Silk Fibroin Gel Research Articles

Inclusion of Reduced Graphene Oxide to Silk Fibroin Hydrogels Improve the Conductive, Swelling and Wound Healing Capacity

AbstractDeveloping dressing for wound dressings represents a significant challenge for the scientific community. In this study, a conductive hydrogel was synthesized to promote the wound‐healing process. This hydrogel is composed of silk fibroin (SF), reduced graphene oxide (rGO), and glycerol (G). The impact of modifying the SF:rGO ratio, and the G content (%), on the physicochemical and biological properties. The hydrogels were characterized using FT‐IR, SEM, XRD, TGA, swelling, mechanical resistance, and conductivity. The cytotoxicity of the materials and their wound‐healing capacity in human fibroblasts were also determined. Chemical analysis revealed that the gelation of SF occurs due to the formation of β sheet structures, which was confirmed by the shift from amide I to amide II. An Increase in the SF:rGO ratio favored swelling behavior, although increasing G reduced this effect. The swelling of the hydrogel followed a Fick diffusion mechanism. Furthermore, the increase in the SF:rGO ratio and the percentage G improved the conductivity of the materials. The hydrogels were found to be non‐cytotoxic to human fibroblasts, and those containing rGO exhibited superior wound healing capacity compared to the positive control cell culture medium. Therefore, SF:rGO hydrogels could be considered promising candidates for wound dressing.

Silk Fibroin-Based Scaffolds: Potential for Applications in Wound Healing

Chronic wounds, such as diabetic foot ulcers, pose significant challenges due to their prolonged inflammation state, slow vascularization, lack of supportive matrix, and frequent recurrence. Biocompatible materials like silk fibroin (SF) and collagen can be promising in chronic wound healing applications due to their biocompatibility, and ability to act as supporting matrix necessary for tissue regeneration. This study explores the development and characterization of SF-based biomaterials in various formats, including gels, lyophilized scaffolds, and films, by combining them with collagen (Col) and heparin (Hep) molecules that are known for the wound-healing properties. SF gels, films, and lyophilized scaffolds were characterized for water retention capacity, porosity, contact angle, and antibacterial properties. Curcumin-loaded films reported moderate wetting behavior but were brittle, thin and hard. Freeze-dried scaffolds possessed higher water retention capacity compared to the sonicated gels and films, and showed a porous network structure, while the fabricated SF gels disintegrated in water. SF with a chelating agent demonstrated mild antibacterial properties, which were retained when combined with Collagen peptides and Heparin. The antimicrobial effect was significantly enhanced when SF+Col+Hep was added with antimicrobial agents such as Gentamicin and Ceftriaxone. The study concludes that SF-based scaffolds, particularly those incorporating collagen peptides and heparin, can be leveraged for molecular delivery application towards wound healing. Future research should focus on improving mechanical properties, measuring release kinetics of heparin and other biomolecules from SF-based lyophilized scaffolds, and conducting in vivo studies to validate the therapeutic value.

Stable Zinc Anode Facilitated by Regenerated Silk Fibroin-modified Hydrogel Protective Layer.

Inherent dendrite growth and side reactions of zinc anode caused by its unstable interface in aqueous electrolytes severely limit the practical applications of zinc-ion batteries (ZIBs). To overcome these challenges, a protective layer for Zn anode inspired by cytomembrane structure is developed with PVA as framework and silk fibroin gel suspension (SFs) as modifier. This PVA/SFs gel-like layer exerts similar to the solid electrolyte interphase, optimizing the anode-electrolyte interface and Zn2+ solvation structure. Through interface improvement, controlled Zn2+ migration/diffusion, and desolvation, this buffer layer effectively inhibits dendrite growth and side reactions. The additional SFs provide functional improvement and better interaction with PVA by abundant functional groups, achieving a robust and durable Zn anode with high reversibility. Thus, the PVA/SFs@Zn symmetric cell exhibits an ultra-long lifespan of 3150 h compared to bare Zn (182 h) at 1.0 mAh cm-2-1.0 mAh cm-2, and excellent reversibility with an average Coulombic efficiency of 99.04% under a large plating capacity for 800 cycles. Moreover, the PVA/SFs@Zn||PANI/CC full cells maintain over 20 000 cycles with over 80% capacity retention under harsh conditions at 5 and 10 A g-1. This SF-modified protective layer for Zn anode suggests a promising strategy for reliable and high-performance ZIBs.

