Search

Objective We sought to determine the biocompatibility of electrospun regenerated silk fibroin (RSF) mats with inner ear progenitors, especially their effect on the differentiation of inner ear progenitors into hair cells. Methods Neonatal mouse cochleae (n = 20) were collected and digested and allowed to form spheres over several days. Cells digested from the spheres were then seeded onto aligned or random RSF mats, with laminin-coated coverslips serving as controls. The inner ear progenitor cell mortality was examined by TUNEL labeling, and the adhesion of cells to the RSF mats or coverslip was determined by scanning electron microscopy. Finally, the number of hair cells that differentiated from inner ear progenitors was determined by Myosin7a expression. Unpaired Student’s t-tests and one-way ANOVA followed by a Dunnett’s multiple comparisons test were used in this study ( p < 0.05). Results After 5 days of culture, the inner ear progenitors had good adhesion to both the aligned and random RSF mats and there was no significant difference in TUNEL+ cells between the mats compared to the coverslip ( p > 0.05). After 7 days of in vitro differentiation culture, the percentage of differentiated hair cells on the control, aligned, and random RSF mats was 2.5 ± 0.5%, 2.7 ± 0.4%, and 2.4 ± 0.2%, respectively, and there was no significant difference between Myosin7a+ cells on either RSF mat compared to controls ( p > 0.05). Conclusion The aligned and random RSF mats had excellent biocompatibility with inner ear progenitors and helped the inner ear progenitors maintain their stemness. Our results thus indicate that RSF mats represent a useful scaffold for the development of new strategies for inner ear tissue engineering research.

Biomemristors have attracted significant attention because of their potential applications in logic operations, nonvolatile memory, and synaptic emulators, thus leading to the urgent need to improve memristive performance. In this work, a silk fibroin (SF)-based memristor, integrated with both low power and low operating current simultaneously, has been reported. Doping the SF with Ag and an ethanol-based post-treatment promote microcrystal formation in the bulk of the SF. This induces carrier transport along fixed, short paths and results in a low set voltage, low operating current, and high memristive stability. Such performances can greatly reduce power consumption and heat generation, beneficial for the accuracy and durability of memristor devices. The memristive mechanism of SF-based memristors with different Ag contents is the space-charge-limited conduction (SCLC) mechanism. In addition, the nonlinear transmission property of SF-based memristors suggests useful applications in bioelectronics.

Generally, electrospun silk fibroin scaffolds collected by traditional plates present limited pore size and mechanical properties, which may restrict their biomedical applications. Herein, regenerated Antheraea pernyi silk fibroin (RASF) with excellent inherent cell adhesion property was chosen as a raw material and the conductive metal meshes were used as collectors to prepare modified RASF scaffolds by electrospinning from its aqueous solution. A traditional intact plate was used as a control. The morphology and mechanical properties of the obtained scaffolds were investigated. Schwann cells were further used to assess the cytocompatibility and cell migration ability of the typical scaffolds. Interestingly, compared with the traditional intact plate, the mesh collector with an appropriate gap size (circa 7 mm) could significantly improve the pore size, porosity and mechanical properties of the RASF scaffolds simultaneously. In addition, the scaffold collected under this condition (RASF-7mmG) showed higher cell viability, deeper cell permeation and faster cell migration of Schwann cells. Combined with the excellent inherent properties of ASF and the obviously enhanced scaffold cytocompatibility and mechanical properties, the RASF-7mmG scaffold is expected to be a candidate with great potential for biomedical applications.

Bio-memristors constitute candidates for the next generation of non-volatile storage and bionic synapses due to their biocompatibility, environmental benignity, sustainability, flexibility, degradability, and impressive memristive performance. Silk fibroin (SF), a natural and abundant biomaterial with excellent mechanical, optical, electrical, and structure-adjustable properties as well as being easy to process, has been utilized and shown to have potential in the construction of bio-memristors. Here, we first summarize the fundamental mechanisms of bio-memristors based on SF. Then, the latest achievements and developments of pristine and composited SF-based memristors are highlighted, followed by the integration of memristive devices. Finally, the challenges and insights associated with SF-based bio-memristors are presented. Advances in SF-based bio-memristors will open new avenues in the design and integration of high-performance bio-integrated systems and facilitate their application in logic operations, complex circuits, and neural networks.

A novel biomaterial ink consisting of regenerated silk fibroin (SF) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose (OBC) nanofibrils was developed for 3D printing lung tissue scaffold. Silk fibroin backbones were cross-linked using horseradish peroxide/H2O2 to form printed hydrogel scaffolds. OBC with a concentration of 7wt% increased the viscosity of inks during the printing process and further improved the shape fidelity of the scaffolds. Rheological measurements and image analyses were performed to evaluate inks printability and print shape fidelity. Three-dimensional construct with ten layers could be printed with ink of 1SF-2OBC (SF/OBC = 1/2, w/w). The composite hydrogel of 1SF-1OBC (SF/OBC = 1/1, w/w) printed at 25 °C exhibited a significantly improved compressive strength of 267 ± 13 kPa and a compressive stiffness of 325 ± 14 kPa at 30% strain, respectively. The optimized printing parameters for 1SF-1OBC were 0.3 bar of printing pressure, 45 mm/s of printing speed and 410 μm of nozzle diameter. Furthermore, OBC nanofibrils could be induced to align along the print lines over 60% degree of orientation, which were analyzed by SEM and X-ray diffraction. The orientation of OBC nanofibrils along print lines provided physical cues for guiding the orientation of lung epithelial stem cells, which maintained the ability to proliferate and kept epithelial phenotype after 7 days’ culture. The 3D printed SF-OBC scaffolds are promising for applications in lung tissue engineering. Electronic supplementary material The online version of this article (10.1007/s10570-020-03526-7) contains supplementary material, which is available to authorized users.

