Enhanced performance of chitosan/keratin membranes with potential application in peripheral nerve repair

Keratin/chitosan film promotes wound healing in rats with combined radiation-wound injury

Human hair keratin, a natural protein derived from human hair, has emerged prominently in the field of wound repair, showcasing its unique regenerative capabilities and extensive application potential. However, it is a challenge for the keratin to efficiently therapy the impaired wound healing, such as combined radiation-wound injury. Here, we report a keratin/chitosan (KRT/CS) film for skin repair of chronic wounds in in rats with combined radiation-wound injury. In brief, the KRT/CS film was characterized by scanning electron microscopy (SEM), mechanical property analysis, water absorption, and swelling analysis. A rat model of combined radiation-wound injury was employed to evaluate the therapeutic efficacy of the KRT/CS film. Finally, the systemic biotoxicity of KRT/CS film was assessed through histological analysis. The surface of KRT/CS film was uniform and smooth compared with the KRT film, and the mechanical property, swelling rate and water absorption rate of KRT/CS film were significantly improved, which can meet the application requirements of wound excipient dressing. Furthermore, the combined radiation-wound injury in rats was established that the wound closure rate was achieved 74.46% after 14 days of treatment with KRT/CS film, comparing to the single KRT membrane and commercially available Band-Aids. Histological analysis demonstrated that the amount of angiogenesis and collagen deposition in wounds treated with KRT/CS were significantly improved. These findings demonstrate the KRT/CS film as a promising therapeutic agent for combined radiation-wound injury.

Biohacking Nerve Repair: Novel Biomaterials, Local Drug Delivery, Electrical Stimulation, and Allografts to Aid Surgical Repair

The regenerative capacity of the peripheral nervous system is limited, and peripheral nerve injuries often result in incomplete healing and poor outcomes even after repair. Transection injuries that induce a nerve gap necessitate microsurgical intervention; however, even the current gold standard of repair, autologous nerve graft, frequently results in poor functional recovery. Several interventions have been developed to augment the surgical repair of peripheral nerves, and the application of functional biomaterials, local delivery of bioactive substances, electrical stimulation, and allografts are among the most promising approaches to enhance innate healing across a nerve gap. Biocompatible polymers with optimized degradation rates, topographic features, and other functions provided by their composition have been incorporated into novel nerve conduits (NCs). Many of these allow for the delivery of drugs, neurotrophic factors, and whole cells locally to nerve repair sites, mitigating adverse effects that limit their systemic use. The electrical stimulation of repaired nerves in the perioperative period has shown benefits to healing and recovery in human trials, and novel biomaterials to enhance these effects show promise in preclinical models. The use of acellular nerve allografts (ANAs) circumvents the morbidity of donor nerve harvest necessitated by the use of autografts, and improvements in tissue-processing techniques may allow for more readily available and cost-effective options. Each of these interventions aid in neural regeneration after repair when applied independently, and their differing forms, benefits, and methods of application present ample opportunity for synergistic effects when applied in combination.

Engineering Innervated Musculoskeletal Tissues for Regenerative Orthopedics and Disease Modeling

Musculoskeletal (MSK) disorders significantly burden patients and society, resulting in high healthcare costs and productivity loss. These disorders are the leading cause of physical disability, and their prevalence is expected to increase as sedentary lifestyles become common and the global population of the elderly increases. Proper innervation is critical to maintaining MSK function, and nerve damage or dysfunction underlies various MSK disorders, underscoring the potential of restoring nerve function in MSK disorder treatment. However, most MSK tissue engineering strategies have overlooked the significance of innervation. This review first expounds upon innervation in the MSK system and its importance in maintaining MSK homeostasis and functions. This will be followed by strategies for engineering MSK tissues that induce post-implantation in situ innervation or are pre-innervated. Subsequently, research progress in modeling MSK disorders using innervated MSK organoids and organs-on-chips (OoCs) is analyzed. Finally, the future development of engineering innervated MSK tissues to treat MSK disorders and recapitulate disease mechanisms is discussed. This review provides valuable insights into the underlying principles, engineering methods, and applications of innervated MSK tissues, paving the way for the development of targeted, efficacious therapies for various MSK conditions.

