Silk Fibroin-based Hydrogels Research Articles

Silk fibroin-based hydrogel as injectable carrier for prolonged immunization of plant-based COVID-19 subunit vaccine

Silk fibroin (SF)-based hydrogel was prepared to serve as an injectable carrier, aimed at prolonging the immunization effect of the plant-derived vaccine for the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2). This vaccine consists of the Receptor-Binding Domain (RBD) linked with the Fragment Crystallizable (Fc) region of Human Immunoglobulin G 1 (IgG1), also referred to as the RBD-Fc vaccine. The formulation also includes Aluminium hydroxide gel (Alum). Ex-vivo experiments demonstrated that both the SARS-CoV-2 RBD-Fc-loaded SF hydrogel (RBD-Fc/SF hydrogel) and the Alum-adjuvanted SARS-CoV-2 RBD-Fc-loaded SF hydrogel (Alum-RBD-Fc/SF hydrogel) indicated localized retention. This resulted in a controlled and prolonged release of 75% and 25% over a period of 60 days, respectively. This facilitated continuous interaction between the immune system and the viral peptide, specifically the RBD, which could have significant implications for geometric mean titer (GMT). In immunization studies, the RBD-Fc/SF hydrogel and Alum-RBD-Fc/SF hydrogel had induced a more prolonged and stronger immunogenic response of mouse-RBD-specific IgG titer and IgG subtypes (IgG1 and IgG2a). The specific IgG1 and IgG2a titers of RBD-Fc/SF hydrogel (with GMTs of 67,559 and 1,056, respectively) and Alum-RBD-Fc/SF hydrogel (with GMTs of 155,209 and 1,838, respectively) were superior to the RBD-Fc vaccine without SF hydrogel (with GMTs of 3200 and 200, respectively). Furthermore, they were comparable to the responses elicited by commercial Alum-adjuvants currently in use (with GMTs of 51,200 and 4,850, respectively). Additionally, a concentration of 0.1%w/v SF exhibited significant adjuvant properties by augmenting the secretion of various cytokines. For instance, it enhanced the secretion of Interleukin-6 (IL-6) to 88.02 pg/mL, which is comparable to the secretion induced by commercial Alum adjuvants (39.48 pg/mL). These findings suggest that SF hydrogel-based vaccine formulations could enhance humoral immunity and induce long-lasting immune responses. However, further investigations are required to assess the neutralizing potential of the antibodies produced against SARS-CoV-2 and its variants. The prospects and outcomes of SF hydrogel-based vaccine formulations indicate their potential as a next-generation vaccine platform. Such innovative strategies could be pivotal in the fight against COVID-19 and other infectious diseases.

Synthesis, characterization, and therapeutic applications of LAP/PDA composite nanomaterials in silk fibroin-based hydrogels for enhanced neuroregeneration in stroke

Addressing the devastating and often irreversible effects of stroke necessitates innovative therapeutic strategies that go beyond the limitations of current treatments. This study heralds a promising interdisciplinary approach by employing LAP/PDA composite nanomaterials integrated into silk fibroin-based hydrogels. These engineered materials not only demonstrated significantly enhanced mechanical properties, but also showed excellent biocompatibility when co-cultured with human mesenchymal stem cells (hMSCs). Importantly, the application of these composite hydrogels in stroke models yielded remarkable therapeutic outcomes. The results indicated a substantial reduction in cerebral infarction volumes, improved survival rates of transplanted hMSCs, and increased neurogenesis, underlining their transformative potential in stroke management. Molecular markers such as AQP4, α-DG, and β-DG were also explored, revealing modulated astrocyte activation and cellular signaling pathways. In summary, the composite LAP/PDA nanomaterials, in conjunction with hMSCs and Brain-Derived Neurotrophic Factor (BDNF), unveil a compelling and multifaceted approach for addressing the unmet needs in stroke treatment, thereby opening new avenues in regenerative medicine and tissue engineering.

