Mussel Byssal Threads Research Articles

An Overview on the Adhesion Mechanisms of Typical Aquatic Organisms and the Applications of Biomimetic Adhesives in Aquatic Environments.

Water molecules pose a significant obstacle to conventional adhesive materials. Nevertheless, some marine organisms can secrete bioadhesives with remarkable adhesion properties. For instance, mussels resist sea waves using byssal threads, sandcastle worms secrete sandcastle glue to construct shelters, and barnacles adhere to various surfaces using their barnacle cement. This work initially elucidates the process of underwater adhesion and the microstructure of bioadhesives in these three exemplary marine organisms. The formation of bioadhesive microstructures is intimately related to the aquatic environment. Subsequently, the adhesion mechanisms employed by mussel byssal threads, sandcastle glue, and barnacle cement are demonstrated at the molecular level. The comprehension of adhesion mechanisms has promoted various biomimetic adhesive systems: DOPA-based biomimetic adhesives inspired by the chemical composition of mussel byssal proteins; polyelectrolyte hydrogels enlightened by sandcastle glue and phase transitions; and novel biomimetic adhesives derived from the multiple interactions and nanofiber-like structures within barnacle cement. Underwater biomimetic adhesion continues to encounter multifaceted challenges despite notable advancements. Hence, this work examines the current challenges confronting underwater biomimetic adhesion in the last part, which provides novel perspectives and directions for future research.

Energetic scope limits growth but not byssal thread production of two mytilid mussels

Anthropogenic warming of the ocean and atmosphere, concurrent with ocean acidification and deoxygenation, has made it even more pressing to quantify the link between environmental stressors and marine organism population dynamics. In marine environments, low food availability, low feeding rates, and/or increased metabolic costs can cause energetic limitation. Energetic limitation affects some functional traits, such as growth rates of body tissue and reproductive output. Other functional traits that are linked with short-term survival are often prioritized in conditions of energy limitation, despite their energetic cost. Mussels are ecosystem engineers in rocky shore ecosystems, and they produce byssal threads to attach to hard substrate and aquaculture line. Previous studies of mytilid mussel bioenergetics suggest tissue and shell growth are energetically-constrained, while production of byssal threads presents a fitness trade-off and could potentially be a fixed or ‘constitutive’ response regardless of energetic state. In this study, we conduct a field test with two congener mussel species, Mytilus trossulus and Mytilus galloprovincialis to determine whether an index of energetic availability, scope for growth (SFG), correlates with growth and byssal thread production, and the extent to which other potential stressors (hypoxia, low pH, low salinity and high temperature) modulate this response. We find a positive correlation between SFG and growth (both tissue and shell) but not the number of byssal threads produced. We also find low pH or low DO, two co-varying physiological stressors, negatively affect tissue growth of both species, but only marginally affect byssal thread production. We also observed mortality in the late summer/early autumn that coincides with the period of greater hypoxia and low pH. Overall, this work suggests that some functional traits, such as shell and tissue growth, are energetically-constrained while other functional traits, such as mussel byssal thread production, may be best described as a fitness trade-off.

First characterization of a nursery ground for the commercial sea cucumber Cucumaria frondosa

This study characterised the nursery ground of the cold-water sea cucumber Cucumaria frondosa for the first time. New recruits and early juveniles 0.9–40 mm in length were discovered at depths of 1.8–2.5 m in Qikiqtait (traditional name of the Belcher Islands, Nunavut, Canada) at a site with salinities ≥27 psu. They were primarily attached to live individuals and empty shells of the blue mussel Mytilus edulis and to stones. Based on laboratory rearing and known spawning times, the smallest individuals (0.9–1.4 mm) found in October 2021 and June 2022 were estimated to be 3–4 and 11–12 months old, respectively (year class 0-I). Other juveniles found at the same time were mostly ≤4-year-old, likely representing subsequent anual recruitment pulses. Densities of juveniles measuring 0.9–40 mm varied between 4 and 104 ind. m−2. Recruits <2 mm occurred in complex substrata, mostly mussel byssal threads, while larger juveniles, especially those >9 mm, were on exposed surfaces of shells and stones. No adults occupied the shallow nursery site. This study draws attention to ontogenetic migration allowing the occurrence of cryptic nursery sites that may occur in shallower environments than the typical adult habitats, of particular significance for the management of commercial species.

