Correlation between processing conditions,microstructure and mechanical behavior in regenerated silkworm silk fibers

Regenerated silkworm fibers spun through a wet‐spinning process followed by an immersion postspinning drawing step show a work to fracture comparable with that of natural silkworm silk fibers in a wide range of spinning conditions. The mechanical behavior and microstructure of these high performance fibers have been characterized, and compared with those fibers produced through conventional spinning conditions. The comparison reveals that both sets of fibers share a common semicrystalline microstructure, but significant differences are apparent in the amorphous region. Besides, high performance fibers show a ground state and the possibility of tuning their tensile behavior. These properties are characteristic of spider silk and not of natural silkworm silk, despite both regenerated and natural silkworm silk share a common composition different from that of spider silk. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Porous 3‐D scaffolds from regenerated Antheraea pernyi silk fibroin

In this study, porous three‐dimensional (3‐D) materials were prepared with the regenerated Antheraea pernyi (A. pernyi) silk fibroin by freeze‐drying from a lithium thiocyanate solution of its fibers. The relationship between preparation conditions and morphological structures of 3‐D materials was also studied. We concluded that with the decrease in A. pernyi silk fibroin solution concentration and the increase in the freezing temperature, the porosity and the average pore diameter of the 3‐D materials were increased while the pore density was decreased. By adjusting the freezing temperature and the silk fibroin solution concentration, the 3‐D materials having the average pore diameter of 75–260 µm and the porosity of 70–90% can efficiently be produced. As a kind of new material with excellent biocompatibility and bioactivity, the material is expected to be applied to tissue regeneration scaffolds. Copyright © 2007 John Wiley & Sons, Ltd.     

Microrheological studies of regenerated silk fibroin solution by video microscopy

We have carried out studies on the rheological properties of regenerated silk fibroin (RSF) solution using video microscopy. The degummed silk from the Bombyx mori silkworm was used to prepare RSF solution by dissolving it in calcium nitrate tetrahydrate‐methanol solvent. Measurements were carried out by tracking the position of an embedded micron‐sized polystyrene bead within the RSF solution through video imaging. The time dependent mean squared displacement (MSD) of the bead in solution and hence the complex shear modulus of this solution was calculated from the bead's position information. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera at full resolution. By examining the distribution of MSD of beads at different locations within the sample volume, we demonstrate that this probe technique enables us to detect local inhomogeneities at nanometre length scales, not detectable either by a rheometer or from diffusing wave spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2555–2562, 2007     

再生蚕丝的制备及其结构和性能初探

在制备高浓度高分子量蚕丝素蛋白水溶液的基础上, 采用湿法纺丝技术, 在一定条件下纺制出力学性能优于天然蚕(茧)丝的再生蚕丝纤维, 其断裂强度及断裂伸长率分别达到0.5 GPa和20%. 扫描电镜观察结果显示: 初生纤维具有典型的“皮芯”结构, 而纤维内部则为疏松多孔的网状或蜂窝状结构; 经过一定的后拉伸处理后, 纤维的表面变得光滑, 且内部结构也趋于致密. 固体 13C核磁共振及拉曼光谱分析结果表明, 后拉伸及热湿处理均有利于提高纤维内部β-折叠结构的含量, 分子链的规整度和取向性也随之改善, 从而使再生蚕丝纤维的力学性能得到进一步提高.     

In situ drawing of high molecular weight poly(ethylene terephthalate) in subcritical and supercritical CO2

The effects of draw conditions were studied for initially amorphous melt‐spun poly(ethylene terephthalate) fibers in the presence of subcritical and supercritical (SC) CO₂. Both in situ and posttreatment mechanical behavior along with morphological characteristics were investigated. Fibers soaked in subcritical CO₂ could be drawn to 30% higher draw ratios (DRs) compared with fibers that were cold‐drawn. In situ force response measured with a custom apparatus showed that fibers in subcritical CO₂ had no measurable resistance to deformation until strain hardening occurred. In contrast, fibers drawn in SC CO₂ displayed a yield response, a significant decrease in ductility, and a significant difference in postyield behavior. Fibers drawn in subcritical CO₂ showed slightly lower tensile properties compared with cold‐drawn samples whereas fibers treated in SC CO₂ had much lower tensile properties because of the limited DR achieved. X‐ray diffraction studies indicated that CO₂ enhances the development of the crystalline phase compared with cold‐drawn samples. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1881–1891, 1999     