Silk fibroin hydrogel adhesive enables sealed-tight reconstruction of meniscus tears

Despite orientationally variant tears of the meniscus, suture repair is the current clinical gold treatment. However, inaccessible tears in company with re-tears susceptibility remain unresolved. To extend meniscal repair tools from the perspective of adhesion and regeneration, we design a dual functional biologic-released bioadhesive (S-PIL10) comprised of methacrylated silk fibroin crosslinked with phenylboronic acid-ionic liquid loading with growth factor TGF-β1, which integrates chemo-mechanical restoration with inner meniscal regeneration. Supramolecular interactions of β-sheets and hydrogen bonds richened by phenylboronic acid-ionic liquid (PIL) result in enhanced wet adhesion, swelling resistance, and anti-fatigue capabilities, compared to neat silk fibroin gel. Besides, elimination of reactive oxygen species (ROS) by S-PIL10 further fortifies localized meniscus tear repair by affecting inflammatory microenvironment with dynamic borate ester bonds, and S-PIL10 continuously releases TGF-β1 for cell recruitment and bridging of defect edge. In vivo rabbit models functionally evidence the seamless and dense reconstruction of torn meniscus, verifying that the concept of meniscus adhesive is feasible and providing a promising revolutionary strategy for preclinical research to repair meniscus tears.

Development of a More Environmentally Friendly Silk Fibroin Scaffold for Soft Tissue Applications.

A push for environmentally friendly approaches to biomaterials fabrication has emerged from growing conservational concerns in recent years. Different stages in silk fibroin scaffold production, including sodium carbonate (Na2CO3)-based degumming and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)-based fabrication, have drawn attention for their associated environmental concerns. Environmentally friendly alternatives have been proposed for each processing stage; however, an integrated green fibroin scaffold approach has not been characterized or used for soft tissue applications. Here, we show that the combination of sodium hydroxide (NaOH) as a substitute degumming agent with the popular "aqueous-based" alternative silk fibroin gelation method yields fibroin scaffolds with comparable properties to traditional Na2CO3-degummed aqueous-based scaffolds. The more environmentally friendly scaffolds were found to have comparable protein structure, morphology, compressive modulus, and degradation kinetics, with increased porosity and cell seeding density relative to traditional scaffolds. Human adipose-derived stem cells showed high viability after three days of culture while seeded in each scaffold type, with uniform cell attachment to pore walls. Adipocytes from human whole adipose tissue seeded into scaffolds were found to have similar levels of lipolytic and metabolic function between conditions, in addition to a healthy unilocular morphology. Results indicate that our more environmentally friendly methodology for silk scaffold production is a viable alternative and well suited to soft tissue applications.

Photopolymerized silk fibroin gel for advanced burn wound care

The future of burn wound treatment lies in developing bioactive dressings for faster and more effective healing and regeneration. Silk fibroin (SF) hydrogels have proven regenerative abilities and are being explored as a burn wound dressing. However, unfavorable gelation conditions limit the processability and clinical application. Herein a white light-responsive photopolymerization technique was adapted for gelation via photooxidation of tyrosine. To render the gel suitable for application to irregular and non-planar burn surfaces, SF gel-incorporated dressing (SFD) was fabricated. The mild gelation conditions using white light afforded the loading of drugs for local delivery. The moisture balance ability of the dressing was confirmed by the favorable measures of swelling capacity (106 ± 1 %) and moisture retention (≈10 h). The in vitro cytocompatibility of the gel was confirmed using HaCaT cells. Finally, in vivo performance of the SFD was tested on a second-degree burn in a rodent model. The gross analysis and histological assessment revealed scarless healing in SFD-treated groups. Overall, the SFD developed in this work is shown to be a promising candidate for advanced burn wound care.

