Biological and artificial attachment devices: Lessons for materials scientists from flies and geckos

Femtosecond Laser Direct Writing of Gecko-Inspired Switchable Adhesion Interfaces on a Flexible Substrate

Biomimetic switchable adhesion interfaces (BSAIs) with dynamic adhesion states have demonstrated significant advantages in micro-manipulation and bio-detection. Among them, gecko-inspired adhesives have garnered considerable attention due to their exceptional adaptability to extreme environments. However, their high adhesion strength poses challenges in achieving flexible control. Herein, we propose an elegant and efficient approach by fabricating three-dimensional mushroom-shaped polydimethylsiloxane (PDMS) micropillars on a flexible PDMS substrate to mimic the bending and stretching of gecko footpads. The fabrication process that employs two-photon polymerization ensures high spatial resolution, resulting in micropillars with exquisite structures and ultra-smooth surfaces, even for tip/stem ratios exceeding 2 (a critical factor for maintaining adhesion strength). Furthermore, these adhesive structures display outstanding resilience, enduring 175% deformation and severe bending without collapse, ascribing to the excellent compatibility of the micropillar's composition and physical properties with the substrate. Our BSAIs can achieve highly controllable adhesion force and rapid manipulation of liquid droplets through mechanical bending and stretching of the PDMS substrate. By adjusting the spacing between the micropillars, precise control of adhesion strength is achieved. These intriguing properties make them promising candidates for various applications in the fields of microfluidics, micro-assembly, flexible electronics, and beyond.

Multifunctionality in Nature: Structure-Function Relationships in Biological Materials

Modern material design aims to achieve multifunctionality through integrating structures in a diverse range, resulting in simple materials with embedded functions. Biological materials and organisms are typical examples of this concept, where complex functionalities are achieved through a limited material base. This review highlights the multiscale structural and functional integration of representative natural organisms and materials, as well as biomimetic examples. The impact, wear, and crush resistance properties exhibited by mantis shrimp and ironclad beetle during predation or resistance offer valuable inspiration for the development of structural materials in the aerospace field. Investigating cyanobacteria that thrive in extreme environments can contribute to developing living materials that can serve in places like Mars. The exploration of shape memory and the self-repairing properties of spider silk and mussels, as well as the investigation of sensing-actuating and sensing-camouflage mechanisms in Banksias, chameleons, and moths, holds significant potential for the optimization of soft robot designs. Furthermore, a deeper understanding of mussel and gecko adhesion mechanisms can have a profound impact on medical fields, including tissue engineering and drug delivery. In conclusion, the integration of structure and function is crucial for driving innovations and breakthroughs in modern engineering materials and their applications. The gaps between current biomimetic designs and natural organisms are also discussed.

Bioinspired energy absorbing material designs using additive manufacturing

Nature provides many biological materials and structures with exceptional energy absorption capabilities. Few, relatively simple molecular building blocks (e.g., calcium carbonate), which have unremarkable intrinsic mechanical properties individually, are used to produce biopolymer-bioceramic composites with unique hierarchical architectures, thus producing biomaterial-architectures with extraordinary mechanical properties. Several biomaterials have inspired the design and manufacture of novel material architectures to address various engineering problems requiring high energy absorption capabilities. For example, the microarchitecture of seashell nacre has inspired multi-material 3D printed architectures that outperform the energy absorption capabilities of monolithic materials. Using the hierarchical architectural features of biological materials, iterative design approaches using simulation and experimentation are advancing the field of bioinspired material design. However, bioinspired architectures are still challenging to manufacture because of the size scale and architectural hierarchical complexity. Notwithstanding, additive manufacturing technologies are advancing rapidly, continually providing researchers improved abilities to fabricate sophisticated bioinspired, hierarchical designs using multiple materials. This review describes the use of additive manufacturing for producing innovative synthetic materials specifically for energy absorption applications inspired by nacre, conch shell, shrimp shell, horns, hooves, and beetle wings. Potential applications include athletic prosthetics, protective head gear, and automobile crush zones.

