Protein Nanofibers Research Articles

Ultrathin, Breathable, Permeable, and Skin‐Adhesive Charge Storage Electronic Tattoos Based on Biopolymer Nanofibers and Carbon Nanotubes

AbstractUltrathin, breathable, and skin‐compatible epidermal electronics are attractive for wearable and implantable healthcare and biomedical applications. However, materializing and integrating all electronic components on ultrathin platforms is still challenging. Here, a charge‐storing electronic tattoo (E‐tattoo) device with ultrathin, breathable, and skin‐compatible properties is reported. Silk protein nanofibers (SNFs) and carbon nanotubes (CNTs) form the top and bottom electrodes that sandwich the intermediate dielectric layer fabricated using poly(vinyl alcohol) nanofibers. The E‐tattoo capacitors on the deformed skin, show excellent mechanical and electrical stability, and 60 µm‐thick capacitors exhibit frequency‐dependent capacitances (up to 350 pF at 5 kHz) and capability for memory operation. Mechanical bending induces capacitance change, which increases as the bending radius is decreased, indicating mechanical sensing capability of the E‐tattoo. SNF/CNT‐based triboelectric nanogenerator E‐tattoos can be connected to the capacitor E‐tattoo, and the charges generated by multiple bare‐finger touches can be stored in the capacitor (0.23 V for 200 touches). Due to the micro/nanopores in the NF networks, the device exhibits a water vapor transmission rate of 115.04 g m−2 d−1, which is better than that of a commercial band‐aid, as well as ethanol sensing capability. Developed E‐tattoo capacitor can be used for constructing multicomponent integrated ultrathin and epidermal electronics.

Sustained release system of paclitaxel based on composite nanofibers for inhibiting renal clear cell carcinoma

The recurrence and metastasis of renal cell carcinoma are severe challenges in clinical treatment. At present, it is urgent to find a strategy to solve this problem and improve the therapeutic effect. In this study, we designed a programmed release system of anticancer drugs by preparing a nanofiber system with two kinds of diameters and biomaterials (polylactic acid-glycolic acid (PLGA) and silk protein) as drug carriers (paclitaxel), which inspired the occurrence and pathological microenvironment of renal cell carcinoma. The controlled degradation of PLGA nanofibers as a drug carrier achieved the short-term release of paclitaxel, which could rapidly inhibit the spread and metastasis of renal cancer, while the silk protein nanofibers as a drug carrier with slow degradation could provide the long time and continuous release of paclitaxel to prevent the proliferation of renal cancer cells and inhibit recurrence. The synergistic effect of the sustained release system of paclitaxel successfully achieved inhibition of the recurrence and metastasis of renal cell carcinoma and improve the therapeutic effect of renal cell carcinoma. The paclitaxel release profile showed that the PLGA nanofiber drug system provided controlled release of paclitaxel in the first 14 days, while the silk protein nanofiber system provided a relatively stable and long-duration release of paclitaxel (1 month). In vitro experiments showed that the sustained release system of paclitaxel had a lasting inhibitory effect on the proliferation of renal clear cell carcinoma cells. These results indicated that the sustained release system of paclitaxel could be used as a promising drug delivery system with highly efficient implementations to reduce the frequency of systemic administration and inhibit tumor growth and recurrence, which could provide a new strategy for the clinical applications in renal cell carcinoma microenvironment.

Production of clove extract loaded pullulan and whey protein nanofibers as antioxidant and antibacterial agent

AbstractIn this study, clove extract loaded nanofibers consisting of pullulan and whey protein were produced by electrospinning method in order to improve antibacterial and antioxidant activity. Diameters of the produced nanofibers varied between 215.7 and 536.8 nm. Fourier Transform Infrared Spectroscopy (FTIR), X‐ray diffraction (XRD) and differential scanning calorimeter (DSC) results showed that there was a close interaction between the obtained nanofibers and clove extract. Although the antioxidant activity of the nanofibers varied between 1535 and 4174 μmol TE/g dm, the antioxidant activity of the clove extract loaded nanofibers tended to increase when compared to their polymer solutions. The total phenolic content of the nanofiber samples varied between 4.93 and 45.05 mg GAE/g dm. It has been determined that clove extract loaded nanofibers showed antibacterial activity against Staphylococcus aureus (ATCC29113) and Micrococcus luteus (NCIMB). As a result, it was seen that the addition of clove extract improved the antioxidant and antibacterial properties of the fibers and these fibers could be a potential coating and packaging material that could have a potential use in food preservation.

