Recent Advances on the Development of Protein-Based Adhesives for Wood Composite Materials—A Review

The industrial market depends intensely on wood-based composites for buildings, furniture, and construction, involving significant developments in wood glues since 80% of wood-based products use adhesives. Although biobased glues have been used for many years, notably proteins, they were replaced by synthetic ones at the beginning of the 20th century, mainly due to their better moisture resistance. Currently, most wood adhesives are based on petroleum-derived products, especially formaldehyde resins commonly used in the particleboard industry due to their high adhesive performance. However, formaldehyde has been subjected to strong regulation, and projections aim for further restrictions within wood-based panels from the European market, due to its harmful emissions. From this perspective, concerns about environmental footprint and the toxicity of these formulations have prompted researchers to re-investigate the utilization of biobased materials to formulate safer alternatives. In this regard, proteins have sparked a new and growing interest in the potential development of industrial adhesives for wood due to their advantages, such as lower toxicity, renewable sourcing, and reduced environmental footprint. This work presents the recent developments in the use of proteins to formulate new wood adhesives. Herein, it includes the historical development of wood adhesives, adhesion mechanism, and the current hotspots and recent progress of potential proteinaceous feedstock resources for adhesive preparation.     

Bioinspired synthetic wet adhesives: from permanent bonding to reversible regulation

Nowadays, robust underwater adhesives products are highly demanded both in industrial and biomedical fields. Meanwhile, study of the underwater adhesion mechanism of natural organisms under fluid environment is necessary, which provides inspiration for engineering adhesive materials that can be used in wet environment. Scientists are committed to discovering the unique adhesion mechanisms of protein adhesives for natural organisms. Especially, recent understanding of wet adhesion mechanisms provides designable inspiration for developing novel synthetic underwater adhesives with high performance by using 3,4-dihydroxyphenylalanine-based and coacervate-enabled strategies. Although pursuing robust interface bonding in these years, controlling the wet adhesion state with reversible/switchable feature is the latest goal for developing intelligent biomimetic adhesives, which implies important applications in multiple fields.     

Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein

Marine mussels secret protein‐based adhesives, which enable them to anchor to various surfaces in a saline, intertidal zone. Mussel foot proteins (Mfps) contain a large abundance of a unique, catecholic amino acid, Dopa, in their protein sequences. Catechol offers robust and durable adhesion to various substrate surfaces and contributes to the curing of the adhesive plaques. In this article, we review the unique features and the key functionalities of Mfps, catechol chemistry, and strategies for preparing catechol‐functionalized polymers. Specifically, we reviewed recent findings on the contributions of various features of Mfps on interfacial binding, which include coacervate formation, surface drying properties, control of the oxidation state of catechol, among other features. We also summarized recent developments in designing advanced biomimetic materials including coacervate‐forming adhesives, mechanically improved nano‐ and micro‐composite adhesive hydrogels, as well as smart and self‐healing materials. Finally, we review the applications of catechol‐functionalized materials for the use as biomedical adhesives, therapeutic applications, and antifouling coatings. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 9–33     

Robust Hydrogel Adhesive with Dual Hydrogen Bond Networks

Hydrogel adhesives are attractive for applications in intelligent soft materials and tissue engineering, but conventional hydrogels usually have poor adhesion. In this study, we designed a strategy to synthesize a novel adhesive with a thin hydrogel adhesive layer integrated on a tough substrate hydrogel. The adhesive layer with positive charges of ammonium groups on the polymer backbones strongly bonds to a wide range of nonporous materials’ surfaces. The substrate layer with a dual hydrogen bond system consists of (i) weak hydrogen bonds between N,N-dimethyl acrylamide (DMAA) and acrylic acid (AAc) units and (ii) strong multiple hydrogen bonds between 2-ureido-4[1H]-pyrimidinone (UPy) units. The dual hydrogen-bond network endowed the hydrogel adhesives with unique mechanical properties, e.g., toughness, highly stretchability, and insensitivity to notches. The hydrogel adhesion to four types of materials like glass, 316L stainless steel, aluminum, Al₂O₃ ceramic, and two biological tissues including pig skin and pig kidney was investigated. The hydrogel bonds strongly to dry solid surfaces and wet tissue, which is promising for biomedical applications.     

