Temporary Adhesion Research Articles

Underwater Adhesives from Redox-Responsive Polyplexes of Thiolated Polyamide Polyelectrolytes.

We report the fabrication of optically clear underwater adhesives using polyplexes of oppositely charged partially-thiolated polyamide polyelectrolytes (TPEs). The thiol content of the constituent PEs was varied to assess its influence on the adhesive properties of the resulting glues. These catechol-free, redox-responsive TPE-adhesives were formulated in aquo and exhibited high optical transparency and strong adhesion even on submerged or moist surfaces of diverse polar substrates such as glass, aluminium, wood, and bone pieces. The adhesives could be cured under water through oxidative disulphide crosslinking of the constituent TPEs. The polyamide backbone provided multi-site H-bonding interactions with the substrates while the disulphide crosslinking provided the cohesive strength to the glue. Strong adhesion of mammalian bones (load bearing capacity upto 7 kg/cm2 ) was achieved using the adhesive containing 30 mol % thiol residues. Higher pH and use of oxidants such as povidone-iodine solution enhanced the curing rate of the adhesives, and so did the use of Tris buffer instead of Phosphate buffer. The porous architecture of the adhesive and its progressive degradation in aqueous medium over the course of three weeks bode well for diverse biomedical applications where temporary adhesion of tissues is required.

Glycoproteins Involved in Sea Urchin Temporary Adhesion.

Biomedical adhesives, despite having been used increasingly in recent years, still face a major technological challenge: strong adhesion in wet environments. In this context, biological adhesives secreted by marine invertebrates have appealing characteristics to incorporate into new underwater biomimetic adhesives: water resistance, nontoxicity and biodegradability. Little is still known about temporary adhesion. Recently, a transcriptomic differential analysis of sea urchin Paracentrotus lividus tube feet pinpointed 16 adhesive/cohesive protein candidates. In addition, it has been demonstrated that the adhesive secreted by this species is composed of high molecular weight proteins associated with N-Acetylglucosamine in a specific chitobiose arrangement. As a follow-up, we aimed to investigate which of these adhesive/cohesive protein candidates were glycosylated through lectin pulldowns, protein identification by mass spectroscopy and in silico characterization. We demonstrate that at least five of the previously identified protein adhesive/cohesive candidates are glycoproteins. We also report the involvement of a third Nectin variant, the first adhesion-related protein to be identified in P. lividus. By providing a deeper characterization of these adhesive/cohesive glycoproteins, this work advances our understanding of the key features that should be replicated in future sea urchin-inspired bioadhesives.

Agile Altering of Road Marking Patterns for Lane Detection Testing

In order to secure and evaluate the functionality of automated driving systems, it is necessary to perform tests under different environmental conditions. One relevant environmental element are road marking patterns, since they serve the purpose to regulate traffic. These patterns need to be changed frequently to display a high variety of different road marking patterns on test tracks. The study investigates and identifies effective and efficient techniques, and materials for agile altering of road marking patterns. Relevant parameters for such flexible road marking methods are the time and effort for application and removal, costs, sustainability, material visibility, removal quality, and reusability. To assess the quality of different road marking materials, the main indicator is the visibility. The authors measured the visibility with camera and Lidar sensors installed on test vehicles. In addition, they performed retroreflectometer measurements. Based on the validation of different materials, the research recommends white type I temporary road marking tape with temporary adhesion for the application on automotive proving grounds.

The Involvement of Cell-Type-Specific Glycans in Hydra Temporary Adhesion Revealed by a Lectin Screen

Hydra is a freshwater solitary polyp, capable of temporary adhesion to underwater surfaces. The reversible attachment is based on an adhesive material that is secreted from its basal disc cells and left behind on the substrate as a footprint. Despite Hydra constituting a standard model system in stem cell biology and tissue regeneration, few studies have addressed its bioadhesion. This project aimed to characterize the glycan composition of the Hydra adhesive, using a set of 23 commercially available lectins to label Hydra cells and footprints. The results indicated the presence of N-acetylglucosamine, N-acetylgalactosamine, fucose, and mannose in the adhesive material. The labeling revealed a meshwork-like substructure in the footprints, implying that the adhesive is mainly formed by fibers. Furthermore, lectins might serve as a marker for Hydra cells and structures, e.g., many labeled as glycan-rich nematocytes. Additionally, some unexpected patterns were uncovered, such as structures associated with radial muscle fibers and endodermal gland cells in the hypostome of developing buds.

