Recombinant Resilin-Based Bioelastomers for Regenerative Medicine Applications

Engineered protein elastomeric materials

Natural evolution endows some insects and marine organisms with a special class of protein-based elastic tissues that possess energy feedback characteristics, providing them with the foundation for jumping and flying, and protecting them from the damage caused by movements or waves. However, the design and fabrication of such protein-based elastomeric materials that can function in human society through biomimetic strategies still remains challenging. Recombinant proteins designed by synthetic biology can mimic the advantageous structures in natural proteins and can be biosynthesized without the requirements for harsh conditions such as high temperatures and cytotoxic agents, which provides a great opportunity to prepare protein-based elastomeric materials. In this review, starting from the design of protein molecules, we highlight an overview of the synthesis of elastomeric materials based on recombinant resilin, recombinant elastin-like proteins and other recombinant folded proteins, etc., and then demonstrate their application progress in the fields of biomedicine and high technology. Finally, the challenges and prospects for the future development of protein-based elastomeric materials are envisioned to provide insights into the design and synthesis of the next generation of protein-based elastomeric materials.

Modifying Naturally Occurring, Nonmammalian-Sourced Biopolymers for Biomedical Applications

Natural biopolymers have a rich history, with many uses across the fields of healthcare and medicine, including formulations for wound dressings, surgical implants, tissue culture substrates, and drug delivery vehicles. Yet, synthetic-based materials have been more successful in translation due to precise control and regulation achievable during manufacturing. However, there is a renewed interest in natural biopolymers, which offer a diverse landscape of architecture, sustainable sourcing, functional groups, and properties that synthetic counterparts cannot fully replicate as processing and sourcing of these materials has improved. Proteins and polysaccharides derived from various sources (crustaceans, plants, insects, etc.) are highlighted in this review. We discuss the common types of polysaccharide and protein biopolymers used in healthcare and medicine, highlighting methods and strategies to alter structures and intra- and interchain interactions to engineer specific functions, products, or materials. We focus on biopolymers obtained from natural, nonmammalian sources, including silk fibroins, alginates, chitosans, chitins, mucins, keratins, and resilins, while discussing strategies to improve upon their innate properties and sourcing standardization to expand their clinical uses and relevance. Emphasis will be placed on methods that preserve the structural integrity and native biological functions of the biopolymers and their makers. We will conclude by discussing the untapped potential of new technologies to manipulate native biopolymers while controlling their secondary and tertiary structures, offering a perspective on advancing biopolymer utility in novel applications within biomedical engineering, advanced manufacturing, and tissue engineering.

Genetic Functionalization of Protein-Based Biomaterials via Protein Fusions

Proteins implement many useful functions, including binding ligands with unparalleled affinity and specificity, catalyzing stereospecific chemical reactions, and directing cell behavior. Incorporating proteins into materials has the potential to imbue devices with these desirable traits. This review highlights recent advances in creating active materials by genetically fusing a self-assembling protein to a functional protein. These fusion proteins form materials while retaining the function of interest. Key advantages of this approach include elimination of a separate functionalization step during materials synthesis, uniform and dense coverage of the material by the functional protein, and stabilization of the functional protein. This review focuses on macroscale materials and discusses (i) multiple strategies for successful protein fusion design, (ii) successes and limitations of the protein fusion approach, (iii) engineering solutions to bypass any limitations, (iv) applications of protein fusion materials, including tissue engineering, drug delivery, enzyme immobilization, electronics, and biosensing, and (v) opportunities to further develop this useful technique.