Antheraea pernyi silk, which is from a kind of non-mulberry silkworm produced in China, has better mechanical properties and cytocompatibility than the extensively studied silk from mulberry silkworm (Bombyx mori). In this work, the regenerated Antheraea pernyi silk fibroin (RASF) scaffolds were prepared from RASF aqueous solutions with different concentrations by a freeze-drying method. The morphologies, structures and properties of the obtained RASF scaffolds were investigated. It was found that with the decrease of RASF solution concentration and the increase of freezing temperature, the porosity of the scaffold increased while its apparent density decreased. The micro-morphology of the scaffold from the 1 wt% RASF solution was irregular. When the solution concentration was increased to the range of 4–13 wt%, the micro-morphologies of the obtained scaffolds mainly showed lamellar-like structure. And with the increase of solution concentration, the lamellar gap of the scaffold decreased while the lamellar thickness of the scaffold increased. However, with the further increase of solution concentration, the morphology of scaffold could gradually transfer into porous structure. In addition, the scaffold micro-morphology could be also affected by freezing temperature. Moreover, with the increase of RASF solution concentration or (and) the decrease of freezing temperature, the obtained scaffold had higher content of β-sheet conformation and higher crystallinity, which could improve its mechanical properties. It was further found that the swelling ratio and degradation rate of RASF scaffold prepared for tissue engineering increased with the decrease of solution concentration. The results of MTT indicated that the obtained RASF scaffold had no cytotoxicity. Moreover, the results of field emission scanning electron microscopy and laser confocal scanning microscopy revealed that the viability, cytocompatibility and migration ability of Schwann cells cultured on RASF scaffold were much better than those cultured on regenerated Bombyx mori silk fibroin (RBSF) scaffold. The RASF scaffold prepared in this work may have great potential applications in the area of nerve tissue engineering.

Incorporation of highly conducting graphene into electrospun biodegradable polymer mats is very promising for the fabrication of electroactive flexible scaffolds toward neural tissue engineering. However, the direct assembly of graphene onto electrospun polymer fibers for preparing stable conducting scaffolds remains a critical challenge due to the inertness of graphene. To overcome this issue, a one-pot assembly approach was developed to trap graphene inside electrospun mats of regenerated silk fibroin (RSF) by applying its ethanol-treatment driven supercontract. This approach is simple, direct, and controllable, loads only a small amount of graphene, and achieves high conductivity for scaffolds (a minimum resistance of (54.9 ± 20.3) Ω/sq). This ensures weak interference on the softness and biodegradability of graphene trapped RSF scaffolds. Thus, the prepared graphene functionalized RSF scaffold remains highly conductive and stable even with ultrasonic washing. It promotes cell spreading and differentiation, and significantly stimulates the neurite outgrowth by 74.5%, while applying an optimized constant electrical potential, thus indicating it as an ideal candidate as electroactive scaffold for tissue engineering. The application of graphene trapped electrospun polymer mats can be extended to electro-tuned tissue engineering, skin electronics, wearable sensors, and e-textiles due to its combination of flexibility, portability, and electrical conductivity.

Silk derived from the silkworm Bombyx mori is among the most important fibrous protein biomaterials due to large-scale production from natural sources, excellent biocompatibility, unique mechanical properties and controllable degradation. Silk fibroin can be processed into a variety of formats to match different applications, such as tissue engineering, drug delivery or as the passive substrate of a bio-device. Advances in fabrication technologies provide new possibilities for the combination of silk fibroin with other nanomaterials to functionalize silk fibroin for specialized purposes, including sensing, cell visualization, resistance to ultraviolet light and provision of antibacterial properties. As the requirement for wearable and intelligent devices has become increasingly important over recent years, silk fibroin has been utilized as the active element in electronic and optical instruments. This review summarizes these recent advances in the innovative applications of silk fibroin.

In this study, nascent silk nanoribbons (SNRs) with an average thickness of 0.4 nm were extracted from natural silkworm silk by partially dissolving degummed silk (DS) in sodium hydroxide (NaOH)/urea solution at -12 °C. In this gentle treatment, the solvent could not destroy the nanofibrillar structure completely, but the chosen conditions would influence the dimensions of resulting SNRs. Molecular dynamics simulations of silk models indicated that the potential of mean force required to break hydrogen bonds between silk fibroin chains was 40% larger than that of van der Waals interactions between β-sheet layers, allowing the exfoliating treatment. It was found that the resulting SNRs contained a single β-sheet layer and amorphous silk fibroin molecules, which could be considered as the basic building block of DS consisting of hierarchical structures. The demonstrated technique for extracting ultrathin SNRs having the height of a single β-sheet layer may provide a useful pathway for creating stronger and tougher silk-based materials and/or adding functionality and durability in materials for various applications. The hierarchical structure model based on SNRs may afford more insight into the structure and property relationship of fabricating silk-based materials.

Fluorescent silk fibroin (SF) fibers have great potential in biomedical application and special functions for marking and tracking. How to fabricate fluorescent SF fibers with good fluorescence stability by a simple and environmentally friendly method has yet to be explored. Here, we successfully produced fluorescent SF fibers by using silkworms as bioreactors to introduce rare-earth upconverting phosphors (UCPs) into silk fibroin. The modified silk exhibited bright green colors under 980 nm laser. This directly feeding method to produce fluorescent SF fibers is green and environmentally friendly and easy to use for mass production. Moreover, it provides an idea that SF fibers can be cooperated with more fluorescent materials which could exhibit different colors with a certain wavelength of light for broad application.

Bioelectronics based on biomaterial substrates are advancing toward biomedical applications. As excellent conductors, poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have been widely developed in this field. However, it is still a big challenge to obtain a functional layer with a good electroconductive property, transparency, and strong adhesion on the biosubstrate. In this work, poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-OH) was chemically polymerized and deposited on the surface of a regenerated silk fibroin (RSF) film in an aqueous system. Sodium dodecyl sulfate (SDS) was used as the surfactant to form micelles which are beneficial to the polymer structure. To overcome the trade-off between transparency and the electroconductive property of the PEDOT-OH coating, a composite oxidant recipe of FeCl3 and ammonium persulfate (APS) was developed. Through electrostatic interaction of oppositely charged doping ions, a well-organized conductive nanoscale coating formed and a transparent conductive RSF/PEDOT-OH film was produced, which can hardly be achieved in a traditional single oxidant system. The produced film had a sheet resistance (Rs) of 5.12 × 104 Ω/square corresponding to a conductivity of 8.9 × 10-2 S/cm and a maximum transmittance above 73% in the visible range. In addition, strong adhesion between PEDOT-OH and RSF and favorable electrochemical stability of the film were demonstrated. Desirable transparency of the film allowed real-time observation of live cells. Furthermore, the PEDOT-OH layer provided an improved environment for adhesion and differentiation of PC12 cells compared to the RSF surface alone. Finally, the feasibility of using the RSF/PEDOT-OH film to electrically stimulate PC12 cells was demonstrated.

