Regenerated Silk Fibroin Films Research Articles

Unlocking giant negative thermal expansion through reversible conformational changes in regenerated silk fibroin film

Developing thermally contractive polymeric materials with controlled conformational changes that enable more efficient actuation mechanisms has long been an ambitious goal. However, the utilization of naturally derived assemblies with biodegradable and reversible capabilities has, thus far, been hindered by the challenges associated with organizing the hierarchical nanostructures. Herein, hierarchically structured building blocks in regenerated fibroin were utilized to construct a thermal-responsive protein film through a friction-induced assemble strategy. By preserving the protofibrils within the regenerated silk film, we enable the efficient storage and transfer of elastic energy to external loads. The freestanding fibroin film, with pre-extended molecular chains, thus produced exhibited an exceedingly high negative thermal expansion (−1220 ppm K−1) and work capacity (∼203 J kg−1). The comprehensive analysis involving synchrotron infrared spectroscopy, in-situ Raman spectroscopy, and molecular dynamics simulations has confirmed that the actuating mechanism entails a reversible conformational change initiated by H-bonds, which is then amplified into macroscopic deformations by the hierarchical structure. This newly discovered, low-energy-driven mechanism paves the way for the creation of flexible protein assemblies with high-performance actuation capabilities.

Transparent silk fibroin film-facilitated infected-wound healing through antibacterial, improved fibroblast adhesion and immune modulation.

The clinical application of regenerated silk fibroin (RSF) films for wound treatment is restricted by its undesirable mechanical properties and lack of antibacterial activity. Herein, different pluronic polymers were introduced to optimize their mechanical properties and the RSF film with 2.5% pluronic F127 (RSFPF127) stood out to address the above issues owing to its satisfactory mechanical properties, hydrophilicity, and transmittance. Diverse antibacterial agents (curcumin, Ag nanoparticles, and antimicrobial peptide KR-12) were separately encapsulated in RSFPF127 to endow it with antibacterial activity. In vitro experiments revealed that the medicated RSFPF127 could persistently release drugs and had desirable bioactivities toward killing bacteria, promoting fibroblast adhesion, and modulating macrophage polarization. In vivo experiments revealed that medicated RSFPF127 not only eradicated methicillin-resistant Staphylococcus aureus in the wound area and inhibited inflammatory responses, but also facilitated angiogenesis and re-epithelialization, regardless of the types of antibacterial agents, thus accelerating the recovery of infected wounds. These results demonstrate that RSFPF127 is an ideal matrix platform to load different types of drugs for application as wound dressings.

CaO2-Cu2O micromotors accelerate infected wound healing through antibacterial functions, hemostasis, improved cell migration, and inflammatory regulation.

During the wound tissue healing process, the relatively weak driving forces of tissue barriers and concentration gradients lead to a slow and inefficient penetration of bioactive substances into the wound area, consequently showing an impact on the effectiveness of deep wound healing. To overcome these challenges, we constructed biocompatible CaO2-Cu2O "micromotors". These micromotors reacted with the fluids at the wound site, releasing oxygen bubbles and propelling particles deep into the wound tissue. In vitro experimental results revealed that these micromotors not only exhibited antibacterial and hemostatic functions but also facilitated the migration of dermal fibroblasts and vascular endothelial cells, while modulating the inflammatory microenvironment. A methicillin-resistant Staphylococcus aureus infected full-thickness-wound model was created in rats, in which CaO2-Cu2O micromotors markedly expedited the wound healing process. Specifically, CaO2-Cu2O provided a sterile microenvironment for wounds and increased the amounts of M1-type macrophages during infection and inflammation. During the proliferation and remodeling stages, the amount of M1 macrophages gradually decreased, while the amount of M2 macrophages increased, and CaO2-Cu2O did not prolong the inflammatory period. Furthermore, the introduction of a regenerated silk fibroin (RSF) film on the wound surface successfully enhanced the therapeutic effects of CaO2-Cu2O against the infected wound. The combined application of oxygen-producing CaO2-Cu2O micromotors and a RSF film demonstrates significant therapeutic potential and emerges as a promising candidate for the treatment of infected wounds.

