Properties Of Silk Fibroin Research Articles

An In Vitro Macrophage Response Study of Silk Fibroin and Silk Fibroin/Nano-Hydroxyapatite Scaffolds for Tissue Regeneration Application.

In recent years, silk fibroin (SF) has been incorporated with low crystallinity nanohydroxyapatite (nHA) as a scaffold for various tissue regeneration applications due to the mechanical strength of SF and osteoconductive properties of nHA. However, currently, there is a lack of understanding of the immune response toward the degradation products of SF with nHA composite after implantation. It is known that particulate fragments from the degradation of a biomaterial can trigger an immune response. As the scaffold is made of degradable materials, the degradation products may contribute to the inflammation. Therefore, in this study, the effects of the enzymatic degradation of the SF/nHA scaffold on macrophage response were investigated in comparison to the control SF scaffold. Since the degradation products of a scaffold can influence macrophage polarization, it can be hypothesized that as the SF and SF/nHA scaffolds were degraded in vitro using protease XIV solution, the degradation products can contribute to the polarization of THP-1-derived macrophages from pro-inflammatory M1 to anti-inflammatory M2 phenotype. The results demonstrated that the initial (day 1) degradation products of the SF/nHA scaffold elicited a pro-inflammatory response, while the latter (day 24) degradation products of the SF/nHA scaffold elicited an anti-inflammatory response. Moreover, the degradation products from the SF scaffold elicited a higher anti-inflammatory response due to the faster degradation of the SF scaffold and a higher amino acid concentration in the degradation solution. Hence, this paper can help elucidate the contributory effects of the degradation products of SF and SF/nHA scaffolds on macrophage response and provide greater insights into designing silk-based biomaterials with tunable degradation rates that can modulate macrophage response for future tissue regeneration applications.

Unravelling the antioxidant behaviour of self-assembly β-Sheet in silk fibroin

Local oxidative stress in diseases or injury severely hinders cell homeostasis and organ regeneration. Antioxidant therapy is an effective strategy for oxidative stress treatment. Biomaterials with good biocompatibility and reactive oxygen species (ROS) scavenging ability are good choices for antioxidant therapeutics. However, there are few natural biomaterials that are identified with both biocompatibility and strong antioxidant activity. Here, we show, for the first time, that silk fibroin (SF) is a strong antioxidant, which can eliminate ROS in both cells and zebrafish. We further demonstrate that the β-sheet structures turn into a random coiled structure when SF is treated with hydrogen peroxide. The content of β-sheet structures can be increased by heating, thus enhancing the antioxidation properties of SF. Therefore, SF can serve as a good antioxidant biomaterial for therapeutics, and its β-sheet structure-based antioxidation mechanism provides a novel theoretical basis, which could be a new cue for more antioxidant biomaterial discovery and identification.

Multifunctional Hydrogel Based on Silk Fibroin Promotes Tissue Repair and Regeneration

AbstractThe creation of functional hydrogels with robust load‐bearing capacity adaptable to complex tissue regeneration remains challenging. Silk fibroin (SF) is a natural biomaterial with excellent mechanical strength and cell adhesion capacity, possessing tremendous potential to solve the aforementioned dilemma. The excellent biodegradability and biocompatibility and the molecular structure with multiple modifiable moieties provide opportunities for the injectability and multifunctionality of hydrogels. Furthermore, the incorporation of other polymers or active ingredients can improve the basic properties, confer biological activities and pharmacological effects, and provide the prerequisites for hydrogels to fulfill specific requirements. Therefore, SF‐based hydrogels are widely applied in tissue repair and regeneration, especially in bone, skin, nerve, liver, myocardium, and cornea, which have effectively addressed the challenges of scaffolds' lack of cell adhesion sites, excessive degradation, as well as the lack of efficient, long‐lasting antimicrobial properties. This review outlines the properties of SF, discusses the types of materials commonly used in the preparation of hydrogels and their characteristics, and describes the current construction methods of SF hydrogels. Simultaneously, recent advancements in applying SF‐based multifunctional hydrogels within biological tissues are explored, with a focus on their role in tissue repair, highlighting the repair mechanism of SF based on bone and skin.

