Cross-linking the protein precursor of marine mussel adhesives: bulk measurements and reagents for curing

Thermosensitive gallic acid-conjugated hexanoyl glycol chitosan as a novel wound healing biomaterial

In the present study, a novel synthetic tissue adhesive material capable of sealing wounds without the use of any crosslinking agent was developed by conjugating thermosensitive hexanoyl glycol chitosan (HGC) with gallic acid (GA). The degree of N-gallylation was manipulated to prepare GA-HGCs with different GA contents. GA-HGCs demonstrated thermosensitive sol-gel transition behavior and formed irreversible hydrogels upon natural oxidation of the pyrogallol moieties in GA, possibly leading to GA-HGC crosslinks through intra/intermolecular hydrogen bonding and chemical bonds. The GA-HGC hydrogels exhibited self-healing properties, high compressive strength, strong tissue adhesive strength and biodegradability that were adjustable according to the GA content. GA-HGCs also presented excellent biocompatibility and wound healing effects. The results of in vivo wound healing efficacy studies on GA-HGC hydrogels indicated that they significantly promote wound closure and tissue regeneration by upregulating growth factors and recruiting fibroblasts compared to the untreated control group.

Preclinical evaluation of a regenerative immiscible bioglue for vesico-vaginal fistula

Currently, there are no clinically available tissue adhesives that work effectively in the fluid-rich and highly dynamic environments of the human body, such as the urinary system. This is especially relevant to the management of vesico-vaginal fistula, and developing a high-performance tissue adhesive for this purpose could vastly expand urologists' surgical repertoire and dramatically reduce patient discomfort. Herein, we developed a water-immiscible mussel protein-based bioadhesive (imWIMBA) with significantly improved properties in all clinical respects, allowing it to achieve rapid and strong underwater adhesion with tunable rheological properties. We evaluated in vivo potential of imWIMBA for sealing thermally injured fistula tracts between the bladder and vagina. Importantly, the use of imWIMBA in the presence of prolonged bladder drainage resulted in perfect closure of the vesico-vaginal fistula in operated pigs. Thus, imWIMBA could be successfully used for many surgical applications and improve treatment efficacy when combined with conventional surgical methods. STATEMENT OF SIGNIFICANCE: Vesico-vaginal fistula (VVF) is an abnormal opening between the bladder and the vagina, which is a stigmatized disease in many developing countries. Leakage of urine into internal organs can induce serious complications and delay wound repair. Conventional VVF treatment requires skillful suturing to provide a tension-free and watertight closure. In addition, there is no clinically approved surgical glue that works in wet and highly dynamic environments such as the urinary system. In this work, for potential clinical VVF closure and regeneration, we developed an advanced immiscible mussel protein-based bioglue with fast, strong, wet adhesion and tunable rheological properties. This regenerative immiscible bioglue could be successfully used for sealing fistulas and further diverse surgical applications as an adjuvant for conventional suture methods.

Adhesive Coacervates Driven by Hydrogen-Bonding Interaction

Coacervation plays a critical role in numerous biological activities such as constructing biological tissues and achieving robust wet adhesion of marine sessile organisms, which conventionally occurs when oppositely charged polyelectrolytes are mixed in aqueous solutions driven by electrostatic attraction. Here, a novel type of adhesive coacervate is reported, driven by hydrogen-bonding interactions, readily formed by mixing silicotungstic acid and nonionic polyethylene glycol in water, providing a new approach for developing coacervates from nonionic systems. The as-prepared coacervate is easily paintable underwater, show strong wet adhesion to diverse substrates, and has been successfully applied as a hemostatic agent to treat organ injuries without displaying hemolytic activity, while with inherent antimicrobial properties thus avoiding inflammations and infections due to microorganism accumulation. This work demonstrates that coacervation can occur in salt-free environments via non-electrostatic interactions, providing a new platform for engineering multifunctional coacervate materials as tissue glues, wound dressings and membrane-free cell systems.

