Multi-scale thermal stability of a hard thermoplastic protein-based material

Bioinspired Squid Peptides─A Tale of Curiosity-Driven Research Leading to Unforeseen Biomedical Applications

The molecular design of many peptide-based materials originates from structural proteins identified in living organisms. Prominent examples that have garnered broad interdisciplinary research interest (chemistry, materials science, bioengineering, etc.) include elastin, silk, or mussel adhesive proteins. The critical first steps in this type of research are to identify a convenient model system of interest followed by sequencing the prevailing proteins from which these biological structures are assembled. In our laboratory, the main model systems for many years have been the hard biotools of cephalopods, particularly their parrot-like tough beak and their sucker ring teeth (SRT) embedded within the sucker cuptions that line the interior surfaces of their arms and tentacles. Unlike the majority of biological hard tissues, these structures are devoid of biominerals and consist of protein/polysaccharide biomolecular composites (the beak) or, in the case of SRT, are entirely made of proteins that are assembled by supramolecular interactions.In this Account, we chronicle our journey into the discovery of these intriguing biological materials. We initially focus on their excellent mechanical robustness followed by the identification and sequencing of the structural proteins from which they are built, using the latest "omics" techniques including next-generation sequencing and high-throughput proteomics. A common feature of these proteins is their modular architecture at the molecular level consisting of short peptide repeats. We describe the molecular design of these peptide building blocks, highlighting the consensus motifs identified to play a key role in biofabrication and in regulating the mechanical properties of the macroscopic biological material. Structure/property relationships unveiled through advanced spectroscopic and scattering techniques, including Raman, infrared, circular dichroism, and NMR spectroscopies as well as wide-angle and small-angle X-ray scattering, are also discussed.We then present recent developments in exploiting the discovered molecular designs to engineer peptides and their conjugates for promising biomedical applications. One example includes short peptide hydrogels that self-assemble entirely under aqueous conditions and simultaneously encapsulate large macromolecules during the gelation process. A second example involves peptide coacervate microdroplets produced by liquid-liquid phase separation. These microdroplets are capable of recruiting and delivering large macromolecular therapeutics (genes, mRNA, proteins, peptides, CRISPR/Cas 9 modalities, etc.) into mammalian cells, which introduces exciting prospects in cancer, gene, and immune therapies.This Account also serves as a testament to how curiosity-driven explorations, which may lack an obvious practical goal initially, can lead to discoveries with unexpected and promising translational potential.

Heteroatom Introduction to Reconstruct Interfacial Chemical Structures for High-Reliability CFRTP/A6061-T6 Hybrid Structures

The application of carbon-fiber-reinforced thermoplastic (CFRTP)/metal hybrid structures is a vital step for realizing the lightweight design concepts in aerospace. However, the CFRTP/metal hybrid structures are usually not reliable enough in practical applications due to the high differences in chemical and physical properties between these two materials. The current work provides a bottom-up strategy of introducing heteroatoms into CFRTP/metal interfaces to reconstruct the interfacial chemical structures and thus manufacture high-reliability hybrid structures. Based on the principle of utmost using reaction sites at metal surfaces, the heteroatoms of oxygen and hydrogen are specially designed and introduced to the CFRTP/A6061-T6 (6061) interfaces by simple and green plasma polymerization. The introduced oxygen and hydrogen heteroatoms react with the aluminum and oxygen of the oxidation film at 6061 surfaces to produce great interfacial Al-O covalencies and hydrogen bonds. The reconstructing interfacial chemical structures strengthen the joint strength of CFRTP/6061 hybrid structures from 8.82 to 23.97 MPa. Our heteroatom introduction strategy is expected to get a fresh insight into the interfacial design concept and has several important implications for the future application of high-reliability CFRTP/metal hybrid structures.