Microstructure of the silk fibroin-based hydrogel scaffolds derived from the orb-web spider Trichonephila clavata

Due to the unique properties of the silk fibroin (SF) made from silkworm, SF-based hydrogels have recently received significant attention for various biomedical applications. However, research on the SF-based hydrogels isolated from spider silks has been rtricted due to the limited collection and preparation of naïve silk materials. Therefore, this study focused on the microstructural characteristics of hydrogel scaffolds derived from two types of woven silk glands: the major ampullate gland (MAG) and the tubuliform gland (TG), in the orb-web spider Trichonephila clavate. We compared these spider glands with those of the silk fibroin (SF) hydrogel scaffold extracted from the cocoon of the insect silkworm Bombyx mori. Our FESEM analysis revealed that the SF hydrogel has high porosity, translucency, and a loose upper structure, with attached SF fibers providing stability. The MAG hydrogel displayed even higher porosity, as well as elongated fibrous structures, and improved mechanical properties: while the TG hydrogel showed increased porosity, ridge-like or wall-like structures, and stable biocapacity formed by physical crosslinking. Due to their powerful and versatile microstructural characteristics, the MAG and TG hydrogels can become tailored substrates, very effective for tissue engineering and regenerative medicine applications.

An injectable photocuring silk fibroin-based hydrogel for constructing an antioxidant microenvironment for skin repair.

Skin has a protein microenvironment dominated by functional collagen fibers, while oxidative stress caused by injury can greatly slow down the progress of wound healing. Here, methacrylated dopamine was incorporated into methacrylated silk fibroin molecule chains to develop an injectable hydrogel with photocuring properties for constructing an antioxidant skin protein microenvironment. This silk fibroin-based hydrogel (SF-g-SDA) showed good tensile and adhesion properties for adapting to the wound shape and skin movement, exhibited stable mechanical properties, good biodegradability and cytocompatibility, and promoted cell adhesion and vascularization in vitro. In addition, its phenolic hydroxyl-mediated antioxidant properties effectively protected cells from damage caused by oxidative stress and supported normal cellular life activities. In animal experiments, SF-g-SDA achieved better skin repair effects in comparison to commercial Tegaderm™ in vivo, showing its ability to accelerate wound healing, improve collagen deposition and alignment in newly fabricated tissues, and promote neovascularization and hair follicle formation. These experimental results indicated that the SF-g-SDA hydrogel is a promising wound dressing.

Recyclable, anti-freezing and anti-drying silk fibroin-based hydrogels for ultrasensitive strain sensors and all-hydrogel-state super-capacitors

Multifunctional conductive hydrogels have triggered extensive research interest owing to their potential in artificial intelligence, human motion detection, soft electronic skins, and energy storage. However, unattainable reusable properties and unsatisfactory environmental tolerance seriously hinder potential applications in these emerging fields. Herein, an anti-freezing, anti-drying, and recyclable conductive hydrogel has been successfully prepared by integrating silk fibroin (SF) into polyvinyl alcohol (PVA)/glycerin (Gly)/lithium chloride (LiCl) hydrogel. Silk fibroin provides a variety of physical interactions for the construction of polymer hydrogels due to its abundant binding sites (–COO–, –NH2, and –OH) on its peptide chain. The obtained SPGL (SF/PVA/Gly/LiCl) hydrogels demonstrate outstanding anti-freezing properties (below −70 °C) and excellent anti-drying properties (17.4% weight loss after 30 days). Meanwhile, the prominent remolding property allows the SPGL hydrogel to be recycled, and the ionic conductivity of the remolded hydrogel remains at 84.7%. The important roles of Gly and LiCl in inhibiting the freezing and dehydration of hydrogels have been further revealed by density functional theory (DFT) simulations at the molecular scale. The SPGL hydrogel-based strain sensors possess relatively high sensitivity with a gauge factor (GF) of 2.18, enabling them to monitor human motions precisely, including macro movements and micro movements. Furthermore, we designed a circuit diagram with the sensor to detect human motion in real-time. In addition, the SPGL hydrogel-based supercapacitors display favorable cycle stability (88.5% capacitance retention after 10,000 cycles) and excellent energy density of 15.4 μWh cm−2 at a power density of 50 μW cm−2. The strain sensors and supercapacitors also have anti-freezing and anti-drying properties, maintaining excellent sensing and electrochemical properties even in extreme environments. Therefore, these SPGL hydrogel-based soft electronics have promising applications in health monitoring, human motion detection, human-machine interactions, and energy storage.

