Squid Sucker Ring Teeth: Multiscale Structure-Property Relationships, Sequencing, and Protein Engineering of a Thermoplastic Biopolymer

Tuning the viscoelastic properties of peptide coacervates by single amino acid mutations and salt kosmotropicity

Coacervation, or liquid-liquid phase separation (LLPS) of biomacromolecules, is increasingly recognized to play an important role both intracellularly and in the extracellular space. Central questions that remain to be addressed are the links between the material properties of coacervates (condensates) and both the primary and the secondary structures of their constitutive building blocks. Short LLPS-prone peptides, such as GY23 variants explored in this study, are ideal model systems to investigate these links because simple sequence modifications and the chemical environment strongly affect the viscoelastic properties of coacervates. Herein, a systematic investigation of the structure/property relationships of peptide coacervates was conducted using GY23 variants, combining biophysical characterization (plate rheology and surface force apparatus, SFA) with secondary structure investigations by infrared (IR) and circular dichroism (CD) spectroscopy. Mutating specific residues into either more hydrophobic or more hydrophilic residues strongly regulates the viscoelastic properties of GY23 coacervates. Furthermore, the ionic strength and kosmotropic characteristics (Hofmeister series) of the buffer in which LLPS is induced also significantly impact the properties of formed coacervates. Structural investigations by CD and IR indicate a direct correlation between variations in properties induced by endogenous (peptide sequence) or exogenous (ionic strength, kosmotropic characteristics, aging) factors and the β-sheet content within coacervates. These findings provide valuable insights to rationally design short peptide coacervates with programmable materials properties that are increasingly used in biomedical applications.

Biomimetic Silk Architectures Outperform Animal Horns in Strength and Toughness

Structural biomimicry is an intelligent approach for developing lightweight, strong, and tough materials (LSTMs). Current fabrication technologies, such as 3D printing and two-photon lithography often face challenges in constructing complex interlaced structures, such as the sinusoidal crossed herringbone structure that contributes to the ultrahigh strength and fracture toughness of the dactyl club of peacock mantis shrimps. Herein, bioinspired LSTMs with laminated or herringbone structures is reported, by combining textile processing and silk fiber "welding" techniques. The resulting biomimetic silk LSTMs (BS-LSTMs) exhibit a remarkable combination of lightweight with a density of 0.6-0.9 g cm-3 , while also being 1.5 times stronger and 16 times more durable than animal horns. These findings demonstrate that BS-LSTMs are among the toughest natural materials made from silk proteins. Finite element simulations further reveal that the fortification and hardening of BS-LSTMs arise primarily from the hierarchical organization of silk fibers and mechanically transferable meso-interfaces. This study highlights the rational, cost-effective, controllable mesostructure, and transferable strategy of integrating textile processing and fiber "welding" techniques for the fabrication of BS-LSTMs with advantageous structural and mechanical properties. These findings have significant implications for a wide range of applications in biomedicine, mechanical engineering, intelligent textiles, aerospace industries, and beyond.

Soft Functionally Gradient Materials and Structures - Natural and Manmade: A Review

Functionally gradient materials (FGM) have gradual variations in their properties along one or more dimensions due to local compositional or structural distinctions by design. Traditionally, hard materials (e.g., metals, ceramics) are used to design and fabricate FGMs; however, there is increasing interest in polymer-based soft and compliant FGMs mainly because of their potential application in the human environment. Soft FGMs are ideally suitable to manage interfacial problems in dissimilar materials used in many emerging devices and systems for human interaction, such as soft robotics and electronic textiles and beyond. Soft systems are ubiquitous in everyday lives; they are resilient and can easily deform, absorb energy, and adapt to changing environments. Here, the basic design and functional principles of biological FGMs and their manmade counterparts are discussed using representative examples. The remarkable multifunctional properties of natural FGMs resulting from their sophisticated hierarchical structures, built from a relatively limited choice of materials, offer a rich source of new design paradigms and manufacturing strategies for manmade materials and systems for emerging technological needs. Finally, the challenges and potential pathways are highlighted to leverage soft materials' facile processability and unique properties toward functional FGMs.