Protein-Based Biological Materials: Molecular Design and Artificial Production

Polymeric materials produced from fossil fuels have been intimately linked to the development of industrial activities in the 20th century and, consequently, to the transformation of our way of living. While this has brought many benefits, the fabrication and disposal of these materials is bringing enormous sustainable challenges. Thus, materials that are produced in a more sustainable fashion and whose degradation products are harmless to the environment are urgently needed. Natural biopolymers─which can compete with and sometimes surpass the performance of synthetic polymers─provide a great source of inspiration. They are made of natural chemicals, under benign environmental conditions, and their degradation products are harmless. Before these materials can be synthetically replicated, it is essential to elucidate their chemical design and biofabrication. For protein-based materials, this means obtaining the complete sequences of the proteinaceous building blocks, a task that historically took decades of research. Thus, we start this review with a historical perspective on early efforts to obtain the primary sequences of load-bearing proteins, followed by the latest developments in sequencing and proteomic technologies that have greatly accelerated sequencing of extracellular proteins. Next, four main classes of protein materials are presented, namely fibrous materials, bioelastomers exhibiting high reversible deformability, hard bulk materials, and biological adhesives. In each class, we focus on the design at the primary and secondary structure levels and discuss their interplays with the mechanical response. We finally discuss earlier and the latest research to artificially produce protein-based materials using biotechnology and synthetic biology, including current developments by start-up companies to scale-up the production of proteinaceous materials in an economically viable manner.

A Conceptual Strategy toward High-Reliability Metal-Thermoplastic Hybrid Structures Based on a Covalent-Bonding Mechanism

Metal-thermoplastic hybrid structures have proven their effectiveness to achieve lightweight design concepts in both primary and secondary structural components of advanced aircraft. However, the drastic differences in physical and chemical properties between metal and thermoplastic make it challenging to fabricate high-reliability hybrid structures. Here, a simple and universal strategy to obtain strong hybrid structures thermoplastics is reported by regulating the bonding behavior at metal/thermoplastic interfaces. To achieve such, we first researched and uncovered the bonding mechanism at metal/thermoplastic interfaces by experimental methods and density functional theory (DFT) calculations. The results suggest that the interfacial covalency, which is formed due to the interfacial reaction between high-electronegativity elements of thermoplastics and metallic elements at metal surfaces, dominates the interfacial bonding interaction of metal-thermoplastic hybrid structures. The differences in electronegativity and atomic size between bonding atoms influence the covalent-bond strength and finally control the interfacial reliability of hybrid structures. Based on our covalent-bonding mechanism, the carboxyl functional group (COOH) is specifically grafted on polyetheretherketone (PEEK) by plasma polymerization to increase the density and strength of interfacial covalency and thus fabricate high-reliability hybrid structures between PEEK and A6061-T6 aluminum alloy. Current work provides an in-depth understanding of the bonding mechanism at metal-thermoplastics interfaces, which opens a fascinating direction toward high-reliability metal-thermoplastic hybrid structures.

In-situ forming hydrogel based on thiolated chitosan/carboxymethyl cellulose (CMC) containing borate bioactive glass for wound healing

Suitable wound dressings for accelerating wound healing are actively being designed and synthesised. In this study, thiolated chitosan (tCh)/oxidized carboxymethyl cellulose (OCMC) hydrogel containing Cu-doped borate bioglass (BG) was developed as a wound dressing to improve wound healing in a full-thickness skin defect of mouse animal model. Thiolation was used to incorporate thiol groups into chitosan (Ch) to enhance its water solubility and mucoadhesion characteristics. Here, the in situ forming hydrogel was successfully developed using the Schiff-based reaction, and its physio-chemical and antibacterial characteristics were examined. Borate BG was also incorporated in the generated hydrogel to promote angiogenesis and tissue regeneration at the wound site. Investigations of in vitro cytotoxicity assays demonstrated that the synthesised hydrogels showed good biocompatibility and promoted cell growth. These results inspired us to investigate the effectiveness of skin wound healing in a mouse model. On the backs of animals, two full-thickness wounds were created and treated utilising two different treatment conditions: (1) OCMC/tCh hydrogel, (2) OCMC/tCh/borate BG, and (3) control defect. The wound closure ratio, collagen deposition, and angiogenesis activity were measured after 14 days to determine the healing efficacy of the in situ hydrogels used as wound dressings. Overall, the hydrogel containing borate BG was maintained in the defect site, healing efficiency was replicable, and wound healing was apparent. In conclusion, we found consistent angiogenesis, remodelling, and accelerated wound healing, which we propose may have beneficial effects on the repair of skin defects.

