Chemical modification of Bombyx mori silk with epoxide EPSIB

Bombyx mori silk fabrics were chemically modified by EPSIB (a multifunctional silicone‐containing epoxy crosslinking agent). The reactivity of the epoxy groups with silk fibroin was studied by using amino acid analysis. The physical properties of the modified silks such as resiliency (both wet and dry), moisture regain, dyeing behaviors, and solubility in a mixture solvent (C₂H₅OH × CaCl₂ : H₂O = 2 : 1 : 8, molar ratio) were examined. The modified silk fabrics exhibited a significantly improved resiliency, a small increase in moisture regain and whiteness, and a slightly decreased tensile strength. The contents of Serine, Trosine, Lysine, and Histidine decreased linearly as the wet crease recovery angle (CRA) increased. The solubility in the mixture solvent also decreased as the wet CRA increased. The changes of physical properties, especially the wet CRA, were mainly due to the presence of stable cross‐links between silk fibroin and epoxy groups. The DSC and TGA analyses showed that EPSIB‐modified silk fibroin had a higher thermal stability compared with the control. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3579–3586, 2004     

Preparation and characterization of silk fibroin nanocrystals

Crystalline silk fibroin nanoparticles (CSFs), a kind of natural protein nanocrystal, were prepared by treatment of silk fibroin (SF) powders with 64 wt% aqueous sulfuric acid. Various treatment periods were tested, and optimal conditions corresponded to 2 h at 45 °C. Transmission electron microscopy observation showed that the CSFs existed as short rod‐like fragments and spherical particles. The content ratio of β‐sheet structure to α‐form/random coil and the percentage crystallinity (χ_c) increased, but the weight‐average molecular weight of CSFs decreased with prolonged degradation time. Compared with native SF, these CSFs of nanometer size and relatively high χ_c showed an upward shift of the glass transition temperature and thermal degradation temperature. Furthermore, high‐strength elastic nanocomposite materials were successfully prepared from the CSFs and waterborne polyurethane (WPU). One of the WPU/CSF films produced exhibited significant increases from 1070 to 2370% for elongation at break, 0.6 to 2.2 MPa for tensile strength and 0.3 to 4.0 MPa for Young's modulus. This work provides a new pathway for the preparation of natural nanocrystals and WPU‐based elastomers with high strength and toughness. Copyright © 2012 Society of Chemical Industry     

Effect of moisture absorption on the thermal properties of Bombyx mori silk fibroin films

Films of regenerated Bombyx mori silk are strongly affected by absorbed moisture, a phenomenon studied here by differential scanning calorimetry (DSC). Exposure of previously dried films to environments of controlled relative humidity produces test samples of well-defined equilibrium moisture content. Ultimate moisture uptake is as high as 20–23% (by weight) at 75% relative humidity. The glass transition temperature, T_g, drops by 40°C at moisture uptakes as low as 2%, and T_g depressions as large as 140°C are observed at higher relative humidity. The moisture-induced decrease of T_g is completely reversible, as a film remoistened and then redried possesses an unchanged T_g. Trends in T_g with water uptake correspond reasonably well to predictions of a classical thermodynamic theory, indicating that the plasticization effect of moisture on the combined silk-water system can be satisfactorily explained from macroscopic properties of the constituents without any reference to specific interactions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 401–410, 1997     

Preparation of regenerated wool keratin films from wool keratin–ionic liquid solutions

The regenerated wool keratin films were prepared from the wool keratin/ionic liquid solutions through water, methanol and ethanol as coagulation solvents in this article. It could be suggested from the results that [AMIM]⁺·Cl^? ionic liquid has higher solubility for wool keratin fibers than [BMIM]⁺·Cl^? ionic liquid. IR data showed the part of the disulfide bonds was broken during the dissolution. It could be seen from XRD data that the regenerated films exhibited a β‐sheet structure and the disappearance of the α‐helix structure. TGA curves indicated that the thermal stability of regenerated wool keratin films decreased slightly compared to nature wool fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

SEDS工艺制备丝素纳米颗粒及其表征

以丝素蛋白为原料,以六氟异丙醇为溶剂,采用超临界流体强制分散溶液（SEDS）工艺制备了丝素纳米颗粒。单因素实验考察了压力、溶液浓度、溶液流速和CO2流速等因素对丝素纳米颗粒平均粒径分布的影响,并通过Zeta电位、HS-GC、FTIR、XRD和DSC等技术手段对制备的丝素纳米颗粒进行了表征。动态激光光散射仪检测结果表明：随压力、溶液浓度和流速的增大,丝素纳米颗粒平均粒径增大;随CO2流速的增大,丝素纳米颗粒平均粒径减小,最小达到298nm。丝素纳米颗粒Zeta电位为?39mV。HS-GC表明丝素纳米颗粒有机溶剂残留量为20μg/L。FTIR表明经SEDS工艺处理后丝素化学结构和官能团不会发生变化。XRD和DSC显示经SEDS工艺处理后丝素内部分子结构发生重排,由无规则卷曲向β折叠转换。     

