Zhengzhong Shao

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 degrees for 5 microL droplets) and low roll-off angle (9 degrees for 20 microL 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.

The effect of spinning conditions on the mechanics of a spider's dragline silk

We studied the mechanical properties of dragline threads of the edible golden silk spider Nephila edulis that are produced under spinning speeds ranging from 0.1 to 400 mm s−1 and temperatures ranging from 5 to 40°C. These conditions affected the silk in all of the mechanical traits we tested (strain at breaking, breaking energy, initial Youngs modulus and point of yielding). We argue that both trade–offs (between mechanical properties) and constraints (in the manufacturing process) have a large role in defining spider silk fibres.

Conformation transition kinetics of Bombyx mori silk protein

Time‐resolved FTIR analysis was used to monitor the conformation transition induced by treating regenerated Bombyx mori silk fibroin films and solutions with different concentrations of ethanol. The resulting curves showing the kinetics of the transition for both films and fibroin solutions were influenced by the ethanol concentration. In addition, for silk fibroin solutions the protein concentration also had an effect on the kinetics. At low ethanol concentrations (for example, less than 40% v/v in the case of film), films and fibroin solutions showed a phase in which β‐sheets slowly formed at a rate dependent on the ethanol concentration. Reducing the concentration of the fibroin in solutions also slowed the formation of β‐sheets. These observations suggest that this phase represents a nucleation step. Such a nucleation phase was not seen in the conformation transition at ethanol concentrations > 40% in films or > 50% in silk fibroin solutions. Our results indicate that the ethanol‐induced conformation transition of silk fibroin in films and solutions is a three‐phase process. The first phase is the initiation of β‐sheet structure (nucleation), the second is a fast phase of β‐sheet growth while the third phase represents a slow perfection of previously formed β‐sheet structure. The nucleation step can be very fast or relatively slow, depending on factors that influence protein chain mobility and intermolecular hydrogen bond formation. The findings give support to the previous evidence that natural silk spinning in silkworms is nucleation‐dependent, and that silkworms (like spiders) use concentrated silk protein solutions, and careful control of the pH value and metallic ion content of the processing environment to speed up the nucleation step to produce a rapid conformation transition to convert the water soluble spinning dope to a tough solid silk fiber. Proteins 2007.

Analysis of spider silk in native and supercontracted states using Raman spectroscopy

Well-defined, fluorescence-free Raman spectra were obtained from native as well as treated (supercontracted) major ampullate dragline silks reeled from four very different spiders: Araneus diadematus, Nephila edulis, Latrodectus mactans and Euprosthenops sp. Conformational sensitive regions were assigned in the spectra. Compared to the silk of the silkworm Bombyx mori, all spider silks showed less β-sheet and more random coil and/or α-helix material. Polarized spectra suggested that the molecular chains of the spider silk were aligned parallel to the axis of the fibre. The differences in the mechanical properties between the native and supercontracted silks were attributed to variations in β-sheet content. The mechanism of contraction of spider silks in solvents was correlated to conformational changes in the supermolecular structure.

The effect of solvents on the contraction and mechanical properties of spider silk

We examined the mechanical characteristics of four major ampullate (MA) dragline silks during and after submersion in a range of solvents. The silks were reeled from four very different spiders: Araneus diadematus, Nephila edulis, Latrodectus mactansand Euprosthenops sp. They displayed significant differences in behaviour in the native state as well as during and after supercontraction in solvents such as water, urea solution and a set of alcohols. The different polarities of the solvents are thought to affect different regions of the silk’s molecular conformation. We hypothesise that the observed mechanical properties of dragline silks are those of a hard elastic polymer; and we explain the supercontraction of the silks as changes of orientation in the molecular chains. q 1999 Elsevier Science Ltd. All rights reserved.

