Hydrophobic enhancement of Dopa-mediated adhesion in a mussel foot protein

Mussel-inspired bifunctional coating for long-term stability of oral implants

Peri-implantitis and osseointegration failure present considerable challenges to the prolonged stability of oral implants. To address these issues, there is an escalating demand for a resilient implant surface coating that seamlessly integrates antimicrobial features to combat bacteria-induced peri‑implantitis, and osteogenic properties to promote bone formation. In the present study, a bio-inspired poly(amidoamine) dendrimer (DA-PAMAM-NH2) is synthesized by utilizing a mussel protein (DA) known for its strong adherence to various materials. Conjugating DA with PAMAM-NH2, inherently endowed with antibacterial and osteogenic properties, results in a robust and multifunctional coating. Robust adhesion between DA-PAMAM-NH2 and the titanium alloy surface is identified using confocal laser scanning microscopy (CLSM) and attenuated total reflectance-infrared (ATR-IR) spectroscopy. Following a four-week immersion of the coated titanium alloy surface in simulated body fluid (SBF), the antimicrobial activity and superior osteogenesis of the DA-PAMAM-NH2-coated surface remain stable. In contrast, the bifunctional effects of the PAMAM-NH2-coated surface diminish after the same immersion period. In vivo animal experiments validate the enduring antimicrobial and osteogenic properties of DA-PAMAM-NH2-coated titanium alloy implants, significantly enhancing the long-term stability of the implants. This innovative coating holds promise for addressing the multifaceted challenges associated with peri‑implantitis and osseointegration failure in titanium-based implants. STATEMENT OF SIGNIFICANCE: Prolonged stability of oral implants remains a clinically-significant challenge. Peri-implantitis and osseointegration failure are two important contributors to the poor stability of oral implants. The present study developed a mussel-bioinspired poly(amidoamine) dendrimer (DA-PAMAM-NH2) for a resilient implant surface coating that seamlessly integrates antimicrobial features to combat bacteria-induced peri‑implantitis, and osteogenic properties to promote bone formation to extend the longevity of oral implants.

Advances in Mussel Adhesion Proteins and Mussel-Inspired Material Electrospun Nanofibers for Their Application in Wound Repair

Mussel refers to a marine organism with strong adhesive properties, and it secretes mussel adhesion protein (MAP). The most vital feature of MAP is the abundance of the 3,4-dihydroxyphenylalanine (DOPA) group and lysine, which have antimicrobial, anti-inflammatory, antioxidant, and cell adhesion-promoting properties and can accelerate wound healing. Polydopamine (PDA) is currently the most widely used mussel-inspired material characterized by good adhesion, biocompatibility, and biodegradability. It can mediate various interactions to form functional coatings on cell-material surfaces. Nanofibers based on MAP and mussel-inspired materials have been exerting a vital role in wound repair, while there is no comprehensive review presenting them. This Review introduces the structure of MAPs and their adhesion mechanisms and mussel-inspired materials. Second, it introduces the functionalized modification of MAPs and their inspired materials in electrospun nanofibers and application in wound repair. Finally, the future development direction and coping strategies of MAP and mussel-inspired materials are discussed. Moreover, this Review can offer novel strategies for the application of nanofibers in wound repair and bring about new breakthroughs and innovations in tissue engineering and regenerative medicine.

Mussel-Bioinspired Lignin Adhesive for Wearable Bioelectrodes

As a natural "binder," lignin fixes cellulose in plants to foster growth and longevity. However, isolated lignin has a poor binding ability, which limits its biomedical applications. In this study, inspired by mussel adhesive proteins, acidic/basic amino acids (AAs) are introduced in alkali lignin (AL) to form ionic-π/spatial correlation interactions, followed by demethylation to create catechol residues for enhanced adhesion activity. Atomic force microscopy reveals that catechol residues are the primary adhesion structures, with basic AAs exhibiting superior synergistic effects compared to acidic AAs. Demethylated lysine-grafted AL exhibits the strongest adhesion force toward skin tissue. Molecular dynamic simulation and density functional theory calculations indicate that adhesion against skin tissue mainly results from hydrogen bonds and cation-π interactions, with the adhesion mechanism being based on the Gibbs free energy of the Schiff base reaction. In summary, a biomimetic electrode based on lignin inspired by mussel adhesive proteins is prepared; the presented method offers a straightforward strategy for the development of biomimetic adhesives. Furthermore, this mussel-inspired adhesive can be used as a wearable bioelectrode in biomedical applications.

Multifunctional hydrogels for the healing of oral ulcers

Oral ulcers are one of the most common oral diseases in clinical practice. Its etiology is complex and varied. Due to the dynamic nature of the oral environment, the wound surface is painful due to contact and wear, which seriously affects the quality of life of patients. Oral ulcers are often treated with topical drug therapy. Studies have shown that functional hydrogels play a positive role in promoting wound healing, showing unique advantages in wound dressings. In this paper, the causes and healing characteristics of oral ulcers are discussed in depth, and then the common treatment methods for oral ulcers are summarized and compared. Finally, the potential of functional hydrogels in the treatment of oral ulcers is discussed and projected through a review of the literature in recent years.

Integrating Bioinspired Natural Adhesion Mechanisms into Modified Polyacrylate Latex Pressure-Sensitive Adhesives

For polyacrylate latex pressure-sensitive adhesives (PSAs), high peel strength is of crucial significance. It is not only a key factor for ensuring the long-lasting and effective adhesive force of polyacrylate latex PSAs but also can significantly expand their application scope in many vital fields, such as packaging, electronics, and medical high-performance composite materials. High peel strength can guarantee that the products maintain stable and reliable adhesive performance under complex and variable environmental conditions. However, at present, the peel strength capacity of polyacrylate latex PSAs is conspicuously insufficient, making it difficult to fully meet the urgent market demand for high peel strength, and severely restricting their application in many cutting-edge fields. Therefore, based on previous experimental studies, and deeply inspired by the adhesion mechanism of natural marine mussels, in this study, a traditional polyacrylate latex PSA was ingeniously graft-modified with 3,4-dihydroxybenzaldehyde (DHBA) through the method of monomer-starved seeded semi-continuous emulsion polymerization, successfully synthesizing novel high-peel-strength polyacrylate latex pressure-sensitive adhesives (HPSAs) with outstanding strong adhesion properties, and the influence of DHBA content on the properties of the HPSAs was comprehensively studied. The research results indicated that the properties of the modified HPSAs were comprehensively enhanced. Regarding the water resistance of the adhesive film, the minimum water absorption rate was 4.33%. In terms of the heat resistance of the adhesive tape, it could withstand heat at 90 °C for 1 h without leaving residue upon tape peeling. Notably, the adhesive properties were significantly improved, and when the DHBA content reached 4.0%, the loop tack and 180° peel strength of HPSA4 significantly increased to 5.75 N and 825.4 gf/25 mm, respectively, which were 2.5 times and 2 times those of the unmodified PSA, respectively. Such superior adhesive performance of HPSAs, on the one hand, should be attributed to the introduction of the bonding functional monomer DHBA with a rich polyphenol structure; on the other hand, the acetal structure formed by the grafting reaction of DHBA with the PSA effectively enhanced the spatial network and crosslink density of the HPSAs. In summary, in this study, the natural biological adhesion phenomenon was ingeniously utilized to increase the peel strength of pressure-sensitive adhesives, providing a highly forward-looking and feasible direct strategy for the development of environmentally friendly polyacrylate latex pressure-sensitive adhesives.

