The degradation behavior of silk fibroin derived from different ionic liquid solvents

Establishing an appropriate degradation rate is critical for tissue engineering scaffolds. In this study, the degradation rate of silk fibroin three-dimensional scaffolds was regulated by changing the molecular weight (MW) of the silk fibroin. The solubility of silk fibroin depends primarily on the ionic ability of the slovent to dissolve silk fibroin, therefore, we regulated the MW of the silk fibroin using LiBr, Ca(NO3)2 and CaCl2 to dissolve the silk fibers. SDS-PAGE analysis showed that the MW of the CaCl2-derived silk fibroin was lower than the MW produced using LiBr and Ca(NO3)2. In vitro and in vivo degradation results showed that the scaffolds prepared by low-MW silk fibroin were more rapidly degraded. Furthermore, FTIR and amino acid analysis suggested that the amorphous regions were preferentially degraded by Collagenase IA, while the SDS-PAGE and amino acid analysis indicated that the scaffolds were degraded into polypeptides (mainly at 10-30 kDa) and amino acids. Because the CaCl2-derived scaffolds contained abundant low MW polypeptides, inter-intramolecular entanglement and traversing of molecular chains in the crystallites reduced, which resulted in rapid degradation. The in vivo degradation results suggested that the degradation rate of the CaCl2-derived scaffolds was better matched to dermis regeneration, indicating that the degradation rate of silk fibroin can be effectively regulated by changing the MW to achieve a suitable dermal tissue regeneration rate.

Preparation of Silk Fibroin Microspheres and Its Cytocompatibility

The goal of this proof-of-concept study was the fabrication of porous silk fibroin (SF) microspheres which could be used as cell culture carriers under very mild processing conditions. The SF solution was differentiated into droplets which were induced by a syringe needle in the high-voltage electrostatic field. They were collected and frozen in liquid nitrogen and water in droplets formed ice crystals which sublimated during lyophilization and a great quantity of micropores shaped in SF microspheres. Finally, the microspheres were treated in ethanol so as to transfer the molecular conformation into β-sheet and then they were insoluble in water. SF particles were spherical in shape with diameters in the range of 208.4 μm to 727.3 μm, while the pore size on the surface altered from 0.3 μm to 10.7 μm. In vitro, the performances of SF microspheres were assessed by culturing L-929 fibroblasts cells. Cells were observed to be tightly adhered and fully extended;also a large number of connections were established between cells. After 5-day culture, it could be observed under a confocal laser scanning microscope that the porous microenvironment offered by SF particles accelerated proliferation of cells significantly. Furthermore, porous SF particles with smaller diameters (200 - 300 μm) might promote cell growth better. These new porous SF microspheres hold a great potential for cell culture carriers and issue engineering scaffolds.

The Cytocompatibility of Genipin-Crosslinked Silk Fibroin Films

There is an increasing demand for crosslinking methods of silk fibroin (SF) scaffolds in biomedical applications that could maintain the biocompatibility, bioactivity as well as improve the water resistance and mechanical properties of SF materials. In this study, SF was crosslinked effectively with genipin which is a naturally occurring iridoid glucoside and the crosslinking mechanism was investigated through FTIR and amino acid analysis. The results showed that genipin could react with the -NH2 groups on the side chains of SF macromolecules and to form inter- and intra-molecular covalent bonds, and improved the stability of SF materials significantly. In vitro, the performances of genipin-crosslinked SF films were assessed by seeding L929 cells and compared with ethanol-processed SF films, glutaraldehyde and polyethylene glycol diglycidyl ether crosslinked ones. The genipin-crosslinked SF films showed a similar affinity to cells as ethanol-processed ones, and a higher bioactivity in promoting cell growth and proliferation, inhibition of cell apoptosis, and maintenance of normal cell cycle compared with glutaraldehyde and polyethylene glycol diglycidyl ether crosslinked SF films. These features, combined with the decrease of brittleness of SF films crosslinked with chemical methods, substantiated genipin as an effective and biocompatible agent for the manufacturing of bioactive SF materials which used as tissue engineering scaffolds and drug delivery carriers.

