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In this study, we fabricated adhesive patches from silkworm-regenerated silk and DNA to safeguard human skin from the sun's rays. The patches are realized by exploiting the dissolution of silk fibers (e.g., silk fibroin (SF)) and salmon sperm DNA in formic acid and CaCl2 solutions. Infrared spectroscopy is used to investigate the conformational transition of SF when combined with DNA; the results indicated that the addition of DNA provides an increase in the SF crystallinity. UV–Visible absorption and circular dichroism spectroscopy showed strong absorption in the UV region and the presence of B-form of DNA once dispersed in the SF matrix, respectively. Water absorption measurements as well as thermal dependence of water sorption and thermal analysis, suggested the stability of the fabricated patches. Biological results on cellular viability (MTT assay) of keratinocyte HaCaT cells after exposures to the solar spectrum showed that both SF and SF/DNA patches are photo-protective by increasing the cellular viability of keratinocytes after UV component exposure. Overall, these SF/DNA patches promise applications in wound dressing for practical biomedical purposes. [ABSTRACT FROM AUTHOR]

As a natural protein fiber with good biocompatibility, silk has a lot of wastes in production, processing, weaving and after-use. Based on the principle of sustainable development, silk fibroin protein can be recycled by chemical method. After recycling, silk fibroin solution can be obtained and recycled silk fibroin materials can beprepared for reuse. Wet spinning is the first to be developed and applied in industrial production because of its uniqueness. As the process has been optimized in industrial production for a long time, wet spinning has become a relatively mature spinning method in all aspects. The choice of coagulating bath plays a key role in the solidification of spinning fluid in the coagulating basin, especially in the mechanical properties of RSF fibers. Sodium dodecyl sulfate (SDS) is a typical anionic surfactant with good emulsification performance, low skin irritation, high safety, and can interact with protein. Based on this, the study intends to establish a wet spinning process using SDS as the solidifying agent. In the paper, SDS was used as the coagulation bath to improve the ductility of regenerated silk fibroin fibers. First of all, the silk was degummed through degumming and other pretreatment, and then the degummed silk obtained after drying was dried for later use. After that, the degummed silk was dissolved with the formic acid-calcium chloride solution to obtain the spinning stock solution. In this way, deionized water, 75% ethanol solution and 50g/LSDS solution were selected as the coagulation bath for wet spinning, and three kinds of RSF fibers were obtained. In the end, the mechanical properties and aggregation structure of three RSF fibers were analyzed. Subsequently, the mechanism of SDS promoting fibrogenesis was verified by the fluorescence probe method. The morphology of the three kinds of RSF fibers was characterized by scanning electron microscope. Deionized water was used as the coagulation bath to obtain the most surface folds and the largest diameter of recycled silk. The recycled silk with ethanol as the coagulation bath has a roughly round cross section, smooth surface and the smallest diameter. When SDS is used as the coagulation bath, the cross section of fiber is approximately elliptic, with a few furrows on the surface and moderate thickness. Tensile tests were conducted to the three kinds of RSF fiber samples. The results show that when SDS is used as the coagulation bath, RSF shows the characteristics of elastic materials, and its fracture strain is 126%, which is much higher than that of the two kinds of regenerated fibers using deionized water (20%) and 75% ethanol solution (26%) as the coagulation bath. In order to explore the effect of the coagulation bath on the aggregation state of recycled silk, Fourier transform infrared spectroscopy (FTIR) was first used to analyze the secondary structure. The contents of three RSF secondary structures were obtained by the peak separation of amide Ⅰ region, and specifically, the recycled silk with SDS as the coagulation bath had the highest β-folding content. The content of β-folding of recycled silk in the coagulating bath with 75% ethanol was the lowest. In order to further explain the relationship between the mechanical properties and protein structure, X-ray diffraction was used to characterize the crystallization of the three kinds of RSF fibers, and it can be seen that the crystallinity degrees of the regenerated fibers are all low. In order to further explain the relationship between β-folding and the crystallization region, differential scanning calorimetry analysis was carried out for the three kinds of RSF, which confirmed the presence of β-folding in large quantities in RSF(SDS) fiber samples. The effect of SDS on silk fibroin protein was characterized by fluorescence probe. The results show that the surface of silk fibroin protein can produce more β-folds at the same time in the presence of SDS. In this study, SDS was used as the coagulating bath for wet spinning, anionic surfactant was innovatively introduced as the composition of coagulating bath, and a recycled silk material with high extensibility was obtained, providing a new research idea for silk fibroin protein wet spinning. In this paper, only the influence of the coagulation bath on the properties of recycled silk has been investigated, and the influence of post-treatment on the properties of recycled silk has not been involved. RSF(SDS) fibers, with excellent fracture elongation, can be treated to further improve the properties of recycled silk fibers. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs), obtained from natural resources, possess great potential as a bioderived reinforcement for natural-fiber-reinforced composites (NFRPs) due to their superior crystallinity and high aspect ratio. To elucidate the specific parameters of CNCs that significantly affect their mechanical performance, various CNCs were investigated to fabricate high-performance nanocomposite fibers together with regenerated silk fibroin (RSF). We confirmed that the high aspect ratio (~9) of the CNCs was the critical factor to increase the tensile strength and stiffness rather than the crystallinity. At a 1 vol% of CNCs, the strength and stiffness reached ~300 MPa and 10.5 GPa, respectively, which was attributed not only to a stable dispersion but also to alignment. This approach has the potential to evaluate the parameters of natural reinforcement and may also be useful in constructing high-performance NFRPs. [ABSTRACT FROM AUTHOR]

