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     

Study on the properties of nano‐TiO2 particles modified silk fibroin porous films

Using the freeze‐drying method, Nano‐TiO₂/silk fibroin porous films were synthesized with different ratios of TiO₂ to silk fibroin solution. Through scanning electron microscopy (SEM), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), tensile strain, and water‐solubility tests, the structures and properties of these porous films were characterized. The SEM results indicated that the pores of the nano‐TiO₂/silk fibroin porous films were uniformly distributed by the freeze‐drying method. The XRD analysis indicated that the formation of nano‐TiO₂ particles might induce a conformational transition of silk fibroin from the typical Silk I to the typical Silk II structure partly with an increase in the crystallinity of the porous films. Compared with the pure silk fibroin porous films, the mechanical properties of nano‐TiO₂/silk fibroin porous films were improved, and its heat transition temperature was also enhanced; however, the water‐solubility of this material was diminished. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Silk I structure formation through silk fibroin self-assembly

Regenerated silk fibroin films are normally produced by increasing the Silk II structure (β-sheet content). In the present study, silk fibroin films were prepared by controlling the environmental temperature and humidity, resulting in the formation of silk films with a predominant Silk I structure instead of Silk II structure. Wide angle X-ray diffraction indicated that when the relative humidity was 55%, the silk films prepared were mainly composed of Silk I structure, whereas silk films formed on other relative humidity had a higher Silk II structure. Fourier transform infrared analysis (FTIR) results also conformed that the secondary structure of silk fibroin can be controlled by changing the humidity of the films formed process. Thermal analysis results revealed Silk I structure was a stable crystal, and the degradation peak increased to 320°C, indicating a greater thermal stability of these films formed under the 55% relative humidity conditions. Atomic force microscopy (AFM) results depicted silk fibroin in the fresh solution had many nanospheres existing with 20–50 nm diameters and mainly maintained a random coil structure without specific nanostructures. At the same time, it also illustrated the self-assembly process of silk fibroin in the aqueous solution without any human intervention. In addition, this present study also provided additional support for self-assembly mechanism of silk fibroin films formation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A new method to prepare porous silk fibroin membranes suitable for tissue scaffolding applications

A new method to prepare porous silk fibroin (SF) membranes without dialysis is proposed. Silk fibers were degummed to remove sericin and the resultant fibroin was dissolved in a CaCl₂‐CH₃CH₂OH‐H₂O ternary solvent. Rather than undergoing dialysis, a fibroin salty solution was diluted in water and then submitted to a mechanical agitation that led to a phase separation through foam formation on the solution surface. This foam was continually collected and then compacted between plates to remove the excess of water. The membranes presented large pores with diameters of greater than 100 μm (as shown by scanning electron microscopy ‐ SEM), porosity of 68% and water content of 91% w/w. X‐ray diffraction (XRD) and infrared spectroscopy (FTIR‐ATR) indicated that the membranes present SF in a β‐sheet structure even before the ethanol treatment. A typical elastic deformation profile and degradation under temperature were observed using calorimetric analysis (DSC), thermal gravimetric analysis (TGA) and mechanical tests. As indicated by the in vitro cytotoxicity tests, these membranes present potential for use as scaffolds. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

Compatibilization of acrylic polymer–silk fibroin blend fibers. I. Graft copolymerzation of acrylonitrile onto silk fibroin

To synthesize effective compatibilizers for the compatibilization of acrylic polymer–silk fibroin blend fibers, the homogeneous graft copolymerization of acrylonitrile onto silk fibroin, initiated by potassium persulfate–sodium bisulfite redox system in 60 wt % ZnCl₂ aqueous solution was investigated. The percentage graft, percentage efficiency, and molecular weight of the grafted polyacrylonitrile increase with the increase of the concentration of initiator, the concentration of acrylonitrile, and the temperature to optimum values, respectively, and then decrease. With the increase of reaction time, the percentage graft and percentage efficiency increase, whereas the molecular weight of the grafted polyacrylonitrile decreases. The influence of the reactionconditions on the molecular architecture of the graft copolymers is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1089–1097, 1998     

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     

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。     

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。     

丝素/羧甲基壳聚糖共混膜的结构性能探讨

将含有甘油和戊二醛的丝素与羧甲基壳聚糖按一定比例混合,制得丝素/羧甲基壳聚糖共混膜,对共混膜的结构与性能进行了探讨。结果表明:随着羧甲基壳聚糖含量的增加,共混膜的透气率增大,加入交联剂戊二醛有效地改善了共混膜的力学性能,但其透气率有所降低;当丝素与羧甲基壳聚糖的质量比为4/1时,共混膜的断裂强度最大,力学性能较好,共混膜相容性较好,其断面光滑、致密。制备丝素/羧甲基壳聚糖共混膜的较佳条件为:丝素中的甘油质量分数为15%,戊二醛质量分数为0.075%,丝素与羧甲基壳聚糖质量比为4/1。     

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。     

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。     

Relationship between structure and physical strength of silk fibroin nanofiber sheet depending on insolubilization treatment

