Mechanical Properties of Tandem-Repeat Proteins Are Governed by Network Defects

Cephalopod inspired self-healing protein foams for oil-water separation

Cephalopods are remarkable creatures, captivating scientists with their advanced neurophysiology, complex behavior, and miraculously effective camouflage. Research into cephalopods has led to many discoveries in neuroscience, cell biology, and materials science. Specifically, squids provide us with remarkable self-healing Squid Ring Teeth protein, which is applied herein to extend the life span of foams. Despite the advantages of porosity in surface science applications, porosity impairs mechanical properties by making materials more prone to structural damage -which traditional polymeric foams also suffer from. Drawing inspiration from Squid Ring Teeth, we developed self-healing tandem repeat proteins to overcome these challenges. By leveraging porosity and self-healing properties inspired by Squid Ring Teeth, we created bioengineered protein foams with high separation capacity (5.1 g g-1) and efficiency (≈94%). The foams healed entirely within minutes which regained over 100% strength after repair. These advances promise applications for efficient continuous water treatment through durable filter cartridges.

Building biomaterials through genetic code expansion

Genetic code expansion (GCE) enables directed incorporation of noncoded amino acids (NCAAs) and unnatural amino acids (UNAAs) into the active core that confers dedicated structure and function to engineered proteins. Many protein biomaterials are tandem repeats that intrinsically include NCAAs generated through post-translational modifications (PTMs) to execute assigned functions. Conventional genetic engineering approaches using prokaryotic systems have limited ability to biosynthesize functionally active biomaterials with NCAAs/UNAAs. Codon suppression and reassignment introduce NCAAs/UNAAs globally, allowing engineered proteins to be redesigned to mimic natural matrix-cell interactions for tissue engineering. Expanding the genetic code enables the engineering of biomaterials with catechols - growth factor mimetics that modulate cell-matrix interactions - thereby facilitating tissue-specific expression of genes and proteins. This method of protein engineering shows promise in achieving tissue-informed, tissue-compliant tunable biomaterials.

Self-Healing Polymeric Soft Actuators

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Functional Chemical Motor Coatings for Modular Powering of Self-Propelled Particles

Inspired by the locomotion of semiaquatic insects, a variety of surface swimming microrobots propelled by surface tension Marangoni forces have been developed over the years. However, most Marangoni micromotor systems present limitations in their applications due to poor performance, short lifetime, low efficiency, and toxicity. We have developed a functional chemical motor coating consisting of protein microfilms with entrapped fuel to functionalize inactive substrates or particles. This motor material system generates large Marangoni propulsive forces with extremely small amounts of fuel due to a self-regulated fuel release mechanism based on dynamic nanostructural changes in the protein matrix, enhancing the lifetime and efficiency performance over other material systems and motors. These motor functional coatings offer great versatility as they can be coated on a wide array of substrates and materials across length scales, with opportunities as modular power sources for microrobots and small-scale devices. The synergy between the protein motor matrix and the chemical fuel enables the wider design of self-powered surface microrobots without previous limitations in their fabrication and performance, including the new design of hybrid microrobots with protein functional coatings as a modular power source.

Plastics in the environment as potential threat to life: an overview

Plastics have become inevitable for human beings in their daily life. Million tons of plastic waste is entering in oceans, soil, freshwater, and sediments. Invasion of plastics in different ecosystems is causing severe problems to inhabitants. Wild animals such as seabirds, fishes, crustaceans, and other invertebrates are mostly effected by plastic entanglements and organic pollutants absorbed and carried by plastics/microplastics. Plastics can also be potentially harmful to human beings and other mammals. Keeping in view the possible harms of plastics, some mitigation strategies must be adopted which may include the use of bioplastics and some natural polymers such as squid-ring teeth protein. This review focuses on the possible sources of intrusion and fate of plastics in different ecosystems, their potential deleterious effects on wildlife, and the measures that can be taken to minimize and avoid the plastic use.