This study aims to utilize the thermosetting behavior of native lignin and the self-assembly of silk in coconut coir (CC) and regenerated silk (RS) microparticles used as blends and natural binders for construction and demolition waste (CDW) wood and their effect on the mechanical, thermal, and structural properties of CDW wood/CC, RS/CC, and CDW wood/RS biomicrocomposites. The obtained biomicrocomposites were prepared by hot-pressing blended microparticles at weight ratios of 80:20, 60:40, 50:50, 40:60, and 20:80 in the temperature range of 170–180°C. The obtained biomicrocomposites were characterized by bending strength, water resistance, scanning electron microscopy (SEM), thermogravimetric analysis/derivative thermogravimetry (TGA/DTG), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements. Findings showed that the incorporation of RS displayed superior enhancement in the mechanical properties and water resistance in CDW/RS. The incorporation of CC slightly improved these properties in CDW/CC and RS/CC but offered greater thermal stability, as shown by thermogravimetric analysis (TGA/DTG). The addition of RS and CC showed good interfacial adhesion, as revealed by SEM. FTIR data revealed strong reactivity among CC, RS, and CDW wood. [ABSTRACT FROM AUTHOR]

This study illustrates the sensing and wound healing properties of silk fibroin in combination with peptide patterns, with an emphasis on the printability of multilayered grids, and envisions possible applications of these next-generation silk-based materials. Functionalized silk fibers covalently linked to an arginine–glycine–aspartic acid (RGD) peptide create a platform for preparing a biomaterial ink for 3D printing of grid-like piezoresistors with wound-healing and sensing properties. The culture medium obtained from 3D-printed silk fibroin enriched with RGD peptide improves cell adhesion, accelerating skin repair. Specifically, RGD peptide-modified silk fibroin demonstrated biocompatibility, enhanced cell adhesion, and higher wound closure rates at lower concentration than the neat peptide. It was also shown that the printing of peptide-modified silk fibroin produces a piezoresistive transducer that is the active component of a sensor based on a Schottky diode harmonic transponder encoding information about pressure. We discovered that such biomaterial ink printed in a multilayered grid can be used as a humidity sensor. Furthermore, humidity activates a transition between low and high conductivity states in this medium that is retained unless a negative voltage is applied, paving the way for utilization in non-volatile organic memory devices. Globally, these results pave the way for promising applications, such as monitoring parameters such as human wound care and being integrated in bio-implantable processors. [ABSTRACT FROM AUTHOR]

