Structural and conformational changes of regenerated Antheraea pernyi silk fibroin films treated with methanol solution

The regenerated Antheraea pernyi silk fibroin films were prepared from calcium nitrate solution and crystallized with aqueous methanol solution. The structural and conformational changes were investigated by the X-ray diffraction method and infrared spectroscopy upon methanol treatment. The concentration and treatment time of aqueous methanol solution have a great influence on the conformation of regenerated films. The conformational change from a random coil to β-sheet structure was occurred within 5 min by the treatment of 40–60% methanol solution. As the methanol concentration increases up to 100%, the transition time of conformational change is delayed, and the structural change is not occurred in the case of 100% methanol used. The content of a α-helix, β-sheet, and random coil conformation was calculated and examined to find out the effect of methanol treatment on the conformation changes. The β-sheet structure can be transformed from a random coil, while the content of α-helix structure is not changed, regardless of methanol treatment. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2887–2894, 1999     

Effect of heat treatment on the structural and conformational changes of regenerated Antheraea pernyi silk fibroin films

Regenerated Antheraea pernyi silk fibroin films prepared from calcium nitrate solution were treated with heat for crystallization. The structural and conformational changes caused by heat treatment were investigated with X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry. The temperature and treatment time of heat greatly influenced the conformation of the regenerated films. The conformational change was caused by heat treatment over 230°C, and the transition was enhanced by increasing time and temperature. The contents of α-helix, β-sheet, and random-coil conformations were calculated and examined to investigate the effect of heat treatment on the conformational changes. The β-sheet structure could be transformed from a random-coil conformation on heat treatment, whereas the content of α-helix structure was nearly unchanged, regardless of heat-treatment conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2271–2276, 2001     

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。     

丝素蛋白在离子液体中的溶解特性研究

文章以离子液体为溶剂,研究了丝素蛋白在离子液体中的溶解特性。首先研究了丝素蛋白在不同结构的离子液体1-烯丙基-3-甲基咪唑氯化物（[AMIM]C1）和1-丁基-3_-甲基咪唑氯化物（[BMIM]c1）中的溶解速率和溶解度。结果发现,相同条件下,丝素蛋白在[AMIM]cl中具有较快的溶解速率和较大的溶解度;随温度的升高,溶解速度加快,合适的温度为95～105℃;随着丝素蛋白浓度的增大,相同条件下丝素蛋白在离子液体中的溶解速度减慢。XRD结果表明,丝素蛋白的非晶相部分首先被溶解,晶相部分结构被破坏后与溶剂作用逐渐被溶解。采用粘度法测定了丝素蛋白分子质量随溶解时间和温度的变化,结果表明：随加热时间增加和温度升高,蛋白质分子质量减小。为保证丝素蛋白的稳定性和溶解速率,温度一般控制在100℃以下,溶解时间小于5h。     

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。     

Structure and properties of regenerated Antheraea pernyi silk fibroin filaments

Degummed Antheraea pernyi silk fibroin (APSF) fibers were dissolved in a lithium thiocyanate solution that was dialyzed against distilled water for 3 days. Solution‐cast APSF films were dissolved in hexafluoroisopropanol to prepare a spinning solution. Wet spinning was employed to prepare APSF filaments. Scanning electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, solid‐state ¹³C cross‐polarization/magic angle spinning nuclear magnetic resonance, and differential scanning calorimetry were employed to study the regenerated APSF filaments. The results showed a uniform distribution of molecular weights, and the largest one may have been greater than 200 kDa. The regenerated filaments contained β‐sheet, α‐helix, and random‐coil conformations, and their breaking strength was 52.20% of the breaking strength of the native fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of iodine treatment on the carbonization behavior of Antheraea pernyi silk fibroin fiber

The effect of iodine treatment on the carbonization behavior of tussah silk fibroin (SF) fiber from a wild cocoon, Antheraea pernyi (A. pernyi), was investigated, and the carbon yield, fiber morphology, structural characteristics, and mechanical properties were evaluated. The SF fiber was treated with iodine vapor at 100°C for 12 h and was heated to 800°C under a multistep heating program as carbonization process, which corresponds to the constant thermal degradation rate of SF determined by dynamic thermogravimetric analysis (TGA). The carbon yield was ca. 39 wt %, which is much higher than those for untreated A. pernyi. Scanning electron microscopic (SEM) observation showed that obtained carbon fibers from iodinated SF were structurally intact, and the strength was higher than that from untreated SF. Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction, and Raman spectroscopy revealed that the structures of the carbon fibers obtained from both untreated and iodinated SF were almost the same and amorphous. At the early stage of carbonization of SF, amide bonding of SF molecules was begin to collapse at temperatures higher than 350°C and was completely dissociated by carbonization at 800°C. Dynamic viscoelastic measurements showed that with heating above 270°C the iodine component introduced intermolecular crosslinking of SF and the melt flow of the SF was inhibited, which enhances higher carbon yield and better performance of silk based carbon fiber. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Deduction of a facile method to construct Antheraea mylitta silk fibroin/gelatin blend films for prospective biomedical applications