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.

3D Printing of Monolithic Proteinaceous Cantilevers Using Regenerated Silk Fibroin

Silk fibroin, regenerated from Bombyx mori, has shown considerable promise as a printable, aqueous-based ink using a bioinspired salt-bath system in our previous work. Here, we further developed and characterized silk fibroin inks that exhibit concentration-dependent fluorescence spectra at the molecular level. These insights supported extrusion-based 3D printing using concentrated silk fibroin solutions as printing inks. 3D monolithic proteinaceous structures with high aspect ratios were successfully printed using these approaches, including cantilevers only supported at one end. This work provides further insight and broadens the utility of 3D printing with silk fibroin inks for the microfabrication of proteinaceous structures.

Biologically Safe, Degradable Self-Destruction System for On-Demand, Programmable Transient Electronics

The lifetime of transient electronic components can be programmed via the use of encapsulation/passivation layers or of on-demand, stimuli-responsive polymers (heat, light, or chemicals), but yet most research is limited to slow dissolution rate, hazardous constituents, or byproducts, or complicated synthesis of reactants. Here we present a physicochemical destruction system with dissolvable, nontoxic materials as an efficient, multipurpose platform, where chemically produced bubbles rapidly collapse device structures and acidic molecules accelerate dissolution of functional traces. Extensive studies of composites based on biodegradable polymers (gelatin and poly(lactic-co-glycolic acid)) and harmless blowing agents (organic acid and bicarbonate salt) validate the capability for the desired system. Integration with wearable/recyclable electronic components, fast-degradable device layouts, and wireless microfluidic devices highlights potential applicability toward versatile/multifunctional transient systems. In vivo toxicity tests demonstrate biological safety of the proposed system.

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.

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.

Amyloids: The History of Toxicity and Functionality

Proteins can perform their specific function due to their molecular structure. Partial or complete unfolding of the polypeptide chain may lead to the misfolding and aggregation of proteins in turn, resulting in the formation of different structures such as amyloid aggregates. Amyloids are rigid protein aggregates with the cross-β structure, resistant to most solvents and proteases. Because of their resistance to proteolysis, amyloid aggregates formed in the organism accumulate in tissues, promoting the development of various diseases called amyloidosis, for instance Alzheimer's diseases (AD). According to the main hypothesis, it is considered that the cause of AD is the formation and accumulation of amyloid plaques of Aβ. That is why Aβ-amyloid is the most studied representative of amyloids. Therefore, in this review, special attention is paid to the history of Aβ-amyloid toxicity. We note the main problems with anti-amyloid therapy and write about new views on amyloids that can play positive roles in the different organisms including humans.

Interaction of Squid (Dosidicus giga) Mantle Protein with a Mixtures of Potato and Corn Starch in an Extruded Snack, as Characterized by FTIR and DSC

The majority of snacks expanded by extrusion (SEE) are made with vegetable sources, to improve their nutritional content; it has been proposed to incorporate squid (Dosidicus gigas), due to its high protein content, low price and high availability. However, the interaction of proteins of animal origin with starch during extrusion causes negative effects on the sensory properties of SEE, so it is necessary to know the type of protein-carbohydrate interactions and their effect on these properties. The objective of this research was to study the interaction of proteins and carbohydrates of SEE elaborated with squid mantle, potato and corn. The nutritional composition and protein digestibility were evaluated, Fourier transform infrared (FTIR) and Differential Scanning Calorimetry (DSC) were used to study the formation of protein-starch complexes and the possible regions responsible for their interactions. The SEE had a high protein content (40-85%) and biological value (>93%). The melting temperature (Tm) was found between 145 and 225 °C; the Tm values in extruded samples are directly proportional to the squid content. The extrusion process reduced the amine groups I and II responsible for the protein-protein interaction and increased the O-glucosidic bonds, so these bonds could be responsible for the protein-carbohydrate interactions.