Engineering poly(dehydroalanine)-based gels via droplet-based microfluidics: from bulk to microspheres

Biomedical applications such as drug delivery, tissue engineering, and functional surface coating rely on switchable adsorption and desorption of specialized guest molecules. Poly(dehydroalanine), a polyzwitterion containing pH-dependent positive and negative charges, shows promise for such reversible loading, especially when integrated into a gel network. Herein, we present the fabrication of poly(dehydroalanine)-derived gels of different size scales and evaluate them with respect to their practical use in biomedicine. Already existing protocols for bulk gelation were remodeled to derive suitable reaction conditions for droplet-based microfluidic synthesis. Depending on the layout of the microfluidic chip, microgels with a size of approximately 30 μm or 200 μm were obtained, whose crosslinking density can be increased by implementing a multi-arm crosslinker. We analyzed the effects of the crosslinker species on composition, permeability, and softness and show that the microgels exhibit advantageous properties inherent to zwitterionic polymer systems, including high hydrophilicity as well as pH- and ionic strength-sensitivity. We demonstrate pH-regulated uptake and release of fluorescent model dyes before testing the adsorption of a small antimicrobial peptide, LL-37. Quantification of the peptide accommodated within the microgels reveals the impact of size and crosslinking density of the microgels. Biocompatibility of the microgels was validated by cell tests.

Characterization of a novel antioxidant byssal protein from Mytilus coruscus foot

Mussel byssal proteins are of biomimetic importance for the development of novel underwater bio-adhesive agents. It is important to maintain a reduced state during the process of byssus adhesion. There are 19 mussel foot proteins (MFPs) have been reported in previous studies, among which only MFP-6 had been confirmed as an antioxidant protein in mussel byssus due to the function of cysteines, and playing an essential role in the redox balance of mussel byssus during adhesion process. Although the other four MFPs (MFP-16 ~ MFP-19) also have abundant cysteines, their function is still unknown. In this study, a novel mussel foot protein, named MFP-20, was identified from Mytilus coruscus foot. The sequential features, expression profile, and function of recombinant MFP-20 were verified. The results showed that MFP-20 has more abundant cysteines than other MFPs, the relative expression of mfp-20 was upregulated in Fe3+ stress and low pH seawater. In addition, different adhesive substrates induced significant changes of expression level of mfp-20. Furthermore, rMFP-20 showed strong antioxidant capacity in the DPPH assay, and the abundant cysteines in its sequence may play vital roles in the antioxidation activity. Our findings revealed the possible function of MFP-20 with a totally different sequence from the reported MFP-6 and provided new clues for exploring the redox balance of mussel byssus during the adhesion process.

Mussel-inspired protein-based nanoparticles for curcumin encapsulation and promoting antitumor efficiency

Curcumin demonstrated therapeutic potential for cancer. However, its medical application is limited due to low solubility, poor stability and low absorption rate. Here, we used the mussel-inspired functional protein (MPKE) to fabricate the curcumin-carrying nanoparticle (Cur-MPKE) for encapsulating and delivering curcumin. The protein MPKE is composed of the mussel module and zwitterionic peptide. The Dopa group bonding characteristic of the mussel module was leveraged for the self-assembly of nanoparticles, while the superhydrophilic property of the zwitterionic peptide was utilized to enhance the stability of nanoparticles. As expected, MPKE and Cur are tightly bound through hydrogen bonds and dynamic imide bonds to form nanoparticles. Cur-MPKE showed improved solubility and stability in aqueous solutions as well as excellent biocompatibility. Besides, Cur-MPKE also exhibited pH-triggered release and enhanced uptake of curcumin by tumor cells, promoting the antioxidant activity and antitumor effect of curcumin. Moreover, systemic experiments of Cur-MPKE to rats demonstrated that Cur-MPKE significantly inhibited tumor tissue growth and proliferation without causing obvious systemic toxicity. This work provides a new strategy for fabricating the delivery system of curcumin with improved stability, sustainability and bioavailability.

Deciphering protein-mediated underwater adhesion in an invasive biofouling ascidian: Discovery, validation, and functional mechanism of an interfacial protein

Discovering macromolecules and understanding the associated mechanisms involved in underwater adhesion are essential for both studying the fundamental ecology of benthos in aquatic ecosystems and developing biomimetic adhesive materials in industries. Here, we employed quantitative proteomics to assess protein expression variations during the development of the distinct adhesive structure - stolon in the model fouling ascidian, Ciona robusta. We found 16 adhesive protein candidates with increased expression in the stolon, with ascidian adhesive protein 1 (AAP1) being particularly rich in adhesion-related signal peptides, amino acids, and functional domains. Western blot and immunolocalization analyses confirmed the prominent AAP1 signals in the mantle, tunic, stolon, and adhesive footprints, indicating the interfacial role of this protein. Surface coating and atomic force microscopy experiments verified AAP1's adhesion to diverse materials, likely through the specific electrostatic and hydrophobic amino acid interactions with various substrates. In addition, molecular docking calculations indicated the AAP1's potential for cross-linking via hydrogen bonds and salt bridges among Von Willebrand factor type A domains, enhancing its adhesion capability. Altogether, the newly discovered interfacial protein responsible for permanent underwater adhesion, along with the elucidated adhesion mechanisms, are expected to contribute to the development of biomimetic adhesive materials and anti-fouling strategies. STATEMENT OF SIGNIFICANCE: Discovering macromolecules and studying their associated mechanisms involved in underwater adhesion are essential for understanding the fundamental ecology of benthos in aquatic ecosystems and developing innovative bionic adhesive materials in various industries. Using multidisciplinary analytical methods, we identified an interfacial protein - Ascidian Adhesive Protein 1 (AAP1) from the model marine fouling ascidian, Ciona robusta. The interfacial functions of AAP1 are achieved by electrostatic and hydrophobic interactions, and the Von Willebrand factor type A domain-based cross-linking likely enhances AAP1's interfacial adhesion. The identification and validation of the interfacial functions of AAP1, combined with the elucidation of adhesion mechanisms, present a promising target for the development of biomimetic adhesive materials and the formulation of effective anti-fouling strategies.