Blend films of two types (I and II) were prepared by mixing Antheraea mylitta silk fibroin (AMF) and gelatin solution in various blend ratios via the solution casting method. Two different crosslinkers, namely glutaraldehyde and genipin, were used during blend preparation. The structural characteristics and thermal properties of the blend films were examined by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), Thermogravimetric analysis (TGA) and Diffrential scanning calorimetery (DSC). The FTIR spectra showed conformational alterations in type I blend films while type II films attained high β‐sheet crystallinity. The XRD diffractograms presented a high degree of crystallinity in type II blend films compared to type I, which showed an almost amorphous structure. Further, thermal and biological studies were conducted on type II films. According to the TGA thermograms, the degradation temperature of the crosslinked blend films shifted compared to pure gelatin and pure AMF films. Partial miscibility of the two components was indicated by DSC thermograms of the blends. The high water uptake capacity of type II blend films was found to imitate hydrogel behaviour. The blend films did not show any toxicity in 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay and supported L929 fibroblast cell spreading and proliferation. The biodegradation of the blend films was significantly faster than the pure silk film. © 2020 Society of Industrial Chemistry     

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。     

再生丝素/丝胶蛋白水溶液的微流体静电纺丝研究

以再生丝素蛋白(SF)水溶液和丝胶蛋白(SS)水溶液为纺丝液,微流体多通道芯片为纺丝器,成功制备了SF/SS和SF/SS/SF纤维毡。制备SF/SS纤维毡时,上述两流体在微通道中以层流方式流动,到达芯片出口处既不共混也不分层,而是各自独立成丝,通过扫描电镜可以观察到粗细差异较大的两种纤维共存,形貌较好。以SS水溶液为微通道的中心流体,SF水溶液为两侧流体,通过微流体静电纺制得SF/SS/SF纤维毡,SF部分与SS部分可能形成了三明治螺旋特殊结构。纺丝液流速会对纤维毡形态结构产生影响,SF溶液流速保持不变,增加SS溶液的流速,纤维粘连严重且容易出现断裂;保持SS流速不变,增大SF溶液流速,纤维粘连性得到改善,且形貌变好。     

Morphology of regenerated silk fibroin: Effects of freezing temperature,alcohol addition,and molecular weight

Regenerated silk fibroin (RSF) was prepared by dissolving in a CaCl₂/ethanol/H₂O solvent system, freezing, and lyophilization. The effect of freezing temperature, alcohol addition, and molecular weight on the morphological and conformational changes were investigated through scanning electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, and differential scanning calorimetry analysis. However, the addition of a small amount of methanol induced the morphological change of RSF to a fine‐particle aggregate, which resulted from the formation of a β‐sheet crystalline structure. The lower the freezing temperature was, the more the formation of aggregates was favored, and the finer powder aggregates were formed. As the amount of added hydrophilic alcohol such as methanol and ethanol increased in the silk fibroin solution, a spherical powder form was changed to fine aggregates with the enhancement of thermal stability and crystallinity. On the other hand, RSFs prepared with a hydrophobic alcohol such as 1‐butanol or 1‐octanol showed a lump‐like or sheet‐like shape of morphology without any changes in conformational transition. It is concluded that the molecular weight of the silk fibroin and the type and amount of alcohol were determining factors in the morphological features of RSF, especially the size and shape of fibroin particles. A uniform ultrafine powder of RSF with a spherical form (～ 1 μm) can be obtained when the molecular weight and the alcohol addition to the silk fibroin solution are controlled. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3008–3021, 2001     

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     

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.     

