Mushroom-shaped Microstructure Research Articles

Effect of the Mechanical Properties of Soft Counter-Faces on the Adhesive Capacity of Mushroom-Shaped Biomimetic Microstructures.

The effects of mechanical properties and contact environment conditions on the adhesiveness of the biomimetic adhesive mushroom-shaped micro-structure have been experimentally investigated. The idea is based on the adhesive micro-structures and surfaces inspired by nature after observing the abilities of some animals. Applications are proposed in various fields of engineering and technology. However, to enable unconventional uses of these biomimetic adhesion surfaces, such as in the biomedical field, it is necessary to adjust and optimize their tribological properties (friction, adhesion, and peeling strength) in contact with soft substrates that can simulate the mechanical features of biological tissues. Our work explores the effect of the combinations of the various parameters on the strength of adhesion. Under dry contact conditions, soft counter-faces lead to lower adhesion than hard counter-faces, whereas under wet conditions, soft counter-faces lead to higher adhesion than harder counter-faces.

A finite element framework for the simulation of bio-inspired adhesives with mushroom-shaped microstructures

This work proposes a finite element procedure for the simulation of biologically inspired adhesives with a mushroom-shaped patterned surface by formulating a novel interface finite element. The proposed computational method can capture the attachment and detachment mechanisms without modeling the microstructures on the surface in detail, which is the major issue of large-scale simulations involving complex surfaces. A data-driven phenomenological interface constitutive law has been formulated starting from pull-out experimental tests on patterned surfaces with different inclination angles to assess Mode Mixity effects in a range of peeling angles of relevance for applications. The proposed computational model represents a versatile tool for modeling structural problems involving arbitrary shape components, as in bio-inspired adhesives.

Biomimetic fracture model of lizard tail autotomy.

Lizard tail autotomy is an antipredator strategy consisting of sturdy attachment at regular times but quick detachment during need. We propose a biomimetic fracture model of lizard tail autotomy using multiscale hierarchical structures. The structures consist of uniformly distributed micropillars with nanoporous tops, which recapitulate the high-density mushroom-shaped microstructures found on the lizard tail's muscle fracture plane. The biomimetic experiments showed adhesion enhancement when combining nanoporous interfacial surfaces with flexible micropillars in tensile and peel modes. The fracture modeling identified micro- and nanostructure-based toughening mechanisms as the critical factor. Under wet conditions, capillarity-assisted energy dissipation pertaining to liquid-filled microgaps and nanopores further increased the adhesion performance. This research presents insights on lizard tail autotomy and provides new biomimetic ideas to solve adhesion problems.

HOT WATER-REPELLENT SUPERHYDROPHOBIC SURFACES WITH LONG-TERM STABILITY

In this paper, we fabricate and evaluate superhydrophobic surfaces with mushroom-shaped microstructures. Using a silicon master and polymer microstructure patterning, polydimethylsiloxane (PDMS) surfaces bearing mushroom-shaped structures with five different spacing ratios are prepared and tested with water droplets of different temperatures. The fabricated PDMS surfaces demonstrate superhydrophobicity even to high-temperature water droplets with decreased surface tension. We compare the experimental data with the theoretical results calculated based on the Cassie state and Eötvös rule. Our work suggests potential applications to control wettability with liquids of various temperatures.

Developing Novel Poly(Lactic-Co-Glycolic Acid) (PLGA) Films with Enhanced Adhesion Capacity by Biomimetic Mushroom-Shaped Microstructures

The adhesion strength of biomimetic mushroom-shaped microstructures made of a biocompatible and biodegradable copolymer, PLGA, is experimentally studied. The adhesive microstructures were successfully produced using a two-step molding technique. The adhesive experiments were performed on a flat and smooth glass substrate using different normal preloads and under both dry (in air) and wet (underwater) contact conditions. Regardless of contact conditions, mushroom-shaped microstructures generate much higher adhesion strength compared to a flat smooth reference sample made of the same PLGA material. Furthermore, PLGA mushroom-shaped microstructures exhibited superior adhesion strength using agar substrate as a representative material for biological tissue. Surface texturing indicates a good approach to modify adhesive properties PLGA without additional excipients. The effect of surface texturing is more pronounced under wet contact condition. The concept of using biomimetic adhesive surfaces made of biocompatible and biodegradable polymers is very promising for potential applications in drug delivery, tissue engineering and biomedical field.