Silk Fibroin-Laponite Porous Microspheres as Cell Microcarriers for Osteogenic Differentiation.

Silk fibroin (SF) has garnered significant attention as a natural polymer for fabricating porous scaffolds in various engineering applications. However, the limited osteoinductive property of SF has hindered its efficacy in bone repair applications. In this study, we constructed an SF-based injectable porous microcarrier that is doped with laponite (LAP), containing magnesium ions (Mg2+). The influence of freezing temperatures and concentrations of SF and LAP on the structural parameters of SF-LAP microcarriers was investigated. The SF-LAP microcarrier exhibited a porosity of 76.7 ± 1.2% and a controlled pore size of 24.6 ± 4.0 μm. At the 6 weeks of in vitro degradation test, a mild alkaline level in culture medium containing SF-LAP microcarriers was detected. The release of Mg2+ from the SF-LAP microcarrier was maintained at a concentration within the range of 1.2-2.3 mM during the 6 weeks. The seeded human adipose-derived stem cells in the SF-LAP microcarrier demonstrated a significant enhancement in osteogenic differentiation compared with cells seeded in the pure SF microcarrier, as evidenced by quantitative alkaline phosphatase activity and the expression of osteogenic marker genes. These findings underscore the potential of the SF-LAP microcarrier as an ideal cell carrier in the treatment of bone defects.

Investigation of Silk Fibroin/Poly(Acrylic Acid) Interactions in Aqueous Solution.

Silk fibroin (SF) is a protein with many outstanding properties (superior biocompatibility, mechanical strength, etc.) and is often used in many advanced applications (epidermal sensors, tissue engineering, etc.). The properties of SF-based biomaterials may additionally be tuned by SF interactions with other (bio)polymers. Being a weak amphoteric polyelectrolyte, SF may form polyelectrolyte complexes (PECs) with other polyelectrolytes of opposite charge, such as poly(acrylic acid) (PAA). PAA is a widely used, biocompatible, synthetic polyanion. Here, we investigate PEC formation between SF and PAA of two different molecular weights (MWs), low and high, using various techniques (turbidimetry, zeta potential measurements, capillary viscometry, and tensiometry). The colloidal properties of SF isolated from Bombyx mori and of PAAs (MW, overlap concentration, the influence of pH on zeta potential, adsorption at air/water interface) were determined to identify conditions for the SF-PAA electrostatic interaction. It was shown that SF-PAA PEC formation takes place at different SF:PAA ratios, at pH 3, for both high and low MW PAA. SF-PAA PEC's properties (phase separation, charge, and surface activity) are influenced by the SF:PAA mass ratio and/or the MW of PAA. The findings on the interactions contribute to the future development of SP-PAA PEC-based films and bioadhesives with tailored properties.

Application of Silk-Fibroin-Based Hydrogels in Tissue Engineering

Silk fibroin (SF) is an excellent protein-based biomaterial produced by the degumming and purification of silk from cocoons of the Bombyx mori through alkali or enzymatic treatments. SF exhibits excellent biological properties, such as mechanical properties, biocompatibility, biodegradability, bioabsorbability, low immunogenicity, and tunability, making it a versatile material widely applied in biological fields, particularly in tissue engineering. In tissue engineering, SF is often fabricated into hydrogel form, with the advantages of added materials. SF hydrogels have mostly been studied for their use in tissue regeneration by enhancing cell activity at the tissue defect site or counteracting tissue-damage-related factors. This review focuses on SF hydrogels, firstly summarizing the fabrication and properties of SF and SF hydrogels and then detailing the regenerative effects of SF hydrogels as scaffolds in cartilage, bone, skin, cornea, teeth, and eardrum in recent years.

Silk Fibroin Microneedles for Transdermal Drug Delivery: Where Do We Stand and How Far Can We Proceed?

Microneedles are a patient-friendly technique for delivering drugs to the site of action in place of traditional oral and injectable administration. Silk fibroin represents an interesting polymeric biomaterial because of its mechanical properties, thermal stability, biocompatibility and possibility of control via genetic engineering. This review focuses on the critical research progress of silk fibroin microneedles since their inception, analyzes in detail the structure and properties of silk fibroin, the types of silk fibroin microneedles, drug delivery applications and clinical trials, and summarizes the future development trend in this field. It also proposes the future research direction of silk fibroin microneedles, including increasing drug loading doses and enriching drug loading types as well as exploring silk fibroin microneedles with stimulation-responsive drug release functions. The safety and effectiveness of silk fibroin microneedles should be further verified in clinical trials at different stages.