A self-healable silk fibroin-based hydrogel electrolyte for silver-zinc batteries with high stability

Due to the intrinsic safety, mechanical flexibility and cost-effectiveness, aqueous batteries with hydrogel electrolytes are particularly advantageous for wearable electronics. Herein, a self-healable silk fibroin-based hydrogel electrolyte with semi-interpenetrating network structure was developed, which possesses both high ionic conductivity (14.4 mS cm−1) and excellent mechanical strength. The supramolecular hydrogen bonding interaction between the amide bond and the polypeptide of silk fibroin enables the hydrogel electrolyte with superior self-healable capability, which largely improves the interfacial compatibility between electrode and electrolyte, thus suppressing the growth of Zn dendrites. The resultant Ag-Zn battery delivers a high capacity of 110 mAh g−1 at 0.5 A g−1 with good cycling stability of 85.7% capacity retention after 800 cycles.

Manipulating Zn 002 deposition plane with zirconium ion crosslinked hydrogel electrolyte toward dendrite free Zn metal anodes

A Zr4+ crosslinked hydrogel electrolyte is demonstrated on side reaction resistance for high-performance aqueous Zn-based devices.

Preparation and Characterization of Natural Silk Fibroin Hydrogel for Protein Drug Delivery.

In recent years, hydrogels have been widely used as drug carriers, especially in the area of protein delivery. The natural silk fibroin produced from cocoons of the Bombyx mori silkworm possesses excellent biocompatibility, significant bioactivity, and biodegradability. Therefore, silk fibroin-based hydrogels are arousing widespread interest in biomedical research. In this study, a process for extracting natural silk fibroin from raw silk textile yarns was established, and three aqueous solutions of silk fibroin with different molecular weight distributions were successfully prepared by controlling the degumming time. Silk fibroin was dispersed in the aqueous solution as “spherical” aggregate particles, and the smaller particles continuously accumulated into large particles. Finally, a silk fibroin hydrogel network was formed. A rheological analysis showed that as the concentration of the silk fibroin hydrogel increased its storage modulus increased significantly. The degradation behavior of silk fibroin hydrogel in different media verified its excellent stability, and the prepared silk fibroin hydrogel had good biocompatibility and an excellent drug-loading capacity. After the protein model drug BSA was loaded, the cumulative drug release within 12 h reached 80%. We hope that these investigations will promote the potential utilities of silk fibroin hydrogels in clinical medicine.

Synthesis and characterization of cellulose, β-cyclodextrin, silk fibroin-based hydrogel containing copper-doped cobalt ferrite nanospheres and exploration of its biocompatibility

Synthesis and characterization of cellulose, β-cyclodextrin, silk fibroin-based hydrogel containing copper-doped cobalt ferrite nanospheres and exploration of its biocompatibility

Preparation of a novel regenerated silk fibroin-based hydrogel for extrusion bioprinting.

Three-dimensional (3D) bioprinting technology, allowing rapid prototyping and personalized customization, has received much attention in recent years, while regenerated silk fibroin (RSF) has also been widely investigated for its excellent biocompatibility, processibility, and comprehensive mechanical properties. However, due to the difficulty in curing RSF aqueous solution and the tendency of conformational transition of RSF chains under shearing, it is rather complicated to fabricate RSF-based materials with high mechanical strength through extrusion bioprinting. To solve this problem, a printable hydrogel with thixotropy was prepared from regenerated silk fibroin with high-molecular-weight (HMWRSF) combined with a small amount of hydroxypropyl methylcellulose (HPMC) in urea containing aqueous solution. It was found that the introduction of urea could not only vary the solid content of the hydrogel to benefit the mechanical properties of the 3D-bioprinted pre-cured hydrogels or 3D-bioprinted sponges, but also expand the "printable window" of this system. Indeed, the printability and rheological properties could be modulated by varying the solid content, the heating time, the urea/HMWRSF weight ratio, etc. Moreover, the microstructure of nanospheres stacked in these lyophilized 3D-bioprinted sponges was interesting to observe, which indicated the existence of microhydrogels and both "the reversible network" and "the irreversible network" in this HMWRSF-based pre-cured hydrogel. Like other HMWRSF materials fabricated in other ways, these 3D-bioprinted HMWRSF-based sponges exhibited good cytocompatibility for dental pulp mesenchymal stem cells. This work may inspire the design of functional HMWRSF-based materials by regulating the relationship between structure and properties.

