Fabrication and characterization of silk fibroin powder/polyurethane fibrous membrane

The blend fibrous membranes with the different mass ratio of silk fibroin (SF) powder to polyurethane (PU) were fabricated by electrospinning. The structure, morphology, mechanical properties, and surface wettabilities of the blend fibrous membrane are characterized by field‐emission scanning electron microscope, Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetry, dynamic mechanical thermal analysis, tensile testing, and contact angle measurements. The results show that the SF was uniformly distributed in the blend fibers. The mass ratio of SF to PU played an important role in influencing the structure and morphology of the blend fibers, and the optimum mass ratio was 5/5. With the increase in SF content in fibers, the fraction of SF in the surface of the SF/PU blend fibers and the crystallinity degree of PU increased, and the molecular orientation of PU along the fiber axis took place. The SF content regulated the hydrophilicity property of the membrane. The thermal stability and the dynamic storage modulus of the fibrous membrane decreased, and the phase separation between soft and hard segments of PU increased. Similarly, the stress at peak and Young's modulus of the fibrous membrane decreased gradually; the strain at peak first increased and then decreased. POLYM. ENG. SCI., 52:2025–2032, 2012. © 2012 Society of Plastics Engineers     

Improvement of histocompatibility of silk fibroin/polyurethane membrane with controlled release of aspirin

The histocompatibility of polyurethane (PU) modified by superfine silk‐fibroin (SF) powder (1 : 1) with different dosage of aspirin to determine the best dosage for histocompatibility was investigated. Aspirin powder was incorporated into SF–PU (1 : 1) blend mixture at doses of 0%, 5%, or 10% (w/w). The influence of different doses of aspirin on histocompatibility of the hybrid material was studied by using morphology examination, infrared spectroscopy, in vitro drug release study, and in vivo tests including an acute toxicity test, an assessment of local reaction in the muscle, hematological examination, and histological examination. SF–PU (50 : 50) blend film had superior performance over the polytetrafluoroethylene (e‐PTFE) film in terms of histocompatibility, and the anti‐inflammatory/anti‐platelet effects were improved after integration with limited doses of aspirin to yield a valuable drug release vascular graft. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40580.     

Preparation of regenerated Antheraea yamamai silk fibroin film and controlled‐molecular conformation changes by aqueous ethanol treatment

The methods of dissolving Antheraea yamamai (A. yamamai) silk fibroin fibers and preparing the regenerated silk fibroin were studied. The molecular conformations of A. yamamai silk fibroin film treated by different concentration ethanol solution were investigated by XRD, FTIR, and Raman spectra. The results indicated that A. yamamai silk fibroin fibers could be completely dissolved in dense lithium thiocyanate solution at about 35°C for 1 h. The initial regenerated film consisted of α‐helix and random coil components. The aqueous ethanol treatment of the film resulted in significant increase in β‐sheet component and improvement of water resistance of the film. This effect was strongly dependent on ethanol concentration, and 60–80% (w/w) ethanol was most effective. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of superfine silk protein powders on mechanical properties of wet‐spun polyurethane fibers

Mechanical measurements were employed to investigate the effects of three types of superfine silk protein powder on tensile strength, elongation, and elasticity of wet‐spun Pellethane^® 2363‐80AE polyurethane (PU) fiber. These superfine silk protein powders included undegummed silk (with both native silk fibroin and sericin, water insoluble), native silk fibroin (with native silk fibroin only, water insoluble), and regenerated silk fibroin (with regenerated silk fibroin only, water soluble) in powder form. Experimental data derived from the mechanical measurements illustrated that the miscibility between the PU and regenerated silk fibroin were superior to that between PU and the other two silk proteins. This may be attributed to the similar chemical structure and microphase separation of PU and regenerated silk fibroin with lower molecular weight than native silk fibroin. This preliminary work may provide some information for biomimetic processing of silk‐inspired PU biofibers, which combine elasticity of synthetic PU with biofunction of natural silk fibroin for special biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

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     

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     

Structural changes and their effect on mechanical properties of silk fibroin/chitosan blends

Silk fibroin/chitosan blend films were prepared by the solvent casting method. Miscibility between silk fibroin and chitosan was examined by dynamic mechanical thermal analysis. Structural changes of silk fibroin by the addition of chitosan were investigated by IR spectroscopy. The conformational transition of silk fibroin from random coil form to β‐sheet structure induced by blending with chitosan resulted in the increase of crystallinity and density of the blend films. The blend film containing 30 wt % chitosan exhibited a maximum increase in crystallinity and density. It was found that the tensile strength and initial tensile modulus of blend films were greatly enhanced with increasing the chitosan content and showed a maximum value at the composition of 30 wt % chitosan. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2571–2575, 1999     