Tyrosinase-Modified UHMW SELP Polymers as Wet and Underwater Adhesives to Achieve Multi-interface Adhesion

The presence of a hydration layer in humid and underwater environments challenges adhesive-substrate interactions and prevents effective bonding, which has become a significant obstacle to the development of adhesives in the industrial and biomedical fields. In this study, ultrahigh-molecular-weight (UHMW) silk-elastin-like proteins (SELP) with 3,4-dihydroxyphenylalanine (DOPA) converted from tyrosine residues by tyrosinase exhibited excellent adhesive properties on different interfaces, such as glass, aluminum, wood, polypropylene sheets, and pigskin, under both dry and wet conditions. Additionally, by incorporating trace amounts of cross-linking agents like Fe3+, NaIO4, and tris(hydroxymethyl) phosphine (THP), the mussel-inspired adhesives maintained a stable and excellent adhesion, broadening the conditions of application. Notably, the UHMW SELP adhesive exhibited remarkable underwater adhesion properties with a shear strength of 0.83 ± 0.17 MPa on glass. It also demonstrated good adhesion to biological tissues including the kidney, liver, heart, and lungs. In vitro cytocompatibility testing using L929 cells showed minimal toxicity, highlighting its potential application in the biomedical field. The sustainable, cytocompatible, cost-effective, and highly efficient adhesive provides valuable insights for the design and development of a new protein-based underwater adhesive for medical application.

Sequence-Encoded Differences in Phase Separation Enable Formation of Resilin-like Polypeptide-Based Microstructured Hydrogels

Microstructured hydrogels are promising platforms to mimic structural and compositional heterogeneities of the native extracellular matrix (ECM). The current state-of-the-art soft matter patterning techniques for generating ECM mimics can be limited owing to their reliance on specialized equipment and multiple time- and energy-intensive steps. Here, a photocross-linking methodology that traps various morphologies of phase-separated multicomponent formulations of compositionally distinct resilin-like polypeptides (RLPs) is reported. Turbidimetry and quantitative 1H NMR spectroscopy were utilized to investigate the sequence-dependent liquid-liquid phase separation of multicomponent solutions of RLPs. Differences between the intermolecular interactions of two different photocross-linkable RLPs and a phase-separating templating RLP were exploited for producing microstructured hydrogels with tunable control over pore diameters (ranging from 1.5 to 150 μm) and shear storage moduli (ranging from 0.2 to 5 kPa). The culture of human mesenchymal stem cells demonstrated high viability and attachment on microstructured hydrogels, suggesting their potential for developing customizable platforms for regenerative medicine applications.

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.

Synthetic biology-guided design and biosynthesis of protein polymers for delivery

Vehicles derived from genetically engineered protein polymers have gained momentum in the field of biomedical engineering due to their unique designability, remarkable biocompatibility and excellent biodegradability. However, the design and production of these protein polymers with on-demand sequences and supramolecular architectures remain underexplored, particularly from a synthetic biology perspective. In this review, we summarize the state-of-the art strategies for constructing the highly repetitive genes encoding the protein polymers, and highlight the advanced approaches for metabolically engineering expression hosts towards high-level biosynthesis of the target protein polymers. Finally, we showcase the typical protein polymers utilized to fabricate delivery vehicles.

Simple production of resilin-like protein hydrogels using the Brevibacillus secretory expression system and column-free purification

Resilin, an insect structural protein, has excellent flexibility, photocrosslinking properties, and temperature responsiveness. Recombinant resilin-like proteins (RLPs) can be fabricated into three-dimensional (3D) structures for use as cell culture substrates and highly elastic materials. A simplified, high-yielding production process for RLPs is required for their widespread application. This study proposes a simple production process combining extracellular expression using Brevibacillus choshinensis (B. choshinensis) and rapid column-free purification. Extracellular production was tested using four representative signal peptides; B. choshinensis was found to efficiently secrete Rec1, an RLP derived from Drosophila melanogaster, regardless of the type of signal peptide. However, it was suggested that Rec1 is altered by an increase in the pH of the culture medium associated with prolonged incubation. Production in a jar fermentor with controllable pH yielded 530 mg Rec1 per liter of culture medium, which is superior to productivity using other hosts. The secreted Rec1 was purified from the culture supernatant via (NH₄ )₂ SO₄ and ethanol precipitations, and the purified Rec1 was applied to ring-shaped 3D hydrogels. These results indicate that the combination of secretory production using B. choshinensis and column-free purification can accelerate the further application of RLPs.

