Hybrid Surface Patterns Mimicking the Design of the Adhesive Toe Pad of Tree Frog

Xue, Longjian; Sanz, Begoña; Luo, Aoyi; Turner, Kevin T.; Wang, Xin; Tan, Di; Zhang, Rui; Du, Hang; Steinhart, Martin; Mijangos, Carmen; Guttmann, Markus; Kappl, Michael; Campo, Aránzazu del

doi:10.1021/acsnano.7b04994

Cited by 119 publications

(117 citation statements)

References 51 publications

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“…The contribution of each of these four moderators to the performance of a nanostructure or microstructure varies between applications. For example, performance of patterned adhesives is predominantly determined by their geometric complexity (e.g., mushroom‐shaped pillars, hierarchical structures), but high resolution (i.e., small size of features) and the use of more than one material in the structure can also be employed for enhancing adhesion. Another example is MEMS, the performance of which is assumed to improve with miniaturization of these systems, leading to higher processing speeds, energy conservation, and cost reduction .…”

Section: Introductionmentioning

confidence: 99%

Nanostructure and Microstructure Fabrication: From Desired Properties to Suitable Processes

Assenbergh

Meinders²,

Geraedts

et al. 2018

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When designing a new nanostructure or microstructure, one can follow a processing-based manufacturing pathway, in which the structure properties are defined based on the processing capabilities of the fabrication method at hand. Alternatively, a performance-based pathway can be followed, where the envisioned performance is first defined, and then suitable fabrication methods are sought. To support the latter pathway, fabrication methods are here reviewed based on the geometric and material complexity, resolution, total size, geometric and material diversity, and throughput they can achieve, independently from processing capabilities. Ten groups of fabrication methods are identified and compared in terms of these seven moderators. The highest resolution is obtained with electron beam lithography, with feature sizes below 5 nm. The highest geometric complexity is attained with vat photopolymerization. For high throughput, parallel methods, such as photolithography (≈10 m h ), are needed. This review offers a decision-making tool for identifying which method to use for fabricating a structure with predefined properties.

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Section: Introductionmentioning

confidence: 99%

Nanostructure and Microstructure Fabrication: From Desired Properties to Suitable Processes

Assenbergh

Meinders²,

Geraedts

et al. 2018

Small

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“…We hypothesise that the longitudinally skewed tonofibrils increase the stiffness of the apical epidermis during the transmission of shear loads deeper into the digital pad, possibly increasing friction by the distribution of mechanical stresses over a larger volume of pad material (Xue et al. ) and maintaining the structural integrity of the epidermal surface. The dense ‘sponge‐like’ network of tonofibrils within the apical regions of the superficial cells may locally increase the mechanical resilience of the epidermis surface (Drotlef et al.…”

Section: Discussionmentioning

confidence: 99%

“…As discussed above, the ventral cutis seems to be adapted primarily towards the transmission of shear rather than normal loads: the naturally skewed trajectories of the tonofibrils in the superficial epidermal cells negate potential adhesion‐enhancing effects found in tree‐frog‐inspired adhesives including normally oriented fibres (Xue et al. ).…”

Section: Discussionmentioning

confidence: 99%

Force‐transmitting structures in the digital pads of the tree frog Hyla cinerea: a functional interpretation

et al. 2018

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The morphology of the digital pads of tree frogs is adapted towards attachment, allowing these animals to attach to various substrates and to explore their arboreal habitat. Previous descriptions and functional interpretations of the pad morphology mostly focussed on the surface of the ventral epidermis, and little is known about the internal pad morphology and its functional relevance in attachment. In this study, we combine histology and synchrotron micro‐computer‐tomography to obtain a comprehensive 3‐D morphological characterisation of the digital pads (in particular of the internal structures involved in the transmission of attachment forces from the ventral pad surface towards the phalanges) of the tree frog Hyla cinerea. A collagenous septum runs from the distal tip of the distal phalanx to the ventral cutis and compartmentalises the subcutaneous pad volume into a distal lymph space and a proximal space, which contains mucus glands opening via long ducts to the ventral pad surface. A collagen layer connects the ventral basement membrane via interphalangeal ligaments with the middle phalanx. The collagen fibres forming this layer curve around the transverse pad‐axis and form laterally separated ridges below the gland space. The topological optimisation of a shear‐loaded pad model using finite element analysis (FEA) shows that the curved collagen fibres are oriented along the trajectories of the maximum principal stresses, and the optimisation also results in ridge‐formation, suggesting that the collagen layer is adapted towards a high stiffness during shear loading. We also show that the collagen layer is strong, with an estimated tensile strength of 2.0–6.5 N. Together with longitudinally skewed tonofibrils in the superficial epidermis, these features support our hypothesis that the digital pads of tree frogs are primarily adapted towards the generation and transmission of friction rather than adhesion forces. Moreover, we generate (based on a simplified FEA model and predictions from analytical models) the hypothesis that dorsodistal pulling on the collagen septum facilitates proximal peeling of the pad and that the septum is an adaptation towards detachment rather than attachment. Lastly, by using immunohistochemistry, we (re‐)discovered bundles of smooth muscle fibres in the digital pads of tree frogs. We hypothesise that these fibres allow the control of (i) contact stresses at the pad–substrate interface and peeling, (ii) mucus secretion, (iii) shock‐absorbing properties of the pad, and (iv) the macroscopic contact geometry of the ventral pad surface. Further work is needed to conclude on the role of the muscular structures in tree frog attachment. Overall, our study contributes to the functional understanding of tree frog attachment, hence offering novel perspectives on the ecology, phylogeny and evolution of anurans, as well as the design of tree‐frog‐inspired adhesives for technological applications.