A Tough and Mildew-Proof Soybean-Based Adhesive Inspired by Mussel and Algae

Despite the recent advances in protein-based adhesives, achieving strong adhesion and mold resistance in wet environment is challenging. Herein, a facile fabrication technology of preparing tough bio-adhesive by incorporating soybean meal and blood meal is presented. Inspired by the marine mussel byssi and brown algae, metal coordination was introduced into a loosely bound protein system to construct multiple chemical cross-linking networks. Mixed alkali-modified blood meal (mBM) was mixed with soybean meal, then 1,6-hexane dioldiglycidyl ether (HDE) and zinc ion were introduced to fabricate soybean meal and blood meal-based adhesives. The attained adhesives exhibited good thermal stability, water resistance (the wet shear strength is 1.1 MPa), and mold resistance, with appropriate solid content (34.3%) and relatively low moisture uptake (11.9%). These outstanding performances would be attributed to the reaction of 1,6-hexane dioldiglycidyl ether with protein to form a preliminary cross-linking network; subsequently, the coordination of zinc ions with amino or carboxyl strengthened and toughened the adhesive. Finally, the calcium ions gelled the adhesives, providing cohesion force and making the network structure more compact. This study realized the value-added utilization of protein co-products and developed a new eco-friendly bio-based adhesive.

Ultratough, Self-Healing, and Tissue-Adhesive Hydrogel for Wound Dressing

A hydrogel for potential applications in wound dressing should possess several peculiar properties, such as efficient self-healing ability and mechanical toughness, so as to repair muscle and skin damage. Additionally, excellent cell affinity and tissue adhesiveness are also necessary for the hydrogel to integrate with the wound tissue in practical applications. Herein, an ultratough and self-healing hydrogel with superior cell affinity and tissue adhesiveness is prepared. The self-healing ability of the hydrogel is obtained through hydrogen bonds and dynamic Schiff cross-linking between dopamine-grafted oxidized sodium alginate (OSA-DA) and polyacrylamide (PAM) chains. The covalent cross-linking is responsible for its stable mechanical structure. The combination of physical and chemical cross-linking contributes to a novel hydrogel with efficient self-healing ability (80% mechanical recovery in 6 h), high tensile strength (0.109 MPa), and ultrastretchability (2550%), which are highly desirable properties and are superior to previously reported tough and self-healing hydrogels for wound dressing applications. More remarkably, due to plenty of catechol groups on the OSA-DA chains, the hydrogel has unique cell affinity and tissue adhesiveness. Moreover, we demonstrate the practical utility of our fabricated hydrogel via both in vivo and in vitro experiments.

Side chain length impacting thermal transitions and water uptake of acrylate–maleimide copolymers with pendent catechols

Significant moisture uptake was observed for a family of catechol side-chain poly(alkyl acrylate-maleimide)s (PAMs) intended to probe the effects of T_g and polarity.

Facile construction of a polydopamine-based hydrophobic surface for protection of metals against corrosion

Metal surfaces with a hydrophobic feature, which could prevent percolation of water droplets and improve their capability against corrosion, arouse extensively interest.

Seawater-Assisted Self-Healing of Catechol Polymers via Hydrogen Bonding and Coordination Interactions

It is highly desirable to prevent crack formation in polymeric materials at an early stage and to extend their lifespan, particularly when repairs to these materials would be difficult for humans. Here, we designed and synthesized catechol-functionalized polymers that can self-heal in seawater through hydrogen bonding and coordination. These bioinspired acrylate polymers are originally viscous materials, but after coordination with environmentally safe, common metal cations in seawater, namely, Ca(2+) and Mg(2+), the mechanical properties of the polymers were greatly enhanced from viscous to tough, hard materials. Reduced swelling in seawater compared with deionized water owing to the higher osmotic pressure resulted in greater toughness (∼5 MPa) and self-healing efficiencies (∼80%).