Biomimetic Natural Silk Nanofibrous Microspheres for Multifunctional Biomedical Applications.

Silk nanofibrils (SNFs) extracted from natural silkworm silk represent a class of high-potential protein nanofiber material with unexplored biomedical applications. In this study, a SNF-assembled microsphere with extracellular matrix (ECM)-mimicking architecture and high specific surface area was developed. The SNFs were exfoliated from silkworm silks through an all-aqueous process and used as the building blocks for constructing the microspheres. Inspired by the structure and bioactive composition of ECM, hyaluronic acid (HA) was used as a bio-glue to regulate SNF assembly. With the assistance of HA, the SNF microspheres with stable fluffy nanofibrous structures were synthesized through electrospray. The biomimetic structure and nature derived composition endow the microspheres with excellent biocompatibility and enhanced osteogenic differentiation-inducing ability to mesenchymal stem cells. As proof of versatility, the SNF microspheres were further functionalized with other molecules and nanomaterials. Taking the advantages of the excellent blood compatibility and modifiability from the molecular level to the nanoscale of SNF microspheres, we demonstrated their versatile applications in protease detection and blood purification. On the basis of these results, we foresee that this natural silk-based nanofibrous microsphere may serve as a superior biomedical material for tissue engineering, early disease diagnosis, and therapeutic devices.

Self-assembled flagella protein nanofibers induce enhanced mucosal immunity

Nanofibers are potential vaccines or adjuvants for vaccination at the mucosal interface. However, how their lengths affect the mucosal immunity is not well understood. Using length-tunable flagella (self-assembled from a protein termed flagellin) as model protein nanofibers, we studied the mechanisms of their interaction with mucosal interface to induce immune responses length-dependently. Briefly, through tuning flagellin assembly, length-controlled protein nanofibers were prepared. The shorter nanofibers exhibited more pronounced toll-like receptor 5 (TLR5) and inflammasomes activation accompanied by pyroptosis, as a result of cellular uptake, lysosomal damage, and mitochondrial reactive oxygen species generation. Accordingly, the shorter nanofibers elevated the IgA level in mucosal secretions and enhanced the serum IgG level in ovalbumin-based intranasal vaccinations. These mucosal and systematic antibody responses were correlated with the mucus penetration capacity of the nanofibers. Intranasal administration of vaccines (human papillomavirus type 16 peptides) adjuvanted with shorter nanofibers significantly elicited cytotoxic T lymphocyte responses, strongly inhibiting tumor growth and improving survival rates in a TC-1 cervical cancer model. This work suggests that length-dependent immune responses of nanofibers can be elucidated for designing nanofibrous vaccines and adjuvants for both infectious diseases and cancer.

Silver nanoparticle-deposited whey protein isolate amyloid fibrils as catalysts for the reduction of methylene blue

The unique structural characteristics and superior biocompatibility make the protein nanofibers promising immobilization platforms/substrates for catalysts/enzymes. Metal nanoparticles have been employed as the catalysts in industries due to their excellent catalytic activity and stability, whereas their high surface energy leads to nanoparticle aggregation, thereby hampering their catalytic performance. Here, amyloid fibril (AF) derived from whey protein isolate (WPI) was chosen as the support of silver nanoparticles (AgNP) and utilized for the catalytic reduction of methylene blue (MB). The one-dimensional amyloid-based hybrid materials (AgNP/WPI-AF) were first synthesized via chemical or photochemical route. The characterization of AgNP/WPI-AF by UV–vis spectrophotometry and electron microscopy revealed that the sizes of AgNP on WPI-AF's surface ranged from 2 to 30 nm. Next, the catalytic performances of AgNP/WPI-AF prepared by various routes for MB degradation were investigated. Additionally, the kinetic data were analyzed using two different models and the apparent rate constants and thermodynamic parameters were further determined accordingly. Moreover, the reusability of AgNP/WPI-AF was assessed by monitoring the percentage removal of MB over consecutive filtering cycles. Our results indicated that Langmuir-Hinshelwood-type mechanism better described the catalytic MB reduction using AgNP/WPI-AF. This work provides a nice example of application of nanoparticle-amyloid fibril composite materials for catalysis.