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In this study, we fabricated adhesive patches from silkworm-regenerated silk and DNA to safeguard human skin from the sun’s rays. The patches are realized by exploiting the dissolution of silk fibers (e.g., silk fibroin (SF)) and salmon sperm DNA in formic acid and CaCl2 solutions. Infrared spectroscopy is used to investigate the conformational transition of SF when combined with DNA; the results indicated that the addition of DNA provides an increase in the SF crystallinity. UV–Visible absorption and circular dichroism spectroscopy showed strong absorption in the UV region and the presence of B-form of DNA once dispersed in the SF matrix, respectively. Water absorption measurements as well as thermal dependence of water sorption and thermal analysis, suggested the stability of the fabricated patches. Biological results on cellular viability (MTT assay) of keratinocyte HaCaT cells after exposures to the solar spectrum showed that both SF and SF/DNA patches are photo-protective by increasing the cellular viability of keratinocytes after UV component exposure. Overall, these SF/DNA patches promise applications in wound dressing for practical biomedical purposes.

Taking inspiration from plant tendril geometry, in this study, 4D bimorph coiled structures with an internal core of graphene nanoplatelets‐modified regenerated silk and an external shell of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) are fabricated by 4D printing. Finite element simulations and experimental tests demonstrate that integrating these biomaterials with different coefficients of thermal expansion results in the temperature induced self‐compression and torsion of the structure. The bimorph spring also exhibits reversible contractive actuation after exposure to water environment that paves its exploitation in regenerative medicine, since core materials also have been proven to be biocompatible. Finally, the authors validate their findings with experimental measurements using such springs for temperature‐mediated lengthening of an artificial intestine. [ABSTRACT FROM AUTHOR]

In this study, we report the fabrication of two different three-dimensional (3D) architectures of regenerated silk (RS) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with embedded functionalities. 3D printed cylinders with an internal layer of PHBV and an external of calcium ions (Ca++) or potassium nitrate (KNO3) modified RS were designed to control the radial shrinkage, water uptake and compression strength. Such cylinders were then used as sutureless thermoresponsive clips, measuring the bursting resistance once applied on an anastomized porcine intestine. Experimental data are supported by finite element simulations that model the tube contraction, demonstrating the possibility to program the shape-changing behavior of 3D printed structures. Printing RS on PHBV, we obtained responsive 3D grids to external force with self-powering properties. The synergic effect obtained by combining materials on appropriate architectures paves the way to potential clinical applications ranging from monitoring of vital signs to sutureless sealant patches.

Issues of fossil fuel and plastic pollution are shifting public demand toward biopolymer-based textiles. For instance, silk, which has been traditionally used during at least 5 milleniums in China, is re-emerging in research and industry with the development of high-tech spinning methods. Various arthropods, e.g. insects and arachnids, produce silky proteinic fiber of unique properties such as resistance, elasticity, stickiness and toughness, that show huge potential for biomaterial applications. Compared to synthetic analogs, silk presents advantages of low density, degradability and versatility. Electrospinning allows the creation of nonwoven mats whose pore size and structure show unprecedented characteristics at the nanometric scale, versus classical weaving methods or modern techniques such as melt blowing. Electrospinning has recently allowed to produce silk scaffolds, with applications in regenerative medicine, drug delivery, depollution and filtration. Here we review silk production by the spinning apparatus of the silkworm Bombyx mori and the spiders Aranea diadematus and Nephila Clavipes. We present the biotechnological procedures to get silk proteins, and the preparation of a spinning dope for electrospinning. We discuss silk's mechanical properties in mats obtained from pure polymer dope and multi-composites. This review highlights the similarity between two very different yarn spinning techniques: biological and electrospinning processes. [ABSTRACT FROM AUTHOR]

The development of bio-glues is still a challenging task, regarding adhesion on wet surfaces; often, high performance and adaption to complex geometries need to be combined in one material. Here, we report biocompatible adhesives obtained by blending regenerated silk (RS) with a soluble plant-derived polyphenol (i.e., chestnut tannin) that was also used to exfoliate graphite to obtain graphene-based RS/tannin (G-RS/T) composites. The resultant G-RS/T hybrid material exhibited outstanding stretchability (i.e., 400%) and high shear strength (i.e., 180 kPa), superior to that of commercial bio-glues, and showed sealant properties for tissue approximation. Moreover, we showed how such nanocomposites exhibit electromechanical properties that could potentially be used for the realization of green and eco-friendly piezoelectric devices. Finally, we demonstrate the in vitro glue’s biocompatibility and anti-oxidant properties that enable their utilization in clinical applications.