Antibacterial scaffolds are highly desirable for the repair and reconstruction of injured soft tissues. However, the direct fabrication of scaffolds with excellent biocompatibility, flexibility, and antibacterial capacity remains a challenge, especially those based on biomaterials. In this study, we report the biomaterial-based antibacterial scaffolds based on regenerated silk fibroin, 2-hydroxypropyltrimethyl ammonium chloride chitosan, and bladder acellular matrix graft by blend and coaxial electrospinning. This approach eliminated the use of organic solvents and inorganic nanoparticles, ensuring greater clinical safety, mimicking physiological extracellular matrix structures, and the required softness for a suture material. Thus, the scaffold obtained in this study exhibited excellent biocompatibility, the required mechanical characteristics, and excellent antibacterial capacity. The rate of bacterial elimination of Staphylococcus aureus and Escherichia coli reached up to 99.5 and 98.3%, respectively. The scaffold design favored cell growth and proliferation and resulted in the significant promotion of repair and reconstruction of the urethra, indicating that it can be an ideal antibacterial suture material for soft tissue restoration.

To investigate the synergistic effect of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) on cavernous nerve regeneration, two different aligned scaffolds consisting of coaxial electrospun silk fibers were prepared by switching the position of the two factors in either core or shell domain. The order and release rate of the dual factors delivery were relatively different because of the distinct location of two factors in coaxial fibers. An in vitro assay showed that the inner-VEGF/outer-BDNF scaffolds could more obviously accelerate Schwann cells growth, proliferation and spreading owing to the rapid release of BDNF. However, in vivo scaffold implantation demonstrated that the inner-BDNF/outer-VEGF scaffolds significantly facilitated more angiogenesis, and promoted more nerve regeneration based on great benefit of angiogenesis. Results showed that the reasonable dual-delivery order of VEGF and BDNF from scaffolds could enhance synergistic effect of the factors and promote cavernous nerve regeneration.

In this work, we described a green and simple approach for fabricating regenerated silk fibroin (RSF)/reduced graphene oxide (RGO) fibrous mats by reducing GO in the RSF/GO mats through hydrothermal treatment. As a comparison, RSF mat incorporated with graphene (Gr) was fabricated by solution mixing method. Results showed that the reduction of GO in the mats did take place during hydrothermal treatment. An increase in the crystallinity of the mats was induced by hydrothermal treatment. The maximum Young's modulus of RSF/RGO mats reached (122.7 ± 3.1) MPa, which was at least 9-fold higher than RSF mats. As the mass ratio of RGO/RSF was 1.5/100, the average sheet resistance of RSF/RGO mats reached (1.2 ± 0.1)×108 Ω/sq, which was better and more stable than that of RSF/Gr mats. Furthermore, cellular tests and antibacterial tests demonstrated that RSF/RGO mats possessed better biocompatibility and antibacterial property in comparison with RSF mats incorporated with GO or Gr. Thus, the RSF/RGO mats could be a good candidate for tissue engineering applications.

Spider dragline silk is of great interest to people for its outstanding mechanical properties including high toughness. Biomimetic spinning of spider silk has attracted people's attention for decades. This paper reports a simple and cheap method to greatly toughen artificial silk by compositing with nanoanatase. The toughness of the artificial silk (breaking energy 93.1 +/- 27.1 MJ m(-3)) exceeded that of silkworm silks. The hydrophilic nanomineral TiO2 with large specific surface area interacted severely with the fibroin matrix through coordination complexes (Ti-protein) and hydrogen bonds (O-H). Due to the interfacial interactions, regenerated silk fibroin (RSF)-TiO2 fibers showed higher alpha-helix/random coil content, lower beta-sheet content, smaller crystallites and lower crystallinity than pure RSF fibers. A nanoconfined crystallite toughening mechanism was proposed to discuss the structure-property relationship of the hybrid fibers.

Considering the high biocompatibility of regenerated silk fibroin (RSF) and the good enhancement effect of graphene oxide (GO), various RSF/GO composite materials have been previously investigated, and found that GO plays a vital role in the fabrication of high-performance RSF/GO materials. However, its effects on the structure of RSF solution are unclear. Therefore, in this work, we studied the rheological and optical properties, as well as the aggregation behavior of concentrated RSF/GO solution in response to applied shear. The results demonstrated that the presence of GO sheets in RSF solution increased the shear resistance, while delayed the sol-gel transition. Moreover, GO sheets were not favorable to the formation of the ordered structures of RSF. The results from small angle X-ray scattering (SAXS) of RSF/GO solution also showed that the shear process promoted the formation of RSF/GO interface. The data also provided insights into the structural evolution within the mixture solutions, which can be beneficial to the future design and fabrication of nanofiller-reinforced high-performance materials.

In order to fabricate high performance artificial silk, hybrid fibers were dry spun from regenerated silk fibroin (RSF) aqueous solution mixed with graphene oxide (GO) nanosheets. The influence of draw ratio on the microstructure and mechanical properties of RSF/GO hybrid fibers was studied through Fourier transform infrared spectroscopy (FT-IR), synchrotron radiation wide-angle X-ray diffraction, Raman spectroscopy and mechanical testing. The results showed that with increasing draw ratio, both amorphous phase and mesophase of the dry-spun artificial fiber gradually converted to crystals. The orientation of crystals and mesophase changed slightly at low draw ratio, but increased significantly at draw ratios of 3 and 4X. The β-sheet content of silk fibroin and the disorder degree of GO sheets in the fibers also increased with the increase of draw ratio. The initial modulus, breaking strength and breaking energy of the hybrid fibers achieved great improvement at a draw ratio of 4X. The structure evolution of the RSF/GO hybrid fibers may benefit the understanding of the structure-property relationship of other composite fibers.