Diffusive Adhesives for Water-Rich Materials: Strong and Tunable Adhesion Beyond the Interface

It is notoriously difficult to adhere water-rich materials, such as hydrogels and biological tissues. Existing adhesives usually suffer from weak and nonadjustable adhesion strength, in part because the contact between the adhesive and substrate is largely restrained to the adhesive/substrate interface. In this study, we have attempted to overcome this shortcoming by developing a class of diffusive adhesives (DAs) that can extend adhesion deep into the substrate to maximize the adhesive/substrate contact. The DAs consist of hydrogel matrices and preloaded water-soluble monomers and crosslinkers that can diffuse extensively into the water-rich substrates after adhesive/substrate contact. Polymerization and crosslinking of the monomers are then triggered leading to a bridging network that interpenetrates the DA and substrate skeletons and topologically binds them together. This kind of adhesion, in the absence of adhesive/substrate covalent bonding, is of high strength and toughness, comparable to those of the best-performing natural and artificial adhesives. More importantly, we can precisely tune the adhesion strength on demand by manipulating the diffusion profile. It is envisioned that the DA family could be extended to include a large pool of hydrogel matrices and monomers, and that they could be particularly useful in biological and medical applications.     

Mechanisms and applications of bioinspired underwater/wet adhesives

In nature, many organisms can effectively fix to contact substrates and move and prey in complex living environments, such as underwater, seawater, and tidal environments, owing to special secreted chemical components and/or special micro/nanostructures on the adhesive surface of these organisms. Inspired by the adhesive performance of organisms, extensive research related to adhesive components and adhesive surfaces has been conducted recently. To better understand the underlying adhesive mechanisms and facilitate further continuous inspiration, a brief overview of recent wet/underwater adhesive materials is provided herein. First, the adhesive processes and underlying mechanisms of commonly researched organisms, such as mussels, octopuses, clingfish, and tree frogs, are discussed, and the corresponding bioinspired artificial adhesives are presented. Then, the applications of these bioinspired adhesives, such as intelligent robots (signal monitoring and sensing devices), wearable devices (including wet climbing and electronic skin), biomedicines (including wound dressings, bone adhesion, and rapid hemostasis), are presented and summarized. Finally, we offer our perspective on the future challenges and development of bioinspired artificial adhesives.     

Surface hydration for antifouling and bio-adhesion

Antifouling properties of materials play crucial roles in many important applications such as biomedical implants, marine antifouling coatings, biosensing, and membranes for separation. Poly(ethylene glycol) (or PEG) containing polymers and zwitterionic polymers have been shown to be excellent antifouling materials. It is believed that their outstanding antifouling activity comes from their strong surface hydration. On the other hand, it is difficult to develop underwater glues, although adhesives with strong adhesion in a dry environment are widely available. This is related to dehydration, which is important for adhesion for many cases while water is the enemy of adhesion. In this research, we applied sum frequency generation (SFG) vibrational spectroscopy to investigate buried interfaces between mussel adhesive plaques and a variety of materials including antifouling polymers and control samples, supplemented by studies on marine animal (mussel) behavior and adhesion measurements. It was found that PEG containing polymers and zwitterionic polymers have very strong surface hydration in an aqueous environment, which is the key for their excellent antifouling performance. Because of the strong surface hydration, mussels do not settle on these surfaces even after binding to the surfaces with rubber bands. For control samples, SFG results indicate that their surface hydration is much weaker, and therefore mussels can generate adhesives to displace water to cause dehydration at the interface. Because of the dehydration, mussels can foul on the surfaces of these control materials. Our experiments also showed that if mussels were forced to deposit adhesives onto the PEG containing polymers and zwitterionic polymers, interfacial dehydration did not occur. However, even with the strong interfacial hydration, strong adhesion between mussel adhesives and antifouling polymer surfaces was detected, showing that under certain circumstances, interfacial water could enhance the interfacial bio-adhesion.