A Novel Method for the Quantitative Detection of Sericin Content in Silk Fiber Based on the Ratio of Aspartate to Alanine

The development of a method for the quantitative determination of the sericin content ratio(SCR)is urgently needed for silk refining and the purification of silk fibroin for biomedical applications.In this work,a series of sericin/fibroin mixed samples with known SCRs were prepared by mixing initial samples of extracted sericin and fibroin from Bombyx mori silk.Significant differences were found in the contents of characteristic hydrophilic amino acids abundant in sericin and hydrophobic amino acids abundant in fibroin,and several linear relation-ships of SCR associated with the content ratios of Ser/Ala,Asp/Ala,Lys/Ala,Asp/Gly and Ser/Gly were estab-lished by amino acid analysis.Subsequently,the linear equation expressing SCR(%)as a function of the Asp to Ala content ratio X(%)was established as SCR=2.5634X−12.5587(R 2=0.9972).The results indicated that the SCR of degummed silks calculated by the equation is more objective and effective than the results obtained by the traditional weight loss method.Our study provides a novel approach for the sensitive and quantitative detection of the sericin content within the detection limit in unknown silks,which can contribute to quality control in the silk production process.

Gelation of <i>Antheraea pernyi</i>Silk Fibroin Accelerated by Shearing

The rapid manufacture of silk fibroin gels in mild conditions is an important subject in the field of silk-based biomaterials. In this study, the gelation of Antheraea pernyi silk fibroin (ASF) aqueous solution was induced by shearing, without chemical cross-linking agents. Simple shearing controlled and accomplished the steady and rapid conformational transition to β-sheets with ease. The conformational transformation and rapid gelation mechanisms of ASF induced by shearing were tracked and analyzed by circular dichroism spectrometry, Fourier transform infrared spectroscopy and X-ray diffractometry, then compared with Bombyx mori silk fibroin (BSF). ASF quickly formed hydrogels within 24 - 48 h after shearing under different shearing rates for 30 - 90 min, resulting in sol-gel transformation when the β-sheet content reached nearly 50%, which is the minimum content needed to maintain a stable hydrogel system in ASF. The gel structures remained stable once formed. The rapid gelation of ASF through shearing compared with BSF was achieved because of ASF’s alternating polyalanine-containing units, which tend to form α-helix structures spontaneously. Further, the entropic cost during the conformational transition from the α-helix to the β-sheet structure is less than the cost of the transition from the random coil structure. This method is a simple, non-chemical cross-linking approach for the promotion of rapid gelation and the protection of the biological properties of ASF, and it may prove useful for application in the field of biomedical materials.

Heterogeneous activity causes a nonlinear increase in the group energy use of ant workers isolated from queen and brood

Increasing evidence has shown that the energy use of ant colonies increases sublinearly with colony size so that large colonies consume less per capita energy than small colonies. It has been postulated that social environment （e.g., in the presence of queen and brood） is critical for the sublinear group energetics, and a few studies of ant workers isolated from queens and brood observed linear relationships between group energetics and size. In this paper, we hypothesize that the sublinear energetics arise from the heterogeneity of activity in ant groups, that is, large groups have relatively more inactive members than small groups. We further hypothesize that the energy use of ant worker groups that are allowed to move freely increases more slowly than the group size even if they are isolated from queen and brood. Previous studies only provided indirect evidence for these hypotheses due to technical difficulties. In this study, we applied the automated behavioral monitoring and respirometry simultaneously on isolated worker groups for long time periods, and analyzed the image with the state-of-the-art algorithms. Our results show that when activity was not confined, large groups had lower per capita energy use, a lower percentage of active members, and lower average walking speed than small groups; while locomotion was confined, however, the per capita energy use was a constant regardless of the group size. The quantitative analysis shows a direct link between variation in group energy use and the activity level of ant workers when isolated from queen and brood.