Modulation of Mechanical Properties of Short Bioinspired Peptide Materials by Single Amino-Acid Mutations

The occurrence of modular peptide repeats in load-bearing (structural) proteins is common in nature, with distinctive peptide sequences that often remain conserved across different phylogenetic lineages. These highly conserved peptide sequences endow specific mechanical properties to the material, such as toughness or elasticity. Here, using bioinformatic tools and phylogenetic analysis, we have identified the GX8 peptide with the sequence GLYGGYGX (where X can be any residue) in a wide range of organisms. By simple mutation of the X residue, we demonstrate that GX8 can be self-assembled into various supramolecular structures, exhibiting vastly different physicochemical and viscoelastic properties, from liquid-like coacervate microdroplets to hydrogels to stiff solid materials. A combination of spectroscopic, electron microscopy, mechanical, and molecular dynamics studies is employed to obtain insights into molecular scale interactions driving self-assembly of GX8 peptides, underscoring that π-π stacking and hydrophobic interactions are the drivers of peptide self-assembly, whereas the X residue determines the extent of hydrogen bonding that regulates the macroscopic mechanical response. This study highlights the ability of single amino-acid polymorphism to tune the supramolecular assembly and bulk material properties of GX8 peptides, enabling us to cover a broad range of potential biomedical applications such as hydrogels for tissue engineering or coacervates for drug delivery.

Squid Suckerin-Spider Silk Fusion Protein Hydrogel for Delivery of Mesenchymal Stem Cell Secretome to Chronic Wounds

Chronic wounds are non-healing wounds characterized by a prolonged inflammation phase. Excessive inflammation leads to elevated protease levels and consequently to a decrease in growth factors at wound sites. Stem cell secretome therapy has been identified as a treatment strategy to modulate the microenvironment of chronic wounds via supplementation with anti-inflammatory/growth factors. However, there is a need to develop better secretome delivery systems that are able to encapsulate the secretome without denaturation, in a sustained manner, and that are fully biocompatible. To address this gap, a recombinant squid suckerin-spider silk fusion protein is developed with cell-adhesion motifs capable of thermal gelation at physiological temperatures to form hydrogels for encapsulation and subsequent release of the stem cell secretome. Freeze-thaw treatment of the protein hydrogel results in a modified porous cryogel that maintains slow degradation and sustained secretome release. Chronic wounds of diabetic mice treated with the secretome-laden cryogel display increased wound closure, presence of endothelial cells, granulation wound tissue thickness, and reduced inflammation with no fibrotic scar formation. Overall, these in vivo indicators of wound healing demonstrate that the fusion protein hydrogel displays remarkable potential as a delivery system for secretome-assisted chronic wound healing.

Preparation of Highly Crystalline Silk Nanofibrils and Their Use in the Improvement of the Mechanical Properties of Silk Films

Due to their commendable biocompatibility, regenerated silk fibroin (RSF) films have attracted considerable research interest. However, the poor mechanical properties of RSF films have limited their use in various biomedical applications. In this study, a novel, highly crystalline silk fibril was successfully extracted from silk by combining degumming with ultrasonication. Ultrasonication accelerated the development of silk nanofibrils measuring 130–200 nm on the surface of the over-degummed silk fibers, which was confirmed via scanning electron microscopy. Additionally, the crystallinity index of silk fibril was found to be significantly higher (~68%) than that of conventionally degummed silk (~54%), as confirmed by the Fourier-transform infrared (FTIR) spectroscopy results. Furthermore, the breaking strength and elongation of the RSF film were increased 1.6 fold and 3.4 fold, respectively, following the addition of 15% silk nanofibrils. Thus, the mechanical properties of the RSF film were remarkably improved by the addition of the silk nanofibrils, implying that it can be used as an excellent reinforcing material for RSF films.

Micro-cracks and micro-fractures reveal radular tooth architecture and its functional significance in the paludomid gastropod Lavigeria grandis

Most molluscan taxa forage with their radula, a chitinous membrane with embedded teeth. The teeth are the actual interfaces between the animal and its ingesta and serve as load-transmitting regions. During foraging, these structures have to withstand high stresses without structural failure and without a high degree of wear. Mechanisms contributing to this failure- and wear-resistance were well studied in the heavily mineralized teeth of Polyplacophora and Patellogastropoda, but for the rather chitinous teeth of non-limpet snails, we are confronted with a large gap in data. The work presented here on the paludomid gastropod Lavigeria grandis aims to shed some light on radular tooth composition and its contribution to failure- and wear-prevention in this type of radula. The teeth were fractured and the micro-cracks studied in detail by scanning electron microscopy, revealing layers within the teeth. Two layers of distinct fibre densities and orientations were detected, covered by a thin layer containing high proportions of calcium and silicon, as determined by elemental dispersive X-ray spectroscopy. Our results clearly demonstrate the presence of failure- and wear-prevention mechanisms in snail radulae without the involvement of heavy mineralization-rendering this an example of a highly functional biological lightweight structure. This article is part of the theme issue 'Nanocracks in nature and industry'.