Antifouling properties of materials play crucial roles in many important applications such as biomedical implants, marine antifouling coatings, biosensing, and membranes for separation.     

POSS-modified PEG adhesives for wound closure

PEG-related adhesives are limited in clinical use because they are easy to swell and cannot support the cell growth.In this study,we produced a series of POSS-modified PEG adhesives with high adhesive strength.Introduction of inorganic hydrophobic POSS units decreased the swelling of the adhesives and enhanced cell adhesion and growth.The in vitro cytotoxicity and in vivo inflammatory response experiments clearly demonstrated that the adhesives were nontoxic and possessed excellent biocompatibility.Compared with the sutured wounds,the adhesive-treated wounds showed an accelerated healing process in wounded skin model of the Bama miniature pig,demonstrating that the POSS-modified PEG adhesive is a promising candidate for wound closure.     

Use of calcium carbonate – fumed silica mixtures as filler in polyurethane adhesives

Natural ultramicronized calcium carbonate and mixtures of fumed silica‐natural ultramicronized calcium carbonate are proposed as fillers of solvent based polyurethane (PU) adhesives. PU adhesive containing only calcium carbonate shows similar rheological, thermal, mechanical, surface and adhesion properties than the PU adhesive without filler. Addition of 90 wt% fumed silica +10 wt% calcium carbonate mixture to PU adhesive produced a similar performance than the PU adhesive containing only famed silica. The increase in the amount of natural calcium carbonate in respect to fumed silica in the filler mixture produced detrimental effect on the rheological and mechanical properties of the PU adhesives (in respect to those provided by the PU adhesive only containing fumed silica), although the surface and adhesion properties were not noticeably modified.     

Contribution of relaxation processes to adhesive-joint strength of viscoelastic polymers

Relaxation processes accompany all stages of the lifetime of viscoelastic pressure-sensitive polymer adhesives, which can form strong adhesive joints with substrates of various chemical natures under application of a slight external pressure to the adhesive film for a few seconds. This review deals with comparison of the adhesion and relaxation properties of a number of typical pressure-sensitive adhesives based on polyisobutylene, butyl rubber, styrene-isoprene-styrene triblock copolymers, alkyl acrylate copolymers, and silicone adhesives as well as pressure-sensitive adhesives based on blends of high-molecular-mass polyvinylpyrrolidone with oligomeric poly(ethylene glycol). Within all three stages of the lifetime of adhesive joints (under adhesive-bond-forming pressure, upon withdrawal of contact pressure in the course of relaxation of the adhesive material, and under the force detaching an adhesive film from the substrate surface), the strength of adhesive joints has been shown to be controlled by large-scale relaxation processes, which are characterized by long relaxation times in the range 150–800 s. All examined pressure-sensitive adhesives can be arbitrarily divided into two groups. The first group is composed of fluid adhesives that relax comparatively fast and exhibit no residual (unrelaxed) stress. The second group includes elastic adhesives capable storing mechanical energy in the course of deformation that are characterized by appreciably longer relaxation times and display residual stress after relaxation. Conditions of adhesive debonding (e.g., strain amplitude and deformation velocity) significantly affect the relaxation process.     

Underwater adhesive using solid–liquid polymer mixes

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

氢键作用驱动原花青素构筑水基抗菌黏合剂北大核心CSCD

水下黏合剂在生物医学和工程应用领域的需求越来越大。然而,目前报道的大多数水下黏合剂的制备方法中通常需要复杂的化学偶联或修饰,以及昂贵的构筑基元。本文利用低成本的葡萄籽提取物原花青素(PA)和商业化的聚乙二醇寡聚物(PEG)为构筑基元,发展了一种简单且经济的水下黏合剂的构筑策略,实现了在氢键作用下诱导仿生黏合剂生成。此黏合剂既可以在水上又可以在水下黏附不同材质的基底,且可重复使用。此外,易于制备的PA/PEG黏合剂也具有良好的抗菌活性和生物相容性。由于PA/PEG黏合剂具有制备简单、广谱黏附性、可循环使用和抗菌性等优点,将在医疗器械和制药应用中得到广泛应用。     