Graphene oxide (GO) with outstanding mechanical properties is a satisfactory filler to reinforce artificial silk. To prepare tough regenerated silk fibroin/graphene oxide (RSF/GO) hybrid fibers, it is important to understand the structural evolution of the hybrid fibers with external deformation. The morphology and microstructural changes of the hybrid fibers at different tensile strains were investigated by SEM, Raman spectra and synchrotron radiation wide angle X-ray diffraction (SR-WAXD). Longer and deeper stripes were found on the surface of RSF/GO fibers with the increase of strain as revealed by SEM. SR-WAXD results revealed that the fraction and orientation of crystals and the mesophase had slight changes in the elastic deformation zone of the fiber. However, in the plastic deformation zone of the fiber with a strain from 5 to 18%, the fraction of crystals gradually increased while the fraction of the mesophase decreased. During this deformation, the orientation of crystals (fc) firstly increased significantly and then increased slightly, while the orientation of the mesophase (fm) increased steadily beyond the yield point. When the strain exceeded 18%, the fraction of crystals decreased while the fraction of mesophase increased. The fc had a rapid increase again at a strain above 18%. A model was proposed to explain how the tensile deformation affects the molecular orientation of the hybrid fibers.

Highlights Intrinsically, super-strong fluorescent silk was fabricated via feeding Bombyx mori silkworms with carbon nanodots.The multi-functional silks showed no cytotoxicity to Schwann cells and exhibited great potential in bioimaging.The reinforcing mechanism of multi-functional silks was proposed. Electronic supplementary material The online version of this article (10.1007/s40820-019-0303-z) contains supplementary material, which is available to authorized users., Fluorescent silk is fundamentally important for the development of future tissue engineering scaffolds. Despite great progress in the preparation of a variety of colored silks, fluorescent silk with enhanced mechanical properties has yet to be explored. In this study, we report on the fabrication of intrinsically super-strong fluorescent silk by feeding Bombyx mori silkworm carbon nanodots (CNDs). The CNDs were incorporated into silk fibroin, hindering the conformation transformation, confining crystallization, and inducing orientation of mesophase. The resultant silk exhibited super-strong mechanical properties with breaking strength of 521.9 ± 82.7 MPa and breaking elongation of 19.2 ± 4.3%, improvements of 55.1% and 53.6%, respectively, in comparison with regular silk. The CNDs-reinforced silk displayed intrinsic blue fluorescence when exposed to 405 nm laser and exhibited no cytotoxic effect on cells, suggesting that multi-functional silks would be potentially useful in bioimaging and other applications. Electronic supplementary material The online version of this article (10.1007/s40820-019-0303-z) contains supplementary material, which is available to authorized users.

We developed a stromal cell-derived factor-1 alpha (SDF-1α)-aligned silk fibroin (SF)/three-dimensional porous bladder acellular matrix graft (3D-BAMG) composite scaffold for long-section ventral urethral regeneration and repair in vivo. SDF-1α-aligned SF microfiber/3D-BAMG, aligned SF microfiber/3D-BAMG, and nonaligned SF microfiber/3D-BAMG scaffolds were prepared using electrostatic spinning and wet processing. Adipose-derived stem cell (ADSC) and bone marrow stromal cell (BMSC) migration was assessed in the SDF-1α-loaded scaffolds. Sustained SDF-1α release in vitro and vivo was analyzed using enzyme-linked immunosorbent assay (ELISA) and western blotting, respectively. The scaffolds were used to repair a 1.5 × 1 cm2 ventral urethral defect in male rabbits in vivo. General observation and retrograde urinary tract contrast assessment were used to examine urethral lumen patency and continuity at 1 and 3 months post-surgery. Postoperative rehabilitation was evaluated using histological detection. The composite scaffolds sustained SDF-1α release for over 16 days in vitro. SDF-1α-aligned SF nanofiber promoted regeneration of urethral mucosa, submucosal smooth muscles, and microvasculature, increased cellular proliferation, and reduced collagen deposition. SDF-1α expression was increased in reconstructed urethra at 3 months post-surgery in SDF-1α-aligned SF group. SDF-1α-aligned SF microfiber/3D-BAMG scaffolds may be used to repair and reconstruct long urethral defects because they accelerate urethral regeneration.

Neural progenitor cell (NPC) transplantation is a promising technique for central nervous system (CNS) reconstruction and regeneration. Biomaterial scaffolds, frameworks, and platforms can support NPC proliferation and differentiation in vitro as well as serve as a temporary extracellular matrix after transplantation. However, further applications of biomaterials require improved biological attributes. Silk fibroin (SF), which is produced by Bombyx mori, is a widely used and studied protein polymer for biomaterial application. Here, we prepared aligned and random eletrospun regenerated SF (RSF) scaffolds, and evaluated their impact on the growth of NPCs. First, we isolated NPCs and then cultured them on either laminin-coated RSF mats or conventional laminin-coated coverslips for cell assays. We found that aligned and random RSF led to increases in NPC proliferation of 143.8 ± 13.3% and 156.3 ± 14.7%, respectively, compared to controls. Next, we investigated neuron differentiation and found that the aligned and the random RSF led to increases in increase in neuron differentiation of about 93.2 ± 6.4%, and 3167.1 ± 4.8%, respectively, compared to controls. Furthermore, we measured the survival of NPCs and found that RSF promoted NPC survival, and found there was no difference among those three groups. Finally, signaling pathways in cells cultured on RSF mats were studied for their contributions in neural cell differentiation. Our results indicate that RSF mats provide a functional microenvironment and represent a useful scaffold for the development of new strategies in neural engineering research.

One of the latest trends in the regenerative medicine is the development of 3D-printing hydrogel scaffolds with biomimetic structures for tissue regeneration and organ reconstruction. However, it has been practically difficult to achieve a highly biomimetic hydrogel scaffolds with proper mechanical properties matching the natural tissue. Here, bacterial cellulose nanofibers (BCNFs) were applied to improve the structural resolution and enhance mechanical properties of silk fibroin (SF)/gelatin composite hydrogel scaffolds. The SF-based hydrogel scaffolds with hierarchical pores were fabricated via 3D-printing followed by lyophilization. Results showed that the tensile strength of printed sample increased significantly with the addition of BCNFs in the bioink. Large pores and micropores in the scaffolds were achieved by designing printing pattern and lyophilization after extrusion. The pores ranging from 10 to 20 μm inside the printed filaments served as host for cellular infiltration, while the pores with a diameter from 300 to 600 μm circled by printed filaments ensured sufficient nutrient supply. These 3D-printed composite scaffolds with remarkable mechanical properties and hierarchical pore structures are promising for further tissue engineering applications.