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“…These flexible and freestanding MSMs are generated by the self-assembly of elastic plastic copolymer nanoparticle photonic crystals on micropatterned PDMS templates. Among them, tree frog's toe pads [13] and gecko feet micro/nanostructures [14] have been mimicked to build skin-adhesive layers for sensitive sensing. MSMs with designed patterns can be fabricated by assembling polymer nanoparticles on patterned molds; complicated and highly integrated electro-microfluidics are generated on one slice of MSMs by utilizing these patterns as microfluidic channels and electrocircuits.…”

mentioning

confidence: 99%

“…Among them, tree frog's toe pads [13] and gecko feet micro/nanostructures [14] have been mimicked to build skin-adhesive layers for sensitive sensing. Among them, tree frog's toe pads [13] and gecko feet micro/nanostructures [14] have been mimicked to build skin-adhesive layers for sensitive sensing.…”

mentioning

confidence: 99%

Biomimetic Meta‐Structured Electro‐Microfluidics

Gao

Liao

Guo

et al. 2019

Adv Funct Materials

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Flexible membranes (i.e., paper, cloth, and polydimethylsiloxane (PDMS)) have received extensive attention. The rapid development of flexible microfluidics and electronics and their integration calls for complex substrate structures to allow for multiple functions. Inspired by nature, meta-structured membranes (MSMs) as substrates for fabricating integrated microfluidics and electronics are presented. These flexible and freestanding MSMs are generated by the self-assembly of elastic plastic copolymer nanoparticle photonic crystals on micropatterned PDMS templates. The final MSMs constitute with integrated ordered micro-and nanostructures and exhibit spontaneous liquid transfer, fluorescence enhancement, and intimate skin contact. MSMs with designed patterns can be fabricated by assembling polymer nanoparticles on patterned molds; complicated and highly integrated electro-microfluidics are generated on one slice of MSMs by utilizing these patterns as microfluidic channels and electrocircuits. They can be used as chip-on-skin sensors for biochemical-physiological hybrid monitoring sensing of the human body and as organ chips for cell culture and metabolite analysis under drug treatment. Their excellent properties show their potential value in cross-scale sensing and have broad potential applications.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201906745. response and initiative manipulation on one single membrane substrate, which demands interdisciplinary integration. In fact, the combination of microfluidics and electronics on a single membrane has shown great potential in fabricating flexible smart devices such as wearable sensors (skin chips) and organ chips.Considerable attention and efforts have been devoted to fabricating membranes with functions such as super adherence, [4] vivid colors, [5] self-healing, [6] energy harvesting [7] based on micro/ nanostructures. However, the monotonous structure of current membranes limits their performance in flexible smart sensing devices. The construction of robust, ordered-structure membranes as flexible substrates with multiple excellent functions is still anticipated.Among many strategies improving the functionality of membranes, metamaterials or metastructures have widespread concerns. In the past decade, there have been increasing interests in metamaterials (structures) in scientific communities. [8] With the rapid development of materials science and physics, metamaterials are interdisciplinary subjects, including electronic engineering, condensed matter physics, microwave, optoelectronics, classical optics, materials science, semiconductor science, and nanotechnology. [9,10] Among many forms of metamaterials, highly ordered, micro-nano hybrid structures are beyond most striking styles. [11,12] Although there have been some attempts in this field, the high processing cost and complex processing process limit its full application in various fields.Nature provides excellent strategies for the re...

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Hybrid Surface Patterns Mimicking the Design of the Adhesive Toe Pad of Tree Frog

Cited by 119 publications

References 51 publications

Nanostructure and Microstructure Fabrication: From Desired Properties to Suitable Processes

Nanostructure and Microstructure Fabrication: From Desired Properties to Suitable Processes

Force‐transmitting structures in the digital pads of the tree frog Hyla cinerea: a functional interpretation

Biomimetic Meta‐Structured Electro‐Microfluidics

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