Recent Advances in 3D Printing with Protein-Based Inks

Three-dimensional (3D) printing is a transformative manufacturing strategy, allowing rapid prototyping, customization, and flexible manipulation of structure-property relationships. Proteins are particularly appealing to formulate inks for 3D printing as they serve as essential structural components of living systems, provide a support presence in and around cells and for tissue functions, and also provide the basis for many essential ex vivo secreted structures in nature. Protein-based inks are beneficial in vivo due to their mechanics, chemical and physical match to the specific tissue, and full degradability, while also to promoting implant-host integration and serving as an interface between technology and biology. Exploiting the biological, chemical, and physical features of protein-based inks can provide key opportunities to meet the needs of tissue engineering and regenerative medicine. Despite these benefits, protein-based inks impose nontrivial challenges to 3D printing such as concentration and rheological features and reconstitution of the structural hierarchy observed in nature that is a source of the robust mechanics and functions of these materials. This review introduces photo-crosslinking mechanisms and rheological principles that underpins a variety of 3D printing techniques. The review also highlights recent advances in the design, development, and biomedical utility of monolithic and composite inks from a range of proteins, including collagen, silk, fibrinogen, and others. One particular focus throughout the review is to introduce unique material characteristics of proteins, including amino acid sequences, molecular assembly, and secondary conformations, which are useful for designing printing inks and for controlling the printed structures. Future perspectives of 3D printing with protein-based inks are also provided to support the promising spectrum of biomedical research accessible to these materials.

Water-processable, biodegradable and coatable aquaplastic from engineered biofilms

Petrochemical-based plastics have not only contaminated all parts of the globe but are also causing potentially irreversible damage to our ecosystem, due to their non-biodegradability. As bioplastics are limited in number, there is an urgent need to design and develop more biodegradable alternatives to mitigate the plastic menace. In this regard, we report aquaplastic, a new class of microbial biofilm-based biodegradable bioplastic that is water-processable, robust, templatable and coatable. Herein, Escherichia coli was genetically engineered to produce protein-based hydrogels, which are cast and dried under ambient conditions to produce aquaplastic that can withstand strong acid/base and organic solvents. In addition, aquaplastic can be healed and welded to form three-dimensional architectures using water. The combination of straightforward microbial fabrication, water-processability, and biodegradability make aquaplastic a unique material worthy of further exploration for packaging and coating applications.

Sustainability in e-commerce packaging: A review

Online purchasing, and hence e-commerce packaging production and use, have grown steadily in recent years, and so has their environmental impact as a result. This paper reviews the evolution of packaging over the last century through a compilation of scientific literature on e-commerce packaging focusing on its environmental side. The primary aims were to identify research gaps in e-commerce packaging and to propose new research lines aimed at reducing its environmental impact. A systematic search of abstracts was conducted to identify articles dealing with sustainability in e-commerce packaging in order to better understand changes in materials and formats, identify problems such as oversizing and allow prospective readers to become acquainted with the latest innovations in materials, sustainability and logistics. Based on existing research, packaging materials and technology evolved rapidly until the 1990s. Later, however, it has become increasingly difficult to further reduce their cost and environmental impact. Also, some packaging products continue to be made from non-renewable materials and thus restrict growth of e-commerce. Further research is needed with a view to producing new packages from renewable sources such as cellulose-containing materials, which are widely available in nature, or from recycled cellulose-based materials such as cartonboard. Improving distribution processes with new, more effective tools could additionally help alleviate the environmental impact of packaging. Similarly, new production processes such as additive manufacturing and 3D printing might help optimize package volume and shape, thereby facilitating more sustainable production through, for example, reduced CO₂ emissions. Currently available technology can be useful to rethink the whole e-commerce packaging paradigm, which has changed very little over the past few decades.

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.

Half a century of amyloids: past, present and future

Amyloid diseases are global epidemics with profound health, social and economic implications and yet remain without a cure. This dire situation calls for research into the origin and pathological manifestations of amyloidosis to stimulate continued development of new therapeutics. In basic science and engineering, the cross-β architecture has been a constant thread underlying the structural characteristics of pathological and functional amyloids, and realizing that amyloid structures can be both pathological and functional in nature has fuelled innovations in artificial amyloids, whose use today ranges from water purification to 3D printing. At the conclusion of a half century since Eanes and Glenner's seminal study of amyloids in humans, this review commemorates the occasion by documenting the major milestones in amyloid research to date, from the perspectives of structural biology, biophysics, medicine, microbiology, engineering and nanotechnology. We also discuss new challenges and opportunities to drive this interdisciplinary field moving forward.