Sequence Context and Complex Hofmeister Salt Interactions Dictate Phase Separation Propensity of Resilin-like Polypeptides

Resilin is an elastic material found in insects with exceptional durability, resilience, and extensibility, making it a promising biomaterial for tissue engineering. The monomeric precursor, pro-resilin, undergoes thermo-responsive self-assembly through liquid-liquid phase separation (LLPS). Understanding the molecular details of this assembly process is critical to developing complex biomaterials. The present study investigates the interplay between the solvent, sequence syntax, structure, and dynamics in promoting LLPS of resilin-like-polypeptides (RLPs) derived from domains 1 and 3 of Drosophila melanogaster pro-resilin. NMR, UV-vis, and microscopy data demonstrate that while kosmotropic salts and low pH promote LLPS, the effects of chaotropic salts with increasing pH are more complex. Subtle variations between the repeating amino acid motifs of resilin domain 1 and domain 3 lead to significantly different salt and pH dependence of LLPS, with domain 3 sequence motifs more strongly favoring phase separation under most conditions. These findings provide new insight into the molecular drivers of RLP phase separation and the complex roles of both RLP sequence and solution composition in fine-tuning assembly conditions.

Emergence of Elastic Properties in a Minimalist Resilin-Derived Heptapeptide upon Bromination

Bromination is herein exploited to promote the emergence of elastic behavior in a short peptide-SDSYGAP-derived from resilin, a rubber-like protein exerting its role in the jumping and flight systems of insects. Elastic and resilient hydrogels are obtained, which also show self-healing behavior, thanks to the promoted non-covalent interactions that limit deformations and contribute to the structural recovery of the peptide-based hydrogel. In particular, halogen bonds may stabilize the β-sheet organization working as non-covalent cross-links between nearby peptide strands. Importantly, the unmodified peptide (i.e., wild type) does not show such properties. Thus, SDSY(3,5-Br)GAP is a novel minimalist peptide elastomer.

Elastomer-Hydrogel Systems: From Bio-Inspired Interfaces to Medical Applications

Novel advanced biomaterials have recently gained great attention, especially in minimally invasive surgical techniques. By applying sophisticated design and engineering methods, various elastomer-hydrogel systems (EHS) with outstanding performance have been developed in the last decades. These systems composed of elastomers and hydrogels are very attractive due to their high biocompatibility, injectability, controlled porosity and often antimicrobial properties. Moreover, their elastomeric properties and bioadhesiveness are making them suitable for soft tissue engineering. Herein, we present the advances in the current state-of-the-art design principles and strategies for strong interface formation inspired by nature (bio-inspiration), the diverse properties and applications of elastomer-hydrogel systems in different medical fields, in particular, in tissue engineering. The functionalities of these systems, including adhesive properties, injectability, antimicrobial properties and degradability, applicable to tissue engineering will be discussed in a context of future efforts towards the development of advanced biomaterials.

Protein-Based Hydrogels: Promising Materials for Tissue Engineering

The successful design of a hydrogel for tissue engineering requires a profound understanding of its constituents' structural and molecular properties, as well as the proper selection of components. If the engineered processes are in line with the procedures that natural materials undergo to achieve the best network structure necessary for the formation of the hydrogel with desired properties, the failure rate of tissue engineering projects will be significantly reduced. In this review, we examine the behavior of proteins as an essential and effective component of hydrogels, and describe the factors that can enhance the protein-based hydrogels' structure. Furthermore, we outline the fabrication route of protein-based hydrogels from protein microstructure and the selection of appropriate materials according to recent research to growth factors, crucial members of the protein family, and their delivery approaches. Finally, the unmet needs and current challenges in developing the ideal biomaterials for protein-based hydrogels are discussed, and emerging strategies in this area are highlighted.

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.

