Sustained Local Release of NGF from a Chitosan-Sericin Composite Scaffold for Treating Chronic Nerve Compression

A review: Carrier-based hydrogels containing bioactive molecules and stem cells for ischemic stroke therapy

Ischemic stroke (IS), a cerebrovascular disease, is the leading cause of physical disability and death worldwide. Tissue plasminogen activator (tPA) and thrombectomy are limited by a narrow therapeutic time window. Although strategies such as drug therapies and cellular therapies have been used in preclinical trials, some important issues in clinical translation have not been addressed: low stem cell survival and drug delivery limited by the blood-brain barrier (BBB). Among the therapeutic options currently sought, carrier-based hydrogels hold great promise for the repair and regeneration of neural tissue in the treatment of ischemic stroke. The advantage lies in the ability to deliver drugs and cells to designated parts of the brain in an injectable manner to enhance therapeutic efficacy. Here, this article provides an overview of the use of carrier-based hydrogels in ischemic stroke therapy and focuses on the use of hydrogel scaffolds containing bioactive molecules and stem cells. In addition to this, we provide a more in-depth summary of the composition, physicochemical properties and physiological functions of the materials themselves. Finally, we also outline the prospects and challenges for clinical translation of hydrogel therapy for IS.

Sericin Electrodes with Self-Adhesive Properties for Biosignaling

The combination of green manufacturing approaches and bioinspired materials is growingly emerging in different scenarios, in particular in medicine, where widespread medical devices (MDs) as commercial electrodes for electrophysiology strongly increase the accumulation of solid waste after use. Electrocardiogram (ECG) electrodes exploit electrolytic gels to allow the high-quality recording of heart signals. Beyond their nonrecyclability/nonrecoverability, gel drying also affects the signal quality upon prolonged monitoring of biopotentials. Moreover, gel composition often causes skin reactions. This study aims to address the above limitation by presenting a composite based on the combination of silk sericin (SS) as a structural material, poly(vinyl alcohol) (PVA) as a robustness enhancer, and CaCl2 as a plasticizer. SS/PVA/CaCl2 formulations, optimized in terms of weight content (wt %) of single constituents, result in a biocompatible, biodegradable "green" material (free from potentially irritating cross-linking agents) that is, above all, self-adhesive on skin. The best formulation, i.e., SS(4 wt %)/PVA(4 wt %)/CaCl2(20 wt %), in terms of long-lasting skin adhesion (favored by calcium-ion coordination in the presence of environmental/skin humidity) and time-stability of electrode impedance, is used to assemble ECG electrodes showing quality trace recording over longer time scales (up to 6 h) than commercial electrodes. ECG recording is performed using customized electronics coupled to an app for data visualization.

Compliant immune response of silk-based biomaterials broadens application in wound treatment

The unique properties of sericin and silk fibroin (SF) favor their widespread application in biopharmaceuticals, particularly in wound treatment and bone repair. The immune response directly influences wound healing cycle, and the extensive immunomodulatory functions of silk-based nanoparticles and hydrogels have attracted wide attention. However, different silk-processing methods may trigger intense immune system resistance after implantation into the body. In this review, we elaborate on the inflammation and immune responses caused by the implantation of sericin and SF and also explore their anti-inflammatory properties and immune regulatory functions. More importantly, we describe the latest research progress in enhancing the immunotherapeutic and anti-inflammatory effects of composite materials prepared from silk from a mechanistic perspective. This review will provide a useful reference for using the correct processes to exploit silk-based biomaterials in different wound treatments.

Compressive stresses in cancer: characterization and implications for tumour progression and treatment

Beyond their many well-established biological aberrations, solid tumours create an abnormal physical microenvironment that fuels cancer progression and confers treatment resistance. Mechanical forces impact tumours across a range of biological sizes and timescales, from rapid events at the molecular level involved in their sensing and transmission, to slower and larger-scale events, including clonal selection, epigenetic changes, cell invasion, metastasis and immune response. Owing to challenges with studying these dynamic stimuli in biological systems, the mechanistic understanding of the effects and pathways triggered by abnormally elevated mechanical forces remains elusive, despite clear correlations with cancer pathophysiology, aggressiveness and therapeutic resistance. In this Review, we examine the emerging and diverse roles of physical forces in solid tumours and provide a comprehensive framework for understanding solid stress mechanobiology. We first review the physiological importance of mechanical forces, especially compressive stresses, and discuss their defining characteristics, biological context and relative magnitudes. We then explain how abnormal compressive stresses emerge in tumours and describe the experimental challenges in investigating these mechanically induced processes. Finally, we discuss the clinical translation of mechanotherapeutics that alleviate solid stresses and their potential to synergize with chemotherapy, radiotherapy and immunotherapies.

Application of cell transplantation in the treatment of neuropathic pain

Nerve injury can not only lead to sensory and motor dysfunction, but also be complicated with neuropathic pain (NPP), which brings great psychosomatic injury to patients. At present, there is no effective treatment for NPP. Based on the functional characteristics of cell transplantation in nerve regeneration and injury repair, cell therapy has been used in the exploratory treatment of NPP and has become a promising treatment of NPP. In this article, we discuss the current mainstream cell types for the treatment of NPP, including Schwann cells, olfactory ensheathing cells, neural stem cells and mesenchymal stem cells in the treatment of NPP. These bioactive cells transplanted into the host have pharmacological properties of decreasing pain threshold and relieving NPP by exerting nutritional support, neuroprotection, immune regulation, promoting axonal regeneration, and remyelination. Cell transplantation can also change the microenvironment around the nerve injury, which is conducive to the survival of neurons. It can effectively relieve pain by repairing the injured nerve and rebuilding the nerve function. At present, some preclinical and clinical studies have shown that some encouraging results have been achieved in NPP treatment based on cell transplantation. Therefore, we discussed the feasible strategy of cell transplantation as a treatment of NPP and the problems and challenges that need to be solved in the current application of cell transplantation in NPP therapy.

Expanding the boundaries of silk sericin biomaterials in biomedical applications

Silk sericin (SS) has a long history as a by-product of the textile industry. SS has emerged as a sustainable material for biomedical engineering due to its material properties including water solubility, diverse impact on biological activities including antibacterial and antioxidant properties, and ability to promote cell adhesion and proliferation. This review addresses the origin, structure, properties, extraction, and underlying functions of this protein. An overview of the growing research studies and market evolution is presented, along with highlights of the most common fabrication matrices (hydrogels, bioinks, porous and fibrous scaffolds) and tissue engineering applications. Finally, the future trends with this protein as a multifaceted toolbox for bioengineering are explored, along with the challenges with SS. Overall, the present review can serve as a foundation for the creation of innovative biomaterials utilizing SS as a fundamental building block that hold market potential.