Curcumin-loaded keratin-chitosan hydrogels for enhanced peripheral nerve regeneration

Peripheral nerve injury often leads to symptoms of motor and sensory impairment, and slow recovery of nerves after injury and limited treatment methods will aggravate symptoms or even lead to lifelong disability. Curcumin can promote peripheral nerve regeneration, but how to accurately deliver the appropriate concentration of curcumin in the local peripheral nerve remains to be solved. In this study, we designed a human hair keratin/chitosan (C/K) hydrogel with sodium tripolyphosphate ions crosslinked to deliver curcumin topically. Chitosan improves the mechanical properties of hydrogels and keratin improves the biocompatibility of hydrogels. C/K hydrogel showed good cytocompatibility, histocompatibility and degradability. In vitro experiments showed that hydrogels can continuously release curcumin for up to 10 days. In addition, a comprehensive analysis of behavioral, electrophysiological, histology, and target organ recovery results in animal experiments showed that locally delivered curcumin can enhance nerve regeneration in addition to hydrogels. In short, we provide a new method that combines the advantages of human hair keratin, chitosan, and curcumin for nerve damage repair.

Unveiling the potential of biomaterials and their synergistic fusion in tissue engineering

Inspired by nature, tissue engineering aims to employ intricate mechanisms for advanced clinical interventions, unlocking inherent biological potential and propelling medical breakthroughs. Therefore, medical, and pharmaceutical fields are growing interest in tissue and organ replacement, repair, and regeneration by this technology. Three primary mechanisms are currently used in tissue engineering: transplantation of cells (I), injection of growth factors (II) and cellular seeding in scaffolds (III). However, to develop scaffolds presenting highest potential, reinforcement with polymeric materials is growing interest. For instance, natural and synthetic polymers can be used. Regardless, chitosan and keratin are two biopolymers presenting great biocompatibility, biodegradability and non-antigenic properties for tissue engineering purposes offering restoration and revitalization. Therefore, combination of chitosan and keratin has been studied and results exhibit highly porous scaffolds providing optimal environment for tissue cultivation. This review aims to give an historical as well as current overview of tissue engineering, presenting mechanisms used and polymers involved in the field.

Preparation of gastrodin modified P(VDF-TrFE)-Eudragit L100-AuNPs nanofiber membranes with piezoelectric property

In recent years, electroactive nerve conduits made from a blend of P(VDF-TrFE) (poly (vinylidene fluoride-trifluoroethylene)) with other materials have shown significant progress. However, research combining P(VDF-TrFE) conduits with drug delivery systems remains sparse. In this study, we developed a novel gastrodin-loaded P(VDF-TrFE)-Eudragit L100-gold nanoparticles (Gas@PT-EL100-AuNPs) nanofiber membrane. Fabricated through electrospinning technique, this composite membrane aimed to investigate the impacts of gastrodin and AuNPs on its properties. Experimental results indicated that the incorporation of gold nanoparticles significantly reduced the fiber diameter of the membrane and enhanced the overall performance by improving hydrophilicity and piezoelectric properties. Specifically, the addition of AuNPs substantially enhanced the piezoelectric performance of the nanofiber membrane. Furthermore, the inclusion of gastrodin not only improved the membrane's hydrophilicity but also enabled effective release of the neuroprotective drug. These findings suggest that the Gas@PT-EL100-AuNPs nanofiber membrane is a novel biomaterial with potential applications in the repair and treatment of nerve injuries.