Regenerated silk fibers were fabricated through dry-wet spinning process using N-methyl morpholine N-oxide and methanol as solvent and coagulant, respectively. Several concentrations of poly (hexamethylene) biguanide (PHMB) (0.27, 0.41, and 0.55 mL per 1 g of fibroin) and silver nanoparticles (AgNPs) (0.0005, 0.0015, 0.0055, 0.0095, and 0.0135% (w/v) were used as antibacterial agents. Antibacterial property of bio-fibers produced by either master batch or dipping methods was compared to each other against a gram-positive bacterium, Staphylococcus aurous. Master batch process indicated the dependency of antibacterial effect on the concentration of antibacterial agents as well as particle size. Maximum bactericidal activity in this process was obtained at concentrations of 0.0055% of AgNPs and 0.55 mL of PHMB per 1 g of fibroin. However for long-lasting effect and from toxicity aspect PHMB with lower concentration (0.27 mL) and with 0.0055% AgNP was seemed to be ideal. The result from dipping process showed that various concentrations of PHMB can greatly influence on the results; the interaction of 0.0055% AgNPs and 0.41 mL of PHMB offered good antibacterial properties with the least amount of toxicity effect in human cells.

Regenerated silk (RS) is a natural polymer that results from the aggregation of liquid silk fibroin proteins. In this work, we observed that RS dispersed in aqueous solution undergoes a reversible solid/liquid transition by programmed heating/cooling cycles. Fourier transform infrared, atomic force microscopy imaging and Raman measurements of the RS reveal that the transition from random coil to β-sheet structures is involved in this liquid–solid transition. The reversible solid-liquid transition of silk fibroin was then found to be helpful to prepare polymer-like carbon nanotube (CNT) dispersions. We demonstrate that the gelation of RS makes the CNTs with the consistency of a dough with polymeric behavior. Such RS can disperse carbon nanotubes at high concentrations of tens of weight percent. Finally, such carbon nanotube dough has been used for the realization of rubber composites. With this method, we pave the way for handling nanopowders (e.g. CNTs or graphene related materials) with safety and reducing the filler volatility that is critical in polymer-processing.

Regenerated silk fibers were fabricated through dry-wet spinning process using N-methyl morpholine N-oxide and methanol as solvent and coagulant, respectively. Several concentrations of poly (hexamethylene) biguanide (PHMB) (0.27, 0.41, and 0.55 mL per 1 g of fibroin) and silver nanoparticles (AgNPs) (0.0005, 0.0015, 0.0055, 0.0095, and 0.0135% (w/v) were used as antibacterial agents. Antibacterial property of bio-fibers produced by either master batch or dipping methods was compared to each other against a gram-positive bacterium,Staphylococcus aurous. Master batch process indicated the dependency of antibacterial effect on the concentration of antibacterial agents as well as particle size. Maximum bactericidal activity in this process was obtained at concentrations of 0.0055% of AgNPs and 0.55 mL of PHMB per 1 g of fibroin. However for long-lasting effect and from toxicity aspect PHMB with lower concentration (0.27 mL) and with 0.0055% AgNP was seemed to be ideal. The result from dipping process showed that various concentrations of PHMB can greatly influence on the results; the interaction of 0.0055% AgNPs and 0.41 mL of PHMB offered good antibacterial properties with the least amount of toxicity effect in human cells. [ABSTRACT FROM PUBLISHER]