Peptide-based assembled nanostructures that can direct cellular responses

Natural originated materials have been well-studied over the past several decades owing to their higher biocompatibility compared to the traditional polymers. Peptides, consisting of amino acids, are among the most popular programable building blocks, which is becoming a growing interest in nanobiotechnology. Structures assembled using those biomimetic peptides allow the exploration of chemical sequences beyond those been routinely used in biology. In this Review, we discussed the most recent experimental discoveries on the peptide-based assembled nanostructures and their potential application at the cellular level such as drug delivery. In particular, we explored the fundamental principles of peptide self-assembly and the most recent development in improving their interactions with biological systems. We believe that as the fundamental knowledge of the peptide assemblies evolves, the more sophisticated and versatile nanostructures can be built, with promising biomedical applications.

Molecular Insights into the Self-Assembly of Block Copolymer Suckerin Polypeptides into Nanoconfined β-Sheets

Suckerin in squid sucker ring teeth is a block-copolymer peptide comprised of two repeating modules-the alanine and histidine-rich M1 and the glycine-rich M2. Suckerin self-assemblies display excellent thermo-plasticity and pH-responsive properties, along with the high biocompatibility, biodegradability, and sustainability. However, the self-assembly mechanism and the detailed role of each module are still elusive, limiting the capability of applying and manipulating such biomaterials. Here, the self-assembly dynamics of the two modules and two minimalist suckerin-mimetic block-copolymers, M1-M2-M1 and M2-M1-M2, in silico is investigated. The simulation results demonstrate that M2 has a stronger self-association but weaker β-sheet propensities than M1. The high self-assembly propensity of M2 allows the minimalist block-copolymer peptides to coalesce with microphase separation, enabling the formation of nanoconfined β-sheets in the matrix formed by M1-M2 contacts. Since these glycine-rich fragments with scatted hydrophobic and aromatic residues are building blocks of many other block-copolymer peptides, the study suggests that these modules function as the "molecular glue" in addition to the flexible linker or spacer to drive the self-assembly and microphase separation. The uncovered molecular insights may help understand the structure and function of suckerin and also aid in the design of functional block-copolymer peptides for nanotechnology and biomedicine applications.

Evolutionary development of the cephalopod arm armature: a review

The cephalopod arm armature is certainly one of the most important morphological innovations responsible for the evolutionary success of the Cephalopoda. New palaeontological discoveries in the recent past afford to review and reassess origin and homology of suckers, sucker rings, hooks, and cirri. Since a priori character state reconstructions are still ambiguous, we suggest and discuss three different evolutionary scenarios. Each of them is based on the following assumptions: (1) Neocoleoidea uniting extant Decabrachia and Octobrachia is monophyletic (= proostracum-bearing coleoids); (2) extinct Belemnitida and Diplobelida are stem decabrachians; (3) proostracum-less coleoids (Hematitida, Donovaniconida, Aulacoceratida) represent stem-neocoleoids; (4) Ammonoidea and Bactritoidea are stem coleoids. We consider a scenario where belemnoid hooks derived from primitive suckers as well-supported. Regarding belemnoid hooks and suckers as homologues implies that belemnoid, oegopsid, and probably ammonoid arm hooks arose through parallel evolution. Our conclusions challenge the widespread opinion, whereupon belemnoid hooks evolved de novo, and instead support earlier ideas formulated by Sigurd von Boletzky.

Diverse silk and silk-like proteins derived from terrestrial and marine organisms and their applications

Organisms develop unique systems in a given environment. In the process of adaptation, they employ materials in a clever way, which has inspired mankind extensively. Understanding the behavior and material properties of living organisms provides a way to emulate these natural systems and engineer various materials. Silk is a material that has been with human for over 5000 years, and the success of mass production of silkworm silk has realized its applications to medical, pharmaceutical, optical, and even electronic fields. Spider silk, which was characterized later, has expanded the application sectors to textile and military materials based on its tough mechanical properties. Because silk proteins are main components of these materials and there are abundant creatures producing silks that have not been studied, the introduction of new silk proteins would be a breakthrough of engineering materials to open innovative industry fields. Therefore, in this review, we present diverse silk and silk-like proteins and how they are utilized with respect to organism's survival. Here, the range of organisms are not constrained to silkworms and spiders but expanded to other insects, and even marine creatures which produce silk-like proteins that are not observed in terrestrial silks. This viewpoint broadening of silk and silk-like proteins would suggest diverse targets of engineering to design promising silk-based materials. STATEMENT OF SIGNIFICANCE: Silk has been developed as a biomedical material due to unique mechanical and chemical properties. For decades, silks from various silkworm and spider species have been intensively studied. More recently, other silk and silk-like proteins with different sequences and structures have been reported, not only limited to terrestrial organisms (honeybee, green lacewing, caddisfly, and ant), but also from marine creatures (mussel, squid, sea anemone, and pearl oyster). Nevertheless, there has hardly been well-organized literature on silks from such organisms. Regarding the relationship among sequence-structure-properties, this review addresses how silks have been utilized with respect to organism's survival. Finally, this information aims to improve the understanding of diverse silk and silk-like proteins which can offer a significant interest to engineering fields.

