Flat-Silk-Cocoon-Based Wearable Flexible Piezoresistive Sensor and Its Performance.

Flexible sensors are becoming the focus of research because they are very vital for intelligent products, real-time data monitoring, and recording. The flat silk cocoon (FSC), as a special form of cocoon, has all the advantages of silk, which is an excellent biomass carbon-based material and a good choice for preparing flexible sensors. In this work, a flexible piezoresistive sensor was successfully prepared by encapsulating carbonized flat silk cocoons (CFSCs) using an elastic matrix polydimethylsiloxane (PDMS). The sensing performance of the material is 0.01 kPa-1, and the monitoring range can reach 680.57 kPa. It is proved that the sensor can detect human motion and has excellent durability (>800 cycles). In addition, a sensor array for a keyboard based on CFSCs was explored. The sensor has a low production cost and a simple preparation process, and it is sustainable and environmentally friendly. Thus, it may have potential applications in wearable devices and human-computer interactions.

PX478-loaded silk fibroin nanoparticles reverse multidrug resistance by inhibiting the hypoxia-inducible factor.

Multidrug resistance (MDR) is the main cause of clinical chemotherapy failure, and new strategies to overcome MDR are needed. We report multi-responsive silk fibroin nanoparticles (SFNs) co-loaded with the chemotherapeutic drug doxorubicin (DOX) and PX478 (a hypoxia-inducible factor inhibitor), which was functionalized with folic acid (FA). This combination could actively target tumor cells and respond to the release of PX478, inhibit the hypoxia-inducible factor (HIF) gene and its related downstream drug-resistant target genes. The FA-PX478-DOX-SFNs (F-P-D-S) combination showed accelerated drug release profiles in the media simulating the tumor microenvironment, which had acidic pH, high levels of reactive oxygen species and high levels of glutathione. Compared with PX478-DOX-SFNs (P-D-S) without targeted modification, the cellular uptake rate of F-P-D-S increased. In addition, F-P-D-S quickly achieved lysosomal escape, enabling DOX to rapidly enter the nucleus to kill the drug-resistant cells. A cytotoxicity test indicated that the IC50 of DOX against MCF-7/ADR cells was 1.0 µg/mL in F-P-D-S, which was 26 times lower than that of free DOX (25.6 µg/mL). F-P-D-S significantly down-regulated HIF-1α, MDR1, VEGF and GLUT-1 and P-gp protein to overcome multidrug resistance. This effective synergistic chemotherapy strategy for HIF inhibition has potential for use in the treatment of multidrug-resistant tumors.

Electrospinning Silk Fibroin/Graphene Nanofiber Membrane Used for 3D Wearable Pressure Sensor.

With the improvement of science and technology, flexible sensors have become a hot research topic. Flexible sensors have broad application in human health detection and motion detection and other fields. In this paper, the silk fibroin/graphene nanofiber membranes were prepared by double needle electrospinning. In addition, the high sensitivity of the three-dimensional composite hierarchy was obtained by superimposing a monolayer silk fibroin/graphene nanofiber membrane, which was prepared via double needle electrospinning. In addition, the three-dimensional hierarchy was encapsulated by polydimethylsiloxane to prepare a pressure sensor. The sensitivity of the pressure sensor can achieve 7.7 Pa−1. In addition, this pressure sensor has excellent durability (>2000 cycles) and shorter response times (490 ms), which has broad research prospects in human health detection and motion detection.

ε-Poly-l-lysine-modified natural silk fiber membrane wound dressings with improved antimicrobial properties.

