Mussel adhesion is dictated by time-regulated secretion and molecular conformation of mussel adhesive proteins

Perceiving and Countering Marine Biofouling: Structure, Forces, and Processes at Surfaces in Sea Water Across the Length Scales

In marine industries, severe economic losses are caused by accumulating organisms on surfaces in biofouling processes. Establishing a universal and nontoxic protocol to eliminate biofouling has been a notoriously difficult task due to the complexity of the marine organisms' interactions with surfaces and the chemical, mechanical, and morphological diversity of the surfaces involved. The tremendous variety of environmental parameters in marine environments further complicates this field. For efficient surface engineering to combat fouling, secretion, chemical structure, and properties of biobased adhesives and adhesion mechanisms must be understood. Advanced characterization techniques, like Atomic Force Microscopy (AFM), now allow one to study the three parameters determining surface adhesion and, eventually, fouling, i.e., morphology, chemistry, and surface mechanical modulus. By AFM, characterization can now be performed across length scales from nanometers to hundreds of micrometers. This review provides an up-to-date account of the most promising AFM-based approaches for imaging and characterizing natural adhesives provided by marine organisms. We summarize the current understanding of the molecular basis and the related relevant processes of marine fouling. We focus on applications of AFM "beyond imaging", i.e., to study interactions between adhesives and the surfaces involved. Additionally, we discuss the performance enhancement of polymer antifouling coatings using information derived from AFM. Knowledge and control of marine adhesion can be applied to prevent marine fouling, as well as to design bioadhesives to enhance potential medical applications. We present some milestone results and conclude with an outlook discussing novel possibilities for designing antifouling coatings and medical bioadhesives.

Extreme pH Tolerance in Peptide Coacervates Mediated by Multivalent Hydrogen Bonds for Enzyme-Triggered Oral Drug Delivery

Biopolymer-based complex coacervates hold promising prospects in the field of biomedicine. However, their low stability in environments with extreme pH and high salt concentrations, largely due to weakly charged biomacromolecules and insufficient understanding of their assembly processes, has hindered their practical applications in oral drug delivery. Here, we have developed Dopa-containing peptide-based complex coacervates that are stable across a wide range of pH (1-11) and salt concentrations. Large-scale all-atom molecular dynamics simulations reveal that multivalent hydrogen bonds control the assembly pathway of the coacervates and boost their stability. Systematic point mutations reveal that various multivalent molecular interactions can synergistically tune the properties of complex coacervates. Such peptide coacervates show high drug encapsulation efficacy and trypsin-triggered release, presenting great potential for oral drug delivery applications. Our multivalent hydrogen bond-mediated peptide coacervates provide new design principles of engineering functional coacervates for diverse applications.

Molecular simulations guiding recombinant mussel protein with enhanced applicable properties for adhesive materials

Mussel foot proteins (mfps) are considered as potential biomaterials due to their excellent adhesive properties. Nevertheless, the lack of expression or adhesion of recombinant mfps in bacterial expression systems has limited their applications. Here, we propose a design strategy based on the structural analysis of adhesive protein Mcofp-3, focusing on the critical role of tyrosine position and quantity in regulating the production and functionality of mfps. A performance-improved mutant, N33Y/Y32A/Y51A, was constructed, demonstrating a 23 % increase in expression, a 150 % increase in adhesion, and a 76 % increase in solubility compared to the native protein. Molecular dynamics simulations reveal that the mutants' solubility and viscosity are influenced by SASA, hydrogen bonds within and radius of gyration. The N33Y/Y32A/Y51 mutant presents a looser conformation and forms expandable adsorption on the SiO2 surface. A Ca2+-triggered mussel-based coacervate coating was subsequently developed, showing excellent water-resistant and biological properties. These results indicate that mutant proteins have the potential to be used as mussel-based adhesive materials, and our proposed strategy will help the rational design of other natural functional proteins.

Mussel Foot Protein Membrane-Enclosed Crystalline Drug with Zero-Order Release Kinetics for Long-Acting Therapy

Injectable formulations with sustained and steady release capabilities are critically required to treat diseases requiring temporary or lifelong continuous therapy, especially for drugs with a short half-life. Additionally, achieving a sufficiently high drug loading in a single dose remains a persistent challenge. Herein, by mimicking the formation principles of mussel adhesive plaques, we have developed membrane-enclosed crystalline systems of insulin and progesterone as model macro- and small-molecular crystalline drugs. The system exhibits a substantial drug loading capacity (>90 %). It exhibits sustained and zero-order release kinetics, thereby facilitating the establishment of a subcutaneous reservoir containing a substantial drug load, enabling progressive and continuous release of the drug into the body. One single injection of membrane-enclosed insulin crystal can maintain normoglycemia in diabetic mice for up to 7 days. Meanwhile, membrane-coated progesterone crystals can sustain drug release in rats for over 7 days. The protein membrane can be cleared from the injection sites in 35 days. This system can serve as a versatile platform for the sustained release of various crystalline pharmaceuticals and the treatment of distinct diseases.

Molecular Mechanism of Oil-Infused Silicone Preventing Mussel Biofouling

Marine biofouling causes severe economical and environmental challenges to marine industries and maritime activities. Biofouling prevention has emerged as one of the most pressing issues in water-related industries. Recently, the slippery liquid-infused porous surfaces (SLIPSs) have shown great potential for biofouling prevention across a broad spectrum of fouling organisms. However, our understanding of the mechanisms by which SLIPSs prevent biofouling remains limited. In this study, we discovered that oil-infused polydimethylsiloxane elastomer (i-PDMS), a silicone-based SLIPS variant, significantly inhibited the sensory responses of the fouling mussel Mytilopsis sallei, particularly at its sensory organ, the foot. Using bioinformatics and molecular biology analyses, we demonstrated that i-PDMS disrupts larval settlement of M. sallei by interfering with the mechanosensitive transient receptor potential melastatin-subfamily member 7 (TRPM7) channel, which is highly expressed in the foot during the settlement process. Furthermore, adhesion assays and molecular dynamics simulations revealed that the secreted foot proteins of the mussel are unable to effectively interact with the i-PDMS surface due to nanoscale fluctuations at the material interface. These findings enhance our understanding of how fouling organisms sense and adhere to surfaces and provide deeper insights into the antifouling mechanisms of SLIPS.