미세 버섯 구조 제작의 내구성을 위한 레플리카 몰딩 공정 개발

In this paper, we present a simple and robust fabrication method for mushroom-shaped microstructures using diverse polymers with various modulus of elasticity. Through the repeated replica molding process, we fabricated the same PDMS mushroom structure negative mold as the prepared silicon master mold. To evaluate the fabricating stability of the fabricated PDMS negative mold, the mushroom-shaped structures were replicated from the mold using six types of polymer resins with different elastic modulus and we measured superhydrophobic properties on the samples. All the fabricated samples exhibited superhydrophobicity, and we proved the structural stability of the proposed replication method through the measured SEM images, contact angles on the samples, and theoretical analysis based on the structural shape.

Strong Wet and Dry Adhesion by Cupped Microstructures.

Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are considerably weakened underwater, fibrillar adhesives are however far less effective in wet environments. Although various strategies have been proposed to achieve strong reversible underwater adhesion, strong adhesives that work both in air and underwater without additional surface treatments have yet to be developed. In this study, we report a novel design—cupped microstructures (CM)—that generates strong controllable adhesion in air and underwater. We measured the adhesive performance of cupped polyurethane microstructures with three different cup angles (15, 30, and 45°) and the same cup diameter of 100 μm in dry and wet conditions in comparison to standard mushroom-shaped microstructures (MSMs) of the same dimensions. In air, 15°CM performed comparably to the flat MSM of the same size with an adhesion strength (force per real contact area) of up to 1.3 MPa, but underwater, 15°CM achieved 20 times stronger adhesion than MSM (∼1 MPa versus ∼0.05 MPa). Furthermore, the cupped microstructures exhibit self-sealing properties, whereby stronger pulls lead to longer stable attachment and much higher adhesion through the formation of a better seal.

Improved in vitro electrophysiology using 3D-structured microelectrode arrays with a micro-mushrooms islets architecture capable of promoting topotaxis

Novelty and significanceA novel MEA architecture with excellent electrophysiological recordings is presented, where planar microelectrodes are replaced by localized 3 × 3 arrays of mushroom-shaped microstructures. The micro-mushrooms in this islets configuration are not for membrane engulfment but rather for somata entrapment and neurites embracement. As extracellular signals have a significant contribution from axons initial segment, this MEA design also addresses the electrode-neurites electrical coupling. These islets act as strong physical cues, causing topotaxis and increasing by two-fold the probability for somata to localize in the islets. We carry this topotaxis study not only with rat cortical neurons but also with human-derived SH-SY5Y cells.Objective. Planar microelectrode arrays are widely used in neuroscience but have relatively low electrical coupling and signal-to-noise ratio (SNR) in electrophysiology recordings. Strong efforts are therefore being made in improving microelectrode arrays (MEAs) performance, exploring both the microelectrode’s shape and the array’s architecture. Topographical features can be used in MEAs for promoting neuron-microelectrode contact, making 3D-microstructured MEAs an interesting design strategy for better electrophysiology measurements. Approach. Here, we present a novel MEA architecture, where planar microelectrodes are replaced by localized 3 × 3 arrays of mushroom-shaped microstructures. Contrarily to previous studies, the purpose for the micro-mushrooms in this islets configuration is not membrane engulfment but rather entrapment, for somata, and embracement, for neurites. Main results. We show that these islet-like agglomerates of micro-mushrooms act as strong physical cues, causing topotaxis and increasing the probability by two-fold for somata to localize in the islets, and neurites to curl on the microelectrodes. Importantly, we carry this topotaxis study not only with rat cortical neurons but also with human-derived SH-SY5Y cells. With recent evidence that extracellular signals have a significant contribution from axons initial segment it becomes clear that MEA designs should also address the electrode-neurites coupling. We detail the fabrication process of these chips, designed to be compatible with a standard MEA recording system, and make the computer-aided design (CAD) publically available. We also demonstrate the electrophysiological capabilities of this new MEA by electrochemical impedance spectroscopy and recordings of cortical and hippocampal neurons, showing excellent SNR. Significance. Overall this new MEA islets configuration has a significant impact in the array efficiency and contributes towards improved high yield and high fidelity/quality extracellular recordings from mammalian neurons.