Thermo-growing ion clusters enabled healing strengthening and tough adhesion for highly reliable skin electronics

Self-healing and self-adhesion capacities are essential for many modern applications such as skin-interfaced electronics for improving longevity and reliability. However, the self-healing efficiency and adhesive toughness of most synthetic polymers are limited to their original network, making reliability under dynamic deformation still challenging. Herein, inspired by the growth of living organisms, a highly stretchable supramolecular elastomer based on thermo-responsive ion clusters and a dynamic polysulfide backbone was developed. Attributed to the synergic growth of ion clusters and dynamic exchange of disulfide bonds, the elastomer exhibited unique healing strengthening (healing efficiency >200%) and thermo-enhanced tough adhesion (interfacial toughness >500 J m-2) performances. To prove its practical application in highly reliable skin electronics, we further composited the elastomer with a zwitterion to prepare a highly conductive ionic elastomer and applied it in wearable strain sensing and long-term electrophysiological detection. This work provides a new avenue to realize high reliability in skin interfaced electronics.

Molecular Crowding: The History and Development of a Scientific Paradigm

It is now generally accepted that macromolecules do not act in isolation but "live" in a crowded environment, that is, an environment populated by numerous different molecules. The field of molecular crowding has its origins in the far 80s but became accepted only by the end of the 90s. In the present issue, we discuss various aspects that are influenced by crowding and need to consider its effects. This Review is meant as an introduction to the theme and an analysis of the evolution of the crowding concept through time from colloidal and polymer physics to a more biological perspective. We introduce themes that will be more thoroughly treated in other Reviews of the present issue. In our intentions, each Review may stand by itself, but the complete collection has the aspiration to provide different but complementary perspectives to propose a more holistic view of molecular crowding.

A Cysteine-Maleimide-Based Design for Hemostatic, Antibacterial, and Biodegradable Wound Dressing

The field of clinical surgery frequently encounters challenges related to atypical wound tissue healing, resulting in the development of persistent chronic wounds or aesthetically displeasing scar tissue. The use of wound dressings crafted from mussel adhesive proteins and hyaluronic acid has demonstrated the potential in mitigating these undesirable outcomes. However, the synergistic effects of these two biomaterials remain underexplored. In this study, we have engineered a versatile, degradable, and biocompatible dressing that comprises recombinant 3,4-dihydroxyphenylalanine (DOPA)-modified mussel adhesive proteins and maleimide-functionalized hyaluronic acid. We have successfully fabricated this biocompatible dressing and conducted comprehensive experimental assessments to confirm its hemostatic, antibacterial, and biocompatible characteristics. Importantly, this dressing exclusively incorporates biologically derived materials characterized by low toxicity and minimal immunogenicity, thus holding immense promise for clinical applications in the field of wound healing.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Selectively Positioned Catechol Moiety Supports Ultrashort Self-Assembling Peptide Hydrogel Adhesion for Coral Restoration

Coral reef survival is threatened globally. One way to restore this delicate ecosystem is to enhance coral growth by the controlled propagation of coral fragments. To be sustainable, this technique requires the use of biocompatible underwater adhesives. Hydrogels based on rationally designed ultrashort self-assembling peptides (USP) are of great interest for various biological and environmental applications, due to their biocompatibility and tunable mechanical properties. Implementing superior adhesion properties to the USP hydrogel compounds is crucial in both water and high ionic strength solutions and is relevant in medical and marine environmental applications such as coral regeneration. Some marine animals secrete large quantities of the aminoacids dopa and lysine to enhance their adhesion to wet surfaces. Therefore, the addition of catechol moieties to the USP sequence containing lysine (IIZK) should improve the adhesive properties of USP hydrogels. However, it is challenging to place the catechol moiety (Do) within the USP sequence at an optimal position without compromising the hydrogel self-assembly process and mechanical properties. Here, we demonstrate that, among three USP hydrogels, DoIIZK is the least adhesive and that the adhesiveness of the IIZDoK hydrogel is compromised by its poor mechanical properties. The best adhesion outcome was achieved using the IIZKDo hydrogel, the only one to show equally sound adhesive and mechanical properties. A mechanistic understanding of this outcome is presented here. This property was confirmed by the successful gluing of coral fragments by means of IIZKDo hydrogel that are still thriving after more than three years since the deployment. The validated biocompatibility of this underwater hydrogel glue suggests that it could be advantageously implemented for other applications, such as surgical interventions.

Tough and On-Demand Detachable Wet Tissue Adhesive Hydrogel Made from Catechol Derivatives with a Long Aliphatic Side Chain

Wet adhesion is critical in cases of wound closure, but it is usually deterred by the hydration layer on tissues. Inspired by dopamine-mediated underwater adhesion in mussel foot proteins, wet tissue adhesives containing catechol with 2-3 carbons side chains are reported mostly. To make wet adhesion of this type of adhesives much tougher, catechol derivatives with a long aliphatic side chain (≈10 atoms length) are synthesized. Then, a series of strong wet tissue adhesive hydrogels are prepared through photoinduced copolymerization of acrylic acid with synthetic monomers. The adhesive hydrogel has a high cohesion strength, that is, tensile strength and strain, and toughness of ≈1800 kPa, ≈540%, and ≈4100 kJ m-3 , respectively. Its interfacial toughness on wet and underwater porcine skin is respectively ≈1300 and ≈1100 J m-2 , and its adhesion strength to wet porcine skin is ≈153 kPa. These values are much higher than those of dopamine-based adhesives in the same conditions, demonstrating that the long aliphatic side chain on catechol can greatly improve the wet tissue-adhesion. Additionally, the tough interfacial adhesion can be broken on demand with 5 wt.% aqueous urea solution. This adhesive hydrogel is highly promising in safe wound closure.

Polyglycerol-Based Biomedical Matrix for Immunomagnetic Circulating Tumor Cell Isolation and Their Expansion into Tumor Spheroids for Drug Screening

Circulating tumor cells (CTCs) are established as distinct cancer biomarkers for diagnosis, as preclinical models, and therapeutic targets. Their use as preclinical models is limited owing to low purity after isolation and the lack of effective techniques to create 3D cultures that accurately mimic in vivo conditions. Herein, a two-component system for detecting, isolating, and expanding CTCs to generate multicellular tumor spheroids that mimic the physiology and microenvironment of the diseased organ is proposed. First, an antifouling biointerface on magnetic beads is fabricated by adding a bioinert polymer layer and conjugation of biospecific ligands to isolate cancer cells, dramatically enhancing the selectivity and purity of the isolated cancer cells. Next, the isolated cells are encapsulated into self-degradable hydrogels synthesized using a thiol-click approach. The hydrogels are mechanochemically tuned to enable tumor spheroid growth to a size greater than 300 µm and to further release the grown spheroids while retaining their tumor-like characteristics. In addition, drug treatment highlights the need for 3D culture environments rather than conventional 2D culture. The designed biomedical matrix shows potential as a universal method to ensure mimicry of in vivo tumor characteristics in individual patients and to improve the predictability of preclinical screening of personalized therapeutics.