Robust-adhesion and high-mechanical strength hydrogel for efficient wet tissue adhesion

Bioadhesive hydrogels show great promise in wound closure due to their minimally invasive nature and ease of use. However, they typically exhibit poor wet adhesion and mechanical properties on wet tissues. Herein, a ready-to-use bioadhesive hydrogel (denoted as PAA-NHS/C-CS) with rapidly robust adhesion and high mechanical strength is developed via a simple one-pot UV crosslinking polymerization of acrylic acid (AA), catechol-functionalized chitosan (C-CS), and acrylic acid N-hydroxysuccinimide ester (AA-NHS ester). Benefitting from the hydrogen bonds and electrostatic attractions formed between PAA-NHS and C-CS, the as-prepared hydrogel exhibits high tensile strength (∼630 kPa), fracture strain (∼1950%), and toughness (∼4250 kJ m-3) in the fully swollen state. Besides, the noncovalent interactions and covalent crosslinking formed between the dual adhesive moieties (the NHS ester and catechol groups) and the tissue surface endow the hydrogel with high shear strength (∼160 kPa), interfacial toughness (∼630 J m-2), and burst pressure (∼447 mmHg) on wet porcine skin. By integrating the high mechanical properties, rapid robust adhesion, and operational convenience, the as-prepared PAA-NHS/C-CS hydrogel shows great promise in wound closure.

Efficient production of recombinant hybrid mussel proteins with improved adhesion

Mussel foot proteins (mfps) play important roles in surface interaction and underwater adhesion. However, limited production and the lack of adhesion of recombinant mfps have restricted their widespread use. Here, we present a general strategy for enhancing both the expression and function of mfps by connecting multiple protein fragments. We demonstrate that fp-535, the fusion protein comprising fp-5 at each fp-3 terminus, exhibits best adhesion strength up to 1.43 MPa and coating ability, while achieving a higher yield of 91.13 mg/L in the flask culture. After optimizing the fermentation parameters such as temperature and volume as well as the culture medium, the yield of fp-535 was increased to 1.70 g/L in a 5-L bioreactor. Our approach highlights the advantage of fusion mfps and provides potential for the sustainable supply of practical bioadhesive materials.

Harnessing Biomimicry for Controlled Adhesion on Material Surfaces

Nature serves as an abundant wellspring of inspiration for crafting innovative adhesive materials. Extensive research is conducted on various complex forms of biological attachment, such as geckos, tree frogs, octopuses, and mussels. However, significant obstacles still exist in developing adhesive materials that truly replicate the behaviors and functionalities observed in living organisms. Here, an overview of biological organs, structures, and adhesive secretions endowed with adhesion capabilities, delving into the intricate relationship between their morphology and function, and potential for biomimicry are provided. First, the design principles and mechanisms of adhesion behavior and individual organ morphology in nature are summarized from the perspective of structural and size constraints. Subsequently, the value of engineered and bioinspired adhesive materials through selective application cases in practical fields is emphasized. Then, a forward-looking gaze on the conceivable challenges and associated opportunities in harnessing biomimetic strategies and biological materials for advancing adhesive material innovation is highlighted and cast.

Nature-Inspired Wet Drug Delivery Platforms

Nature has created various organisms with unique chemical components and multi-scale structures (e.g., foot proteins, toe pads, suckers, setose gill lamellae) to achieve wet adhesion functions to adapt to their complex living environments. These organisms can provide inspirations for designing wet adhesives with mediated drug release behaviors in target locations of biological surfaces. They exhibit conformal and enhanced wet adhesion, addressing the bottleneck of weaker tissue interface adhesion in the presence of body fluids. Herein, it is focused on the research progress of different wet adhesion and bioinspired fabrications, including adhesive protein-based adhesion and inspired adhesives (e.g., mussel adhesion); capillarity and Stefan adhesion and inspired adhesive surfaces (e.g., tree frog adhesion); suction-based adhesion and inspired suckers (e.g., octopus' adhesion); interlocking and friction-based adhesion and potential inspirations (e.g., mayfly larva and teleost adhesion). Other secreted protein-induced wet adhesion is also reviewed and various suckers for other organisms and their inspirations. Notably, one representative application scenario of these bioinspired wet adhesives is highlighted, where they function as efficient drug delivery platforms on target tissues and/or organs with requirements of both controllable wet adhesion and optimized drug release. Finally, the challenges of these bioinspired wet drug delivery platforms in the future is presented.

Poly(phenylalanine) and poly(3,4-dihydroxy-L-phenylalanine): Promising biomedical materials for building stimuli-responsive nanocarriers

Cancer is a serious threat to human health because of its high annual mortality rate. It has attracted significant attention in healthcare, and identifying effective strategies for the treatment and relief of cancer pain requires urgency. Drug delivery systems (DDSs) offer the advantages of excellent efficacy, low cost, and low toxicity for targeting drugs to tumor sites. In recent decades, copolymer carriers based on poly(phenylalanine) (PPhe) and poly(3,4-dihydroxy-L-phenylalanine) (PDopa) have been extensively investigated owing to their good biocompatibility, biodegradability, and controllable stimulus responsiveness, which have resulted in DDSs with loading and targeted delivery capabilities. In this review, we introduce the synthesis of PPhe and PDopa, highlighting the latest proposed synthetic routes and comparing the differences in drug delivery between PPhe and PDopa. Subsequently, we summarize the various applications of PPhe and PDopa in nanoscale-targeted DDSs, providing a comprehensive analysis of the drug release behavior based on different stimulus-responsive carriers using these two materials. In the end, we discuss the challenges and prospects of polypeptide-based DDSs in the field of cancer therapy, aiming to promote their further development to meet the growing demands for treatment.