Development and Application of an Advanced Biomedical Material-Silk Sericin

Sericin, a protein derived from silkworm cocoons, is considered a waste product derived from the silk industry for thousands of years due to a lack of understanding of its properties. However, in recent decades, a range of exciting properties of sericin are studied and uncovered, including cytocompatibility, low-immunogenicity, photo-luminescence, antioxidant properties, as well as cell-function regulating activities. These properties make sericin-based biomaterials promising candidates for biomedical applications. This review summarizes the properties and bioactivities of silk sericin and highlights the latest developments in sericin in tissue engineering and regenerative medicine. Furthermore, the extended application of sericin in developing flexible electronic devices and 3D bioprinting is also discussed. It is believed that sericin-based biomaterials have great potential of being developed into novel tissue engineering products and smart implantable devices for various medical applications toward improving clinical outcomes.

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.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

Transparent injectable sericin-honey hydrogel with antioxidant and antibacterial activities combined with feeding sericin accelerates diabetic wound healing

Wound healing in diabetics is often impaired or delayed due to the presence of high reactive oxygen species and low antioxidant levels. Here, a sericin-honey semi-interpenetrating network hydrogel with excellent antioxidant activity was prepared. Besides, the sericin-honey hydrogel is transparent, injectable, sticky, highly porous, and has good swelling properties, antibacterial activity, and cell compatibility. Based on its good performancein vitro, sericin-honey hydrogel achieved effectivein vivotreatment on a mouse diabetic wound model, significantly accelerating the wound healing process. Furthermore, the combined effect of feeding sericin solution played a positive role in strengthening the effect of diabetic wound repair.

Comparative evaluation of divergent concoction of NGF, BDNF, EGF, and FGF growth factor's role in enhancing neuronal differentiation of adipose-derived mesenchymal stem cells

MSCs (Mesenchymal Stem Cells) can differentiate into various lineages, including neurons and glial cells. In the past few decades, MSCs have been well explored in the context of neuronal differentiation and have been reported to have the immense potential to form distinct kinds of neurons. The distinguishing features of MSCs make them among the most desired cell sources for stem cell therapy. This study involved the trans-differentiation of Adipose-derived human Mesenchymal Stem Cells (ADMSCs) into neurons. The protocol employs a cocktail of chemical inducers in different combinations, including Brain-derived neurotrophic factor (BDNF), epidermal growth factor (EGF), and Nerve growth factor (NGF) Fibroblastic growth factor (FGF), in induction media. Both types have been successfully differentiated into neurons, confirmed by morphological aspects and the presence of neural-specific markers through RT-PCR (Reverse transcription polymerase chain reaction) studies and immunocytochemistry assay. They have shown excellent morphology with long neurites, synaptic connections, and essential neural markers to validate their identity. The results may significantly contribute to cell replacement therapy for neurological disorders.

Multifunctional wet-adhesive chitosan/acrylic conduit for sutureless repair of peripheral nerve injuries

The incidence of peripheral nerve injury (PNI) is high worldwide, and a poor prognosis is common. Surgical closure and repair of the affected area are crucial to ensure the effective treatment of peripheral nerve injuries. Despite being the standard treatment approach, reliance on sutures to seal the severed nerve ends introduces several limitations and restrictions. This technique is intricate and time-consuming, and the application of threading and punctate sutures may lead to tissue damage and heightened tension concentrations, thus increasing the risk of fixation failure and local inflammation. This study aimed to develop easily implantable chitosan-based peripheral nerve repair conduits that combine acrylic acid and cleavable N-hydroxysuccinimide to reduce nerve damage during repair. In ex vivo tissue adhesion tests, the conduit achieved maximal interfacial toughness of 705 J m-2 ± 30 J m-2, allowing continuous bridging of the severed nerve ends. Adhesive repair significantly reduces local inflammation caused by conventional sutures, and the positive charge of chitosan disrupts the bacterial cell wall and reduces implant-related infections. This promises to open new avenues for sutureless nerve repair and reliable medical implants.

Challenges and progress of neurodrug: bioactivities, production and delivery strategies of nerve growth factor protein

Nerve growth factor (NGF) is a vital cytokine that plays a crucial role in the development and regeneration of the nervous system. It has been extensively studied for its potential therapeutic applications in various neural diseases. However, as a protein drug, limited natural source seriously hinders its translation and clinical applications. Conventional extraction of NGF from mouse submandibular glands has a very high cost and potentially induces immunogenicity; total synthesis and semi-synthesis methods are alternatives, but have difficulty in obtaining correct protein structure; gene engineering of plant cells is thought to be non-immunogenic, bioactive and economical. Meanwhile, large molecular weight, high polarity, and negative electrical charge make it difficult for NGF to cross the blood brain barrier to reach therapeutic targets. Current delivery strategies mainly depend on the adenovirus and cell biodelivery, but the safety and efficacy remain to be improved. New materials are widely investigated for the controllable, safe and precise delivery of NGF. This review illustrates physiological and therapeutic effects of NGF for various diseases. Moreover, new progress in production and delivery technologies for NGF are summarized. Bottlenecks encountered in the development of NGF as therapeutics are also discussed with the countermeasures proposed.

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.

Prospects of Using Chitosan-Based Biopolymers in the Treatment of Peripheral Nerve Injuries

Peripheral nerve injuries are common neurological disorders, and the available treatment options, such as conservative management and surgical repair, often yield limited results. However, there is growing interest in the potential of using chitosan-based biopolymers as a novel therapeutic approach to treating these injuries. Chitosan-based biopolymers possess unique characteristics, including biocompatibility, biodegradability, and the ability to stimulate cell proliferation, making them highly suitable for repairing nerve defects and promoting nerve regeneration and functional recovery. Furthermore, these biopolymers can be utilized in drug delivery systems to control the release of therapeutic agents and facilitate the growth of nerve cells. This comprehensive review focuses on the latest advancements in utilizing chitosan-based biopolymers for peripheral nerve regeneration. By harnessing the potential of chitosan-based biopolymers, we can pave the way for innovative treatment strategies that significantly improve the outcomes of peripheral nerve injury repair, offering renewed hope and better prospects for patients in need.