Production of whey protein nanofiber as a carrier for copper entrapment

Novel electrospun fibers from aqueous whey protein solution with and without a carrier polymer have been developed and characterized, exploring the ability of those fibers to carry nutrients that are considered attractive. In this study, whey protein concentrate (WPC) solution electrospun into nanofibers in conjunction with (1% w/w in solution) and without a spinnable polymer, polyethylene oxide (PEO), for carrying copper. The electrospun fibers were successfully produced from WPC/copper and a PEO/WPC/copper polymer solution under the applied voltage of 15–23 kV, when the copper concentration was relatively low. The applied voltage has no significant effect on the size of the fibers produced by WPC/copper and PEO/WPC/copper polymer systems (p > 0.05). The copper concentration in WPC/copper and the PEO/WPC/copper polymer solution significantly affect the viscosity of the solution and the size of the fiber (p < 0.05), but it has no observable change on the morphology of the fiber. The addition of PEO in the polymer solution slightly increases the solution viscosity, but the fiber of the polymer solution with PEO was 100–400times smaller than that without PEO. Micron fibers prepared by WPC polymer solution and nanofibers prepared by PEO/WPC polymer solution successfully carried copper.

A disposable ultrasensitive surface enhanced Raman spectroscopy biosensor platform fabricated from biodegradable zein nanofibers

AbstractIn this paper, a natural polymer, zein, is converted into a disposable and environmentally friendly surface enhanced Raman spectroscopy (SERS) biosensor platform to detect toxins. First, protein nanofiber mats were fabricated using electrospinning. Next, the surface of the fibers was decorated with metallic nanoparticles to create hotspots for the detection of the target molecule. Four types of metallic nanoparticles were tested for sensitivity optimization: gold, silver, silver‐shelled‐gold, and a mixture of gold and silver nanoparticles. Silver‐shelled‐gold nanoparticles gave the highest SERS intensity, and at the concentration of 1012 particles/ml, the highest enhancement factor (EF) of 2.49 × 106 was reached, which is the highest EF ever reported for a zein‐based biodegradable platform. Acrylamide was used as the model food carcinogenic toxin and its detection with this nanofiber‐based platform gave a limit of detection of 2.06 ng/ml. This LOD is 104 times lower than the limit of detection that was achieved previously with a zein‐based SERS platform. Other sensitive analytical methods (GC–MS and LC–MS/MS) gave LODs of 5–10 and 20–50 ng/ml for acrylamide, much higher than the method used in this study. This sensitivity is much lower than any other previous attempts to detect acrylamide with biodegradable sensors.

Feasibility of bionanocomposite films fabricated using capsicum leaf protein and cellulose nanofibers

In this study, the feasibility of fabricating protein-based bionanocomposite films (PBBFs) was analysed by applying capsicum leaf protein (CLP) and cellulose nanofiber (CNF) as raw materials. The effects of different amounts of CNF (solid content 2%) on physicochemical and material properties of PBBFs were investigated. The results showed nanoscale CNFs exhibited good interfacial compatibility with CLP. The hydroxyl groups on the CNF surface promoted the association of hydrogen bonds between CLP, glycerol and CNF, which improved the crystal structure and thermal stability of PBBFs. Concurrently, the mechanical properties and hydrophobicity of PBBFs are also enhanced. PBBFs with 60% CNF content have maximum flexibility and hydrophobicity. All PBBFs exhibited ultraviolet barrier performance, indicating that PBBFs had potential application prospects in the development of degradable food packaging materials. The results of the present study can provide a theoretical basis for the efficient utilisation of capsicum planting waste while improving the ecosystem.