Silk Gland Factor 1 Plays a Pivotal Role in Larval Settlement of the Fouling Mussel Mytilopsis sallei

Most fouling organisms have planktonic larval and benthic adult stages. Larval settlement, the planktonic-benthic transition, is the critical point when biofouling begins. However, our understanding of the molecular mechanisms of larval settlement is limited. In our previous studies, we identified that the AMP-activated protein kinase-silk gland factor 1 (AMPK-SGF1) pathway was involved in triggering the larval settlement in the fouling mussel M. sallei. In this study, to further confirm the pivotal role of SGF1, multiple targeted binding compounds of SGF1 were obtained using high-throughput virtual screening. It was found that the targeted binding compounds, such as NAD+ and atorvastatin, could significantly induce and inhibit the larval settlement, respectively. Furthermore, the qRT-PCR showed that the expression of the foot proteins' genes was significantly increased after the exposure to 10 μM NAD+, while the gene expression was significantly suppressed after the exposure to 10 μM atorvastatin. Additionally, the production of the byssus threads of the adults was significantly increased after the exposure to 10-20 μM of NAD+, while the production of the byssus threads was significantly decreased after the exposure to 10-50 μM of atorvastatin. This work will deepen our understanding of SGF1 in triggering the larval settlement in mussels and will provide insights into the potential targets for developing novel antifouling agents.

Biopolymer Drug Delivery Systems for Oromucosal Application: Recent Trends in Pharmaceutical R&D

Oromucosal drug delivery, both local and transmucosal (buccal), is an effective alternative to traditional oral and parenteral dosage forms because it increases drug bioavailability and reduces systemic drug toxicity. The oral mucosa has a good blood supply, which ensures that drug molecules enter the systemic circulation directly, avoiding drug metabolism during the first passage through the liver. At the same time, the mucosa has a number of barriers, including mucus, epithelium, enzymes, and immunocompetent cells, that are designed to prevent the entry of foreign substances into the body, which also complicates the absorption of drugs. The development of oromucosal drug delivery systems based on mucoadhesive biopolymers and their derivatives (especially thiolated and catecholated derivatives) is a promising strategy for the pharmaceutical development of safe and effective dosage forms. Solid, semi-solid and liquid pharmaceutical formulations based on biopolymers have several advantageous properties, such as prolonged residence time on the mucosa due to high mucoadhesion, unidirectional and modified drug release capabilities, and enhanced drug permeability. Biopolymers are non-toxic, biocompatible, biodegradable and may possess intrinsic bioactivity. A rational approach to the design of oromucosal delivery systems requires an understanding of both the anatomy/physiology of the oral mucosa and the physicochemical and biopharmaceutical properties of the drug molecule/biopolymer, as presented in this review. This review summarizes the advances in the pharmaceutical development of mucoadhesive oromucosal dosage forms (e.g., patches, buccal tablets, and hydrogel systems), including nanotechnology-based biopolymer nanoparticle delivery systems (e.g., solid lipid particles, liposomes, biopolymer polyelectrolyte particles, hybrid nanoparticles, etc.).

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 nature-inspired multifunctional adhesive for cartilage tissue-biomaterial integration

Surgical adhesives play a crucial role in tissue integration and repair, yet their application in wet conditions has been severely limited by inadequate adhesive strength and subpar biocompatibility. Furthermore, tissue adhesives have rarely been reported in cartilage tissue repair. In this study, a three-armed dopamine-modified hyaluronic acid derivative adhesive was prepared to function as a bio-inspired adhesive in moist environments. To meet the clinical requirements for cartilage tissue adhesion, we studied its chemical structure, including microscopic morphology, adhesion properties with materials and tissues, in vivo degradation rules, and biological evaluation. The OGMHA8-DOPA adhesive with the optimal aldehyde substitution degree and dopamine-grafting rate was determined by analyzing the experimental conditions. SEM results revealed that the cartilage tissue adhered to a porous interconnected structure. The excellent biocompatibility of the material not only facilitated chondrocyte adhesion but also supported their proliferation on its surface. Animal experiments have demonstrated that this material has no observable inflammatory response or incidence of fibrous capsule formation. The degradation timeline of the material extends beyond the duration of two weeks. The dopamine-modified adhesive exhibited a tight interfacial binding force between the biomaterial and cartilage tissue and excellent biocompatibility in watery tissue, revealing its potential for application in cartilage tissue repair and minimally invasive surgery.

Adaptive Adhesions of Barnacle-Inspired Adhesive Peptides

The strategy of robust adhesion employed by barnacles renders them fascinating biomimetic candidates for developing novel wet adhesives. Particularly, barnacle cement protein 19k (cp19k) has been speculated to be the key adhesive protein establishing the priming layer in the initial barnacle cement construction. In this work, we systematically studied the sequence design rationale of cp19k by designing adhesive peptides inspired by the low-complexity STGA-rich and the charged segments of cp19k. Combining structure analysis and the adhesion performance test, we found that cp19k-inspired adhesive peptides possess excellent disparate adhesion strategies for both hydrophilic mica and hydrophobic self-assembled monolayer surfaces. Specifically, the low-complexity STGA-rich segment offers great structure flexibility for surface adhesion, while the hydrophobic and charged residues can contribute to the adhesion of the peptides on hydrophobic and charged surfaces. The adaptive adhesion strategy identified in this work broadens our understanding of barnacle adhesion mechanisms and offers valuable insights for designing advanced wet adhesives with exceptional performance on various types of surfaces.

Genetic Diversity, Population Structure, and Environmental Adaptation Signatures of Chinese Coastal Hard-Shell Mussel Mytilus coruscus Revealed by Whole-Genome Sequencing

The hard-shell mussel (Mytilus coruscus) is widespread in the temperate coastal areas of the northwest Pacific and holds a significant position in the shellfish aquaculture market in China. However, the natural resources of this species have been declining, and population genetic studies of M. coruscus are also lacking. In this study, we conducted whole-genome resequencing (WGR) of M. coruscus from eight different latitudes along the Chinese coast and identified a total of 25,859,986 single nucleotide polymorphism (SNP) markers. Our findings indicated that the genetic diversity of M. coruscus from the Zhoushan region was lower compared with populations from other regions. Furthermore, we observed that the evolutionary tree clustered into two primary branches, and the Zhangzhou (ZZ) population was in a separate branch. The ZZ population was partly isolated from populations in other regions, but the distribution of branches was not geographically homogeneous, and a nested pattern emerged, consistent with the population differentiation index (FST) results. To investigate the selection characteristics, we utilized the northern M. coruscus populations (Dalian and Qingdao) and the central populations (Zhoushan and Xiangshan) as reference populations and the southern ZZ population as the target population. Our selection scan analysis identified several genes associated with thermal responses, including Hsp70 and CYP450. These genes may play important roles in the adaptation of M. coruscus to different living environments. Overall, our study provides a comprehensive understanding of the genomic diversity of coastal M. coruscus in China and is a valuable resource for future studies on genetic breeding and the evolutionary adaptation of this species.