Many complex diseases, such as bacterial infections, frequently accompany cutaneous wound healing, adding to the difficulty of clinical wound management. Consequently, in addition to displaying strong biocompatibility and actively promoting wound healing, an optimal wound dressing should also possess antimicrobial qualities to address issues with bacterial infection. This paper developed natural silk fiber (SF) membranes (also known as a flat silk cocoon (FSC)) with antimicrobial properties as a dressing for skin wounds. By changing the spinning tools and environment of silkworm larvae, a novel natural SF membrane with a cocoon structure and controllable size was prepared. The functional SF membranes were obtained via a hot press process and grafted with ε-Poly-l-lysine (EPL). The results showed that the SF membrane dressing was adjustable in size with a similar structure to the extracellular matrix (ECM), displaying inherent mechanical properties, excellent antimicrobial qualities, and biocompatibility. In vivo experiments using a full-thickness skin defect model indicated that EPL-modified SF membranes significantly promoted the rate of wound healing, exhibiting thicker granulation tissue and higher collagen disposition than commercial dressings (Tegaderm™ film). Therefore, the excellent mechanical qualities and cytocompatibility of the antimicrobial EPL-modified SF membranes substantially promote their potential application as a chronic wound dressing.

Preparation and characterization of silk fibroin/polyethylene oxide nanofiber membranes with antibacterial activity.

Bacterial infection is among the most common diseases that threaten human health. Antibiotics are effective in treating bacterial infections. However, the overuse of antibiotics will lead to an increase in bacterial resistance. To reduce the overuse of antibiotics and improve the effective use of antibiotics through slow release, silk fibroin (SF)/polyethylene oxide (PEO) nanofiber membranes with different SF and PEO proportions were prepared by electrospinning. The ecofriendly solvent ethanol solution was used for electrospinning for better protection of antibiotic activity. The SEM showed that the surface of SF/PEO (2:8) and SF/PEO (3:7) was smoother and more uniform. With the increase of SF content, the thermal stability and hydrophilicity of SF/PEO nanofiber membranes were improved. The SF/PEO (3:7) nanofiber membrane had the best mechanical property and its maximum stress and strain were 4.6 1 ± 0.24 MPa and 16.36 ± 0.41%, respectively. Based on these good properties, SF/PEO (3:7) nanofiber membrane was chosen for loading and releasing gentamicin sulfate (GS). The fabricated (GS)/SF/PEO (3:7) nanofiber membrane exhibited good release efficiency and showed the good antibacterial activity against Staphylococcus aureus and Escherichia coli. These investigations indicated the GS/SF/PEO (3:7) nanofiber membrane (GS/SF/PEO) has a great potential for application in antibacterial materials.

Skin-friendly corrugated multilayer microspherical sensor fabricated with silk fibroin, poly (lactic-co-glycolic acid), polyaniline, and kappa-carrageenan for wide range pressure detection.

To enlarge the linear detection range without sacrificing the sensitivity is one of the urgent problems in the development of high-performance piezoresistive flexible sensors. Inspired by a multilayer corrugated board, this study develops a new multilayer microspherical sensor in which conductive core-shell SiO2/Polyaniline (PANI) (PS) microspheres serve as active particles, while insulated silk fibroin (SF)/poly lactic-co-glycolic acid (PLGA) (SP) fibers are used as the support. The size of conductive microspheres attached to the insulated layer is controllable. The multiple layers of assembly endow the flexible sensor with a high sensitivity (0.071 kPa-1) and a wide linear detection (from 10 Pa to 380 kPa) simultaneously. This corrugated sensor also have a fast response time (145 ms) and an excellent durability (over 2000 cycles), and it can be used to detect human joint pressure signals and transmit encrypted information. Moreover, flexible keyboard, safety protection of machinery, as well as object position tracking can be achieved based on this sensor. Most importantly, the sensor encapsulated by biological polysaccharide kappa-carrageenan (KC) is skin-friendly and breathable, and it can be decomposed in 90 °C hot water. In conclusion, this multilayer microspherical sensor presents great potential for flexible wearable devices.

Electrospun PLGA/SF/artemisinin composite nanofibrous membranes for wound dressing.