Multi-stimuli-responsive, liposome-crosslinked poly(ethylene glycol) hydrogels for drug delivery

The development of hybrid hydrogels has been of great interest over recent decades, especially in the field of biomaterials. Such hydrogels provide various opportunities in tissue engineering, drug delivery, and regenerative medicine due to their ability to mimic cellular environments, sequester and release therapeutic agents, and respond to stimuli. Herein we report the synthesis and characterization of an injectable poly(ethylene glycol) hydrogel crosslinked via thiol-maleimide reactions and containing both chemically crosslinked temperature-sensitive liposomes (TSLs) and matrix metalloproteinase-sensitive peptide crosslinks. Rheological studies demonstrate that the hydrogel is mechanically stable and can be synthesized to achieve a range of physically applicable moduli. Experiments characterizing the in situ drug delivery and degradation of these materials indicate that the TSL gel responds to both thermal and enzymatic stimuli in a local environment. Doxorubicin, a widely used anticancer drug, was loaded in the TSLs with a high encapsulation efficiency and the subsequent release was temperature dependent. Finally, TSLs did not compromise viability and proliferation of human and murine fibroblasts, supporting the use of these hydrogel-linked liposomes as a thermo-responsive drug carrier for controlled release.

Controllable Fibrillization Reinforces Genetically Engineered Rubberlike Protein Hydrogels

Rubberlike protein hydrogels are unique in their remarkable stretchability and resilience but are usually low in strength due to the largely unstructured nature of the constitutive protein chains, which limits their applications. Thus, reinforcing protein hydrogels while retaining their rubberlike properties is of great interest and has remained difficult to achieve. Here, we propose a fibrillization strategy to reinforce hydrogels from engineered protein copolymers with photo-cross-linkable resilin-like blocks and fibrillizable silklike blocks. First, the designer copolymers with an increased ratio of the silk to resilin blocks were photochemically cross-linked into rubberlike hydrogels with reinforced mechanical properties. The increased silk-to-resilin ratio also enabled self-assembly of the resulting copolymers into fibrils in a time-dependent manner. This allowed controllable fibrillization of the copolymer solutions at the supramolecular level for subsequent photo-cross-linking into reinforced hydrogels. Alternatively, the as-prepared chemically cross-linked hydrogels could be reinforced at the material level by inducing fibrillization of the constitutive protein chains. Finally, we demonstrated the advantage of reinforcing these hydrogels for use as piezoresistive sensors to achieve an expanded pressure detection range. We anticipate that this strategy may provide intriguing opportunities to generate robust rubberlike biomaterials for broad applications.

Resilin-mimetics as a smart biomaterial platform for biomedical applications

Intrinsically disordered proteins have dramatically changed the structure-function paradigm of proteins in the 21st century. Resilin is a native elastic insect protein, which features intrinsically disordered structure, unusual multi-stimuli responsiveness and outstanding resilience. Advances in computational techniques, polypeptide synthesis methods and modular protein engineering routines have led to the development of novel resilin-like polypeptides (RLPs) including modular RLPs, expanding their applications in tissue engineering, drug delivery, bioimaging, biosensors, catalysis and bioelectronics. However, how the responsive behaviour of RLPs is encoded in the amino acid sequence level remains elusive. This review summarises the milestones of RLPs, and discusses the development of modular RLP-based biomaterials, their current applications, challenges and future perspectives. A perspective of future research is that sequence and responsiveness profiling of RLPs can provide a new platform for the design and development of new modular RLP-based biomaterials with programmable structure, properties and functions.

An in vitro assessment of the response of THP-1 macrophages to varying stiffness of a glycol-chitosan hydrogel for vocal fold tissue engineering applications

The physical properties of a biomaterial play an essential role in regulating immune and reparative activities within the host tissue. This study aimed to evaluate the immunological impact of material stiffness of a glycol-chitosan hydrogel designed for vocal fold tissue engineering. Hydrogel stiffness was varied via the concentration of glyoxal cross-linker applied. Hydrogel mechanical properties were characterized through atomic force microscopy and shear plate rheometry. Using a transwell setup, macrophages were co-cultured with human vocal fold fibroblasts that were embedded within the hydrogel. Macrophage viability and cytokine secretion were evaluated at 3, 24, and 72 hr of culture. Flow cytometry was applied to evaluate macrophage cell surface markers after 72 hr of cell culture. Results indicated that increasing hydrogel stiffness was associated with increased anti-inflammatory activity compared to relevant controls. In addition, increased anti-inflammatory activity was observed in hydrogel co-cultures. This study highlighted the importance of hydrogel stiffness from an immunological viewpoint when designing novel vocal fold hydrogels.