Functional Gradient Metallic Biomaterials: Techniques, Current Scenery, and Future Prospects in the Biomedical Field

Functional gradient materials (FGMs), as a modern group of materials, can provide multiple functions and are able to well mimic the hierarchical and gradient structure of natural systems. Because biomedical implants usually substitute the bone tissues and bone is an organic, natural FGM material, it seems quite reasonable to use the FGM concept in these applications. These FGMs have numerous advantages, including the ability to tailor the desired mechanical and biological response by producing various gradations, such as composition, porosity, and size; mitigating some limitations, such as stress-shielding effects; improving osseointegration; and enhancing electrochemical behavior and wear resistance. Although these are beneficial aspects, there is still a notable lack of comprehensive guidelines and standards. This paper aims to comprehensively review the current scenery of FGM metallic materials in the biomedical field, specifically its dental and orthopedic applications. It also introduces various processing methods, especially additive manufacturing methods that have a substantial impact on FGM production, mentioning its prospects and how FGMs can change the direction of both industry and biomedicine. Any improvement in FGM knowledge and technology can lead to big steps toward its industrialization and most notably for much better implant designs with more biocompatibility and similarity to natural tissues that enhance the quality of life for human beings.

Structural and mechanical properties of fish scales for the bio-inspired design of flexible body armors: A review

Natural protection offered to living beings is the result of millions of years of biological revolution. The protections provided in fishes, armadillos, and turtles by unique hierarchal designs help them to survive in surrounding environments. Natural armors offer protections with outstanding mechanical properties, such as high penetration resistance and toughness to weight ratio. The mechanical properties are not the only key features that make scales unique; they are also highly flexible and breathable. In this study, we aim to review the structural and mechanical characteristics of the scales from ray-finned or teleost fishes, which can be used for new bio-inspired armor designs. It is also essential to consider the hierarchical structure of extinct and existing natural armors. The basic characteristics, as mentioned above, are the foundation for developing high-performance, well-structured flexible natural armors. Furthermore, the present review justifies the importance of interaction between toughness, hardness, and deformability in well-engineered bio-inspired body armor. At last, some suggestions are proposed for the design and fabrication of new bio-inspired flexible body armors.

Biological and bioinspired materials: Structure leading to functional and mechanical performance

Nature has achieved materials with properties and mechanisms that go far beyond the current know-how of the engineering-materials industry. The remarkable efficiency of biological materials, such as their exceptional properties that rely on weak constituents, high performance per unit mass, and diverse functionalities in addition to mechanical properties, has been mostly attributed to their hierarchical structure. Key strategies for bioinspired materials include formulating the fundamental understanding of biological materials that act as inspiration, correlating this fundamental understanding to engineering needs/problems, and fabricating hierarchically structured materials with enhanced properties accordingly. The vast, existing literature on biological and bioinspired materials can be discussed in terms of functional and mechanical aspects. Through essential representative properties and materials, the development of bioinspired materials utilizes the design strategies from biological systems to innovatively augment material performance for various practical applications, such as marine, aerospace, medical, and civil engineering. Despite the current challenges, bioinspired materials have become an important part in promoting innovations and breakthroughs in the modern materials industry.

Progress in Bioinspired Dry and Wet Gradient Materials from Design Principles to Engineering Applications

Nature does nothing in vain. Through millions of years of revolution, living organisms have evolved hierarchical and anisotropic structures to maximize their survival in complex and dynamic environments. Many of these structures are intrinsically heterogeneous and often with functional gradient distributions. Understanding the convergent and divergent gradient designs in the natural material systems may lead to a new paradigm shift in the development of next-generation high-performance bio-/nano-materials and devices that are critically needed in energy, environmental remediation, and biomedical fields. Herein, we review the basic design principles and highlight some of the prominent examples of gradient biological materials/structures discovered over the past few decades. Interestingly, despite the anisotropic features in one direction (i.e., in terms of gradient compositions and properties), these natural structures retain certain levels of symmetry, including point symmetry, axial symmetry, mirror symmetry, and 3D symmetry. We further demonstrate the state-of-the-art fabrication techniques and procedures in making the biomimetic counterparts. Some prototypes showcase optimized properties surpassing those seen in the biological model systems. Finally, we summarize the latest applications of these synthetic functional gradient materials and structures in robotics, biomedical, energy, and environmental fields, along with their future perspectives. This review may stimulate scientists, engineers, and inventors to explore this emerging and disruptive research methodology and endeavors.

What Do We Learn from Good Practices of Biologically Inspired Design in Innovation?