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.

3D Printing of Silk Protein Structures by Aqueous Solvent-Directed Molecular Assembly

Hierarchical molecular assembly is a fundamental strategy for manufacturing protein structures in nature. However, to translate this natural strategy into advanced digital manufacturing like three-dimensional (3D) printing remains a technical challenge. This work presents a 3D printing technique with silk fibroin to address this challenge, by rationally designing an aqueous salt bath capable of directing the hierarchical assembly of the protein molecules. This technique, conducted under aqueous and ambient conditions, results in 3D proteinaceous architectures characterized by intrinsic biocompatibility/biodegradability and robust mechanical features. The versatility of this method is shown in a diversity of 3D shapes and a range of functional components integrated into the 3D prints. The manufacturing capability is exemplified by the single-step construction of perfusable microfluidic chips which eliminates the use of supporting or sacrificial materials. The 3D shaping capability of the protein material can benefit a multitude of biomedical devices, from drug delivery to surgical implants to tissue scaffolds. This work also provides insights into the recapitulation of solvent-directed hierarchical molecular assembly for artificial manufacturing.

Converting Peanut Protein Biomass Waste into "Double Green" Meat Substitutes Using a High-Moisture Extrusion Process: A Multiscale Method to Explore a Process for Forming a Meat-Like Fibrous Structure

Converting peanut protein biomass waste into environmentally friendly meat substitutes by a high-moisture extrusion process can help solve both resource and waste problems and be "double green". A multiscale method combined with some emerging techniques such as atomic force microscopy-based infrared spectroscopy and X-ray microscopy was used to make the whole extrusion process visible to show the process of forming a meat-like fibrous structure using two-dimensional and three-dimensional perspectives. The results showed that the protein molecules underwent dramatic structural changes and unfolded in the extruder barrel, which created favorable conditions for molecular rearrangement in the subsequent zones. It was confirmed that the meat-like fibrous structure started to form at the junction of the die and the cooling zone and that this structure was caused by the phase separation and rearrangement of protein molecules in the cooling zone. Moreover, the interactions between hydrogen bonds and disulfide bonds formed in the cooling zone maintained the meat-like fibrous structure with an α-helix > β-sheet > β-turn > random coil. Of the two main peanut proteins, arachin played a greater role in forming the fibrous structure than conarachin, especially those subunits of arachin with a molecular weight of 42, 39, and 22 kDa.

Shear-Induced β-Crystallite Unfolding in Condensed Phase Nanodroplets Promotes Fiber Formation in a Biological Adhesive

Natural materials provide an increasingly important role model for the development and processing of next-generation polymers. The velvet worm Euperipatoides rowelli hunts using a projectile, mechanoresponsive adhesive slime that rapidly and reversibly transitions into stiff glassy polymer fibers following shearing and drying. However, the molecular mechanism underlying this mechanoresponsive behavior is still unclear. Previous work showed the slime to be an emulsion of nanoscale charge-stabilized condensed droplets comprised primarily of large phosphorylated proteins, which under mechanical shear coalesce and self-organize into nano- and microfibrils that can be drawn into macroscopic fibers. Here, we utilize wide-angle X-ray diffraction and vibrational spectroscopy coupled with in situ shear deformation to explore the contribution of protein conformation and mechanical forces to the fiber formation process. Although previously believed to be unstructured, our findings indicate that the main phosphorylated protein component possesses a significant β-crystalline structure in the storage phase and that shear-induced partial unfolding of the protein is a key first step in the rapid self-organization of nanodroplets into fibers. The insights gained here have relevance for sustainable production of advanced polymeric materials.