Development of a bioactive silk fibroin bilayer scaffold for wound healing and scar inhibition

In cases of deep skin defects, spontaneous tissue regeneration and excessive collagen deposition lead to hyperplastic scars. Conventional remedial action after scar formation is limited with a high recurrence rate. In this study, we designed a new artificial skin bilayer using silk fibroin nanofibers films (SNF) as the epidermis, and silk fibroin (SF) / hyaluronic acid (HA) scaffold as the dermal layer. The regenerated SF film was used as a binder to form a functional SNF-SF-HA bilayer scaffold. The bilayer scaffold showed high porosity, hydrophilicity, and strength, and retained its shape over 30 days in PBS. In vitro, human umbilical vein endothelial cells were seeded into the bilayer scaffold and showed superior cell viability. In vivo analyses using the rabbit ear hypertrophic scar (HS) model indicated that the bilayer scaffold not only supported the reconstruction of new tissue, but also inhibited scar formation. The scaffold possibly achieved scar inhabitation by reducing wound contraction, weakening inflammatory reactions, and regulating collagen deposition and type conversion, which was partly observed through the downregulation of type I collagen, transforming growth factor-β, and α-smooth muscle actin. This study describes a new strategy to expand the application of silk-based biomaterials for the treatment of hyperplastic skin scars.

Partially insoluble regenerated silk fibroin film induced by UV irradiation for electronic skins

The regenerated silk fibroin (RSF) film has been regarded as an ideal substrate for biocompatible, flexible, and biodegradable electronic skin (e-skin) devices. However, it is still a great challenge to balance the flexibility and solubility of the RSF film by adjusting its secondary structure. Herein, a film prepared with the hydrolyzed RSF was exposed to the 254 nm ultraviolet (UV) light to prepare a crosslinked and partially water-insoluble substrate for a strain-sensing e-skin. The hydrolyzed low-molecular-weight RSF was produced by heating the LiBr-silk fibroin solution at 85 °C for a certain duration. The film cast with the hydrolyzed RSF solution could be thoroughly dissolved in water rapidly. The UV irradiation could induce the crosslinking of the low-molecular-weight RSF to form insoluble substances, thus producing a partially insoluble RSF film. After silver nanowires painting, an e-skin strain sensor was successfully constructed based on the UV-irradiated film. The sensor shows a fast response time (2.01 s), high sensitivity (GF = 1.03 within 0%–40% strain range), and good stability. The device could be tightly attached to human skin with a drop of water. The finger, wrist, elbow, and knee bending could be sensitively detected in real-time. The head nodding and mouth opening could also be sensed by sticking the e-skin at the neck and cheek, respectively. This work may provide a facile way to prepare a stretchable and stickable RSF film, which could serve as an ideal substrate of low-cost, biodegradable, direct-to-skin sensors for wearable applications.

Effect of degumming degree on the structure and tensile properties of RSF/RSS composite films prepared by one-step extraction

Regenerated silk fibroin (RSF) and regenerated sericin (RSS) have attracted much attention for tissue engineering due to excellent biocompatibility and controllable degradation. However, pure RSF films prepared by existing methods are brittle, which limits applications in the field of high-strength and/or flexible tissues (e.g. cornea, periosteum and dura). A series of RSF/RSS composite films were developed from solutions prepared by dissolving silks with different degumming rates. The molecular conformation, crystalline structure and tensile properties of the films and the effect of sericin content on the structure and properties were investigated. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction results revealed more β-sheets in films prepared by boiling water degumming than in Na2CO3-degummed RSFC film. Analysis of mechanical properties showed that the breaking strength (3.56 MPa) and elongation (50.51%) of boiling water-degummed RSF/RSS film were significantly increased compared with RSFC film (2.60 MPa and 32.31%), and the flexibility of films could be further improved by appropriately reducing the degumming rate.

Silk Fibroin/Silk Braiding Fabric Composite Grafts via Layer-by-Layer Self-Assembly: Water Permeability and Cytocompatibility

ABSTRACT Stent grafts play an important role in sealing vessel perforations, ruptures or aneurysms for remodeling vascular access, but maintaining long-term patency remains a major challenge after implantation. Silk fibroin (SF) is an ideal vascular graft material with excellent biocompatibility and physicochemical properties. In this study, we developed a series of composite grafts consisting of regenerated SF (RSF) and silk fabric, prepared using braiding technology and layer-by-layer (LBL) self-assembly, and investigated morphology, water permeability and cytotoxicity. The results showed that silk fabrics were covered effectively and tightly by RSF films, and the anti-water permeability of grafts was closely related to fabric structural parameters and self-assembly layers, in which the braiding angle of 90° and number of axial yarns above 60 threads/10 cm obtained very low water leakage. In particular, the graft prepared by 1 × 2 silk yarn had a thinner and more uniform thickness (70–80 μm), and showed lower water permeability (8.8 mL/min·cm2). Tests on L929 fibroblast cells showed that grafts had no significant cytotoxicity, and unreacted substances could be removed by LBL rinsing. These composite grafts may be promising biomaterials for the repair and regeneration of vascular access.