Bioinspired short peptide hydrogel for versatile encapsulation and controlled release of growth factor therapeutics

A short bioinspired octapeptide, GV8, can self-assemble under mild conditions into biodegradable supramolecular physical hydrogels with high storage modulus and good biocompatibility. GV8 hydrogels can encapsulate both single or multiple macromolecular protein-based therapeutics in a simple one-pot formulation manner, making it a promising candidate to address challenges faced by existing synthetic polymer or peptide hydrogels with complex gelation and drug-encapsulation processes. Alongside its versatility, the hydrogel exhibits concentration-dependent storage modulus and controlled drug-release action. We demonstrate that GV8 hydrogels loaded with adipose-derived mesenchymal stem cells (ADMSC) secretome remain mechanically robust, and exhibit promising potential for wound healing applications by preserving secretome activity while maintaining a constant supply of ADMSC secretome to promote epithelial cell migration. Overall, our work highlights the potential of GV8 peptide hydrogel as a versatile and safe carrier for encapsulation and delivery of macromolecular therapeutics. STATEMENT OF SIGNIFICANCE: Supramolecular peptide hydrogels are a popular choice for protein-based macromolecular therapeutics delivery; however, despite the development of abundant hydrogel systems, several challenges limit their adaptability and practical applications. GV8 short peptide hydrogel circumvents these drawbacks and demonstrates the ability to function as a versatile growth factor (GF) encapsulant. It can encapsulate precise concentrations of complex adipose-derived mesenchymal stem cells secretome mixtures with a one-pot formulation approach and perform controlled release of GFs with preserved activity without compromising the self-assembly and mechanical properties of the hydrogel's supramolecular network. The significance of GV8 hydrogel lies in its gelation simplicity and versatility to encapsulate and deliver macromolecular therapeutics, thus representing a promising biomaterial for regenerative medicine applications.

Counterplotting the Mechanosensing-Based Fouling Mechanism of Mussels against Fouling

Marine organisms react to various factors when building colonies for survival; however, severe accumulation of diverse organisms on artificial structures located close to water causes large industrial losses. Herein, we identify a concept in the development of antifouling surfaces based on understanding the surface stiffness recognition procedure of mussel adhesion at the genetic level. It was found that on a soft surface the combination of decreased adhesive plaque size, adhesion force, and plaque protein downregulation synergistically weakens mussel wet adhesion and sometimes prevents mussels from anchoring, mainly due to transcriptional changes within the mechanosensing pathway and the adhesive proteins in secretory glands. In addition, the use of soft substrates or antagonists of surface mechanosensing behavior suppresses mussel fouling significantly.

Mechanical property gradients of taenioglossan radular teeth are associated with specific function and ecological niche in Paludomidae (Gastropoda: Mollusca)

Biological tissues may exhibit graded heterogeneities in structure and mechanical properties that are crucial to their function. One biological structure that shows variation in both structure and function is the molluscan radula: the organ comprises a chitinous membrane with embedded teeth and serves to process and gather food. The tooth morphologies had been well studied in the last decades, but the mechanical properties of the teeth are not known for the vast majority of molluscs. This knowledge gap restricts our understanding of how the radula is able to act effectively on a target surface whilst simultaneously resisting structural failure. Here we employed nanoindentation technique to measure mechanical properties (hardness and Young's modulus) on distinct localities of individual radular teeth from 24 species of African paludomid gastropods. These species have distinct ecological niches as they forage on algae on different feeding substrates. A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. The presence or absence of large-scale gradients in these taenioglossan teeth could directly be linked with their specific function and in general with the species ecology, whereas the radular tooth morphologies do not always and fully reflect ecology. STATEMENT OF SIGNIFICANCE: African Lake Tanganyika is well known for harbouring endemic and morphologically distinct genera. Its paludomid gastropods form a flock of high interest because of its diversity. As they show distinct radular tooth morphologies hypotheses about potential trophic specializations had always been at hand. Here we evaluated the mechanical properties Young's modulus and hardness of 9027 individual teeth from 24 species along the tooth by nanoindentation and related them with the gastropods' specific feeding substrate. We find that hard substrate feeders have teeth that are hard at the tips but much less stiff at the base and thus heterogeneous with respect to material properties, whereas soft substrate feeders have teeth that are flexible and homogenous with respect to material properties.