Silk has attracted the attention of biomedical researchers because of its good biocompatibility. Although various characteristics of silk are needed for its successful application in biomedical fields, the performance of silk material is limited. Although there are many varieties of Bombyx mori silkworm, the effect of different silkworm varieties on regenerated silk has not been considered in detail. That is, the use of a diverse variety of silkworms has not been considered in non-textile applications resulting in limited performance of silk materials. In this study, the effects of different silkworm varieties on the structural characteristics and properties of silk cocoon and regenerated silk fibroin (SF) were examined. Structural characteristics of silk cocoon including color, fiber diameter, and porosity, differed depending on the silkworm variety. Furthermore, molecular weight, solution viscosity, and mechanical properties of regenerated SF were influenced by the variety of silkworm, while the amino acid composition, β-sheet crystallization by formic acid, and cyto-compatibility of regenerated SF did not differ between the samples from different varieties of silkworm. These results imply that diverse performance of silk can be obtained by controlling the silkworm variety, and that the use of different varieties of silkworm might be a good way to strengthen the performance of silk in biomedical fields. [ABSTRACT FROM AUTHOR]

Abstract: Electro-spun silk webs are potentially good candidates as tissue engineering scaffolds owing to their good bio- and cyto-compatibility. However, the low fabrication rate of electro-spun silk mats has been one of the obstacles in the mass production of such nanofibrous silk mats in applications to the biomedical field. In this study, the effects of degumming ratio and silk concentration on the electro-spinning process were investigated by using regenerated silk with different residual sericin contents and different silk concentrations in terms of the morphology and structure of the electro-spun silk web. The rate of production of electro-spun silk mats could be increased by approximately 5 fold at a degumming ratio of 19.5%. The electro-spinning rate of silk was affected by two main factors: (1) dope solution viscosity and (2) degumming ratio of silk. The conductivity of the silk dope solution, however, had little effects on the electro-spinning of regenerated silk. A constant spun fiber morphology was observed within the electro-spinning rate range (0.3–1.4ml/h). Fourier transform infrared spectroscopy showed that partial β-sheet crystallization occurred during electro-spinning. The molecular conformation was relatively unaffected by the electro-spinning rate of silk. [Copyright &y& Elsevier]

Abstract: The application of silk on tissue engineering scaffolds has been studied intensively because silk has an electrospinning technique using a good blood compatibility, excellent cytocompatibility and biodegradability. Silk consists of two polymers, fibroin and sericin. In spite of importance of sericin, most studies were focused on the fibroin only and the effect of residual sericin on the electrospinning performance of silk has not been considered. In this study, regenerated silk with different residual sericin contents was prepared by controlling the degumming conditions. The effects of the degumming conditions on the solution properties and electrospinning performance of silk were examined. The fast protein liquid chromatography (FPLC) measurements confirmed that the molecular weight of the regenerated silk decreased slightly with increasing residual sericin content. More molecular aggregation of silk occurred with increasing sericin content, resulting in an increase in the solution turbidity of formic acid. All silk formic acid solutions exhibited almost Newtonian fluid behavior and the viscosity increased with increasing sericin content. Interestingly, the dope solution viscosity of silk increased remarkably at sericin contents <1% (or degumming ratio >25%) leading to significant improvements in electrospinnability and an increase in the fiber diameter of the silk web. [Copyright &y& Elsevier]

Abstract: Making artificial fibers inspired in spider silks is considered as one of the milestones in the field of biomimetics. The interest is usually justified by the outstanding tensile properties of natural fibers, but it is usually overlooked that spider silk is endowed with a number of related properties – supercontraction, recovery and the existence of a ground state – that impart the material with additional desirable features, such as the possibility of tuning its mechanical behaviour. In this work we present a review on the experimental analysis and significance of these properties, stressing the contributions of our research group to the field. It is also demonstrated how the knowledge gained in the basic study of the natural material has been essential for the improvement of the properties exhibited by artificially processed bio-inspired silk fibers. [Copyright &y& Elsevier]

