Silk Layer Research Articles

Fabrics tested for their ability to filter aerosols

Tightly woven cotton, such as that used to make high-thread-count sheets; four layers of silk; and mixtures of fabric, such as cotton and flannel or cotton and chiffon, are good materials for making masks to prevent the spread of the novel coronavirus, SARS-CoV-2, scientists report. According to a new study, masks made from these fabrics are good at filtering saltwater aerosols 10 nm to 6 µm—the same size as droplets that are known to spread respiratory viruses (ACS Nano 2020, DOI: 10.1021/acsnano.0c03252). Droplets this size tend to stay suspended in air. Last month, upon learning the Centers for Disease Control and Prevention would recommend that people wear face coverings, scientists at the Pritzker School of Molecular Engineering, the University of Chicago, and Argonne National Laboratory decided to test the filtration properties of various fabrics. “There was very little scientific data taken with laboratory-grade instruments on this,” says Supratik Guha, who

Silk: A bio-derived coating for optical fiber sensing applications

Optical fiber chemical sensing is generally achieved through attachment of sensor molecules to the fiber, a process that involves chemicals that are not biologically compatible or are limited to thin monolayer coatings. To address these limitations and enable in-vivo biosensing, we report here, for the first time, silk fibroin coating of optical fibers for encapsulating fluorescent sensor molecules. Silica exposed core fiber (ECF) samples were coated with a thin layer of silk – a naturally derived biopolymer composed entirely of proteins and amino acids. The silk was doped with the fluorophore 5,6-carboxynapthofluorescein (CNF), which allows optical measurement of pH by a robust ratiometric fluorescence method. The fluorescent signal from the doped-silk layer is coupled into the core of the ECF, enabling remote measurement of pH along the length of the fiber. We have demonstrated real time in vivo pH sensing measurements in a mouse model of hypoxia. Our results showed a continuous drop in the subcutaneous pH in the mouse lumbar area as hypoxia developed. The work explores, for the first time, the potential of a natural silk protein coating to perform fiber sensing inside the body.

Synthesis, secretion, and antifungal mechanism of a phosphatidylethanolamine-binding protein from the silk gland of the silkworm Bombyx mori

A silkworm cocoon contains several antimicrobial proteins such as protease inhibitors and seroins to provide protection for the enclosed pupa. In this study, we identified a new Bombyx mori phosphatidylethanolamine-binding protein (BmPEBP) with antimicrobial activity in the cocoon silk using semi-quantitative and quantitative RT-PCR, western blotting, and immunofluorescence. The results indicated that BmPEBP was synthesized in the middle silk gland and secreted into the sericin layer of the cocoon silk. Functional analysis showed that BmPEBP could inhibit the spore growth of four types of fungi, Candida albicans, Saccharomyces cerevisiae, Beauveriabassiana, and Aspergillus fumigates, by binding to the fungal cell membrane. Investigation of the interaction of BmPEBP with membrane phospholipids revealed that the protein showed a strong binding affinity to phosphatidylethanolamine, weak affinity to phosphatidylinositol, and no affinity to phosphatidylserine or phosphatidylcholine. Circular dichroism spectroscopy showed that binding to phosphatidylethanolamine caused conformational changes in the BmPEBP molecule by reducing β-sheet formation and inducing the appearance of an α-helix motif. We speculate that BmPEBP performs antifungal function in the cocoon silk through interaction with phosphatidylethanolamine in the fungal membrane.

A New Method for Testing Filtration Efficiency of Mask Materials Under Sneeze-like Pressure

Sneezes produce many pathogen-containing micro-droplets with high velocities of 4.5-50.0 m/s. Face masks are believed to protect people from infection by blocking those droplets. However, current filtration efficiency tests can't evaluate masks under sneeze-like pressure. The goal of this study was to establish a method to evaluate the filtration efficiency of mask materials under extreme conditions. Efficiency of surgical masks, gauze masks, gauze, cotton, silk, linen and tissue paper on blocking micro-droplet sized starch particles (average 8.2 μm) and latex microspheres (0.75 μm) with a velocity of 44.4 m/s created by centrifugation was qualitatively analyzed by using imaging-based analysis. The 4 layers of silk could block 93.8% of microspheres and 88.9% of starch particles, followed by the gauze mask (78.5% of microspheres and 90.4% of starch particles) and the 2 layers of cotton (74.6% of microspheres and 87.5-89.0% of particles). Other materials also blocked 53.2-66.5% of microspheres and 76.4%-87.9% of particles except the 8 layers of gauze which only blocked 36.7% of particles. The filtration efficiency was improved by the increased layers of materials. Centrifugation-based filtration efficiency test not only compensates shortcomings of current tests for masks, but also offers a simple way to explore new mask materials during pandemics. Common mask materials can potentially provide protection against respiratory droplet transmission.