Diffusive Dynamic Modes of Recombinant Squid Ring Teeth Proteins by Neutron Spectroscopy

Stimuli-responsive structural proteins are emerging as promising biocompatible materials for a wide range of biological and nonbiological applications. To understand the physical properties of structural proteins and to replicate their performance in biosynthetic systems, there is a need to understand the molecular mechanisms and relationships that regulate their structure, dynamics, and properties. Here, we study the dynamics of a recombinant squid-inspired protein from Loligo vulgaris (Lv18) by elastic and quasielastic neutron scattering (QENS) to understand the connection between nanostructure, chain dynamics, and mechanical properties. Lv18 is a semicrystalline structural protein, which is plasticized by water above its glass transition temperature at 35 °C. Elastic scans revealed an increased protein chain mobility upon hydration, superimposed dynamic processes, and a decrease in dynamic transition temperatures. Further analysis by QENS revealed that while dry Lv18 protein dynamics are dominated by localized methyl group rotations, hydrated Lv18 dynamics are dominated by the confined diffusion of flexible chains within a β-sheet nanocrystalline network (8 Å of confinement radius). Our findings establish a relationship between the segment block architecture of Lv18, the diffusive motions within the protein structure, and the mechanical properties of recombinant squid proteins, which will advance the molecular design of novel high-performance protein-inspired materials with tailored dynamics and mechanical properties.

Optimized Loopable Translation as a Platform for the Synthesis of Repetitive Proteins

The expression of long proteins with repetitive amino acid sequences often presents a challenge in recombinant systems. To overcome this obstacle, we report a genetic construct that circularizes mRNA in vivo by rearranging the topology of a group I self-splicing intron from T4 bacteriophage, thereby enabling "loopable" translation. Using a fluorescence-based assay to probe the translational efficiency of circularized mRNAs, we identify several conditions that optimize protein expression from this system. Our data suggested that translation of circularized mRNAs could be limited primarily by the rate of ribosomal initiation; therefore, using a modified error-prone PCR method, we generated a library that concentrated mutations into the initiation region of circularized mRNA and discovered mutants that generated markedly higher expression levels. Combining our rational improvements with those discovered through directed evolution, we report a loopable translator that achieves protein expression levels within 1.5-fold of the levels of standard vectorial translation. In summary, our work demonstrates loopable translation as a promising platform for the creation of large peptide chains, with potential utility in the development of novel protein materials.

Cephalopods-Inspired Rapid Self-Healing Nanoclay Composite Coatings with Oxygen Barrier and Super-Bubble-Phobic Properties

Polymeric coatings with oxygen barrier properties are an important technology in food packaging that can extend the shelf life of food products and reduce waste. Although a typical technology in practical use is the deposition of metal or inorganic materials between multilayer films to reduce the oxygen transmission rate, once the film is damaged, oxygen permeates through the damaged area, damaging the packaged food. In addition, nanobrick wall structures consisting of nanoplatelet bricks have the potential to replace barrier films made of inorganic materials; however, they similarly lack repair performance or have slow repair speed despite having repair performance. Inspired by the rapid self-repair mechanism of cephalopods, the study develops a nanoclay-containing coating that can rapidly repair surface damage via water within 10 s. By introducing CaCl₂-derived counterions and montmorillonite for nanobrick wall structures into polyelectrolyte multilayers stacked by layer-by-layer self-assembly, the noncovalent polymer network is increased, resulting in mimicking a strong cephalopod-derived β-sheet structure and noncovalent intermolecular interactions derived from cephalopods. The high water retention at the surface showed super-bubble-phobicity in water and inhibited gas permeation. The oxygen permeability of the coatings with more than a certain amount of montmorillonite was less than 1/100 of that of bare polyethylene. The ultrafast self-healing gas barrier coating has the potential to be used not only for food products but also for electronics and pharmaceutical packaging and gas separation applications. The key technology developed in this study provides novel insights into the construction of self-healing membranes made of composite materials and will contribute to the formation of a sustainable society.