Redox-Responsive Resilin-Like Hydrogels for Tissue Engineering and Drug Delivery Applications

Resilin, a protein found in insect cuticles, is renowned for its outstanding elastomeric properties. The authors' laboratory previously developed a recombinant protein, which consisted of consensus resilin-like repeats from Anopheles gambiae, and demonstrated its potential in cartilage and vascular engineering. To broaden the versatility of the resilin-like protein, this study utilizes a cleavable crosslinker, which contains a disulfide bond, to develop smart resilin-like hydrogels that are redox-responsive. The hydrogels exhibit a porous structure and a stable storage modulus (G') of ≈3 kPa. NIH/3T3 fibroblasts cultured on hydrogels for 24 h have a high viability (>95%). In addition, the redox-responsive hydrogels show significant degradation in a reducing environment (10 mm glutathione (GSH)). The release profiles of fluorescently labeled dextrans encapsulated within the hydrogels are assessed in vitro. For dextran that is estimated to be larger than the mesh size of the gel, faster release is observed in the presence of reducing agents due to degradation of the hydrogel networks. These studies thus demonstrate the potential of using these smart hydrogels in a variety of applications ranging from scaffolds for tissue engineering to drug delivery systems that target the intracellular reductive environments of tumors.

Characterization of resilin-like proteins with tunable mechanical properties

Resilin is an elastomeric protein abundant in insect cuticle. Its exceptional properties, which include high resilience and efficient energy storage, motivate its potential use in tissue engineering and drug delivery applications. Our lab has previously developed recombinant proteins based on the resilin-like sequence derived from Anopheles gambiae and demonstrated their promise as a scaffold for cartilage and vascular engineering. In this work, we describe a more thorough investigation of the physical properties of crosslinked resilin-like hydrogels. The resilin-like proteins rapidly form crosslinked hydrogels in physiological conditions. We also show that the mechanical properties of these resilin-like hydrogels can be modulated simply by varying the protein concentration or the stoichiometric ratio of crosslinker to crosslinking sites. Crosslinked resilin-like hydrogels were hydrophilic and had a high water content when swollen. In addition, these hydrogels exhibited moderate resilience values, which were comparable to those of common synthetic rubbers. Cryo-scanning electron microscopy showed that the crosslinked resilin-like hydrogels at 16 wt% featured a honeycomb-like structure. These studies thus demonstrate the potential to use recombinant resilin-like proteins in a wide variety of applications such as tissue engineering and drug delivery due to their tunable physical properties.

Genetically Encoded Cholesterol-Modified Polypeptides

Biological systems use post-translational modifications (PTMs) to control the structure, location, and function of proteins after expression. Despite the ubiquity of PTMs in biology, their use to create genetically encoded recombinant biomaterials is limited. We have utilized a natural lipidation PTM (hedgehog-mediated cholesterol modification of proteins) to create a class of hybrid biomaterials called cholesterol-modified polypeptides (CHaMPs) that exhibit programmable self-assembly at the nanoscale. To demonstrate the biomedical utility of CHaMPs, we used this approach to append cholesterol to biologically active peptide exendin-4 that is an approved drug for the treatment of type II diabetes. The exendin-cholesterol conjugate self-assembled into micelles, and these micelles activate the glucagon-like peptide-1 receptor with a potency comparable to that of current gold standard treatments.