Silk fibroin microgels as a platform for cell microencapsulation

Cell microencapsulation has been utilized for years as a means of cell shielding from the external environment while facilitating the transport of gases, general metabolites, and secretory bioactive molecules at once. In this light, hydrogels may support the structural integrity and functionality of encapsulated biologics whereas ensuring cell viability and function and releasing potential therapeutic factors once in situ. In this work, we describe a straightforward strategy to fabricate silk fibroin (SF) microgels (µgels) and encapsulate cells into them. SF µgels (size ≈ 200 µm) were obtained through ultrasonication-induced gelation of SF in a water-oil emulsion phase. A thorough physicochemical (SEM analysis, and FT-IR) and mechanical (microindentation tests) characterization of SF µgels were carried out to assess their nanostructure, porosity, and stiffness. SF µgels were used to encapsulate and culture L929 and primary myoblasts. Interestingly, SF µgels showed a selective release of relatively small proteins (e.g., VEGF, molecular weight, MW = 40 kDa) by the encapsulated primary myoblasts, while bigger (macro)molecules (MW = 160 kDa) were hampered to diffusing through the µgels. This article provided the groundwork to expand the use of SF hydrogels into a versatile platform for encapsulating relevant cells able to release paracrine factors potentially regulating tissue and/or organ functions, thus promoting their regeneration.Graphical

3D cell culture based on artificial cells and hydrogel under microgravity for bottom-up microtissue constructs.

The use of hydrogel as a filling medium to recombine dispersed microencapsulated cells to form an embedded gel-cell microcapsule complex is a new idea based on bottom-up tissue construction, which is benefit for cell distribution and of great significance for tissue construction research in vitro. In this experiment, sodium alginate and chitosan were used as the main materials, rat normal liver cell BRL-3A was used as the model cell to prepare "artificial cells". Silkworm pupa was used as raw material to extract silk fibroin solution, which was prepared by ultrasound to be the silk fibroin gel; silk fibroin hydrogel-microencapsulated hepatocyte embedded complex was then prepared by using silk fibroin gel as filling medium; the complex was cultured under three modes (static, shaking, and 3D microgravity), and the tissue forming ability of rat hepatocytes was investigated. The results showed that the microgravity culture condition can enhance the cell proliferation and promote the formation of cell colonies in the microcapsules; silk fibroin can form an embedded gel-cell microcapsule complex with microencapsulated cells, which provided mechanical support for the structure of the composite. We hope that this bottom-up construction system will have potential applications in the fields of cell culture and tissue construction.

Amino Acid Surfactant‐Induced Superfast Gelation of Silk Fibroin for Treating Noncompressible Hemorrhage

AbstractThe gelation of silk fibroin (SF) aqueous solution cross‐linked by externally induced β‐sheets generally takes longer times, and requires relatively strict conditions, limiting their biomedical application possibilities. Here, a simplified and straightforward strategy is proposed to induce superfast gelation of SF by a biocompatible Food and Drug Administration‐approved amino acid surfactant, ethyl lauroyl arginine hydrochloride (LAE). The gelation time is as short as 15 s at 60 °C and falls within 1 min around body temperature. The distinct pathway and thermodynamics of superfast gelation of SF is deciphered, and three important factors including superfast and complete unfolding, heterogeneous nucleation seeds, and faster formation of more β‐sheets that are crucial for superfast SF assembly are revealed. The LAE‐induced in situ superfast gelation mechanism is first harnessed to fabricate an injectable antibacterial biodegradable hemostatic hydrogel for treatment of noncompressible liver bleeding. The amphiphilicity of LAE and superfast gelation is exploited to quickly entrap different sizes of air bubbles in the upper and lower part of the hydrogel, which is then lyophilized to form an asymmetric hierarchical porous SF‐LAE sponge, where the large pores serve to drain blood, and dense pores prevent the outflow of blood to seal the wound.