Highly stretchable porous regenerated silk fibroin film for enhanced wound healing.

Silk fibroin (SF) has received interest in tissue engineering owing to its biocompatibility, biodegradability, and favorable mechanical properties. However, the complex preparation, brittleness, and lack of pores in the structure of the silk fibroin film limit its application. Herein, we show that facile dissolution of SF in aqueous phosphoric acid followed by regeneration in aqueous ammonium sulfate ((NH4)2SO4) could afford highly stretchable films with nano-pores formed in the nonsolvent-induced phase separation process. The named phase separation, which determines the morphology and mechanical properties of the regeneration silk fibroin (RSF) films, is highly dependent on the (NH4)2SO4 concentration as well as the initial concentration of the SF solution. Therefore, the RSF films exhibit a tunable pore size ranging from 230 to 510 nm and excellent stretchability with tensile strain up to 143 ± 16%. Most interestingly, the RSF films were shown to support the proliferation of human skin fibroblasts in vitro as well as speed up full-thickness skin wound healing in a rat model. This work establishes an easy and feasible method to access porous RSF membranes that can be used for wound dressing in clinical settings.

Preparation of Highly Crystalline Silk Nanofibrils and Their Use in the Improvement of the Mechanical Properties of Silk Films.

Due to their commendable biocompatibility, regenerated silk fibroin (RSF) films have attracted considerable research interest. However, the poor mechanical properties of RSF films have limited their use in various biomedical applications. In this study, a novel, highly crystalline silk fibril was successfully extracted from silk by combining degumming with ultrasonication. Ultrasonication accelerated the development of silk nanofibrils measuring 130–200 nm on the surface of the over-degummed silk fibers, which was confirmed via scanning electron microscopy. Additionally, the crystallinity index of silk fibril was found to be significantly higher (~68%) than that of conventionally degummed silk (~54%), as confirmed by the Fourier-transform infrared (FTIR) spectroscopy results. Furthermore, the breaking strength and elongation of the RSF film were increased 1.6 fold and 3.4 fold, respectively, following the addition of 15% silk nanofibrils. Thus, the mechanical properties of the RSF film were remarkably improved by the addition of the silk nanofibrils, implying that it can be used as an excellent reinforcing material for RSF films.

A facile and green approach toward precise fabrication of silk fibroin-based microfluidic devices using water as etchant

Regenerated silk fibroin (RSF) is considered as a superior substrate material for biocompatible and biodegradable microfluidic devices. However, the manufacture of RSF-based microfluidic chips in a simple, low-cost, and environmentally friendly manner remains a difficulty. We devised a tape mask-assisted approach for preparing RSF-based microfluidic chips for cell adhesion and growth utilizing water as an eco-friendly etchant. The RSF solution was pre-hydrolyzed to assure the RSF film's water-solubility. The UV–visible spectra reveal that the RSF film, as made, is easily dissolved in water. The film could be turned into a water-insoluble state after being treated with ethanol for 40 min. Concave and convex micro-patterns may be formed on the RSF film using tape mask-assisted water etching and ethanol-induced insolubilization. Controlling the etching period allowed the tape-mask designs to be carefully transferred to the RSF film. Unlike LiBr etching, water treatment creates channels that are covered by a smooth RSF hydrogel layer, which may aid cell adhesion and development. The creation of the hydrogel layer might be explained by the insoluble RSF chains exposed after water etching and the ethanol-induced conformation change. Human umbilical vein endothelial cells were seeded in a blood vessel-like RSF-based channel, demonstrating the quick attachment and growth tendency. After 7 days of growth, a micro-vessel-like structure was visible in the channel, suggesting the device's high biocompatibility and vast potential. This work introduces a low-cost, facile and eco-friendly approach to fabricating RSF-based microfluidic devices for cell- or tissue-based assays.