Design of Xylose-Based Semisynthetic Polyurethane Tissue Adhesives with Enhanced Bioactivity Properties

Developing biocompatible tissue adhesives with high adhesion properties is a highly desired goal of the tissue engineering due to adverse effects of the sutures. Therefore, our work involves synthesis, characterization, adhesion properties, protein adsorption, in vitro biodegradation, in vitro and in vivo biocompatibility properties of xylose-based semisynthetic polyurethane (NPU-PEG-X) bioadhesives. Xylose-based semisynthetic polyurethanes were developed by the reaction among 4,4'-methylenebis(cyclohexyl isocyanate) (MCI), xylose and polyethylene glycol 200 (PEG). Synthesized polyurethanes (PUs) showed good thermal stability and high adhesion strength. The highest values in adhesion strength were measured as 415.0 ± 48.8 and 94.0 ± 2.8 kPa for aluminum substrate and muscle tissue in 15% xylose containing PUs (NPU-PEG-X-15%), respectively. The biodegradation of NPU-PEG-X-15% was also determined as 19.96 ± 1.04% after 8 weeks of incubation. Relative cell viability of xylose containing PU was above 86%. Moreover, 10% xylose containing NPU-PEG-X (NPU-PEG-X-10%) sample has favorable tissue response, and inflammatory reaction between 1 and 6 weeks implantation period. With high adhesiveness and biocompatibility properties, NPU-PEG-X can be used in the medical field as supporting materials for preventing the fluid leakage after abdominal surgery or wound closure.

Silk Fibroin Aqueous-Based Adhesives Inspired by Mussel Adhesive Proteins

Silk fibroin from the domesticated silkworm Bombyx mori is a naturally occurring biopolymer with charged hydrophilic terminal regions that end-cap a hydrophobic core consisting of repeating sequences of glycine, alanine, and serine residues. Taking inspiration from mussels that produce proteins rich in L-3,4-dihydroxyphenylalanine (DOPA) to adhere to a variety of organic and inorganic surfaces, the silk fibroin was functionalized with catechol groups. Silk fibroin was selected for its high molecular weight, tunable mechanical and degradation properties, aqueous processability, and wide availability. The synthesis of catechol-functionalized silk fibroin polymers containing varying amounts of hydrophilic polyethylene glycol (PEG, 5000 g/mol) side chains was carried out to balance silk hydrophobicity with PEG hydrophilicity. The efficiency of the catechol functionalization reaction did not vary with PEG conjugation over the range studied, although tuning the amount of PEG conjugated was essential for aqueous solubility. Adhesive bonding and cell compatibility of the resulting materials were investigated, where it was found that incorporating as little as 6 wt % PEG prior to catechol functionalization resulted in complete aqueous solubility of the catechol conjugates and increased adhesive strength compared with silk lacking catechol functionalization. Furthermore, PEG-silk fibroin conjugates maintained their ability to form β-sheet secondary structures, which can be exploited to reduce swelling. Human mesenchymal stem cells (hMSCs) proliferated on the silks, regardless of PEG and catechol conjugation. These materials represent a protein-based approach to catechol-based adhesives, which we envision may find applicability as biodegradable adhesives and sealants.

K S, A G. Handling and managing bleeding wounds using tissue adhesive hydrogel: a comparative assessment on two different hydrogels

The present study explores the preparation and a comparative assessment on the physical, mechanical and biological properties of two different tissue adhesive hydrogels (TAHs) for the management of bleeding wounds.

Understanding the relative binding ability of hydroxyfullerene to divalent and trivalent metals

Metal contamination of water is a serious challenge faced by environmental chemists, but there is also economic value in the removal of metals for recycling or extraction.

Surgical Materials: Current Challenges and Nano-enabled Solutions

Surgical adhesive biomaterials have emerged as substitutes to sutures and staples in many clinical applications. Nano-enabled materials containing nanoparticles or having a distinct nanotopography have been utilized for generation of a new class of surgical materials with enhanced functionality. In this review, the state of the art in the development of conventional surgical adhesive biomaterials is critically reviewed and their shortcomings are outlined. Recent advancements in generation of nano-enabled surgical materials with their potential future applications are discussed. This review will open new avenues for the innovative development of the next generation of tissue adhesives, hemostats, and sealants with enhanced functionality for various surgical applications.