同轴静电纺丝素蛋白纤维支架的制备及结构性能表征

以再生丝素蛋白水溶液为皮层纺丝液,去离子水为芯层纺丝液,探讨了同轴静电纺制备丝素蛋白组织工程支架材料的最佳工艺参数。结果表明,随着皮层纺丝液质量分数的提高,支架材料的表观形貌逐渐变好;当皮层纺丝液的质量分数为39%(w)、流速为1.2 m L/h,芯层纺丝液流速为0.3 m L/h时,可制备出表观形貌好、纤维粗细均匀且具有稳定皮芯结构的支架材料。文章探索得到的同轴静电纺丝工艺可用于载药组织工程支架材料的制备,并在组织工程修复领域具有良好的应用前景。     

Preparation of silk fibroin and polyallylamine composites

Composite films made of silk fibroin (SF) and polyallylamine (PAA) are prepared that contain various compositional ratios. These materials are analyzed to elucidate the resulting physical properties and to assess their potential toward advanced applications as industrial materials. The composite films are obtained from a SF and PAA binary system by dry casting from aqueous solution. These composite films exhibit excellent processability such as film forming capabilities, and the elongation at break is increased in the wet state. The differential scanning calorimetry (DSC) curves of the composites suggest that a mutual interaction takes place between the SF and PAA. This interaction is believed to occur because the endothermic peak, corresponding to the individual polymer, shifts with increasing SF content. The random coil conformation of the SF is present, regardless of the PAA blending, as confirmed by FTIR and DSC measurements. Additionally, living cells from Antheraea pernyi and Bombyx mori insect tissues are shown to grow effectively on the composite films. Maximum growth levels occur when the cultivation flask is coated with the material in SF/PAA ratios of 75:25 to 25:75. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1963–1970, 2002; DOI 10.1002/app.10491     

聚乳酸/丝素共混膜的制备及其性能

用分子量为10万的聚乳酸（PLLA）对丝素膜进行改性,研究不同的聚乳酸加入量对丝素膜性能的影响,对聚乳酸/丝素共混膜进行了一系列表征。万能电子试验机的测试结果表明,经聚乳酸改性后,丝素膜的断裂强度,断裂伸长率有了较大的改善,当加入聚乳酸占丝素质量为5%时,丝素膜的强度可达到27.1 MPa,伸长率达4.4%; 改性后的丝素膜的亲水性有一定程度降低,溶失率则明显减小,透汽透湿性也有所提高;红外光谱测试表明,改性后的丝素膜含有较多的β构象成分。     

Production of silk sericin/silk fibroin blend nanofibers

Silk sericin (SS)/silk fibroin (SF) blend nanofibers have been produced by electrospinning in a binary SS/SF trifluoroacetic acid (TFA) solution system, which was prepared by mixing 20 wt.% SS TFA solution and 10 wt.% SF TFA solution to give different compositions. The diameters of the SS/SF nanofibers ranged from 33 to 837 nm, and they showed a round cross section. The surface of the SS/SF nanofibers was smooth, and the fibers possessed a bead-free structure. The average diameters of the SS/SF (75/25, 50/50, and 25/75) blend nanofibers were much thicker than that of SS and SF nanofibers. The SS/SF (100/0, 75/25, and 50/50) blend nanofibers were easily dissolved in water, while the SS/SF (25/75 and 0/100) blend nanofibers could not be completely dissolved in water. The SS/SF blend nanofibers could not be completely dissolved in methanol. The SS/SF blend nanofibers were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and differential thermal analysis. FTIR showed that the SS/SF blend nanofibers possessed a random coil conformation and ß-sheet structure.     

Study on porous silk fibroin materials. II. Preparation and characteristics of spongy porous silk fibroin materials

Porous silk fibroin materials, with average pore size 10 ∼ 300 μm, pore density 1 ∼ 2000/mm², and porosity 35 ∼ 70%, were prepared by freeze drying aqueous solution of silk fibroin obtained by dissolving silk fibroin in ternary solvent CaCl₂ · CH₃CH₂OH · H₂O. Pore size distribution of such materials mostly accorded with logarithmic normal distribution. It is possible to control the aforementioned structural parameters and the physical properties of moisture permeability, compressibility, strength, elongation, etc., by adjusting freezing temperature and concentration of silk fibroin solution. Above glass transition zone (−34 ∼ −20°C) of silk fibroin, the freezing temperature has more significant effect on the structure and properties of porous silk fibroin materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2192–2199, 2001     

