Yaopeng Zhang

Significantly Reinforced Composite Fibers Electrospun from Silk Fibroin/Carbon Nanotube Aqueous Solutions

Microcomposite fibers of regenerated silk fibroin (RSF) and multiwalled carbon nanotubes (MWNTs) were successfully prepared by an electrospinning process from aqueous solutions. A quiescent blended solution and a three-dimensional Raman image of the composite fibers showed that functionalized MWNTs (F-MWNTs) were well dispersed in the solutions and the RSF fibers, respectively. Raman spectra and wide-angle X-ray diffraction (WAXD) patterns of RSF/F-MWNT electrospun fibers indicated that the composite fibers had higher β-sheet content and crystallinity than the pure RSF electrospun fibers, respectively. The mechanical properties of the RSF electrospun fibers were improved drastically by incorporating F-MWNTs. Compared with the pure RSF electrospun fibers, the composite fibers with 1.0 wt % F-MWNTs exhibited a 2.8-fold increase in breaking strength, a 4.4-fold increase in Youngs modulus, and a 2.1-fold increase in breaking energy. Cytotoxicity test preliminarily demonstrated that the electrospun fiber mats have good biocompatibility for tissue engineering scaffolds.

Formation and characterization of cellulose membranes from N-methylmorpholine-N-oxide solution

Regenerated cellulose membranes have been raditionally manufactured using the viscose or the copper-ammonia process. Today, membranes made by this process are still used in many fields such as dialysis. However, there are some serious environmental problems inherent in the existing processing routes. The new N methylmorpholine-N-oxide (NMMO) process can over-come these disadvantages and provides membranes with improved mechanical properties. In the present work, cellulose membranes were successfully prepared from NMMO solution under various conditions. It was found that the cellulose concentration is a decisive factor in controlling the membrane permeation properties. For a given coagulation system, higher cellulose concentration leads to membranes with greater rejection of bovine serum albumin (BSA) and lower pure water flux. It was also found that both the degree of polymerization (DP) and the type of cellulose pulp have great effect on the morphology and permeation properties of the membrane support layer. With increasing NMMO concentration and temperature of the coagulation bath, the pure water flux increases while the rejection of BSA decreases; a result of the larger mean pore size formed during coagulation.

Preparation of regenerated silk fibroin/silk sericin fibers by coaxial electrospinning

The coaxial electrospinning using the regenerated silk fibroin (SF) and silk sericin (SS) aqueous solutions as the core and shell spinning dopes, respectively, was carried out to prepare regenerated SF/SS composite fibers with components and core-shell structure similar to the natural silkworm silks. It was found from the scanning electron microscope (SEM) and transmission electron microscope (TEM) results that the core dope (SF aqueous solution) flow rate (Q(c)) and the applied voltage (V) had some effects on the morphology of the composite fiber. With an increase in Q(c), the diameter nonuniformity and eccentricity of the core fiber became serious, while the increasing V played an inverse role. In this work, the suitable Q(c) for the fiber formation with better electrospinnability was about 6 μL/min, and the corresponding optimum V was 40 kV. Moreover, the results from Raman spectra analysis, modulated differential scanning calorimetry (MDSC), thermogravimetry (TG) measurement and mechanical property test showed that, compared with the pure SF fiber, the coaxially electrospun SF/SS fiber had more β-sheet conformation, better thermostability and mechanical properties. This was probably because that SS played significant roles in dehydrating SF molecules and inducing the conformational transition of SF to β-sheet structure.

The structure–property relationships of artificial silk fabricated by dry-spinning process

Regenerated silk fibroin (RSF) fibers were dry-spun from RSF aqueous solution and then post-treated in ethanol aqueous solution. In order to prepare artificial silk which are tougher and stronger than their natural counterpart, the structure–property relationships of the RSF fibers and natural silkworm silks were investigated by using synchrotron radiation X-ray microdiffraction technology, birefringence measurements and Raman spectroscopy. The as-spun RSF fibers with poor mechanical properties exhibited a strong diffraction peak of the [021] lattice plane and a weak diffraction peak of the [020]/[200] lattice plane. However, both the natural silk and the post-treated RSF fibers with exceptional mechanical properties showed weak diffraction peaks of the [021] lattice plane and strong diffraction peaks of the [020]/[200] lattice plane. Nevertheless, the two crystalline peaks are attributed to the silk II structure of silk fibroin. By deconvoluting the one-dimensional wide-angle X-ray microdiffraction pattern, the crystallinity and the degree of crystalline orientation were obtained. The as-spun fibers showed low crystallinity and low crystalline orientation, but the microstructure of the RSF fibers could be improved greatly and even become similar to that of degummed cocoon silk by post-treatment. When the as-spun RSF fibers were first drawn 3 to 4 times with a draw rate of 0.9 mm s−1 in ethanol aqueous solution and then immersed in the same solution for another hour, the breaking strain and breaking energy of the post-treated fibers were significantly greater than those of degummed cocoon silk.

Tough silk fibers prepared in air using a biomimetic microfluidic chip.

Microfluidic chips with single channel were built to mimic the shear and elongation conditions in the spinning apparatus of spider and silkworm. Silk fibers dry-spun from regenerated silk fibroin (RSF) aqueous solution using the chip could be tougher than degummed natural silk. The artificial silk exhibited a breaking strength up to 614 MPa, a breaking elongation up to 27% and a breaking energy of 101 kJ/kg.