Compliant Clients: Catechols Exhibit Enhanced Solubility and Stability in Diverse Complex Coacervates

Polyelectrolyte coacervates, with their greater-than-water density, low interfacial energy, shear thinning viscosity, and ability to undergo structural arrest, mediate the formation of diverse load-bearing macromolecular materials in living organisms as well as in industrial material fabrication. Coacervates, however, have other useful attributes that are challenging to study given the metastability of coacervate colloidal droplets and a lack of suitable analytical methods. We adopt solution electrochemistry and nuclear magnetic resonance measurements to obtain remarkable insights about coacervates as solvent media for low-molecular-weight catechols. When catechols are added to dispersions of coacervated polyelectrolytes, there are two significant consequences: (1) catechols preferentially partition up to 260-fold into the coacervate phase, and (2) coacervates stabilize catechol redox potentials by up to +200 mV relative to the equilibrium solution. The results suggest that the relationship between phase-separated polyelectrolytes and their client molecules is distinct from that existing in aqueous solution and has the potential for insulating many redox-unstable chemicals.

Gene co-option, duplication and divergence of cement proteins underpin the evolution of bioadhesives across barnacle life histories

Acquisition of new genes often results in the emergence of novel functions and is a key step in lineage-specific adaptation. As a group of sessile crustaceans, barnacles establish permanent attachment through initial cement secretion at the larval phase followed by continuous cement secretion in juveniles and adults. However, the origins and evolution of barnacle larval and adult cement proteins remain poorly understood. By performing microdissection of larval cement glands, transcriptome and shotgun proteomics and immunohistochemistry validation, we identified 30 larval and 27 adult cement proteins of the epibiotic turtle barnacle Chelonibia testudinaria, of which the majority are stage- and barnacle-specific. While only two proteins, SIPC and CP100K, were expressed in both larvae and adults, detection of protease inhibitors and the cross-linking enzyme lysyl oxidase paralogs in larvae and adult cement. Other barnacle-specific cement proteins such as CP100k and CP52k likely share a common origin dating back at least to the divergence of Rhizocephala and Thoracica. Different CP52k paralogues could be detected in larval and adult cement, suggesting stage-specific cement proteins may arise from duplication followed by changes in expression timing of the duplicates. Interestingly, the biochemical properties of larval- and adult-specific CP52k paralogues exhibited remarkable differences. We conclude that barnacle larval and adult cement systems evolved independently, and both emerged from co-option of existing genes and de novo formation, duplication and functional divergence of lineage-specific cement protein genes. Our findings provide important insights into the evolutionary mechanisms of bioadhesives in sessile marine invertebrates.

Designing Bio-Inspired Wet Adhesives through Tunable Molecular Interactions

Marine organisms, such as mussels and sandcastle worms, can master rapid and robust adhesion in turbulent seawater, becoming leading archetypes for the design of underwater adhesives. The adhesive proteins secreted by the organisms are rich in catecholic amino acids along with ionic and amphiphilic moieties, which mediate the adaptive adhesion mainly through catechol chemistry and coacervation process. Catechol allows a broad range of molecular interactions both at the adhesive-substrate interface and within the adhesive matrix, while coacervation promotes the delivery and surface spreading of the adhesive proteins. These natural design principles have been translated to synthetic systems toward the development of biomimetic adhesives with water-resist adhesion and cohesion. This review provides an overview of the recent progress in bio-inspired wet adhesives, focusing on two aspects: (1) the elucidation of the versatile molecular interactions (e.g., electrostatic interactions, metal coordination, hydrogen bonding, and cation-π/anion-π interactions) used by natural adhesives, mainly through nanomechanical characterizations; and (2) the rational designs of wet adhesives based on these biomimetic strategies, which involve catechol-functionalized, coacervation-induced, and hydrogen bond-based approaches. The emerging applications (e.g., tissue glues, surgical implants, electrode binders) of the developed biomimetic adhesives in biomedical, energy, and environmental fields are also discussed, with future research directions proposed.

Biospecific cation-π interaction by modulating molecular hydration and supramolecular structure of short peptides

This study presents novel adhesive materials that use cation-π interactions to achieve highly specific cohesive interaction under water. The materials are short length peptides based on the FKF motif flanked by different side groups. Using the surface forces apparatus, we show that the composition of the side group allows to finely tune the strength of the cohesive and adhesive energies of the peptide and its specificity, meaning its capacity to bind strongly only to substrates bearing the same peptide. The interfacial properties of these adhesive peptides are shown to strongly depend on the composition of the deposition solvent, with DMSO being the solvent of choice to achieve high cohesive and adhesive energies. This result was correlated with the supramolecular structure of the peptide film and confirmed that needle-like structures can significantly enhance the adhesion of the material. Altogether, we showed that cation-π interaction can be used efficiently to create adhesive materials that incorporate features already known for underwater adhesives such as activation via solvent displacement, as well as new ones such as specificity and supramolecular structure enhanced adhesion.

Protein-Based Biological Materials: Molecular Design and Artificial Production

Polymeric materials produced from fossil fuels have been intimately linked to the development of industrial activities in the 20th century and, consequently, to the transformation of our way of living. While this has brought many benefits, the fabrication and disposal of these materials is bringing enormous sustainable challenges. Thus, materials that are produced in a more sustainable fashion and whose degradation products are harmless to the environment are urgently needed. Natural biopolymers─which can compete with and sometimes surpass the performance of synthetic polymers─provide a great source of inspiration. They are made of natural chemicals, under benign environmental conditions, and their degradation products are harmless. Before these materials can be synthetically replicated, it is essential to elucidate their chemical design and biofabrication. For protein-based materials, this means obtaining the complete sequences of the proteinaceous building blocks, a task that historically took decades of research. Thus, we start this review with a historical perspective on early efforts to obtain the primary sequences of load-bearing proteins, followed by the latest developments in sequencing and proteomic technologies that have greatly accelerated sequencing of extracellular proteins. Next, four main classes of protein materials are presented, namely fibrous materials, bioelastomers exhibiting high reversible deformability, hard bulk materials, and biological adhesives. In each class, we focus on the design at the primary and secondary structure levels and discuss their interplays with the mechanical response. We finally discuss earlier and the latest research to artificially produce protein-based materials using biotechnology and synthetic biology, including current developments by start-up companies to scale-up the production of proteinaceous materials in an economically viable manner.