Nontransient silk sandwich for soft, conformal bionic links

• Soft flexible bionic links on nontransient hydrated silk fibroin films are reported. • Silk links conform to the challenging wet slimy surfaces of the biological milieu. • First of its kind development of silk links for the peripheral nerves and the cortex. • Silk links validated through neural recording experiments in an anesthetized rodent model. • Silk bionic links can enable nontransient silk bioelectronics for in vivo use. Soft biointerfaces that maintain intimate contact with the smooth but curved tissue and organ surfaces are critical for providing reliable readouts of in vivo electrical activity. In contrast to conventional biodegradable class of silk scaffolds, we report for the first time, nontransient, or sustainable and implantable silk fibroin bionic interfaces for direct electrical recording of a variety of biopotentials such as neural activity from the peripheral nerves and the cortex. This new class of soft and flexible interfaces are enabled by a silk fibroin-based strategy that relies on substrates and superstrates of nontransient water-stable silk for supporting the electrode constructs. We present SILK-SEAL that involves soft assembly of thin silk layers resulting in a silk sandwich, and QUICK-SILK, an elastomer-silk bandage backing enabling fully functional silk electrode sensors that can be securely deployed in vivo . The resulting novel thin film devices achieve biopotential recording from the peripheral nerve and the cortex in a rodent model, thanks to the thin form factor of the silk film appliqués that enable conformal lamination on the target tissue surfaces, and the adhesive elastomer-silk backing, a suture-free approach that assists in pasting and securing the arrays in place. The neural recording experiments demonstrate a novel mode of use for the silk sensors as non-dissolvable biointerfaces, providing evidence for their application in preclinical research studies. The silk interfaces reported here, serve as the first significant leap towards non-dissolvable silk bioelectronics for in vivo use.

Natural Silk Film for Magnesium Protection: Hydrophobic/Hydrophilic Interaction and Self‐Healing Effect

AbstractBiodegradable implants are required in order to provide successful treatment of injuries. Temporary magnesium‐based implants with particular properties are needed in cases when it is desirable not only to maintain vital activity, but also to initiate the self‐healing process of damaged bones or tissues as well. Unfortunately, the use of magnesium alloys is limited due to the fast biodegradability of the applied material. The aim of this research is to improve the corrosion resistance of magnesium alloys by sonochemical treatment in silk solution followed by additional layer‐by‐layer deposition of natural silk on the magnesium surface. The sonication process is carried out at a frequency of 20 kHz during 5–10 min, while the duration of the silk layer deposition is 15 min. The corrosion behavior of magnesium substrates modified by natural silk layer‐by‐layer assembly is studied. Magnesium substrates sonochemically treated in silk solution demonstrate three times better corrosion resistance compared to control samples sonochemically treated in water. Additional deposition of a silk layer enhances obtained corrosion resistance by 18 times, resulting in a 54‐fold increase overall.

Steady-State Behavior and Endothelialization of a Silk-Based Small-Caliber Scaffold In Vivo Transplantation.

A silk-based small-caliber tubular scaffold (SFTS), which is fabricated using a regenerated silk fibroin porous scaffold embedding a silk fabric core layer, has been proved to possess good cell compatibility and mechanical properties in vitro. In this study, the endothelialization ability and the steady-state blood flow of SFTSs were evaluated in vivo by implanting and replacing a common carotid artery in a rabbit. The results of the color doppler ultrasound and angiographies showed that the blood flow was circulated in the grafts without aneurysmal dilations or significant stenoses at any time point, and ran stronger and close to the autologous blood vessel from one month after implantation. The SFTSs presented an initial tridimensionality without being distorted or squashed. SEM and immunohistochemistry results showed that a clear and discontinuous endodermis appeared after one month of implantation; when implanted for three months, an endothelial layer fully covered the inner surface of SFTSs. RT-PCR results indicated that the gene expression level of CD31 in SFTSs was 45.8% and 75.3% by that of autologous blood vessels at 3 months and 12 months, respectively. The VEGF gene showed a high expression level that continued to increase after implantation.