Recent advances in keratin for biomedical applications

The development of keratin-based biomaterials provides an approach to addressing related environmental pollutants and turns waste into wealth. Keratin possesses various merits, such as biocompatibility, biodegradability, hemostasis, non-immunogenicity, antibacterial activity, antioxidation, multi-responsiveness, and abundance in nature. Additionally, keratin biomaterials have been extensively employed in various biomedical applications such as drug delivery, wound healing, and tissue engineering. This review focuses on the properties and biomedical applications of keratin biomaterials. It is anticipated to provide valuable insights for the research and development of keratin biomaterials.

Advances in Large Gap Peripheral Nerve Injury Repair and Regeneration with Bridging Nerve Guidance Conduits

Peripheral nerve injury is a common complication of accidents and diseases. The traditional autologous nerve graft approach remains the gold standard for the treatment of nerve injuries. While sources of autologous nerve grafts are very limited and difficult to obtain. Nerve guidance conduits are widely used in the treatment of peripheral nerve injuries as an alternative to nerve autografts and allografts. However, the development of nerve conduits does not meet the needs of large gap peripheral nerve injury. Functional nerve conduits can provide a good microenvironment for axon elongation and myelin regeneration. Herein, the manufacturing methods and different design types of functional bridging nerve conduits for nerve conduits combined with electrical or magnetic stimulation and loaded with Schwann cells, etc., are summarized. It summarizes the literature and finds that the technical solutions of functional nerve conduits with electrical stimulation, magnetic stimulation and nerve conduits combined with Schwann cells can be used as effective strategies for bridging large gap nerve injury and provide an effective way for the study of large gap nerve injury repair. In addition, functional nerve conduits provide a new way to construct delivery systems for drugs and growth factors in vivo.

A Review of Patents and Innovative Biopolymer-Based Hydrogels

Biopolymers represent a great resource for the development and utilization of new functional materials due to their particular advantages such as biocompatibility, biodegradability and non-toxicity. "Intelligent gels" sensitive to different stimuli (temperature, pH, ionic strength) have different applications in many industries (e.g., pharmacy, biomedicine, food). This review summarizes the research efforts presented in the patent and non-patent literature. A discussion was conducted regarding biopolymer-based hydrogels such as natural proteins (i.e., fibrin, silk fibroin, collagen, keratin, gelatin) and polysaccharides (i.e., chitosan, hyaluronic acid, cellulose, carrageenan, alginate). In this analysis, the latest advances in the modification and characterization of advanced biopolymeric formulations and their state-of-the-art administration in drug delivery, wound healing, tissue engineering and regenerative medicine were addressed.

Fabrication of Wet-Spun Wool Keratin/Poly(vinyl alcohol) Hybrid Fibers: Effects of Keratin Concentration and Flow Rate

Sheep wool is one of the most common wastes derived from agriculture and also a great source of keratin. In this study, chemical reduction and alkali hydrolysis methods of extracting keratin from wool were studied for the purpose of reusing the waste wool, and the products were used to fabricate wet-spun hybrid fibers by mixing with PVA. The comparative yield of the two extraction methods was investigated, and the optimal precursor concentration ratio for keratin extraction was identified. The effects of keratin concentration and wet-spinning flow rate on the mechanical properties of fabricated fibers were studied. Therefore, this study encourages the further investigation of wool keratin-based hybrid biomaterials, which could provide a new way to reuse waste wool.

Development of Scaffolds from Bio-Based Natural Materials for Tissue Regeneration Applications: A Review

Tissue damage and organ failure are major problems that many people face worldwide. Most of them benefit from treatment related to modern technology's tissue regeneration process. Tissue engineering is one of the booming fields widely used to replace damaged tissue. Scaffold is a base material in which cells and growth factors are embedded to construct a substitute tissue. Various materials have been used to develop scaffolds. Bio-based natural materials are biocompatible, safe, and do not release toxic compounds during biodegradation. Therefore, it is highly recommendable to fabricate scaffolds using such materials. To date, there have been no singular materials that fulfill all the features of the scaffold. Hence, combining two or more materials is encouraged to obtain the desired characteristics. To design a reliable scaffold by combining different materials, there is a need to choose a good fabrication technique. In this review article, the bio-based natural materials and fine fabrication techniques that are currently used in developing scaffolds for tissue regeneration applications, along with the number of articles published on each material, are briefly discussed. It is envisaged to gain explicit knowledge of developing scaffolds from bio-based natural materials for tissue regeneration applications.