Bioinspired Soft Multistate Resistive Memory Device Based on Silk Fibroin Gel for Neuromorphic Computing

Brain‐inspired computation is a promising field toward the next generation of intelligent computing systems. To mimic the brain functions, this field requires devices that can support the goal of computing efficiency, size, and cost. Therefore, researchers are trying to fabricate soft and flexible devices using synthetically organic and inorganic materials like solid‐state or ionic liquids. Herein, a soft and flexible bioinspired neuromorphic computing device based on organic silk fibroin gel, which is robust under external forces, is proposed. Silk fibroin protein is composed of essential and nonessential amino acids. with special amount of positively charged glycine, alanine, which plays an essential role during ionic movement to perform neuromorphic computing. Detailed electrical characterization of the proposed (Cu/silk fibroin gel/Cu) discrete device confirms the synaptic behavior by applying different pulse amplitudes, pulse widths, and frequencies. In addition, the proposed device delivers stable performance during mechanical deformations. The analysis of the present results defines that the proposed device is a potential candidate for environmentally friendly wearable intelligent electronics.

Multifunctional Biosensors Made with Self-Healable Silk Fibroin Imitating Skin.

We report on robust silk fibroin (SF) gels fabricated by incorporating cellulose nanocrystals (SF/CNC) as a "tough" unit and photopolymerization of acrylamide as an "elastic" segment. The addition of CNC affects the refolding process of SF molecules controlled by nucleation via templating, resulting in a stable mesoscopic structure. The gel shows robust mechanical stability (88.8% of initial stress after 1000 compression cycles) and excellent adhesion to various materials. The connected gel can recover its ionic conductivity within 20 s and be stretched to a maximum strain of 498% after healing for 10 h with an efficiency of 95.2%. This multifunctional gel sensor can sensitively detect different toxic gases and small-scale and large-scale human motions in real-time. Its sensitivity is calculated as GF = 3.84 at 0-200% strain. Especially, the gel with 5 wt % thermochromic pigments as a visual temperature indicator can quickly reflect abnormal human body temperature according to the color change. Therefore, the strategy shows potential applications in flexible electrodes, biomimetic sensors, and visual biosensors.

Gold, Silver, and Iron Oxide Nanoparticle Incorporation into Silk Hydrogels for Biomedical Applications: Elaboration, Structure, and Properties.

Silk fibroin (SF) is a versatile material with biodegradable and biocompatible properties, which make it fit for broad biomedical applications. In this context, the incorporation of nanosized objects into SF allows the development of a variety of bionanocomposites with tailored properties and functions. Herein, we report a thorough investigation on the design, characterization, and biological evaluation of SF hydrogels incorporating gold, silver, or iron oxide nanoparticles. The latter are synthesized in aqueous media using a biocompatible ligand allowing their utilization in various biomedical applications. This ligand seems to play a pivotal role in nanoparticle dispersion within the hydrogel. Results show that the incorporation of nanoparticles does not greatly influence the mechanism of SF gelation and has a minor impact on the mechanical properties of the so-obtained bionanocomposites. By contrast, significant changes are observed in the swelling behavior of these materials, depending on the nanoparticle used. Interestingly, the main characteristics of these bionanocomposites, related to their potential use for biomedical purposes, show the successful input of nanoparticles, including antibacterial properties for gold and silver nanoparticles and magnetic properties for iron oxide ones.

Silk gel recruits specific cell populations for scarless skin regeneration

Scarless skin regeneration is not achieved although various biomaterials have been investigated on trial-and-error manner. There is no predictable way to link a specific biomaterial with in vivo cell populations which dominate the skin repair. In this study, single-cell RNA sequencing was conducted to investigate the cellular mechanism of two prevailing biomaterials used in skin regeneration, silk fibroin gel and alginate gel. We found that these two gels induced different cell population structures in vivo. Compared with the alginate-derived hydrogel, silk fibroin-derived hydrogel induced more pro-regenerative macrophages and recruited more hair follicle stem cells, which contributed to almost scarless skin regeneration. Besides, an off-the-shelf silk gel scaffold was fabricated and exhibited more efficacy than autologous skin grafts in porcine models. These findings exhibited the promises of the silk gel for skin regeneration and illustrated a predictable strategy for biomaterial selection based on cell populations recruitment.

Viscoelastic Silk Fibroin Hydrogels with Tunable Strength.