Preparation, structure and properties of soy protein and silk fibroin composite nanofiber membrane by jet spinning

<p indent=0mm>It is a hot topic in science nowadays and of great practical significance for developing abundant green natural resources and their applications in the research of biomedicine and tissue engineering. This article successfully prepared the biocompatible and biodegradable soy protein and silk fibroin composite nanofiber membrane by spinning technique. The apparent morphologies, structural changes and interactions of the two materials were characterized by scanning electron microscopy, Raman and Fourier transform infrared spectroscopy and X-ray diffraction. Differential scanning calorimetry and thermogravimetric analysis were used to investigate the blending properties of the two phases. The water retention, <italic>in vitro</italic> degradation, and cytocompatibility of the composite films were also evaluated. The results showed mainly hydrogen bond interactions between silk fibroin and soy protein molecular chains, which had thermodynamic compatibility and showed good morphology and thermal properties of nanofibers. With the increase of soybean protein content, the <italic>β</italic>-sheet content of the composite nanofiber membrane increases gradually. At the same time, the glass transition temperature decreases, the specific heat capacity increases a little more, and the water retention ability increases as well as the enzymatic degradation speed. Simultaneously, compared with pure silk fibroin, soy protein/silk fibroin composite nanofiber membrane can provide a better environment for cell adhesion and proliferation, which can be used as a wound dressing and drug delivery system. Especially, the composite fiber membrane containing 60% soy protein showed the strongest cell activity. This study provides a new view for preparing natural materials such as silk fibroin and soy protein and supplies the experimental and theoretical basis for the wide applications of green natural resources.

Nerve Growth Factor-Laden Anisotropic Silk Nanofiber Hydrogels to Regulate Neuronal/Astroglial Differentiation for Scarless Spinal Cord Repair.

Scarless spinal cord regeneration remains a challenge due to the complicated microenvironment at lesion sites. In this study, the nerve growth factor (NGF) was immobilized in silk protein nanofiber hydrogels with hierarchical anisotropic microstructures to fabricate bioactive systems that provide multiple physical and biological cues to address spinal cord injury (SCI). The NGF maintained bioactivity inside the hydrogels and regulated the neuronal/astroglial differentiation of neural stem cells. The aligned microstructures facilitated the migration and orientation of cells, which further stimulated angiogenesis and neuron extensions both in vitro and in vivo. In a severe rat long-span hemisection SCI model, these hydrogel matrices reduced scar formation and achieved the scarless repair of the spinal cord and effective recovery of motor functions. Histological analysis confirmed the directional regenerated neuronal tissues, with a similar morphology to that of the normal spinal cord. The in vitro and in vivo results showed promising utility for these NGF-laden silk hydrogels for spinal cord regeneration while also demonstrating the feasibility of cell-free bioactive matrices with multiple cues to regulate endogenous cell responses.

Structural and Thermal Properties of Electrospun Whey Protein/PEO Nanofibers

Nano-scale fibers or films obtained by adding natural active agents to natural food proteins are promising materials for packaging purposes. Whey proteins (WPs) are one of the most popular matrices in application with their cheap and sustainable availability. They have many functional properties and their antimicrobial, antiviral and anticarcinogenic properties are highlighted as well. Enzymatic hydrolysis can increase their functionality such as inducing gelation and revealing bioactive peptides. These features can make whey proteins good candidates for the fabrication of talented fiber structures through electrospinning. Electrospinning technique based on the deposition of fine fibers on a collector surface under electrical forces can be used to form protein nanofibers. The purpose of this research is to produce whey-based protein nanofibers and determine their structural and thermal features by infra-red spectroscopy and thermogravimetric analysis. A high molecular polymer, polyethylene oxide (PEO) was used in combination with whey protein concentrate (WPC) to increase spinnability. Besides, enzymatic hydrolysis of WPC enhanced the viscosity of the protein/polymer solution and helped electrospinning ability. Both non-hydrolyzed and hydrolyzed WPC/PEO nanofibers exhibited promising morphological, structural and thermal properties for targeted use in food and biomedical applications. Further research will focus on the application of these protein nanofibers for food packaging purposes.

Simple Affinity-Based Method for Concentrating Viruses from Wastewater Using Engineered Curli Fibers.