Recent progress in polymer hydrogel bioadhesives

Adhesive hydrogels have broad applications in tissue adhesives, hemostatic agents, and biomedical sensors. Various bio-inspired glues and synthetic adhesives are clinically used as conventional hemostatic agents and auxiliary tools for wound closure. Medical adhesives are needed to effectively and quickly control bleeding, thereby reducing the risk of complications caused by severe blood loss. Medical sensors need to have excellent skin compliance, mechanical properties, sensitivity, and biological safety. This review focuses on recent progress in adhesive hydrogel systems, their structures, adhesion mechanisms, construction strategies, and emerging applications in the biomedical field.     

Intrinsic Surface‐Drying Properties of Bioadhesive Proteins

Sessile marine mussels must “dry” underwater surfaces before adhering to them. Synthetic adhesives have yet to overcome this fundamental challenge. Previous studies of bioinspired adhesion have largely been performed under applied compressive forces, but such studies are poor predictors of the ability of an adhesive to spontaneously penetrate surface hydration layers. In a force‐free approach to measuring molecular‐level interaction through surface‐water diffusivity, different mussel foot proteins were found to have different abilities to evict hydration layers from surfaces—a necessary step for adsorption and adhesion. It was anticipated that DOPA would mediate dehydration owing to its efficacy in bioinspired wet adhesion. Instead, hydrophobic side chains were found to be a critical component for protein–surface intimacy. This direct measurement of interfacial water dynamics during force‐free adsorptive interactions at solid surfaces offers guidance for the engineering of wet adhesives and coatings.     

A Mesostructure Multivariant-Assembly Reinforced Ultratough Biomimicking Superglue

The imitation of mussels and oysters to create high-performance adhesives is a cutting-edge field. The introduction of inorganic fillers is shown to significantly alter the adhesive's properties, yet the potential of mesoporous materials as fillers in adhesives is overlooked. In this study, the first report on the utilization of mesoporous materials in a biomimetic adhesive system is presented. Incorporating mesoporous silica nanoparticles (MSN) profoundly enhances the adhesion of pyrogallol (PG)–polyethylene imine (PEI) adhesive. As the MSN concentration increases, the adhesion strength to glass substrates undergoes an impressive fivefold improvement, reaching an outstanding 2.5 mPa. The adhesive forms an exceptionally strong bond, to the extent that the glass substrate fractures before joint failure. The comprehensive tests involving various polyphenols, polymers, and fillers reveal an intriguing phenomenon—the molecular structure of polyphenols significantly influences adhesive strength. Steric hindrance emerges as a crucial factor, regulating the balance between π-cation and charge interactions, which significantly impacts the multicomponent assembly of polyphenol-PEI-MSN and, consequently, adhesive strength. This groundbreaking research opens new avenues for the development of novel biomimetic materials.     

Thermal behavior and dismantlability of adhesives containing various inorganic salts

As a fundamental study on the development of dismantlable adhesives containing chemically reactive materials, the thermal behavior and dismantlability of an epoxy adhesive containing one of the twenty-seven inorganic salts (chlorides, perchlorates, and nitrates) were observed. In the thermal behavior measured by the differential scanning calorimetry, epoxy adhesives with inorganic salts containing iron, copper, zinc, and aluminum cations released heats of reaction at lower temperatures than the adhesive alone or the adhesives with other inorganic salts. Since such inorganic salts were considered to be effective candidates as fillers in dismantlable adhesives, the adhesion strengths of their mixtures with the adhesive were observed after heat aging at 270 °C for 30 min. The results showed that both chloride and perchlorate salts specifically decreased the adhesion strength after heating. On the other hand, the effect of nitrate salts on the decrease in adhesion strength was low in comparison with the chloride and perchlorate salts.     