Bioinspired Design of High Vibration-Damping Supramolecular Elastomers Based on Multiple Energy-Dissipation Mechanisms.

Suppressing vibrations and noises is essential for our automated society. Here, inspired by the hierarchical dynamic bonds and phase separation of mussel byssal threads, we synthesize high-damping supramolecular elastomers (HDEs) via simple one-pot radical polymerization of butyl acrylate (BA), acrylic acid (AA), and vinylimidazole (VI). Interestingly, AA and VI not only form hydrogen bonds and ionic bonds simultaneously but also segregate into aggregates of different sizes, thereby successfully mimicking the hierarchical structure of mussel byssal threads. When applying external forces, the weak hydrogen bonds are broken at first and then the ionic bonds and aggregates are disrupted progressively from small to large deformations. Such multiple energy-dissipation mechanisms lead to the outstanding damping property of the HDEs. Therefore, the HDEs outperform commercially available rubbers in terms of sound absorption and vibration damping. Furthermore, the multiple energy-dissipation mechanisms impart the HDEs with high toughness (41.1 MJ/m3), tensile strength (21.3 MPa), and self-healing ability.

Cooperative Multivalent Weak and Strong Interfacial Interactions Enhance the Adhesion of Mussel-Inspired Adhesives

Inspired by the strong adhesion of mussel byssal threads to surfaces, the incorporation of 3,4-dihydroxyphenylalanine (DOPA) in polymer architecture has become a popular strategy to improve the adhesion of the polymers. There are numerous literature reports of this bioinspired method to improve the adhesion performance of polymers. However, the mechanism behind the success of DOPA-based adhesion continues to be a puzzle as decoupling the contribution of interfacial adhesion to the alteration in chemistry is experimentally challenging. Herein, we designed mussel-inspired elastomers with four different functionalities to test the importance of aromatic and hydroxyl groups in determining the adhesion performance. With a combination of adhesion measurements, surface-sensitive spectroscopy, and molecular dynamics simulations, we show that the aromatic groups form weak multivalent acid–base interactions with the surface hydroxyl groups on sapphire. Also, the interaction of both phenyl (weak acid–base interaction) and −OH groups (strong acid–base interaction) of DOPA with sapphire −OH groups increases the adhesion of DOPA-based polymers compared to polymer analogs functionalized with either phenylalanine (only aromatic), serine (only hydroxyl), or tyrosine (aromatic and one hydroxyl) groups. Thus, this study illustrates the importance of both strong and weak acid–base interactions in enhancing adhesion.

Cooperativity of Catechols and Amines in High-Performance Dry/Wet Adhesives.

The outstanding adhesive performance of mussel byssal threads has inspired materials scientists over the past few decades. Exploiting the amino-catechol synergy, polymeric pressure-sensitive adhesives (PSAs) have now been synthesized by copolymerizing traditional PSA monomers, butyl acrylate and acrylic acid, with mussel-inspired lysine- and aromatic-rich monomers. The consequences of decoupling amino and catechol moieties from each other were compared (that is, incorporated as separate monomers) against a monomer architecture in which the catechol and amine were coupled together in a fixed orientation in the monomer side chain. Adhesion assays were used to probe performance at the molecular, microscopic, and macroscopic levels by a combination of AFM-assisted force spectroscopy, peel and static shear adhesion. Coupling of catechols and amines in the same monomer side chain produced optimal cooperative effects in improving the macroscopic adhesion performance.

Cooperativity of Catechols and Amines in High‐Performance Dry/Wet Adhesives

AbstractThe outstanding adhesive performance of mussel byssal threads has inspired materials scientists over the past few decades. Exploiting the amino‐catechol synergy, polymeric pressure‐sensitive adhesives (PSAs) have now been synthesized by copolymerizing traditional PSA monomers, butyl acrylate and acrylic acid, with mussel‐inspired lysine‐ and aromatic‐rich monomers. The consequences of decoupling amino and catechol moieties from each other were compared (that is, incorporated as separate monomers) against a monomer architecture in which the catechol and amine were coupled together in a fixed orientation in the monomer side chain. Adhesion assays were used to probe performance at the molecular, microscopic, and macroscopic levels by a combination of AFM‐assisted force spectroscopy, peel and static shear adhesion. Coupling of catechols and amines in the same monomer side chain produced optimal cooperative effects in improving the macroscopic adhesion performance.

