Segmented molecular design of self-healing proteinaceous materials

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.

A facile approach to fabricate room temperature intrinsic self-healing fabrics

Self-healing fabrics have garnered a lot of attention due to their recovering functionality upon damage. This work describes a facile technique for developing a novel self-healing coating with the goal of producing autonomous intrinsic self-healing fabrics that can recover from damage at room temperature without the use of external stimuli. The coating was developed using natural rubber latex (NRL) and consisted of a dynamic reversible metal thiolate ionic network. The formation of the reversible ionic network was assessed by Differential Scanning Calorimetry (DSC), Ultraviolet-visible spectroscopy (UV-vis), Fourier Transform Infrared (FTIR) and zeta potential analysis. Scanning electron microscope (SEM) images revealed that the coating impregnated the fibres of the fabric and improved their structural integrity. The morphology of the punctured area revealed that intermolecular diffusion had occurred during the recovery and the sample had completely healed. The results also showed that the tensile strength, tear strength and puncture strength of the fabric achieved 100% healing efficiency when the damaged fabrics were brought into contact with each other and allowed to be healed at room temperature. This technology is expected to open up a new avenue in the textile industry.

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.

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.

Fabrication of Curli Fiber-PEDOT:PSS Biomaterials with Tunable Self-Healing, Mechanical, and Electrical Properties

Poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) is a highly conductive, easily processable, self-healing polymer. It has been shown to be useful in bioelectronic applications, for instance, as a biointerfacing layer for studying brain activity, in biosensitive transistors, and in wearable biosensors. A green and biofriendly method for improving the mechanical properties, biocompatibility, and stability of PEDOT:PSS involves mixing the polymer with a biopolymer. Via structural changes and interactions with PEDOT:PSS, biopolymers have the potential to improve the self-healing ability, flexibility, and electrical conductivity of the composite. In this work, we fabricated novel protein-polymer multifunctional composites by mixing PEDOT:PSS with genetically programmable amyloid curli fibers produced byEscherichia coli bacteria. Curli fibers are among the stiffest protein polymers and, once isolated from bacterial biofilms, can form plastic-like thin films that heal with the addition of water. Curli-PEDOT:PSS composites containing 60% curli fibers exhibited a conductivity 4.5-fold higher than that of pristine PEDOT:PSS. The curli fibers imbued the biocomposites with an immediate water-induced self-healing ability. Further, the addition of curli fibers lowered the Young's and shear moduli of the composites, improving their compatibility for tissue-interfacing applications. Lastly, we showed that genetically engineered fluorescent curli fibers retained their ability to fluoresce within curli-PEDOT:PSS composites. Curli fibers thus allow to modulate a range of properties in conductive PEDOT:PSS composites, broadening the applications of this polymer in biointerfaces and bioelectronics.

Designed protein- and peptide-based hydrogels for biomedical sciences

Proteins are fundamentally the most important macromolecules for biochemical, mechanical, and structural functions in living organisms. Therefore, they provide us with diverse structural building blocks for constructing various types of biomaterials, including an important class of such materials, hydrogels. Since natural peptides and proteins are biocompatible and biodegradable, they have features advantageous for their use as the building blocks of hydrogels for biomedical applications. They display constitutional and mechanical similarities with the native extracellular matrix (ECM), and can be easily bio-functionalized via genetic and chemical engineering with features such as bio-recognition, specific stimulus-reactivity, and controlled degradation. This review aims to give an overview of hydrogels made up of recombinant proteins or synthetic peptides as the structural elements building the polymer network. A wide variety of hydrogels composed of protein or peptide building blocks with different origins and compositions - including β-hairpin peptides, α-helical coiled coil peptides, elastin-like peptides, silk fibroin, and resilin - have been designed to date. In this review, the structures and characteristics of these natural proteins and peptides, with each of their gelation mechanisms, and the physical, chemical, and mechanical properties as well as biocompatibility of the resulting hydrogels are described. In addition, this review discusses the potential of using protein- or peptide-based hydrogels in the field of biomedical sciences, especially tissue engineering.

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.

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.

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.

Biomimetic Water-Responsive Self-Healing Epoxy with Tunable Properties

As dynamic cross-linking networks are intrinsically weaker than permanent covalent networks, it is a big challenge to obtain a stiff self-healing polymer using reversible networks. Inspired by the self-healable and mechanically adaptive nature of sea cucumber, we design a water-responsive self-healing polymer system with reversible and permanent covalent networks by cross-linking poly(propylene glycol) with boroxine and epoxy. This double cross-linked structure is self-healing due to the boroxine reversible network as well as showing a room-temperature tensile modulus of 1059 MPa and a tensile stress of 37 MPa, on a par with classic thermosets. The dynamic boroxine bonds provide the self-healing response and enable up to 80% recovery in modulus and tensile strength upon water contact. The system shows superior adhesion to metal substrates by comparison with the commercial epoxy-based structural adhesive. Besides, this system can change modulus from a stiff thermoset to soft rubber (by a factor of 150) upon water stimulus, enabling potential applications of either direct or transform printing for micro/nanofabrication. Moreover, by incorporating conductive nanofillers, it becomes feasible to fabricate self-healing and versatile strain/stress sensors based on a single thermoset, with potential applications in wearable electronics for human healthcare.

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.