Evaluation of peripheral nerve regeneration in Murphy Roths Large mouse strain following transection injury

Aim: Murphy Roths Large (MRL/MpJ) mice have demonstrated the ability to heal with minimal or no scar formation in several tissue types. In order to identify a novel animal model, this study sought to evaluate whether this attribute applies to peripheral nerve regeneration. Materials & methods: This was a two-phase study. 6-week-old male mice were divided into two interventional groups: nerve repair and nerve graft. The MRL/MpJ was compared with the C57BL/6J strain for evaluation of both functional and histological outcomes. Results: MRL/MpJ strain demonstrated superior axon myelination and less scar formation, however functional outcomes did not show significant difference between strains. Conclusion: Superior histological outcomes did not translate into superior peripheral nerve regeneration in MRL/MpJ strain.

Zwitterionic keratin coating on silk-Laponite fibrous membranes for guided bone regeneration

Implant-related infection is one of the main challenges in periodontal diseases. According to the zwitterionic properties of keratin, we aim to develop guided bone regeneration (GBR) membrane with antibacterial and bioactivity properties using a keratin coating. In this study, electrospun silk fibroin (SF)-Laponite (LAP) fibrous membranes were developed as GBR membranes, and keratin extracted from sheep wool was electrosprayed on them. Here, the role of electrospraying time (2, 3, and 4h) on the properties of the GBR membranes was investigated. After physicochemical characterization of the keratin-modified membranes, in vitro bioactivity and degradation rate of the membranes were studied in simulated body fluid and phosphate buffer saline, respectively. Moreover, proliferation and differentiation of mesenchymal stem cells were evaluated in contact with the keratin-modified SF-LAP membrane. Finally, the antibacterial activity of membranes against gram-positive bacteria (Staphylococcus aureus) was investigated. Results demonstrated the successful formation of homogeneous wool keratin coating on SF-LAP fibrous membranes using a simple electrospray process. While wool keratin coating significantly enhanced the elongation and hydrophilicity of the SF-LAP membrane, the mechanical strength was not changed. In addition, keratin coating significantly improved the bioactivity and degradation rate of SF-LAP membranes, owing to the carboxyl groups of amino acids in keratin coating. In addition, the synergic role of LAP nanoparticles and keratin coating drastically improved osteoblast proliferation and differentiation. Finally, the zwitterionic property of wool keratin coating originating from their equal positive (NH₃ ⁺ ) and negative (COO^- ) charges considerably improved the antibacterial activity of the SF-LAP membrane. Overall, keratin-coated SF-LAP fibrous membranes with significant mechanical and biological properties could have the potential for GBR membranes.

A keratin/chitosan sponge with excellent hemostatic performance for uncontrolled bleeding

Uncontrolled bleeding leads to a higher fatality rate in the situation of surgery, traffic accidents and warfare. Traditional hemostatic materials such as bandages are not ideal for uncontrolled or incompressible bleeding. Therefore, it is of great significance to develop a new medical biomaterial with excellent rapid hemostatic effect. Keratin is a natural, biocompatible and biodegradable protein which contains amino acid sequences that induce cell adhesion. As a potential biomedical material, keratin has been developed and paid attention in tissue engineering fields such as promoting wound healing and nerve repair. Herein, a keratin/chitosan (K/C) sponge was prepared to achieve rapid hemostasis. The characterizations of K/C sponge were investigated, including SEM, TGA, liquid absorption and porosity, showing that the high porosity up to 90.12 ± 2.17 % resulted in an excellent blood absorption. The cytotoxicity test and implantation experiment proved that the K/C sponge was biocompatible and biodegradable. Moreover, the prepared K/C sponge showed better hemostatic performance than chitosan sponge (CS) and the commercially available gelatin sponge in both rat tail amputation and liver trauma bleeding models. Further experiments showed that K/C sponge plays a hemostatic role through the endogenous coagulation pathway, thus shortening the activated partial thromboplastin time (APTT) effectively. Therefore, this study provided a K/C sponge which can be served as a promising biomedical hemostatic material.