Competition between delamination and tearing in multiple peeling problems.

Adhesive attachment systems consisting of multiple tapes or strands are commonly found in nature, for example in spider web anchorages or in mussel byssal threads, and their structure has been found to be ingeniously architected in order to optimize mechanical properties: in particular, to maximize dissipated energy before full detachment. These properties emerge from the complex interplay between mechanical and geometric parameters, including tape stiffness, adhesive energy, attached and detached lengths and peeling angles, which determine the occurrence of three main mechanisms: elastic deformation, interface delamination and tape fracture. In this paper, we introduce a formalism to evaluate the mechanical performance of multiple tape attachments in different parameter ranges, where an optimal (not maximal) adhesion energy emerges. We also introduce a numerical model to simulate the multiple peeling behaviour of complex structures, illustrating its predictions in the case of the staple-pin architecture. Finally, we present a proof-of-principle experiment to illustrate the predicted behaviour. We expect the presented formalism and the numerical model to provide important tools for the design of bioinspired adhesive systems with tuneable or optimized detachment properties.

Metal Coordination-Mediated Functional Grading and Self-Healing in Mussel Byssus Cuticle.

Metal‐containing polymer networks are ubiquitous in biological systems, and their unique structures enable a variety of fascinating biological behaviors. Cuticle of mussel byssal threads, containing Fe‐catecholate complexes, shows remarkably high hardness, high extensibility, and self‐healing capability. Understanding strengthening and self‐healing mechanisms is essential for elucidating animal behaviors and rationally designing mussel‐inspired materials. Here, direct evidence of Fe3+ and Fe2+ gradient distribution across the cuticle thickness is demonstrated, which shows more Fe2+ inside the inner cuticle, to support the hypothesis that the cuticle is a functionally graded material with high stiffness, extensibility, and self‐healing capacity. The mechanical tests of the mussel threads show that both strength and extensibility of the threads decrease with increasing oxygen contents, but this property degradation can be restored upon removing the oxygen. The first‐principles calculations explain the change in iron coordination, which plays a key role in strengthening, degradation, and self‐healing of the polymer networks. The oxygen absorbs on metal ions, weakening the iron‐catecholate bonds in the cuticle and collagen core, but this process can be reversed by sea water. These findings can have important implications in the design of next‐generation bioinspired robust, highly extensible materials, and catalysis.

The Thiol-Rich Interlayer in the Shell/Core Architecture of Mussel Byssal Threads.

The mussel byssus thread is an extremely tough core-shelled fiber that dissipates substantial amounts of energy during tensile loading. The mechanical performance of the shell is critically reliant on 3,4-dihydroxyphenylalanine's (Dopa) ability to form reversible iron-catecholate complexes at pH 8. However, the formation of these coordinate cross-links is undercut by Dopa's oxidation to Dopa-quinone, a spontaneous process at seawater conditions. The large mechanical mismatch between the cuticle and the core lends itself to further complications. Despite these challenges, the mussel byssus thread performs its tethering function over long periods of time. Here, we address these two major questions: (1) how does the mussel slow/prevent oxidation in the cuticle, and (2) how is the mechanical mismatch at the core/shell interface mitigated? By combining a number of microscopy and spectroscopy techniques we have discerned a previously undescribed layer. Our results indicate this interlayer is thiol rich and thus will be called the thiol-rich interlayer (TRL). We propose the TRL serves as a long-lasting redox reservoir as well as a mechanical barrier.