The necessity of optical waveguides with low-loss light guiding of biomedical devices is driving increasing demands for development of biocompatible photonic components. Spider silks have extraordinary mechanical properties; thus, the design of high-performance artificial silk fibers as optical waveguides for low-loss light guiding has been one of the focuses of researches in the field of biomimetic fibers. In this study, regenerated silk fibroin (RSF)/cellulose nanofibers (CNF) hybrid fibers were wet-spun through a microfluidic channel that mimics the shape of spider’s major ampullate gland. The generated RSF/CNF fibers with high crystallinity, high mesophase content and small crystallite size, thus showed a low light loss of 1.0 dB/cm, which was much lower than that of degummed-silk and most commercial waveguides. Additionally, the fibers had high sound velocity and was knittable. The break strength of the RSF/CNF fiber containing 5 wt% CNF was as high as 710 ± 33 MPa, which was significantly higher than that of silkworm silk fiber. The developed optical waveguides had high performance, biocompatibility, biodegradability, flexibility, and toughness, thus may be suitably applied in biological media, biophotonics and brain-machine interfaces.

Fluorescent silk fibroin materials have wide applications in tissue engineering and bioassay system, but the inhomogeneity of fluorescence and high amount of additive hinder their development. In this study, we reported a super-strong composite silk with excellent blue fluorescence intensity and uniformity by feeding silkworm trace amount of hexaphenylsilole (HPS) (0.0012‰ in the diet), an important aggregation-induced emission (AIE) molecule. The incorporation of HPS nanoparticles in silk altered the second structures of silk fibroin, reduced crystallinity and crystallite size and induced orientation of crystalline region. In addition, the obtained composite silk exhibited strong mechanical properties with breaking elongation of 11.9 ± 1.7% and breaking strength of 503.0 ± 44.4 MPa, improvement of 17.8% and 54.0%, respectively, in comparison with regular silk. These super-strong and uniform fluorescent silks may pave a route to prevent the quenching effect of conventional fluorescent silk fibroin materials and be potentially applied in biomedical field.

To improve the therapeutic effect of a damaged peripheral nerve, aligned scaffolds based on regenerated silk fibroin (RSF) were fabricated by electrospinning, and were simultaneously loaded with dual factors of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF). An ELISA assay measurement in vitro demonstrated that the release of dual factors from the scaffolds was well maintained up to 2 weeks. Schwann cell (SC) morphologies on the RSF scaffolds were obtained using scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) after cell seeding. Cell viability and proliferation on the scaffolds were investigated using an MTT assay. Furthermore, the scaffolds were implanted in a mouse model to support nerve regeneration and angiogenesis in vivo, which was evaluated by histological and immunohistochemical (IHC) analyses at 4 and 8 weeks after implantation. In all retrieved scaffolds, de novo innervation and vascularization, indicated by a positive endothelial marker (von Willebrand factor, vWF) and an innervation marker (S-100 protein), were evident without chronic inflammatory responses. Compared to the control group, the dual-factor loaded scaffolds significantly promoted nerve regeneration and possessed great potential in peripheral nerve repair and regeneration, and for the repair of other tissues.

Triboelectric nanogenerators (TENGs) convert mechanical energy into electrical energy, providing the possibility of self-powered implantable electronic devices. However, most implantable electronic devices still require an external power source. In addition, TENGs must have outstanding biocompatibility, biodegradability, and controllable degradation rate to prevent the need for a second surgery and avoid an inflammatory response. In this work, a silk nanoribbon (SNR)-based bio-TENG is fabricated using a nascent SNR film (SNRF) and regenerative silk fibroin film (RSFF). To maintain the original meso/nanoscale structure of silk, SNRs with a thickness of 0.38 nm are directly exfoliated from natural silk. RSFF and SNRF have different microstructure and work functions. The output performance of the bio-TENG with the maximum voltage, current, and power density (PD) reach up to 41.64 V, 0.5 μA, and 86.7 mW/m2, respectively. The lifetime of the TENG depends on post-treatment of the RSFF package. The raw materials of the proposed TENG, including silk and magnesium (Mg), are completely biodegradable and biocompatible in vitro. With its high sensitivity and the ability to generate power from just a human pulse, the all silk-based bio-TENG may be an attractive power source for implantable self-powered electronic devices, such as pacemakers and implantable sensors.

Various attractive materials are being used in bioelectronics recently. In this paper, hydroxymethyl-3,4-ethylenedioxythiophene (EDOT-OH) has been in situ integrated and polymerized on the surface of the regenerated silk fibroin (RSF) film to construct a biocompatible electrode. In order to improve the efficiency of in situ polymerization, sodium dodecyl sulfate (SDS) was adopted as surfactant to construct a well-organized and stable poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-OH) coating, whereas ammonium persulfate was used as oxidant. The effects of dosages of surfactant and oxidant, initial pH value, and monomer concentration on the polymerization were studied. Under the optimal conditions, the RSF/PEDOT-OH film exhibited a square resistance of 3.28 × 105 Ω corresponding to a conductance of 6.1 × 10–3 S/cm. Scanning electron microscope images indicated that PEDOT-OH was deposited uniformly on the surface of the RSF film with SDS. Furthermore, Fourier transform infrared spectroscopy confirmed...

The fabrication of bone tissue engineering scaffolds with high osteogenic ability and favorable mechanical properties is of huge interest. In this study, a silk fibroin (SF) solution of 30 wt% was extracted from cocoons and combined with mesoporous bioactive glass (MBG) to fabricate MBG/SF composite scaffolds by 3D printing. The porosity, compressive strength, degradation and apatite forming ability were evaluated. The results illustrated that MBG/SF scaffolds had superior compressive strength (ca. 20 MPa) and good biocompatibility, and stimulated bone formation ability compared to mesoporous bioactive glass/polycaprolactone (MBG/PCL) scaffolds. We subcutaneously transplanted hBMSCs-loaded MBG/SF and MBG/PCL scaffolds into the back of nude mice to evaluate heterotopic bone formation assay in vivo, and the results revealed that the gene expression levels of common osteogenic biomarkers on MBG/SF scaffolds were significantly better than MBG/PCL scaffolds. These results showed that 3D-printed MBG/SF composite scaffolds are great promising for bone tissue engineering.