Fabrication of silk fibroin film with properties of thermal insulation and temperature monitoring

Silk fibroin exhibits excellent mechanical properties, good biocompatibility, and biodegradability combined with benign processing conditions, attracting considerable research interest for the application as biomedical materials. Among the diverse forms of sponges, hydrogels, films, and mats manufactured from silk fibroin, films are especially appealing due to the high water and oxygen permeability, good cell attachment, and low immunogenicity. Fabrication of silk fibroin films with novel properties has been successfully developed simply by incorporating various functional components into it. In the present study, the properties of thermal insulation and temperature monitoring for the silk fibroin film are demonstrated for the first time through the incorporation of thermochromic microcapsules within it. Moreover, the silk fibroin film is also endowed with improved mechanical properties in terms of tension strength and elongation at break because of the reinforcing effect of thermochromic microcapsules. The silk fibroin film fabricated with novel features in this study can be a good candidate for the application of wound dressings, tissue engineering scaffolds, and bio‐related devices in the future. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1846–1852     

Effect of processing conditions on the properties of high molecular weight conductive polyaniline fiber

Polyaniline–emeraldine base (EB) fiber with excellent mechanical and electrical properties have been spun from highly concentrated (20% w/w), EB/N‐methyl‐2‐pyrrolidinone (NMP)/2‐methylaziridine (2 MA) solution. These solutions had gelation times, which varied from hours to days depending on the molar ratio of 2 MA to EB tetramer repeating unit in the N‐methyl‐2‐pyrrolidinone (NMP) solvent. To better compare the mechanical and electrical properties, dense films were also prepared by thermal evaporation of less concentrated solution (1% w/w). Both fibers and films were amenable to thermal stretching with maximum draw ratios of 4 : 1 and these stretched samples exhibited the greatest tensile strength overall. Wide‐angle X‐ray diffraction (WAXD) of as‐spun and 4‐times stretched fiber showed a completely amorphous structure. Fiber subjected to heat treatment at 250 °C under N₂ flux for 2 h displayed further improvements in mechanical properties because of crosslinking between the polymer chains. Fibers and films were later doped by immersion in a variety of aqueous acid solutions. Room temperature DC conductivities for the doped samples ranged from 6 × 10⁻⁴ to 45 S/cm depending on the specific choice of acid. Scanning electron microscopy of fiber samples shows the presence of macrovoid formation during fiber spinning. Continued refinement of the processing parameters and fiber post‐treatment, to enhance chain alignment and increase fiber density, will likely lead to additional improvements in the fiber mechanical and electrical properties. Characterization of emeraldine base (EB) powder, solution, films, and fibers by UV‐Vis, DSC, TGA, and WAXD were also performed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 194–204, 2000     

Concentration‐dependent conformation transition of regenerated silk fibroin induced by graphene oxide nanosheets incorporation

Regenerated silk fibroin (RSF)/graphene oxide (GO) nanocomposite has been substantially investigated due to its significant multifunctional potential. Here, in combination of micromorphology, crystalline conformation, dynamic mechanical property characterization, and Fourier self‐deconvolution (FSD) quantitative analysis, we investigated the RSF molecular chains conformation transition induced by GO nanosheet incorporation, and its influence on the structural and mechanical properties of solution casted RSF/GO composite films. The GO nanosheet promoted the silk fibroin molecular chains conformation transition from random coil to β‐sheet structure, and a correlation between β‐sheet structure fraction and GO concentration was revealed. The β‐sheet structure fraction increases further improved the dynamic mechanical property of composite films. Moreover, based on nucleation‐dependent aggregation of silk fibroin molecular chains, a mechanism considering the competition effect between GO concentration and its total surface area was proposed to explain the observed concentration‐dependent conformation transition phenomenon. The study improves our understanding on silk fibroin conformation transition process in RSF/GO composite and would provide a valuable reference for the rational design of bioinspired multifunctional materials with enhanced mechanical properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1506–1515     

