As environmental humidity increases, the wettability of biological adhesive elements transitions from hydrophobic to hydrophilic, reflecting a trend that correlates with the level of environmental humidity. [Pictures of the gecko, fly, and beetle were reprinted with permission from ref (18). Copyright 2003 The National Academy of Sciences. Pictures of the spider were reprinted with permission from ref (23). Copyright 1994 American Arachnological Society. Pictures of bush cricket were reprinted with permission from ref (21). Copyright 2004 The Society. Pictures of tree frog were reprinted with permission from ref (12). Copyright 2009 The Company of Biologists. Pictures of diving beetle were reprinted with permission from ref (22). Copyright 2014 Royal Society. Pictures of octopus were reprinted with permission from ref (32). Copyright 2018 The Authors under a Creative Commons Attribution 4.0 International License, published by Wiley-VCH. Pictures of remora were reprinted with permission from refs (24) and (25). Copyright 2012 Wiley-VCH. Copyright 2015 The Company of Biologists. Pictures of mussel were reprinted with permission from ref (26). Copyright 2011 Annual Reviews.].

Figure 3

Physical and chemical mechanisms of biological attachment surfaces. (a) Schematic diagram of van der Waals force between two flat surfaces. (b) A liquid bridge with two principal radii of curvature between two solid cylinders. (c) Schematic diagram of a liquid bridge formed between a flat-ended fiber and a rigid substrate. Reprinted with permission from ref (51). Copyright 2006 Elsevier. (d) Schematic diagram of liquid bridge splitting. (e) Deformation of two elastic substrates induced by capillary force. Reprinted with permission from ref (54). Copyright 2014 American Physical Society. (f) Differential pressure between inside and outside the suction cup. (g) Four typical structures of mechanical interlocking. Reprinted with permission from ref (65). Copyright 2010 Springer-Verlag. (h) Multiple physical and chemical interactions of catechol groups in wet adhesion. Reprinted with permission from ref (86). Copyright 2018 Wiley-VCH.

Figure 4

Attachment mechanisms of typical natural organisms. (a1) Photograph of a gecko and scanning electron micrograph (SEM) of its pad setae. Reprinted with permission from ref (37). Copyright 2000 Nature. (a2) Diagram of attachment of a single seta by rolling in the toes. Reprinted with permission from ref (6). Copyright 2006 The National Academy of Sciences of the USA. (a3) The adhesion force between the gecko spatula and substrates increases apparently with increasing humidity at ambient temperature. Reprinted with permission from ref (40). Copyright 2005 The National Academy of Sciences of the USA. (a4) Simulation of the variation in adhesion forces between a silicon nitride sphere and a mica at different relative humidities, including van der Waals and capillary forces. Reprinted with permission from ref (41). Copyright 2005 Elsevier. (b1) Photograph of a tree frog and SEM of its toe pads. Reprinted with permission from ref (55). Copyright 2015 Wiley-VCH. (b2) Characterization of the interfacial fluid layer between tree frog toe pad and glass substrate using interference reflection microscopy. Reprinted with permission from ref (7). Copyright 2006 The Royal Society. (b3) Deformation of a soft pillar surface caused by an interfacial liquid bridge. (b4) The friction of tree frog toe pads varies during successive frog-like-crawling (FLC) steps and reaches a maximum at the boundary friction. Reprinted with permission from ref (11). Copyright 2020 The Authors under a Creative Commons Attribution 4.0 International License, published by Wiley-VCH. (c1) Photograph of an octopus and schematic diagram of the sucker structure. (c2, c3) Illustrations of octopus suckers attached to substrates in underwater and dry states, showing the sealing effects induced by cohesive forces of water and van der Waals forces, respectively. (c4) Confocal fluorescence image showing the adhesion stage of the sucker, with liquid trapped in the upper chamber. Reprinted with permission from ref (9). Copyright 2017 Springer Nature. (d1) Photograph of a cricket leg. Reprinted with permission from ref (66). Copyright 2018 The Authors under a Creative Commons Attribution 4.0 International License, published by the Royal Society. (d2) SEM of ventral side setae in gill lamellae of mayfly larvae. Reprinted with permission from ref (68). Copyright 2010 Company of Biologists. (e1) Schematic drawing of a mussel attached to a substrate by byssal plaque. Reprinted with permission from ref (75). Copyright 2007 Springer. (e2) Photograph of sandcastle worms using adhesive proteins to glue sand grains together to build tubular shelters. Reprinted with permission from ref (76). Copyright 2018 Wiley-VCH. (e3) Barnacles adhered to the skin of a whale. Reprinted with permission from ref (78). Copyright 2021 Springer Nature.

Figure 5

Adhesive structures prepared by mold-assisted replication. (a) The structure of mushroom tip prepared by a template method and its SEM images. Reprinted with permission from ref (111). Copyright 2021 Wiley-VCH. (b) Micronano structure of hexagonal prism prepared by a template method and its SEM diagram. Reprinted with permission from ref (118). Copyright 2023 American Association for the Advancement of Science. (c) Fractal hexagonal prism structure prepared by a template method and its SEM images. Reprinted with permission from ref (11). Copyright 2020 The Authors under a Creative Commons Attribution 4.0 International License, published by Wiley-VCH.