In the footsteps of sea stars: deciphering the catalogue of proteins involved in underwater temporary adhesion.

Sea stars adhere strongly but temporarily to underwater substrata via the secretion of a blend of proteins, forming an adhesive footprint that they leave on the surface after detachment. Their tube feet enclose a duo-gland adhesive system comprising two types of adhesive cells, contributing different layers of the footprint and de-adhesive cells. In this study, we characterized the catalogue of sea star footprint proteins (Sfps) in the species Asterias rubens to gain insights in their potential function. We identified 16 Sfps and mapped their expression to type 1 and/or type 2 adhesive cells or to de-adhesive cells by double fluorescent in situ hybridization. Based on their cellular expression pattern and their conserved functional domains, we propose that the identified Sfps serve different functions during attachment, with two Sfps coupling to the surface, six providing cohesive strength and the rest forming a binding matrix. Immunolabelling of footprints with antibodies directed against one protein of each category confirmed these roles. A de-adhesive gland cell-specific astacin-like proteinase presumably weakens the bond between the adhesive material and the tube foot surface during detachment. Overall, we provide a model for temporary adhesion in sea stars, including a comprehensive list of the proteins involved.

Diffusion mechanisms of DNA in agarose gels: NMR studies and Monte Carlo simulations.

We report on the diffusion mechanism of short, single-stranded DNA molecules with up to 100 nucleobases in agarose gels with concentrations of up to 2.0% with the aim to characterize the DNA-agarose interaction. The diffusion coefficients were measured directly, i.e., without any model assumptions, by pulsed field gradient nuclear magnetic resonance (PFG-NMR). We find that the diffusion coefficient decreases, as expected, with an increase in both DNA strand length and gel concentration. In addition, we performed Monte Carlo simulations of particle diffusion in a model network of polymer chains, considering our experimental conditions. Together, the Monte Carlo simulations and the PFG-NMR results show that the decrease in diffusion coefficients in the presence of the agarose gel is due to a temporary adhesion of the DNA molecules to the surface of gel fibers. The average adhesion time to a given gel fiber increases with the length of the DNA strands but is independent of the number of gel fibers. The corresponding magnitude of the binding enthalpies of DNA strands to gel fibers indicates that a mixture of van der Waals interactions and hydrogen bonding contributes to the decreased diffusion of DNA in agarose gels.

Sticking Together an Updated Model for Temporary Adhesion.

Non-parasitic flatworms are known to temporarily attach to the substrate by secreting a multicomponent bioadhesive to counteract water movements. However, to date, only species of two higher-level flatworm taxa (Macrostomorpha and Proseriata) have been investigated for their adhesive proteins. Remarkably, the surface-binding protein is not conserved between flatworm taxa. In this study, we sequenced and assembled a draft genome, as well as a transcriptome, and generated a tail-specific positional RNA sequencing dataset of the polyclad Theama mediterranea. This led to the identification of 15 candidate genes potentially involved in temporary adhesion. Using in situ hybridisation and RNA interference, we determined their expression and function. Of these 15 genes, 4 are homologues of adhesion-related genes found in other flatworms. With this work, we provide two novel key components on the flatworm temporary adhesion system. First, we identified a Kringle-domain-containing protein (Tmed-krg1), which was expressed exclusively in the anchor cell. This in silico predicted membrane-bound Tmed-krg1 could potentially bind to the cohesive protein, and a knockdown led to a non-adhesive phenotype. Secondly, a secreted tyrosinase (Tmed-tyr1) was identified, which might crosslink the adhesive proteins. Overall, our findings will contribute to the future development of reversible synthetic glues with desirable properties for medical and industrial applications.

(Un)expected Similarity of the Temporary Adhesive Systems of Marine, Brackish, and Freshwater Flatworms.

Many free-living flatworms have evolved a temporary adhesion system, which allows them to quickly attach to and release from diverse substrates. In the marine Macrostomum lignano, the morphology of the adhesive system and the adhesion-related proteins have been characterised. However, little is known about how temporary adhesion is performed in other aquatic environments. Here, we performed a 3D reconstruction of the M. lignano adhesive organ and compared it to the morphology of five selected Macrostomum, representing two marine, one brackish, and two freshwater species. We compared the protein domains of the two adhesive proteins, as well as an anchor cell-specific intermediate filament. We analysed the gene expression of these proteins by in situ hybridisation and performed functional knockdowns with RNA interference. Remarkably, there are almost no differences in terms of morphology, protein regions, and gene expression based on marine, brackish, and freshwater habitats. This implies that glue components produced by macrostomids are conserved among species, and this set of two-component glue functions from low to high salinity. These findings could contribute to the development of novel reversible biomimetic glues that work in all wet environments and could have applications in drug delivery systems, tissue adhesives, or wound dressings.