Preparation and characterization of conducting silk fibroin by Ag nanocoating for electrical applications

This research work proposes the fabrication of novel bio-based multifunctional biomaterials in order to avoid synthetic materials to reduce environmental hazards for the sustainability of nature. The decoration of Ag nanoparticles on silk fibroin (SF) surface to achieve the transport properties of SF. This functional biomaterial has numerous amino acid residues so that it acts as a good reducing and stabilizing agent for conversion of metal ions into a neutral atom (Ag+ to Agο). A standard protocol is adopted for the preparation of SF and Ag-coated SF nanocomposites under the influence of light radiation (Incandescent bulb). The SF-AgNPs composites were subjected to XRD, TGA, DSC, SEM, AC & DC conductivity to investigate the structural, thermal and surface morphology and electrical properties of the composites. The formed nanoparticles exhibit a face-centered cubic structure (FCC) with an average particle size of 35–40 nm. The features of SF are altered by the inclusion of AgNPs on the fibroin surface. Since silk is an excellent dielectric material with strong electrical and heat stability after mixing with AgNPs, it can be used for wearable electronic devices and biomedical applications.

Preparation and characterization of fibroin nanoparticles obtained from Bombyx mori L. Pilamo 1 cocoons

Silk fibroin (SF) is a biomacromolecule composed of proteins with properties, such as biocompatibility, biodegradability, and low immunogenicity. Thus, Silk fibroin nanoparticles (FNps) overcome the disadvantages of non-degradable synthetic nanoparticles. We studied the structural and thermal properties of SF and FNps from Bombyx mori L. cross-breed Pilamo I cocoons. Raw fibroin (RF) was obtained using a sodium Na2CO3 solution as part of an experimental design to improve extraction, and FNps were obtained by denaturing RF with a ternary solution of CaCl2:H2O:CH3CH2OH, followed by precipitation using an anti-solvent method with propanol. Pilamo I cocoon, RF, and FNps were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy(SEM), and elemental chemical analysis of energy dispersive X-rays (EDS). The Light Scattering (DLS) and the thermal properties of RF and FNps were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The FTIR results showed that sericin-free raw fibroin was obtained, and the SEM results showed that the nanometer-sized particles had a globular structure and apparent porosity. The differences in the enthalpy of the crystallization peaks in the DSC and TGA curves showed that the FNps had higher thermal stability than RF fibers. This result furthers the development of alternative materials as vehicles of active compounds from natural extracts.

Instructive electroactive electrospun silk fibroin-based biomaterials for peripheral nerve tissue engineering.

Aligned sub-micron fibres are an outstanding surface for orienting and promoting neurite outgrowth; therefore, attractive features to include in peripheral nerve tissue scaffolds. A new generation of peripheral nerve tissue scaffolds is under development incorporating electroactive materials and electrical regimes as instructive cues in order to facilitate fully functional regeneration. Herein, electroactive fibres composed of silk fibroin (SF) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) were developed as a novel peripheral nerve tissue scaffold. Mats of SF with sub-micron fibre diameters of 190±50nm were fabricated by double layer electrospinning with thicknesses of ∼100μm (∼70-80μm random fibres and ∼20-30μm aligned fibres). Electrospun SF mats were modified with interpenetrating polymer networks (IPN) of PEDOT:PSS in various ratios of PSS/EDOT (α) and the polymerisation was assessed by hard X-ray photoelectron spectroscopy (HAXPES). The mechanical properties of electrospun SF and IPNs mats were characterised in the wet state tensile and the electrical properties were examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The cytotoxicity and biocompatibility of the optimal IPNs (α=2.3 and 3.3) mats were ascertained via the growth and neurite extension of mouse neuroblastoma x rat glioma hybrid cells (NG108-15) for 7days. The longest neurite outgrowth of 300μm was observed in the parallel direction of fibre alignment on laminin-coated electrospun SF and IPN (α=2.3) mats which is the material with the lowest electron transfer resistance (Ret, ca. 330Ω). These electrically conductive composites with aligned sub-micron fibres exhibit promise for axon guidance and also have the potential to be combined with electrical stimulation treatment as a further step for the effective regeneration of nerves.