Sericin from Fibroin-Deficient Silkworms Served as a Promising Resource for Biomedicine

Sericin, a fascinating natural biomaterial derived from silkworms, has received increasing interest in recent years for its unique bioactivity and high compatibility. Silkworms can be divided into wild-type or silk fibroin-deficient mutants according to whether they synthesize and secrete silk fibroin. Silk fibroin-deficient mutant silkworms and their cocoons are convenient for us to obtain diverse and high-quality sericin, which has been applicated in various fields such as cell culture, tissue engineering, drug delivery, and cosmetics. Here, we present an overview of our silkworm varieties resources, especially silk fibroin-deficient mutant silkworms. We optimized various extraction methods of sericin and summarized the characteristics and advantages of sericin. Finally, we developed and discussed a series of sericin-based biomaterials for promising applications for a diverse set of needs.

A hyaluronic acid/silk fibroin/poly-dopamine-coated biomimetic hydrogel scaffold with incorporated neurotrophin-3 for spinal cord injury repair

Bio-factor stimulation is essential for axonal regeneration in the central nervous system. Thus, persistent and efficient factor delivery in the local microenvironment is an ideal strategy for spinal cord injury repair. We developed a biomimetic hydrogel scaffold to load biofactors in situ and release them in a controlled way as a promising therapeutic modality. Hyaluronic acid and silk fibroin were cross-linked as the basement of the scaffolds, and poly-dopamine coating was used to further increase the loading of factors and endow the hydrogel scaffolds with ideal physical and chemical properties and proper biocompatibility. Notably, neurotrophin-3 release from the hydrogel scaffolds was prolonged to 28 days. A spinal cord injury model was constructed for hydrogel scaffold transplantation. After eight weeks, significant NF200-positive nerve fibers were observed extending across the glial scar to the center of the injured area. Due to the release of neurotrophin-3, spinal cord regeneration was enhanced, and the cavity area of the injury graft site and inflammation associated with CD68 positive cells were reduced, which led to a significant improvement in hind limb motor function. The results show that the hyaluronic acid/silk fibroin/poly-dopamine-coated biomimetic hydrogel scaffold achieved locally slow release of neurotrophin-3, thus facilitating the regeneration of injured spinal cord. STATEMENT OF SIGNIFICANCE: Hydrogels have received great attention in spinal cord regeneration. Current research has focused on more efficient and controlled release of bio-factors. Here, we adopted a mussel-inspired strategy to functionalize the hyaluronic acid/silk fibroin hydrogel scaffold to increase the load of neurotrophin-3 and extend the release time. The hydrogel scaffolds have ideal physiochemical properties, proper release rate, and biocompatibility. Owing to the continuous neurotrophin-3 release from implanted scaffolds, cavity formation is reduced, inflammation alleviated, and spinal cord regeneration enhanced, indicating great potential for bio-factor delivery in soft tissue regeneration applications.

Silk sericin as building blocks of bioactive materials for advanced therapeutics

Silk sericin is a class of protein biopolymers produced by silkworms. Increasing attention has been paid to silk sericin for biomedical applications in the last decade, not only because of its excellent biocompatibility and biodegradability but also due to the pharmacological activities stemming from its unique amino acid compositions. In this review, the biological properties of silk sericin, including curing specific diseases and promoting tissue regeneration, as well as underlying mechanisms are summarized. We consider the antioxidant activity of silk sericin as a fundamental property, which could account for partial biological activities, despite the exact mechanisms of silk sericin's effect remaining unknown. Based on the reactive groups on silk sericin, approaches of bottom-up fabrication of silk sericin-based biomaterials are highlighted, including non-covalent interactions and chemical reactions (reduction, crosslinking, bioconjugation, and polymerization). We then briefly present the cutting-edge advances of silk sericin-based biomaterials applied in tissue engineering and drug delivery. The challenges of silk sericin-based biomaterials are proposed. With more bioactivities and underlying mechanisms of silk sericin uncovered, it is going to boost the therapeutic potential of silk sericin-based biomaterials.

Biomechanically-Adapted Immunohydrogels Reconstructing Myelin Sheath for Peripheral Nerve Regeneration

Myelin sheath reconstruction plays an important role in peripheral nerve regeneration. But the hindered reconstruction of myelin sheath, due to the inadequate repair phenotypes of macrophages and Schwann cells after peripheral nerve injury, often causes poor functional nerve recovery. Here, biomechanically-adapted immunohydrogels are prepared as the FK506-loaded platforms and nerve tissue engineering scaffolds to reconstruct myelin sheath for peripheral nerve regeneration. By immunofluorescent staining, an increase in the proportion of F4/80⁺ markers reveals that the biomechanically-adapted scaffolds facilitate recruitment of macrophages. Furthermore, the high Interleukin 10 (IL-10) mRNA expression level suggests the anti-inflammation learning effects of FK506 in vitro, which is further confirmed by a high CD206/TNF-α ratio in the FK506 Gel group in vivo. The immune learning effects are positively related to the increase in compactness and thickness of myelin sheath, indicating the synergy of structural reconstruction of myelin sheath and M2 phenotype polarization of macrophages. All these data indicate that the biomechanically-adapted immunohydrogels enhance recruitment of macrophages, educate M2 polarization of macrophages and promote a neuroprotective environment, which in consequence reconstructs myelin sheath for peripheral nerve regeneration.

Silk sericin patches delivering miRNA-29-enriched extracellular vesicles-decorated myoblasts (SPEED) enhances regeneration and functional repair after severe skeletal muscle injury

Severe skeletal muscle injuries usually lead to a series of poor recovery issues, such as massive myofibers loss, scar tissue formation, significant muscle function impairment, etc. Here, a silk sericin patch delivering miRNA-29-enriched extracellular vesicles-decorated myoblasts (SPEED) is designed for the rapid regeneration and functional repair after severe skeletal muscle injury. Specifically, miR29-enriched extracellular vesicles (miR29-EVs) are prepared and used to deliver miR29 into primary myoblasts, which promote the myotube formation of myoblasts and increase the expression of myogenic genes while inhibiting the expression of fibrotic genes. Our results indicate that miR29-EVs promote the integration of primary myoblasts and host muscle in a severe mouse tibialis anterior (TA) muscle injury model. Moreover, implantation of SPEED drastically stimulates skeletal muscle regeneration, inhibits fibrosis of injured muscles, and leads to significant improvement of muscle contraction forces and motor ability of mice about 3 weeks after treatment. Subsequently, we further evaluate the transcriptomes of TA muscles and find that SPEED can significantly ameliorate energy metabolism and muscular microenvironment of TA muscles on day 9 after implantation. Additionally, bioinformatic analysis and comprehensive molecular biology studies also reveal that the down-regulation of CDC20-MEF2C signaling axis may participate in the muscle repair process. Together, SPEED may serve as an effective alternative for the rapid repair of severe skeletal muscle injuries in the future.