Hydrogels are often used as synthetic extracellular matrices (ECMs) for biomedical applications. Natural ECMs are viscoelastic and exhibit partial stress relaxation. However, commonly used hydrogels are typically elastic. Hydrogels developed from ECM-based proteins are viscoelastic, but they often have weak mechanical properties. Here, biocompatible viscoelastic hydrogels with excellent mechanical performance are fabricated by an all aqueous process at body or room temperature. These hydrogels offer obvious stress relaxation and tunable mechanical properties and gelation kinetics. Their compressive modulus can be controlled between 2 kPa and 1.2 MPa, covering a significant portion of the properties of native tissues. Investigation of the gelation mechanism revealed that silk fibroin gelation is caused by the synergistic effects of hydrophobic interaction and hydrogen bonding between silk fibroin molecules. Newly formed crystals serve as the cross-link sites and form a network endowing the hydrogel with stable structure, and the flexible noncrystalline silk nanofibers connect disparate silk fibroin crystals, endowing hydrogels with viscoelastic properties. The all aqueous gelation process avoids complex chemical and physical treatments and is beneficial for encapsulating cells or biomolecules. Encapsulation of chondrocytes results in high initial survival rate (95% ± 1%). These silk fibroin-based viscoelastic hydrogels, combined with superior biocompatible and tunable mechanical properties, represent an exciting option for tissue engineering and regenerative medicine.

Low voltage electric field governs fibrous silk electrogels

Silk fibroin gels, formed with electric fields, have been studied and potential utility in medical materials. However, silk electrogels with controllable nanofiber network morphology have rarely been reported. In this work, low voltage electric field was developed to control the nanofiber network morphology formation and resulting electrogelation of silk fibroin aqueous solution, inducing a transition from an overall protein structure that is initially rich in random coil to one that is rich in β-sheet. Under low voltage (3–24 V), solution concentration (≤5.0 wt%), and neutral, alkaline conditions, silk fibroin fibrous electrogels were easily formed. At the same time, compression test result exhibited the compressive stress of silk fibroin fibrous electrogels was 250.17 ± 16.50 kPa at dry state, which formed from silk fibroin concentration 3.0 wt%. Moreover, the recovery rate of electrogels can reach more than 50% after 10 compression-recovery circles, exhibiting excellent flexibility. In addition, silk fibroin electrogels loaded cefixime drugs have obvious antibacterial effect against Staphylococcus aureus and Escherichia coli than commercial medical band-aids. Drug-loaded silk fibroin fibrous electrogels supported mouse embryonic fibroblasts 3 T3 cells attachment and proliferation over 7 days. This study offers an effective approach to design and synthesis of new dressings.

Enhanced mechanical performance of biocompatible silk fibroin films through mesoscopic construction of hierarchical structures

Silk fibroin (SF) material receives a great deal of attention in the biomedical field for its extensive mechanical performance and applications due to its singular structure/properties and applications, especially hierarchical structure. Here, we blended polyethylene glycol (PEG) into SF solutions that reconstruct the hierarchical micro structure of SF. The effect of PEG on the SF gelation process was in situ observed through rheological measurement and optical density changes. The structural change of SF/PEG blended films with different concentrations and their effects on the mechanical performance were investigated. The results indicated that with increasing PEG content, the β-sheet content of the films increased with the α-helix declining, which enables a composite film with a fracture strain exceeding 300%, Young's modulus exceeding 200 MPa and a fracture strength exceeding 20 MPa. The culture of MC-3T3 proves that the film is beneficial for cell proliferation and adhesion. By constructing the mesoscopic structure of SF, the plasticized silk materials provide great options for biodegradable and flexible protein-based materials.