Generalized assembly of sandwich-like 0D/2D/0D heterostructures with highly exposed surfaces toward superior electrochemical performances

Heterostructures composed of two-dimensional(2D)nanosheets and zero-dimensional(0D)nanoparticles(NPs)have attracted increasing attention because of the synergy arising from the coupling interactions between the two mixed-dimensional components.Despite recent advances,it remains a challenge to fabricate 2D/0D heterostructures with clean and accessible surfaces,which is highly desirable for the diversity of catalytic,sensing,and energy storage applications.Herein,we report a generalized methodology that enables the facile assembly of sandwich-like 0D/2D/0D heterostructures with facilitated mass-transport channels and exposed surface active sites.A ligand-exchange strategy with HBF4 is employed to strip off the surface-coating ligands of colloidal NPs,rendering them positively charged and dispersible in polar solvents.This allows subsequent electrostatic assembly of NPs with oppositely charged 2D nanosheets to afford sandwich-like 0D/2D/0D heterostructures.The barely covered surfaces and the advantageous architectures of such sandwich-like 0D/2D/0D heterostructures induce the desired synergistic effect,making them particularly suitable for electrochemical energy storage and conversion.We demonstrate this by employing MXene/NiFe_(2)O_(4) and MXene/Fe3O4 heterostructures for high-performance electrocatalytic oxygen evolution and supercapacitors,respectively.

Bio-inspired Superhydrophobic Coating with Low Hydrate Adhesion for Hydrate Mitigation

In this paper,we fabricate a biomimetic superhydrophobic coating on an X90 pipeline steel substrate by electrodeposition of copper,hydrothermal treatment to form a copper oxide layer,and subsequent surface modification with Stearic Acid(SA).The coating exhibits static contact angles of water of 160°±-3.1°in the air and 170.7°±2.5°in cyclopentane,indicating the strongly water-repelling nature of the coating.The morphologies of the cyclopentane hydrate formed on steel substrates with and without the superhydrophobic coating are investigated.The results show that the hydrate particle on the coating exhibits spherical morphology and herein the interfacial contact area and adhesion force to the solid surface can be essentially reduced.The adhesion force reduction may be resulted by the decrease in the contact area between the hydrate and the solid surface.

The special shaped laser spot for driving indirect-drive hohlraum with multi-beam incidence

In indirect drive, reducing peak intensity of a single beam and controlling overlap of multi-beams are two opposite requirements for laser focal spot design. In this paper, an improved laser spot design technique for indirect drive built upon the geometric structures of laser propagation into hohlraum has been introduced. The proposed technique is able to generate appropriate continuous phase plate(CPP) producing a special shaped spot that can balance the opposite requirements. The corresponding CPP does not bring difficulties to the design and fabrication. Phase aberrations are more sensitive to the special shaped spot; however, it can be tolerable for the current beam control level.

Multi-chambered,carbon-coated Ni_(0.4)Fe_(2.6)O_(4) nanoparticle superlattice microspheres for boosting water oxidation reaction

Developing active and robust non-noble-metal-based electrocatalysts for the oxygen evolution reaction(OER)is of vital practical significance for accelerating the kinetics of water splitting.Here,a novel double emulsion template method is proposed to design and prepare hierarchically multichambered,carbon-coated Ni_(0.4)Fe_(2.6)O_(4) nanoparticle superlattice microspheres(M-NFO@C-NSMs)for the highly efficient oxygen evolution.The high-temperature calcination under inert gas enables an improved electrochemical property by rationally transforming the long-chain organic capping ligands into partially graphitized uniform carbon coatings.More importantly,benefiting from the unique hierarchical superstructure with macro-/meso-/microporosities and three-dimensional continuous conductive carbon frameworks,M-NFO@C-NSMs exhibit comprehensively enhanced OER activity in a dilute alkaline electrolyte as compared to their solid counterparts and most spinelbased electrocatalysts reported to date.Notably,the collective property of supraparticles endowed M-NFO@C-NSMs with superior long-term cyclic stability.This work sheds light on the sophisticated design of functionalized supraparticles for efficient water splitting.