Bioinspired nanoplatform for enhanced delivery efficiency of doxorubicin into nucleus with fast endocytosis, lysosomal pH-triggered drug release, and reduced efflux

A novel bioinspired nanoplatform capable of fast endocytosis, lysosomal pH-triggered drug release, and reduced drug efflux based on PBA-PEG-b-P(Glu-co-GluDA) copolymer was developed in this study. The synthesized copolymer could facilitate doxorubicin encapsulation with relatively high drug-loading content and efficiency. Inspired by mussel byssal threads, a core crosslinking strategy based on the coordination between catechol and ferric ions was introduced to improve the stability of nanomicelles and realize lysosomal pH-controlled drug release. This nanoplatform could maintain integrity even after being dissolved in a good solvent, demonstrating its the potential to withstand infinite dilution of plasma after intravenous injection. Moreover, this nanoplatform demonstrated lysosomal pH-triggered drug release, and the cumulative release amount of doxorubicin under a simulated lysosomal condition was 13 times higher than that under a simulated plasma condition. Moreover, as a result of the high binding capacity between phenylboronic acid (PBA) and sialic acid on the surface of human hepatoma cell line (HepG2), the fast and enhanced endocytosis in addition to lysosomal pH-triggered release property and significantly low efflux, this nanoplatform exhibits improved delivery efficiency of doxorubicin into the nucleus and notably outstanding antiproliferative effects compared with doxorubicin. Furthermore, the PBA modification remarkably increased the mean fluorescence intensity of this nanoplatform endocytosed by HepG2 cells to twice that of doxorubicin after one hour of incubation. The nanoplatform exhibited an inhibition rate of 70% against tumor growth. Thus, this novel nanoplatform based on PBA-PEG-b-P(Glu-co-GluDA) copolymer displayed multifunctionality and exhibited great potential as an intelligent nanoplatform for antitumor drug delivery.

Exploring mussel byssus fabrication with peptide-polymer hybrids: Role of pH and metal coordination in self-assembly and mechanics of histidine-rich domains

Mussel byssal threads are biopolymeric fibers that possess high toughness and self-healing capacity owing to a hierarchical arrangement of collagenous protein building blocks known as preCols. To investigate the proposed role of histidine-rich domains (HRDs) at preCol termini in the rapid self-assembly and properties of mussel byssus, we functionalized 4-arm star-shaped polyethyleneglycol (star-PEG) molecules with peptides based on an evolutionarily-conserved HRD sequence motif. PEG-HRD hybrid molecules instantly and reversibly form physical hydrogels without metal ions, using a simple pH trigger mimicking the natural assembly process. Spectroscopic analysis indicates that gelation is mediated via a conformational transition into β-sheet crystalline structure, comprised of multiple peptide groups that cross-link the star-PEGs. Additionally, metal ions introduced during gelation form His-metal coordination bonds within the network and increase viscoelastic damping of the gels, as proposed for native fibers. These findings help disentangle the different roles of pH and metal coordination during natural byssus formation/function and may have important implications for generating novel metallopolymeric materials with hierarchical structure.

PYRROLO isolated from marine sponge associated bacterium Halobacillus kuroshimensis SNSAB01 - Antifouling study based on molecular docking, diatom adhesion and mussel byssal thread inhibition.

In the present study, an attempt has been made to explore the antifouling potential of bioactive compound isolated from sponge associated bacterium Halobacillus kuroshimensis SNSAB01. The crude extract of SNSAB01 strongly inhibited the growth of fouling bacterial strains with least minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The bioactive compound was characterized through FT-IR, HPLC, GCMS and NMR predicted as 'pyrrolo". From the mass spectral library, structure was elucidated as pyrrolo [1, 2-a] pyrazine-1, 4-dione, hexahydro. The in silico studies provided encouraging docking scores with two interactions by GLN 200 and GLU 304. The extract inhibited 89% diatom adhesion at 350 μg/ml concentration against Amphora sp. An EC50 value of 150 μg/ml for 50% inhibition of byssal thread of Perna viridis and LC50 was found to be 500 μg/ml. The LC50/EC50 ratio of 3.0 indicated nontoxic to nature. The result suggested that pyrrolo[1,2-a]pyrazine-1,4-dione can be used for antifouling coating.

Influence of Aspartate Moieties on the Self-Healing Behavior of Histidine-Rich Supramolecular Polymers.