Silk sericin-based materials for biomedical applications

Silk sericin, a natural protein extracted from silkworm cocoons, has been extensively studied and utilized in the biomedical field because of its superior biological activities and controllable chemical-physical properties. Sericin is biocompatible and naturally cell adhesive, enabling cell attachment, proliferation, and differentiation in sericin-based materials. Moreover, its abundant functional groups from variable amino acids composition allow sericin to be chemically modified and cross-linked to form versatile constructs serving as alternative matrixes for biomedical applications. Recently, sericin has been constructed into various types of biomaterials for tissue engineering and regenerative medicine, including various bulk constructions (films, hydrogels, scaffolds, conduits, and devices) and micro-nano formulations. In this review, we systemically summarize the properties of silk sericin, introduce its different forms, and demonstrate their newly-developed as well as potential biomedical applications.

Design and Fabrication of Polymeric Hydrogel Carrier for Nerve Repair

Nerve regeneration and repair still remain a huge challenge for both central nervous and peripheral nervous system. Although some therapeutic substances, including neuroprotective agents, clinical drugs and stem cells, as well as various growth factors, are found to be effective to promote nerve repair, a carrier system that possesses a sustainable release behavior, in order to ensure high on-site concentration during the whole repair and regeneration process, and high bioavailability is still highly desirable. Hydrogel, as an ideal delivery system, has an excellent loading capacity and sustainable release behavior, as well as tunable physical and chemical properties to adapt to various biomedical scenarios; thus, it is thought to be a suitable carrier system for nerve repair. This paper reviews the structure and classification of hydrogels and summarizes the fabrication and processing methods that can prepare a suitable hydrogel carrier with specific physical and chemical properties. Furthermore, the modulation of the physical and chemical properties of hydrogels is also discussed in detail in order to obtain a better therapeutic effect to promote nerve repair. Finally, the future perspectives of hydrogel microsphere carriers for stroke rehabilitation are highlighted.

Silk Sericin Enrichment through Electrodeposition and Carbonous Materials for the Removal of Methylene Blue from Aqueous Solution

The recycling and reuse of biomass waste for the preparation of carbon-based adsorbents is a sustainable development strategy that has a positive environmental impact. It is well known that a large amount of silk sericin (SS) is dissolved in the wastewater from the silk industry. Utilizing the SS instead of discharging it into the environment without further treatment would reduce environmental and ecological problems. However, effective enrichment of the SS from the aqueous solution is a challenge. Here, with the help of carboxymethyl chitosan (CMCS), which can form a gel structure under low voltage, an SS/CMCS hydrogel with SS as the major component was prepared via electrodeposition at a 3 V direct-current (DC) voltage for five minutes. Following a carbonization process, an SS-based adsorbent with good performance for the removal of methylene blue (MB) from an aqueous solution was prepared. Our results reveal that the SS/CMCS hydrogel maintains a porous architecture before and after carbonization. Such structure provides abundant adsorption sites facilitating the adsorption of MB molecules, with a maximum adsorptive capacity of 231.79 mg/g. In addition, it suggests that the adsorption is an exothermic process, has a good fit with the Langmuir model, and follows the intra-particle diffusion model. The presented work provides an economical and feasible path for the treatment of wastewater from dyeing and printing.

Stimulation of Neurite Outgrowth Using Autologous NGF Bound at the Surface of a Fibrous Substrate

Peripheral nerve injury still remains a major clinical challenge, since the available solutions lead to dysfunctional nerve regeneration. Even though autologous nerve grafts are the gold standard, tissue engineered nerve guidance grafts are valid alternatives. Nerve growth factor (NGF) is the most potent neurotrophic factor. The development of a nerve guidance graft able to locally potentiate the interaction between injured neurons and autologous NGF would be a safer and more effective alternative to grafts that just release NGF. Herein, a biofunctional electrospun fibrous mesh (eFM) was developed through the selective retrieval of NGF from rat blood plasma. The neurite outgrowth induced by the eFM-NGF systems was assessed by culturing rat pheochromocytoma (PC12) cells for 7 days, without medium supplementation. The biological results showed that this NGF delivery system stimulates neuronal differentiation, enhancing the neurite growth more than the control condition.

Immune Response to Silk Sericin-Fibroin Composites: Potential Immunogenic Elements and Alternatives for Immunomodulation

The unique properties of silk proteins (SPs), particularly silk sericin (SS) and silk fibroin (SF), have attracted attention in the design of scaffolds for tissue engineering over the past decades. Since SF has good mechanical properties, while SS displays bioactivity, scaffolds combining both proteins should exhibit complementary properties enhancing the potential of these materials. Unfortunately, SS-SF composites can generate chronic immune responses and their immunogenic element is not completely clear. The potential of SS-SF composites in tissue engineering, elements which may contribute to their immunogenicity, and alternatives for their preparation and design, to modulate the immune response and take advantage of their useful properties, are discussed in this review. It is known that SS can enhance β-sheet formation in SF, which may act as hydrophobic regions with a strong affinity for adsorption proteins inducing the chronic recruitment of inflammatory cells. Therefore, tailoring the exposure of hydrophobic regions at the scaffold surface should represent a viable strategy to modulate the immune response. This can be achieved by coating SS-SF composites with SS or other hydrophilic polymers, to take advantage of their antibiofouling properties. Research is still needed to realize the full potential of these composites for tissue engineering.

A new model of chronic peripheral nerve compression for basic research and pharmaceutical drug testing

Aim: To develop a consistent model to standardize research in the field of chronic peripheral nerve neuropathy. Methods: The left sciatic nerve of 8-week-old Sprague-Dawley rats was compressed using a customized instrument leaving a defined post injury nerve lumen (400 μm, 250 μm, 100 μm, 0 μm) for 6 weeks. Sensory and motor outcomes were measured weekly, and histomorphology and electrophysiology after 6 weeks. Results: The findings demonstrated compression depth-dependent sensory and motor pathologies. Quantitative measurements revealed a significant myelin degeneration, axon irregularities and muscle atrophy. At the functional level, we highlighted the dynamics of the different injury profiles. Conclusion: Our novel model of chronic peripheral nerve compression is a useful tool for research on pathophysiology and new therapeutic approaches.