A fundamental understanding of catechol and water adsorption on a hydrophilic silica surface: exploring the underwater adhesion mechanism of mussels on an atomic scale

Mussels have a remarkable ability to bond to solid surfaces under water. From a microscopic perspective, the first step of this process is the adsorption of dopa molecules to the solid surface. In fact, it is the catechol part of the dopa molecule that is interacting with the surface. These molecules are able to make reversible bonds to a wide range of materials, even underwater. Previous experimental and theoretical efforts have produced only a limited understanding of the mechanism and quantitative details of the competitive adsorption of catechol and water on hydrophilic silica surfaces. In this work, we uncover the nature of this competitive absorption by atomic scale modeling of water and catechol adsorbed at the geminal (001) silica surface using density functional theory calculations. We find that catechol molecules displace preadsorbed water molecules and bond directly on the silica surface. Using molecular dynamics simulations, we observe this process in detail. We also calculate the interaction force as a function of distance, and observe a maximum of 0.5 nN of attraction. The catechol has a binding energy of 23 kcal/mol onto the silica surface with adsorbed water molecules.

Thiol–ene adhesives from clove oil derivatives

This paper reports the synthesis of catechol-functionalized thiol–ene networks as photocurable adhesives, where adhesive interactions are derived from 4-allylpyrocatechol – an alkene readily obtained from Syzygium aromaticum flower buds (clove oil).

Interfacial structure of a DOPA-inspired adhesive polymer studied by sum frequency generation vibrational spectroscopy

Marine mussels deposit adhesive proteins containing 3,4-dihydroxyphenylalanine (DOPA) to attach themselves to different surfaces. Isolating such proteins from biological sources for adhesion purposes tends to be challenging. Recently, a simplified synthetic adhesive polymer, poly[(3,4-dihydroxystyrene)-co-styrene] (PDHSS), was developed to mimic DOPA-containing proteins. The pendant catechol group in this polymer provides cross-linking and adhesion much like mussel proteins do. In this work, sum frequency generation (SFG) vibrational spectroscopy was applied to reveal the structures of this DOPA-inspired polymer at air, water, and polymer interfaces. SFG spectroscopy results showed that when underwater, the catechol rings and the quinone rings were ordered, ready to adhere to surfaces. At the hydrophobic polystyrene interface, benzene π-π stacking is likely the adhesive force, whereas at the hydrophilic poly(allylamine) interface, primary amines may form hydrogen bonds with catechol or react with quinones for adhesion.

Barnacle Balanus amphitrite adheres by a stepwise cementing process

Barnacles adhere permanently to surfaces by secreting and curing a thin interfacial adhesive underwater. Here, we show that the acorn barnacle Balanus amphitrite adheres by a two-step fluid secretion process, both contributing to adhesion. We found that, as barnacles grow, the first barnacle cement secretion (BCS1) is released at the periphery of the expanding base plate. Subsequently, a second, autofluorescent fluid (BCS2) is released. We show that secretion of BCS2 into the interface results, on average, in a 2-fold increase in adhesive strength over adhesion by BCS1 alone. The two secretions are distinguishable both spatially and temporally, and differ in morphology, protein conformation, and chemical functionality. The short time window for BCS2 secretion relative to the overall area increase demonstrates that it has a disproportionate, surprisingly powerful, impact on adhesion. The dramatic change in adhesion occurs without measurable changes in interface thickness and total protein content. A fracture mechanics analysis suggests the interfacial material's modulus or work of adhesion, or both, were substantially increased after BCS2 secretion. Addition of BCS2 into the interface generates highly networked amyloid-like fibrils and enhanced phenolic content. Both intertwined fibers and phenolic chemistries may contribute to mechanical stability of the interface through physically or chemically anchoring interface proteins to the substrate and intermolecular interactions. Our experiments point to the need to reexamine the role of phenolic components in barnacle adhesion, long discounted despite their prevalence in structural membranes of arthropods and crustaceans, as they may contribute to chemical processes that strengthen adhesion through intermolecular cross-linking.