Catechol-Amine-Decorated Epoxy Resin as an Underwater Adhesive: A Coacervate Concept Using a Liquid Marble Strategy

The attachment phenomena of various hierarchical architectures found in nature, especially underwater adhesion, have drawn extensive attention to the development of similar biomimicking adhesives. Marine organisms show spectacular adhesion characteristics because of their foot protein chemistry and the formation of an immiscible phase (coacervate) in water. Herein, we report a synthetic coacervate derived using a liquid marble route composed of catechol amine-modified diglycidyl ether of bisphenol A (EP) polymers wrapped by silica/PTFE powders. The adhesion promotion efficiency of catechol moieties is established by functionalizing EP with monofunctional amines (MFA) of 2-phenyl ethylamine and 3,4-dihydroxy phenylethylamine (DA). The curing activation of MFA-incorporated resin pointed toward a lower activation energy (50.1-52.1 kJ mol^-1) compared with the neat system (56.7-58 kJ mol^-1). The viscosity build-up and gelation are faster for the catechol-incorporated system, making it ideal for underwater bonding performance. The PTFE-based adhesive marble of the catechol-incorporated resin was stable and exhibited an adhesive strength of 7.5 MPa under underwater bonding conditions.

Tuning Water-Resistant Networks in Mussel-Inspired Hydrogels for Robust Wet Tissue and Bioelectronic Adhesion

Hydrogels with robust wet adhesion are desirable for applications in aqueous environments. Wet adhesion arising from synergy between hydrophobic and catechol components in mussel foot proteins has been highlighted. However, optimizing hydrogels with multiple components is challenging because of their complex structure-property relationships. Herein, high-throughput screening of a series of hydrophobic alkyl monomers and adhesive catechol derivatives was used to systematically develop wet adhesive hydrogels. Short alkyl chains promote wet adhesion by repelling water at the adhesive interface, whereas long alkyl chains form strong hydrophobic interactions inside the hydrogel network that impede or dissipate energy for wet adhesion. The optimized wet adhesive hydrogel, containing short alkyl chain, was applied for rapid hemostasis and wound healing because of the synergistic effect of catechol and alkyl groups and its immunomodulation ability, which is revealed through a transcriptomic analysis. Conductive nanocomponents were incorporated into the optimized hydrogel to produce a wearable device, which was used for continuous monitoring human electrocardiogram (ECG) during swimming, and in situ epicardial ECG on a porcine living and beating heart. This study demonstrated an efficient and generalized molecular design strategy for multifunctional wet adhesive hydrogels.

Structural features of interfacial water predict the hydrophobicity of chemically heterogeneous surfaces

The hydrophobicity of an interface determines the magnitude of hydrophobic interactions that drive numerous biological and industrial processes. Chemically heterogeneous interfaces are abundant in these contexts; examples include the surfaces of proteins, functionalized nanomaterials, and polymeric materials. While the hydrophobicity of nonpolar solutes can be predicted and related to the structure of interfacial water molecules, predicting the hydrophobicity of chemically heterogeneous interfaces remains a challenge because of the complex, non-additive contributions to hydrophobicity that depend on the chemical identity and nanoscale spatial arrangements of polar and nonpolar groups. In this work, we utilize atomistic molecular dynamics simulations in conjunction with enhanced sampling and data-centric analysis techniques to quantitatively relate changes in interfacial water structure to the hydration free energy (a thermodynamically well-defined descriptor of hydrophobicity) of chemically heterogeneous interfaces. We analyze a large data set of 58 self-assembled monolayers (SAMs) composed of ligands with nonpolar and polar end groups of different chemical identity (amine, amide, and hydroxyl) in five mole fractions, two spatial patterns, and with scaled partial charges. We find that only five features of interfacial water structure are required to accurately predict hydration free energies. Examination of these features reveals mechanistic insights into the interfacial hydrogen bonding behaviors that distinguish different surface compositions and patterns. This analysis also identifies the probability of highly coordinated water structures as a unique signature of hydrophobicity. These insights provide a physical basis to understand the hydrophobicity of chemically heterogeneous interfaces and connect hydrophobicity to experimentally accessible perturbations of interfacial water structure.

Silk Fibroin-Based Tough Hydrogels with Strong Underwater Adhesion for Fast Hemostasis and Wound Sealing

Rapid and strong adhesion of hydrogel adhesives is required for instant wound closure and hemostasis. However, in situ hydrogel formation and sufficient adhesion at target tissue sites in biological environments are severely compromised by the presence of blood and body fluids. In this work, an underwater adhesive hydrogel (named SHCa) is fabricated with rapid in situ gelation, enhanced mechanical toughness, and robust underwater adhesion. The SHCa can undergo rapid UV irradiation-induced gelation under water within 5 s and adhere firmly to underwater surfaces for 6 months. The synergistic effects of crystalline β-sheet structures and dynamic energy-dissipating mechanisms enhance the mechanical toughness and cohesion, supporting the balance between adhesion and cohesion in wet environments. Importantly, the SHCa can achieve rapid in situ gelation and robust underwater adhesion at various tissue surfaces in highly dynamic fluid environments, substantially outperforming the commercially available tissue adhesives. The lap shear adhesion strength and wound closure strength of SHCa on blood-covered substrates are 7.24 and 12.68 times higher than those of cyanoacrylate glue, respectively. Its fast hemostasis and wound sealing performance are further demonstrated in in vivo animal models. The proposed hydrogel with strong underwater adhesion provides an effective tool for fast wound closure and hemostasis.

Mussel adhesion: A fundamental perspective on factors governing strong underwater adhesion

Protein-based underwater adhesives of marine organisms exhibit extraordinary binding strength in high salinity based on utilizing a variety of molecular interaction mechanisms. These include acid-base interactions, bidentate bindings or complex hydrogen bonding interactions, and electrochemical manipulation of interfacial bonding. In this Perspective, we briefly review recent progress in the field, and we discuss how interfacial electrochemistry can vary interfacial forces by concerted tuning of surface charging, hydration forces, and tuning of the interfacial ion concentration. We further discuss open questions, controversial findings, and new paths into understanding and utilizing redox-proteins and derived polymers for enhancing underwater adhesion in a complex salt environment.

Mussel-inspired biomaterials: From chemistry to clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis-blue mussel and Mytilus californianus-California mussel are the most well-known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle-inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle-inspired biomaterials in various medical applications are summarized for future developments in the field.