Top-down extraction of surface carboxylated-silk nanocrystals and application in hydrogel preparation

Bionanomaterial based hydrogels originated from natural biopolymer have drawn much attention for advanced applications. However, nanosilk-based hydrogels derived from top-down approaches remain in their infancy. First, nanosilks based on existing methods fail to prepare hydrogels; second, both nanosilk extraction and surface modification remain a challenge due to high crystallinity and sophisticated hierarchical structures. To produce nanosilk-based hydrogels, pretreatment and oxidation are necessary. In this work, pretreatments were conducted first to loosen the sophisticated structures of natural silk fibers, NaClO oxidation was utilized in succession to introduce carboxyl groups onto silk fibroin. Combined with moderate mechanical disintegration, silk nanocrystals with additional carboxyl groups were prepared facilely. Finally, silk nanocrystal-based hydrogels were prepared successfully through gas phase coagulation. An optimization of pretreatment approaches and oxidation conditions was carried out. The morphologies, chemical and crystalline structures of original, pretreated and oxidized silk fibroin as well as nanofibrillated silk were investigated. In addition, the silk nanocrystal-based hydrogel exhibited outstanding mechanical properties compared to those of dissolved and regenerated silk fibroin-based hydrogels. Moreover, silk nanocrystal-based aerogels present highly porous, interconnected, and crisscrossed network nanostructures, which are ideal candidates for tissue regeneration and provide new prospects as porous scaffolds for bioengineering applications.

Novel supramolecular self-healing silk fibroin-based hydrogel via host–guest interaction as wound dressing to enhance wound healing

• A novel approach to prepare supramolecular silk fibroin-based hydrogel. • The hydrogel showed good self-healing, syringeability, and biocompatibility. • The hydrogel exhibited a sustained drug release for hydrophobic drug curcumin. • The hydrogel showed enhanced wound healing efficiency in vivo . Silk fibroin (SF) based hydrogels possess great potential in wound healing. However, they have limitations as wound dressings, such as long-gelation time, high temperature or organic solvent-assisted treatment, and lack of self-healing property. In this study, a supramolecular hydrogel based on SF, acryloyl- β -cyclodextrin (Ac-CD) and 2-hydroxyethyl acrylate was developed through a facile method by photo-polymerization of acrylate under UV irradiation, and showed enhanced performance as wound dressing than commercial dressing. This SF based hydrogel was confirmed to be dually crosslinked by host–guest interaction and hydrophobic β -sheet conformation, and demonstrated improved mechanical properties, long-term stability, rapid self-healing behavior, injectability, and good biocompatibility, benefiting its application as wound dressing. Moreover, as a drug carrier owing abundant CDs, the hydrophobic drug curcumin with antioxidant and anti-inflammatory activity was loaded in SF-based hydrogel, accompanying with a controlled and sustained release profile, therewith boosting better wound healing performance with generating higher granulation tissue thickness, collagen disposition, upregulating vascular endothelial growth factor (VEGF), and decreasing inflammatory response in a full-thickness skin defect model. In conclusion, this novel self-healing SF-based hydrogel is of great value in wound healing and enriches the fabrication methodology of SF-based self-healing biomaterials as well.

High-Strength and High-Toughness Silk Fibroin Hydrogels: A Strategy Using Dynamic Host-Guest Interactions.

Natural polymer-based hydrogels attract great attention because of their inherent biocompatibility and controllable biodegradability. However, the broad applications of these hydrogels require a combination of high mechanical strength, high toughness, fatigue resistance, as well as self-healing. The integration of this combination into one natural polymer-based hydrogel remains challenging. Here, a molecular design strategy was proposed to fabricate mechanically robust silk fibroin-based hydrogels using host-guest interactions. Silk fibroin molecules was chemically modified with cholesterol (Chol, guest) or β-cyclodextrin (β-CD, host), and host-guest interaction between Chol and β-CD moieties drove the supramolecular assemblies of hydrogels. The dissociation/reassociation behavior of host-guest complexation, serving as sacrificial bonds, endowed hydrogels with effective energy dissipation and rapid self-healing ability. The prepared silk fibroin-based hydrogels exhibited high mechanical strength, high toughness, and remarkable fatigue resistance, superior to conventional silk fibroin hydrogels. Moreover, due to reversible host-guest interactions, hydrogels achieved facile functional recovery after damage without any external stimuli. This design strategy provides an avenue to develop natural polymer-based materials with robust mechanical properties, thus broadening current hydrogel applications.