Biologically inspired design (BID) is an emerging field of research with increasing achievements in engineering for design and problem solving. Its economic, societal, and ecological impact is considered to be significant. However, the number of existing products and success stories is still limited when compared to the knowledge that is available from biology and BID research. This article describes success factors for BID solutions, from the design process to the commercialization process, based on case studies and market analyses of biologically inspired products. Furthermore, the paper presents aspects of an effective knowledge transfer from science to industrial application, based on interviews with industrial partners. The accessibility of the methodological approach has led to promising advances in BID in practice. The findings can be used to increase the number of success stories by providing key steps toward the implementation and commercialization of BID products, and to point out necessary fields of cooperative research.

Re-designing materials for biomedical applications: from biomimicry to nature-inspired chemical engineering

Gathering inspiration from nature for the design of new materials, products and processes is a topic gaining rapid interest among scientists and engineers. In this review, we introduce the concept of nature-inspired chemical engineering (NICE). We critically examine how this approach offers advantages over straightforward biomimicry and distinguishes itself from bio-integrated design, as a systematic methodology to present innovative solutions to challenging problems. The scope of application of the nature-inspired approach is demonstrated via examples from the field of biomedicine, where much of the inspiration is still more narrowly focused on imitation or bio-integration. We conclude with an outlook on prospective future applications, offered by the more systematic and mechanistically based NICE approach, complemented by rapid progress in manufacturing, computation and robotics. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology'.

Additive Manufacturing as a Method to Design and Optimize Bioinspired Structures

Additive manufacturing (AM) is a current technology undergoing rapid development that is utilized in a wide variety of applications. In the field of biological and bioinspired materials, additive manufacturing is being used to generate intricate prototypes to expand our understanding of the fundamental structure-property relationships that govern nature's spectacular mechanical performance. Herein, recent advances in the use of AM for improving the understanding of the structure-property relationship in biological materials and for the production of bioinspired materials are reviewed. There are four essential components to this work: a) extracting defining characteristics of biological designs, b) designing 3D-printed prototypes, c) performing mechanical testing on 3D-printed prototypes to understand fundamental mechanisms at hand, and d) optimizing design for tailorable performance. It is intended to highlight how the various types of additive manufacturing methods are utilized, to unravel novel discoveries in the field of biological materials. Since AM processing techniques have surpassed antiquated limitations, especially with respect to spatial scales, there has been a surge in their demand as an integral tool for research. In conclusion, current challenges and the technical perspective for further development of bioinspired materials using AM are discussed.

Deformation and fracture behavior of a natural shell ceramic: Coupled effects of shell shape and microstructure

Common seashells possess their most adaptive functions benefiting from the macro-geometry and unique microstructures. The Cymbiola nobilis shell exhibits a logarithmic spiral-like shape and it is hierarchically constructed by the fiber-like crossed-lamellar structure. Three-point bending tests are conducted on three groups of samples taken from different locations (G1 with two macro-layers, G2 with three macro-layers, and G3 containing three macro-layers but with an arch-like curved shape). A novel method was developed to evaluate the bending stress of the curved samples and understand the bending fracture resistance of such curved samples. Due to the presence of a horizontal force that can decrease or shield the bending moment at the bottom center of samples, the arch-like G3 samples demonstrate the highest bending fracture resistance, revealing the significance of the curved shape of shell in the protection against the external attacks. The number of macro-layers and the curved shape of shell play an important role in the mechanical properties of the shell. The orientation of building blocks in a single crossed-lamellar layer is critical to the fracture resistance, and five types of fracture modes based on interfacial debonding, inter- and trans-lamella fracture are identified. The results obtained in this study would help open a new pathway to the development of bio-inspired high-performance structural materials.

Promoting biomimetic materials for a sustainable construction industry

This paper reviews the current knowledge of biomimicry and its potential in the sustainability of the South African construction industry through selection of materials. Biomimicry is the applied science that derives inspiration for solutions to human problems through the study of nature’s designs, processes and systems. The paper evaluates, promotes and encourages the use of biomimetic materials in the South African construction industry. A review of the extant literature was conducted on biomimetic materials and their applications and roles in the achievement of sustainability in the South African construction industry. The study shows that there is a misconception on bioprospected and biopirated materials as biomimetic materials. The study also found that there are already existing materials that were designed based on biomimicry principles. The paper offers a new approach and strategy to achieving sustainability in the South African construction industry through the use and incorporation of biomimetic materials into construction activities. Hence, it is envisaged that new ideas and innovations will be proffered which require an interdisciplinary collaboration between biologists and other stakeholders in the industry. This study challenges all stakeholders in the South African construction industry to adopt biomimicry in their construction practices.