In silico prediction and in vitro validation of the effect of pH on adhesive behaviour of the fused CsgA-MFP3 protein

Recombinant production of mussel foot proteins among marine-inspired proteinaceous adhesive materials has been attracted high attention for medical applications, due to their exceptional versatility potential of hierarchically arranged nanostructures. Various biochemical and proteinous factors such as amyloid CsgA curli protein have been used as a synergistic factor to enhance the constancy of obtained bio-adhesion but their mechanistic interactions have not yet been deeply investigated widely in different pH conditions. To this end, the present study has first sought to assess molecular simulation and prediction by using RosettaFold to predict the 3-dimensional structure of the fused CsgA subunit and the MFP3 protein followed by in vitro verification. It was developed an ensemble of quantitative structure-activity relationship models relying on simulations according to the surface area and molecular weight values of the fused proteins in acidic to basic situations using PlayMolecule (protein preparation app for MD simulations) online databases followed by molecular dynamic simulation at different pHs. It was found that acidic conditions positively affect adhesive strength throughout the chimeric structure based on comparative structure-based analyses along with those obtained in prevailing literature. Atomic force microscopy analysis was confirmed obtained in silico data which showed enhanced adhesive properties of fused protein after self-assembly in low pH conditions. In conclusion, the augmented model for reactivity predictions not only unravels the performance and explain ability of the adhesive proteins but in turn paves the way for the decision-making process for chimeric subunits modifications needed for future industrial production.

Liquid-Liquid Phase Separation of the Green Mussel Adhesive Protein Pvfp-5 is Regulated by the Post-Translated Dopa Amino Acid

The underwater adhesive prowess of aquatic mussels has been largely attributed to the abundant post-translationally modified amino acid l-3,4-dihydroxyphenylalanine (Dopa) in mussel foot proteins (MFPs) that make up their adhesive threads. More recently, it has been suggested that during thread fabrication, MFPs form intermediate fluidic phases such as liquid crystals or coacervates regulated by a liquid-liquid phase separation (LLPS) process. Here, it is shown that Dopa plays another central role during mussel fiber formation, by enabling LLPS of Pvfp-5β, a main MFP of the green mussel Perna viridis. Using residue-specific substitution of Tyrosine (Tyr) for Dopa during recombinant expression, Dopa-substituted Pvfp-5β is shown to exhibit LLPS under seawater-like conditions, whereas the Tyr-only version forms insoluble aggregates. Combining quantum chemistry calculations and solution NMR, a transient H-bonding network requiring the two hydroxyl groups of Dopa is found to be critical to enable LLPS in Dopa-mutated Pvfp-5β. Overall, the study suggests that Dopa plays an important role in regulating LLPS of MFPs, which may be critical to concentrate the adhesive proteins at the plaque/substrate interface and therefore produce a more robust adhesive. The findings also provide molecular-level lessons to guide biomanufacturing of protein-based materials such as bioadhesives and load-bearing fibers.

Ultrastrong underwater adhesion on diverse substrates using non-canonical phenolic groups

Robust underwater adhesion is challenging because a hydration layer impedes the interaction between substrates and adhesives. Phenolic adhesives inspired by marine creatures such as mussels were extensively studied, but these adhesives have not reached the adhesion strength and substrate diversity of Man-made dry adhesives. Here, we report a class of ultrastrong underwater adhesives with molecular phenolic designs extending beyond what nature has produced. These non-canonical phenolic polymers show versatile adhesion on various materials, with adhesion strengths exceeding 10 MPa on metal. Incorporating even just a small amount (<10%) of non-canonical phenolic groups into a polymer is sufficient for dramatically enhancing underwater adhesion, suggesting that this new class of phenolic materials will be incorporated into various industrial polymer systems in the future.

Realizing robust underwater adhesion is challenging because a hydration layer impedes the interaction between substrates and adhesives. Here, the authors report a class of ultrastrong underwater adhesives with molecular non-canonical phenolic groups in a polymer to realize strong adhesion on various substrates.

Biomaterials and Bioactive Natural Products from Marine Invertebrates: From Basic Research to Innovative Applications

Aquatic invertebrates are a major source of biomaterials and bioactive natural products that can find applications as pharmaceutics, nutraceutics, cosmetics, antibiotics, antifouling products and biomaterials. Symbiotic microorganisms are often the real producers of many secondary metabolites initially isolated from marine invertebrates; however, a certain number of them are actually synthesized by the macro-organisms. In this review, we analysed the literature of the years 2010–2019 on natural products (bioactive molecules and biomaterials) from the main phyla of marine invertebrates explored so far, including sponges, cnidarians, molluscs, echinoderms and ascidians, and present relevant examples of natural products of interest to public and private stakeholders. We also describe omics tools that have been more relevant in identifying and understanding mechanisms and processes underlying the biosynthesis of secondary metabolites in marine invertebrates. Since there is increasing attention on finding new solutions for a sustainable large-scale supply of bioactive compounds, we propose that a possible improvement in the biodiscovery pipeline might also come from the study and utilization of aquatic invertebrate stem cells.

Revisiting the adhesion mechanism of mussel-inspired chemistry

Mussel-inspired chemistry has become an ideal platform to engineer a myriad of functional materials, but fully understanding the underlying adhesion mechanism is still missing. Particularly, one of the most pivotal questions is whether catechol still plays a dominant role in molecular-scale adhesion like that in mussel adhesive proteins. Herein, for the first time, we reveal an unexplored adhesion mechanism of mussel-inspired chemistry that is strongly dictated by 5,6-dihydroxyindole (DHI) moieties, amending the conventional viewpoint of catechol-dominated adhesion. We demonstrate that polydopamine (PDA) delivers an unprecedented adhesion of 71.62 mN m-1, which surpasses that of many mussel-inspired derivatives and is even 121-fold higher than that of polycatechol. Such a robust adhesion mainly stems from a high yield of DHI moieties through a delicate synergy of leading oxidation and subsidiary cyclization within self-polymerization, allowing for governing mussel-inspired adhesion by the substituent chemistry and self-polymerization manner. The adhesion mechanisms revealed in this work offer a useful paradigm for the exploitation of functional mussel-inspired materials.

Surface Force Measurements of Mussel-Inspired Pressure-Sensitive Adhesives

Translating fundamental studies of marine mussel adhesion into practical mussel-inspired wet adhesives remains an important technological challenge. To adhere, mussels secrete adhesive proteins rich in the catecholic amino acid 3,4-dihydroxyphenylalanine (Dopa) and positively charged lysine. Consequently, numerous synthetic adhesives incorporating catecholic and cationic functionalities have been designed. However, despite widespread research, uncertainties remain about the optimal design of synthetic mussel-inspired adhesives. Here, we present a study of the adhesion of mussel-inspired pressure-sensitive adhesives. We explore the effects of catechol content, molecular architecture, and solvent quality on pressure-sensitive adhesive (PSA) adhesion and cohesion measured in a surface forces apparatus. Our findings demonstrate that the influence of catechol content depends on the choice of solvent and that adhesive performance is dictated by film composition rather than molecular architecture. Our results also highlight the importance of electrostatic and hydrophobic interactions for adhesion and cohesion in aqueous environments. Together, our findings contribute to an improved understanding of the interplay between materials chemistry, environmental conditions, and adhesive performance to facilitate the design of bioinspired wet adhesives.