Materials such as expanded polytetrafluoroethylene and glutaraldehyde‐fixed bovine pericardium are currently used for cardiac tissue regeneration. However, patches made from these materials remain permanently without being absorbed by the body and must be replaced overtime because of degeneration or lack of growth. To improve the long‐term outcomes for cardiac tissue regeneration, biocompatible and biodegradable materials must be used. In this study, we used two biocompatible polymers, silk fibroin (SF), which is biodegradable and segmented polyurethane, to prepare nonwoven sheets that were then insolubilized by water vapor or methanol treatment. The tensile stress increased significantly on adding segmented polyurethane to pure SF and the water vapor processed sheets showed higher extension on strain than the methanol‐processed sheets. The different insolubilization treatments also resulted in different SF structures. Our results show that it is possible to obtain the physical properties required for cardiac tissue repair patch by varying the insolubilization treatment. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45560.     

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。     

Study on the properties of the electrospun silk fibroin/gelatin blend nanofibers for scaffolds

Silk fibroin (SF)/gelatin blend nanofibers membranes as scaffolds were fabricated successfully via electrospinning with different composition ratios in formic acid. The formation of intermolecular hydrogen bonds and the conformational transition of SF provided scaffolds with excellent mechanical properties. FTIR and DTA analysis showed the SF/gelatin nanofibers had more β‐sheet structures than the pure SF nanofibers. The former's breaking tenacity increased from 0.95 up to 1.60 MPa, strain at break was 7.6%, average fiber diameter was 89.2 nm, porosity was 87%, and pore diameter was 142 nm. MTT, H&E stain, and SEM results showed that the adhesion, spreading, and proliferation of human umbilic vein endothelium cells (HUVECs) and mouse fibroblasts on the SF/gelatin nanofibers scaffolds were definitely better than that on the SF nanofibers scaffolds. The scaffolds could replace the natural ECM proteins, support long‐term cell growth, form three‐dimensional networks of the nanofibrous structure, and grow in the direction of fiber orientation. Our results prove that the addition of gelatin improved the mechanical and biological properties of the pure SF nanofibers, these SF/gelatin blend nanofiber membranes are desirable for the scaffolds and may be a good candidate for blood vessel engineering scaffolds. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of additives on porosity of alumina materials obtained by freeze casting

The influence of two different additives, glycerol and polyvinyl alcohol (PVA), on the rheological behaviour and freeze casting performance of 35?vol.-% aqueous alumina suspensions is studied. Suspensions with PVA were prepared by either mixing all the components together or adding the PVA in a second step on the dispersed slurry. Although the slight increase in viscosity suggests that competitive adsorption occurs, the microstructure seems not to change depending on the order of addition of additives. Considering its lower molecular weight, glycerol provides lower viscosity, and as a consequence of its cryoprotective character, sintering leads to smaller pore size, being the porosity 35% for an added content of 10?wt-% with respect to solids. In the case of PVA, contents of 2?wt-% are enough to obtain solid firm bodies with a porosity of 48%. The porosity and the size of the pores decrease with increasing concentration of PVA.     

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。     

Effects of addition of condensed tannin on the structure and properties of silk fibroin film

Condensed tannin is a polymeric polyphenol compound, which has considerable protein‐binding ability and a variety of bioactivities, such as anti‐inflammatory, antithrombotic and antimicrobial activities. In this study, silk fibroin film was modified by adding condensed tannin. It was found that strong intermolecular interactions occurred between silk fibroin and tannin, and incorporation of 1–10% (w/w) tannin in the blend films resulted in more compact, stiffer but less elastic films. Swelling and dissolution trials showed that the addition of tannin significantly reduced the swelling and solubility of the films. The mechanical properties, swelling and solubility of the blend films varied as a function of tannin concentration, showing optimum values when containing 10% (w/w) tannin. The silk fibroin–tannin films all showed significant antioxidant activity and antibacterial activity against Gram‐positive bacteria, and the activities were positively related to the concentration of tannin. The results emphasized that the addition of condensed tannin could simultaneously improve the structural stability of silk fibroin film and impart functional properties. © 2016 Society of Chemical Industry     

Supercritical carbon dioxide assisted fabrication of biomimetic sodium alginate/silk fibroin nanofibrous scaffolds

In this study, biomimetic sodium alginate (SA)/silk fibroin (SF) scaffolds were successfully fabricated by supercritical CO₂ technology. The SA/SF scaffolds exhibited an interconnected porous and extracellular matrix (ECM)-like nanofibrous structures. Moreover, the SA microparticles were embedded in the SF scaffolds. Increasing the content of SA microparticles could improve tensile strength and compressive strength of the SF scaffolds and reduce the porosity of the SF scaffolds. The addition of the SA microparticles could also regulate the degradation rate of the SA/SF scaffolds. Furthermore, the results of in vitro biocompatibility evaluation, indicated that the SA/SF scaffolds exhibited no obvious cytotoxicity and higher cell adhesion ability and were more favorable for L929 fibroblasts proliferation than pure SF scaffolds. Therefore, the SA/SF scaffolds with ECM-like nanofibrous and interconnected porous structure have potential application in skin tissue engineering.     

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