Stretchable, Biocompatible, and Multifunctional Silk Fibroin-Based Hydrogels toward Wearable Strain/Pressure Sensors and Triboelectric Nanogenerators.

Nowadays, great effort has been devoted to establishing wearable electronics with excellent stretchability, high sensitivity, good mechanical strength, and multifunctional characteristics. Herein, a soft conductive hydrogel is rationally designed by proportionally mixing silk fibroin, polyacrylamide, graphene oxide, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). The resultant hydrogel has considerable stretchability and compressibility, which enables it to be assembled into a strain/pressure sensor with a wide sensing range (strain, 2%-600%; pressure, 0.5-119.4 kPa) and reliable stability. Then, the corresponding sensor is capable of monitoring a series of physical signals of the human body (e.g., joint movement, facial gesture, pulse, breathing, etc.). In particular, the hydrogel-based sensor is biocompatible, with no anaphylactic reaction on human skin. More interestingly, this conductive hydrogel exhibits a positive response when it works in a triboelectric nanogenerator; consequently, it lights up 20 commericial green light-emitting diodes. Thus, this silk fibroin-based hydrogel is a kind of multifunctional material toward wearable electronics with versatile applications in health and exercise monitors, soft robots, and power sources.

Processing, Mechanical Properties and Bio-Applications of Silk Fibroin-Based High Strength Hydrogels

Hydrogels are an attractive class of materials that possess similar structural and functional characteristics to biological tissues, and demonstrate a diversity of applications in biomedical engineering. Silk fibroin (SF) is a unique natural polymer for its versatile formats, excellent processability, biocompatibility, tunable biodegradation and thus a good hydrogel candidate for bio-applications. Compared to synthetic polymer hydrogels, poor mechanical performance is still a fatal drawback that hinders the application of SF hydrogels. Researchers have attempted to develop strategies to construct silk fibroin-based high strength hydrogels (SF-HSHs). Herein, we review the processing approaches to prepare SF-HSHs with a focus on the gelation mechanisms. The mechanical properties of SF-HSHs are summarized under four categories according to the gelation mechanism, physical-crosslinked, dual-crosslinked, double network and composites. Furthermore, a brief description of the utility of SF-HSHs in biomedicine and devices is presented. Finally, the potential challenges and future development of SF-HSHs are briefly discussed. This review will enhance our understanding on the structure-property-function relationships of soft materials from natural polymers, and guide future biomedical applications of silk fibroin-based hydrogels.

Topical application of silk fibroin-based hydrogel in preventing hypertrophic scars

Current medications for the treatment of hypertrophic scars suffer from bottlenecks of limited therapeutic efficacy and a slow recovery rate. Silk fibroin (SF) has gained attention for its ability to promote wound healing in burns and cutaneous wounds, but its therapeutic effects against hypertrophic scar have not been thoroughly investigated. We prepared SF-based hydrogels (SFHs) with various SF concentrations (1.5 %, 3 %, and 6 %) and characterized their physicochemical properties. Cell experiments showed that these SFHs had favorable biocompatibility in vitro. Further animal experiments in rabbits revealed that the SFH (3 %)-treated group achieved scars on their ears that were thinner and significantly lighter in color compared with the negative control group. Moreover, treatment with SFHs reduced the density and led to the orderly arrangement of collagen fibers. It was found that the therapeutic effects of SFHs were attributed to the reduced expression levels of α-smooth muscle actin. These results are the first to demonstrate that SFH can be exploited as an effective therapeutic agent for the treatment of hypertrophic scars.

Design of Self-Healing and Electrically Conductive Silk Fibroin-Based Hydrogels.