Biomimetics and its tools

Biomimetics, as the transfer of strategies from biology to technology, is an emerging research area and has led to significant concepts over the past decades. The development of such concepts is described by the process of biomimetics, encompassing several steps. In Practice, beneficiaries of the process face challenges. Therefore, to overcome challenges and to facilitate the steps, tools have been developed in various areas, such as engineering, computing and design. However, these tools are not widely used yet. This paper presents an overview and a classification study of more than 40 tools with qualitative criteria. The criteria included, for example, the year of development, the accessibility of tools, the facilitated steps of the process or their contribution to sustainability. The classification shows that certain steps of the process and their challenges are well addressed by the tools, while other steps are not. The presented results contribute to the proposal of an improvement of the state of the art, and they build the foundation for future theoretical and practical analyses. These findings could contribute to increasing the implementation of biomimetics in various disciplines in the long term.

Morphogenesis and mechanostabilization of complex natural and 3D printed shapes

The natural selection and the evolutionary optimization of complex shapes in nature are closely related to their functions. Mechanostabilization of shape of biological structure via morphogenesis has several beautiful examples. With the help of simple mechanics-based modeling and experiments, we show an important causality between natural shape selection as evolutionary outcome and the mechanostabilization of seashells. The effect of biological growth on the mechanostabilization process is identified with examples of two natural shapes of seashells, one having a diametrically converging localization of stresses and the other having a helicoidally concentric localization of stresses. We demonstrate how the evolved shape enables predictable protection of soft body parts of the species. The effect of bioavailability of natural material is found to be a secondary factor compared to shape selectivity, where material microstructure only acts as a constraint to evolutionary optimization. This is confirmed by comparing the mechanostabilization behavior of three-dimensionally printed synthetic polymer structural shapes with that of natural seashells consisting of ceramic and protein. This study also highlights interesting possibilities in achieving a new design of structures made of ordinary materials which have bio-inspired optimization objectives.

Single macroscopic pillars as model system for bioinspired adhesives: influence of tip dimension, aspect ratio, and tilt angle

The goal of our study is to better understand the design parameters of bioinspired dry adhesives inspired by geckos. For this, we fabricated single macroscopic pillars of 400 μm diameter with different aspect ratios and different tip shapes (i.e., flat tips, spherical tips with different radii, and mushroom tips with different diameters). Tilt-angle-dependent adhesion measurements showed that although the tip shape of the pillars strongly influences the pull-off force, the pull-off strength is similar for flat and mushroom-shaped tips. We found no tilt-angle dependency of adhesion for spherical tip structures and, except for high tilt angle and low preload experiments, no tilt-angle effect for mushroom-tip pillars. For flat-tip pillars, we found a strong influence of tilt angle on adhesion, which decreased linearly with increasing aspect ratio. The experiments show that for the tested aspect ratios between 1 and 5, a linear decrease of tilt-angle dependency is found. The results of our studies will help to design bioinspired adhesives for application on smooth and rough surfaces.

Optimal characteristic nanosizes of mineral bridges in mollusk nacre

The nanosizes of mineral bridges linking neighboring platelets in various types of mollusk nacre dictate the optimal interfacial strength.

Nanomaterial processing using self-assembly-bottom-up chemical and biological approaches

Nanotechnology is touted as the next logical sequence in technological evolution. This has led to a substantial surge in research activities pertaining to the development and fundamental understanding of processes and assembly at the nanoscale. Both top-down and bottom-up fabrication approaches may be used to realize a range of well-defined nanostructured materials with desirable physical and chemical attributes. Among these, the bottom-up self-assembly process offers the most realistic solution toward the fabrication of next-generation functional materials and devices. Here, we present a comprehensive review on the physical basis behind self-assembly and the processes reported in recent years to direct the assembly of nanoscale functional blocks into hierarchically ordered structures. This paper emphasizes assembly in the synthetic domain as well in the biological domain, underscoring the importance of biomimetic approaches toward novel materials. In particular, two important classes of directed self-assembly, namely, (i) self-assembly among nanoparticle-polymer systems and (ii) external field-guided assembly are highlighted. The spontaneous self-assembling behavior observed in nature that leads to complex, multifunctional, hierarchical structures within biological systems is also discussed in this review. Recent research undertaken to synthesize hierarchically assembled functional materials have underscored the need as well as the benefits harvested in synergistically combining top-down fabrication methods with bottom-up self-assembly.