Interacting Metal-Insulator-Metal Resonator by Nanoporous Silver and Silk Protein Nanomembranes and Its Water-Sensing Application.

Planar and lithography-free metal–insulator–metal (MIM) resonators based on the Fabry–Pérot etalon are attractive for biochemical sensing applications because of their acceptable optical performance and cost-effectiveness. However, injecting analytes into the insulating layer where the optical field is localized (high light–matter interaction) is difficult. Here, planar and lithography-free MIM resonators interacting with their environment are reported. In the MIM, molecules of a liquid can infiltrate the inherent nanopores in the deposited silver nanomembrane and be absorbed into the silk protein hydrogel membrane. The silk layer is swollen when water molecules are absorbed, inducing a large shift in the resonance wavelength. Thus, in this study, the proposed MIM resonator was applied as a highly sensitive water sensor, and a water content as low as 0.008% in organic solvents could be determined by reading the shift in the transmission peak. This limit can be lowered further by using a high-resolution spectrometer and a thicker silk layer. In addition, the area of interaction can be artificially selected by applying an elastomer stamp and a patterned photoresist window.

Imaging of bacteria in burn wounds treated with split-thicknessgrafts in MEEK/MESH technique: a pilot study with first experiences in clinical wound evaluation with autofluorescence

Partial and full thickness burns require surgical treatment, such as early débridement and skin transplantation in MEEK/MESH technique or further reconstructive surgery. Infections of burns or transplanted areas limit surgical success and increase patient mortality. For split-thickness grafts in MEEK technique a superficial silk is applied as a protective on-top dressing, whereas in MESH technique fatty gauze and foam are used as standard protective covers over five to seven days. However, wound occlusion by both materials provides the soil for growth of microorganisms. The timely identification of impending infections is necessary to initiate early removal in order to safe and preserve skin grafts. Early identification of infections and removal of foreign material should therefore be attempted. Burn wounds treated with split-thickness skin grafts processed by MEEK/MESH technique and covered with silk or foam overlayers were analyzed for signs of bacterial infection using the MolecuLight i:X™ device. In addition, swaps for microbiological analysis where taken from fluorescent areas and correlated with florescent image results. We examined burn wounds (n = 14) of three different intensive care patients. The MolecuLight i:X™ camera showed a strong colonization of the transplanted areas and foreign materials, that were in line with microbiological analysis findings. The representation of the excitation load showed high values in the foreign materials. The take rate of MEEK-transplants was 90 % compared to MESH-transplanted with about 60 %. The positive predictive value was 81.8 % for detection of a wound infection with autofluorescence. The negative predictive value was 90.3 % with a sensitivity of 86.7 % and a specificity of 87.5 %. The representation of the fluorescence exciter load shows high concentrations of pathogens both in the MEEK silk layer as well as in foam linkers. Overall split-thickness grafts according to the MEEK technique showed a higher healing rate compared to MESH technique. Screening of burns wounds with autofluorescence imaging can be helpful for an additive wound assessment. Split-thickness graft covers should be applied only for a minimum time period required to ensure stable grafting.

Sterile Capsule-Egg Cocoon Covering Constitutes an Antibacterial Barrier for Spider Parasteatoda tepidariorum Embryos.

Coexistence of organisms and pathogens has resulted in the evolution of efficient antimicrobial defense, especially at the embryonic stage. This investigation aimed to substantiate the hypothesis that the layers of silk in a spider cocoon play a role in the immunity of the embryos against microorganisms present in the external environment. A two-step interdisciplinary attempt has been made. First, the eggs and empty cocoons of the spider Parasteatoda tepidariorum were incubated on lysogeny broth agar media for 3 d. In the samples of eggs, no growth of bacteria was detected. This indicated that the eggs inside cocoons were sterile. Therefore, in the second step, the cocoons and egg surface were analyzed using SEM, TEM, and LM. The obtained images demonstrated that both inner and outer layers of the silk are built of threads of the same diameter, set in an irregular manner, and randomly clustered into groups. The threads in the outer layer were packed more densely than in the inner one. TEM analysis revealed threads of two types of fibrils and their arrangement. The resultant thread tangle of the cocoon, possibly correlated with the ultrastructure of the fibers, seems to be an example of a structure-function relationship playing a crucial ecoimmunological role in spider embryonic development.