Electrical Behavior of a Natural Polyelectrolyte Hydrogel : Chitosan/Carboxymethylcellulose Hydrogel

An amphoteric hydrogel film was prepared by solution blending of two natural polyelectrolytes, chitosan and carboxymethylcellulose, and cross-linking with glutaraldehyde. The bending of the film in an electric field was studied in different electrolyte solutions. Because of its amphoteric nature, the hydrogel can bend toward either anode or cathode depending on the pH of the solution. Other factors such as ionic strength and electric field strength also influence the electromechanical behavior of the hydrogels. The equilibrium bending angle of the hydrogel was found to reach a maximum at about 90 degrees in pH = 6 Britton-Robinson buffer solution with an ionic strength of 0.2 M. The sensitivity of the films over a wide range of pH and the good reversibility of this natural amphoteric electric-sensitive hydrogel suggest its future use in microsensor and actuator applications, especially in the biomedical field.

Synchrotron FTIR Microspectroscopy of Single Natural Silk Fibers

Synchrotron FTIR (S-FTIR) microspectroscopy was used to monitor the silk protein conformation in a range of single natural silk fibers (domestic and wild silkworm and spider dragline silk). With the selection of suitable aperture size, we obtained high-resolution S-FTIR spectra capable of semiquantitative analysis of protein secondary structures. For the first time, we have determined from S-FTIR the β-sheet content in a range of natural single silk fibers, 28 ± 4, 23 ± 2, and 17 ± 4% in Bombyx mori, Antheraea pernyi, and Nephila edulis silks, respectively. The trend of β-sheet content in different silk fibers from the current study accords quite well with published data determined by XRD, Raman, and (13)C NMR. Our results indicate that the S-FTIR microspectroscopy method has considerable potential for the study of single natural silk fibers.

The preparation of regenerated silk fibroin microspheres

The objective of the present study is to investigate the possibility of preparing pure protein microspheres from regenerated silk fibroin (RSF). It is found that RSF microspheres, with predictable and controllable sizes ranging from 0.2 to 1.5 µm, can be prepared mild self-assembling of silk fibroin molecular chains. The merits of this novel method include a rather simple production apparatus and no potentially toxic agents, such as surfactants, initiators, cross-linking agents, The results show that the particle size and size distribution of RSF microspheres are greatly affected by the amount of ethanol additive, the freezing temperature and the concentration of silk fibroin. Finally, the mechanism of RSF microspheres formation is also discussed based on our experimental results.

Doxorubicin‐Loaded Magnetic Silk Fibroin Nanoparticles for Targeted Therapy of Multidrug‐Resistant Cancer

A strategy to prepare doxorubicin-loaded magnetic silk fibroin nanoparticles is presented. The nanoparticles serve as a nanometer-scale drug-delivery system in the chemotherapy of multidrug-resistant cancer under the guidance of a magnetic field. The magnetic tumor-targeting ability broadens the range of biomedical applications of silk fibroin, and the nanoparticle-assisted preparation strategy is useful for the advancement of other biomacromolecule-based materials.

Surface-modified silicon nanoparticles with ultrabright photoluminescence and single-exponential decay for nanoscale fluorescence lifetime imaging of temperature.

In this Communication, we report fabrication of ultrabright water-dispersible silicon nanoparticles (SiNPs) with quantum yields (QYs) up to 75% through a novelly designed chemical surface modification. A simple one-pot surface modification was developed that improves the photoluminescent QYs of SiNPs from 8% to 75% and meanwhile makes SiNPs water-dispersible. Time-correlated single photon counting and femtosecond time-resolved photoluminescence techniques demonstrate the emergence of a single and uncommonly highly emissive recombination channel across the entire NP ensemble induced by surface modification. The extended relatively long fluorescence lifetime (FLT), with a monoexponential decay, makes such surface-modified SiNPs suitable for applications involving lifetime measurements. Experimental results demonstrate that the surface-modified SiNPs can be utilized as an extraordinary nanothermometer through FLT imaging.