Structural biological materials: critical mechanics-materials connections

Spider silk is extraordinarily strong, mollusk shells and bone are tough, and porcupine quills and feathers resist buckling. How are these notable properties achieved? The building blocks of the materials listed above are primarily minerals and biopolymers, mostly in combination; the first weak in tension and the second weak in compression. The intricate and ingenious hierarchical structures are responsible for the outstanding performance of each material. Toughness is conferred by the presence of controlled interfacial features (friction, hydrogen bonds, chain straightening and stretching); buckling resistance can be achieved by filling a slender column with a lightweight foam. Here, we present and interpret selected examples of these and other biological materials. Structural bio-inspired materials design makes use of the biological structures by inserting synthetic materials and processes that augment the structures' capability while retaining their essential features. In this Review, we explain this idea through some unusual concepts.

FABRICATION OF LARGE-AREA SILICON NANOWIRE ARRAYS FOR SOLAR CELLS

In this paper, a simple, low-cost and efficient method was adopted to fabricate large-area Si nanowire ( SiNW ) arrays by inserting the p-type (100) silicon wafer into aqueous HF + AgNO3 solution for a certain time at room temperature. Surface of the silicon wafer with high aspect ratio SiNW shows the characteristics of low-reflection as low as 5% in the 450–800 nm wavelength range, especially less than 1% after etching for 60 min. The surface also exhibits super-hydrophobicity with water contact angle up to 150°. We investigated the relationship between the etching duration and aspect ratio of the SiNW systematically and demonstrated that the aspect ratio of the SiNW can be controlled. The antireflection surface shows a potential implication in increasing the conversation efficiency for solar cells, and the self-cleaning properties will further enhance the resistance to environment conditions for a long-life work.

Novel application of polyelectrolyte multilayers as nanoscopic closures with hermetic sealing

Closure systems for personnel protection applications, such as protective clothing or respirator face seals, should provide effective permeation barrier to toxic gases. Currently available mechanical closure systems based on the hook and loop types (example, Velcro) do not provide adequate barrier to gas permeation. To achieve hermetic sealing, we propose a nonmechanical, nanoscopic molecular closure system based on complementary polyelectrolyte multilayers, one with a polycation outermost layer and the other with a polyanion outermost layer. The closure surfaces were prepared by depositing polyelectrolyte multilayers under a variety of deposition conditions, on conformable polymer substrates (thin films of polyethylene teraphthalate, PET or polyimide, PI). The hermetic sealing property of the closures was evaluated by measuring the air flow resistance using the dynamic moisture permeation cell (DMPC) at different humidity conditions. The DMPC measurements show that the polyelectrolyte multilayer closures provide significantly large resistance to air flow, approximately 20-800 times larger than that possible with conventional hook and loop type closure systems, at all humidity levels (from 5 to 95% relative humidity). Hence, from the point of view of providing a hermetic seal against toxic gas permeation, the polyelectrolyte multilayer closures are viable candidates for further engineering development. However, the adhesive strength of the multilayer closures measured by atomic force microscopy suggests that the magnitude of adhesion is much smaller than what is possible with mechanical closures. Therefore, we envisage the development of a composite closure system combining the mechanical closure to provide strong adhesion and the multilayer closure to provide hermetic sealing.

Mechanisms of temporary adhesion in benthic animals

Adhesive systems are ubiquitous in benthic animals and play a key role in diverse functions such as locomotion, food capture, mating, burrow building, and defence. For benthic animals that release adhesives, surface and material properties and external morphology have received little attention compared to the biochemical content of the adhesives. We address temporary adhesion of benthic animals from the following three structural levels: (a) the biochemical content of the adhesive secretions, (b) the micro- and mesoscopic surface geometry and material properties of the adhesive organs, and (c) the macroscopic external morphology of the adhesive organs. We show that temporary adhesion of benthic animals is affected by three structural levels: the adhesive secretions provide binding to the substratum at a molecular scale, whereas surface geometry and external morphology increase the contact area with the irregular and unpredictable profile of the substratum from micro- to macroscales. The biochemical content of the adhesive secretions differs between abiotic and biotic substrata. The biochemistry of the adhesives suitable for biotic substrata differentiates further according to whether adhesion must be activated quickly (e.g. as a defensive mechanism) or more slowly (e.g. during adhesion of parasites). De-adhesion is controlled by additional secretions, enzymes, or mechanically. Due to deformability, the adhesive organs achieve intimate contact by adapting their surface profile to the roughness of the substratum. Surface projections, namely cilia, cuticular villi, papillae, and papulae increase the contact area or penetrate through the secreted adhesive to provide direct contact with the substratum. We expect that the same three structural levels investigated here will also affect the performance of artificial adhesive systems.