Squid Ring Teeth-coated Mesh Improves Abdominal Wall Repair

Background

Hernia repair is a common surgical procedure with polypropylene (PP) mesh being the standard material for correction because of its durability. However, complications such as seroma and pain are common, and repair failures still approach 15% secondary to poor tissue integration. In an effort to enhance mesh integration, we evaluated the applicability of a squid ring teeth (SRT) protein coating for soft-tissue repair in an abdominal wall defect model. SRT is a biologically derived high-strength protein with strong mechanical properties. We assessed tissue integration, strength, and biocompatibility of a SRT-coated PP mesh in a first-time pilot animal study.

Methods

PP mesh was coated with SRT (SRT-PP) and tested for mechanical strength against uncoated PP mesh. Cell proliferation and adhesion studies were performed in vitro using a 3T3 cell line. Rats underwent either PP (n = 3) or SRT-PP (n = 6) bridge mesh implantation in an anterior abdominal wall defect model. Repair was assessed clinically and radiographically, with integration evaluated by histology and mechanical testing at 60 days.

Results

Cell proliferation was enhanced on SRT-PP mesh. This was corroborated in vivo by abdominal wall histology, dramatically diminished craniocaudal mesh contraction, improved strength testing, and higher tissue failure strain. There was no increase in seroma or visceral adhesion formation. No foreign body reactions were noted on liver histology.

Conclusions

SRT applied as a coating appears to augment mesh-tissue integration and improve abdominal wall stability following bridged repair. Further studies in larger animals will determine its applicability for hernia repair in patients.

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

Topological defects in highly repetitive structural proteins strongly affect their mechanical properties. However, there are no universal rules for structure-property prediction in structural proteins due to high diversity in their repetitive modules. Here, we studied the mechanical properties of tandem-repeat proteins inspired by squid ring teeth proteins using rheology and tensile experiments as well as spectroscopic and X-ray techniques. We also developed a network model based on entropic elasticity to predict structure-property relationships for these proteins. We demonstrated that shear modulus, elastic modulus, and toughness scale inversely with the number of repeats in these proteins. Through optimization of structural repeats, we obtained highly efficient protein network topologies with 42 MJ/m³ ultimate toughness that are capable of withstanding deformations up to 350% when hydrated. Investigation of topological network defects in structural proteins will improve the prediction of mechanical properties for designing novel protein-based materials.

Self-Healing of Polymer in Acidic Water toward Strength Restoration through the Synergistic Effect of Hydrophilic and Hydrophobic Interactions

To improve reliability, durability, and reworkability of bulk polymers utilized in ubiquitous acidic water, the authors develop a novel hyperbranched polymer capable of self-healing and recycling in a low-pH aqueous environment. The hyperbranched polymer has many hydrophilic and hydrophobic terminal groups. When it is damaged in acidic water, the hydrophilic groups are protonated, forming hydrogen bonds, and closing the crack. Meanwhile, hydrophobic interactions of hydrophobic groups are gradually established across the interface because of the intimate contact of the cracked surface, further reinforcing the rebonded portion. The amphiphilic structure proves to meet both the thermodynamic and kinetic requirements for autonomous rehabilitation. As a result, the unfavored water, which used to impede adhesion between hydrophobic polymeric materials, turns into a positive aid to crack healing. The mechanism involved is carefully analyzed and verified in terms of micro- and macroscopic techniques. The proposed operating environment-oriented design of the stimulus-responsive macromolecule may help to broaden the family of underwater self-healing polymers and their application scope.

Ultrafast laser-probing spectroscopy for studying molecular structure of protein aggregates

We report the development of a new technique to screen protein aggregation based on laser-probing spectroscopy with sub-picosecond resolution.

Self-Healing Textile: Enzyme Encapsulated Layer-by-Layer Structural Proteins

Self-healing materials, which enable an autonomous repair response to damage, are highly desirable for the long-term reliability of woven or nonwoven textiles. Polyelectrolyte layer-by-layer (LbL) films are of considerable interest as self-healing coatings due to the mobility of the components comprising the film. In this work mechanically stable self-healing films were fabricated through construction of a polyelectrolyte LbL film containing squid ring teeth (SRT) proteins. SRTs are structural proteins with unique self-healing properties and high elastic modulus in both dry and wet conditions (>2 GPa) due to their semicrystalline architecture. We demonstrate LbL construction of multilayers containing native and recombinant SRT proteins capable of self-healing defects. Additionally, we show these films are capable of utilizing functional biomolecules by incorporating an enzyme into the SRT multilayer. Urease was chosen as a model enzyme of interest to test its activity via fluorescence assay. Successful construction of the SRT films demonstrates the use of mechanically stable self-healing coatings, which can incorporate biomolecules for more complex protective functionalities for advanced functional fabrics.

Molecular tandem repeat strategy for elucidating mechanical properties of high-strength proteins

Many globular and structural proteins have repetitions in their sequences or structures. However, a clear relationship between these repeats and their contribution to the mechanical properties remains elusive. We propose a new approach for the design and production of synthetic polypeptides that comprise one or more tandem copies of a single unit with distinct amorphous and ordered regions. Our designed sequences are based on a structural protein produced in squid suction cups that has a segmented copolymer structure with amorphous and crystalline domains. We produced segmented polypeptides with varying repeat number, while keeping the lengths and compositions of the amorphous and crystalline regions fixed. We showed that mechanical properties of these synthetic proteins could be tuned by modulating their molecular weights. Specifically, the toughness and extensibility of synthetic polypeptides increase as a function of the number of tandem repeats. This result suggests that the repetitions in native squid proteins could have a genetic advantage for increased toughness and flexibility.