Natural Chlorogenic Acid Planted Nanohybrids with Steerable Hyperthermia for Osteosarcoma Suppression and Bone Regeneration

Surgical resection is the most common approach for the treatment of osteosarcoma. However, two major complications, including residual tumor cells and large bone defects, often arise from the surgical resection of osteosarcoma. Discovering new strategies for programmatically solving the two above-mentioned puzzles has become a worldwide challenge. Herein, a novel one-step strategy is reported for natural phenolic acid planted nanohybrids with desired physicochemical properties and steerable photothermal effects for efficacious osteosarcoma suppression and bone healing. Nanohybrids are prepared based on the self-assembly of chlorogenic acid and gold nanorods through robust Au-catechol interface actions, featuring precise nanostructures, great water solubility, good stability, and adjustable hyperthermia generating capacity. As expected, on the one hand, these integrated nanohybrids can severely trigger apoptosis and suppress tumor growth with strong hyperthermia. On the other hand, with controllable mild NIR irradiation, the nanohybrids promote the expression of heat shock proteins and induce prominent osteogenic differentiation. This work initiates a brand-new strategy for assisting osteosarcoma surgical excision to resolve the blockage of residual tumor cells elimination and bone regeneration.

Synthesis of robust underwater glues from common proteins via unfolding-aggregating strategy

Underwater adhesive proteins secreted by organisms greatly inspires the development of underwater glue. However, except for specific proteins such as mussel adhesive protein, barnacle cement proteins, curli protein and their related recombinant proteins, it is believed that abundant common proteins cannot be converted into underwater glue. Here, we demonstrate that unfolded common proteins exhibit high affinity to surfaces and strong internal cohesion via amyloid-like aggregation in water. Using bovine serum albumin (BSA) as a model protein, we obtain a stable unfolded protein by cleaving the disulfide bonds and maintaining the unfolded state by means of stabilizing agents such as trifluoroethanol (TFE) and urea. The diffusion of stabilizing agents into water exposes the hydrophobic residues of an unfolded protein and initiates aggregation of the unfolded protein into a solid block. A robust and stable underwater glue can thus be prepared from tens of common proteins. This strategy deciphers a general code in common proteins to construct robust underwater glue from abundant biomass.

Increase in Charge and Density Improves the Strength and Toughness of Mussel Foot Protein 5 Inspired Protein Materials

Mussel foot protein 5 (fp5) found in the adhesive byssal plaque of Mediterranean mussel Mytilus galloprovincialis exhibits exceptional underwater adhesion to diverse surfaces to the extent that adhesion strength typically exceeds the cohesive strength of the plaque. While sequence effects such as presence of charged residues, metal ion coordination, and high catechol content have been identified to govern fp5's interaction with surfaces, molecular contributors to its cohesive strength remain to be fully understood. Addressing this issue is critical for designing mussel-inspired sequences for new adhesives and biomaterials enabled by synthetic biology. Here we carry out all-atom molecular dynamics simulations on hydrated model fp5 biopolymer melts to understand how sequence features such as tyrosine and charge content affect packing density and inter-residue and ionic interaction strengths and consequently influence the cohesive strength and toughness. Systematic serine (S) substitutions for lysine (K), arginine (R) and tyrosine (Y) residues reveal that Y to S substitution surprisingly results in improvement of cohesive strength due to densification of the material by removal of steric hindrances, whereas the removal of charge in K and R to S substitutions has a detrimental impact on strength and toughness as it reduces cohesive interactions facilitated by electrostatic interactions. Additionally, melts formed from split fp5 sequences with only C or N terminal halves show distinct mechanical responses that further illustrate the role of charge. Our findings provide new insights for designing materials that could potentially surpass the performance of existing biomolecular and bioinspired adhesives, specifically by tailoring sequences for balancing charge and excluded volume effects.

Enzymatic polymerization of enantiomeric L-3,4-dihydroxyphenylalanine into films with enhanced rigidity and stability

_L-3,4-dihydroxyphenylalanine is an important molecule in the adhesion of mussels, and as an oxidative precursor of natural melanin, it plays an important role in living system. Here, we investigate the effect of the molecular chirality of 3,4-dihydroxyphenylalanine on the properties of the self-assembled films by tyrosinase-induced oxidative polymerization. The kinetics and morphology of pure enantiomers are completely altered upon their co-assembly, allowing the fabrication of layer-to-layer stacked nanostructures and films with improved structural and thermal stability. The different molecular arrangements and self-assembly mechanisms of the _L+D-racemic mixtures, whose oxidation products have increased binding energy, resulting in stronger intermolecular forces, which significantly increases the elastic modulus. This study provides a simple pathway for the fabrication of biomimetic polymeric materials with enhanced physicochemical properties by controlling the chirality of monomers.

Purification of Intramineral Peptides from Cuttlebones and In Vitro Activity in CaCO3 Biomineralization

Living organisms develop functional hard structures such as teeth, bones, and shells from calcium salts through mineralization for managing vital functions to sustain life. However, the exact mechanism or role of biomolecules such as proteins and peptides in the biomineralization process to form defect-free hierarchical structures in nature is poorly understood. In this study, we have extracted, purified, and characterized five major peptides (CBP1-CBP5) from the soluble organic materials (SOMs) of cuttlefish bone (CB) and used for the in vitro mineralization of calcium carbonate crystals. The SOMs induced nucleation of the calcite phase at low concentrations and the vaterite phase at high concentrations. The purified peptides nucleated calcite crystals and enhanced aggregation under laboratory conditions. Among five peptides, only CBP2 and CBP3 showed concentration-dependent nucleation, aggregation, and morphological changes of the calcite crystals within 12 h. Circular dichroism studies showed that the peptides CBP2 and CBP3 are in alpha helix and β-sheet conformation, respectively, in solution. CBP1 and CBP4 and CBP5 are in random coil and β-sheet conformation, respectively. In addition, the peptides showed different sizes in solution in the absence (∼27 nm, low aggregation) and presence (∼118 nm, high aggregation) of calcium ions. Aragonite crystals with needle-type morphologies were nucleated in the presence of Mg²⁺ ions in solution. Overall, exploring the activities of such intramineral peptides from CB help to unravel the mechanism of calcium salt deposition in nature.