含多巴胺的贻贝仿生聚氨酯

将具有神奇黏附效果的贻贝黏附蛋白中的功能元——儿茶酚(catechol)与具有结构可设计、简单易得、低成本的聚氨酯相结合,制备新型高性能的贻贝仿生聚氨酯黏附材料.首先,通过异氰酸酯化学合成了含羧基的聚氨酯,接着通过碳二亚胺化学将含有儿茶酚功能团的多巴胺(dopamine)和含羧基的聚氨酯相结合制备了含多巴胺的聚氨酯.经过傅立叶转换红外光谱(FTIR)、核磁共振(NMR)和紫外-可见分光光度仪(UV-Vis)等分析测试研究结果表明,多巴胺确实已被引入到聚氨酯中;同时,通过测试搭接剪切强度研究了其粘接性能,结果表明含多巴胺的聚氨酯相对于含羧基的聚氨酯的粘接性能得到大幅提高,其对金属基材的粘接强度提高了30%左右,达到5.2MPa,可以与贻贝黏附蛋白相媲美.     

仿贻贝粘性高分子的应用进展

海洋贻贝类生物的足丝分泌蛋白几乎能够在所有基底材料上实现高强度、高韧性的粘附,且不受水或者潮湿环境影响。这种环境友好、条件温和的高效生物粘附剂引起了研究人员的兴趣,尤其在粘附机理和应用前景方面更是研究人员关注的重点。大量研究表明,贻贝超强的粘附能力与其分泌的粘附蛋白中高含量的3,4-二羟基苯丙氨酸(多巴,DOPA)单元相关。受贻贝粘附蛋白的启发,人们研究发现,多巴胺(DA)分子具有与之相似的官能团,聚合后有相似分子结构,使用聚多巴胺替代聚多巴,可以在基体表面达到相似的粘附性能。本文简单介绍了仿贻贝粘性物质中的代表多巴胺自聚合形成聚多巴胺(PDA)与粘附机理,并重点介绍了近年来DOPA衍生物在表面改性、催化、生物防污及生物医学领域的应用和前景。     

Unusual Stability of a Recombinant <Emphasis Type="Italic">Verrucomicrobium spinosum</Emphasis> Tyrosinase to Denaturing Agents and Its Use for a Production of a Protein with Adhesive Properties

Tyrosinases catalyze oxidation of phenols with a formation of biphenols, quinones, and highly polymerized melanins. Tyrosinases have prospects for industrial use to remove phenols, also in biosensors, in bioorganic synthesis, and for a production of biocompatible adhesives (medical glues). Despite growing fields of potential applications, a selection of commercially available tyrosinases are currently limited to a single enzyme which is isolated from fruiting bodies of mushrooms. This article describes a preparation of recombinant tyrosinase from a bacterium Verrucomicrobium spinosum using a heterologous expression in Escherichia coli. Recombinant V. spinosum tyrosinase has high specific activity (13,200 U/mg). A resistance of the enzyme was investigated to chemical agents used to denature proteins and keep poorly solvable proteins in a solution. The enzyme preserves activity in the presence of urea and retains at least a fraction of its enzymatic activity at concentrations of urea up to 4.5 M. An addition of sodium lauroyl sarcosinate to 1 or 2% activates the tyrosinase. Novel means of quantitatively expressing tyrosinase activity is described in this article. The method uses a set of parameters obtained from non-linear estimation of the progress curves and is suitable for enzymatic reactions which do not comply with Michaelis–Menten kinetics. Tyrosinase may be used to introduce into proteins a post-translational modification which is a conversion of tyrosine residues (Tyr) into residues of 3,4-dioxyphenylalanine (DOPA). The presence of DOPA provides the polypeptides with a capability of strong molecular adhesion. Co-expression of tyrosinase and a recombinant protein mimicking marine mussel-encoded adhesive proteins resulted in obtaining of the protein in which at least a part of Tyr residues had been converted to DOPA. The DOPA-containing protein had high adhesion strength (2.5 MPa).