Electrospun scaffold with three-dimensional (3D) geometry and appropriate pore structure is an important challenge to mimic natural tissues such as skin, cartilage, etc. In this work, 3D silk fibroin (SF) electrospun scaffolds with gradient pore size were prepared by combining multi-step electrospinning with low temperature (LTE) collecting. The LTE electrospun scaffolds achieved 3D macro-structure with large pore size. The effects of relative humidity (RH), collecting temperature on the morphology of the scaffolds were investigated by scanning electron microscopy and computed tomography. The pore size of the scaffolds was tailored by adjusting SF concentration, electric field, flow rate, needle gauge and collector temperature during electrospinning at 50% RH. L929 cell infiltration results of the scaffolds showed that conventional electrospun scaffolds with small pore size (average diameter 5.9 ± 1.4 μm) restrained cell proliferation and infiltration. On the contrary, LTE electrospun scaffolds with medium pore size (average diameter 11.6 ± 1.4 μm) improved cell proliferation obviously. Large pore size scaffolds (average diameter 37.2 ± 12.9 μm) was beneficial to cell infiltration depth in the thickness direction of the scaffolds. The scaffolds, which were integrated with layers of small, medium and large pores, are promising in the repair of tissue with gradient pore structures.

As the perfect combination of strength and luster, silkworm silks have been widely used in many fields but still need improvements. This paper demonstrates an in vivo uptake of titanium dioxide (TiO2) nanoparticles by silkworms, leading to the direct production of intrinsically modified silk. The nanoparticles can be easily incorporated into the silk gland of silkworm by using this method due to the interactions between TiO2 and silk fibroin molecules. Infrared spectra indicate that TiO2 nanoparticles confine the conformation transition of silk fibroin from random coil/α-helix to β-sheet. Results of synchrotron radiation wide-angle X-ray diffraction and small-angle X-ray scattering suggest that modified silks have lower crystallinity, higher mesophase content, and higher Herman’s orientation functions of crystalline region and mesophase region than control group. The breaking strength and elongation at break of the modified silk can be improved up to 548 ± 33 MPa and 16.7 ± 0.8%, respectively, by adding 1...

The goal of this study was to investigate the tissue performance of bladder following stretched electrospun silk fibroin matrix (SESFM) implantation compared with bladder acellular matrix (BAM). We compared SESFM with BAM based on porosity and pore size. Scaffolds were separately transplanted into opposite walls of the bladder of 30 rabbits after stripping the bladder mucosa and smooth muscle (1.5 × 2.0 cm(2)). Gross anatomical observation, histological analysis and muscle contractility studies were performed at 2, 4, and 8 weeks post-op. SESFM has higher porosity and larger pore size compared with BAM (p 0.05). However, SESFM promoted a higher degree of smooth muscle and vessel regeneration compared to BAM (p

Bombyx mori silk is of great interest to people for its outstanding mechanical and biological properties. However, the traditional electrospun regenerated silk fibroin (RSF) scaffolds from aqueous solution were weak and had limited applications. This study was to fabricate reinforced scaffolds with well-aligned RSF fibers electrospun on a layer of native extracellular matrix, bladder acellular matrix graft (BAMG). The silk fibroin fibers were well-aligned as a grill in multiple layers. Both the BAMG and the grill structure significantly improved the tensile properties and suture retention of the composite scaffolds, which can be sutured well with tissue during implantation. In vitro assay indicates that the scaffolds had a good biocompatibility. Porcine iliac endothelial cells (PIECs) attached and proliferated well on the vascular endothelial growth factor (VEGF) loaded scaffolds compared with those without VEGF. Moreover, the grill-like structure guides PIECs well along the aligned fiber.

Regenerated silk fibroin (RSF) scaffolds electrospun from aqueous solutions have great potential for tissue engineering. However, the traditional RSF mats are weak and limit the applications. A bladder acellular matrix graft (BAMG), a tough natural material, was used as an electrospinning substrate to toughen the RSF scaffolds. Compared with bare RSF scaffolds, the composite scaffolds with breaking energies ranging from 458 to 970 J kg−1 show significantly improved tensile properties and suture retention strength, which may satisfy the requirements for implantation. Vascular endothelial growth factor (VEGF) was encapsulated in the RSF/BAMG composite scaffolds by means of blend and coaxially electrospinning to promote the ability of vasculogenesis and angiogenesis. Transmission electron microscope (TEM) images show that the coaxially electrospun fibers had a core–sheath structure. An ELISA assay measurement indicates that VEGF can be released for more than 16 days. The samples annealed in water vapor exhibit higher release profiles than those immersed in ethanol. An in vitro assay indicates that VEGF loaded scaffolds evidently induced the attachment and proliferation of porcine iliac endothelial cells (PIECs) compared with those without VEGF. Moreover, the VEGF remained bioactive for up to 7 days. Thus the VEGF loaded composite scaffolds could be a promising candidate for tissue engineering applications.

In this paper, the structures and properties of regenerated silk fibroin (RSF) aqueous solutions under shear were investigated by using a polarizing microscope, an optical shearing instrument, a rotational rheometer, a Raman spectrometer and a synchrotron radiation small angle X-ray scattering facility. It was found that after being sheared at a constant shear rate for a suitable time, the RSF aqueous solution showed gradually decreased viscosity and enhanced birefringence before protein denaturation. Meantime, rod-like structures were formed and conformational transition happened in the solution. These results indicated that the RSF molecules in the solution might gradually form rod-like liquid crystal structures after applying sufficient shear. Moreover, it was also found that the increase of the shear rate could reduce the critical shear time for the solution to begin to form the liquid crystal structure.