Mechanistic understanding of catechols and integration into an electrochemically cross-linked mussel foot inspired adhesive hydrogel

Catechol reaction mechanisms form the basis of marine mussel adhesion, allowing for bond formation and cross-linking in wet saline environments. To mimic mussel foot adhesion and develop new bioadhesive underwater glues, it is essential to understand and learn to control their redox activity as well as their chemical reactivity. Here, we study the electrochemical characteristics of functionalized catechols to further understand their reaction mechanisms and find a stable and controllable molecule that we subsequently integrate into a polymer to form a highly adhesive hydrogel. Contradictory to previous hypotheses, 3,4-dihydroxy-L-phenylalanine is shown to follow a Schiff-base reaction whereas dopamine shows an intramolecular ring formation. Dihydrocaffeic acid proved to be stable and was substituted onto a poly(allylamine) backbone and electrochemically cross-linked to form an adhesive hydrogel that was tested using a surface forces apparatus. The hydrogel's compression and dehydration dependent adhesive strength have proven to be higher than in mussel foot proteins (mfp-3 and mfp-5). Controlling catechol reaction mechanisms and integrating them into stable electrochemically depositable macroscopic structures is an important step in designing new biological coatings and underwater and biomedical adhesives.

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.

Beetle and mussel-inspired chimeric protein for fabricating anti-icing coating

Ice accretion on surfaces can cause serious damages and economic losses in industries and civilian facilities. Antifreeze proteins (AFPs) as evolutionary adaptation products of organisms to cold climates, provide solutions for alleviating icing problems. In this work, a chimeric protein Mfp-AFP was rationally designed combining mussel-inspired adhesive domain with Tenebrio molitor-derived antifreeze protein domain. Expectedly, the multifunctional Mfp-AFP can lower the freezing point of water and inhibit ice recrystallization. The chimeric protein could also readily modify diverse solid surfaces due to the adhesive domain containing Dopa, and resist frosting and delay ice formation due to the beetle-derived antifreeze fragment. Moreover, Mfp-AFP coatings display excellent biocompatibility proved by cytocompatibility and hemolysis assays. Here, the designed multifunctional protein coatings provide an alternative strategy for fabricating anti-icing surfaces.

Design principles for creating synthetic underwater adhesives

Water and adhesives have a conflicting relationship as demonstrated by the failure of most man-made adhesives in underwater environments. However, living creatures routinely adhere to substrates underwater. For example, sandcastle worms create protective reefs underwater by secreting a cocktail of protein glue that binds mineral particles together, and mussels attach themselves to rocks near tide-swept sea shores using byssal threads formed from their extracellular secretions. Over the past few decades, the physicochemical examination of biological underwater adhesives has begun to decipher the mysteries behind underwater adhesion. These naturally occurring adhesives have inspired the creation of several synthetic materials that can stick underwater - a task that was once thought to be "impossible". This review provides a comprehensive overview of the progress in the science of underwater adhesion over the past few decades. In this review, we introduce the basic thermodynamics processes and kinetic parameters involved in adhesion. Second, we describe the challenges brought by water when adhering underwater. Third, we explore the adhesive mechanisms showcased by mussels and sandcastle worms to overcome the challenges brought by water. We then present a detailed review of synthetic underwater adhesives that have been reported to date. Finally, we discuss some potential applications of underwater adhesives and the current challenges in the field by using a tandem analysis of the reported chemical structures and their adhesive strength. This review is aimed to inspire and facilitate the design of novel synthetic underwater adhesives, that will, in turn expand our understanding of the physical and chemical parameters that influence underwater adhesion.

Following the thread: Mytilus mussel byssus as an inspired multi-functional biomaterial

Over the last 15 years, the byssus of marine mussels (Mytilus spp.) has emerged as an important model system for the bio-inspired development and synthesis of advanced polymers and adhesives. But how did these seemingly inconsequential fibers that are routinely discarded in mussel hors d’oeuvres become the focus of intense international research. In the present review, we take a historical perspective to understand this phenomenon. Our purpose is not to review the sizeable literature of mussel-inspired materials, as there are numerous excellent reviews that cover this topic in great depth. Instead, we explore how the byssus became a magnet for bio-inspired materials science, with a focus on the specific breakthroughs in the understanding of composition, structure, function, and formation of the byssus achieved through fundamental scientific investigation. Extracted principles have led to bio-inspired design of novel materials with both biomedical and technical applications, including surgical adhesives, self-healing polymers, tunable hydrogels, and even actuated composites. Continued study into the byssus of Mytilid mussels and other species will provide a rich source of inspiration for years to come.

A catechol-chitosan-based adhesive and injectable hydrogel resistant to oxidation and compatible with cell therapy

Injectable hydrogels designed for cell therapy need to be adhesive to the surrounding tissues to maximize their retention and the communication between the host and the encapsulated cells. Catechol grafting is an efficient and well-known strategy to improve the adhesive properties of various polymers, including chitosan. However, catechol groups are also known to be cytotoxic as they oxidize into quinones in alkaline environments. Usually, hydrogels made from catechol-grafted chitosan (cat-CH) oxidize quickly, which tends to limit adhesion and prevent cell encapsulation. In this work, we limited oxidation and improved the cytocompatibility of cat-CH hydrogels by grafting chitosan with dihydroxybenzoic acid (DHBA), a small cat-bearing molecule known to have a high resistance to oxidation. We show that DHBA-grafted CH (dhba-CH) oxidized significantly slower and to a lesser extent that cat-CH made with hydrocaffeic acid (hca-CH). By combining dhba-CH with sodium bicarbonate and phosphate buffer, we fabricated thermosensitive injectable hydrogels with higher mechanical properties, quicker gelation and significantly lower oxidation than previously designed cat-CH systems. The resulting gels are highly adhesive on inorganic substrates and support L929 fibroblast encapsulation with high viability (≥90% after 24 hours), something that was not possible in any previously designed cat-CH gel system. These properties make the dhba-CH hydrogels excellent candidates for minimally invasive and targeted cell therapy in applications that require high adhesive strength.

A Novel Copper-Binding Peptide That Self-Assembles Into a Transparent Antibacterial and Antiviral Coating

The health, economy, and quality of life all over the world are greatly affected by bacterial infections and viral outbreaks. Bacterial cells and viruses, such as influenza, can spread through contaminated surfaces and fomites. Therefore, a possible way to fight these pathogens is to utilize antibacterial and antiviral coatings, which reduce their numbers on contaminated surfaces. Here, we present a novel short peptide that can self-assemble, adhere to various surfaces, and bind different metal ions such as copper, which provides the surface with antibacterial and antiviral properties. For these functions, the peptide incorporates the amino acid 3,4-dihydroxyphenylalanine (DOPA), which provides the peptide with adhesive capabilities; a diphenylalanine motif that induces the self-assembly of the peptide; the metal-binding hexahistidine sequence. Our results demonstrate that the coating, which releases monovalent cuprous ions and hydrogen peroxide, provides the surfaces with significant antibacterial and antiviral properties. Additionally, the coating remains transparent, which is favorable for many objects and especially for display screens.