Effect of post-treatment methods and nanoparticles on the conformation of silk fibroin and their impact on electrical properties

ABSTRACT This paper investigates the effect of different plasticizers (glycerol and dextrose), post-treatment methods, and metal oxide nanoparticles, i.e. zinc oxide and copper oxide on the structural properties of silk fibroin films and their effect on electrical properties, i.e. dielectric strength. Structural properties of the silk fibroin films have been evaluated using Fourier transform infrared spectroscopy and X-ray diffraction technique. It was found that plasticizers and post-treatment applied on the regenerated silk fibroin films have impacted the β-sheet conformation significantly. The dielectric strength of the silk fibroin films was measured using the parallel plate capacitor method and an interrelation with structural properties was observed. Nanoparticles have been introduced into the silk fibroin films as a progressive method to impart substantial effect on the dielectric strength of the silk fibroin films. However, an unexpected change in dielectric strength has been obtained. The mechanism behind the change in dielectric strength has been explored in this work.

Bidirectional Actuation of Silk Fibroin Films: Role of Water and Alcohol Vapors

Three-dimensional (3D) shape morphism observed in nature inspires the development of stimuli-responsive soft actuators. Vapor-responsive actuators are promising among the different stimuli-responsive materials due to their capability to produce macroscale movements in response to a minuscule amount of specific chemical vapor. Here, we report unusual multiple vapor-responsive bidirectional macroscale actuation behaviors of single-layer regenerated silk fibroin films. The vapor-responsive silk fibroin actuator exhibits antagonistic actuation characteristics in a reversible manner to both water and ethanol vapors. For instance, it produces an upward bending in the presence of water vapor and downward bending in ethanol vapor, which demonstrates the chemical vapor-specific actuation. However, the actuation characteristics remain largely invariant upon changing the polarity of alcohol molecules. The silk fibroin actuators effectively utilize the vapor-induced minuscule expansion and contraction of the film surface to produce large-scale actuation, which is fully reversible. The intrinsic water content of the films and the vapor pressure of the stimulants are exploited to control the actuation performance. Further, we demonstrated the 3D shape morphing ability of the actuator by generating an undulating wavelike motion via preprogrammed water and ethanol vapor exposure conditions. The change in the actuation direction is instantaneous, which ensures the sensitivity and rapid response of the fabricated actuators.

Fabrication of silk fibroin film enhanced by acid hydrolyzed silk fibroin nanowhiskers to improve bacterial inhibition and biocompatibility efficacy

In this study, silk fibroin nanowhiskers (SNWs) were extracted from natural silk fiber by sulfuric acid hydrolysis with the assistance of ultrasonic wave treatment. The obtained SNWs were mixed with regenerated silk fibroin (RSF) solution to fabricate the SNWs/RSF films. The fabricating SNWs were systematically characterized by using SEM, FTIR, and the SNWs/RSF films were observed by digital camera, PM, etc. The results show that the monodisperse SNWs are evenly distributed in the RSF film. The presence of SNWs in RSF film significantly improves the performances of the film, including the swelling ability, mechanical properties, hydrophilicity, antibacterial efficacy, cytocompatibility. Meanwhile, the SNWs/RSF film can endorse the wound healing efficiency in vivo mice wound site. The proposed techniques for extracting SNWs and fabricating silk fibroin composite film may provide a valuable method for creating an ideal silk-based material for biomedical applications.

One-Step Approach to Prepare Transparent Conductive Regenerated Silk Fibroin/PEDOT:PSS Films for Electroactive Cell Culture.