Polymer composition and substrate influences on the adhesive bonding of a biomimetic, cross-linking polymer

Hierarchical biological materials such as bone, sea shells, and marine bioadhesives are providing inspiration for the assembly of synthetic molecules into complex structures. The adhesive system of marine mussels has been the focus of much attention in recent years. Several catechol-containing polymers are being developed to mimic the cross-linking of proteins containing 3,4-dihydroxyphenylalanine (DOPA) used by shellfish for sticking to rocks. Many of these biomimetic polymer systems have been shown to form surface coatings or hydrogels; however, bulk adhesion is demonstrated less often. Developing adhesives requires addressing design issues including finding a good balance between cohesive and adhesive bonding interactions. Despite the growing number of mussel-mimicking polymers, there has been little effort to generate structure-property relations and gain insights on what chemical traits give rise to the best glues. In this report, we examine the simplest of these biomimetic polymers, poly[(3,4-dihydroxystyrene)-co-styrene]. Pendant catechol groups (i.e., 3,4-dihydroxystyrene) are distributed throughout a polystyrene backbone. Several polymer derivatives were prepared, each with a different 3,4-dihyroxystyrene content. Bulk adhesion testing showed where the optimal middle ground of cohesive and adhesive bonding resides. Adhesive performance was benchmarked against commercial glues as well as the genuine material produced by live mussels. In the best case, bonding was similar to that obtained with cyanoacrylate "Krazy Glue". Performance was also examined using low- (e.g., plastics) and high-energy (e.g., metals, wood) surfaces. The adhesive bonding of poly[(3,4-dihydroxystyrene)-co-styrene] may be the strongest of reported mussel protein mimics. These insights should help us to design future biomimetic systems, thereby bringing us closer to development of bone cements, dental composites, and surgical glues.

Competition between Oxidation and Coordination in Cross-Linking of Polystyrene Copolymer Containing Catechol Groups

In gelation chemistry, catechol groups are used as cross-linking points. Both oxidation and coordination effects of catechol were investigated for their unique features in chemistry by spectroscopic measurements. Polystyrene copolymers containing catechol groups were synthesized by free radical copolymerization of styrene and N-2-(3',4'-ditriethylsilyloxyphenyl)ethyl methacrylamide, and the successive deprotection reaction was catalyzed by tetra-n-butylammonium fluoride. The copolymer containing catechol units afforded a dual cross-linking system based on completely different coordination and oxidation chemistries, and the competing cross-linking mechanisms are discussed. These findings are useful and important for paving the way for designing a novel bioinspired artificial adhesive surface coating and curing system.

In vivo post-translational modifications of recombinant mussel adhesive protein in insect cells

Mussel adhesive proteins (MAPs) have been suggested as promising bioadhesives for diverse application fields, including medical uses. Previously, we successfully constructed and produced a new type of functional recombinant MAP, fp-151, in a prokaryotic Escherichia coli expression system. Even though the E. coli-derived MAP showed several excellent features, such as high production yield and efficient purification, in vitro enzymatic modification is required to convert tyrosine residues to l-3,4-dihydroxyphenyl alanine (dopa) molecules for its adhesive ability, due to the intrinsic inability of E. coli to undergo post-translational modification. In this work, we produced a soluble recombinant MAP in insect Sf9 cells, which are widely used as an effective and convenient eukaryotic expression system for eukaryotic foreign proteins. Importantly, we found that insect-derived MAP contained converted dopa residues by in vivo post-translational modification. In addition, insect-derived MAP also had other post-translational modifications including phosphorylation of serine and hydroxylation of proline that originally occurred in some natural MAPs. To our knowledge, this is the first report on in vivo post-translational modifications of MAP containing dopa and other modified amino acid residues.

Compounds from silicones alter enzyme activity in curing barnacle glue and model enzymes

BACKGROUND

Attachment strength of fouling organisms on silicone coatings is low. We hypothesized that low attachment strength on silicones is, in part, due to the interaction of surface available components with natural glues. Components could alter curing of glues through bulk changes or specifically through altered enzyme activity.