Submicron Topographically Patterned 3D Substrates Enhance Directional Axon Outgrowth of Dorsal Root Ganglia Cultured Ex Vivo

A peripheral nerve injury results in disruption of the fiber that usually protects axons from the surrounding environment. Severed axons from the proximal nerve stump are capable of regenerating, but axons are exposed to a completely new environment. Regeneration recruits cells that produce and deposit key molecules, including growth factor proteins and fibrils in the extracellular matrix (ECM), thus changing the chemical and geometrical environment. The regenerating axons thus surf on a newly remodeled micro-landscape. Strategies to enhance and control axonal regeneration and growth after injury often involve mimicking the extrinsic cues that are found in the natural nerve environment. Indeed, nano- and micropatterned substrates have been generated as tools to guide axons along a defined path. The mechanical cues of the substrate are used as guides to orient growth or change the direction of growth in response to impediments or cell surface topography. However, exactly how axons respond to biophysical information and the dynamics of axonal movement are still poorly understood. Here we use anisotropic, groove-patterned substrate topography to direct and enhance sensory axonal growth of whole mouse dorsal root ganglia (DRG) transplanted ex vivo. Our results show significantly enhanced and directed growth of the DRG sensory fibers on the hemi-3D topographic substrates compared to a 0 nm pitch, flat control surface. By assessing the dynamics of axonal movement in time-lapse microscopy, we found that the enhancement was not due to increases in the speed of axonal growth, but to the efficiency of growth direction, ensuring axons minimize movement in undesired directions. Finally, the directionality of growth was reproduced on topographic patterns fabricated as fully 3D substrates, potentially opening new translational avenues of development incorporating these specific topographic feature sizes in implantable conduits in vivo.

A hemostatic keratin/alginate hydrogel scaffold with methylene blue mediated antimicrobial photodynamic therapy

Uncontrollable bleeding and infection are two of the most common causes of trauma-related death. Yet, developing safe materials with high hemostatic and antibacterial effectiveness remains a challenge. Keratin-based biomaterials have been reported to exhibit the functions of enhancing platelet binding and activating and facilitating fibrinogen polymerization. In this study, we designed a hemostatic material with good biodegradability, biocompatibility, hemostatic ability, and antibacterial function to solve the shortcomings of common hemostatic materials. Methylene blue-loaded keratin/alginate composite scaffolds were prepared by the freeze-gelation method. The composite scaffolds exhibited over 1600% liquid absorption, well-interconnected pores, good biocompatibility, and biodegradability. We find that the keratin/alginate composite scaffolds' synergistic action may significantly reduce hemostasis time. To prevent infection, the drug-loaded scaffolds generated high burst release by absorbing wound exudate in the early stages of wound healing. The results obtained by the antimicrobial photoinactivation assay in vitro suggest that an antimicrobial photodynamic effect might be triggered, thereby preventing the fast growth of colonies.

Engineering Biomimetic Extracellular Matrix with Silica Nanofibers: From 1D Material to 3D Network

Biomaterials at nanoscale is a fast-expanding research field with which extensive studies have been conducted on understanding the interactions between cells and their surrounding microenvironments as well as intracellular communications. Among many kinds of nanoscale biomaterials, mesoporous fibrous structures are especially attractive as a promising approach to mimic the natural extracellular matrix (ECM) for cell and tissue research. Silica is a well-studied biocompatible, natural inorganic material that can be synthesized as morpho-genetically active scaffolds by various methods. This review compares silica nanofibers (SNFs) to other ECM materials such as hydrogel, polymers, and decellularized natural ECM, summarizes fabrication techniques for SNFs, and discusses different strategies of constructing ECM using SNFs. In addition, the latest progress on SNFs synthesis and biomimetic ECM substrates fabrication is summarized and highlighted. Lastly, we look at the wide use of SNF-based ECM scaffolds in biological applications, including stem cell regulation, tissue engineering, drug release, and environmental applications.