Lauric Acid Sophorolipid: Accelerating the Gelation of Silk Fibroin

Silk fibroin (SF) hydrogels find wide applications in tissue engineering. However, their scope has been limited due to the long gelation time in ambient conditions. This paper shows the reduction in gelation time of silk fibroin to minutes upon doping with a newly synthesized lauric acid sophorolipid (LASL). LASL comprises a fatty acid, lauric acid (with a 12-carbon aliphatic chain), that is derivatized by glucose molecules using a non-pathogenic yeast Candida bombicola. LASL was characterized using spectroscopic (Fourier transform infrared spectroscopy) and chromatographic (high-performance liquid chromatography, thin-layer chromatography, and high-resolution mass spectrometry) methods. This gelation of SF is comparable to the effect of an anionic surfactant, sodium dodecyl sulfate (SDS). The microstructure of SF-LASL hydrogels was investigated by small-angle neutron scattering (SANS) measurements and exhibited the beads-on-a-necklace model. The rheological properties of these hydrogels show similarity to SF-SDS hydrogels, therefore presenting a greener alternative for tissue engineering applications.

Programing Performance of Silk Fibroin Superstrong Scaffolds by Mesoscopic Regulation among Hierarchical Structures.

To design higher-strength natural scaffold materials, wool keratin (WK) rich in α-helix structures is used as a well-defined foreign substrate, which induces the formation of β-crystallites in silk fibroin (SF). Consequently, the macroscopic properties of silk materials (such as the rheological properties of SF hydrogels and the mechanical properties of stents) can be manipulated by governing the change in the hierarchical mesoscopic structure of silk materials. In this work, by monitoring the structure and morphology in the SF gel process, the mechanism of the effect of keratin on SF network formation was speculated, which was further used to design ultra-high-strength protein scaffolds. It has been confirmed that WK accelerates the gelation of SF by reducing the multistep nucleation barrier and increasing the primary nucleation sites, and then establishing a high-density SF domain network. The modulus of the protein composite scaffold prepared by this facile strategy can reach 11.55 MPa, and the MC-3T3 cells can grow well on the scaffold surface. The results suggest that freeze-dried biocompatible SF-based scaffolds are potential candidates for bone tissue engineering.

Dual-functional liposomes for curcumin delivery and accelerating silk fibroin hydrogel formation.

The administration of a drug-loaded implantable hydrogel at the tumor site after surgical resection is a viable approach to prevent the local recurrence or metastasis. Dimyristoyl glycerophosphorylglycerol (DMPG)-based liposomes were developed for inducing the rapid gelation of silk fibroin (SF) and delivering an anticancer drug, curcumin. Curcumin was loaded in the liposomes and the stability of curcumin was enhanced. The gelation time of liposome-induced SF hydrogels ranged from 3min to more than 6h. The biological activity of liposome-SF hydrogels was evaluated in vitro using L929 fibroblasts and MDA-MB-231 breast cancer cells. The release of curcumin can inhibit the growth of cancer cells. Both cells cultured on the surface of the hydrogels loaded with curcumin displayed low cell survival due to the combination of low cell attachment and cytotoxicity of curcumin. Liposome-SF hydrogels show potential as a sealant administered at the tumor site to eliminate residual cancer cells after tumor removal.

Berberine/Ag nanoparticle embedded biomimetic calcium phosphate scaffolds for enhancing antibacterial function

Abstract In the past decade, biomimetic calcium phosphate (CaP) ceramics have been considered as practicable grafts and biomaterial substitutes in repairing jaw bone defect after tumor resection or traffic accident. Nowadays, increasing incidence of biomedical material-associated infection has raised a concern when applying these materials. In this work, a new porous CaP scaffold with antibacterial coating was proposed. This biomimetic scaffold was composited with berberine (BBR), Ag nanoparticles (nAg), and silk fibroin (SF). The microstructures and phase composition of the scaffolds were analyzed. The cytocompatibility and osteogenic potential of the prepared samples were evaluated in vitro. The scaffolds held hierarchical structure: the first-level porous CaP ceramic with micron pores ranged from 250 to 600 µm; the second-level spongy-like structure with abundant capillary pores ranged from 500 nm to 10 µm; and the third-level structure was achieved by filling BBR, nAg, and SF gel coatings into the above porous structures. The experimental results showed that the antimicrobial capability of single BBR coating is inconspicuous. However, the introduction of nAg could significantly promote the antibacterial effect of scaffolds. At the same time, such scaffolds showed improved osteoinductivity. This new biomimetic CaP scaffold with antibacterial and osteoinductive properties may be a promising candidate for bone tissue engineering.