Fabrication and characterization of electrospun PCL/Antheraea pernyi silk fibroin nanofibrous scaffolds

To engineer tissue restoration, it is necessary to provide a bioactive, mechanically robust scaffold. Electrospun poly(ε‐caprolactone) (PCL) nanofiber is a promising biomaterial candidate with excellent mechanical properties, but PCL scaffolds are inert and lack natural cell recognition sites. To overcome this problem we investigated the incorporation of Antheraea pernyi silk fibroin (ASF) containing inherent RGD tripeptides with PCL in electrospinning process. The mixing ratios showed remarkable impact on the properties of hybrid nanofibers. Increasing PCL content significantly enhanced the mechanical properties of nanofibers. In particular, the mechanical properties were remarkably enhanced when PCL content increased from 50 wt% to 70 wt%. Moreover, the biological assays based on endothelial cells showed promoted cell viability when ASF content reached to 30 wt%. The data demonstrated that the nanofiber containing 70% of PCL and 30% of ASF achieved the most balanced performances for integrating the mechanical properties of PCL and the bioactivity of ASF. Furthermore, biomimetic alignment of 70PCL/30ASF nanofibers was achieved, which could support PC12 neuron‐like cell growth and guide neurite outgrowth, providing a potentially useful option for the engineering of oriented tissues. The results show that the PCL/ASF hybrid nanofibers can be considered as a promising candidate for tissue engineering scaffolds. POLYM. ENG. SCI., 57:206–213, 2017. © 2016 Society of Plastics Engineers     

交联剂对再生丝素蛋白结构与性能的影响

分别从形貌、结构、力学性能、生物性能等方面综述了交联剂京尼平与戊二醛对再生丝素蛋白的影响。表明京尼平由于毒性低和生物相容性好的特点,发现它比戊二醛更适合运用于蛋白类的物质组织工程。     

Physical properties of silk fibroin/chitosan blend films

Silk fibroin/chitosan blend films were examined through IR spectroscopy to determine the conformational changes of silk fibroin. The effects of the fibroin/chitosan blend ratios (chitosan content) on the physical and mechanical properties were investigated to discover the feasibility of using these films as biomedical materials such as artificial skin and wound dressing. The mechanical properties of the blend films containing 10–40% chitosan were found to be excellent. The tensile strength, breaking elongation, and Young's modulus were affected by the chitosan contents of the blend films, which were also related to the density and degree of swelling. The coefficient of water vapor permeability of the blend films increased linearly with the chitosan content, and the values of 1000–2000 g m^?2 day^?1 were comparable to those of commercial wound dressings. Silk fibroin/chitosan blend films had good oxygen and water vapor permeabilities, making them useful as biomaterials. In particular, the blend film containing 40–50% chitosan showed very high oxygen permeability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 928–934, 2001     

Structural and physical properties of silk fibroin/alginate blend sponges

Silk fibroin/alginate blend sponges were examined through IR spectroscopy, X‐ray diffractometry, and differential scanning calorimetry to determine the structural changes of silk fibroin. The effects of fibroin/alginate blend ratios on the physical and mechanical properties were investigated to discover the feasibility of using these blend sponges as biomedical materials such as wound dressings. The compressive modulus of silk fibroin was increased up to 30 kPa, from 7.1 kPa, by blending with alginate. Thermal crystallization behavior of fibroin induced by heat treatment was restricted by blending with alginate. In spite of that, the structural characteristics of fibroin were not changed by incorporation with alginate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2174–2179, 2004     

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。     

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。     

Structure and physical properties of silk fibroin/polyacrylamide blend films

This article deals with the characterization of blend films obtained by mixing silk fibroin (SF) and polyacrylamide (PAAm). The DSC curves of SF/PAAm blend films showed overlapping of the main thermal transitions characteristic of the individual polymers. The exothermic peak at 218°C, assigned to the β‐sheet crystallization of silk fibroin, slightly shifted to a lower temperature by blending. The weight‐retention properties (TG) of the blend films were intermediate between those of the two constituents. The TMA response was indicative of a higher thermal stability of the blend films, even at low PAAm content (≤25%), the final breaking occurring at about 300°C (100°C higher than pure SF film). The peak of dynamic loss modulus of silk fibroin at 193°C gradually shifted to lower temperature in the blend films, suggesting an enhancement of the molecular motion of the fibroin chains induced by the presence of PAAm. Changes in the NH stretching region of silk fibroin were detected by FTIR analysis of blend films. These are attributable to disturbance of the hydrogen bond pattern of silk fibroin and formation of new hydrogen bonds with PAAm. The values of strength and elongation at break of blend films slightly improved at 20–25% PAAm content. A sea–island structure was observed by examining the air surface of the blend films by scanning electron microscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1563–1571, 1999