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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.

In this study, regenerated silk (RS) obtained from Bombyx Mori cocoons is compounded with carboxyl-functionalized carbon nanotubes (f-CNTs) in an aqueous environment for the fabrication of functional bio-adhesives. Molecular interactions between RS and carboxyl groups of CNTs result in structural increase of the β-sheet formation, obtaining a resistant adhesive suitable for a wet biological substrate. Moreover, the functionalization of CNTs promotes their dispersion in RS, thus enabling the production of films with controlled electrical conductivity. The practical utility of such a property is demonstrated through the fabrication of a piezoelectric device implanted in a rat to monitor the breathing in vivo and to be used as a self-powered system. Finally, RS/f-CNTs were used as a printable biomaterial ink to three dimensionally print bilayer hollow tubular structures composed of poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) and RS. Initial tests carried out by seeding and growing human skin fibroblasts demonstrated that the 3D printed bilayer hollow cylindrical structures offer a suitable surface for the seeded cells to attach and proliferate. In general, the herein proposed RS/f-CNT composite serves as a versatile material for solvent-free dispersion processing and 3D printing, thus paving a new approach to prepare multifunctional materials with potential applications of great interest in sealing biological substrates and implantable devices for regenerative medicine.

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.

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., (Copyright © 2015 Elsevier B.V. All rights reserved.)

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 (0.3-1.4 ml/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 © 2013 Elsevier B.V. All rights reserved.)

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 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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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]

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]

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]

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]

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 (KNO 3) 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. Unlabelled Image • 3D printing of hybrid natural proteins and bio-based polymers • Digitally designed 3D objects with self-powering properties • Modeling the different thermal coefficient of expansion of the protein layer onto a biopolymer • Engineering strategy to seal an anastomosis without the aid of mechanical sutures [ABSTRACT FROM AUTHOR]