Silk fibroin (SF)-based electroactive biomaterials with favorable electroconductive property and transparency have great potential applications for cell culture and tissue engineering. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is an excellent candidate as a conductive component, which has been widely used in the field of bioelectronics; however, it is hard to be directly coated onto the surface of regenerated SF (RSF) materials with good stability under a cell culture environment. In this study, a one-step facile PEDOT:PSS modification approach for RSF films based on a suitable post-treatment process of RSF was developed. PEDOT:PSS was successfully embedded and fixed into the shallow surface of an RSF film, forming a tightly conjunct conductive layer on the film surface based on the conformation transition of RSF during the post-treatment process. The conductive layer demonstrated a PSS-rich surface and a PEDOT-rich bulk structure and showed excellent stability under a cell culture environment. More specifically, the robust RSF/PEDOT:PSS film achieved in the post-treatment formula with 70% ethanol proportion possessed best comprehensive properties such as a sheet resistance of 3.833 × 103 Ω/square, a conductivity of 1.003 S/cm, and transmittance over 80% at maximum in the visible range. This kind of electroactive biomaterial also showed good electrochemical stability and degradable properties. Moreover, pheochromocytoma-derived cell line (PC12) cells were cultured on the RSF/PEDOT:PSS film, and an effective electrical stimulation cell response was demonstrated. The facile preparation strategy and the good electroconductive property and transparency make this RSF/PEDOT:PSS film an ideal candidate for neuronal tissue engineering and further for biomedical applications.

Constructing Silk Fibroin-Based Three-Dimensional Microfluidic Devices via a Tape Mask-Assisted Multiple-Step Etching Technique

Regenerated silk fibroin (RSF) has been regarded as a very promising biomaterial for the preparation of microfluidic devices. However, the facile and low-cost fabrication of three-dimensional (3D) RSF microfluidic devices is still a great challenge. Herein, we developed a tape-mask-assisted multiple-step etching technique to fabricate 3D microfluidic devices based on water-annealed RSF films. Several rounds of tape adhesion- or peeling-etching cycles need to be conducted to produce 3D features on the RSF films with the LiBr aqueous solution as the etchant. The water-annealed RSF films could be effectively etched with 1.0 g·mL-1 LiBr solution at 60 °C. The shape, width, and height of the 3D structures could be precisely tailored by controlling the mask pattern, etching conditions, and the number of etchings. Using the tape adhesion- and peeling-assisted multiple-etching techniques, the convex-pyramid-shaped and the concave-step-shaped structures could be successfully prepared on the RSF films, respectively. The RSF-film-based 3D micromixers and microfluidic separator were also manufactured with the proposed approach, exhibiting excellent liquid mixing and size-dependent particle sorting capabilities, respectively. The enzymatic degradation of RSF-film-based devices was also investigated to show their environmental friendliness. This work may not only provide a facile and low-cost method for the fabrication of RSF-based 3D microfluidic devices but also extend the applications of RSF in the fields of biomedical and chemical analysis.

Preparation and Biocompatibility Characterization of Regenerated Silk Fibroin Films

Silk fibroin (SF) has excellent biocompatibility, biodegradability and mechanical properties and has been widely applied in the fields of scaffold materials for tissue engineering, drug delivery materials, etc. Mouse embryonic fibroblasts (MEFs), as one of the most commonly used cells with many remarkable properties for modern biomedicine research fields, can serve as the indicator to characterize the biocompatibility of culture materials according to the cell proliferation. In the research described in this paper we studied the effects of SF films formed by various dissolution methods and various kinds of SF materials on the MEFs cell cultivation. Three groups of different SF films were prepared, namely, mulberry SF films prepared by a LiBr dissolution system, mulberry SF films prepared by a HCOOH/CaCl2 dissolution system and tussah SF films prepared by a HCOOH/CaCl2 dissolution system. The prepared SF films were characterized for morphology and structure by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Further, laser scanning confocal microscopy (LSCM) and cell counting kit-8 (CCK-8) were utilized to examine the growth of the MEFs on the SF films. The experimental results of the three groups of SF films were compared; they showed that the mulberry SF film, prepared by the LiBr dissolution system, had the best biocompatibility and a positive effect on the growth and proliferation of the MEFs.

Development of robust, ultra-smooth, flexible and transparent regenerated silk composite films for bio-integrated electronic device applications

Regenerated Silk Fibroin (RSF) films are considered promising substrate candidates primarily in the field of bio-integrated electronic device applications. The key issues that ought to be addressed to exploit the inherent advantages of silk thin films include enhancing their flexibility and chemical durability. Such films find a plethora of applications, the significant one being conformal, transparent microelectrode arrays. Elevated temperatures that are regularly used in lithographic processes tend to dehydrate RSF films, making them brittle. Furthermore, the solvents/etchants used in typical device fabrication results in the formation of micro-cracks. This paper addressed both these issues by developing composite films and studying the effect of biodegradable additives in enhancing flexibility and chemical durability without compromising on optical transparency and surface smoothness. Through our rigorous experimentation, regenerated silk blended with Polyvinyl Alcohol (Silk/PVA) is identified as the composite for achieving the objectives. Furthermore, the Cyto-compatibility studies suggest that Silk/PVA, along with all other silk composites, have shown above 80% cell viability, as verified using L929 fibroblast cell lines. Going a step further, we demonstrated the successful patterning of 32 channel optically transparent microelectrode array (MEA) pattern, with a minimum feature size of 5 μm above the free-standing and optically transparent Silk/PVA composite film.