METHODOLOGY/PRINCIPAL FINDINGS

GC-MS analysis of silicone coatings showed surface-available siloxanes when the coatings were gently rubbed with a cotton swab for 15 seconds or given a 30 second rinse with methanol. Mixtures of compounds were found on 2 commercial and 8 model silicone coatings. The hypothesis that silicone components alter glue curing enzymes was tested with curing barnacle glue and with commercial enzymes. In our model, barnacle glue curing involves trypsin-like serine protease(s), which activate enzymes and structural proteins, and a transglutaminase which cross-links glue proteins. Transglutaminase activity was significantly altered upon exposure of curing glue from individual barnacles to silicone eluates. Activity of purified trypsin and, to a greater extent, transglutaminase was significantly altered by relevant concentrations of silicone polymer constituents.

CONCLUSIONS/SIGNIFICANCE

Surface-associated silicone compounds can disrupt glue curing and alter enzyme properties. Altered curing of natural glues has potential in fouling management.

Enhanced adhesion of dopamine methacrylamide elastomers via viscoelasticity tuning

We present a study on the effects of cross-linking on the adhesive properties of bio-inspired 3,4-dihydroxyphenylalanine (DOPA). DOPA has a unique catechol moiety found in adhesive proteins in marine organisms, such as mussels and polychaete, which results in strong adhesion in aquatic conditions. Incorporation of this functional group in synthetic polymers provides the basis for pressure-sensitive adhesives for use in a broad range of environments. A series of cross-linked DOPA-containing polymers were prepared by adding divinyl cross-linking agent ethylene glycol dimethacrylate (EGDMA) to monomer mixtures of dopamine methacrylamide (DMA) and 2-methoxyethyl acrylate (MEA). Samples were prepared using a solvent-free microwave-assisted polymerization reaction and compared to a similar series of cross-linked MEA materials. Cross-linking with EGDMA tunes the viscoelastic properties of the adhesive material and has the advantage of not reacting with the catechol group that is responsible for the excellent adhesive performance of this material. Adhesion strength was measured by uniaxial indentation tests, which indicated that 0.001 mol % of EGDMA-cross-linked copolymer showed the highest work of adhesion in dry conditions, but non-cross-linked DMA was the highest in wet conditions. The results suggest that there is an optimal cross-linking degree that displays the highest adhesion by balancing viscous and elastic behaviors of the polymer but this appears to depend on the conditions. This concentration of cross-linker is well below the theoretical percolation threshold, and we propose that subtle changes in polymer viscoelastic properties can result in significant improvements in adhesion of DOPA-based materials. The properties of lightly cross-linked poly(DMA-co-MEA) were investigated by measurement of the frequency dependence of the storage modulus (G') and loss modulus (G''). The frequency-dependence of G' and magnitude of G'' showed gradual decreases with the fraction of EGDMA. Loosely cross-linked DMA copolymers, containing 0% and 0.001 mol % of EGDMA-cross-linked copolymers, displayed rheological behavior appropriate for pressure-sensitive adhesives characterized by a higher G' at high frequencies and lower G' at low frequencies. Our results indicate that dimethacrylate cross-linking of DMA copolymers can be used to enhance the adhesive properties of this unique material.

The Contribution of DOPA to Substrate-Peptide Adhesion and Internal Cohesion of Mussel-Inspired Synthetic Peptide Films

Mussels use a variety of 3, 4-dihydroxyphenyl-l-alanine (DOPA) rich proteins specifically tailored to adhering to wet surfaces. Synthetic polypeptide analogues of adhesive mussel foot proteins (specifically mfp-3) are used to study the role of DOPA in adhesion. The mussel-inspired peptide is a random copolymer of DOPA and N(5) -(2-hydroxyethyl)-l-glutamine synthesized with DOPA concentrations of 0-27 mol% and molecular weights of 5.9-7.1 kDa. Thin films (3-5 nm thick) of the mussel-inspired peptide are used in the surface forces apparatus (SFA) to measure the force-distance profiles and adhesion and cohesion energies of the films in an acetate buffer. The adhesion energies of the mussel-inspired peptide films to mica and TiO(2) surfaces increase with DOPA concentration. The adhesion energy to mica is 0.09 μJ m(-2) mol(DOPA) (-1) and does not depend on contact time or load. The adhesion energy to TiO(2) is 0.29 μJ m(-2) mol(DOPA) (-1) for short contact times and increases to 0.51 μJ m(-2) mol(DOPA) (-1) for contact times >60 min in a way suggestive of a phase transition within the film. Oxidation of DOPA to the quinone form, either by addition of periodate or by increasing the pH, increases the thickness and reduces the cohesion of the films. Adding thiol containing polymers between the oxidized films recovers some of the cohesion strength. Comparison of the mussel-inspired peptide films to previous studies on mfp-3 thin films show that the strong adhesion and cohesion in mfp-3 films can be attributed to DOPA groups favorably oriented within or at the interface of these films.