Hydration-Induced Structural Transitions in Biomimetic Tandem Repeat Proteins

A major challenge in developing biomimetic, high-performance, and sustainable products is the accurate replication of the biological materials' striking properties, such as high strength, self-repair, and stimuli-responsiveness. The rationalization of such features on the microscopic scale, together with the rational design of synthetic materials, is currently hindered by our limited understanding of the sequence-structure-property relationship. Here, employing state-of-the-art nuclear magnetic resonance (NMR) spectroscopy, we link the atomistic structural and dynamic properties of an artificial bioinspired tandem repeat protein TR(1,11) to its stunning macroscopic properties including high elasticity, self-healing capabilities, and record-holding proton conductivity among biological materials. We show that the hydration-induced structural rearrangement of the amorphous Gly-rich soft segment and the ordered Ala-rich hard segment is the key to the material's outstanding physical properties. We found that in the hydrated state both the Ala-rich ordered and Gly-rich disordered parts contribute to the formation of the nanoconfined β-sheets, thereby enhancing the strength and toughness of the material. This restructuring is accompanied by fast proline ring puckering and backbone cis-trans isomerization at the water-protein interface, which in turn enhances the elasticity and the thermal conductivity of the hydrated films. Our in-depth characterization provides a solid ground for the development of next-generation materials with improved properties.

Biosynthetic self-healing materials for soft machines

Self-healing materials are indispensable for soft actuators and robots that operate in dynamic and real-world environments, as these machines are vulnerable to mechanical damage. However, current self-healing materials have shortcomings that limit their practical application, such as low healing strength (below a megapascal) and long healing times (hours). Here, we introduce high-strength synthetic proteins that self-heal micro- and macro-scale mechanical damage within a second by local heating. These materials are optimized systematically to improve their hydrogen-bonded nanostructure and network morphology, with programmable healing properties (2-23 MPa strength after 1 s of healing) that surpass by several orders of magnitude those of other natural and synthetic soft materials. Such healing performance creates new opportunities for bioinspired materials design, and addresses current limitations in self-healing materials for soft robotics and personal protective equipment.

Trimers Conjugated to Fibrin Hydrogels Promote Salivary Gland Function

New strategies for tissue engineering have great potential for restoring and revitalizing impaired tissues and organs, including the use of smart hydrogels that can be modified to enhance organization and functionality of the salivary glands. For instance, monomers of laminin-111 peptides chemically conjugated to fibrin hydrogel (L_1pM-FH) promote cell cluster formation in vitro and salivary gland regeneration in vivo when compared with fibrin hydrogel (FH) alone; however, L_1pM-FH produce only weak expression of acinar differentiation markers in vivo (e.g., aquaporin-5 and transmembrane protein 16). Since previous studies demonstrated that a greater impact can be achieved when trimeric forms were used as compared with monomeric or dimeric forms, we investigated the extent to which trimers of laminin-111 chemically conjugated to FH (L_1pT-FH) can increase the expression of acinar differentiation markers and elevate saliva secretion. In vitro studies using Par-C10 acinar cells demonstrated that when compared with L_1pM-FH, L_1pT-FH induced similar levels of acinar-like cell clustering, polarization, lumen formation, and calcium signaling. To assess the performance of the trimeric complex in vivo, we compared the ability of L_1pM-FH and L_1pT-FH to increase acinar differentiation markers and restore saliva flow rate in a salivary gland wound model of C57BL/6 mice. Our results show that L_1pT-FH applied to wounded mice significantly improved the expression of the acinar differentiation markers and saliva secretion when compared with the monomeric form. Together, these positive effects of L_1pT-FH warrant its future testing in additional models of hyposalivation with the ultimate goal of applying this technology in humans.