Nanocapsules Produced by Nanoprecipitation of Designed Suckerin-Silk Fusion Proteins

Herein, we report on the precise design of a modular fusion protein amenable to the construction of nanocapsules by nanoprecipitation. The central squid suckerin-derived peptide block provides structural stability, whereas both termini from spider silk fibroins make the protein highly soluble at physiological pH, a critical requirement for the nanoprecipitation process. With this design, nanocapsules consisting of fusion protein shells and oily cores with sizes in the range of 190-250 nm are built in a straightforward manner.

Recent Advances in Biopolymeric Composite Materials for Tissue Engineering and Regenerative Medicines: A Review

The polymeric composite material with desirable features can be gained by selecting suitable biopolymers with selected additives to get polymer-filler interaction. Several parameters can be modified according to the design requirements, such as chemical structure, degradation kinetics, and biopolymer composites' mechanical properties. The interfacial interactions between the biopolymer and the nanofiller have substantial control over biopolymer composites' mechanical characteristics. This review focuses on different applications of biopolymeric composites in controlled drug release, tissue engineering, and wound healing with considerable properties. The biopolymeric composite materials are required with advanced and multifunctional properties in the biomedical field and regenerative medicines with a complete analysis of routine biomaterials with enhanced biomedical engineering characteristics. Several studies in the literature on tissue engineering, drug delivery, and wound dressing have been mentioned. These results need to be reviewed for possible development and analysis, which makes an essential study.

Characterizing and Controlling Nanoscale Self-Assembly of Suckerin-12

Structural proteins such as "suckerins" present promising avenues for fabricating functional materials. Suckerins are a family of naturally occurring block copolymer-type proteins that comprise the sucker ring teeth of cephalopods and are known to self-assemble into supramolecular networks of nanoconfined β-sheets. Here, we report the characterization and controllable, nanoscale self-assembly of suckerin-12 (S12). We characterize the impacts of salt, pH, and protein concentration on S12 solubility, secondary structure, and self-assembly. In doing so, we identify conditions for fabricating ∼100 nm nanoassemblies (NAs) with narrow size distributions. Finally, by installing a noncanonical amino acid (ncAA) into S12, we demonstrate the assembly of NAs that are covalently conjugated with a hydrophobic fluorophore and the ability to change self-assembly and β-sheet content by PEGylation. This work presents new insights into the biochemistry of suckerin-12 and demonstrates how ncAAs can be used to expedite and fine-tune the design of protein materials.

Marine Structural Protein Stability Induced by Hofmeister Salt Annealing and Enzymatic Cross-Linking

The Humboldt squid is one of the fiercest marine predators thanks in part to its sucker ring teeth that are biopolymer blends of a protein isoform family called suckerin with compression strength that rivals silkworm silk. Here, we focus on the popular suckerin-12 isoform to understand what makes the secondary structure of this biopolymer different in water and the potential role of diverse physical and chemical cross-linkings. By choosing a salt post-treatment, in accordance with the Hofmeister series, we achieved film stability with salt annealing that is comparable to chemical cross-links. By correlating the film morphology with the protein secondary structure changes, suckerin-12 films were shown to contract upon treatment with kosmotropic salts and exhibited increased stability in water. These changes are related to the rearrangement of suckerin-12 secondary structure from random coils and helices to β-sheets. Overall, understanding secondary structure changes caused by aqueous and ionic environments can be instructive for the tuning of the suckerin film sclerotization, its conversion to a tough biological material, and to ultimately produce the natural squid sucker ring teeth.

Light, Strong, and Ductile Architectures Achieved by Silk Fiber "Welding" Processing

Light, strong, and ductile materials (LSDMs) are desired in many emerging fields, such as biomedicine, aerospace industries, and structural engineering materials. However, producing such materials remains a significant challenge because their structures cannot confer the desired mechanical properties. In this study, we developed a silk fiber "welding" strategy to construct bioinspired LSDMs. The key to the welding process is to etch the surface of silk fiber through a partial dissolution process. The dissolved silk proteins further serve as welding materials or glues to bond the silk fibers together. Remarkably, these silk-LSDMs are not only lightweight (with the densities of around 0.28 g cm^-3) but also strong and tough. Their compression strength reaches up to 13.8 ± 3.4 MPa, which is higher than those of most natural and engineered porous materials. These favorable structural and mechanical characteristics, together with outstanding biocompatibility of silk proteins, render these silk-LSDMs applicable in regenerated engineered tissues and water treatment materials.