Hybrid Silk Fibers Dry-Spun from Regenerated Silk Fibroin/Graphene Oxide Aqueous Solutions

Regenerated silk fibroin (RSF)/graphene oxide (GO) hybrid silk fibers were dry-spun from a mixed dope of GO suspension and RSF aqueous solution. It was observed that the presence of GO greatly affect the viscosity of RSF solution. The RSF/GO hybrid fibers showed from FTIR result lower β-sheet content compared to that of pure RSF fibers. The result of synchrotron radiation wide-angle X-ray diffraction showed that the addition of GO confined the crystallization of silk fibroin (SF) leading to the decrease of crystallinity, smaller crystallite size, and new formation of interphase zones in the artificial silks. Synchrotron radiation small-angle X-ray scattering also proved that GO sheets in the hybrid silks and blended solutions were coated with a certain thickness of interphase zones due to the complex interaction between the two components. A low addition of GO, together with the mesophase zones formed between GO and RSF, enhanced the mechanical properties of hybrid fibers. The highest breaking stress of the hybrid fibers reached 435.5 ± 71.6 MPa, 23% improvement in comparison to that of degummed silk and 72% larger than that of pure RSF silk fiber. The hybrid RSF/GO materials with good biocompatibility and enhanced mechanical properties may have potential applications in tissue engineering, bioelectronic devices, or energy storage.

Evaluation of stretched electrospun silk fibroin matrices seeded with urothelial cells for urethra reconstruction

BACKGROUND We investigated the feasibility of urethral reconstruction using stretched electrospun silk fibroin matrices. MATERIALS AND METHODS A novel electrospun silk fibroin matrix was prepared. The structure of the material was assessed by scanning electron microscopy and a porosity test. Canine urothelial cells were isolated, expanded, and seeded onto the material for 1 wk to obtain a tissue-engineered graft. The tissue-engineered graft was assessed using hematoxylin and eosin staining and scanning electron microscopy. A dorsal urethral mucosal defect was created in nine female beagle dogs. In the experimental group, tissue-engineered mucosa was used to repair urethra mucosa defects in six dogs. No substitute was used in the three dogs of the control group. Retrograde urethrography was performed at 1, 2, and 6 mo after grafting. The urethral grafts were analyzed grossly and histologically. RESULTS Scanning electron microscope and a porosity test revealed that the material had a three-dimensional porous structure. Urothelial cells grew on the material and showed good biocompatibility with the stretched silk fibroin matrices. Canines implanted with tissue-engineered mucosa voided without difficulty. Retrograde urethrography revealed no signs of stricture. Histologic staining showed gradual epithelial cell development and stratified epithelial layers at 1, 2, and 6 mo. The canines in the control group showed difficulty in voiding. Retrograde urethrography showed urethra stricture. Histologic staining showed that no or only one layer of epithelial cells developed. A severe inflammatory reaction was also observed in the control group. CONCLUSIONS Stretched electrospun silk fibroin matrices have good biocompatibility with urothelial cells, which could prove to be a potential material for use in urethra reconstruction.

In vitro studies on the structure and properties of silk fibroin aqueous solutions in silkworm

The spinning process of silkworm in vivo attracts great attentions. In this work, the structures and properties of the silk fibroin (SF) aqueous solutions from different divisions of silk glands of silkworms were investigated by using polarized microscope, rotational rheometer, Raman spectrometer and dynamic laser light scattering instrument. It was found that only the anterior (A) division and the anterior part of middle division (MA) of silk gland showed birefringence. With flowing from the posterior part (MP) to the MA part in the middle division of silk gland, the SF aqueous solutions was gradually transformed from random coil/α-helix to β-sheet conformation. Meantime, the elastic and viscous nature of the SF aqueous solution changed, and the mean diameter of SF aggregates increased from 118 nm to 331 nm. It could be concluded that the structures and properties of the SF aqueous solutions were gradually changed along the silk gland and the liquid crystal structure was initially formed in the MA part of silk gland.

Antheraea pernyi Silk Fiber: A Potential Resource for Artificially Biospinning Spider Dragline Silk

The outstanding properties of spider dragline silk are likely to be determined by a combination of the primary sequences and the secondary structure of the silk proteins. Antheraea pernyi silk has more similar sequences to spider dragline silk than the silk from its domestic counterpart, Bombyx mori. This makes it much potential as a resource for biospinning spider dragline silk. This paper further verified its possibility as the resource from the mechanical properties and the structures of the A. pernyi silks prepared by forcible reeling. It is surprising that the stress-strain curves of the A. pernyi fibers show similar sigmoidal shape to those of spider dragline silk. Under a controlled reeling speed of 95 mm/s, the breaking energy was 1.04 × 105 J/kg, the tensile strength was 639 MPa and the initial modulus was 9.9 GPa. It should be noted that this breaking energy of the A. pernyi silk approaches that of spider dragline silk. The tensile properties, the optical orientation and the β-sheet structure contents of the silk fibers are remarkably increased by raising the spinning speeds up to 95 mm/s.

Nanoconfined crystallites toughen artificial silk

Spider dragline silk is of great interest to people for its outstanding mechanical properties including high toughness. Biomimetic spinning of spider silk has attracted peoples attention for decades. This paper reports a simple and cheap method to greatly toughen artificial silk by compositing with nanoanatase. The toughness of the artificial silk (breaking energy 93.1 ± 27.1 MJ m-3) exceeded that of silkworm silks. The hydrophilic nanomineral TiO2 with large specific surface area interacted severely with the fibroin matrix through coordination complexes (Ti-protein) and hydrogen bonds (O-H). Due to the interfacial interactions, regenerated silk fibroin (RSF)-TiO2 fibers showed higher α-helix/random coil content, lower β-sheet content, smaller crystallites and lower crystallinity than pure RSF fibers. A nanoconfined crystallite toughening mechanism was proposed to discuss the structure-property relationship of the hybrid fibers.