A compendium of current developments on polysaccharide and protein-based microneedles

Microneedles (MNs), i.e. minimally invasive three-dimensional microstructures that penetrate the stratum corneum inducing relatively little or no pain, have been studied as appealing therapeutic vehicles for transdermal drug delivery. Over the last years, the fabrication of MNs using biopolymers, such as polysaccharides and proteins, has sparked the imagination of scientists due to their recognized biocompatibility, biodegradability, ease of fabrication and sustainable character. Owing to their wide range of functional groups, polysaccharides and proteins enable the design and preparation of materials with tunable properties and functionalities. Therefore, these biopolymer-based MNs take a revolutionary step offering great potential not only in drug administration, but also in sensing and response to physiological stimuli. In this review, a critical and comprehensive overview of the polysaccharides and proteins employed in the design and engineering of MNs will be given. The strategies adopted for their preparation, their advantages and disadvantages will be also detailed. In addition, the potential and challenges of using these matrices to deliver drugs, vaccines and other molecules will be discussed. Finally, this appraisal ends with a perspective on the possibilities and challenges in research and development of polysaccharide and protein MNs, envisioning the future advances and clinical translation of these platforms as the next generation of drug delivery systems.

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.

Functional Polymers and Nanocomposites for 3D Printing of Smart Structures and Devices

Three-dimensional printing (3DP) has attracted a considerable amount of attention during the past years, being globally recognized as one of the most promising and revolutionary manufacturing technologies. Although the field is rapidly evolving with significant technological advancements, materials research remains a spotlight of interest, essential for the future developments of 3DP. Smart polymers and nanocomposites, which respond to external stimuli by changing their properties and structure, represent an important group of materials that hold a great promise for the fabrication of sensors, actuators, robots, electronics, and medical devices. The interest in exploring functional materials and their 3DP is constantly growing in an attempt to meet the ever-increasing manufacturing demand of complex functional platforms in an efficient manner. In this review, we aim to outline the recent advances in the science and engineering of functional polymers and nanocomposites for 3DP technologies. The report covers temperature-responsive polymers, polymers and nanocomposites with electromagnetic, piezoresistive and piezoelectric behaviors, self-healing polymers, light- and pH-responsive materials, and mechanochromic polymers. The main objective is to link the performance and functionalities to the fundamental properties, chemistry, and physics of the materials, and to the process-driven characteristics, in an attempt to provide a multidisciplinary image and a deeper understanding of the topic. The challenges and opportunities for future research are also discussed.

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.

Unraveling the Molecular Requirements for Macroscopic Silk Supercontraction

Spider dragline silk is a protein material that has evolved over millions of years to achieve finely tuned mechanical properties. A less known feature of some dragline silk fibers is that they shrink along the main axis by up to 50% when exposed to high humidity, a phenomenon called supercontraction. This contrasts the typical behavior of many other materials that swell when exposed to humidity. Molecular level details and mechanisms of the supercontraction effect are heavily debated. Here we report a molecular dynamics analysis of supercontraction in Nephila clavipes silk combined with in situ mechanical testing and Raman spectroscopy linking the reorganization of the nanostructure to the polar and charged amino acids in the sequence. We further show in our in silico approach that point mutations of these groups not only suppress the supercontraction effect, but even reverse it, while maintaining the exceptional mechanical properties of the silk material. This work has imminent impact on the design of biomimetic equivalents and recombinant silks for which supercontraction may or may not be a desirable feature. The approach applied is appropriate to explore the effect of point mutations on the overall physical properties of protein based materials.

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.

Artificial hagfish protein fibers with ultra-high and tunable stiffness

Stiff fibers are used as reinforcing phases in a wide range of high-performance composite materials. Silk is one of the most widely studied bio-fibers, but alternative materials with specific advantages are also being explored. Among these, native hagfish (Eptatretus stoutii) slime thread is an attractive protein-based polymer. These threads consist of coiled-coil intermediate filaments (IFs) as nano-scale building blocks, which can be transformed into extended β-sheet-containing chains upon draw-processing, resulting in fibers with impressive mechanical performance. Here, we report artificial hagfish threads produced by recombinant protein expression, which were subsequently self-assembled into coiled-coil nanofilaments, concentrated, and processed into β-sheet-rich fibers by a "picking-up" method. These artificial fibers experienced mechanical performance enhancement during draw-processing. We exploited the lysine content to covalently cross-link the draw-processed fibers and obtained moduli values (E) in tension as high as ∼20 GPa, which is stiffer than most reported artificial proteinaceous materials.