Adhesive tape-assisted etching of silk fibroin film with LiBr aqueous solution for microfluidic devices

The regenerated silk fibroin (RSF)-based microfluidic device has attracted tremendous interests in recent years due to its excellent biocompatibility, mild processing conditions, and all aqueous casting production. However, the need of a micro-fabricated mold in the manufacture process greatly hinder its practical applications. Herein, we introduce an adhesive tape-assisted etching method with LiBr solution as the etchant to prepare RSF microfluidic devices. An engraved adhesive tape is used as the mask to cover on the surface of a RSF film. Then, LiBr solution is dropped on the mask to etch RSF in concentration- and duration-dependent manners. During this process, the LiBr-treated RSF transits from insoluble β-sheet crystallites to soluble conformations. The as-prepared RSF microfluidic devices possess good chemical resistance and excellent tolerance to mechanical deformation. RSF microfluidic systems with different patterns were fabricated to demonstrate the universality of the approach. A concentration gradient generator and a blood vessel-like channel were manufactured for the preparation of solutions with gradient pHs and the growth of living cells, respectively. The proposed strategy has great potentials in the facile fabrication of low-cost RSF microfluidic devices for tissue engineering and biomedical analysis.

Patterning the neuronal cells via inkjet printing of self-assembled peptides on silk scaffolds

The patterning of neuronal cells and guiding neurite growth are important for neuron tissue engineering and cell-based biosensors. In this paper, inkjet printing has been employed to pattern self-assembled I3QGK peptide nanofibers on silk substrates for guiding the growth of neuron-like PC12 cells. Atomic force microscopy (AFM) confirmed the dynamic self-assembly of I3QGK into nanofiber structures. The printed self-assembled peptide strongly adheres to regenerated silk fibroin (RSF) substrates through charge-charge interactions. It was observed that in the absence of I3QGK, PC12 cells exhibited poor attachment to RSF films, while for RSF surfaces coated or printed with peptide nanofibers, cellular attachment was significantly improved in terms of both cell density and morphology. AFM results revealed that peptide nanofibers can promote the generation of axons and terminal buttons of PC12 cells, indicating that I3QGK nanofibers not only promote cellular attachment but also facilitate differentiation into neuronal phenotypes. Inkjet printing allows complex patterning of peptide nanofibers onto RSF substrates, which enabled us to engineer cell alignment and provide an opportunity to direct axonal development in vitro. The live/dead assay showed that printed I3QGK patterns exhibit no cytotoxicity to PC12 cells demonstrating potential for future nerve tissue engineering applications.

Tailoring of electrical and optical properties of regenerated silk fibroin films with metal oxides

In this study, silk fibroin was used as a matrix to incorporate the metal oxide nanoparticles i.e. zinc oxide (ZnO) and copper oxide (CuO) to form transparent nanocomposite films by solvent casting method. The effect of metal oxide nanoparticles and their concentrations on the conductivity of silk fibroin film were detected by a four-point probe instrument. As the thickness of the films was reduced, the conductivity increased. Hall Effect experiment was carried out to determine the carrier (electron or holes) concentration and identification of the semiconducting behaviour of nanocomposite films. Pure silk fibroin (SF) film showed p-type semiconducting behaviour. Incorporation of zinc oxide and copper oxide nanoparticles in the silk fibroin matrix makes it n-type and p-type semiconductor, respectively. Uniform dispersion of metal oxide nanoparticles in the silk fibroin matrix was observed through field emission scanning electron microscopy. The UV–Vis spectra of nanocomposite films showed 82–84% transmittance and reduction in refractive index. Addition of metal oxide nanoparticles reduced the β sheet content and percentage crystallinity of silk fibroin as observed by FTIR and XRD, respectively. The structural alterations at the molecular level reveal their relationship with electrical and optical properties.