Characterization of direct ink write pure silk fibroin based on alcohol post-treatments

Silk fibroin (SF) has been successfully used for medical devices due to its biodegradability with non-toxic end products, high tensile strength and mechanical robustness, but also because of its high flexibility potential. Although natural silk fibers have excellent strength and flexibility, regenerated silk materials generally become brittle in the dry state. For this reason, researchers have studied the effects that manufacturing and post-treatment parameters have on their mechanical properties, but they have also studied the impact on other factors such as biodegradability on the environment. This work presents an optimized process for direct ink write a regenerated SF bioink and its possible post-treatments. A simple method to concentrate the aqueous SF has been reported. The technique was then employed to 3D print test specimens for multiple mechanical analysis to characterize the resulting parameters of the processed silk. The effect of post-treating the material with different processes (no-treatment, immersion in ethanol for 24 h, and subsequently immersion in methanol for 30, 60 or 120 min) was explored. The different post-treatments resulted in distinct effects on the silk properties, suggesting that SF molecular structure could be controlled by the post-treatment process. The results showed a transition to phosphate-buffered saline (PBS)-insoluble silk when the silk was treated with alcohols. This resulted in a more brittle material than the untreated group, with a lower strain at break. Nevertheless, the post-treatments enhanced the stability of silk in water, as they reported greater insolubility in PBS than the untreated group. This study characterizes and discusses the mechanical properties of SF processed with a novel additive manufacturing method intended for customization of medical devices.

Recent Research Progress of Ionic Liquid Dissolving Silks for Biomedicine and Tissue Engineering Applications.

Ionic liquids (ILs) show a bright application prospect in the field of biomedicine and energy materials due to their unique recyclable, modifiability, structure of cation and anion adjustability, as well as excellent physical and chemical properties. Dissolving silk fibroin (SF), from different species silkworm cocoons, with ILs is considered an effective new way to obtain biomaterials with highly enhanced/tailored properties, which can significantly overcome the shortcomings of traditional preparation methods, such as the cumbersome, time-consuming and the organic toxicity caused by manufacture. In this paper, the basic structure and properties of SF and the preparation methods of traditional regenerated SF solution are first introduced. Then, the dissolving mechanism and main influencing factors of ILs for SF are expounded, and the fabrication methods, material structure and properties of SF blending with natural biological protein, inorganic matter, synthetic polymer, carbon nanotube and graphene oxide in the ILs solution system are introduced. Additionally, our work summarizes the biomedicine and tissue engineering applications of silk-based materials dissolved through various ILs. Finally, according to the deficiency of ILs for dissolving SF at a high melting point and expensive cost, their further study and future development trend are prospected.

Use of Bombyx mori silk fibroin in tissue engineering: From cocoons to medical devices, challenges, and future perspectives

Silk fibroin has become a prominent material in tissue engineering (TE) over the last 20years with almost 10,000 published works spanning in all the TE applications, from skeleton to neuronal regeneration. Fibroin is an extremely versatile biopolymer that, due to its ease of processing, has enabled the development of an entire plethora of materials whose properties and architectures can be tailored to suit target applications. Although the research and development of fibroin TE materials and devices is mature, apart from sutures, only a few medical products made of fibroin are used in the clinical routines. <40 clinical trials of Bombyx mori silk-related products have been reported by the FDA and few of them resulted in a commercialized device. In this review, after explaining the structure and properties of silk fibroin, we provide an overview of both fibroin constructs existing in the literature and fibroin devices used in clinic. Through the comparison of these two categories, we identified the burning issues faced by fibroin products during their translation to the market. Two main aspects will be considered. The first is the standardization of production processes, which leads both to the standardization of the characteristics of the issued device and the correct assessment of its failure. The second is the FDA regulations, which allow new devices to be marketed through the 510(k) clearance by demonstrating their equivalence to a commercialized medical product. The history of some fibroin medical devices will be taken as a case study. Finally, we will outline a roadmap outlining what actions we believe are needed to bring fibroin products to the market.

