Using Solvents with Different Molecular Sizes to Investigate the Structure of Antheraea Pernyi Silk

The interaction between silk and polar solvents of different molecular size can be an important tool for understanding the structural features of natural silk; in particular, the disordered regions associated with the key property of mechanical toughness. In this work, we investigate the transitions induced in the tensile performance and structure of as-reeled Antheraea pernyi silks from different silkworms by a range of solvents that can only soften the protein chains in the amorphous regions. The results indicate that polar solvents with different molecular sizes affect the silk to different degrees, and silks with slightly different structures display significantly different tensile performance in the same solvent. The solvent molecular size is quantitatively correlated with the accessible volume in the amorphous regions before and after the yield point, which suggests that the volume accessible to the solvent molecules decreases as the solvent radius increases. Moreover, silks with more ordered structure (less free volume) in the amorphous regions are less sensitive to solvents than those with more disordered structures. However, silks with higher free volume have higher toughness due to the greater strain to failure

Natural Electroactive Hydrogel from Soy Protein Isolation

A natural electroactive protein hydrogel was prepared from soy protein isolate (SPI) solution by cross-linking with epichlorohydrin. Under electrical stimulus, such SPI hydrogel quickly bends toward one electrode, showing a good electroactivity. Because of its amphoteric nature, the SPI hydrogel bends either toward the anode (pH 6), depending on the pH of the electrolyte solution. Other factors, such as electric field strength, ionic strength and gel thickness also influence the electromechanical behavior of the SPI hydrogels. Moreover, this SPI hydrogel exhibits a good electroactive behavior under strong acidic (pH = 2 − 3) or basic (pH = 11 − 12) solutions, which is a significant improvement over two other kinds of natural electroactive hydrogels, i.e., chitosan/carboxymethylcellulose and chitosan/carboxymethylchitosan hydrogel, which we reported previously. The wide pH range and good electroactivity of this natural protein hydrogel suggests its great potential for microsensor and actuator applications, especially in the biomedical field, and also to increase the scope of natural polymer-based electroactive hydrogels

Moisture Effects on <i>Antheraea pernyi</i> Silk’s Mechanical Property

Water plays an essential role in determining the mechanical properties of silks and other structural proteins. Here we study the effects of moisture on the elastic modulus of Antheraea pernyi silks, which exhibit an abrupt drop over a narrow range of relative humidity in the same way as synthetic polymers do in a temperature scan through their glass transition. A linear relationship between relative humidity and the transition temperature allows a simple transformation of the modulus−humidity curves into a general modulus−temperature relation for Antheraea pernyi silks. A model is presented to explain these observations quantitatively at the molecular level

Enhancing the Toughness of Regenerated Silk Fibroin Film through Uniaxial Extension

Films of regenerated silk fibroin (RSF) are usually brittle and weak, which prevents its wide application as a structural material. To improve the mechanical properties of RSF film, uniaxial extension under swollen conditions was employed to introduce preferred orientation of molecular chains of silk fibroin. Such a prestretching treatment resulted in the strain at break, ultimate stress, Young’s modulus, and energy to break along the predrawn direction of the RSF film increasing from approximate 5%, 90 MPa, 2.7 GPa, and 2.1 kJ/kg to 35%, 169 MPa, 3.5 GPa, and 38.9 kJ/kg, respectively, which is an attractive combination of strength and toughness. The mechanism of these property enhancements was investigated using techniques such as small-angle X-ray scattering, wide-angle X-ray diffraction, atomic force microscopy, and dynamic mechanical analysis

Effect of Fe³⁺ on the Silk Fibroin Regulated Direct Growth of Nacre-like Aragonite Hybrids

Silk fibroin (SF), which has been used as an analogue of the silk-like proteins in studying the biomineralization process of calcium carbonate in vitro, shows a high preference for the formation of aragonite polymorph. In this study, Fe³⁺, which has been found with relatively high levels in the shells of marine mollusks, was introduced into the SF-regulated biomineralization system. The addition of Fe³⁺ into the SF aqueous solutions induced a conformational transition of SF from random coil to β-sheet. The promoted β-sheet structures provided Ca²⁺-binding sites for SF and, accordingly, enabled the formation of an amorphous calcium carbonate precursor. Such a precursor has an aligned parallel structure and acts as a template for the direct growth of aragonite. The corresponding aragonite products showed similar organic–inorganic hierarchical structure to nacre building in vivo as well as higher thermal stability compared with that of the other Fe³⁺-free aragonite products in terms of the polymorph. It is indicated that Fe³⁺ plays multiple roles in this nacre-mimetic biomineralization process. By examining the coeffect of SF and Fe³⁺ as multiple additives, this study has provided a deeper understanding on the valuable contribution of Fe³⁺ in the nacre-mimetic system, which could facilitate the fabrication of similar synthetic materials with good mechanical performance from cheap abundant materials