Physical and chemical properties of tussah silk fibroin films

Physical and chemical structure, as well as thermal behavior of solution-cast regenerated films, prepared from tussah (Antheraea pernyi) silk fibroin, were compared with those of solution-cast native films, in order to ascertain whether treatment (degumming, dissolution) used for preparation affected their properties. Regenerated fibroin films exhibited a higher thermal stability than native ones, as shown by differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical behavior. Glass transition temperature and other relevant thermal transitions of the regenerated silk specimen shifted to higher temperatures compared with those of native specimen. Molecular conformation and crystalline structure did not show significant differences between the two kinds of silk films. Amino acid composition and molecular weight, however, distribution changed markedly after dissolving tussah silk fibroin fiber in concentrated LiSCN in polypeptide size was the main features for the regenerated silk fibroin. © 1994 John Wiley & Sons, Inc.     

Fabrication and Characterization of Conductive Conjugated Polymer‐Coated Antheraea mylitta Silk Fibroin Fibers for Biomedical Applications

Conductive polymers are interesting materials for a number of biological and medical applications requiring electrical stimulation of cells or tissues. Highly conductive polymers (polypyrrole and polyaniline)/Antheraea mylitta silk fibroin coated fibers are fabricated successfully by in situ polymerization without any modification of the native silk fibroin. Coated fibers characterized by scanning electron microscopy confirm the silk fiber surface is covered by conductive polymers. Thermogravimetric analysis reveals preserved thermal stability of silk fiber after coating process. X‐ray diffraction of degummed fiber diffraction peaks at around 2θ = 20.4 and 16.5 confirms the preservation of the β‐sheet structure typical of degummed silk II fibers. This phenomenon implies that both polypyrrole and polyaniline chains form interactions with peptide linkages in degummed fiber macromolecules, without significantly disrupting protein assembly. Fourier transform infrared spectroscopy of coated fibers indicates hydrogen bonding and electrostatic interactions exist between silk fibroin macromolecules and conductive polymers. Resulting fibers display good conductive properties compared to corresponding conjugated polymers. In vitro analysis (live/dead assay) of the behavior of human immortalized keratinocytes (HaCaTs) on coated fibers demonstrates improved cell‐adhesive properties and viability after polymers coating. Hence, polypyrrole‐ and polyaniline‐coated A. mylitta silk fibers are suitable for application in cell culture and for tissue engineering, where electrical conduction properties are required.

     

Thermal and rheological characterization of cellulose spinning dopes modified with nanosilica and antibacterial agents

The present study concerns cellulose spinning solutions prepared with the use of the organic solvent N‐methylmorpholine‐N‐oxide (NMMO). These solutions were modified with two types of antibacterial agents: an inorganic agent zirconium‐silver phosphate (Alphasan®) and an organic one Triclosan (Irgasan® DP300). Such spinning solutions allow to obtain antibacterial fibers of the Lyocell type. A nanomodifier, colloidal silica (Ludox SM 30®), was also incorporated into the spinning solutions as an additional component to increase the antibacterial activity of fibers. The effect of the compounds incorporated into the spinning solutions on their rheological and thermal properties was assessed by means of the oscillatory method and differential scanning calorimetry (DSC), respectively. The incorporation of nanosilica exerts a clear influence on the rheological properties of spinning solutions, whereas this effect is negligible in the simultaneous presence of nanosilica and antibacterial agents. The results of thermal measurements show that nanosilica affects the crystallization of the solutions examined. Depending on the type of antibacterial agent, nanosilica brings about either a delay or acceleration of the crystallization of the modified solutions. The effect of nanosilica can be explained in terms of interactions between hydroxyl groups occurring on the surface of silica nanoparticles and NMMO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