Nerve Growth Factor Biodelivery: A Limiting Step in Moving Toward Extensive Clinical Application?

Nerve growth factor (NGF) was the first-discovered member of the neurotrophin family, a class of bioactive molecules which exerts powerful biological effects on the CNS and other peripheral tissues, not only during development, but also during adulthood. While these molecules have long been regarded as potential drugs to combat acute and chronic neurodegenerative processes, as evidenced by the extensive data on their neuroprotective properties, their clinical application has been hindered by their unexpected side effects, as well as by difficulties in defining appropriate dosing and administration strategies. This paper reviews aspects related to the endogenous production of NGF in healthy and pathological conditions, along with conventional and biomaterial-assisted delivery strategies, in an attempt to clarify the impediments to the clinical application of this powerful molecule.

Nerve growth factor (NGF) and NGF receptors in mesenchymal stem/stromal cells: Impact on potential therapies

Mesenchymal stem/stromal cells (MSCs) are promising for the treatment of degenerative diseases and traumatic injuries. However, MSC engraftment is not always successful and requires a strong comprehension of the cytokines and their receptors that mediate the biological behaviors of MSCs. The effects of nerve growth factor (NGF) and its two receptors, TrkA and p75NTR, on neural cells are well studied. Increasing evidence shows that NGF, TrkA, and p75NTR are also involved in various aspects of MSC function, including their survival, growth, differentiation, and angiogenesis. The regulatory effect of NGF on MSCs is thought to be achieved mainly through its binding to TrkA. p75NTR, another receptor of NGF, is regarded as a novel surface marker of MSCs. This review provides an overview of advances in understanding the roles of NGF and its receptors in MSCs as well as the effects of MSC‐derived NGF on other cell types, which will provide new insight for the optimization of MSC‐based therapy.

Injectable silk sericin scaffolds with programmable shape-memory property and neuro-differentiation-promoting activity for individualized brain repair of severe ischemic stroke

Severe ischemic stroke damages neuronal tissue, forming irregular-shaped stroke cavities devoid of supporting structure. Implanting biomaterials to provide structural and functional support is thought to favor ingrowth of regenerated neuronal networks. Injectable hydrogels capable of in situ gelation are often utilized for stroke repair, but challenged by incomplete gelation and imprecise control over end-macrostructure. Injectable shape-memory scaffolds might overcome these limitations, but are not explored for stroke repair. Here, we report an injectable, photoluminescent, carbon-nanotubes-doped sericin scaffold (CNTs-SS) with programmable shape-memory property. By adjusting CNTs' concentrations, CNTs-SS' recovery dynamics can be mathematically calculated at the scale of seconds, and its shapes can be pre-designed to precisely match any irregular-shaped cavities. Using a preclinical stroke model, we show that CNTs-SS with the customized shape is successfully injected into the cavity and recovers its pre-designed shape to well fit the cavity. Notably, CNTs-SS' near-infrared photoluminescence enables non-invasive, real-time tracking after in vivo implantation. Moreover, as a cell carrier, CNTs-SS not only deliver bone marrow mesenchymal stem cells (BMSCs) into brain tissues, but also functionally promote their neuronal differentiation. Together, we for the first time demonstrate the feasibility of applying injectable shape-memory scaffolds for stroke repair, paving the way for personalized stroke repair.

Fabrication of 3D Scaffolds Displaying Biochemical Gradients along Longitudinally Oriented Microchannels for Neural Tissue Engineering

Biochemical and physical guidance cues are both pivotal for axonal guidance and nerve regeneration. However, fabrication of a platform that can integrate biochemical gradients and topographical guidance cues remains challenging, especially in a three-dimensional (3D) scaffold that closely mimics in vivo axonal outgrowth conditions and ready to be used for in vivo nerve repair. In this study, a new method was introduced to construct 3D scaffolds displaying continuous biochemical gradients along longitudinally oriented microchannels by combining the modified 3D printing and directional freezing techniques. Fluorescence analysis and ELISA results demonstrated that a continuous biochemical gradient was formed, and scanning electron microscopy revealed a longitudinally oriented microstructure. Dorsal root ganglia explants seeded on the longitudinal sections of the newly developed scaffold (scaffold with nerve growth factor gradient along oriented microstructure, G-NGF + OS) showed that 81.3 ± 4.5% of neurites oriented within ±10°, 0.3 ± 0.1 of guidance ratio, and 1.5-fold of the average length of neurites on the high-nerve growth factor (NGF) concentration side compared to that on the low-NGF concentration side, which were significantly higher than those in the other groups. In addition, the G-NGF + OS scaffold was used to repair a 15 mm sciatic nerve defect in rats. Immunofluorescence staining, Fluoro-Gold retrograde tracing, and transmission electron microscopy results confirmed that the G-NGF + OS scaffold enhanced nerve regeneration to the distal target and promoted myelination of regenerated axons. More importantly, the sciatic functional index and the von Frey test demonstrated that the G-NGF + OS scaffold accelerated sensory and motor functional recovery. These results provide new insights into the importance of combining topographical guidance cues with bioactive molecule gradient cues for neural tissue engineering. The 3D scaffold displaying biochemical gradients along longitudinally oriented microchannels represents a promising platform for the development of advanced devices for severe nervous system injuries.

CNT/Sericin Conductive Nerve Guidance Conduit Promotes Functional Recovery of Transected Peripheral Nerve Injury in a Rat Model

Peripheral nerve injury usually leads to poor outcomes such as painful neuropathies and disabilities. Autogenous nerve grafting is the current gold standard; however, the limited source of a donor nerve remains a problem. Numerous tissue engineering nerve guidance conduits have been developed as substitutes for autografts. However, a few conduits can achieve the reparative effect equivalent to autografts. Here, we report for the development and application of a carbon nanotube (CNT)/sericin nerve conduit with electrical conductivity and suitable mechanical properties for nerve repair. This CNT/sericin conduit possesses favorable properties including biocompatibility, biodegradability, porous microarchitecture, and suitable swelling property. We thus applied this conduit for bridging a 10 mm gap defect of a transected sciatic nerve combined with electrical stimulation (ES) in a rat injury model. By the end of 12 weeks, we observed that the CNT/sericin conduit combined with electrical stimulation could effectively promote both structural repair and functional recovery comparable to those of the autografts, evidenced by the morphological and histological analyses, electrophysiological responses, functional studies, and target muscle reinnervation evaluations. These findings suggest that this electric conductive CNT/sericin conduit combined with electrical stimulation may have the potential to serve as a new alternative for the repair of transected peripheral nerves.