The protocol demonstrates a method for mimicking the spinning process of silkworm. In the native spinning process, the contracting spinning duct enables the silk proteins to be compact and ordered by shearing and elongation forces. Here, a biomimetic microfluidic channel was designed to mimic the specific geometry of the spinning duct of the silkworm. Regenerated silk fibroin (RSF) spinning doped with high concentration, was extruded through the microchannel to dry-spin fibers at ambient temperature and pressure. In the post-treated process, the as-spun fibers were drawn and stored in ethanol aqueous solution. Synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) technology was used to investigate the microstructure of single RSF fibers, which were fixed to a sample holder with the RSF fiber axis normal to the microbeam of the X-ray. The crystallinity, crystallite size, and crystalline orientation of the fiber were calculated from the WAXD data. The diffraction arcs near the equator of the two-dimensional WAXD pattern indicate that the post-treated RSF fiber has a high orientation degree.

Silk-based materials have great potentials in medical applications because of the proper mechanical properties and outstanding biocompatibility. This paper reports a novel method to prepare multi-layered silk fibroin (SF) tissue engineering scaffolds with well-aligned fibers oriented in different angles by an electrospinning process. The resulted aligned fibers construct the scaffolds with a grill-like structure, large area and improved mechanical properties, which have been demonstrated by scanning electron microscopy and tensile test. Biocompatibility analysis proves that the grill-like structure well guides the adhesion, proliferation and differentiation of porcine iliac endothelial cells along the aligned SF fibers in different directions.

Microfluidic chips with single channel were built to mimic the shear and elongation conditions in the spinning apparatus of spider and silkworm. Silk fibers dry-spun from regenerated silk fibroin (RSF) aqueous solution using the chip could be tougher than degummed natural silk. The artificial silk exhibited a breaking strength up to 614 MPa, a breaking elongation up to 27% and a breaking energy of 101 kJ/kg.

It has been known that the concentration of Ca2+ gradually increased along the silk gland of silkworm and it played an important role in the spinning process of silk fibre in vivo. In this work, Raman spectrometer, synchrotron radiation wide angle X-ray diffraction facility and material testing instrument were used to investigate the effect of Ca2+ on the structures and properties of regenerated silk fibroin (RSF) in its aqueous solutions and dry spun fibres. It was found that as the concentration of Ca2+ increased in the RSF aqueous solutions and fibres, the conformational transition to β-sheet was promoted, and the resultant post-treated RSF fibre showed higher crystallinity, higher crystalline orientation as well as better mechanical properties. Therefore, it could be concluded that the addition of Ca2+ had improved the structures of RSF aqueous solutions and the resultant fibres, and it might be a feasible approach to obtaining high performance RSF fibres.

Protein concentration, pH, the types and concentrations of metallic ions, and extensional flow are thought to be important environment parameters affecting the natural spinning process. In this study, we investigate the effects of the types and concentrations of metallic ions (Ca2+, Mg2+, and K+ ions), pH, and silk fibroin concentration on the sol-gel transition and the rheological behavior of a regenerated silk fibroin (RSF) aqueous solution. The results show that with an increase in the silk fibroin concentration, the weak acidic RSF aqueous solutions containing Mg2+ or Ca2+ ions undergo a phase transition to a weak gel state. Moreover, the rheological characterization of RSF aqueous solutions shows a dramatic change, and their apparent viscosities increase by almost three orders of magnitude and approach the apparent viscosity of the native dope in the silkworm gland. By using conventional pressure equipment, we investigate the dry-spinnability of weak gels. Further, we observe that the as-spun fibers exhibit a smooth surface and have inferior mechanical properties. The structure of the as-spun fibers is predominantly in a random coil or Silk I conformation.

The conventional process for preparing dry spinnable regenerated silk fibroin (RSF) aqueous solution needs not only an addition of Ca2+ but also an adjustment of pH value. In this work, an RSF dry spinning dope was prepared by using a simplified method with solely adding Ca2+. Compared with the conventional RSF solution, the simply prepared aqueous solution showed similar content of β-sheet conformation and diameter of RSF aggregates but lower viscosity. Furthermore, the posttreated RSF fiber dry-spun from this simply prepared solution showed higher crystallinity and crystalline orientation, smaller crystallite size, and better mechanical properties. It could be concluded that Ca2+ played a much more important role than pH value in improving the structures and properties of RSF spinning solution and fibers. Therefore, the step of adjusting pH value could be excluded in the process of preparing high performance RSF fibers.

OBJECTIVE To evaluate the effects of urethral regeneration with prevascularized bladder acellular matrix hydrogel (BAMH)/silk fibroin (SF) composite scaffolds in a rabbit model. MATERIALS AND METHODS BAMH/SF and collagen Type I hydrogel/SF (CH/SF) scaffolds were prepared and the structure of the scaffolds was assessed using scanning electron microscopy. BAMH/SF, CH/SF and SF scaffolds were incubated in the omentum of male rabbits for two weeks and then harvested for repairing autologous urethral defects. Histological analysis of the incubated scaffolds was performed to evaluate the neovascularization capacity, and the outcomes of urethroplasty were evaluated at one and three months post-operatively. RESULTS The composited scaffolds were composed of a highly porous BAMH or CH buttressed by compact SF outer layer. The histological analysis of the incubated BAMH/SF revealed a signifcant increase of the neovascularization among three groups after a two-week incubation. At three months, the urethra maintained wide caliber in the BAMH/SF group. Strictures were found in the CH/SF and SF groups. Histologically, at one month, intact and multilayer epithelium occurred in the BAMH/SF group, and one layer epithelium was found in the CH/SF and SF groups. However, there was similar epithelial regeneration in BAMH/SF and CH/SF groups at three months (p > 0.05). Comparisons of smooth muscle content and vessel density among the SF, CH/SF and BAMH/SF revealed a significant increase at each time point (p

In this paper, a simple and effective method was applied to enhance regenerated silk fibroin (RSF) mats electrospun from aqueous solution. The mats were first mechanically drawn in 90 vol.% ethanol aqueous solution and then immersed in the same solution for 30 min. The morphology, structure, thermal and mechanical properties of the RSF mats with different draw rates and draw ratios were investigated by scanning electron microscope (SEM), Raman spectroscopy, wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and tensile test. Results revealed that the content of β-sheet conformation, the crystallinity and the number of fibers aligned to the drawing direction increased evidently with the draw ratio. The breaking strength and breaking energy of the post-treated mats at 1.4× draw ratio and 0.1mm/s draw rate were 8.6 MPa and 172.2 J/kg, respectively. However, those of the as-spun mats were only 1.8 MPa and 93.2 J/kg, respectively. The enhanced RSF mats prepared from entirely aqueous solutions may have extensive applications for tissue engineering.

