Obtaining high mechanical performance silk fibers by feeding purified carbon nanotube/lignosulfonate composite to silkworms

From Basic Principles of Protein-Polysaccharide Association to the Rational Design of Thermally Sensitive Materials

Biology resolves design requirements toward functional materials by creating nanostructured composites, where individual components are combined to maximize the macroscale material performance. A major challenge in utilizing such design principles is the trade-off between the preservation of individual component properties and emerging composite functionalities. Here, polysaccharide pectin and silk fibroin were investigated in their composite form with pectin as a thermal-responsive ion conductor and fibroin with exceptional mechanical strength. We show that segregative phase separation occurs upon mixing, and within a limited compositional range, domains ∼50 nm in size are formed and distributed homogeneously so that decent matrix collective properties are established. The composite is characterized by slight conformational changes in the silk domains, sequestering the hydrogen-bonded β-sheets as well as the emergence of randomized pectin orientations. However, most dominant in the composite's properties is the introduction of dense domain interfaces, leading to increased hydration, surface hydrophilicity, and increased strain of the composite material. Using controlled surface charging in X-ray photoelectron spectroscopy, we further demonstrate Ca ions (Ca2+) diffusion in the pectin domains, with which the fingerprints of interactions at domain interfaces are revealed. Both the thermal response and the electrical conductance were found to be strongly dependent on the degree of composite hydration. Our results provide a fundamental understanding of the role of interfacial interactions and their potential applications in the design of material properties, polysaccharide-protein composites in particular.

Highly strong and tough silk by feeding silkworms with rare earth ion-modified diets

Nature-derived silk fibers possess excellent biocompatibility, sustainability, and mechanical properties, yet producing strong and tough silk fibers in a facile and large-scale manner remains a significant challenge. Herein, we report a simple method for preparing strong and tough silk fibers by feeding silkworms rare earth ion-modified diets. The resulting silk fibers exhibit significantly increased tensile strength and toughness, with average values of 0.85 ± 0.07 GPa and 156 ± 13 MJ m-3, respectively, and maximum values of 0.97 ± 0.04 GPa and 188 ± 19 MJ m-3, approaching those of spider dragline silk. Our findings suggest that the incorporation of rare earth ions (La3+ or Eu3+) into the silk fibers contributes to this enhancement. Structure analysis reveals a reduction in content and an improvement in orientation of β-sheet nanocrystals in silk fibers. X-ray photoelectron spectroscopy analysis confirms the chemical interaction between rare earth ions with β-sheet nanocrystals. The structural evolution and chemical interactions lead to the simultaneous enhancement in both strength and toughness. This work presents a simple, scalable, and effective strategy for producing ultra-strong and tough silk fibers with potential applications in areas requiring super structural materials, such as personal protection and aerospace.

Hierarchically structured bioinspired nanocomposites

Next-generation structural materials are expected to be lightweight, high-strength and tough composites with embedded functionalities to sense, adapt, self-repair, morph and restore. This Review highlights recent developments and concepts in bioinspired nanocomposites, emphasizing tailoring of the architecture, interphases and confinement to achieve dynamic and synergetic responses. We highlight cornerstone examples from natural materials with unique mechanical property combinations based on relatively simple building blocks produced in aqueous environments under ambient conditions. A particular focus is on structural hierarchies across multiple length scales to achieve multifunctionality and robustness. We further discuss recent advances, trends and emerging opportunities for combining biological and synthetic components, state-of-the-art characterization and modelling approaches to assess the physical principles underlying nature-inspired design and mechanical responses at multiple length scales. These multidisciplinary approaches promote the synergetic enhancement of individual materials properties and an improved predictive and prescriptive design of the next era of structural materials at multilength scales for a wide range of applications.