Combining biodegradable materials with natural plant components for wound dressing has been receiving significant attention. ART is a sesquiterpene lactone compound extracted from Artemisia annua L., possessing multiple pharmacological effects including antibacterial activity and anti-inflammatory property. Herein, the blended polylactic acid glycolic acid (PLGA)/silk fibroin (SF) membranes loaded with artemisinin (ART) are fabricated through electrospinning. With aid of SF, the fabricated membranes have a good sustained-release effect, and the accumulated ART release can reach 69% after three weeks. PLGA/SF/ART membranes exhibit favorable anti-inflammatory and cell compatibility in vitro evaluations. The in vivo experiment indicates that PLGA/SF/ART2 membranes can shorten the inflammation period and enhance skin regeneration in a full-thickness wound model through down-regulating the expressions of pro-inflammatory cytokines IL-1ß and TNF-α. To sum up, the fabricated PLGA/SF/ART2 composite membranes with anti-inflammatory properties can be a proposal wound dressing for chronic wound healing.

Multifunctional Dual Ionic-Covalent Membranes for Wound Healing.

Wound healing generally has four stages: hemostasis, inflammation, proliferation, and remolding. Most wound dressings only just take one or two phases into account. Herein, to develop a novel wound dressing that works at different stages, the blended alginate sodium/carboxymethyl chitosan membranes with a hydrogel-like structure are fabricated through a freeze-drying process together with a dual-ion (Sr2+ and Zn2+) cross-linking approach. The fabricated membranes show excellent properties in the swelling ratio, water vapor transmission rate, tensile strength, sustained release, cell adhesiveness, and biocompatibility, proving its general performance for application in wound healing. In particular, the membranes with optimal ion concentrations of 45 mM Sr2+ and 0.74 mM Zn2+ presented the antibacterial activity and accelerating function of wound healing. More specifically, the formation of epithelium and blood vessels is evidently advanced compared with a commercial dressing in vivo experiment, and the expression of main growth factors such as epidermal growth factor, basic fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor is upregulated which also have good effects on the remolding of skin. The prepared wound dressings in this study have good effects on each stage of wound healing, which is important for the healing of chronic wounds. It provides more choices for wound healing, especially for chronic wound healing.

Artemisinin is highly soluble in polyethylene Glycol 4000 and such solution has multiple biological effects.

Artemisinin has a significant role in treatment of malaria, as well as effective anti-inflammatory and anti-cancer activities. However, such problems as poor water solubility and easy recrystallization limit its application. In this study, polyethylene glycol, a solvent which is widely used in pharmaceutics, was introduced to prepare an artemisinin dissolution. Under the action of hydrogen bonding in 12% polyethylene glycol 4000 solvent, the maximum solubility of artemisinin could reach up to 1 mg/mL. Meanwhile, biological functions of such artemisinin solution were evaluated. The obtained artemisinin solution had a significant inhibitory effect on Gram-positive bacteria, Gram-negative bacteria and fungi. As for the anti-inflammatory property, 0.031 mg/mL artemisinin solution had an obvious inhibitory effect on nitric oxide release in inflammatory cells, and the survival rate of cells was greater than 50%. Low concentration of the obtained artemisinin solution (0.031 mg/mL) had no significant cytotoxicity, while it displayed selective inhibition in cancer cells. IC50 for human hepatoma cells BEL-7404, SMMC7721 and Hep G2 is 0.0016 mg/mL, 0.0084 mg/mL and 0.0541 mg/mL, respectively. In conclusion, the 12% PEG4000-assisted artemisinin solution has a good biological effect and it can be further applied in pharmaceutics, biomaterials and medicine.

Fabrication of silk fibroin/poly(lactic-co-glycolic acid)/graphene oxide microfiber mat via electrospinning for protective fabric.