Wastewater surveillance is a proven method for tracking community spread and prevalence of some infectious viral diseases. A primary concentration step is often used to enrich viral particles from wastewater prior to subsequent viral quantification and/or sequencing. Here, we present a simple procedure for concentrating viruses from wastewater using bacterial biofilm protein nanofibers known as curli fibers. Through simple genetic engineering, we produced curli fibers functionalized with single-domain antibodies (also known as nanobodies) specific for the coat protein of the model virus bacteriophage MS2. Using these modified fibers in a simple spin-down protocol, we demonstrated efficient concentration of MS2 in both phosphate-buffered saline (PBS) and in the wastewater matrix. Additionally, we produced nanobody-functionalized curli fibers capable of binding the spike protein of SARS-CoV-2, showing the versatility of the system. Our concentration protocol is simple to implement, can be performed quickly under ambient conditions, and requires only components produced through bacterial culture. We believe this technology represents an attractive alternative to existing concentration methods and warrants further research and optimization for field-relevant applications.

Bioinspired Silk Fiber Spinning System via Automated Track-Drawing.

Regenerated silk fibroin (SF) fiber is a multifaceted protein matrix suitable for engineering a wide variety of biological materials. Numerous artificial spinning systems have been developed to mimic the molecular structure and hierarchical properties found in native silks. Here, we show a bioinspired technique that can readily form nanofibers and induce both orientation and structure formation of crystalline β-sheet assemblies seen in natural silk. In this study, electrospun postdrawn SF nanofibers were fabricated using an automated track-drawing (TD) approach for the continuous production of highly aligned protein nanofibers. This one-step postdrawing process simulates the dominant pulling force seen in natural spinning. The mechanical performance of the postdrawn SF nanofibers with a draw ratio of 2 (DR2) via TD exhibited a 115% increase in Young's modulus and an 80% increase in ultimate tensile strength, compared with the undrawn SF fibers after water treatment. It was also determined that the intermolecular β-sheet content in DR2 nanofibers increased by 75%. This contribution led to higher glass-transition and degradation temperatures. These biomimetic fibers with structural hierarchy and mechanical properties may be used to build high-performance load-bearing and directionally propagating structures relevant in biomaterial and sustainable material applications.

Programmable microbial ink for 3D printing of living materials produced from genetically engineered protein nanofibers

Living cells have the capability to synthesize molecular components and precisely assemble them from the nanoscale to build macroscopic living functional architectures under ambient conditions. The emerging field of living materials has leveraged microbial engineering to produce materials for various applications but building 3D structures in arbitrary patterns and shapes has been a major challenge. Here we set out to develop a bioink, termed as “microbial ink” that is produced entirely from genetically engineered microbial cells, programmed to perform a bottom-up, hierarchical self-assembly of protein monomers into nanofibers, and further into nanofiber networks that comprise extrudable hydrogels. We further demonstrate the 3D printing of functional living materials by embedding programmed Escherichia coli (E. coli) cells and nanofibers into microbial ink, which can sequester toxic moieties, release biologics, and regulate its own cell growth through the chemical induction of rationally designed genetic circuits. In this work, we present the advanced capabilities of nanobiotechnology and living materials technology to 3D-print functional living architectures.

Development of Antioxidant and Stable Conjugated Linoleic Acid Pickering Emulsion with Protein Nanofibers by Microwave-Assisted Self-Assembly.

Whey protein isolate nanofibrils (WPNFs) can be used as a novel stabilizer in the Pickering emulsion system to improve the water solubility, stability and bioavailability of lipophilic bioactive ingredients. In this study, conjugated linoleic acid (CLA) and WPNFs were used to prepare a stable Pickering emulsion. We used a transmission electron microscope, low-temperature scanning electron micrographs and other methods to evaluate the micromorphology, surface hydrophobicity and structural units of the obtained WPNFs. Compared with whey protein isolate/CLA Pickering emulsion, the WPNFs/CLA Pickering emulsion has greater ability to remove 2,2-Diphenyl-1-picrylhydrazyl and 2,2′-amino-di(2-ethyl-benzothiazoline sulphonic acid-6) ammonium salt free radicals. Furthermore, the WPNFs/CLA Pickering emulsion has a more stable effect in terms of droplet size and zeta potential over a wider range of ionic strength and temperature conditions. These findings indicate that Pickering emulsion stabilized by WPNFs is more suitable as a carrier of CLA, as it increases the solubility of CLA and has better active applications in biology and food.