Sustainable Applications of Animal Waste Proteins

Currently, the growth of the global population leads to an increase in demand for agricultural products. Expanding the obtaining and consumption of food products results in a scale up in the amount of by-products formed, the development of processing methods for which is becoming an urgent task of modern science. Collagen and keratin make up a significant part of the animal origin protein waste, and the potential for their biotechnological application is almost inexhaustible. The specific fibrillar structure allows collagen and keratin to be in demand in bioengineering in various forms and formats, as a basis for obtaining hydrogels, nanoparticles and scaffolds for regenerative medicine and targeted drug delivery, films for the development of biodegradable packaging materials, etc. This review describes the variety of sustainable sources of collagen and keratin and the beneficial application multiformity of these proteins.

Electrospun Polycaprolactone (PCL)-Amnion Nanofibrous Membrane Promotes Nerve Regeneration and Prevents Fibrosis in a Rat Sciatic Nerve Transection Model

Functional recovery after peripheral nerve injury repair is typically unsatisfactory. An anastomotically poor microenvironment and scarring at the repair site are important factors impeding nerve regeneration. In this study, an electrospun poly-e-caprolactone (PCL)-amnion nanofibrous membrane comprising an amnion membrane and nonwoven electrospun PCL was used to wrap the sciatic nerve repair site in the rat model of a sciatic nerve transection. The effect of the PCL-amnion nanofibrous membrane on improving nerve regeneration and preventing scarring at the repair site was evaluated by expression of the inflammatory cytokine, sciatic functional index (SFI), electrophysiology, and histological analyses. Four weeks after repair, the degree of nerve adhesion, collagen deposition, and intraneural macrophage invasion of the PCL-amnion nanofibrous membrane group were significantly decreased compared with those of the Control group. Moreover, the PCL-amnion nanofibrous membrane decreased the expression of pro-inflammatory cytokines such as interleukin(IL)-6, Tumor Necrosis Factor(TNF)-a and the number of pro-inflammatory M1 macrophages, and increased the expression of anti-inflammatory cytokine such as IL-10, IL-13 and anti-inflammatory M2 macrophages. At 16 weeks, the PCL-amnion nanofibrous membrane improved functional recovery, including promoting nerve Schwann cell proliferation, axon regeneration, and reducing the time of muscle denervation. In summary, the PCL-amnion nanofibrous membrane effectively improved nerve regeneration and prevent fibrosis after nerve repair, which has good clinical application prospect for tissue repair.

Application of wool keratin: an anti-ultraviolet wall material in spray drying

Low-molecular-weight keratin (LMWK) obtained from wool was employed as a wall material for the spray drying encapsulation of fish oil. Microcapsules with different LMWK contents were prepared, and their anti-ultraviolet performance and other features were studied. The results showed that LMWK was able to improve the encapsulation efficiency of fish oil because of its good emulsifying properties. When the LMWK content was increased from 0 to 10, 30 and 50%, the shelf life of the microcapsules under ultraviolet irradiation increased from 48 to 96 h, 144 h and 168 h, respectively. The strongest absorption efficiency of LMWK is shown in the UVc band. The chemical structure of LMWK did not change during an ultraviolet accelerating ageing test.