Thermo- and pH-responsive fibrillization of squid suckerin A1H1 peptide

Stimuli-responsive smart materials have attracted considerable attention with numerous applications in nanotechnology, sensing, and biomedicine. Suckerin family proteins found in squid ring teeth represent such a class of peptide-based smart materials with their self-assemblies featuring excellent thermo-plasticity and pH-dependence. Similar to block copolymers, suckerin proteins are comprised of two repeating sequence motifs, where M1 motifs are abundant in alanine and histidine residues and M2 are rich in glycine. Experimental studies of suckerin assemblies suggested that M1 regions mainly formed nano-confined β-sheets within an amorphous matrix made of M2 modules stabilizing these β-rich nano-assemblies. The histidine-containing M1 modules are believed to govern the pH- and temperature-sensitive properties of suckerin assemblies. To better understand the stimuli-responsive properties of suckerin assemblies at the molecular level, we systematically studied the self-assembly dynamics of A1H1 peptides - a representative M1 sequence - at different temperatures and pH conditions with atomistic discrete molecular dynamic simulations. Our simulations with twenty A1H1 peptides demonstrated that below the transition temperature Tagg, they could readily self-assemble from isolated monomers into well-defined β-sheet nanostructures by both primary and secondary nucleation of β-sheets and subsequent aggregation growth via elongation and coagulation. Interestingly, the dissociation of pre-formed A1H1 β-sheet nanostructures featured a melting temperature Tm higher than Tagg, exhibiting the thermal hysteresis that is characteristic of first-order phase transitions with high energy barriers. In acidic environments where all histidine residues were protonated, the stability of the A1H1 β-sheet nano-assemblies was reduced and the β-rich assemblies easily dissociated into unstructured monomers at significantly lower temperatures than in the neutral solution. The computationally derived molecular mechanisms for pH- and temperature-dependent A1H1 self-assembly will help to understand the supramolecular assembly structures and functions of the large suckerin family and aid in the future design of peptide-based stimuli-responsive smart materials.

A Short Peptide Hydrogel with High Stiffness Induced by 310-Helices to β-Sheet Transition in Water

Biological gels generally require polymeric chains that produce long-lived physical entanglements. Low molecular weight colloids offer an alternative to macromolecular gels, but often require ad-hoc synthetic procedures. Here, a short biomimetic peptide composed of eight amino acid residues derived from squid sucker ring teeth proteins is demonstrated to form hydrogel in water without any cross-linking agent or chemical modification and exhibits a stiffness on par with the stiffest peptide hydrogels. Combining solution and solid-state NMR, circular dichroism, infrared spectroscopy, and X-ray scattering, the peptide is shown to form a supramolecular, semiflexible gel assembled from unusual right-handed 310-helices stabilized in solution by π-π stacking. During gelation, the 310-helices undergo conformational transition into antiparallel β-sheets with formation of new interpeptide hydrophobic interactions, and molecular dynamic simulations corroborate stabilization by cross β-sheet oligomerization. The current study broadens the range of secondary structures available to create supramolecular hydrogels, and introduces 310-helices as transient building blocks for gelation via a 310-to-β-sheet conformational transition.

Nature of Amorphous Hydrophilic Block Affects Self-Assembly of an Artificial Viral Coat Polypeptide

Consensus motifs for sequences of both crystallizable and amorphous blocks in silks and natural structural analogues of silks vary widely. To design novel silklike polypeptides, an important question is therefore how the nature of either the crystallizable or the amorphous block affects the self-assembly and resulting physical properties of silklike polypeptides. We address herein the influence of the amorphous block on the self-assembly of a silklike polypeptide that was previously designed to encapsulate single DNA molecules into rod-shaped viruslike particles. The polypeptide has a triblock architecture, with a long N-terminal amorphous block, a crystallizable midblock, and a C-terminal DNA-binding block. We compare the self-assembly behavior of a triblock with a very hydrophilic collagen-like amorphous block (GXaaYaa)132 to that of a triblock with a less hydrophilic elastin-like amorphous block (GSGVP)80. The amorphous blocks have similar lengths and both adopt a random coil structure in solution. Nevertheless, atomic force microscopy revealed significant differences in the self-assembly behavior of the triblocks. If collagen-like amorphous blocks are used, there is a clear distinction between very short polypeptide-only fibrils and much longer fibrils with encapsulated DNA. If elastin-like amorphous blocks are used, DNA is still encapsulated, but the polypeptide-only fibrils are now much longer and their size distribution partially overlaps with that of the encapsulated DNA fibrils. We attribute the difference to the more hydrophilic nature of the collagen-like amorphous block, which more strongly opposes the growth of polypeptide-only fibrils than the elastin-like amorphous blocks. Our work illustrates that differences in the chemical nature of amorphous blocks can strongly influence the self-assembly and hence the functionality of engineered silklike polypeptides.