Bioinspired polydimethylsiloxane-based composites with high shear resistance against wet tissue

Patterned microstructures represent a potential approach for improving current wound closure strategies. Microstructures can be fabricated by multiple techniques including replica molding of soft polymer-based materials. However, polymeric microstructures often lack the required shear resistance with tissue needed for wound closure. In this work, scalable microstructures made from composites based on polydimethylsiloxane (PDMS) were explored to enhance the shear resistance with wet tissue. To achieve suitable mechanical properties, PDMS was reinforced by incorporation of polyethylene (PE) particles into the pre-polymer and by coating PE particle reinforced substrates with parylene. The reinforced microstructures showed a 6-fold enhancement, the coated structures even a 13-fold enhancement in Young׳s modulus over pure PDMS. Shear tests of mushroom-shaped microstructures (diameter 450µm, length 1mm) against chicken muscle tissue demonstrate first correlations that will be useful for future design of wound closure or stabilization implants.

Continuous and scalable fabrication of bioinspired dry adhesives via a roll-to-roll process with modulated ultraviolet-curable resin.

A simple yet scalable strategy for fabricating dry adhesives with mushroom-shaped micropillars is achieved by a combination of the roll-to-roll process and modulated UV-curable elastic poly(urethane acrylate) (e-PUA) resin. The e-PUA combines the major benefits of commercial PUA and poly(dimethylsiloxane) (PDMS). It not only can be cured within a few seconds like commercial PUA but also possesses good mechanical properties comparable to those of PDMS. A roll-type fabrication system equipped with a rollable mold and a UV exposure unit is also developed for the continuous process. By integrating the roll-to-roll process with the e-PUA, dry adhesives with spatulate tips in the form of a thin flexible film can be generated in a highly continuous and scalable manner. The fabricated dry adhesives with mushroom-shaped microstructures exhibit a strong pull-off strength of up to ∼38.7 N cm(-2) on the glass surface as well as high durability without any noticeable degradation. Furthermore, an automated substrate transportation system equipped with the dry adhesives can transport a 300 mm Si wafer over 10,000 repeating cycles with high accuracy.

Effect of counterface roughness on adhesion of mushroom-shaped microstructure

In this study, the effect of the substrate roughness on adhesion of mushroom-shaped microstructure was experimentally investigated. To do so, 12 substrates having different isotropic roughness were prepared from the same material by replicating topography of different surfaces. The pull-off forces generated by mushroom-shaped microstructure in contact with the tested substrates were measured and compared with the pull-off forces generated by a smooth reference. It was found that classical roughness parameters, such as average roughness (Ra) and others, cannot be used to explain topography-related variation in pull-off force. This has led us to the development of an integrated roughness parameter capable of explaining results of pull-off measurements. Using this parameter, we have also found that there is a critical roughness, above which neither smooth nor microstructured surface could generate any attachment force, which may have important implications on design of both adhesive and anti-adhesive surfaces.

Charge Contribution to the Adhesion Performance of Polymeric Microstructures

Strong attachment of many insects with microstructured attachment pads is due to the Van der Waals interactions or/and the capillary forces between the pads and substrates. To establish initial contact between two surfaces a certain normal force should be applied. The presence of the charges on surfaces could facilitate or impede the initial contact formation. In this study, forces appearing due to the contact electrification of microstructured material mimicking beetle adhesive pads were measured and their influence on the contact formation was discussed. The experiments have clearly demonstrated that static charges contribute to an initial contact establishment in materials with the mushroom-shaped microstructure, whereas Van der Waals interactions or/and capillary forces have the main contribution at pull-off. A simple model was successfully used for data analysis and extraction information about the charge distribution. The effect of the jump-in due to the electrostatic interaction has to be considered during the development of further implementation of biologically inspired microstructured adhesives.