Applications of synthetic biology in medical and pharmaceutical fields

Synthetic biology aims to design or assemble existing bioparts or bio-components for useful bioproperties. During the past decades, progresses have been made to build delicate biocircuits, standardized biological building blocks and to develop various genomic/metabolic engineering tools and approaches. Medical and pharmaceutical demands have also pushed the development of synthetic biology, including integration of heterologous pathways into designer cells to efficiently produce medical agents, enhanced yields of natural products in cell growth media to equal or higher than that of the extracts from plants or fungi, constructions of novel genetic circuits for tumor targeting, controllable releases of therapeutic agents in response to specific biomarkers to fight diseases such as diabetes and cancers. Besides, new strategies are developed to treat complex immune diseases, infectious diseases and metabolic disorders that are hard to cure via traditional approaches. In general, synthetic biology brings new capabilities to medical and pharmaceutical researches. This review summarizes the timeline of synthetic biology developments, the past and present of synthetic biology for microbial productions of pharmaceutics, engineered cells equipped with synthetic DNA circuits for diagnosis and therapies, live and auto-assemblied biomaterials for medical treatments, cell-free synthetic biology in medical and pharmaceutical fields, and DNA engineering approaches with potentials for biomedical applications.

Hydrogel-Anchored Fe-Based Amorphous Coatings with Integrated Antifouling and Anticorrosion Functionality

Biofouling and corrosion of underwater equipment induced by marine organisms have become major issues in the marine industry. The superior corrosion resistance of Fe-based amorphous coatings makes them suitable for marine applications; however, they have a poor antifouling ability. In this work, a hydrogel-anchored amorphous (HAM) coating with satisfactory antifouling and anticorrosion performance is designed, utilizing an interfacial engineering strategy involving micropatterning, surface hydroxylation, and a dopamine intermediate layer to increase the adhesion strength between the hydrogel layer and the amorphous coating. The as-obtained HAM coating exhibits exceptional antifouling properties, achieving 99.8% resistance to algae, 100% resistance to mussels, and excellent biocorrosion resistance against Pseudomonas aeruginosa. Antifouling and anticorrosion performance of the HAM coating was also explored by conducting a marine field test in the East China Sea, and no signs of corrosion and fouling are observed after 1 month of immersion. It is revealed that the outstanding antifouling properties stem from the killing-resisting-camouflaging trinity that resists organism attachment across different length scales, and the excellent anticorrosion performance originates from the remarkable barrier of the amorphous coating against Cl^- ion diffusion and microbe-induced biocorrosion. This work presents a novel methodology for designing marine protective coating with excellent antifouling and anticorrosion properties.

Multi-crosslinked hydrogels with strong wet adhesion, self-healing, antibacterial property, reactive oxygen species scavenging activity, and on-demand removability for seawater-immersed wound healing

In general, seawater-immersed wounds are associated with tissue necrosis, infection, prolonged healing period, and high mortality because of high salinity, hyperosmosis, and the presence of various pathogenic bacteria in seawater. However, current wound dressings can hardly achieve strong and stable wet adhesion and antibacterial properties, thus limiting their application to seawater-immersed wounds. Here a multifunctional hydrogel (OD/EPL@Fe) comprising catechol-modified oxidized hyaluronic acid (OD), ε-poly-L-lysine (EPL), and Fe³⁺ was prepared primarily through Schiff-base reaction, metal chelation, cation-π, and electrostatic interaction. The hydrogel with high wet adhesion (about 78 kPa) was achieved by combining the mussel-inspired strategy, dehydration effect, and cohesion enhancement, which is higher than that of commercial fibrin glues and cyanoacrylate glues. Meanwhile, the hydrogel can eliminate Marine bacteria (V. vulnificus and P. aeruginosa) and inhibit their biofilm formation. In addition, the hydrogel demonstrated injectability, self-healing, reactive oxygen species scavenging activity, photothermal effect, seawater isolation, on-demand removal, and hemostatic properties. In vivo results showed that the hydrogel had good adhesion to dynamic wounds in a rat neck full-thickness skin wound model. In particular, the hydrogel exhibited antibacterial, anti-inflammatory, and antioxidant properties in a rat seawater-immersed infected wound model and accelerated the reconstruction of skin structure and functions. The results demonstrated that the OD/EPL@Fe would be a potential wound dressing for seawater-immersed wound healing. STATEMENT OF SIGNIFICANCE: A multifunctional OD/EPL@Fe hydrogel has been prepared for the treatment of seawater-immersed wounds. The hydrogel with high wet adhesion was achieved by combining the mussel-inspired strategy, dehydration effect, and cohesion enhancement. The results revealed that the wet adhesion value of hydrogel was about eight times greater than commercial fibrin glues and 1.5 times greater than commercial cyanoacrylate glues. The hydrogel can be easily removed after being sprayed with deferoxamine mesylate. Notably, the inherent antimicrobial material of the hydrogel combined with the photothermal effect can eliminate marine bacteria and inhibit their biofilm formation. Moreover, the hydrogel can accelerate the healing of seawater-immersed infected wound on mice.

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.

Biological Materials Processing: Time-Tested Tricks for Sustainable Fiber Fabrication

There is an urgent need to improve the sustainability of the materials we produce and use. Here, we explore what humans can learn from nature about how to sustainably fabricate polymeric fibers with excellent material properties by reviewing the physical and chemical aspects of materials processing distilled from diverse model systems, including spider silk, mussel byssus, velvet worm slime, hagfish slime, and mistletoe viscin. We identify common and divergent strategies, highlighting the potential for bioinspired design and technology transfer. Despite the diversity of the biopolymeric fibers surveyed, we identify several common strategies across multiple systems, including: (1) use of stimuli-responsive biomolecular building blocks, (2) use of concentrated fluid precursor phases (e.g., coacervates and liquid crystals) stored under controlled chemical conditions, and (3) use of chemical (pH, salt concentration, redox chemistry) and physical (mechanical shear, extensional flow) stimuli to trigger the transition from fluid precursor to solid material. Importantly, because these materials largely form and function outside of the body of the organisms, these principles can more easily be transferred for bioinspired design in synthetic systems. We end the review by discussing ongoing efforts and challenges to mimic biological model systems, with a particular focus on artificial spider silks and mussel-inspired materials.