Fabrication of silk microcapsules by layer-by-layer desolvation

The procedure to increase shell thickness of multilayer silk microcapsules fabricated by layer-by-layer assembly (LbL assembly) are tedious and time-consuming. To address this, layer-by-layer desolvation (LbL desolvation), a more efficient technique, was developed with PLGA microspheres as sacrificial templates. Due to high efficiency of desolvation in increasing the shell thickness, self-supporting structures were obtained with merely seven silk layers. Permeability of the microcapsules was manipulated with high efficiency as well. Moreover, crosslinking was found to reduce surface charge of the shell. We attributed this to crosslinking-induced conformational change of silk fibroin based on secondary structure analysis. The LbL desolvation technique will facilitate fabrication of multilayer silk microcapsules for biomedical applications.

The egg sac of Benoitia lepida (Araneae: Agelenidae): structure, placement and the function of its layers

We describe the remarkable egg sac of Benoitia lepida (O.P.-Cambridge, 1876) (Agelenidae) from the Negev Desert, Israel. It consists of four layers: (from outside) a papery envelope, an outer loose silk layer, a “dirt layer”, and an inner flocculent silk layer surrounding the eggs. The dirt layer consists of loess soil, and may include stones, snail shells, or twigs from the surroundings. Some sacs hang from a silken string over the female's web sheet, attached to barrier threads or overhanging vegetation. In these “hanging sacs”, the outer papery wall is shiny white and covers the inner layers completely. Other sacs (“attached sacs”) are attached to a top branch of a shrub, away from the female's web. These sacs often have little or no outer papery envelope; the outer silk wrapping encloses the branch, and the sac may be dull brown in color. We studied the species at two sites; at one the hanging sac type predominated, while at the other the attached type was most common. A field experiment revealed that the dirt layer is effective in protecting the sacs against predation from ants but had no effect on spider predators of the egg sacs.

Sub-Millimeter-Wave Transmission of Silk Fabric

Millimeter wave technology is one of the technologies developed rapidly in recent years. The research was mainly to study the transmission of millimeter wave through textile material named silk fabric. We observed the phenomenon of sub-millimeter-wave transmission and reflection of the silk fabric, and concluded that with the number of silk fabric layers increasing, effect of scattering and absorption of the millimeter wave enhanced. The conclusion could be further employed in millimeter wave and THz imaging, dangerous goods inspection and other security application.

Nanosized CaP-silk fibroin-PCL-PEG-PCL/PCL based bilayer membranes for guided bone regeneration

Guided bone regeneration (GBR) concept has been developed to prevent the formation of non-functional scar tissue layer on defect site by undertaking barrier role. In this study, a new bilayer membrane which consisted of one layer of electrospun silk fibroin/PCL-PEG-PCL incorporating nanocalcium phosphate (SPCA)11Silk fibroin/PCL-PEG-PCL incorporating nanocalcium phosphate (SPCA) and one layer of PCL membrane was developed for GBR. To improve the osteoconductivity of membranes, nanosized calcium phosphate particles synthesized by Flame Spray Pyrolysis method were incorporated into membranes at 10% (wt) (SPCA10) and 20% (wt) (SPCA20) of the polymer content. The structural and chemical analyses revealed the well-integrated two layers of membranes with a total thickness of ca 100μm. In the regenerative layer, the highly porous mesh structure had a thickness of 12.6μm with randomly oriented fibers having diameters around 760nm, and nanoparticles dispersed homogenously. The mechanical test results showed remarkable improvement on the tensile strength of membranes with incorporation of nanoparticles. Higher water affinity of nanoCaP included membranes was proved by lower contact angle values and higher percent water uptake capacity. Biomineralization assay revealed that nucleation and growth of apatites around fibers of SPCA10 and SPCA20 were apparent while on SPCA0 apatite minerals were barely detected after 10days. Human dental pulp stem cells (DPSC) were seeded on electrospun layer of the bilayer membranes for biocompatibility and osteo-compatibility study. Increasing nanoCaP amount resulted in higher cell adhesion, proliferation, ALP activity and calcium deposition on membranes. These overall results confirmed the biocompatibility and potential applicability of proposed membranes for GBR treatments.