Stimuli-responsive temporary adhesives: enabling debonding on demand through strategic molecular design.

Stimuli-responsive temporary adhesives constitute a rapidly developing class of materials defined by the modulation of adhesion upon exposure to an external stimulus or stimuli. Engineering these materials to shift between two characteristic properties, strong adhesion and facile debonding, can be achieved through design strategies that target molecular functionalities. This perspective reviews the recent design and development of these materials, with a focus on the different stimuli that may initiate debonding. These stimuli include UV light, thermal energy, chemical triggers, and other potential triggers, such as mechanical force, sublimation, electromagnetism. The conclusion discusses the fundamental value of systematic investigations of the structure–property relationships within these materials and opportunities for unlocking novel functionalities in future versions of adhesives.

Anatomy and Ultrastructure of the Cyprid Temporary Adhesive System in Two Species of Acorn Barnacle

Acorn barnacles are sessile as adults and select their settlement site as a cypris larva. Cyprids are well adapted to exploring surfaces in dynamic environments, using a temporary adhesive secreted from the antennules to adhere during this process. The temporary adhesive and the secretory structures are poorly characterized. This study used serial block-face scanning electron microscopy and three-dimensional modelling to elucidate the anatomy related to temporary adhesion. The temporary adhesive glands of two acorn barnacle species, Balanus amphitrite and Megabalanus coccopoma, were located in the proximal region of the first antennular segment, contrary to previous descriptions that placed them in the more distal second segment. The temporary adhesive systems of these acorn barnacles are therefore similar to that described for the stalked barnacle, Octolasmis angulata, although not identical. Knowledge of the true location of the temporary adhesive glands will underpin future studies of the production, composition and secretion of the adhesive.

Crystal Engineering of Molecular Solids as Temporary Adhesives

Crystal engineering of temporary adhesion is important in diverse fields ranging from healthcare to manufacturing. Molecular solids—a broad class of crystalline materials characterized by discrete ...

(Invited) Improved Copper Electrode Integration for Thin Film Electronics on Glass

We demonstrate single layer Cu interconnects using thin CuMn alloy as a temporary adhesion layer. After short annealing at 300°C for 60 s of a 10 nm CuMn alloy with 500 nm of Cu film, CuMn alloy layer is converted to pure Cu and the Mn is reacted with glass to form MnOx serving as an adhesion layer. After optimization of Mn concentration, alloy thickness, annealing environment, time and temperature, a resistivity lower than 1.8 μΩ·cm of the electrode was achieved. We also evaluated the effect of glass surface treatment to confirm the sensitivity of this process depending on substrate preparation conditions. This process has been shown to be very stable for different acid treatments on display glasses. It is also compared to a Ti/Cu stack as a reference.

Vertical Fibrous Morphology and Structure-Function Relationship in Natural and Biomimetic Suction-Based Adhesion Discs

Summary Recent years have seen rapid development in bio-inspired materials for adhesion. However, it remains challenging to realize robust adhesion on rough aquatic surfaces. An inspiring natural model is the remora fish, which has evolved to retain powerful adhesion to hosts using a dorsal suction disc. We find that the remora suction disc has a unique fibrous architecture of vertically oriented collagen fibers that enable anisotropic mechanical properties and enhanced adhesion performance. In the engineered prototype, vertically oriented nylon fibers are embedded into the soft silicone matrix using electrostatic flocking. The anisotropic mechanical properties are validated in both natural and biomimetic suction discs. Furthermore, the biomimetic suction disc demonstrates an enhanced adhesion function with a maximum 62.5% increase in pull-off force and a 340% increase in attachment time compared with the silicone control. This work can shed light on natural adhesion mechanisms and inspire novel designs for aquatic soft adhesives and actuators.