Polymer Scaffolds for Biomedical Applications in Peripheral Nerve Reconstruction

The nervous system is a significant part of the human body, and peripheral nerve injury caused by trauma can cause various functional disorders. When the broken end defect is large and cannot be repaired by direct suture, small gap sutures of nerve conduits can effectively replace nerve transplantation and avoid the side effect of donor area disorders. There are many choices for nerve conduits, and natural materials and synthetic polymers have their advantages. Among them, the nerve scaffold should meet the requirements of good degradability, biocompatibility, promoting axon growth, supporting axon expansion and regeneration, and higher cell adhesion. Polymer biological scaffolds can change some shortcomings of raw materials by using electrospinning filling technology and surface modification technology to make them more suitable for nerve regeneration. Therefore, polymer scaffolds have a substantial prospect in the field of biomedicine in future. This paper reviews the application of nerve conduits in the field of repairing peripheral nerve injury, and we discuss the latest progress of materials and fabrication techniques of these polymer scaffolds.

Protein-Based 3D Biofabrication of Biomaterials

Protein/peptide-based hydrogel biomaterial inks with the ability to incorporate various cells and mimic the extracellular matrix's function are promising candidates for 3D printing and biomaterials engineering. This is because proteins contain multiple functional groups as reactive sites for enzymatic, chemical modification or physical gelation or cross-linking, which is essential for the filament formation and printing processes in general. The primary mechanism in the protein gelation process is the unfolding of its native structure and its aggregation into a gel network. This network is then stabilized through both noncovalent and covalent cross-link. Diverse proteins and polypeptides can be obtained from humans, animals, or plants or can be synthetically engineered. In this review, we describe the major proteins that have been used for 3D printing, highlight their physicochemical properties in relation to 3D printing and their various tissue engineering application are discussed.

Newer guar gum ester/chicken feather keratin interact films for tissue engineering

This work intends to synthesis newer guar gum indole acetate ester and design film scaffolds based on protein-polysaccharide interactions for tissue engineering applications. Guar gum indole acetate(GGIA) was synthesized for the first time from guar gum in presence of aprotic solvent activated hofmeister ions. The newer biopolymer was fully characterized in FT-IR,¹³C NMR, XRD and TGA analysis. High DS (Degree of Substitution, DS = 0.61) GGIA was cross-linked with hydrolyzed keratin, extracted from chicken feather wastes. Films were synthesized from different biopolymer ratios and the surface chemistry appeared interesting. Physicochemical properties for GGIA-keratin association were notable. Fully bio-based films were non-cytotoxic and exhibited excellent biocompatibility for human dermal fibroblast cell cultivations. The film scaffold showed 63% porosity and the recorded tensile strength at break was 6.4 MPa. Furthermore, the standardised film exerted superior antimicrobial activity against both the Gram-positive and Gram-negative bacteria. MICs were recorded at 130 μg/mL and 212 μg/mL for E. coli and S. aureus respectively. In summary, GGIA-keratin film scaffolds represented promising platforms for skin tissue engineering applications.

Electrofabrication of flexible and mechanically strong tubular chitosan implants for peripheral nerve regeneration

The development of peripheral nerve tissue engineering requires a safe and reliable methodology to construct biodegradable conduits. Herein, a new type of chitosan-based nerve-guide hydrogel conduit (CNHC) with enhanced mechanical flexibility in the wet state was fabricated using a one-step electrofabrication technology. The formation of the chitosan conduit is a physical process which can be conducted in a mild water phase without toxic crosslinks. The current density during electrofabrication has a profound effect on the physical and structural properties of the conduits. Cytocompatibility results indicate that the CNHC can promote cell proliferation and adhesion. Functional and histological tests indicate that the CNHC has the ability to guide the growth of axons through the conduit to reach a distal stump, which is closely similar to the autograft group. Overall, the results of this study demonstrate that the CNHCs from electrofabrication have a great potential in peripheral nerve regeneration.