Self-healing and electrically conductive silk fibroin (SF)-based hydrogels were developed based on the dynamic assembly/disassembly nature of supramolecular complexes and the conductive nature of polypyrrole (PPy). The self-healing properties of the hydrogels were achieved through host-guest interactions between β-cyclodextrin and amino acid side chains (tyrosine, tryptophan, phenylalanine, and histidine) on SF. PPy deposition was achieved via in situ polymerization of pyrrole using ammonium persulfate as an oxidant and laccase as a catalyst. The PPy-coated hydrogels behaved as an elastomer and displayed excellent electrical properties, with adjustable electrical conductivities ranging from 0.8 ± 0.2 to (1.0 ± 0.3) × 10-3 S·cm-1. Furthermore, possibility of potential utilization of the hydrogels in electrochemistry applications as flexible yet self-healable electrode materials was explored. This study not only shows great potential in expanding the role of silk-based devices for various applications but also provides a useful approach for designing multifunctional self-healing protein-based hydrogels.

The therapeutic effect of secretome from human umbilical cord-derived mesenchymal stem cells in age-related osteoporosis

Senile osteoporosis is closely related to the loss of function of stem cells. In this study, we tried to investigate the potential of secretome from human umbilical cord-derived mesenchymal stem cells (hUCMSCs) in recovering stem cell ability from senescence and then delaying bone loss. We first harvested bone marrow-derived mesenchymal stem cells (BMSCs) from young and old rats and then compared their cellular characteristics such as cell growth, anti-senescence and differentiation. The results showed that these abilities were negatively affected by animal aging. Subsequently, aged BMSCs were exposed to secretome from hUCMSCs, and we found that this loss of cell potential can be modified by secretome treatment. Thereafter, the secretome was loaded into silk fibroin-based hydrogels and used for an in vivo animal study. The results showed that compared to the old untreated group, the bone formation capacity of aged rats was improved by local treatment of secretome-loaded silk fibroin hydrogels. In conclusion, these findings demonstrated that secretome from hUCMSCs has the capacity to recover stem cell potential and delay local bone loss in age-related osteoporosis, which could potentially be applied in osteoporosis therapy in the future.

Silk fibroin-based hydrogels as a protective matrix for stabilization of enzymes against pH denaturation

A significant challenge remains to protect proteins (including enzymes) from inactivation against pH. This study investigated stabilization against pH denaturation of carbonic anhydrase (CA) in silk fibroin (SF)-based hydrogels. CA was immobilized into SF-based hydrogels by a Ru(II) mediated photochemical method, giving rise to ∼100% immobilization efficiency and >60% activity of the free enzyme at the optimum pH value of 8. At an unfavorable acidic pH value of 3, the immobilized CA achieved >20% of the initial activity and ∼8% in the second cycle even after 12 h storage, while the free enzyme lost its activity completely. Fourier transform infrared spectroscopy (FTIR) results suggested that the protective effect of the SF-based hydrogels on the pH stability of CA could be attributed to unique structural feature of the SF molecules, enabling strong intermolecular interactions between SF and CA, and thus increasing protein rigidity against pH denaturation. The same approach was applied to lysozyme and xylanase, and achieved protein stabilization of both enzymes at an unfavorable basic pH value of 9. The SF-based hydrogels demonstrated great potential as a promising matrix for protein immobilization against pH denaturation.

Silk Fibroin-Based Hydrogels and Scaffolds for Osteochondral Repair and Regeneration.

Osteochondral lesions treatment and regeneration demands biomimetic strategies aiming physicochemical and biological properties of both bone and cartilage tissues, with long-term clinical outcomes. Hydrogels and scaffolds appeared as assertive approaches to guide the development and structure of the new osteochondral engineered tissue. Moreover, these structures alone or in combination with cells and bioactive molecules bring the mechanical support after in vitro and in vivo implantation. Moreover, multilayered structures designed with continuous interfaces furnish appropriate features of the cartilage and subchondral regions, namely microstructure, composition, and mechanical properties. Owing the potential as scaffolding materials, natural and synthetic polymers, bioceramics, and composites have been employed. Particularly, significance is attributed to the natural-based biopolymer silk fibroin from the Bombyx mori silkworm, considering its unique mechanical and biological properties. The significant studies on silk fibroin-based structures, namely hydrogels and scaffolds, towards bone, cartilage, and osteochondral tissue repair and regeneration are overviewed herein. The developed biomimetic strategies, processing methodologies, and final properties of the structures are summarized and discussed in depth.