Cell-binding peptides on the material surface guide stem cell fate of adhesion, proliferation and differentiation

Human cells, especially stem cells, need to communicate and interact with extracellular matrix (ECM) proteins, which not only serve as structural components but also guide and support cell fate and properties such as cell adhesion, proliferation, survival and differentiation. The binding of the cells with ECM proteins or ECM-derived peptides via cell adhesion receptors such as integrins activates several signaling pathways that determine the cell fate, morphological change, proliferation and differentiation. The development of synthetic ECM protein-derived peptides that mimic the biological and biochemical functions of natural ECM proteins will benefit academic and clinical application. Peptides derived from or inspired by specific ECM proteins can act as agonists of each ECM protein receptor. Given that most ECM proteins function in cell adhesion via integrin receptors, many peptides have been developed that bind to specific integrin receptors. In this review, we discuss the peptide sequence, immobilization design, reaction method, and functions of several ECM protein-derived peptides. Various peptide sequences derived from mainly ECM proteins, which are used for coating or grafting on dishes, scaffolds, hydrogels, implants or nanofibers, have been developed to improve the adhesion, proliferation or differentiation of stem cells and to culture differentiated cells. This review article will help to inform the optimal choice of ECM protein-derived peptides for the development of scaffolds, implants, hydrogels, nanofibers and 2D cell culture dishes to regulate the proliferation and direct the differentiation of stem cells into specific lineages.

Molecular cloning, expression, mRNA secondary structure and immunological characterization of mussel foot proteins (Mfps) (Mollusca: Bivalvia)

The macroscale production of mussel foot proteins (Mfps) in the expression system has not succeeded to date. The principal reasons for this are low levels of expression and yield of Mfps, lack of post-translational modifications (PTMs), and immunological toxic effects on the host system. Identification of post-translational modification sites, suitable expression hosts, and immunological responses through an experimental approach is very costly and time-consuming. However, in the present study, in silico post-translation modification, antigenicity, allergenicity, and the immunological reaction of all available Mfps were characterized. Furthermore, all Mfps were codon optimized in three different expression systems to determine the best expression host. Finally, we performed the in-silico cloning of all codon-optimized Mfps in a suitable host (E. coli K12, pET28a(+) vector) and analyzed the secondary structure of mRNA and its structural stability. Among the 78 Mfps, six fps are considered potential allergenic proteins, six fps are considered non-allergenic proteins, and all other fps are probably allergenic. High antigenicity was observed in bacterial cells as compared to yeast and tumor cells. Nevertheless, the predicted expression of Mfps in a bacterial host is higher than in other expression hosts. Important to note that all Mfps showed significant immunological activity in the human system, and we concluded that these antigenic, allergenic, and immunological properties are directly correlated with their amino acid composition. The study's major goal is to provide a comprehensive understanding of Mfps and aid in the future genetic engineering and expression of Mfps and its diverse applications in different fields.Communicated by Ramaswamy H. Sarma.

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.

Mussels Fabricate Porous Glues via Multiphase Liquid-Liquid Phase Separation of Multiprotein Condensates

Mussels (Mytilus edulis) adhere to hard surfaces in intertidal marine habitats with a porous underwater glue called the byssus plaque. The plaque is an established role model for bioinspired underwater glues and comprises at least six proteins, most of which are highly cationic and enriched in the post-translationally modified amino acid 3,4-dihydroxyphenylalanine (DOPA). While much is known about the chemistry of plaque adhesion, less is understood about the natural plaque formation process. Here, we investigated plaque structure and formation using 3D electron microscopic imaging, revealing that micro- and nanopores form spontaneously during secretion of protein-filled secretory vesicles. To better understand this process, we developed a method to purify intact secretory vesicles for in vitro assembly studies. We discovered that each vesicle contains a sulfate-associated fluid condensate consisting of ∼9 histidine- and/or DOPA-rich proteins, which are presumably the required ingredients for building a plaque. Rupturing vesicles under specific buffering conditions relevant for natural assembly led to controlled multiphase liquid-liquid phase separation (LLPS) of different proteins, resulting in formation of a continuous phase with coexisting droplets. Rapid coarsening of the droplet phase was arrested through pH-dependent cross-linking of the continuous phase, producing native-like solid porous "microplaques" with droplet proteins remaining as fluid condensates within the pores. Results indicate that histidine deprotonation and sulfates figure prominently in condensate cross-linking. Distilled concepts suggest that combining phase separation with tunable cross-linking kinetics could be effective for microfabricating hierarchically porous materials via self-assembly.

Polyoxometalate-peptide hybrid materials: from structure-property relationships to applications

Organo-functionalisation of polyoxometalates (POMs) represents an effective approach to obtain diverse arrays of functional structures and materials, where the introduction of organic moieties into the POM molecules can dramatically change their surface chemistry, charge, polarity, and redox properties. The synergistic combination of POMs and peptides, which perform a myriad of essential roles within cellular biochemistry, including protection and transport in living organisms, leads to functional hybrid materials with unique properties. In this Perspective article, we present the principal synthetic routes to prepare and characterise POM-peptide hybrids, together with a comprehensive description of how their properties - such as redox chemistry, stereochemistry and supramolecular self-assembly - give rise to materials with relevant catalytic, adhesive, and biomedical applications. By presenting the state-of-the-art of the POM-peptide field, we show specifically how emerging chemical approaches can be harnessed to develop tailored POM-peptide materials with synergistic properties for applications in a variety of disciplines.