In this study, a biodegradable silk fibroin/poly(lactic-co-glycolic acid)/graphene oxide (SF/PLGA/GO) microfiber mat was successfully fabricated via electrospinning for use in protective fabrics. The morphology of the microfiber mat was characterized by Scanning Electron Microscope (SEM). The thermal and mechanical properties, water contact angle, surface area and pore size of the microfiber mats were characterized. Due to the introduction of graphene which can interact with silk fibroin, the SF/PLGA/GO microfiber mat, compared with the silk fibroin/poly (lactic-co-glycolic acid) (SF/PLGA) microfiber mat, has higher strength, greater Young's modulus and better thermal stability which can meet the requirements of protective fabric. The microfiber mat is biodegradable because its main component is silk fibroin and PLGA. In particular, the microfiber mat has a small pore size range of 4 ∼ 10 nm in diameter, a larger surface area of 2.63 m2 g-1 and pore volume of 7.09 × 10-3 cm3 g-1. The small pore size of the mat can effectively block the particulate pollutants and pathogenic particles in the air. The larger surface area and pore volume of the mat are effective for breathability. Therefore, the fabricated SF/PLGA/GO microfiber mat has great application potentials for protective fabrics.

Structure analysis of the spinneret from Bombyx mori and its influence on silk qualities.

Silk is an excellent natural fiber, which has been widely used in versatile fields. Silk spinning is a complex process involving the larval spinneret. The spinneret is essential for silk spinning, but the sectional morphology of the spinneret that determines the silk monofilament, the muscular activities around the silk press as well as the relationships between the spinneret and the properties of the resulting silk remain poorly understood. We studied these factors by dissecting the spinneret and analyzing silk from different Bombyx mori strains. The sectional morphology of silk monofilament was found to be largely determined by the spinneret, especially by the silk press. Moreover, contractile activity of the muscles around the silk press is high, and the contraction frequency of the muscles was estimated to range from 11.42 to 50 HZ. A comparison of the fibroin filaments before they entered the common tube indicated that the spinneret determines both silk shape and silk size. This study provides insight into the silk spinning process, which may help develop bionic spinning in further studies and also provides a rationale to study the effect of the spinneret on silk fineness at the molecular level.

Effect of Different Additives in Diets on Secondary Structure, Thermal and Mechanical Properties of Silkworm Silk.

In this study, eight types of materials including nanoparticles (Cu and CaCO3), metallic ions (Ca2+ and Cu2+), and amino acid substances (serine, tyrosine, sericin amino acid, and fibroin amino acid) were used as additives in silkworm diets to obtain in-situ modified silk fiber composites. The results indicate that tyrosine and fibroin amino acids significantly increase potassium content in silk fibers and induce the transformation of α-helices and random coils to ß-sheet structures, resulting in higher crystallinities and better mechanical properties. However, the other additives-modified silk fibers show a decrease in ß-sheet contents and a slight increase or even decrease in tensile strengths. This finding provides a green and effective approach to produce mechanically enhanced silk fibers with high crystallinity on a large scale. Moreover, the modification mechanisms of these additives were discussed in this study, which could offer new insights into the design and regulation of modified fibers or composites with desirable properties and functions.

Natural Silkworm Cocoon Composites with High Strength and Stiffness Constructed in Confined Cocooning Space.

In this study, using round paper tubes (PTs) and rectangular cardboard boxes (CBs) as external constraints to control the size of the cocooning space, we fabricated a series of modified silkworm cocoons (PT cocoons and CB cocoons). Their microstructures, morphologies, compositions, and mechanical properties were characterized and compared with normal silkworm cocoons. These two kinds of modified silkworm cocoons exhibit dense and homogeneous layer structures. Tensile test results indicate that above a size limit of cocooning space, their tensile strengths, Young's moduli, and strain energy densities increase with the decrease in cocooning space. Especially in comparison with the normal cocoons, the tensile strength and Young's modulus of the PT-14 cocoon increase by 44% and 100%, respectively. Meanwhile, PT cocoons and CB cocoons, except PT-12, also possess better peeling resistance than normal cocoons. Owing to the dense structure and low porosity, the modified cocoons form robust fiber networks that result in high strength and toughness. This study provides a green and efficient method to fabricate mechanically enhanced silkworm cocoons with special shapes and dense layer structures. The method can be easily subjected to further modification processes and has potential applications in the production of high-performance green cocoon composites and biomimetic materials.