Biological Effect Evaluation of Different Sized Titanium Dioxide Nanoparticles Using Bombyx mori (Silkworm) as a Model Animal

Titanium dioxide nanoparticles (TiO₂ NPs) are widely used in various disciplines, and it is imperative to evaluate their safety in the environment. In this paper, Bombyx mori (silkworm) was used as a model organism to evaluate the biological effects of different sized TiO₂ NPs, taking into consideration their effect on the larval growth, cocoon shell weight, tissues, and silk produced. The effect of the different sized TiO₂ NPs on the larval and cocoon shell weight was dose-dependent. The highest accumulation of titanium (Ti) following a modified TiO₂ NPs-treated mulberry diet was observed in the midgut. The expression of the light chain fibroin (FIBL) was three times higher in 0.33 g TiO₂ NPs-treated silk gland after 96 h. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis demonstrated that TiO₂ NPs-treated silk fiber (TiSF) exhibited a diminutive decrease in silk fiber (SF) crystallization and β-sheet compared to the control SF, respectively. The tensile tests of SF from silkworm fed with 0.03 g of 25 nm TiO₂ NPs were significantly improved when compared to the control SF. Significant changes in the surface morphology and thermal stability of SF were observed. The antimicrobial activity of TiSF was investigated against Pseudomonas aeruginosa and Staphylococcus aureus, with ciprofloxacin-treated SF acting as a control. It was documented that 0.09 g of 60 nm TiSF was most effective against P. aeruginosa at a zone of inhibition (ZOI) of 21.06 mm when compared with the control SF which recorded a ZOI of 17.19 mm. This study highlighted a different approach in evaluating the biological effects of TiO₂ NPs using the silkworm as a model and assessing their impact on the silk intrinsic property, which will be effective in biotechnology applications.

Silk Fiber Multiwalled Carbon Nanotube-Based Micro-/Nanofiber Composite as a Conductive Fiber and a Force Sensor

Silk cocoon fibers (SFs) are natural polymers that are made up of fibroin protein. These natural fibers have higher mechanical stability and good elasticity properties. In this work, we coated multiwalled carbon nanotubes (MWCNTs) on the surface of SFs using a simple stirring technique with vinegar as the medium. This SF-MWCNT micro-/nanofiber composite was prepared without any adhesives. The characterization results revealed that the SF-MWCNT micro-/nanofiber composite exhibited excellent electrical conductivity (995 Ω cm^-1), tensile strength (up to 200% greater elongation), and durability characteristics. In addition, this micro-/nanofiber composite shows a change in resistance from 1450 to 960 Ω cm^-1 for an applied mechanical force of 0.3-1 N kg^-1. Based on our findings, SF-MWCNT micro-/nanofiber composite-based conductive fibers (CFs) and force sensors (FSs) were developed.

Synthesis and Processing of Nanomaterials Mediated by Living Organisms

Nanomaterials offer exciting properties and functionalities. However, their production and processing frequently involve complex methods, cumbersome equipment, harsh conditions, and hazardous media. The capability of organisms to accomplish this using mild conditions offers a sustainable, biocompatible, and environmentally friendly alternative. Different nanomaterials such as metal nanoparticles, quantum dots, silica nanostructures, and nanocellulose are being synthesized increasingly through living entities. In addition, the bionanofabrication potential enables also the in situ processing of nanomaterials inside biomatrices with unprecedented outcomes. In this Minireview we present a critical state‐of‐the‐art vision of current nanofabrication approaches mediated by living entities (ranging from unicellular to higher organisms), in order to expand this knowledge and scrutinize future prospects. An efficient interfacial interaction at the nanoscale by green means is within reach through this approach.

A review on the biological effects of nanomaterials on silkworm (Bombyx mori)

The production of high-quality silkworm silk is of importance in sericulture in addition to the production of biomass, silk proteins, and animal feed. The distinctive properties of nanomaterials have the potential to improve the development of various sectors including medicine, cosmetics, and agriculture. The application of nanotechnology in sericulture not only improves the survival rate of the silkworm, promotes the growth and development of silkworm, but also improves the quality of silk fiber. Despite the positive contributions of nanomaterials, there are a few concerns regarding the safety of their application to the environment, in humans, and in experimental models. Some studies have shown that some nanomaterials exhibit toxicity to tissues and organs of the silkworm, while other nanomaterials exhibit therapeutic properties. This review summarizes some reports on the biological effects of nanomaterials on silkworm and how the application of nanomaterials improves sericulture.