In vivo bone regeneration ability of different layers of natural silk cocoon processed using an eco-friendly method

Silk cocoons are primarily composed of the proteins fibroin and sericin. To achieve guided bone regeneration (GBR), we have developed a simple and ecofriendly processing technique to obtain microperforated thin membranes from cocoons. The separated silk membranes composed of both fibroin and sericin were classified by the cocoon layers (i.e., inner, middle, or outer) from which they originated. This report details the biological properties and the cellular responses of the three silk layers. The different cocoon layers were compared for their bone regeneration capabilities in vivo. The porosity of the silk nets increased from the inner layer to the outer layer when all of the membranes were compared using scanning electron microscopy (SEM). A difference in spectral intensity was observed in the Fourier transform infrared (FT-IR) spectra, indicating different amino acid compositions in these layers. An amino acid composition test demonstrated that the serine content decreased from the outer layer to the inner layer. Characterization of the protein release from each net demonstrated that the highest amount of protein release was observed in the inner layer group. The middle layer showed higher alkaline phosphatase (ALP) activity than the other layers in cellular experiments. Animal experiments indicated that the middle layers exhibit the highest bone volume 8 weeks post-operation (p<0.05). The membranes obtained directly from the thin middle layer of silk cocoons without any regeneration protocol have the potential to be used as an eco-friendly bone regeneration material for in vivo applications.

Biocompatible silk-conducting polymer composite trilayer actuators

Biocompatible materials capable of controlled actuation are in high demand for use in biomedical applications such as dynamic tissue scaffolding, valves, and steerable surgical tools. Conducting polymer actuators are of interest because they operate in aqueous electrolytes at low voltages and can generate stresses similar to natural muscle. Recently, our group has demonstrated a composite material of silk and poly(pyrrole) (PPy) that is mechanically robust, made from biocompatible materials, and bends under an applied voltage when incorporated into a simple bilayer device architecture and actuated using a biologically relevant electrolyte. Here we present trilayer devices composed of two silk-PPy composite layers separated by an insulating silk layer. The trilayer architecture allows one side to expand while the other contracts, resulting in improved performance over bilayer devices. Specifically, this configuration shows a larger angle of deflection per volt applied than the analogous bilayer system, while maintaining a consistent current response throughout cycling. In addition, the overall motion of the trilayer devices is more symmetric than that of the bilayer analogs, allowing for fully reversible operation.

Silk protein as a new optically transparent adhesion layer for an ultra-smooth sub-10 nm gold layer

Ultra-thin and ultra-smooth gold (Au) films are appealing for photonic applications including surface plasmon resonances and transparent contacts. However, poor adhesion at the Au–dielectric interface prohibits the formation of a mechanically stable, ultra-thin, and ultra-smooth Au film. A conventional solution is to use a metallic adhesion layer, such as titanium and chromium, however such layers cause the optical properties of pure Au to deteriorate. Here we report the use of silk protein to enhance the adhesion at the Au–dielectric interface, thus obtaining ultra-smooth sub-10 nm Au films. The Au films that were deposited onto the silk layer exhibited superior surface roughness to those deposited on SiO2, Si, and poly(methyl methacrylate), along with improved adhesion, electrical conductivity, and optical transparency. Additionally, we confirm that a metal–insulator–metal optical resonator can be successfully generated using a silk insulating layer without the use of a metallic adhesion layer.

Structural and Mechanical Properties of Cocoons of Antherina suraka (Saturniidae, Lepidoptera), an Endemic Species Used for Silk Production in Madagascar.