Adsorption, Surface Viscoelasticity, and Foaming Properties of Silk Fibroin at the Air/Water Interface

Like other proteins, the natural silk fibroin (SF) extracted from domesticated silkworms can adsorb at the air/water interface and stabilize foam due to its amphiphilic character and surface activity. At the interface, the adsorbed SF molecules experience structural reorganization and form water-insoluble viscoelastic films, which protect foam bubbles from coalescence and rupture. The solution conditions, such as protein concentration, pH, and additives, have significant influences on the molecular adsorption, layer thickness, interfacial mechanical strength, and, thus, on the foaming properties of SF. The understanding of the relationship between the interfacial adsorption, surface viscoelasticity, and foaming properties of SF is very important for the design, preparation, and application of SF foams in different fields.

Silk Fibroin-Based Biomaterials for Tissue Engineering Applications

Tissue engineering (TE) involves the combination of cells with scaffolding materials and appropriate growth factors in order to regenerate or replace damaged and degenerated tissues and organs. The scaffold materials serve as templates for tissue formation and play a vital role in TE. Among scaffold materials, silk fibroin (SF), a naturally occurring protein, has attracted great attention in TE applications due to its excellent mechanical properties, biodegradability, biocompatibility, and bio-absorbability. SF is usually dissolved in an aqueous solution and can be easily reconstituted into different forms, including films, mats, hydrogels, and sponges, through various fabrication techniques, including spin coating, electrospinning, freeze drying, and supercritical CO2-assisted drying. Furthermore, to facilitate the fabrication of more complex SF-based scaffolds, high-precision techniques such as micro-patterning and bio-printing have been explored in recent years. These processes contribute to the diversity of surface area, mean pore size, porosity, and mechanical properties of different silk fibroin scaffolds and can be used in various TE applications to provide appropriate morphological and mechanical properties. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have recently been developed. The typical applications of SF-based scaffolds for TE of bone, cartilage, teeth and mandible tissue, cartilage, skeletal muscle, and vascular tissue are highlighted and discussed followed by a discussion of issues to be addressed in future studies.

Influence of surfactant charge and concentration on the surface and foaming properties of biocompatible silk fibroin

As a kind of fibrous amphiphilic protein, the biocompatible silk fibroin (SF) extracted from domesticated silkworms can adsorb at the air/water interface, form thick interfacial layers, and stabilize foams that can be used to fabricate porous scaffolds and regenerate soft tissue. In this study, three surfactants, cationic cetyl trimethyl ammonium bromide (C16TAB), nonionic polyoxyethylene sorbitan monolaurate (Tween 20), and anionic sodium dodecyl sulphate (SDS) were utilized to investigate the effects of surfactant charge and concentration on the adsorption dynamics, interfacial viscoelasticity, and foaming properties of SF. SF is negatively charged at neutral pH in aqueous solution. All these surfactants tend to enhance the surface activity of SF, thus leading to faster interfacial adsorption and establishment of the adsorption equilibrium, thicker interfacial layers, and an increase in the foaming rate. Meanwhile, these surfactants also improve the toughness of interfacial SF networks, and then promote the foam stability. However, at high concentrations, the nonionic Tween 20 and anionic SDS reduce the interfacial elasticity and stability due to the emergence of surfactant domains that interrupt the interfacial SF networks, while the cationic C16TAB thickens the interfacial layers and significantly decreases the interfacial stability and foamability due to its counter-ion screening effect that promotes the aggregation of SF molecules.

Recent Advances in Environmentally Friendly and Green Degumming Processes of Silk for Textile and Non-Textile Applications

Silk has been widely used not only in the textile field but also in non-textile applications, which is composed of inner fibrous protein, named fibroin, and outer global protein, named sericin. Due to big differences, such as appearance, solubility, amino acid composition and amount of reactive groups, silk fibroin and sericin usually need to be separated before further process. The residual sericin may influence the molecular weight, structure, morphology and properties of silk fibroin, so that degumming of silk is important and necessary, not only in textile field but also in non-textile applications. Traditional textile degumming processes, including soap, alkali or both, could bring such problems as environmental damage, heavy use of water and energy, and damage to silk fibroin. Therefore, this review aims to present a systematic work on environmentally friendly and green degumming processes of raw silk, including art of green degumming process, quantitative and qualitative evaluation, influence of degumming on molecular weight, structure, morphology and properties of silk. It is anticipated that rational selection and design of environmentally friendly and green degumming process is quite important and meaningful, not only for textile application but also for non-textile application.