Fabrication and characterization of electrospun nanofibers of Hypophthalmichthys molitrix sarcoplasmic protein recovered by acid‐chitosan flocculation coupling treatment

AbstractFish sarcoplasmic proteins (FSP) account for 20%–40% of the muscle protein and its high‐value utilization has become an urgent problem to be solved. Here, directly freeze‐dried sarcoplasmic protein (DFSP) and chitosan flocculated sarcoplasmic protein (CFSP) nanofibers were successfully fabricated by electrospinning technology and characterized in terms of morphology, chemical interaction, surface and mechanical properties, and thermal stability. SDS‐PAGE indicated similar protein bands for both DFSP and CFSP. Scanning electron microscopy observation showed good spinnability for CFSP and DFSP. Fourier transform infrared spectrometry and X‐ray diffraction results unveiled an interaction between sarcoplasmic protein and chitosan in CFSP nannofiber. Furthermore, CFSP nanofiber exhibited better performance than DFSP nanofiber in surface hydrophobicity, thermal stability, elasticity and flexibility. These results suggest the potential application of FSP nanofiber in functional components or drugs delivery, contributing to high‐value utilization of FSP.

Self‐Powered and Imperceptible Electronic Tattoos Based on Silk Protein Nanofiber and Carbon Nanotubes for Human–Machine Interfaces (Adv. Energy Mater. 29/2021)

Self‐Powered and Imperceptible Electronic Tattoos Based on Silk Protein Nanofiber and Carbon Nanotubes for Human–Machine Interfaces (Adv. Energy Mater. 29/2021)

Importance of Substrate-Particle Repulsion for Protein-Templated Assembly of Metal Nanoparticles.

We study the protein-directed assembly of colloidal gold nanoparticles on de novo designed protein nanofiber templates. Using sequential assembly on glass substrates, we attach positively charged gold nanoparticles to protein nanofibers engineered to have a high density of negatively charged surface residues. Using a combination of electron and optical microscopy, we measure the density of particle attachment and characterize binding specificity. By varying nanoparticle size and pH of the solution, we explore the importance of charge-dependent particle-fiber and particle-substrate interactions. We find an inverse correlation between particle size and attachment density to protein nanofibers, attributed to the balance between size-dependent electrostatic particle-fiber attraction and particle-substrate repulsion. We show pH-dependent particle attachment density and binding specificity in relation to the protonation fraction of each assembly layer. Finally, we employ hyperspectral scattering microscopy to draw conclusions about particle density and interparticle spacings of optically observable particle assemblies.

Self‐Powered and Imperceptible Electronic Tattoos Based on Silk Protein Nanofiber and Carbon Nanotubes for Human–Machine Interfaces

AbstractTriboelectric electronic skins (E‐skins) can be used as primary interactive devices for human–machine interfaces (HMIs). However, devices for seamless on‐skin operations must be soft and deformable, and attachable to and compatible with the skin. In this paper, a substrate‐free, skin‐compatible, skin‐attachable, mechanically deformable, and self‐powered E‐tattoo sticker consisting of carbon nanotubes (CNTs) and silk nanofibers (SNFs) is presented. The E‐tattoo can be imperceptibly tattooed on the skin and removed with water. When the device touches naked skin, triboelectric signals are generated. Because of the micro‐to‐nano hierarchical pores (with high surface‐to‐volume ratios), contact‐induced electrification generates a power density of ≈6 mW m−2 and pressure sensitivity of ≈0.069 kPa−1. The power generated on the tattooed skin can activate small electronic devices. Moreover, whole‐body joint movements can be monitored and tactile movements can be mapped by reading the generated electrical signals. The presented E‐tattoo system can promote the development of flexible energy and sensor systems for self‐powered, energy‐autonomous, imperceptible E‐skin devices for HMIs and artificial intelligent robotics and prostheses.