Self-Assembly of Topologically Networked Protein-Ti3C2Tx MXene Composites

Hierarchical organization plays an important role in the stunning physical properties of natural and synthetic composites. Limits on the physical properties of such composites are generally defined by percolation theory and can be systematically altered using the volumetric filler fraction of the inorganic/organic phase. In natural composites, organic materials such as proteins that interact with inorganic filler materials can further alter the hierarchical order and organization of the composite via topological interactions, expanding the limits of the physical properties defined by percolation theory. However, existing polymer systems do not offer a topological parameter that can systematically modulate the assembly characteristics of composites. Here, we present a composite based on proteins and titanium carbide (Ti₃C₂T_x) MXene that manifests a topological network that regulates the organization, and hence physical properties, of these biomimetic composites. We designed, recombinantly expressed, and purified synthetic proteins consisting of polypeptides with repeating amino acid sequences (tandem repeats) that have the ability to self-assemble into topologically networked biomaterials. We demonstrated that the interlayer distance between MXene sheets can be controlled systematically by the number of tandem repeat units. We varied the filler fraction and number of tandem repeat units to regulate the in-plane and out-of-plane electrical conductivities of these composites. Once Ti₃C₂T_x MXene sheets are separated enough to facilitate formation of cross-links in our proteins with the number of tandem repeat units reaching 11, the linear I-V characteristics of the composites switched into nonlinear I-V curves with a distinct hysteresis for out-of-plane electron transport, while the in-plane I-V characteristics remained linear. This highlights the impact of synthetic protein templates, which can be designed to modulate electronic transport in composites both isotropically and anisotropically.

Multifunctional and biodegradable self-propelled protein motors

A diversity of self-propelled chemical motors, based on Marangoni propulsive forces, has been developed in recent years. However, most motors are non-functional due to poor performance, a lack of control, and the use of toxic materials. To overcome these limitations, we have developed multifunctional and biodegradable self-propelled motors from squid-derived proteins and an anesthetic metabolite. The protein motors surpass previous reports in performance output and efficiency by several orders of magnitude, and they offer control of their propulsion modes, speed, mobility lifetime, and directionality by regulating the protein nanostructure via local and external stimuli, resulting in programmable and complex locomotion. We demonstrate diverse functionalities of these motors in environmental remediation, microrobot powering, and cargo delivery applications. These versatile and degradable protein motors enable design, control, and actuation strategies in microrobotics as modular propulsion sources for autonomous minimally invasive medical operations in biological environments with air-liquid interfaces.

Synthetic biology for fibres, adhesives and active camouflage materials in protection and aerospace

Synthetic biology has huge potential to produce the next generation of advanced materials by accessing previously unreachable (bio)chemical space. In this prospective review, we take a snapshot of current activity in this rapidly developing area, focussing on prominent examples for high-performance applications such as those required for protective materials and the aerospace sector. The continued growth of this emerging field will be facilitated by the convergence of expertise from a range of diverse disciplines, including molecular biology, polymer chemistry, materials science and process engineering. This review highlights the most significant recent advances and address the cross-disciplinary challenges currently being faced.

Squid-Inspired Tandem Repeat Proteins: Functional Fibers and Films

Production of repetitive polypeptides that comprise one or more tandem copies of a single unit with distinct amorphous and ordered regions have been an interest for the last couple of decades. Their molecular structure provides a rich architecture that can micro-phase-separate to form periodic nanostructures (e.g., lamellar and cylindrical repeating phases) with enhanced physicochemical properties via directed or natural evolution that often exceed those of conventional synthetic polymers. Here, we review programmable design, structure, and properties of functional fibers and films from squid-inspired tandem repeat proteins, with applications in soft photonics and advanced textiles among others.

Tunable thermal transport and reversible thermal conductivity switching in topologically networked bio-inspired materials

The dynamic control of thermal transport properties in solids must contend with the fact that phonons are inherently broadband. Thus, efforts to create reversible thermal conductivity switches have resulted in only modest on/off ratios, since only a relatively narrow portion of the phononic spectrum is impacted. Here, we report on the ability to modulate the thermal conductivity of topologically networked materials by nearly a factor of four following hydration, through manipulation of the displacement amplitude of atomic vibrations. By varying the network topology, or crosslinked structure, of squid ring teeth-based bio-polymers through tandem-repetition of DNA sequences, we show that this thermal switching ratio can be directly programmed. This on/off ratio in thermal conductivity switching is over a factor of three larger than the current state-of-the-art thermal switch, offering the possibility of engineering thermally conductive biological materials with dynamic responsivity to heat.