Molecular Context of Dopa Influences Adhesion of Mussel-Inspired Peptides

Improving adhesives for wet surfaces is an ongoing challenge. While the adhesive proteins of marine mussels have inspired many synthetic wet adhesives, the mechanisms of mussel adhesion are still not fully understood. Using surface forces apparatus (SFA) measurements and replica-exchange and umbrella-sampling molecular dynamics simulations, we probed the relationships between the sequence, structure, and adhesion of mussel-inspired peptides. Experimental and computational results reveal that peptides derived from mussel foot protein 3 slow (mfp-3s) containing 3,4-dihydroxyphenylalanine (Dopa), a post-translationally modified variant of tyrosine commonly found in mussel foot proteins, form adhesive monolayers on mica. In contrast, peptides with tyrosine adsorb as weakly adhesive clusters. We further considered simulations of mfp-3s derivatives on a range of hydrophobic and hydrophilic organic and inorganic surfaces (including silica, self-assembled monolayers, and a lipid bilayer) and demonstrated that the chemical character of the target surface and proximity of cationic and hydrophobic residues to Dopa affect peptide adsorption and adhesion. Collectively, our results suggest that conversion of tyrosine to Dopa in hydrophobic, sparsely charged peptides influences peptide self-association and ultimately dictates their adhesive performance.

Slippery-Liquid-Infused Electrostatic Flocking Surfaces for Marine Antifouling Application

Most marine antifouling coatings rely on the release of toxic biocides to prevent fouling organisms from attaching, causing environmental pollution. This work proposes a biocide-free environmentally friendly marine antifouling strategy. Slippery-liquid-infused electrostatic flocking surfaces (S-EFSs) were prepared by combining electrostatic flocking and slippery liquid infusion. They exhibited complete mussel resistance after comparing adhesion to the surface of different materials in the laboratory. In addition, the unique surface morphology including lubricant was found to be crucial to their antifouling performance. Real-time polymerase chain reaction showed that different surfaces significantly affected the gene-expression levels of the mussels' foot proteins, where higher levels on S-EFSs meant that the mussels tried to secrete more proteins but they failed to adhere. Moreover, a 148-day field test showed that S-EFSs can resist not only mussels but also tubeworms, tunicates, and barnacles, and the total fouling area decreased by more than 50% compared to control samples. Notably, the maturity of electrostatic flocking technology and the simplicity of the modification steps used endow this strategy with the potential to significantly reduce the economic loss caused by marine biofouling in practical applications.

Facile fabrication of superhydrophobic polyester fabric based on rapid oxidation polymerization of dopamine for oil-water separation

Through the special chemical structure of dopamine (DA), superhydrophobic polyester (PET) fabric was fabricated by introducing the low surface energy substance hexadecyltrimethoxysilane (HDS) into the PET fabric and chelating Fe ions with phenolic hydroxyl groups of polydopamine (PDA) to form a rough surface. The water contact angle (WCA) of the prepared PDA/Fe/HDS PET fabric was higher than 160° and the scrolling angle (SA) was lower than 2.09°. The excellent adhesion property of polydopamine (PDA) on the substrate is helpful to improve the stability of superhydrophobic PDA/Fe/HDS PET fabric. The tests results showed that the modified PET fabric maintains excellent mechanical properties. Its superhydrophobic property had good stability and durability in the harsh environment of washing, mechanical friction, UV irradiation, seawater immersion, acid–base and organic reagents erosion. The PDA/Fe/HDS PET fabric also had good self-cleaning and oil–water separation properties. It still had good oil–water separation performance after repeated use for 25 times, and the separation efficiency was more than 95%. The preparation method was facile, the treatment time can be shortened, the cost of the modified substrate was low, and fluorine-free substances were used in the process. This work provides a new way to expand the added value of PET fabrics and develop durable superhydrophobic fabrics in practical application.

Through the special chemical structure of dopamine, superhydrophobic polyester fabric was fabricated by introducing the low surface energy substance hexadecyltrimethoxysilane into the PET fabric and chelating Fe ions to form rough surface.

Protein-mediated bioadhesion in marine organisms: A review

Protein-mediated bioadhesion is one of the crucial physiological processes in marine organisms, by which they can firmly adhere to underwater substrates. Most marine adhesive organisms are biofoulers, causing negative effects on marine ecosystems and huge economic losses to aquaculture and maritime industries. Furthermore, adhesive proteins in these organisms are promising bionic candidates for high-performance artificial materials with great application value. In-depth understanding of the bioadhesion in marine ecosystems is of dual significance for resolving biofouling issue and developing marine bionic products. Here, we review the research progress of protein-mediated bioadhesion in marine organisms. The adhesion processes such as protein biosynthesis and secretion are similar among organisms, but the detailed features such as compositions, structures, and molecular functions of adhesive proteins are distinct. Hydroxylation, glycosylation, and phosphorylation are important post-translational modifications during the processes of adhesion. The contents of some amino acids such as glycine, tyrosine and cysteine involved in underwater adhesion are significantly higher, which is a sequence feature of barnacle cement and mussel foot proteins. The amyloid structures and conserved domains/motifs such as EGF and vWFA distributed in adhesive proteins are involved in the underwater adhesion. In addition, the oxidative cross-linking also plays an important role in marine bioadhesion. Overall, the unique and common features identified for the protein-mediated bioadhesion in diverse marine organisms here provide background information and essential reference for characterizing marine adhesive proteins and associated functional domains, formulating antifouling strategies, and developing novel biomimetic adhesives.

From Folding to Assembly: Functional Supramolecular Architectures of Peptides Comprised of Non-Canonical Amino Acids

The engineering of biological molecules is the fundamental concept behind the design of complex materials with desirable functions. Over the last few decades, peptides and proteins have emerged as useful building blocks for well-defined nanostructures with controlled size and dimensions. Short peptides in particular have received much attention due to their inherent biocompatibility, lower synthetic cost, and ease of tunability. In addition to the diverse self-assembling properties of short peptides comprising coded amino acids and their emerging applications in nanotechnology, there is now growing interest in the properties of peptides composed of non-canonical amino acids. Such non-natural oligomers have been shown in recent years to form well-defined secondary structures similar to natural proteins, with the ability to self-assemble to generate a wide variety of nanostructures with excellent biostability. This review describes recent events in the development of supramolecular assemblies of peptides composed completely of non-coded amino acids and their hybrid analogues. Special attention is paid to understanding the supramolecular assemblies at the atomic level and to considering their potential applications in nanotechnology.