Figure 6

Adhesive structures prepared by two-photon polymerization lithography. (a) Schematic diagram of wedge structure prepared by two-photon polymerization photolithography and its SEM. Reprinted with permission from ref (133). Copyright 2020 Elsevier. (b) Schematic diagram of Winglike structure prepared by two-photon polymerization photolithography and its SEM. Reprinted with permission from ref (134). Copyright 2015 American Chemical Society. (c) Schematic diagram of mushroom structure prepared by two-photon polymerization photolithography and its SEM. Reprinted with permission from ref (135). Copyright 2021 Wiley-VCH.

Figure 7

Adhesive structures prepared by self-assembly. (a) Self-assembly using PS microspheres. Reprinted with permission from ref (136). Copyright 2014 American Chemical Society. (b) Preparation of micronano suction cups by expandable colloid self-assembly. Reprinted with permission from ref (137). Copyright 2023 American Chemical Society.

Figure 8

Adhesive structures prepared by field-induced molding. (a) The micro and nanostructures of the mushroom tip were prepared by electric field induction. Reprinted with permission from ref (113). Copyright 2022 Springer Nature. (b) The array of micro and nanostructures were prepared by magnetic field induced molding. Reprinted with permission from ref (139). Copyright 2023 Springer Nature. (c) Micronano structures of array suckers were prepared by flow field induced molding. Reprinted with permission from ref (9). Copyright 2017 Springer Nature.

Figure 9

A Comparison of four different preparation methods. (a–d) refer to the preparation processes of the template method, the two-photon lithography polymerization method, the self-assembly method, and the field-induced molding method, respectively. This section also outlines the common microstructures prepared by these methods and their technical characteristics.

Figure 10

Bioinspired attachment structures for surgical grippers. (a, b) are photos of 1 mm and 0.5 mm dental grips, respectively. (c) The deformation of fresh pig liver when 10 N normal force is applied to the surgical instrument with a hexagonal column pattern. (d) Comparison of the largest tissue deformation induced by 1 mm and 0.5 mm macroscale teeth and hexagonal pillar pattern under normal forces of 1, 5, and 10 N. Reprinted with permission from ref (27). Copyright 2015 American Chemical Society. (e) Schematic illustration of perforated microcylinders with mushroom-shaped tips and snapshots of porcine liver grasping using a conventional surgical grasper and PMMS, respectively. Top-view snapshots show severe damage, while bottom-view snapshots demonstrate no significant damage when using the proposed PMMS. Reprinted with permission from ref (142). Copyright 2021 Elsevier. (f) A sucker structure with an origami process is used for artificial denture adhesion. Reprinted with permission from ref (144). Copyright 2024 American Chemical Society. (g) Adhesion mechanism of plasma adhesive patch under normal temperature, high-temperature environment, and infrared irradiation. (h) Photograph showing high adhesion on the mouse liver under NIR light irradiation (85 mW·cm^–2, 3 min) (strong adhesive state). Reprinted with permission from ref (145). Copyright 2024 American Chemical Society.

Figure 11

Bioinspired adhesive patches for wound closure and drug delivery. (a) Gross images showing hemostatic effects of the gauze and C-CTS/SA-Ag/dECM hydrogel with no treatment as a control (scale bars = 1 cm). Reprinted with permission from ref (150). Copyright 2022 Wiley-VCH. (b) Schematic illustration of the diabetic rabbit model, with quantification of wound contraction at days 7 and 14. (c) Granulation tissue thickness. Reprinted with permission from ref (153). Copyright 2024 American Chemical Society. (d) Four different structures: the normal group, the d-MN group, the n-MN group, and the control group, respectively. (e) Digital images of knee joints of rats in different treatment groups. Reprinted with permission from ref (160). Copyright 2020 The Authors under a Creative Commons Attribution 4.0 International License, published by American Association for the Advancement of Science. (f) Hydrogel microneedle suction cup drug delivery platform structure. (g) Average tumor growth curves of the tumors receiving treatments of Silk-Fp patch, Silk-F patch, and no treatment. (h) Gross inspection of buccal mucosa ulcers in rabbits treated with Silk-Fp patch, Silk-F patch, and no treatment at days 0 and 8. Reprinted with permission from ref (161). Copyright 2023 The Authors under a Creative Commons Attribution 4.0 International License, published by American Association for the Advancement of Science.

Figure 12

Bioinspired adhesive surfaces for flexible sensor adhesion interfaces. (a) Flexible electronic sensor with fractal hexagonal microcolumn structure. (b) Changes of pulse signal under different volumes of sweat. Reprinted with permission from ref (11). Copyright 2020 The Authors under a Creative Commons Attribution 4.0 International License, published by Wiley-VCH. (c) The adhesive strength of the bilayer composite hydrogel to different substrates. (d) Detect changes in the signal as the finger moves. (e) Statistics results of wound healing rate. Reprinted with permission from ref (164). Copyright 2021 Elsevier. (f, g) Comparison of the heart signals measured by an electrophysiologic monitor, the piezoelectric thin film, and the Biopatch, respectively. Reprinted with permission from ref (165). Copyright 2024 Wiley-VCH. (h) Images show commercial electrodes (1), PDMS/PI/Au mesh electrodes (2) and 3D LD/PI/Au mesh electrodes (3) on the skin before and after exercise. Scale bars, 5 cm. (i) ECG signals recorded from different electrodes before and after exercise. Reprinted with permission from ref (166). Copyright 2024 Springer Nature.