Bio-inspired adhesive hydrogel for biomedicine-principles and design strategies

The adhesiveness of hydrogels is urgently required in various biomedical applications such as medical patches, tissue sealants, and flexible electronic devices. However, biological tissues are often wet, soft, movable, and easily damaged. These features pose difficulties for the construction of adhesive hydrogels for medical use. In nature, organisms adhere to unique strategies, such as reversible sucker adhesion in octopuses and nontoxic and firm catechol chemistry in mussels, which provide many inspirations for medical hydrogels to overcome the above challenges. In this review, we systematically classify bioadhesion strategies into structure-related and molecular-related ones, which cover almost all known bioadhesion paradigms. We outline the principles of these strategies and summarize the corresponding designs of medical adhesive hydrogels inspired by them. Finally, conclusions and perspectives concerning the development of this field are provided. For the booming bio-inspired adhesive hydrogels, this review aims to summarize and analyze the various existing theories and provide systematic guidance for future research from an innovative perspective.

Rational design of adhesives for effective underwater bonding

Underwater adhesives hold great promises in our daily life, biomedical fields and industrial engineering. Appropriate underwater bonding can reduce the huge cost from removing the target substance from water, and greatly lift working efficiency. However, different from bonding in air, underwater bonding is quite challenging. The existence of interfacial water prevents the intimate contact between the adhesives and the submerged surfaces, and water environment makes it difficult to achieve high cohesiveness. Even so, in recent years, various underwater adhesives with macroscopic adhesion abilities were emerged. These smart adhesives can ingeniously remove the interfacial water, and enhance cohesion by utilizing their special physicochemical properties or functional groups. In this mini review, we first give a detail introduction of the difficulties in underwater bonding. Further, we overview the recent strategies that are used to construct underwater adhesives, with the emphasis on how to overcome the difficulties of interfacial water and achieve high cohesiveness underwater. In addition, future perspectives of underwater adhesives from the view of practical applications are also discussed. We believe the review will provide inspirations for the discovery of new strategies to overcome the obstacles in underwater bonding, and therefore may contribute to designing effective underwater adhesives.

Hydrogen-bonds mediate liquid-liquid phase separation of mussel derived adhesive peptides

Marine mussels achieve strong underwater adhesion by depositing mussel foot proteins (Mfps) that form coacervates during the protein secretion. However, the molecular mechanisms that govern the phase separation behaviors of the Mfps are still not fully understood. Here, we report that GK-16*, a peptide derived from the primary adhesive protein Mfp-5, forms coacervate in seawater conditions. Molecular dynamics simulations combined with point mutation experiments demonstrate that Dopa- and Gly- mediated hydrogen-bonding interactions are essential in the coacervation process. The properties of GK-16* coacervates could be controlled by tuning the strength of the electrostatic and Dopa-mediated hydrogen bond interactions via controlling the pH and salt concentration of the solution. The GK-16* coacervate undergoes a pH induced liquid-to-gel transition, which can be utilized for the underwater delivery and curing of the adhesives. Our study provides useful molecular design principles for the development of mussel-inspired peptidyl coacervate adhesives with tunable properties.

The phase separation in the coacervates of adhesive muscle foot proteins is not fully understood. Here, the authors use simulations and point mutations of a mussel foot derived protein to show that hydrogen bonding is essential in the formation of coacervates in sea water which can help develop underwater adhesives.

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.

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.

Solution structure of recombinant Pvfp-5β reveals insights into mussel adhesion

Some marine organisms can resist to aqueous tidal environments and adhere tightly on wet surface. This behavior has raised increasing attention for potential applications in medicine, biomaterials, and tissue engineering. In mussels, adhesive forces to the rock are the resultant of proteinic fibrous formations called byssus. We present the solution structure of Pvfp-5β, one of the three byssal plaque proteins secreted by the Asian green mussel Perna viridis, and the component responsible for initiating interactions with the substrate. We demonstrate that Pvfp-5β has a stably folded structure in agreement with the presence in the sequence of two EGF motifs. The structure is highly rigid except for a few residues affected by slow local motions in the µs-ms time scale, and differs from the model calculated by artificial intelligence methods for the relative orientation of the EGF modules, which is something where computational methods still underperform. We also show that Pvfp-5β is able to coacervate even with no DOPA modification, giving thus insights both for understanding the adhesion mechanism of adhesive mussel proteins, and developing of biomaterials.

Recombinant mussel protein Pvfp5β enhances cell adhesion of poly(vinyl alcohol)/k-carrageenan hydrogel scaffolds

Polymeric hydrogels are increasingly considered as scaffolds for tissue engineering due to their extraordinary resemblance with the extracellular matrix (ECM) of many tissues. As cell adhesion is a key factor in regulating important cell functions, hydrogel scaffolds are often functionalized or loaded with a variety of bioactive molecules that can promote adhesion. Interesting biomimetic approaches exploit the properties of mussel-inspired recombinant adhesive proteins. In this work, we prepared hydrogel scaffolds with a 50%w mixture of k-carrageenan (kC) and polyvinyl alcohol (PVA), by a two-step physical gelation process, and we coated them with Perna viridis foot protein-5β (Pvfp5β). The mechanical and morphological properties of hydrogels were investigated both after conditioning with typical cell culture media and also after coating with the Pvfp5β. The protein resulted strongly adsorbed onto the surface of the hydrogel and also able to penetrate in its interiors to a certain depth, mainly interacting with the kC component of the scaffold as resulted from the confocal analysis. Mouse embryonic fibroblasts NIH-3T3 were seeded on top of the hydrogels and cultured up to two weeks. The role of Pvfp5β in promoting cell adhesion, spreading and colonization of the scaffold was demonstrated.

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.