Aspartate incorporated into the protein structure of mussel byssal threads is believed to play an important role, besides the reversible histidine-zinc interactions, in the self-healing behavior of mussel byssal threads. Therefore, copolymers containing both aspartate and histidine moieties are synthesized in order to investigate the influence of aspartate on the complexation of zinc(II) as well as on the self-healing behavior and the mechanical properties of the resulting supramolecular networks. For this purpose, isothermal titration calorimetry measurements of a model aspartate compound as well as of these copolymers are performed and the thermodynamic parameters are utilized for the design of self-healing copolymers. For this purpose, n-lauryl methacrylate-based copolymers containing histidine and aspartate are synthesized and crosslinked with zinc(II) acetate. The self-healing behavior of the supramolecular networks is investigated using scratch healing tests and the mechanical properties by nanoindentation.

Metal-Tunable Self-Assembly of Hierarchical Structure in Mussel-Inspired Peptide Films.

Bottom-up control over structural hierarchy from the nanoscale through the macroscale is a critical aspect of biological materials fabrication and function, which can inspire production of advanced materials. Mussel byssal threads are a prime example of protein-based biofibers in which hierarchical organization of protein building blocks coupled via metal complexation leads to notable mechanical behaviors, such as high toughness and self-healing. Using a natural amino acid sequence from byssal thread proteins, which functions as a pH-triggered self-assembly point, we created free-standing peptide films with complex hierarchical organization across multiple length scales that can be controlled by inclusion of metal ions (Zn2+ and Cu2+) during the assembly process. Additionally, analysis of film mechanical performance indicates that metal coordination bestows up to an order of magnitude increase in material stiffness, providing a paradigm for creating tunable polymeric materials with multiscale organizational structure.

A translation of the structure of mussel byssal threads into synthetic materials by the utilization of histidine-rich block copolymers

The self-healing capacities of mussel-inspired metallopolymers based on block copolymers containing histidine are briefly presented.

Histidine–Zinc Interactions Investigated by Isothermal Titration Calorimetry (ITC) and their Application in Self‐Healing Polymers

Histidine–zinc interactions are believed to play a key role in the self‐healing behavior of mussel byssal threads due to their reversible character. Taking this as inspiration, the authors synthesize here histidine‐rich copolymers, as well as model histidine compounds and characterize them using isothermal titration calorimetry (ITC). With this approach, the influence of two different zinc(II) salts and the role in the complex formation of the amine function of the imidazole ring are investigated in detail. The extracted metal–ligand ratios are utilized to design novel self‐healing metallopolymers. For this purpose, n‐lauryl methacrylate is copolymerized with the histidine monomer via reversible addition‐fragmentation chain transfer polymerization. The copolymers are crosslinked using different zinc salts, and the resulting coatings are characterized with Raman spectroscopy to investigate the metal coordination behavior and with scratch healing tests to investigate the self‐healing capacity. Finally, the self‐healing behavior of the different materials is correlated with the metal–ligand binding affinity measured by ITC. image

Cooperative behavior of a sacrificial bond network and elastic framework in providing self-healing capacity in mussel byssal threads.

The dissipative and self-healing properties of mussel byssal threads are critical for their function as anchoring fibers in wave-battered habitats and central to their emergence as an exciting model system for bio-inspired polymers. Much is now understood about the structure-function relationships defining this remarkable proteinaceous bio-fiber; however, the molecular mechanisms underlying the distinctive tough, viscoelastic and self-healing behavior are still unclear. Here, we investigate elastic and dissipative contributions from the primary load-bearing proteins in the distal region of byssal threads (the preCols) using X-ray diffraction (XRD) combined with in situ tensile testing. Specifically, we identified cross β-sheet structure in the preCol flanking domains that functions as an elastic framework, providing hidden length. Dissipative behavior was associated with a strain-rate dependent phase transition of a sacrificial network stabilized by strong, reversible cross-links. Based on these findings, we posit a new model for byssal thread deformation and self-healing.