Chinese Oak Tasar Silkworm Antheraea pernyi Silk Proteins: Current Strategies and Future Perspectives for Biomedical Applications

Chinese nonmulberry temperate oak tasar/tussah, Antheraea pernyi (Ap) silk is a natural biopolymer that has attracted considerable attention as a biomaterial. The proteinaceous components of Ap silk proteins, namely fibroin and sericin may represent an alternative over mulberry Bombyx mori silk proteins. In fact, the silk fibroin (SF) of Ap is rich in Arginyl‐Glycyl‐Aspartic acid (RGD) peptides, which facilitate the adhesion and proliferation of various cell types. The possibility of processing Ap silk proteins into different distinct 2D‐ and 3D‐based matrices is described in earlier studies, such as membranes, nanofibers, scaffolds, and micro/nanoparticles, contributing to a different rate of degradation, mechanical properties, and biological performance useful for various biomedical applications. This review summarizes the current advances and developments on nonmulberry Chinese oak tasar silk protein (fibroin and sericin)‐based biomaterials and their potential uses in tissue engineering, regenerative medicine, and therapeutic delivery strategies.     

Thymine‐based,water‐soluble phototerpolymers: Their preparation and synthesis

Terpolymers of vinylbenzylthymine, vinylbenzyltriethylammonium chloride, and N‐butyl‐N,N‐dimethyl‐(4‐vinylbenzyl)ammonium chloride with different monomer ratios have been prepared, and the effect of the monomer ratios on the properties of the terpolymers has been investigated. These polymers are water‐soluble and, when irradiated with low levels of UV light, undergo a 2π+2π photodimerization reaction of thymine. This photodimerization significantly reduces the water solubility, immobilizing the polymer to the substrate, and shows potential for water‐soluble photoresists. Thermogravimetric analysis has revealed that the terpolymers have two degradation stages corresponding to the quaternary ammonium pendant groups and to the thymine. An evaluation of the contact‐angle measurements has shown that the surface properties and hydrophobicity can be controlled by the variation of the monomer ratios. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1296–1303, 2007     

Melt spinning and laser‐heated drawing of a new semiaromatic polyamide,PA9‐T fiber

Fibers of PA9‐T, a new semiaromatic polyamide containing a long aliphatic chain, were prepared by melt spinning. As‐spun fibers were subsequently drawn with a CO₂ laser‐heated drawing system at different draw ratios and various drawing velocities. On‐line observations of drawing points deciphered two drawing states; namely, flow drawing and neck drawing, over the entire range of drawing. Drawing stress revealed that flow drawing is induced by slight drawing stress under a low draw ratio up to 3, and neck drawing is induced by relatively high drawing stress under a higher draw ratio. The effect of drawing stress and drawing velocity on the development of the structure and properties has been characterized through analysis of birefringence, density, WAXD patterns, and tensile, thermal, and dynamic viscoelastic properties. For the neck‐drawn fibers, almost proportional enhancements of crystallinity and molecular orientation with drawing stress were observed. The flow‐drawn fibers have an essentially amorphous structure, and birefringence and density do not always have a linear relation with properties. The fibers drawn at high drawing speed exhibit improved fiber structure and superior mechanical properties. The maximum tensile strength and Young's modulus of PA9‐T drawn fibers were found to be 652 MPa and 5.3 GPa, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 433–444, 2004     

Dissolution of Silk Fibroin in N-methylmorpholine-N-oxide and Its Mixtures with Organic Solvents

Preparation of concentrated solutions of natural silk fibroin in N-methylmorpholine-N-oxide and its mixtures with protonic and aprotic solvents was experimentally studied. Solutions with the fibroin concentration of 6 wt % and more were prepared.     