Wet versus dry adhesion of biomimetic mushroom-shaped microstructures

Currently, biomimetic geometry-controlled adhesives are based mostly on dry adhesion, whereas the majority of adhesive systems in biology involve fluids. Here, we assess the influence of the presence of oil on a pull-off force measured in a flat-on-flat contact between a mushroom-shaped microstructured adhesive and chemically identical smooth and rough substrates. A microstructured surface has stronger adhesion compared to a smooth control on both smooth and rough substrates in both dry and oiled contacts. In the presence of oil, the microstructured surface has stronger adhesion on both smooth and rough substrates compared to the dry contact. We found that, after detachment from the substrate, a microstructured surface retains fluid more effectively compared to the smooth control. The study demonstrates that covering an adhesive microstructure with an oil film may expand its application range, showing that this method is potentially attractive for the creation of new biomimetic adhesives.

Suction component in adhesion of mushroom-shaped microstructure

To shed light on the role of suction in adhesion of microstructure with mushroom-shaped terminal elements, we compared pull-off forces measured at different retraction velocities on structured and smooth surfaces under different pressure conditions. The results obtained allow us to suggest that suction may contribute up to 10 per cent of the pull-off force measured on the structured surfaces at high velocities. We therefore conclude that the attachment ability of this biomimetic adhesive must not be solely based on van der Waals forces. Our experiments also suggest a change in visco-elastic properties of the structured surfaces compared with the bulk material. Based on the results obtained, it is assumed that this adhesive may be suitable in dynamic pick-and-drop processes even under vacuum conditions at which sufficiently high adhesive capability is maintained.

Three-dimensional microfabrication process using Bi electrodeposition for a highly sensitive X-ray imaging sensor

A microscale Bi electrodeposition process was developed and applied to the three-dimensional fabrication of a highly sensitive X-ray imaging sensor, so called X-ray microcalorimeter, which has an array of sensing elements with a mushroom-shaped X-ray absorber. The composition and operating conditions for Bi electrodeposition were optimized and flat, smooth Bi deposits were obtained by applying additives such as diethylenetriamine pentaacetic acid (DTPA) and sodium n-dodecyl sulfate (SDS). The results of ultraviolet (UV)–visible absorption spectroscopy and polarization curves from the Bi electrodeposition solution indicated that the formation of a DTPA–Bi(III) complex and an increase of overpotential for Bi electrodeposition in the presence of SDS improved the solution stability as well as the surface morphology of the deposited film. The mold for the mushroom-shaped microstructure array was formed from a single-layered photoresist coating by applying sequential exposure steps for the “stem” part and the “roof” part. The absorber array was successfully fabricated by the Bi electrodeposition into the mold, precise polishing, and mold removal processes.

Wound closure materials in the new millennium

Patterned microstructures represent a potential approach for improving current wound closure strategies. Microstructures can be fabricated by multiple techniques including replica molding of soft polymer-based materials. However, polymeric microstructures often lack the required shear resistance with tissue needed for wound closure. In this work, scalable microstructures made from composites based on polydimethylsiloxane (PDMS) were explored to enhance the shear resistance with wet tissue. To achieve suitable mechanical properties, PDMS was reinforced by incorporation of polyethylene (PE) particles into the pre-polymer and by coating PE particle reinforced substrates with parylene. The reinforced microstructures showed a 6-fold enhancement, the coated structures even a 13-fold enhancement in Young׳s modulus over pure PDMS. Shear tests of mushroom-shaped microstructures (diameter 450 µm, length 1 mm) against chicken muscle tissue demonstrate first correlations that will be useful for future design of wound closure or stabilization implants.