Chitin and Chitosan Derivatives as Biomaterial Resources for Biological and Biomedical Applications

Chitin is a long-chain polymer of N-acetyl-glucosamine, which is regularly found in the exoskeleton of arthropods including insects, shellfish and the cell wall of fungi. It has been known that chitin can be used for biological and biomedical applications, especially as a biomaterial for tissue repairing, encapsulating drug for drug delivery. However, chitin has been postulated as an inducer of proinflammatory cytokines and certain diseases including asthma. Likewise, chitosan, a long-chain polymer of N-acetyl-glucosamine and d-glucosamine derived from chitin deacetylation, and chitosan oligosaccharide, a short chain polymer, have been known for their potential therapeutic effects, including anti-inflammatory, antioxidant, antidiarrheal, and anti-Alzheimer effects. This review summarizes potential utilization and limitation of chitin, chitosan and chitosan oligosaccharide in a variety of diseases. Furthermore, future direction of research and development of chitin, chitosan, and chitosan oligosaccharide for biomedical applications is discussed.

Peripheral Nerve Regeneration and Muscle Reinnervation

Injured peripheral nerves but not central nerves have the capacity to regenerate and reinnervate their target organs. After the two most severe peripheral nerve injuries of six types, crush and transection injuries, nerve fibers distal to the injury site undergo Wallerian degeneration. The denervated Schwann cells (SCs) proliferate, elongate and line the endoneurial tubes to guide and support regenerating axons. The axons emerge from the stump of the viable nerve attached to the neuronal soma. The SCs downregulate myelin-associated genes and concurrently, upregulate growth-associated genes that include neurotrophic factors as do the injured neurons. However, the gene expression is transient and progressively fails to support axon regeneration within the SC-containing endoneurial tubes. Moreover, despite some preference of regenerating motor and sensory axons to “find” their appropriate pathways, the axons fail to enter their original endoneurial tubes and to reinnervate original target organs, obstacles to functional recovery that confront nerve surgeons. Several surgical manipulations in clinical use, including nerve and tendon transfers, the potential for brief low-frequency electrical stimulation proximal to nerve repair, and local FK506 application to accelerate axon outgrowth, are encouraging as is the continuing research to elucidate the molecular basis of nerve regeneration.

Gene set enrichment analysis and protein-protein interaction network analysis after sciatic nerve injury

Background

Peripheral nerves are able to regenerate spontaneously after injury. An increasing number of studies have investigated the mechanism of peripheral nerve regeneration and attempted to find potential therapeutic targets. The various bioinformatics analysis tools available, gene set enrichment analysis (GSEA) and protein-protein interaction (PPI) networks can effectively screen the crucial targets of neuroregeneration.

Methods

GSEA and PPI networks were constructed through ingenuity pathway analysis and sequential gene expression validation ex vitro to investigate the molecular processes at 1, 4, 7, and 14 days following sciatic nerve transection in rats.

Results

Immune response and the activation of related canonical pathways were classified as crucial biological events. Additionally, neural precursor cell expressed developmentally downregulated 4-like (NEDD4L), neuregulin 1 (NRG1), nuclear factor of activated T cells 2 (NFATC2), midline 1 (MID1), GLI family zinc finger 2 (GLI2), and ventral anterior homeobox 1 (VAX1), which were jointly involved in both immune response and axonal regeneration, were screened and their mRNA and protein expressions following nerve injury were validated. Among them, the expression of VAX1 continuously increased following nerve injury, and it was considered to be a potential therapeutic target.

Conclusions

The combined use of GSEA and PPI networks serves as a valuable way to identify potential therapeutic targets for neuroregeneration.

The progress of biomaterials in peripheral nerve repair and regeneration

Repair and regeneration of the injured peripheral nerve (PN) is a challenging issue in clinics. Although the regeneration outcome of large PN defects is currently unsatisfactory, recently, the study of PN repair has considerably progressed. In particular, biomaterials for repairing PNs, such as nerve guidance conduits and nerve repair membranes, have been well developed. Herein, we summarize the anatomy of the PN, the pathophysiological features of the nerve injury, and the repair process post injury. Then, we highlight the progress in the development of natural and synthetic biomaterials and summarize the applications, advantages, and disadvantages of these materials. These materials can be used as nerve repair membranes and nerve conduits in the field of PN repair. Finally, we discuss the challenges encountered and development strategies for PN repair in the future.