Biomimetic soy protein nanocomposites with calcium carbonate crystalline arrays for use as wood adhesive

Despite the biodegradability, non-toxicity, and renewability, commercially available soy protein-based adhesives still have not been widely adopted by industry, partially due to their disappointing performances, i.e., low glue strength in the dry state and no glue strength in the wet state. In this study, biomimetic soy protein/CaCO(3) hybrid wood glue was devised and an attempt made to improve the adhesion strength. The structure and morphology of the adhesive and its fracture bonding interface and adhesion strength were investigated. Results showed that the compact rivets or interlocking links, and ion crosslinking of calcium, carbonate, hydroxyl ions in the adhesive greatly improving the water-resistance and bonding strength of soy protein adhesives. Glue strength of soy protein hybrid adhesive was higher than 6 MPa even after three water-immersion cycles. This green and sustainable proteinous hybrid adhesive, with high glue strength and good water-resistance, is a good substitute for formaldehyde wood glues.

Characterization of the adhesive plaque of the barnacle Balanus amphitrite: amyloid-like nanofibrils are a major component

The nanoscale morphology and protein secondary structure of barnacle adhesive plaques were characterized using atomic force microscopy (AFM), far-UV circular dichroism (CD) spectroscopy, transmission Fourier transform infrared (FTIR) spectroscopy, and Thioflavin T (ThT) staining. Both primary cement (original cement laid down by the barnacle) and secondary cement (cement used for reattachment) from the barnacle Balanus amphitrite (= Amphibalanus amphitrite) were analyzed. Results showed that both cements consisted largely of nanofibrillar matrices having similar composition. Of particular significance, the combined results indicate that the nanofibrillar structures are consistent with amyloid, with globular protein components also identified in the cement. Potential properties, functions, and formation mechanisms of the amyloid-like nanofibrils within the adhesive interface are discussed. Our results highlight an emerging trend in structural biology showing that amyloid, historically associated with disease, also has functional roles.

The adhesive properties of coacervated recombinant hybrid mussel adhesive proteins

Marine mussels attach to substrates using adhesive proteins. It has been suggested that complex coacervation (liquid-liquid phase separation via concentration) might be involved in the highly condensed and non-water dispersed adhesion process of mussel adhesive proteins (MAPs). However, as purified natural MAPs are difficult to obtain, it has not been possible to experimentally validate the coacervation model. In the present work, we demonstrate complex coacervation in a system including recombinant MAPs and hyaluronic acid (HA). Our recombinant hybrid MAPs, fp-151 and fp-131, can be produced in large quantities, and are readily purified. We observed successful complex coacervation using cationic fp-151 or fp-131, and an anionic HA partner. Importantly, we found that highly condensed complex coacervates significantly increased the bulk adhesive strength of MAPs in both dry and wet environments. In addition, oil droplets were successfully engulfed using a MAP-based interfacial coacervation process, to form microencapsulated particles. Collectively, our results indicate that a complex coacervation system based on MAPs shows superior adhesive properties, combined with additional valuable features including liquid/liquid phase separation and appropriate viscoelasticity. Our microencapsulation system could be useful in the development of new adhesive biomaterials, including self-adhesive microencapsulated drug carriers, for use in biotechnological and biomedical applications.