Effect of Various Dissolution Systems on the Molecular Weight of Regenerated Silk Fibroin

Effect of Various Dissolution Systems on the Molecular Weight of Regenerated Silk Fibroi

Investigation of Rheological Properties and Conformation of Silk Fibroin in the Solution of AmimCl

The conformation and eventual morphology of silk fibroin (SF) chains are crucial for the mechanical properties of SF materials, and are strongly related to the solvation step as a key stage in their processing conditions. In this work, a novel SF/AmimCl (1-allyl-3-methylimidazolium chloride) solution with unique properties is reported and compared with conventional regenerated SF aqueous solutions, based on an investigation of its rheological properties. The steady shearing behavior suggested that AmimCl is a good solvent for SF molecules, and shear thinning of semidiluted SF/AmimCl solution at high shear rates showed behavior similar to that in native spinning, which is due to the rearrangement and orientation of SF molecular chains. Fitting of experimental dynamic viscoelastic data to the Rouse model provided an effective method to estimate the molecular weight of SF. We believe that this work not only provides a better understanding of the relationship between properties of silk protein and aggregation states of their molecular chains, but also provides tools to fabricate high-performance SF-based materials

Superoleophobic Cotton Textiles

Common cotton textiles are hydrophilic and oleophilic in nature. Superhydrophobic cotton textiles have the potential to be used as self-cleaning fabrics, but they typically are not super oil-repellent. Poor oil repellency may easily compromise the self-cleaning property of these fabrics. Here, we report on the preparation of superoleophobic cotton textiles based on a multilength-scale structure, as demonstrated by a high hexadecane contact angle (153° for 5 μL droplets) and low roll-off angle (9° for 20 μL droplets). The multilength-scale roughness was based on the woven structure, with additional two layers of silica particles (microparticles and nanoparticles, respectively) covalently bonded to the fiber. Superoleophobicity was successfully obtained by incorporating perfluoroalkyl groups onto the surface of the modified cotton. It proved to be essential to add the nanoparticle layer in achieving superoleophobicity, especially in terms of low roll-off angles for hexadecane

Biomimetic Synthesis of Multilayered Aragonite Aggregates Using Alginate as Crystal Growth Modifier

Polysaccharides were believed to play an important role in the mineralization process of many organisms. As the source of continuously and uniformly releasing alginate molecules and Ca2+, alginate/Ca nanospherical gel was employed in the solution to induce the nucleation and growth of CaCO3. Time-resolved transmission electron microscopy (TEM) was applied to study the crystallization at a very early stage. It was found that the initially formed lens-like vaterite particles gradually dissolved from the middle of the particle and released alginate molecules and Ca2+ back into the system. As reaction time increased, the released substances were involved in the next stage of crystallization of CaCO3, in the form of needle-like and shuttle-like aragonite particles sequentially depending on the concentration of alginate molecules and Ca2+. “Egg-box” conformation of alginate and Ca2+ was considered a skeleton for the growth of such aragonite particles. Notably, shuttle-like aragonite particles were composed of “bricks” of several hundred nanometers in size, which were very similar to biogenetic nacreous layers in shells

Superoleophobic Cotton Textiles

Common cotton textiles are hydrophilic and oleophilic in nature. Superhydrophobic cotton textiles have the potential to be used as self-cleaning fabrics, but they typically are not super oil-repellent. Poor oil repellency may easily compromise the self-cleaning property of these fabrics. Here, we report on the preparation of superoleophobic cotton textiles based on a multilength-scale structure, as demonstrated by a high hexadecane contact angle (153° for 5 μL droplets) and low roll-off angle (9° for 20 μL droplets). The multilength-scale roughness was based on the woven structure, with additional two layers of silica particles (microparticles and nanoparticles, respectively) covalently bonded to the fiber. Superoleophobicity was successfully obtained by incorporating perfluoroalkyl groups onto the surface of the modified cotton. It proved to be essential to add the nanoparticle layer in achieving superoleophobicity, especially in terms of low roll-off angles for hexadecane