Proteomic Analysis of Silk Fibroin Reveals Diverse Biological Function of Different Degumming Processing From Different Origin.

Silk, as a kind of natural fibrin, has been prepared into various biomaterials due to its excellent biocompatibility and mechanicalness. However, there are some controversies on the biocompatibility of silk fibroin (SF), especially when it coexists with sericin. In this study, two kinds of silk from Jiangsu and Zhejiang were degummed with two concentrations of Na2CO3 solution, respectively, to obtain four kinds of silk fibroin. The effects of different degumming treatments on silk fibroin properties were analyzed by means of color reaction, apparent viscosity measurement, and transmission electron microscope and isobaric tags for relative and absolute quantification analyses, and the effects of different silk fibroin membranes on the growth of Schwann cells were evaluated. The results showed that the natural silk from Zhejiang treated with 0.05% Na2CO3 solution had a fuller structure, higher apparent viscosity, and better protein composition. While SF obtained by degumming with 0.5% Na2CO3 solution was more beneficial to cell adhesion and proliferation due to the thorough removal of sericin. This study may provide important theoretical and experimental bases for the selection of biomaterials for fabricating artificial nerve grafts.

Enzymatically Crosslinked In Situ Synthesized Silk/Gelatin/Calcium Phosphate Hydrogels for Drug Delivery.

Our research focuses on combining the valuable properties of silk fibroin (SF) and calcium phosphate (CaP). SF is a natural protein with an easily modifiable structure; CaP is a mineral found in the human body. Most of the new age biocomposites lack interaction between organic/inorganic phase, thus SF/CaP composite could not only mimic the natural bone, but could also be used to make drug delivery systems as well, which can ensure both healing and regeneration. CaP was synthesized in situ in SF at different pH values, and then crosslinked with gelatin (G), horseradish peroxide (HRP), and hydrogen peroxide (H2O2). In addition, dexamethasone phosphate (DEX) was incorporated in the hydrogel and drug delivery kinetics was studied. Hydrogel made at pH 10.0 was found to have the highest gel fraction 110.24%, swelling degree 956.32%, and sustained drug delivery for 72 h. The highest cell viability was observed for the hydrogel, which contained brushite (pH 6)—512.43%.

N‐type silk fibroin/TiO2 nanocomposite transparent films: electrical and optical properties

AbstractThis paper highlights the effect of different concentrations of titanium dioxide (TiO2) nanoparticles on the electrical and optical properties of silk fibroin (SF). TiO2 based SF nanocomposite films were prepared using the solvent casting method. Uniform dispersion and agglomeration of nanoparticles, in nanocomposite films, were observed by field emission SEM. The conductivity of pure SF and nanocomposite films was determined by a four‐point probe and the TiO2 nanoparticles were found to bring high conductivity to the nanocomposite films. Dielectric strength improved with the addition of nanoparticles to the SF matrix. Dielectric constant and capacitance of the pure SF and nanocomposite films were measured using an LCR meter, which showed a 10‐fold enhancement on the addition of nanoparticles in SF. A very unusual property, i.e. negative resistance, was observed during LCR meter analysis for the nanocomposite films for a particular range of frequency (200–550 kHz), voltage (1 V) and current (0.5–1.5 μA). TiO2 nanoparticles changed the semiconducting behavior of the SF films from p‐type to n‐type as measured by the Hall effect experiment. The optical properties of pure SF and nanocomposite films were measured using a UV–visible spectrophotometer. The increased concentration of nanoparticles in the SF has effectively enhanced the absorbing coefficient, refractive index and percentage transmittance and reduced the bandgap energy. These SF/TiO2 nanocomposite films have shown the potential to be used as dielectric and high refractive index material for optoelectronics applications. © 2021 Society of Industrial Chemistry.