Fracture surfaces and tensile properties of UV‐irradiated spider silk fibers

A study of the influence of UV radiation on the tensile properties of spider silk has shown that the shape of the stress–strain curves is not affected by 254‐nm irradiation, except for a significant decrease in the tensile strength and strain at breaking. This decrease has been found in both forcibly silked and maximum‐supercontracted fibers, despite the different initial alignments of the protein chains. Local damage is also induced by UV radiation. With this procedure, it is possible to recover and analyze fracture surfaces. These show different granular microstructures that are characteristic of fibers spun from a solution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 786–793, 2007     

Wet-spinning of Regenerated Silk Fiber fromAqueous Silk Fibroin Solutions: Influence ofCalcium Ion Addition in Spinning Dope on thePerformance of Regenerated Silk Fiber简

Ca（II） ions are added in the spinning dope to adjust the solidification rate of regenerated silk fibroin （RSF） solution during the wet-spinning process since Ca（II） ions are proved to be favorable to maintain the stable silk fibroin network in our previous work. The results show that when Ca（II）/RSF ratios are 1/50 and 1/20, the resulted RSF fibers exhibit good performance with the breaking energy more than 70 kJ/kg. However, higher Ca（II）/RSF ratio （for example, 1/10） hinders the solidification of spinning dope and results in poor RSF fibers. These observations together with earlier papers from this laboratory confirm that to produce tough silk fibers the spinning conditions must allow sufficient time for the adjustment of silk fibroin molecular chains.     

Correlation between the tensile properties and network draw ratio of CO2‐laser‐heated drawn poly(ethylene terephthalate) fibers

Low‐orientation and amorphous poly(ethylene terephthalate) fibers were drawn continuously with heating by carbon dioxide (CO₂) laser radiation. The tensile properties were examined in terms of the birefringence and network draw ratio, which was estimated from the strain shift of true stress–strain curves. Two drawing forms, neck drawing with a draw efficiency (the ratio of the network draw ratio to the actual draw ratio) of about unity and flow drawing with a draw efficiency of about zero, were found to be stable in the continuous drawing process. Meanwhile, any draw‐efficiency value between zero and unity could be obtained in the batch‐drawing process. The object whose orientation was estimated by the network draw ratio differed from that estimated by birefringence. Two linear relationships were found, between the network draw ratio and tensile strength and between the birefringence and initial modulus. The true stress at breaking increased with the network draw ratio of the CO₂‐laser‐heated drawn fibers, and when the draw ratio exceeded 5.0, it became higher than that for batch‐drawn fibers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2322–2331, 2003     

Thermochromic cellulose fibers

A method of obtaining thermochrome cellulose fibers has been developed. The basis technology used to form fibers was the Lyocell process. This method is based on spinning fibers from concentrated solvents of cellulose, using dry‐wet method in aqueous solidification bath. The cellulose solvent used in this process was N‐oxide‐N‐methylomorpholine (NMMO). The studies were to check on the features of the fibers obtained from solvents with thermochrome pigmentation, in order to evaluate their practical use. Thermochrome modifier used in the experiment was Chromicolor®AQ‐INK, Magenta type#27 pigmentation. This modifier was introduced into the spinning solutions in such amounts that fibers obtained from them would contain 1–10 wt% of pigmentation. Fibers formed out of modified solvents underwent spectral values, thermal, physicomechanical analyses, also their sorption features were evaluated. Copyright © 2007 John Wiley & Sons, Ltd.     

天然蚕丝与丝素蛋白多孔膜的生物降解性研究

较为详细地研究了经不同条件处理的丝素蛋白多孔膜材料和天然蚕丝在蛋白酶作用下的降解性能以及降解前后材料的微观形貌和结构的变化. 结果表明, 丝素蛋白材料中不同结构(构象)的含量是影响其降解速度的一个重要因素. 对于由再生丝素溶液所制备的材料, 调控其中Silk II结构(β-折叠构象)的比例可能是控制丝素蛋白材料降解速度的有效途径.