Silk biomaterials in wound healing and skin regeneration therapeutics: From bench to bedside

Silk biomaterials are known for biomedical and tissue engineering applications including drug delivery and implantable devices owing to their biocompatible and a wide range of ideal physico-chemical properties. Herein, we present a critical overview of the progress of silk-based matrices in skin regeneration therapeutics with an emphasis on recent innovations and scientific findings. Beginning with a brief description of numerous varieties of silks, the review summarizes our current understanding of the biological properties of silk that help in the wound healing process. Various silk varieties such as silkworm silk fibroin, silk sericin, native spider silk and recombinant silk materials have been explored for cutaneous wound healing applications from the past few decades. With an aim to harness the regenerative properties of silk, numerous strategies have been applied to develop functional bioactive wound dressings and viable bio-artificial skin grafts in recent times. The review examines multiple inherent properties of silk that aid in the critical events of the healing process such as cell migration, cell proliferation, angiogenesis, and re-epithelialization. A detailed insight into the progress of silk-based cellular skin grafts is also provided that discusses various co-culture strategies and development of bilayer and tri-layer human skin equivalent under in vitro conditions. In addition, functionalized silk matrices loaded with bioactive molecules and antibacterial compounds are discussed, which have shown great potential in treating hard-to-heal wounds. Finally, clinical studies performed using silk-based translational products are reviewed that validate their regenerative properties and future applications in this area. STATEMENT OF SIGNIFICANCE: The review article discusses the recent advances in silk-based technologies for wound healing applications, covering various types of silk biomaterials and their properties suitable for wound repair and regeneration. The article demonstrates the progress of silk-based matrices with an update on the patented technologies and clinical advancements over the years. The rationale behind this review is to highlight numerous properties of silk biomaterials that aid in all the critical events of the wound healing process towards skin regeneration. Functionalization strategies to fabricate silk dressings containing bioactive molecules and antimicrobial compounds for drug delivery to the wound bed are discussed. In addition, a separate section describes the approaches taken to generate living human skin equivalent that have recently contributed in the field of skin tissue engineering.

Transgenic PDGF-BB/sericin hydrogel supports for cell proliferation and osteogenic differentiation

The present study demonstrates fabrication of PDGF-BB functionalized sericin hydrogel to explore biomaterials-related utility in bone tissue engineering.

Signatures of altered DNA methylation gene expression after central and peripheral nerve injury

Nerve damage can lead to movement and sensory dysfunction, with high morbidity and disability rates causing severe burdens on patients, families, and society. DNA methylation is a kind of epigenetics, and a great number of previous studies have demonstrated that DNA methylation plays an important role in the process of nerve regeneration and remodeling. However, compared with the central nervous system, the peripheral nervous system shows stronger recovery after injury, which is related to the complex microenvironment and epigenetic changes occurring at the site of injury. Therefore, what common epigenetic changes between the central and peripheral nervous systems remain to be elucidated. We first screened differential methylation genes after spinal cord injury and sciatic nerve injury using whole-genome bisulfite sequencing and methylated DNA immunoprecipitation sequencing, respectively. Subsequently, a total of 16 genes had the same epigenetic changes after spinal cord injury and sciatic nerve injury. The Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were performed to identify the critical biological processes and pathways. Furthermore, a protein-protein interaction network analysis indicated that Dnm3, Ntrk3, Smurf1, Dpysl2, Kalrn, Shank1, Dlg2, Arsb, Reln, Bmp5, Numbl, Prickle2, Map6, and Htr7 were the core genes. These outcomes may provide novel insights into the molecular mechanism of the subacute phase of nerve injury. These verified genes can offer potential diagnostic and therapeutic targets for nerve injury.

Rational Design and Fabrication of ZnONPs Functionalized Sericin/PVA Antimicrobial Sponge

The interests of developing antimicrobial biomaterials based on silk sericin from Bombyx mori cocoon, have been shooting up in the last decades. Sericin is a valuable natural protein owing to its hydrophilicity, biodegradability, and biocompatibility. Here, we fabricated a sponge with antibacterial capacities for potential wound dressing application. By co-blending of sericin, polyvinyl alcohol (PVA) and zinc oxide nanoparticles (ZnONPs), the ZnONPs-sericin/PVA composite sponge (ZnONPs-SP) was successfully prepared after freeze-drying. Scanning electron microscopy showed the porous structure of ZnONPs-SP. Energy dispersive spectroscopy indicated the existence of Zn in the sponge. X-ray diffractometry revealed the hexagonal wurtzite structure of ZnONPs. Fourier transform infrared spectroscopy showed the biologic coupling of ZnONPs and sericin resulted in a decrease of α-helix and random coil contents, and an increase of β-sheet structure in the sponge. The swelling experiment suggested ZnONPs-SP has high porosity, good hydrophilicity, and water absorption capability. The plate bacterial colony counting coupled with growth curve assays demonstrated that the composite sponge has an efficiently bacteriostatic effect against Staphylococcus aureus and Escherichia coli, respectively. Furthermore, the cell compatibility analysis suggested the composite sponge has excellent cytocompatibility on NIH3T3 cells. In all, ZnONPs-SP composite sponge has significant potentials in biomaterials such as wound dressing and tissue engineering.

Application of stem cells and chitosan in the repair of spinal cord injury

Cytology and histology obstacles have been the main barriers to multiple tissues injury repair. In search of the most promising treatment strategies for spinal cord injury (SCI), stem cell-based transplantation coupled with various materials/technologies have been explored extensively to enhance SCI repair. Chitosan (CS) has demonstrated immense potential for widespread application in the form of scaffolds and micro-particles for SCI repair. The current review summarizes the evidences for stem cell-based transplantation and CS in SCI repair. Stem cells transplantation, which plays a key role in the repair of SCI, mainly results from its neural differentiation potential and neurotrophic effects. Application of CS enhances the survival of grafted stem cells, upregulates the expression level of neurotrophic factors and heightens the neural differentiation of stem cells as well as the functional recovery of spinal cord. Meanwhile, CS can also be exploited as growth factors/RNA carriers to control the release of regenerating molecules which are beneficial to damage spinal cord repair.