Adhesive Materials Inspired by Barnacle Underwater Adhesion: Biological Principles and Biomimetic Designs

Wet adhesion technology has potential applications in various fields, especially in the biomedical field, yet it has not been completely mastered by humans. Many aquatic organisms (e.g., mussels, sandcastle worms, and barnacles) have evolved into wet adhesion specialists with excellent underwater adhesion abilities, and mimicking their adhesion principles to engineer artificial adhesive materials offers an important avenue to address the wet adhesion issue. The crustacean barnacle secretes a proteinaceous adhesive called barnacle cement, with which they firmly attach their bodies to almost any substrate underwater. Owing to the unique chemical composition, structural property, and adhesion mechanism, barnacle cement has attracted widespread research interest as a novel model for designing biomimetic adhesive materials, with significant progress being made. To further boost the development of barnacle cement-inspired adhesive materials (BCIAMs), it is necessary to systematically summarize their design strategies and research advances. However, no relevant reviews have been published yet. In this context, we presented a systematic review for the first time. First, we introduced the underwater adhesion principles of natural barnacle cement, which lay the basis for the design of BCIAMs. Subsequently, we classified the BCIAMs into three major categories according to the different design strategies and summarized their research advances in great detail. Finally, we discussed the research challenge and future trends of this field. We believe that this review can not only improve our understanding of the molecular mechanism of barnacle underwater adhesion but also accelerate the development of barnacle-inspired wet adhesion technology.

From Sticky to Slippery: Self-Functionalizing Lubricants for In Situ Fabrication of Liquid-Infused Surfaces

Liquid-infused surfaces offer a versatile approach to create self-cleaning coatings. In such coatings, a thin film of a fluid lubricant homogeneously coats the substrate and thus prevents direct contact with a second, contaminating liquid. For stable repellency, the interfacial energies need to be controlled to ensure that the lubricant is not replaced by the contaminating liquid. Here, we introduce the concept of self-functionalizing lubricants. Functional molecular species that chemically match the lubricant but possess selective anchor groups are dissolved in the lubricant and self-adhere to the surface, forming the required surface chemistry in situ from within the applied lubricant layer. To add flexibility to the self-functionalizing concept, the substrate is first primed with a thin polydopamine base layer, which can be deposited to nearly any substrate material from aqueous solutions and retains reactivity toward electron-donating groups such as amines. The temporal progression of the in situ functionalization is investigated by ellipsometry and quartz crystal microbalance and correlated to macroscopic changes in contact angle and contact angle hysteresis. The flexibility of the approach is underlined by creating repellent coatings with various substrate/lubricant combinations. The prepared liquid-infused surfaces significantly reduce cement adhesion and provide easy-to-clean systems under real-world conditions on shoe soles.

Peptidomimetic Wet-Adhesive PEGtides with Synergistic and Multimodal Hydrogen Bonding

The remarkable underwater adhesion of mussel foot proteins has long been an inspiration in the design of peptidomimetic materials. Although the synergistic wet adhesion of catechol and lysine has been recently highlighted, the critical role of the polymeric backbone has remained largely underexplored. Here, we present a peptidomimetic approach using poly(ethylene glycol) (PEG) as a platform to evaluate the synergistic compositional relation between the key amino acid residues (i.e., DOPA and lysine), as well as the role of the polyether backbone in interfacial adhesive interactions. A series of PEG-based peptides (PEGtides) were synthesized using functional epoxide monomers corresponding to catechol and lysine via anionic ring-opening polymerization. Using a surface force apparatus, highly synergistic surface interactions among these PEGtides with respect to the relative compositional ratio were revealed. Furthermore, the critical role of the catechol-amine synergy and diverse hydrogen bonding within the PEGtides in the superior adhesive interactions was verified by molecular dynamics simulations. Our study sheds light on the design of peptidomimetic polymers with reduced complexity within the framework of a polyether backbone.

Attachment of zebra and quagga mussel adhesive plaques to diverse substrates

Like marine mussels, freshwater zebra and quagga mussels adhere via the byssus, a proteinaceous attachment apparatus. Attachment to various surfaces allows these invasive mussels to rapidly spread, however the adhesion mechanism is not fully understood. While marine mussel adhesion mechanics has been studied at the individual byssal-strand level, freshwater mussel adhesion has only been characterized through whole-mussel detachment, without direct interspecies comparisons on different substrates. Here, adhesive strength of individual quagga and zebra mussel byssal plaques were measured on smooth substrates with varying hydrophobicity-glass, PVC, and PDMS. With increased hydrophobicity of substrates, adhesive failures occurred more frequently, and mussel adhesion strength decreased. A new failure mode termed 'footprint failure' was identified, where failure appeared to be adhesive macroscopically, but a microscopic residue remained on the surface. Zebra mussels adhered stronger and more frequently on PDMS than quagga mussels. While their adhesion strengths were similar on PVC, there were differences in the failure mode and the plaque-substrate interface ultrastructure. Comparisons with previous marine mussel studies demonstrated that freshwater mussels adhere with comparable strength despite known differences in protein composition. An improved understanding of freshwater mussel adhesion mechanics may help explain spreading dynamics and will be important in developing effective antifouling 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.

Bioengineered Protein-based Adhesives for Biomedical Applications

Protein-based adhesives with their robust adhesion performance and excellent biocompatibility have been extensively explored over years. In particular, the unique adhesion behaviours of mussel and sandcastle worm inspired the development of synthetic adhesives. However, the chemical synthesized adhesives often demonstrate weak underwater adhesion performance and poor biocompatibility/biodegradability, limiting their further biomedical applications. In sharp contrast, genetically engineering endows the protein-based adhesives the ability to maintain underwater adhesion property as well as biocompatibility/biodegradability. Herein, we outline recent advances in the design and development of protein-based adhesives by genetic engineering. We summarize the fabrication and adhesion performance of elastin-like polypeptide-based adhesives, followed by mussel foot protein (mfp) based adhesives and other sources protein-based adhesives, such as, spider silk spidroin and suckerin. In addition, the biomedical applications of these bioengineered protein-based adhesives are presented. Finally, we give a brief summary and perspective on the future development of bioengineered protein-based adhesives.

Emerging bioadhesives: from traditional bioactive and bioinert to a new biomimetic protein-based approach

Bioadhesives have reached significant milestones over the past two decades. Research has shown not only to produce adhesives capable of adhering to dry tissue but recently wet tissue as well. However, most bioadhesives developed have exhibited high adhesion strength yet lack other properties required for versatility in application, such as elasticity, biocompatibility and biodegradability. Adapting from limitations met from early bioadhesives and meeting the current demand allows novel bioadhesives to reach new milestones for the future. In this review, we overview the progression and variations of bioadhesives, current trends, characterisation techniques and conclude with future perspectives for bioadhesives for tissue engineering applications.