Marine-Inspired Polymers in Medical Adhesion

Medical adhesives that are strong, easy to apply and biocompatible are promising alternatives to sutures and staples in a large variety of surgical and clinical procedures. Despite progress in the development and regulatory approval of adhesives for use in the clinic, adhesion to wet tissue remains challenging. Marine organisms have evolved a diverse set of highly effective wet adhesive approaches that have inspired the design of new medical adhesives. Here we provide an overview of selected marine animals and their chemical and physical adhesion strategies, the state of clinical translation of adhesives inspired by these organisms, and target applications where marine-inspired adhesives can have a significant impact. We will focus on medical adhesive polymers inspired by mussels, sandcastle worms, and cephalopods, emphasize the history of bioinspired medical adhesives from the peer reviewed and patent literature, and explore future directions including overlooked sources of bioinspiration and materials that exploit multiple bioinspired strategies.

Reclamation of Fishery Processing Waste: A Mini-Review

: Seafood such as fish, shellfish, and squid are a unique source of nutrients. However, many marine processing byproducts, such as viscera, shells, heads, and bones, are discarded, even though they are rich sources of structurally diverse bioactive nitrogenous components. Based on emerging evidence of their potential health benefits, these components show significant promise as functional food ingredients. Fish waste components contain significant levels of high-quality protein, which represents a source for biofunctional peptide mining. The chitin contained in shrimp shells, crab shells, and squid pens may also be of value. The components produced by bioconversion are reported to have antioxidative, antimicrobial, anticancer, antihypertensive, antidiabetic, and anticoagulant activities. This review provides an overview of the extraordinary potential of processing fish and chitin-containing seafood byproducts via chemical procedures, enzymatic and fermentation technologies, and chemical modifications, as well as their applications.

Biological composites-complex structures for functional diversity

The bulk of Earth's biological materials consist of few base substances-essentially proteins, polysaccharides, and minerals-that assemble into large varieties of structures. Multifunctionality arises naturally from this structural complexity: An example is the combination of rigidity and flexibility in protein-based teeth of the squid sucker ring. Other examples are time-delayed actuation in plant seed pods triggered by environmental signals, such as fire and water, and surface nanostructures that combine light manipulation with mechanical protection or water repellency. Bioinspired engineering transfers some of these structural principles into technically more relevant base materials to obtain new, often unexpected combinations of material properties. Less appreciated is the huge potential of using bioinspired structural complexity to avoid unnecessary chemical diversity, enabling easier recycling and, thus, a more sustainable materials economy.

Controlling Supramolecular Chiral Nanostructures by Self-Assembly of a Biomimetic β-Sheet-Rich Amyloidogenic Peptide

Squid sucker ring teeth (SRT) have emerged as a promising protein-only, thermoplastic biopolymer with an increasing number of biomedical and engineering applications demonstrated in recent years. SRT is a supra-molecular network whereby a flexible, amorphous matrix is mechanically reinforced by nanoconfined β-sheets. The building blocks for the SRT network are a family of suckerin proteins that share a common block copolymer architecture consisting of amorphous domains intervened by smaller, β-sheet forming modules. Recent studies have identified the peptide A1H1 (peptide sequence AATAVSHTTHHA) as one of the most abundant β-sheet forming domains within the suckerin protein family. However, we still have little understanding of the assembly mechanisms by which the A1H1 peptide may assemble into its functional load-bearing domains. In this study, we conduct a detailed self-assembly study of A1H1 and show that the peptide undergoes β-strands-driven elongation into amyloid-like fibrils with a rich polymorphism. The nanostructure of the fibrils was elucidated by small and wide-angle X-ray scattering (SAXS and WAXS) and atomic force microscopy (AFM). The presence of His-rich and Ala-rich segments results in an amphiphilic behavior and drives its assembly into fibrillar supramolecular chiral aggregates with helical ribbon configuration in solution, with the His-rich region exposed to the solvent molecules. Upon increase in concentration, the fibrils undergo gel formation, while preserving the same mesoscopic features. This complex phase behavior suggests that the repeat peptide modules of suckerins may be manipulated beyond their native biological environment to produce a wider variety of self-assembled amyloid-like nanostructures.

Injectable network biomaterials via molecular or colloidal self-assembly

Self-assembly is a powerful tool to create functional materials. A specific application for which self-assembled materials are ideally suited is in creating injectable biomaterials. Contrasting with traditional biomaterials that are implanted through surgical means, injecting biomaterials through the skin offers numerous advantages, expanding the scope and impact for biomaterials in medicine. In particular, self-assembled biomaterials prepared from molecular or colloidal interactions have been frequently explored. The strategies to create these materials are varied, taking advantage of engineered oligopeptides, proteins, and nanoparticles as well as affinity-mediated crosslinking of synthetic precursors. Self-assembled materials typically facilitate injectability through two different mechanisms: i) in situ self-assembly, whereby materials would be administered in a monomeric or oligomeric form and self-assemble in response to some physiologic stimulus, or ii) self-assembled materials that, by virtue of their dynamic, non-covalent interactions, shear-thin to facilitate flow within a syringe and subsequently self-heal into its reassembled material form at the injection site. Indeed, many classes of materials are capable of being injected using a combination of these two mechanisms. Particular utility has been noted for self-assembled biomaterials in the context of tissue engineering, regenerative medicine, drug delivery, and immunoengineering. Given the controlled and multifunctional nature of many self-assembled materials demonstrated to date, we project a future where injectable self-assembled biomaterials afford improved practice in advancing healthcare.