Molecular nature of dominant naked pupa mutation reveals novel insights into silk production in Bombyx mori

Silks are natural protein biopolymers with desirable mechanical properties and play crucial roles in insect survival and reproduction. However, the mechanisms by which large amounts of silk fibroin are efficiently secreted from the protein production organs (silk glands) remain elusive. Here, we focus on a dominant silkworm mutation, naked pupa (Nd), which enables carriers to lose spinning behaviors, produce a deficiency of silk fibroin production, and result in degenerate posterior silk gland (PSG). Linkage mapping and sequencing analyses revealed a deletion of 19 bp of the fibroin heavy chain (FibH), which results in a frameshift-caused deletion of the C-terminal domain (CT) responsible for the Nd locus. Immunofluorescence and immunoblot analysis showed that the PSG cells with truncated FibH exhibit blockades in the secretion of all three fibroins (FibH, FibL, and P25) from silk gland cell to silk gland lumen (a secretion-deficiency). By comparing the hereditary characters of three naked silkworm mutations (Nd, Nd-s, and fibH-ko), we explored the relationship between dominant and recessive inheritances in naked silkworms and found that high-molecular-weight/repetitive FibH with secretion-deficiency was in positive correlation with PSG atrophy phenotype, and moreover, the repetitive region of Nd-FibH accounted for the dominant phenotypes of fibroin secretion-deficiency, PSG atrophy, and naked pupa in B. mori. Our results uncovered the molecular nature of the silkworm Nd mutation and significantly improved our understanding of fibroin synthesis and secretion in silk-spinning caterpillars.

The wound healing and antibacterial potential of triple-component nanocomposite (chitosan-silver-sericin) films loaded with moxifloxacin

AIM

The current study reports the development and evaluation of chitosan-sericin-silver nanocomposite (CSSN) films without and with moxifloxacin (Mox).

METHODOLOGY

The film preparation method involved the in-situ synthesis of silver nanoparticles within the chitosan-sericin colloidal composite followed by preparation into a film by solvent casting technique. In-situ formation and the particle size analysis of the silver nanoparticles was performed via UV-Visible and zeta-size spectrometer. The prepared films were tested for swelling ratio, contents uniformity, in-vitro Mox release, and permeation analysis. The morphological (SEM), elemental (EDX), spectral (FT-IR), structural (XRD), and thermal (TGA and DSC) properties of the composites were also inspected. The antibacterial activity of the CSSN films was performed against seven pathogenic bacterial strains including five ATCC and two clinical strains. The potential wound healing activity of the composite films was evaluated on burn wound model induced in Sprague Dawley male rats.

RESULTS

The prepared films displayed good swelling profile with a sustained in-vitro Mox release and permeation profile; attaining maximum of 78.57% (CSSM3) release and 55.05% (CSSM1) permeation (CSSM1) in 24 h. The prepared films, particularly the Mox-loaded CSSN films displayed a promising antibacterial activity against all the tested strains with the activity being highest against MRSA (clinical isolates). The prepared films indicated a remarkable wound healing applications with successful fibrosis, collagen reorganization, neovascularization, and mild epidermal regeneration after 7 days of treatment with no silver ions detection in animal's blood.

CONCLUSION

The obtained findings strongly suggest the use of the prepared novel composite dressing for wound care applications.

An ultrasensitive electrochemiluminescence biosensor for MicroRNA detection based on luminol-functionalized Au NPs@ZnO nanomaterials as signal probe and dissolved O2 as coreactant

In this work, the ZnO nanostars with excellent catalytic performance were firstly used as the coreaction accelerator of luminol-O₂ system to construct a biosensor for ultrasensitively detecting microRNA-21 (miRNA-21) in cancer cells. Specifically, ZnO nanostars could expedite the reduction of dissolved O₂, generating more reactive oxygen species (ROSs) to extremely promote electrochemiluminescence (ECL) luminous efficiency of luminol. Thus luminol-functionalized Au NPs@ZnO (L-Au NPs@ZnO) nanomaterials were employed as signal probe to fabricate sensing nano-platform for achieving significant ECL emission as "signal on" state. Moreover, upon the addition of a tiny minority of target miRNA-21, massive ferrocene (Fc) could be immobilized on the sensing interface through hybridization chain reaction (HCR) triggered-DNA dendrimers self-assembly, in which Fc consumed dissolved O₂ for prominently quenching the ECL emission of signal probe and then reached a "signal off" state. As a result, the biosensor performed a good linearity in 100 aM - 100 pM and a low limit of detection (LOD) down to 18.6 aM. In general, this work utilized a new coreaction accelerator as an efficient amplification approach for ultrasensitively detecting target analyses, providing a promising approach in luminol-centric ECL bioanalysis fields.

Relevance and Recent Developments of Chitosan in Peripheral Nerve Surgery

Developments in tissue engineering yield biomaterials with different supporting strategies to promote nerve regeneration. One promising material is the naturally occurring chitin derivate chitosan. Chitosan has become increasingly important in various tissue engineering approaches for peripheral nerve reconstruction, as it has demonstrated its potential to interact with regeneration associated cells and the neural microenvironment, leading to improved axonal regeneration and less neuroma formation. Moreover, the physiological properties of its polysaccharide structure provide safe biodegradation behavior in the absence of negative side effects or toxic metabolites. Beneficial interactions with Schwann cells (SC), inducing differentiation of mesenchymal stromal cells to SC-like cells or creating supportive conditions during axonal recovery are only a small part of the effects of chitosan. As a result, an extensive body of literature addresses a variety of experimental strategies for the different types of nerve lesions. The different concepts include chitosan nanofibers, hydrogels, hollow nerve tubes, nerve conduits with an inner chitosan layer as well as hybrid architectures containing collagen or polyglycolic acid nerve conduits. Furthermore, various cell seeding concepts have been introduced in the preclinical setting. First translational concepts with hollow tubes following nerve surgery already transferred the promising experimental approach into clinical practice. However, conclusive analyses of the available data and the proposed impact on the recovery process following nerve surgery are currently lacking. This review aims to give an overview on the physiologic properties of chitosan, to evaluate its effect on peripheral nerve regeneration and discuss the future translation into clinical practice.