Biocompatibility of injectable resilin-based hydrogels

Vocal folds are connective tissues housed in the larynx, which can be subjected to various injuries and traumatic stimuli that lead to aberrant tissue structural alterations and fibrotic-induced biomechanical stiffening observed in patients with voice disorders. Much effort has been devoted to generate soft biomaterials that are injectable directly to sites of injury. To date, materials applied toward these applications have been largely focused on natural extracellular matrix-derived materials such as collagen, fibrin or hyaluronic acid; these approaches have suffered from the fact that materials are not sufficiently robust mechanically nor offer sufficient flexibility to modulate material properties for targeted injection. We have recently developed multiple resilin-inspired elastomeric hydrogels that possess similar mechanical properties as those reported for vocal fold tissues, and that also show promising in vitro cytocompatibility and in vivo biocompatibility. Here we report studies that test the delivery of resilin-based hydrogels through injection to the subcutaneous tissue in a wild-type mice model; histological and genetic expression outcomes were monitored. The rapid kinetics of crosslinking enabled facile injection and ensured the rapid transition of the viscous resilin precursor solution to a solid-like hydrogel in the subcutaneous space in vivo; the materials exhibited storage shear moduli in the range of 1000-2000 Pa when characterized through oscillatory rheology. Histological staining and gene expression profiles suggested minimal inflammatory profiles three weeks after injection, thereby demonstrating the potential suitability for site-specific in vivo injection of these elastomeric materials. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2229-2242, 2018.

Micromechanical characterization of soft, biopolymeric hydrogels: stiffness, resilience, and failure

Detailed understanding of the local structure-property relationships in soft biopolymeric hydrogels can be instrumental for applications in regenerative tissue engineering. Resilin-like polypeptide (RLP) hydrogels have been previously demonstrated as useful biomaterials with a unique combination of low elastic moduli, excellent resilience, and cell-adhesive properties. However, comprehensive mechanical characterization of RLP hydrogels under both low-strain and high-strain conditions has not yet been conducted, despite the unique information such measurements can provide about the local structure and macromolecular behavior underpinning mechanical properties. In this study, mechanical properties (elastic modulus, resilience, and fracture initiation toughness) of equilibrium swollen resilin-based hydrogels were characterized via oscillatory shear rheology, small-strain microindentation, and large-strain puncture tests as a function of polypeptide concentration. These methods allowed characterization, for the first time, of the resilience and failure in hydrogels with low polypeptide concentrations (<20 wt%), as the employed methods obviate the handling difficulties inherent in the characterization of such soft materials via standard mechanical techniques, allowing characterization without any special sample preparation and requiring minimal volumes (as low as 50 μL). Elastic moduli measured from small-strain microindentation showed good correlation with elastic storage moduli obtained from oscillatory shear rheology at a comparable applied strain rate, and evaluation of multiple loading-unloading cycles revealed decreased resilience values at lower hydrogel concentrations. In addition, large-strain indentation-to-failure (or puncture) tests were performed to measure large-strain mechanical response and fracture toughness on length scales similar to biological cells (∼10-50 μm) at various polypeptide concentrations, indicating very high fracture initiation toughness for high-concentration hydrogels. Our results establish the utility of employing microscale mechanical methods for the characterization of the local mechanical properties of biopolymeric hydrogels of low concentrations (<20 wt%), and show how the combination of small and large-strain measurements can provide unique insight into structure-property relationships for biopolymeric elastomers. Overall, this study provides new insight into the effects on local mechanical properties of polypeptide concentration near the overlap polymer concentration c* for resilin-based hydrogels, confirming their unique elastomeric features for applications in regenerative medicine.