The effect of contaminants on the adhesion of the spatulae of a gecko

Many researchers have reported that the robust adhesion that enables geckos to move quickly and securely across a range of vertical and horizontal surfaces is provided by the hierarchical structure of their feet (i.e. lamellae, setae, spatulae, etc.). Maintaining this robust adhesion requires an intimate contact between the terminal tips of the spatulae and the surface. The aim of this study was to investigate the effect on the adhesive properties of the spatulae when a particle becomes trapped at the contact surface. Using the Johnson, Kendall and Roberts (JKR) theory, a model was constructed to assist in the analysis of the interactions between the spatula tip, the particle and the surface. The results showed that the keratin (the natural material of the spatula) provides a robust system for adhesion even when there is a particle in the contact area, and the effective contact area of spatulae will be 80%. When the particle is significantly harder than the surface, the adhesion properties of the contact surface influenced by the particle will be more obvious. The results also reveal that the generated adhesion is considerably higher when the spatula is in contact with a softer surface, such as wood or concrete, rather than a hard surface, such as glass or SiO2.

Gecko-inspired surfaces: a path to strong and reversible dry adhesives

The amazing adhesion of gecko pads to almost any kind of surfaces has inspired a very active research direction over the last decade: the investigation of how geckos achieve this feat and how this knowledge can be turned into new strategies to reversibly join surfaces. This article reviews the fabrication approaches used so far for the creation of micro- and nanostructured fibrillar surfaces with adhesive properties. In the light of the pertinent contact mechanics, the adhesive properties are presented and discussed. The decisive design parameters are fiber radius and aspect ratio, tilt angle, hierarchical arrangement and the effect of the backing layer. Also first responsive systems that allow thermal switching between nonadhesive and adhesive states are described. These structures show a high potential of application, providing the remaining issues of robustness, reliability, and large-area manufacture can be solved.

Structure and mechanical properties of selected biological materials

Mineralized biological tissues offer insight into how nature has evolved these components to optimize multifunctional purposes. These mineral constituents are weak by themselves, but interact with the organic matrix to produce materials with unexpected mechanical properties. The hierarchical structure of these materials is at the crux of this enhancement. Microstructural features such as organized, layered organic/inorganic structures and the presence of porous and fibrous elements are common in many biological components. The organic and inorganic portions interact at the molecular and micro-levels synergistically to enhance the mechanical function. In this paper, we report on recent progress on studies of the abalone and Araguaia river clam shells, arthropod exoskeletons, antlers, tusks, teeth and bird beaks.

Gecko-inspired carbon nanotube-based self-cleaning adhesives

The design of reversible adhesives requires both stickiness and the ability to remain clean from dust and other contaminants. Inspired by gecko feet, we demonstrate the self-cleaning ability of carbon nanotube-based flexible gecko tapes.

A reversible wet/dry adhesive inspired by mussels and geckos

The adhesive strategy of the gecko relies on foot pads composed of specialized keratinous foot-hairs called setae, which are subdivided into terminal spatulae of approximately 200 nm (ref. 1). Contact between the gecko foot and an opposing surface generates adhesive forces that are sufficient to allow the gecko to cling onto vertical and even inverted surfaces. Although strong, the adhesion is temporary, permitting rapid detachment and reattachment of the gecko foot during locomotion. Researchers have attempted to capture these properties of gecko adhesive in synthetic mimics with nanoscale surface features reminiscent of setae; however, maintenance of adhesive performance over many cycles has been elusive, and gecko adhesion is greatly diminished upon full immersion in water. Here we report a hybrid biologically inspired adhesive consisting of an array of nanofabricated polymer pillars coated with a thin layer of a synthetic polymer that mimics the wet adhesive proteins found in mussel holdfasts. Wet adhesion of the nanostructured polymer pillar arrays increased nearly 15-fold when coated with mussel-mimetic polymer. The system maintains its adhesive performance for over a thousand contact cycles in both dry and wet environments. This hybrid adhesive, which combines the salient design elements of both gecko and mussel adhesives, should be useful for reversible attachment to a variety of surfaces in any environment.