Sericin Nerve Guidance Conduit Delivering Therapeutically Repurposed Clobetasol for Functional and Structural Regeneration of Transected Peripheral Nerves

Peripheral nerve injury often causes significant function loss. Autologous nerve grafting as a gold-standard repair strategy for treating such an injury is limited by donor nerve supply. Tissue-engineered nerve guidance conduits (TENGCs) as a promising alternative for autografting are challenged by large nerve gaps. Herein, we fabricate a glutaraldehyde-cross-linked sericin nerve guidance conduit (GSC) incorporated with clobetasol, a glucocorticoid receptor agonist, for repairing a 10 mm long sciatic nerve gap in a rat model. The GSC exhibits biocompatibility and regeneration-favorable physicochemical properties. GSC's degradation products promote the secretion of neurotrophic factors in Schwann cells. By repurposing clobetasol for peripheral nerve regeneration, our work uncovers clobetasol's previously unknown functions in promoting Schwann cell proliferation and upregulating the expression of myelin-related genes. Importantly, the implantation of this clobetasol-loaded GSC in vivo leads to successful regeneration of the transected sciatic nerve. Strikingly, the regeneration outcome is functionally comparable to that of autologous nerve grafting (evidenced by three parameters). Specifically, the static sciatic index (SSI), relative reaction time (RRT) and nerve conduction velocity (NCV) in Clobetasol/GSC group are -74.55, 1.30, and 46.4 mm/s at Week 12, respectively, while these parameters are -64.53, 1.23, and 49.8 mm/s in Autograft group. Thus, this work represents the first report unveiling clobetasol's potential in peripheral nerve regeneration, reveals the feasibility of applying a sericin conduit for repairing a large nerve defect, and demonstrates the effectiveness of the clobetasol-loaded-GSC based strategy in transected nerves' regeneration.

Tissue engineering for the repair of peripheral nerve injury

Peripheral nerve injury is a common clinical problem and affects the quality of life of patients. Traditional restoration methods are not satisfactory. Researchers increasingly focus on the field of tissue engineering. The three key points in establishing a tissue engineering material are the biological scaffold material, the seed cells and various growth factors. Understanding the type of nerve injury, the construction of scaffold and the process of repair are necessary to solve peripheral nerve injury and promote its regeneration. This review describes the categories of peripheral nerve injury, fundamental research of peripheral nervous tissue engineering and clinical research on peripheral nerve scaffold material, and paves a way for related research and the use of conduits in clinical practice.

Three-Dimensionally Printed Silk-Sericin-Based Hydrogel Scaffold: A Promising Visualized Dressing Material for Real-Time Monitoring of Wounds

A wound dressing which can be convenient for real-time monitoring of wounds is particularly attractive and user-friendly. In this study, a nature-originated silk-sericin-based (SS-based) transparent hydrogel scaffold was prepared and evaluated for the visualization of wound care. The scaffold was fabricated from a hybrid interpenetrating-network (IPN) hydrogel composed of SS and methacrylic-anhydride-modified gelatin (GelMA) by 3D printing. The scaffold transformed into a highly transparent hydrogel upon swelling in PBS, and thus, anything underneath could be easily read. The scaffold had a high degree of swelling and presented a regularly macroporous structure with pores around 400 μm × 400 μm, which can help maintain the moist and apinoid environment for wound healing. Meanwhile, the scaffolds were conducive to adhesion and proliferation of L929 cells. A coculture of HaCaT and HSF cells on the scaffold showed centralized proliferation of the two cells in distributed layers, respectively, denoting a promising comfortable environment for re-epithelialization. Moreover, in vivo studies demonstrated that the scaffold showed no excessive inflammatory reaction. In short, this work presented an SS-based transparent hydrogel scaffold with steerable physical properties and excellent biocompatibility through 3D printing, pioneering promising applications in the visualization of wound care and drug delivery.

Fabrication of the FGF1-functionalized sericin hydrogels with cell proliferation activity for biomedical application using genetically engineered Bombyx mori (B. mori) silk

Sericin, as the major component of Bombyx mori silk, is a useful biomaterial for tissue engineering due to its hydrophilicity, biocompatibility and biodegradability. Here, we report the fabrication of a human acidic fibroblast growth factor (FGF1)-functionalized sericin hydrogel using a transgenic silkworm spun silk with FGF1 incorporated in its sericin layer. Sericin, together with FGF1, were simultaneously extracted from the silk fiber and then exposed to cold-induced hydrogel formation without additional crosslinking. The fabricated FGF1 sericin hydrogels demonstrated injectability, useful mechanical properties and a porous microstructure, which contributed to cell adhesion and survival. In addition, FGF1 achieved long-term storage in the sericin hydrogels over a wide range of temperatures. Further, the sericin-FGF1 demonstrated sustained release to promote cell proliferation and wound healing. Furthermore, cellular inflammatory responses showed that the FGF1 sericin hydrogels exhibited biocompatibility and no immunogenicity. This study revealed the successful exploration of FGF1-functionalized sericin hydrogels as a new protein-based biomaterial to expand applications of FGF1 and sericin in tissue and medical engineering. Further, we demonstrated a strategy for the predesign of exogenous protein-functionalized sericin hydrogels through genetically modifying silk fibers as sources for their cost effective production at a large scale.

STATEMENT OF SIGNIFICANCE

Sericin from the Bombyx mori silk, is regarded as a desirable biomaterial for tissue engineering due to its hydrophilicity, biocompatibility and biodegradability. Genetically engineering the sericin with functional exogenous proteins would enhance its biofunctions and further expand its application in tissue engineering. In this study, we demonstrated a method to fabricate a human acidic fibroblast growth factor (FGF1)-functionalized sericin hydrogel using a transgenic silkworm spun silk with FGF1 incorporated in its sericin layer. The fabricated FGF1 sericin hydrogels demonstrated injectability, porous microstructure, biocompatibility and no immunogenicity which contributed to cell adhesion and survival. Remarkably, FGF1 could achieve a long-term stability in the sericin hydrogels over a wide range of temperatures and sustained release to promote cell proliferation and wound healing. This study revealed the successful exploration of FGF1-functionalized sericin hydrogels as a new protein-based biomaterial in tissue and medical engineering application, and provided a strategy for the predesign of exogenous protein-functionalized sericin hydrogels through genetically modifying silk fibers as sources for their cost effective production at a large scale.