The present review is devoted to the application of biomaterials from regenerated silk for designing tissue-engineered constructs-the basis for hybrid organs and tissues. Fibroin, the main structural protein of silkworm silk, can be used to design artificial cartilages, bone tissue fragments, blood vessels, as well as to regenerate nervous tissue. Fibroin capsules containing bioactive compounds are successfully applicable in medicinal therapy, such as controlled drug delivery in cancer treatment. Apart from fibroin, tissue engineering can successfully be based on biopolymer spidroin, a spider net protein, which is also a biocompatible material with valuable mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: Silk nanofibers were successfully prepared by electrospinning an aqueous solution of regenerated silk fibroin (RSF, from Bombyx mori) with higher molecular weight. Many factors, such as concentration, electrical conductivity of the fibroin solution and applied electric field were found to influence the morphology of these nanofibers. The conformation of RSF nanofibers was transformed from random coil/helical to β-sheet after the post treatment with pure ethanol. Under optimal conditions, the as-spun non-woven mats achieved good mechanical properties. The apparent stress and strain at break were 11.1±0.7 MPa and 10.2±1.6%, respectively, which is important for the application of such a unique fibrous protein. [Copyright &y& Elsevier]

Abstract: The microstructures of N-methylmorpholine-N-oxide (NMMO) regenerated silk fibers have been characterized by atomic force microscopy from the micrometer to the nanometer scale and compared with those previously found from natural silks. Regenerated fibers show poor tensile properties and a brittle behavior, but their mechanical properties improve if subjected to post-spinning drawing. Consequently, it was hypothesized that post-spinning drawing would lead to a microstructure more similar to that of the natural material. Here we show that the microstructure of the samples not subjected to post-spinning drawing is composed of nanoglobules that differ from those found in natural silkworm silk both in size and orientation with respect to the macroscopic axis of the fiber. The microstructure of samples subjected to post-spinning drawing evolves in the sense of decreasing the size but increasing the orientation of the nanoglobules, but these effects are only observed in some regions of the fibers. [Copyright &y& Elsevier]

Flexible and biocompatible adhesives with sensing capabilities can be integrated onto human body and organ surfaces, characterized by complex geometries, thus having the potential to sense their physiological stimuli offering monitoring and diagnosis of a wide spectrum of diseases. The challenges in this innovative field are the following: (i) the coupling method between the smart adhesive and the soft human substrates, (ii) the bioresorbable behavior of the material, and (iii) the electrical exchange with the substrate. Here, we introduce a multifunctional composite by mixing silk fibroin, featuring piezoelectric properties, with a soluble plant-derived polyphenol ( i.e. , chestnut tannin) modified with graphene nanoplatelets. This material behaves as a glue on different substrates and gives rise to high elongation at break, conformability, and adhesive performances to gastrointestinal tissues in a rat model and favors the printability via extrusion-based 3D printing. Exploiting these properties, we designed a bioresorbable 3D printed flexible and self-adhesive piezoelectric device that senses the motility once applied onto a phantom intestine and the hand gesture by signal translation. Experimental results also include the biocompatibility study using gastrointestinal cells. These findings could have applicability in animal model studies, and, thanks to the bioresorbable behavior of the materials, such an adhesive device could be used for monitoring the motility of the gastrointestinal tract and for the diagnosis of motility disorders.

Wet spinning of silkworm silk has the potential to overcome the limitations of the natural spinning process, producing fibers with exceptional mechanical properties. However, the complexity of the extraction and spinning processes have meant that this potential has so far not been realized. The choice of silk processing parameters, including fiber degumming, dissolving, and concentration, are critical in producing a sufficiently viscous dope, while avoiding silk's natural tendency to gel via self-assembly. This study utilized recently developed rapid Bayesian optimization to explore the impact of these variables on dope viscosity. By following the dope preparation conditions recommended by the algorithm, a 13% (w/v) silk dope was produced with a viscosity of 0.46 Pa·s, approximately five times higher than the dope obtained using traditional experimental design. The tensile strength, modulus, and toughness of fibers spun from this dope also improved by a factor of 2.20×, 2.16×, and 2.75×, respectively. These results represent the outcome of just five sets of experimental trials focusing on just dope preparation. Given the number of parameters in the spinning and post spinning processes, the use of Bayesian optimization represents an exciting opportunity to explore the multivariate wet spinning process to unlock the potential to produce wet spun fibers with truly exceptional mechanical properties.