Materials Nanoarchitecturing via Cation-Mediated Protein Assembly: Making Limpet Teeth without Mineral

Teeth are designed to deliver high forces while withstanding the generated stresses. Aside from isolated mineral-free exception (e.g., marine polychaetes and squids), minerals are thought to be indispensable for tooth-hardening and durability. Here, the unmineralized teeth of the giant keyhole limpet (Megathura crenulata) are shown to attain a stiffness, which is twofold higher than any known organic biogenic structures. In these teeth, protein and chitin fibers establish a stiff compact outer shell enclosing a less compact core. The stiffness and its gradients emerge from a concerted interaction across multiple length-scales: packing of hydrophobic proteins and folding into secondary structures mediated by Ca²⁺ and Mg²⁺ together with a strong spatial control in the local fiber orientation. These results integrating nanoindentation, acoustic microscopy, and finite-element modeling for probing the tooth's mechanical properties, spatially resolved small- and wide-angle X-ray scattering for probing the material ordering on the micrometer scale, and energy-dispersive X-ray scattering combined with confocal Raman microscopy to study structural features on the molecular scale, reveal a nanocomposite structure hierarchically assembled to form a versatile damage-tolerant protein-based tooth, with a stiffness similar to mineralized mammalian bone, but without any mineral.

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.

Programming function into mechanical forms by directed assembly of silk bulk materials

We report simple, water-based fabrication methods based on protein self-assembly to generate 3D silk fibroin bulk materials that can be easily hybridized with water-soluble molecules to obtain multiple solid formats with predesigned functions. Controlling self-assembly leads to robust, machinable formats that exhibit thermoplastic behavior consenting material reshaping at the nanoscale, microscale, and macroscale. We illustrate the versatility of the approach by realizing demonstrator devices where large silk monoliths can be generated, polished, and reshaped into functional mechanical components that can be nanopatterned, embed optical function, heated on demand in response to infrared light, or can visualize mechanical failure through colorimetric chemistries embedded in the assembled (bulk) protein matrix. Finally, we show an enzyme-loaded solid mechanical part, illustrating the ability to incorporate biological function within the bulk material with possible utility for sustained release in robust, programmably shapeable mechanical formats.

Modular peptides from the thermoplastic squid sucker ring teeth form amyloid-like cross-β supramolecular networks

The hard sucker ring teeth (SRT) from decapodiforme cephalopods, which are located inside the sucker cups lining the arms and tentacles of these species, have recently emerged as a unique model structure for biomimetic structural biopolymers. SRT are entirely composed of modular, block co-polymer-like proteins that self-assemble into a large supramolecular network. In order to unveil the molecular principles behind SRT's self-assembly and robustness, we describe a combinatorial screening assay that maps the molecular-scale interactions between the most abundant modular peptide blocks of suckerin proteins. By selecting prominent interaction hotspots from this assay, we identified four peptides that exhibited the strongest homo-peptidic interactions, and conducted further in-depth biophysical characterizations complemented by molecular dynamic (MD) simulations to investigate the nature of these interactions. Circular Dichroism (CD) revealed conformations that transitioned from semi-extended poly-proline II (PII) towards β-sheet structure. The peptides spontaneously self-assembled into microfibers enriched with cross β-structures, as evidenced by Fourier-Transform Infrared Spectroscopy (FTIR) and Congo red staining. Nuclear Magnetic Resonance (NMR) experiments identified the residues involved in the hydrogen-bonded network and demonstrated that these self-assembled β-sheet-based fibers exhibit high protection factors that bear resemblance to amyloids. The high stability of the β-sheet network and an amyloid-like model of fibril assembly were supported by MD simulations. The work sheds light on how Nature has evolved modular sequence design for the self-assembly of mechanically robust functional materials, and expands our biomolecular toolkit to prepare load-bearing biomaterials from protein-based block co-polymers and self-assembled peptides.