Antherina suraka Boisduval (Saturniidae, Lepidoptera) produces a silken cocoon that has been the focus of efforts to create a commercial wild silk industry in Madagascar. In this study, structural and mechanical properties of the cocoon of A. suraka from two sites were measured and compared to the cocoon of Bombyx mori L. (Bombycidae, Lepidoptera) the world's most common source for silk. Results of environmental scanning electron microscopy and mechanical testing showed that the silk sheet of A. suraka cocoon is less compact, with greater thickness and lower tensile strength and stiffness than that of B. mori. Confirming these results, stiffness and cell and thread density were found to be negatively correlated with thickness, and the cell and thread volumes were positively correlated with thickness. Antherina suraka showed no major differences between silk sheets from Kirindy and Isalo sites in either structural or mechanical properties, except for mean cell volume, which was greater in cocoons from Kirindy. Comparison between the two layers forming the cocoon showed that the inner layer has greater elastic modulus, denser silk distribution and lower porosity. Cocoons from both Kirindy and Isalo are suitable for sericulture. Although the inner layer of cocoon silk is of higher quality than the outer layer, the fact that both layers are of great but lower tensile strength than B. mori silk suggests that the current practice of sewing the two layers together for making one single layer fabric should be continued in efforts to produce a commercially viable product.

Aspects of mast building and the fine structure of “amphipod silk” glands in Dyopedos bispinis (Amphipoda, Dulichiidae)

In the present study, we investigated the biology of Dyopedos bispinis, a mast-building amphipod that is abundant near the N. Pertsov White Sea Biological Station. To examine the peculiarities of mast building in Dyopedos bispinis, we studied the social structure of individuals inhabiting the masts and identified the preferred substrata through underwater photography and direct observations, characterized the internal and external structures of the masts, and studied the ultrastructure of pereopodal silk glands using scanning and transmission electron microscopy (SEM and TEM, respectively). The most frequent substrata for mast building are other fouling organisms, including hydroids, bryozoans, ascidians and sponges. As in other corophiids, each Dyopedos bispinis mast represents the territory of one female and, occasionally, one male, but unique collective masts occupied by three or more (up to 23) adults were also observed. Masts comprise one or 2-4 central cylinders and a laminated cortex that contains detritus and amphipod silk layers. The pereopodal glandular complex of Dyopedos bispinis is composed of two distinct gland groups, proximal and distal, in each pereopod 3-4, and ducts in the glandular complex lead into a common chamber in the dactylus. The proximal glands are multicellular; their secretory cells are uninuclear, unlike in certain other amphipods; and the cell membrane is deeply invaginated. The invaginations are filled with extensions of the cytoplasm of lining cells, but the origin of the lining is unclear. Axon terminals were observed adjacent to the secretory cells, and it is assumed that these axons regulate amphipod silk glands. The proximal silk glands of Dyopedos bispinis have similarities with the lobed and rosette glands of isopods, but they have strongly elongated forms. We refer to these glands as pseudotubular glands. Such glands are rarely observed in Crustacea and have only been described in silk-producing pereopodal systems of marine Peracarida and in the antenna of terrestrial Malacostraca.

Grain characteristics of silicic Katla tephra layers indicate a fairly stable eruption environment between 2800 and 8100 years ago

Grain size and shape analyses were performed on silicic to intermediate Katla tephra (SILK) formed 2800–8100 years ago to examine whether the grain characteristics had changed with time, and in such a case, could they reflect changes in the eruption environment and/or changes in chemical composition. No systematic changes with time were observed in the grain shape parameters (elongation, ruggedness and circularity), however, the second oldest tephra layer SILK-A11 does not have the typical elongated grain shape that characterizes the other SILK tephra layers. Chemical analyses indicate that the SILK layers can be divided into three subgroups but no correlation between chemical composition and the grain parameters is observed. Changes in grain size of the SILK tephra layers with time indicate an apparent increase in grain size occurring about 6000 years ago, where largest grains are of category -3 Φ compared to 0 Φ in the older layers, all sampled at similar distance from source. This change in grain size could result from variation in ice thickness in the Katla caldera, with finer grain size between 6000–8200 years ago being due to thicker ice cover and greater availability of meltwater for magma fragmentation. Conversely, the younger coarser grained SILK layers may have formed under a thinner ice cover. A shift of the eruption sites to an area with thinner ice is also a possibility. However, no radical changes in the eruption environment 2800–8100 years ago are demonstrated by variations in grain characteristics, a conclusion further supported by large jökulhlaups from Mýrdalsjökull ice cap during this period