Preparation and characterization of biomimetic silk fibroin/chitosan composite nanofibers by electrospinning for osteoblasts culture

ABSTRACT: In this study, we have successfully fabricated electrospun bead-free silk fibroin [SF]/chitosan [CS] composite nanofibers [NFs] covering the whole range of CS content (0%, 25%, 50%, 75%, and 100%). SF/CS spinning solutions were prepared in a mixed solvent system of trifluoroacetic acid [TFA] and dichloromethane. The morphology of the NFs was observed by scanning electron microscope, and the average fiber diameter ranges from 215 to 478 nm. Confocal laser scanning microscopy confirms the uniform distribution of SF and CS within the composite NFs. To increase biocompatibility and preserve nanostructure when seeded with cells in culture medium, NFs were treated with an ethanol/ammonia aqueous solution to remove residual TFA and to change SF protein conformation. After the chemical treatment, SF/CS NFs could maintain the original structure for up to 54 days in culture medium. Properties of pristine and chemically treated SF/CS NFs were investigated by Fourier transform infrared spectroscopy [FT-IR], X-ray diffraction [XRD], and thermogravimetry/differential scanning calorimetry [TG/DSC]. Shift of absorption peaks in FT-IR spectra confirms the conformation change of SF from random coil to β-sheet by the action of ethanol, which is also consistent with the SF crystalline diffraction patterns measured by XRD. From TG/DSC analysis, the decomposition temperature peaks due to salt formation from TFA and protonated amines disappeared after chemical treatment, indicating complete removal of TFA by binding with ammonium ions during the treatment. This was also confirmed with the disappearance of F1s peak in X-ray photoelectron spectroscopy spectra and disappearance of TFA salt peaks in FT-IR spectra. The composite NFs could support the growth and osteogenic differentiation of human fetal osteoblastic [hFOB] cells, but each component in the composite NF shows distinct effect on cell behavior. SF promotes hFOB proliferation while CS enhances hFOB differentiation. The composite SF/CS NFs will be suitable for bone tissue engineering applications by choosing a suitable blend composition.PACS: 87.85.jf; 87.85.Rs; 68.37.Hk.     

新型丝素复合膜的微结构表征及热稳定性

基于丝素的高分子复合材料可以广泛地应用于组织工程、生物医药和半导体材料等领域。通过物理-共混技术制备了一种新型生物高分子丝素/聚乳酸复合膜。利用扫描电镜、傅里叶红外光谱、拉曼光谱、X射线衍射和热分析技术对其形貌、结构和相态组分以及热稳定性进行了表征,探究了不同比例复合膜的微结构、相互作用机理和热稳定性。结果表明：随着丝素含量的增加,复合膜中的β-折叠含量增多,α-螺旋和无规卷曲含量减少,玻璃化转变温度提高;由于丝素与聚乳酸间的相互作用,提高了复合膜的热稳定性。     

Dissolution and characterization of regenerated Antheraea pernyi silk fibroin

Dissolution of Antheraea pernyi silk fiber was carried out in a calcium nitrate solution with various dissolving conditions. The solubility was significantly dependent on the concentration of calcium nitrate, dissolving temperature, and time. The proper conditions of dissolution were found as 7M calcium nitrate, 100°C temperature, and 3 h dissolving time. The aqueous solution of A. pernyi silk fibroin was composed of a mixture of polypeptides with several molecular weights above 14 kDa. FTIR and XRD showed that regenerated A. pernyi silk fibroin was composed of an α-helix as well as a random-coil conformation while silk fiber had a traditional β-sheet structure. The endo–exo transition in the temperature ranges of 228–232°C also supports these conformations of regenerated silk fibroin film. TGA and DTG curves showed that the thermal decomposition of regenerated A. pernyi silk fibroin proceeded by three steps, not dependent on the conformation. The mechanical damping peaks (tan δ) appeared about 227°C with a minor shoulder maximum about 240°C, which were somewhat lower than those of tussah silk fiber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 750–758, 2001     

Preparation of nanosize cadmium sulfide particles with a silk fibroin membrane and their photocatalytic activity

We present a novel method for the synthesis of nanosize CdS particles with a silk fibroin membrane, which were characterized with UV spectrometry, X‐ray diffraction (XRD), and atomic force microscopy. The UV spectra showed a clear blueshift in the absorption edge for the CdS particles prepared at different concentrations. XRD showed the prevailing crystal were the cube ZnS crystals formed. The particle sizes were calculated from the band gaps with the effective mass approximate model, suggesting that they were dependent on the concentration of the precursors. Meanwhile, nanosize CdS had good photocatalytic activity throughout the photocatalytic degradation experiments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2162–2166, 2006     