STATEMENT OF SIGNIFICANCE

The sucker ring teeth (SRT) located on the arms and tentacles of cephalopods represent as a very promising protein-based biopolymer with the potential to rival silk in biomedical and engineering applications. SRT are made of modular, block co-polymer like proteins (suckerins), which assemble into a semicrystalline polymer reinforced by nano-confined β-sheets, resulting in a supramolecular network with mechanical properties that match those of the strongest engineering polymers. In this study, we aimed to understand the molecular mechanisms behind SRT's self-assembly and robustness. The most abundant modular peptidic blocks of suckerin proteins were studied by various spectroscopic methods, which demonstrate that SRT peptides form amyloid-like cross-β structures.

The role of water on the structure and mechanical properties of a thermoplastic natural block co-polymer from squid sucker ring teeth

Hard biological polymers exhibiting a truly thermoplastic behavior that can maintain their structural properties after processing are extremely rare and highly desirable for use in advanced technological applications such as 3D-printing, biodegradable plastics and robust composites. One exception are the thermoplastic proteins that comprise the sucker ring teeth (SRT) of the Humboldt jumbo squid (Dosidicus gigas). In this work, we explore the mechanical properties of reconstituted SRT proteins and demonstrate that the material can be re-shaped by simple processing in water and at relatively low temperature (below 100 °C). The post-processed material maintains a high modulus in the GPa range, both in the dry and the wet states. When transitioning from low to high humidity, the material properties change from brittle to ductile with an increase in plastic deformation, where water acts as a plasticizer. Using synchrotron x-ray scattering tools, we found that water mostly influences nano scale structure, whereas at the molecular level, the protein structure remains largely unaffected. Furthermore, through simultaneous in situ x-ray scattering and mechanical tests, we show that the supramolecular network of the reconstituted SRT material exhibits a progressive alignment along the strain direction, which is attributed to chain alignment of the amorphous domains of SRT proteins. The high modulus in both dry and wet states, combined with their efficient thermal processing characteristics, make the SRT proteins promising substitutes for applications traditionally reserved for petroleum-based thermoplastics.

Physical, Chemical and Biochemical Modifications of Protein-Based Films and Coatings: An Extensive Review

Protein-based films and coatings are an interesting alternative to traditional petroleum-based materials. However, their mechanical and barrier properties need to be enhanced in order to match those of the latter. Physical, chemical, and biochemical methods can be used for this purpose. The aim of this article is to provide an overview of the effects of various treatments on whey, soy, and wheat gluten protein-based films and coatings. These three protein sources have been chosen since they are among the most abundantly used and are well described in the literature. Similar behavior might be expected for other protein sources. Most of the modifications are still not fully understood at a fundamental level, but all the methods discussed change the properties of the proteins and resulting products. Mastering these modifications is an important step towards the industrial implementation of protein-based films.

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

The arms and tentacles of Decapodiform cephalopods (squids and cuttlefish) are lined with suckers, each of which contains embedded sucker ring teeth (SRT), which are used by the animal for prey capture and handling. SRT exhibit intriguing physicochemical and thermomechanical characteristics that have so far not been observed in other protein-based biomaterials. Notably, despite their comparatively high mechanical properties, SRT are almost fully soluble in chaotropic solvents and can be readily reconstituted after solvent evaporation into three-dimensional structures. SRT also exhibit thermoplastic characteristics: they can be melted and reshaped multiple times with no-or only minimal-loss of mechanical performance postprocessing. Intrigued by these unusual material characteristics, in recent years, we have conducted in-depth fundamental studies to unveil structure/property relationships of SRT from the molecular (genetic) level to the macroscopic scale. These investigations have demonstrated that SRT are entirely assembled from a protein family called "suckerins" that self-assemble into semicrystalline polymer infinite networks. Suckerins are block copolymers at the molecular level, whose closest analogy appears to be silk fibroins, although significant differences exist between these two protein families. Parallel to these studies, there have been efforts to mimic and engineer suckerins by protein engineering and to demonstrate potential applications through proof-of-concept studies, with a focus on the biomedical field. Both fundamental aspects and emerging applications are presented in this short review. Given the rather unusual source of this model structure, we start by a brief historical account of SRT and suckerin discovery.