Advances in Protein-Based Materials: From Origin to Novel Biomaterials

Biomaterials play a very important role in biomedicine and tissue engineering where they directly affect the cellular activities and their microenvironment . Myriad of techniques have been employed to fabricate a vast number natural, artificial and recombinant polymer s in order to harness these biomaterials in tissue regene ration , drug delivery and various other applications. Despite of tremendous efforts made in this field during last few decades, advanced and new generation biomaterials are still lacking. Protein based biomaterials have emerged as an attractive alternatives due to their intrinsic properties like cell to cell interaction , structural support and cellular communications. Several protein based biomaterials like, collagen , keratin , elastin , silk protein and more recently recombinant protein s are being utilized in a number of biomedical and biotechnological processes. These protein-based biomaterials have enormous capabilities, which can completely revolutionize the biomaterial world. In this review, we address an up-to date review on the novel, protein-based biomaterials used for biomedical field including tissue engineering, medical science, regenerative medicine as well as drug delivery. Further, we have also emphasized the novel fabrication techniques associated with protein-based materials and implication of these biomaterials in the domain of biomedical engineering .

Chemical Synthesis of Biomimetic Hydrogels for Tissue Engineering

Owing to the high water content, porous structure, biocompatibility and tissue-like viscoelasticity, hydrogels have become attractive and promising biomaterials for use in drug delivery, 3D cell culture and tissue engineering applications. Various chemical approaches have been developed for hydrogel synthesis using monomers or polymers carrying reactive functional groups. For in vivo tissue repair and in vitro cell culture purposes, it is desirable that the crosslinking reactions occur under mild conditions, do not interfere with biological processes and proceed at high yield with exceptional selectivity. Additionally, the cross-linking reaction should allow straightforward incorporation of bioactive motifs or signaling molecules, at the same time, providing tunability of the hydrogel microstructure, mechanical properties, and degradation rates. In this review, we discuss various chemical approaches applied to the synthesis of complex hydrogel networks, highlighting recent developments from our group. The discovery of new chemistries and novel materials fabrication methods will lead to the development of the next generation biomimetic hydrogels with complex structures and diverse functionalities. These materials will likely facilitate the construction of engineered tissue models that may bridge the gap between 2D experiments and animal studies, providing preliminary insight prior to in vivo assessments.

Polymeric Biomaterials: Diverse Functions Enabled by Advances in Macromolecular Chemistry

Biomaterials have been extensively used to leverage beneficial outcomes in various therapeutic applications, such as providing spatial and temporal control over the release of therapeutic agents in drug delivery as well as engineering functional tissues and promoting the healing process in tissue engineering and regenerative medicine. This perspective presents important milestones in the development of polymeric biomaterials with defined structures and properties. Contemporary studies of biomaterial design have been reviewed with focus on constructing materials with controlled structure, dynamic functionality, and biological complexity. Examples of these polymeric biomaterials enabled by advanced synthetic methodologies, dynamic chemistry/assembly strategies, and modulated cell-material interactions have been highlighted. As the field of polymeric biomaterials continues to evolve with increased sophistication, current challenges and future directions for the design and translation of these materials are also summarized.

Tissue engineering-based therapeutic strategies for vocal fold repair and regeneration

Vocal folds are soft laryngeal connective tissues with distinct layered structures and complex multicomponent matrix compositions that endow phonatory and respiratory functions. This delicate tissue is easily damaged by various environmental factors and pathological conditions, altering vocal biomechanics and causing debilitating vocal disorders that detrimentally affect the daily lives of suffering individuals. Modern techniques and advanced knowledge of regenerative medicine have led to a deeper understanding of the microstructure, microphysiology, and micropathophysiology of vocal fold tissues. State-of-the-art materials ranging from extracecullar-matrix (ECM)-derived biomaterials to synthetic polymer scaffolds have been proposed for the prevention and treatment of voice disorders including vocal fold scarring and fibrosis. This review intends to provide a thorough overview of current achievements in the field of vocal fold tissue engineering, including the fabrication of injectable biomaterials to mimic in vitro cell microenvironments, novel designs of bioreactors that capture in vivo tissue biomechanics, and establishment of various animal models to characterize the in vivo biocompatibility of these materials. The combination of polymeric scaffolds, cell transplantation, biomechanical stimulation, and delivery of antifibrotic growth factors will lead to successful restoration of functional vocal folds and improved vocal recovery in animal models, facilitating the application of these materials and related methodologies in clinical practice.