从丝素水溶液中再生的丝纤维的结构与性能

通过使用表面皿直接拉伸、毛细管重力纺丝和人工拉伸3种不同的成丝方法,从高浓度再生丝素水溶液中制得了丝纤维。用偏光显微镜观察了丝纤维的取向,用拉曼光谱仪和Instron拉力仪表征了丝纤维的结构和力学性能。结果发现,经毛细管剪切流动后再拉伸有利于再生丝性能的提高,所得的丝有较好的取向和较多的β折叠结构,力学性能也相对较好。剪切在丝纤维的成形过程中起重要的作用。     

离子液体对丝素蛋白溶解性能的影响

合成了一系列碱性离子液体,其中离子液体1-丁基-3-甲基咪唑乙酸盐([Bmim]AC)对丝素蛋白具有良好的溶解性能。考察了丝素蛋白在该离子液体中的溶解特性及在离子液体中的溶解温度和溶解时间,结果表明,在75℃下,溶解840 min,该离子液体对丝素蛋白的溶解能力达到15%(质量分数)。XRD和FTIR分析表明,再生丝素蛋白的构象以α-螺旋为主,丝素蛋白在溶解过程中没有发生衍生化。因此,[Bmim]AC离子液体是丝素蛋白的优良溶剂。     

纳米二氧化钛/丝素复合膜的制备及其光催化甲基橙的研究

制备了纳米二氧化钛/丝素复合膜,并用原子力显微镜、X射线能谱和红外光谱对复合膜进行了表征,以甲基橙为例,考察了复合膜的光催化行为。结果表明复合膜制备方法合理,当纳米二氧化钛与丝素质量比为0.1%时,其以粒径50nm左右均匀分散于复合膜中,复合膜与普通丝素膜仅存在细微的构象差异,复合膜表现出较优异的光催化性能,甲基橙降解率可达91%,符合Langmuir Himshelwood模型。     

用二维FTIR研究纳米TiO2改性丝素蛋白聚集态结构转变

采用溶胶-凝胶方法制备纳米TiO₂复合丝素膜。UV和SEM测试结果表明,该丝素膜中纳米TiO₂均匀分散在丝素中,TiO₂粒径约为80 nm;同时采用一维红外光谱、二维红外相关光谱对纯丝素膜及复合丝素膜结构进行表征。结果表明,随着纳米TiO₂的生成,丝素蛋白中弱氢键缔合的N—H键以及自由的N—H键发生断裂及重组,生成了强氢键;丝素分子从无序状态转变为有序排列,同时无规线团构象及α螺旋构象向β折叠构象发生转变,最后促使丝素蛋白的结晶构象从Silk Ⅰ转变为Silk Ⅱ。     

Biodegradation of Bombyx mori silk fibroin fibers and films

The in vitro biodegradation of Bombyx mori silk fibroin was studied by incubating fibers and films with proteolytic enzymes (collagenase type F, α‐chymotrypsin type I‐S, protease type XXI), for times ranging from 1 to 17 days. The changes in sample weight and degree of polymerization of silk fibers exposed to proteolytic attack were negligible. However, tensile properties were significantly affected, as shown by the drop of strength and elongation as a function of the degradation time. Upon incubation with proteolytic enzymes, silk films exhibited a noticeable decrease of sample weight and degree of polymerization, the extent of which depended on the type of enzyme, on the enzyme‐to‐substrate ratio, and on the degradation time. Protease was more aggressive than α‐chymotrypsin or collagenase. Film fragments resistant to enzymatic degradation were enriched in glycine and alanine. FT‐IR measurements showed that the degree of crystallinity of biodegraded films increased. Soluble degradation products of silk films consisted of a range of peptides widely differing in size, deriving from the amorphous sequences of the silk fibroin chains. Biodegraded fibers showed an increase of surface roughness, while films displayed surface cracks and cavities with internal voids separated by fiber‐like elements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2383–2390, 2004     

Preparation of semi‐interpenetrating polymer networks composed of silk fibroin and poly(ethylene glycol) macromer

Semi‐interpenetrating polymer networks (SIPNs) composed of silk fibroin (SF) and a poly(ethylene glycol) (PEG) diacrylate macromer were synthesized and characterized. The conformation of SF in SIPNs was changed from a random coil to a β‐sheet structure by formation of SIPNs with PEG, while the crystalline structures of SF and PEG in SIPNs was not changed. The decomposition temperature of SF in the SIPNs was inner‐shifted, an indication of SIPN formation between the SF and the PEG macromer. The tensile strength and elongation of the SIPNs were much higher than were those of SF itself or the SF/PEG blend and increased with an increase of the PEG content. The equilibrium water content of SF was remarkably increased by formation of SIPNs with PEG due to the hydrophilic property of PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1848–1853, 2001