Barnacle cement: a polymerization model based on evolutionary concepts

Enzymes and biochemical mechanisms essential to survival are under extreme selective pressure and are highly conserved through evolutionary time. We applied this evolutionary concept to barnacle cement polymerization, a process critical to barnacle fitness that involves aggregation and cross-linking of proteins. The biochemical mechanisms of cement polymerization remain largely unknown. We hypothesized that this process is biochemically similar to blood clotting, a critical physiological response that is also based on aggregation and cross-linking of proteins. Like key elements of vertebrate and invertebrate blood clotting, barnacle cement polymerization was shown to involve proteolytic activation of enzymes and structural precursors, transglutaminase cross-linking and assembly of fibrous proteins. Proteolytic activation of structural proteins maximizes the potential for bonding interactions with other proteins and with the surface. Transglutaminase cross-linking reinforces cement integrity. Remarkably, epitopes and sequences homologous to bovine trypsin and human transglutaminase were identified in barnacle cement with tandem mass spectrometry and/or western blotting. Akin to blood clotting, the peptides generated during proteolytic activation functioned as signal molecules, linking a molecular level event (protein aggregation) to a behavioral response (barnacle larval settlement). Our results draw attention to a highly conserved protein polymerization mechanism and shed light on a long-standing biochemical puzzle. We suggest that barnacle cement polymerization is a specialized form of wound healing. The polymerization mechanism common between barnacle cement and blood may be a theme for many marine animal glues.

Ultrathin and stable active layer of dense composite membrane enabled by poly(dopamine)

We demonstrate that dopamine is able to self-polymerize and adhere firmly onto the substrate, which can create a hierarchical structure comprising an ultrathin active layer and a porous support layer. Such an approach opens a novel way to fabricating highly efficient and stable composite materials including composite membranes. More specifically, in this study the composite membranes are fabricated by simply dipping microporous substrate in aqueous dopamine solution under mild conditions. Nanoindentation measurement reveals the tight adhesion of dopamine onto microporous substrate, which is ascribed to numerous pi-pi and hydrogen-bonding interactions. The chemical composition of the active layer is analyzed by XPS, which demonstrates the self-polymerization of dopamine. The water contact angle of the dopamine coated membranes is reduced remarkably compared with that of the uncoated counterpart. Stylus profiler measurements display that the poly(dopamine) thickness increases as the coating time increases. FESEM images of the membranes' cross section show that an active layer (<100 nm) is deposited on the porous polysulfone (PS) substrate. Positron annihilation spectroscopy (PAS) is introduced to probe the fractional free volume properties throughout the cross section of the composite membranes and reveal that after dopamine double-coating the active layer becomes thicker and more compact. Moreover, pH and concentration of the dopamine solution exert notable influence on the fractional free volume of the composite membranes. The as-prepared membranes are tentatively employed for pervaporative desulfurization and exhibits satisfying separation performance as well as durability. This facile, versatile, and efficient approach enables a promising prospect for the wide applications of such novel kinds of ultrathin composite materials.

Inkjet printing of bioadhesives

Over the past century, synthetic adhesives have largely displaced their natural counterparts in medical applications. However, rising concerns over the environmental and toxicological effects of the solvents, monomers, and additives used in synthetic adhesives have recently led the scientific community to seek natural substitutes. Marine mussel adhesive protein is a formaldehyde-free natural adhesive that demonstrates excellent adhesion to several classes of materials, including glasses, metals, metal oxides, and polymers. In this study, we have demonstrated computer aided design (CAD) patterning of various biological adhesives using piezoelectric inkjet technology. A MEMS-based piezoelectric actuator was used to control the flow of the mussel adhesive protein solution through the ink jet nozzles. Fourier transform infrared spectroscopy (FTIR), microscopy, and adhesion studies were performed to examine the chemical, structural, and functional properties of these patterns, respectively. FTIR revealed the piezoelectric inkjet technology technique to be nondestructive. Atomic force microscopy was used to determine the extent of chelation caused by Fe(III). The adhesive strength in these materials was correlated with the extent of chelation by Fe(III). Piezoelectric inkjet printing of naturally-derived biological adhesives may overcome several problems associated with conventional tissue bonding materials. This technique may significantly improve wound repair in next generation eye repair, fracture fixation, wound closure, and drug delivery devices.