Extraordinary structure and properties of mussel byssus protein fibers

A naturally available single protein fiber that is stiff and strong at one end but at the same time highly flexible with moderate strength at the other end is quite exceptional. Such exceptional protein fibers called byssus threads are produced by mussels. A unique arrangement of collagen proteins along the length of the fibers and a specific amount and distribution of the β-sheet and α-helix regions provide extraordinary properties to byssus threads. Due to the unique configuration of the threads and a distinct adhesive plaque, mussels are able to adhere to substrates and withstand large amounts of external forces. However, significant variations in composition and tensile properties exist between the mussels threads obtained from different species and even along the length of a single byssal thread. Similarly, environmental conditions such as the presence of salt water and chemicals affect the properties of the fibers. Extensive studies have been done to understand the composition, the structure and the properties of the byssal threads. This review provides an insight into the unique structure and properties of the byssal threads and discusses the potential of developing biomimetic materials based on the mussel byssal threads.

Development of collagen-byssus protein hydrolysate matrix to improve elasticity in scaffolds for vascular tissue engineering applications

Event Abstract Back to Event Development of collagen-byssus protein hydrolysate matrix to improve elasticity in scaffolds for vascular tissue engineering applications Erica Rosella1, Caroline Loy1, Lucie Levesque1, Bernard Drouin1, 2, Isabelle Marcotte3 and Diego Mantovani1 1 Laval University, Lab. for Biomaterials & Bioengineering (CRC-I), Dept. Min-Met-Materials Engineering & CHU de Quebec, Canada 2 Cegep Garneau, Department of Physics, Canada 3 Université de Québec à Montréal, Department of Chemistry, Canada Type-1 collagen from rat-tail tendon has been widely used as scaffold in the field of tissue engineering. In the form of hydrogel, collagen serves as a matrix that mechanically and biologically supports three-dimensional cell growth and tissue regeneration. Considering their application as scaffold for small caliber engineered blood vessels (d<6 mm), the ability to withstand blood cyclic stress and compliance are crucial requirements. To address the elasticity in the collagen scaffold, we have explored the addition in the collagen hydrogel of byssus protein hydrolysate (BPH)[1] extracted from mussel byssal threads, which show remarkable combination of strength and extensibility. In vitro self-assembly process leading to hydrogel gelation was optimized at pH 10 in 48-multiwell plates. The protocol of collagen gelation at pH 10 was adapted and modified from the work of Achilli et al[2]. Collagen buffer solutions with 101 mM of salt concentration (NaCl and NaOH) was used to solubilize the BPH, and mixed with the collagen solution to reach a final protein concentration of 2.8 mg/mL. The effect of temperature (4 and 22°C) on the gelation process was assessed by turbidimetric measurements. The resulting microstructure and matrix density were observed by scanning electron microscopy (SEM). The swelling ratio of the scaffold was also determined and compression-relaxation tests were carried to investigate the mechanical properties of the scaffold under compression. Figure 1 shows the results of the turbidimetry measurements where the gelation time (t1/2) is defined as the required time to reach half of the final absorbance. The gelation time of collagen-BPH gel is longer (3.4 and 4.5 days) compared to the collagen control which took 4 and 13 hours at respective temperatures of 22°C and 4°C. Comparison of SEM images of collagen and collagen-BPH mixture at 22°C shows a denser matrix of collagen-BPH at the microstructural level (Figure 2). Moreover, collagen-BPH has a lower (58±5%) water uptake ratio than collagen (71±8%), suggesting greater chemical interactions within the gel leading to a more compact matrix. Compression test shows that BPH incorporation increases scaffold relaxation time, which corresponds to the higher residual force. The compressive and tensile modulus also increases by 12±4% compared to collagen control at pH 10. In conclusion, the addition of BPH to collagen hydrogel increases the density and strength of the scaffold, and shows great potential to improve the collagen matrix elasticity. Further work is required to assess the biological properties of this new scaffold. Figure 1. Turbidity measurements for collagen-BPH gels prepared at pH 10 at 4 °C and 22 °C Figure 2. SEM images of collagen control (left) and collagen-BPH (right) samples prepared at pH 10 and 22°C This work was partially funded by NSERC-Canada, FRQ-NT-Quebec, CFI-Canada, and the Centre Québécois sur les Matériaux Fonctionnels (CMQF).