A mechanism for temporary bioadhesion

The flatworm Macrostomum lignano features a duo-gland adhesive system that allows it to repeatedly attach to and release from substrates in seawater within a minute. However, little is known about the molecules involved in this temporary adhesion. In this study, we show that the attachment of M. lignano relies on the secretion of two large adhesive proteins, M. lignano adhesion protein 1 (Mlig-ap1) and Mlig-ap2. We revealed that both proteins are expressed in the adhesive gland cells and that their distribution within the adhesive footprints was spatially restricted. RNA interference knockdown experiments demonstrated the essential function of these two proteins in flatworm adhesion. Negatively charged modified sugars in the surrounding water inhibited flatworm attachment, while positively charged molecules impeded detachment. In addition, we found that M. lignano could not adhere to strongly hydrated surfaces. We propose an attachment-release model where Mlig-ap2 attaches to the substrate and Mlig-ap1 exhibits a cohesive function. A small negatively charged molecule is secreted that interferes with Mlig-ap1, inducing detachment. These findings are of relevance for fundamental adhesion science and efforts to mitigate biofouling. Further, this model of flatworm temporary adhesion may serve as the starting point for the development of synthetic reversible adhesion systems for medicinal and industrial applications.

Properties of temporary adhesion systems of marine and freshwater organisms.

Underwater adhesive secretions are a promising source of inspiration for biomedical and industrial applications. Although marine permanent adhesives have been extensively investigated, reversible adhesion, e.g. as used for locomotion and feeding, is still poorly understood. Here, we summarise the current knowledge on secretion-based, temporary adhesive systems in aquatic environments, with a special emphasis on the morphology and structure of adhesive organs and adhesive material. Many animals employing temporary adhesion to the substratum rely on so-called duo-gland adhesive organs, consisting of two secretory gland cells and one supportive cell. We give a detailed depiction of a basic duo-gland adhesive organ and variations thereof. Additionally, we discuss temporary adhesive systems with an alternative building plan. Next, the topography of secreted adhesive footprints is described based on examples. The limited data on the composition of temporary adhesives are summarised, separating known protein components and carbohydrate residues. There are still large gaps in our understanding of temporary adhesion. We discuss three proposed models for detachment, although the actual mechanism of voluntary detachment is still a matter for debate.

Underwater adhesive using solid–liquid polymer mixes

Instantaneous adhesion between different materials is a requirement for several applications ranging from electronics to biomedicine. Approaches such as surface patterning, chemical cross-linking, surface modification, and chemical synthesis have been adopted to generate temporary adhesion between various materials and surfaces. Because of the lack of curing times, temporary adhesives are instantaneous, a useful property for specific applications that need quick bonding. However, to this day, temporary adhesives have been mainly demonstrated under dry conditions and do not work well in submerged or humid environments. Furthermore, most rely on chemical bonds resulting from strong interactions with the substrate such as acrylate based. This work demonstrates the synthesis of a universal amphibious adhesive solely by combining solid polytetrafluoroethylene (PTFE) and liquid polydimethylsiloxane (PDMS) polymers. While the dipole-dipole interactions are induced by a large electronegativity difference between fluorine atoms in PTFE and hydrogen atoms in PDMS, strong surface wetting allows the proposed adhesive to fully coat both substrates and PTFE particles, thereby maximizing the interfacial chemistry. The two-phase solid–liquid polymer system displays adhesive characteristics applicable both in air and water, and enables joining of a wide range of similar and dissimilar materials (glasses, metals, ceramics, papers, and biomaterials). The adhesive exhibits excellent mechanical properties for the joints between various surfaces as observed in lap shear testing, T-peel testing, and tensile testing. The proposed biocompatible adhesive can also be reused multiple times in different dry and wet environments. Additionally, we have developed a new reactive force field parameterization and used it in our molecular dynamics simulations to validate the adhesive nature of the mixed polymer system with different surfaces. This simple amphibious adhesive could meet the need for a universal glue that performs well with a number of materials for a wide range of conditions.

The structural and chemical basis of temporary adhesion in the sea star Asterina gibbosa.