The coaxial electrospinning using the regenerated silk fibroin (SF) and silk sericin (SS) aqueous solutions as the core and shell spinning dopes, respectively, was carried out to prepare regenerated SF/SS composite fibers with components and core-shell structure similar to the natural silkworm silks. It was found from the scanning electron microscope (SEM) and transmission electron microscope (TEM) results that the core dope (SF aqueous solution) flow rate (Q(c)) and the applied voltage (V) had some effects on the morphology of the composite fiber. With an increase in Q(c), the diameter nonuniformity and eccentricity of the core fiber became serious, while the increasing V played an inverse role. In this work, the suitable Q(c) for the fiber formation with better electrospinnability was about 6 μL/min, and the corresponding optimum V was 40 kV. Moreover, the results from Raman spectra analysis, modulated differential scanning calorimetry (MDSC), thermogravimetry (TG) measurement and mechanical property test showed that, compared with the pure SF fiber, the coaxially electrospun SF/SS fiber had more β-sheet conformation, better thermostability and mechanical properties. This was probably because that SS played significant roles in dehydrating SF molecules and inducing the conformational transition of SF to β-sheet structure.

Regenerated silk fibroin (RSF)/graphene oxide (GO) hybrid silk fibers were dry-spun from a mixed dope of GO suspension and RSF aqueous solution. It was observed that the presence of GO greatly affect the viscosity of RSF solution. The RSF/GO hybrid fibers showed from FTIR result lower β-sheet content compared to that of pure RSF fibers. The result of synchrotron radiation wide-angle X-ray diffraction showed that the addition of GO confined the crystallization of silk fibroin (SF) leading to the decrease of crystallinity, smaller crystallite size, and new formation of interphase zones in the artificial silks. Synchrotron radiation small-angle X-ray scattering also proved that GO sheets in the hybrid silks and blended solutions were coated with a certain thickness of interphase zones due to the complex interaction between the two components. A low addition of GO, together with the mesophase zones formed between GO and RSF, enhanced the mechanical properties of hybrid fibers. The highest breaking stress of the hybrid fibers reached 435.5 ± 71.6 MPa, 23% improvement in comparison to that of degummed silk and 72% larger than that of pure RSF silk fiber. The hybrid RSF/GO materials with good biocompatibility and enhanced mechanical properties may have potential applications in tissue engineering, bioelectronic devices, or energy storage.

Microcomposite fibers of regenerated silk fibroin (RSF) and multiwalled carbon nanotubes (MWNTs) were successfully prepared by an electrospinning process from aqueous solutions. A quiescent blended solution and a three-dimensional Raman image of the composite fibers showed that functionalized MWNTs (F-MWNTs) were well dispersed in the solutions and the RSF fibers, respectively. Raman spectra and wide-angle X-ray diffraction (WAXD) patterns of RSF/F-MWNT electrospun fibers indicated that the composite fibers had higher β-sheet content and crystallinity than the pure RSF electrospun fibers, respectively. The mechanical properties of the RSF electrospun fibers were improved drastically by incorporating F-MWNTs. Compared with the pure RSF electrospun fibers, the composite fibers with 1.0 wt % F-MWNTs exhibited a 2.8-fold increase in breaking strength, a 4.4-fold increase in Young's modulus, and a 2.1-fold increase in breaking energy. Cytotoxicity test preliminarily demonstrated that the electrospun fiber mats have good biocompatibility for tissue engineering scaffolds.

By mimicking the spinning process of silkworm, regenerated silk fibroin (RSF) biofibers were dry-spun from RSF aqueous solutions and then post-treated. The effects of post-treatment agents on the conformation, surface morphology, orientation and mechanical properties of the fibers were studied. Compared to inorganic salt system, alcohol/water system obviously induced the fibroin conformation transition from random coil/α-helix to β-sheet. In addition, the post-drawing process induced the orientation of the β-sheet crystallites, which contributed to the improved breaking stress of the fiber. When the fiber was drawn two times in 80 vol.% ethanol aqueous solution, and then immersed in the solution for 1 h, the breaking stress and the elongation at break of the fiber were increased to 199 MPa and 55%, respectively.

In this work, the silk fibroin/sericin (SF/SS) blend aqueous solutions with different SF/SS mass ratios (100/0, 90/10, 85/15, 75/25, and 65/35) were prepared and electrospun to get regenerated fibers. It was found that the addition of SS in the SF solution could increase the apparent viscosity of the solution and improve its electrospinnability so that the fine uniform electrospun SF/SS fibers could be obtained. The quantitative analysis result of Raman spectroscopy showed that the presence of SS facilitated the conformational transition of SF from random coil/α-helix structure to β-sheet structure. Combined with the differential scanning calorimetry result, it was further hypothesized that SS could affect the structural change of SF by dehydrating SF and inducing the formation of hydrogen bonds between SF molecules. Consequently, SS also played an important and positive role in the thermal and mechanical properties of the resultant SF/SS fibers.

To biomimic the spinning process of silkworm or spider, a capillary spinning equipment was applied to spin regenerated silk fibroin (RSF) fibers from RSF aqueous solutions in air. This equipment exhibits a wide processing window for various RSF aqueous solutions. The effects of pH, metal ions, RSF concentration and spinning parameters on the spinnability of the spinning dope and the mechanical properties of the obtained fibers were investigated. As a result, spinning dopes with a pH from 5.2 to 6.9 have good spinnability, especially for the dope with a pH of 6.0 and a Ca2+ concentration of 0.3 M. The RSF concentration of this dope ranges from 44% to 48%. Under optimized conditions of our dry spinning experiments (L/D, 133; take-up speed, 30 mm/s), the obtained as-spun fiber has a breaking strength of 46 MPa, which can be improved up to 359 MPa after a preliminary post-drawing in 80 vol.% ethanol aqueous solution.