Supramolecular propensity of suckerin proteins is driven by β-sheets and aromatic interactions as revealed by solution NMR

The solution structure of a suckerin protein obtained by NMR illustrates β-sheet conformation with stabilising aromatic interactions in dynamic domains.

Squid Suckerin Biomimetic Peptides Form Amyloid-like Crystals with Robust Mechanical Properties

We present the self-assembly of fibers formed from a peptide sequence (A1H1) derived from suckerin proteins of squid sucker ring teeth (SRT). SRT are protein-only biopolymers with an unconventional set of physicochemical and mechanical properties including high elastic modulus coupled with thermoplastic behavior. We have identified a conserved peptide building block from suckerins that possess the ability to assemble into materials with similar mechanical properties as the native SRT. A1H1 displays amphiphilic characteristics and self-assembles from the bottom-up into mm-scale fibers initiated by the addition of a polar aprotic solvent. A1H1 fibers are thermally resistant up to 239 °C, coupled with an elastic modulus of ∼7.7 GPa, which can be explained by the tight packing of β-sheet-enriched crystalline building blocks as identified by wide-angle X-ray scattering (WAXS), with intersheet and interstrand distances of 5.37 and 4.38 Å, respectively. A compact packing of the peptides at their Ala-rich terminals within the fibers was confirmed from molecular dynamics simulations, and we propose a hierarchical model of fiber assembly of the mature peptide fiber.

Squid suckerin microneedle arrays for tunable drug release

Microneedles are increasingly used in transdermal delivery of therapeutic agents due to the elimination of first-pass metabolism, simplicity of operation, and lack of pain, which collectively lead to improved patient compliance. However, microneedles are still met by challenges with regard to the choice of biocompatible materials and the control of drug release profiles. Herein, we tackle these limitations by producing microneedles from a biocompatible robust biopolymer, namely squid sucker ring teeth (SRT) proteins (suckerins), using a soft lithography method. Taking advantage of the modular sequence design of suckerins leading to their self-assembly into β-sheet enriched structures, suckerin microneedles display an accurate replication of their templates with robust mechanical properties, endowing them with a high skin penetration capability. Critically, the β-sheet content in the microneedles can be modulated by varying the solvent conditions, which allows tuning of the mechanical response, and in turn the drug release rates by more than one order of magnitude. In vitro skin permeation studies of suckerin microneedles using human cadaver skin samples suggest a fast onset and enhanced skin permeation of drugs compared to flat patches. The skin permeation can also be tailored 10-fold by applying hydrogen bond disruptor solutions. As a proof-of-concept, the anti-bacterial drug kanamycin is encapsulated within the microneedles, leading to efficient anti-bacterial activity and offering an additional benefit to further minimize the risk of infections caused by microneedle-based drug delivery systems. Lastly, suckerin microneedles are found to be biocompatible in cell culture studies, opening the door to further clinical applications.

Supramolecular β-Sheets Stabilized Protein Nanocarriers for Drug Delivery and Gene Transfection

Suckerin proteins, recently discovered in the sucker ring teeth of squids, represent a family of promising structural biomacromolecules that can form supramolecular networks stabilized by nanoconfined β-sheets. Exploiting this feature as well as their specific amino acid composition, we demonstrate that artificial suckerin-19 (S-19) can be engineered into nanocarriers for efficient drug delivery and gene transfection in vitro and in vivo. First, we demonstrate that S-19 self-assembles into β-sheet stabilized nanoparticles with controlled particle sizes of 100-200 nm that are able to encapsulate hydrophobic drugs for pH-dependent release in vitro, and that can effectively inhibit tumor growth in vivo. We also show that S-19 can complex and stabilize plasmid DNA, with the complexes stabilized by hydrophobic interactions of the β-sheet domains as opposed to electrostatic interactions commonly achieved with cationic polymers, thus lowering cytotoxicity. The elevated Histidine content of S-19 appears critical to trigger endosomal escape by the proton sponge effect, thereby ensuring efficient gene transfection both in vitro and in vivo. Our study demonstrates that S-19 represents a promising functional protein nanocarrier that could be used for various drug and gene delivery applications.