Background: Marine biological adhesives are a promising source of inspiration for biomedical and industrial applications. Nevertheless, natural adhesives and especially temporary adhesion systems are mostly unexplored. Sea stars are able to repeatedly attach and detach their hydraulic tube feet. This ability is based on a duo-gland system and, upon detachment, the adhesive material stays behind on the substrate as a 'footprint'. In recent years, characterization of sea star temporary adhesion has been focussed on the forcipulatid species Asterias rubens.Results: We investigated the temporary adhesion system in the distantly related valvatid species Asterina gibbosa. The morphology of tube feet was described using histological sections, transmission-, and scanning electron microscopy. Ultrastructural investigations revealed two adhesive gland cell types that both form electron-dense secretory granules with a more lucid outer rim and one de-adhesive gland cell type with homogenous granules. The footprints comprised a meshwork on top of a thin layer. This topography was consistently observed using various methods like scanning electron microscopy, 3D confocal interference microscopy, atomic force microscopy, and light microscopy with crystal violet staining. Additionally, we tested 24 commercially available lectins and two antibodies for their ability to label the adhesive epidermis and footprints. Out of 15 lectins labelling structures in the area of the duo-gland adhesive system, only one also labelled footprints indicating the presence of glycoconjugates with α-linked mannose in the secreted material.Conclusion: Despite the distant relationship between the two sea star species, the morphology of tube feet and topography of footprints in A. gibbosa shared many features with the previously described findings in A. rubens. These similarities might be due to the adaptation to a benthic life on rocky intertidal areas. Lectin- and immuno-labelling indicated similarities but also some differences in adhesive composition between the two species. Further research on the temporary adhesive of A. gibbosa will allow the identification of conserved motifs in sea star adhesion and might facilitate the development of biomimetic, reversible glues.

Quantitative analysis of the complete larval settlement process confirms Crisp's model of surface selectivity by barnacles.

For barnacle cypris larvae at the point of settlement, selection of an appropriate surface is critical. Since post-settlement relocation is usually impossible, barnacles have evolved finely tuned surface-sensing capabilities to identify suitable substrata, and a temporary adhesion system for extensive surface exploration. The pattern of exploratory behaviour appears complex and may last for several hours, imposing significant barriers to quantitative measurement. Here, we employ a novel tracking system that enables simultaneous analysis of the larval body movement of multiple individuals over their entire planktonic phase. For the first time, to our knowledge, we describe quantitatively the complete settlement process of cyprids as they explore and select surfaces for attachment. We confirm the 'classic' behaviours of wide searching, close searching and inspection that comprise a model originally proposed by Prof. Dennis Crisp FRS. Moreover, a short-term assay of cyprid body movement has identified inspection behaviour as the best indicator of propensity to settle, with more inspection-related movements occurring in conditions that also promote higher settlement. More than half a century after the model was first proposed by Crisp, there exists a precise method for quantifying cyprid settlement behaviour in wide-ranging investigations of barnacle ecology and applied studies of fouling management.

Involvement of sulfated biopolymers in adhesive secretions produced by marine invertebrates.

ABSTRACTMany marine invertebrates use adhesive secretions to attach to underwater surfaces and functional groups borne by their adhesive proteins and carbohydrates, such as catechols and phosphates, play a key role in adhesion. The occurrence of sulfates as recurrent moieties in marine bioadhesives suggests that they could also be involved. However, in most cases, their presence in the adhesive material remains speculative. We investigated the presence of sulfated biopolymers in five marine invertebrates representative of the four types of adhesion encountered in the sea: mussels and tubeworms for permanent adhesion, limpets for transitory adhesion, sea stars for temporary adhesion and sea cucumbers for instantaneous adhesion. The dry adhesive material of mussels, sea stars and sea cucumbers contained about 1% of sulfate. Using anti-sulfotyrosine antibodies and Alcian Blue staining, sulfated proteins and sulfated proteoglycans and/or polysaccharides were identified in the secretory cells and adhesive secretions of all species except the tubeworm. Sulfated proteoglycans appear to play a role only in the non-permanent adhesion of sea stars and limpets in which they could mediate cohesion within the adhesive material. In mussels and sea cucumbers, sulfated biopolymers would rather have an anti-adhesive function, precluding self-adhesion.

Tunable denture adhesives using biomimetic principles for enhanced tissue adhesion in moist environments.

Mussel adhesive proteins have proven to be promising biomimetic adhesive candidates for soft tissues and here for the first time we have adapted marine adhesive technology into a denture fixative application. Importantly, we have incorporated a soft tissue mimic in our in vitro adhesion technique that more closely resembles the oral mucosa than previously studied substrates. The novel biomimetic-modified adhesives showed the ability to score the highest adhesive bonding out of all the formulations included in this study, across all moisture levels. This paper will be of major interest to the Acta Biomaterialia readership since the study has illustrated the potential of biomimetic principles in the design of effective prosthodontic tissue adhesives in a series of purpose-designed in vitro experiments in the context of the challenging features of the oral environment.