Rapid formation of flexible silk fibroin gel‐like films

Flexible silk fibroin gel‐like films with microporous morphology were prepared from B. mori silk fibroin fibers directly solubilized in formic acid/CaCl₂ solvent. These films were characterized by several analysis techniques to determine the structure and properties of films. The pore size of gel‐like films can be adjusted through SF concentration and Ca ions concentration. The controllable pore size in gel‐like films was grew from 3–5 μm to 100 μm under the increase of fibroin concentration from 1.0 wt % to 8.0 wt %. At the same time, the water content of silk fibroin gel‐like film decreased from 83.5 ± 3.4% to 68.2 ± 2.6%. With increasing Ca ions contents from 2.0 wt % to 10.0 wt % in dissolution process, the pore size and water content of silk fibroin gel‐like films grew larger, especially its water content values reached 86.2 ± 4.0% at 10.0 wt % Ca ions concentration. At wet condition, the gel‐like film with β‐sheet structure showed higher breaking stress (4.26 ± 0.31 MPa) and elongation (45.45 ± 15.79%) at 8.0 wt % concentration. With the preparation method, the membrane is hydrophilic and the pore size is adjustable, which contributes to high toughness and favorable cell growth environment, suggesting that these silk fibroin gel‐like films can be a potential candidate scaffold for biomedical applications, such as wound dressing, facial mask, contact lenses, etc. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41842.     

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     

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。     

Structure for electro‐spun silk fibroin nanofibers

Electro‐spinning was made using silk fibroin and it was found that silk fibroin nanofibers of partially oriented amorphous structure are producible using HFIP(1,1,1,3,3,3 hexafluoro‐2‐propanol) as a solvent for fibroin via the electro‐spinning setup equipped with parallel electrodes as a collector. Transformation from amorphous to silk I of a highly contracted beta‐turn form or amorphous to silk II of a regular array of antiparallel beta‐sheets occurred preferentially via the treatment with water vapor or ethanol, respectively. In addition the c‐axis of crystallites was oriented parallel to the fiber axis. When the electro‐spinning was made using a dish‐type collector filled with ethanol, a peculiar web texture was obtained. Such a web texture seems to be brought about by the shrinkage of fiber due to the crystallization of fibroin and/or surface tension of ethanol droplets formed between the fibers. In this spinning setup, the c‐axis of crystallites was also oriented parallel to the fiber axis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Process optimization of electrospun silk fibroin fiber mat for accelerated wound healing

Considering the outstanding biocompatibility of Bombyx mori silk fibroin, this study is designed to fabricate biomimetic nanofibrous structure made of silk fibroin, which can enhance cell activities for tissue formation. The electrospinning of blend of silk fibroin with low molecular weight poly(ethylene‐oxide) (PEO) is explored with ease of preparation for high productivities. The average diameter of electrospun silk fibroin (eSF) is decreased from 414 ± 73 to 290 ± 46 nm after PEO extraction. To induce the desired cellular activity, the surface of the eSF fibers is modified with fibronectin by using the carbodiimide chemistry method. The potential use of the obtained wound healing material is assessed by indirect cytotoxicity evaluation on normal human dermal fibroblast (NHDF) in terms of their attachment and cell proliferation. The surface‐modified eSF nanofiber mats show good support for cellular adhesion and spreading as a result of fibronectin grafting on the fiber surface, especially for cell migration inside the fibrous structure. These results demonstrate a new fabrication technique of surface‐modified silk fibroin electrospun nanofibers for biomedical application; with the ability to accelerate wound healing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3634–3644, 2013     

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 fine powder from silk by radiation

Silk fine powder was prepared directly from silk fibers irradiated with an accelerated electron beam (EB). Irradiated silk fibers were well pulverized only by physical crushing using a ball mill without any chemical pretreatment. Silk fibroin fibers were irradiated at ambient temperature in the dose range of 250–1 000 kGy. Although unirradiated silk fibers were not pulverized at all, irradiated fibers were easily pulverized and showed a high conversion efficiency from fiber to powder at high irradiation doses. The presence of oxygen in the irradiation atmosphere enhanced pulverization of the silk fibers. The electron microscopic observation showed that the minimum particle size of silk powder obtained from fibers irradiated at 1 000 kGy in oxygen was less than 10 μm. It was found that fibroin powder obtained in this work dissolved remarkably in water, thought unirradiated fibroin fibers were insoluble even in hot water. The soluble fraction was about 60% of fibroin powder for 1 000 kGy irradiation in oxygen.     

X‐ray photoelectron spectroscopic study of silk fibroin surface

X‐ray photoelectron spectroscopy (XPS) has been used to probe the nature of silk fibroin surface, in particular the tyrosine content and sulfur species on the surface. The iodine labelling treatment of silk, followed by XPS surface analysis, reveals that silk fibroin has a tyrosine‐enriched surface, and that there are sulfur‐containing amino acids present on the surface, mainly occurring in the S⁶⁺ component. UV/ozone treatment modifies/removes the surface tyrosine‐ and sulfur‐containing species. © 2002 Society of Chemical Industry     

聚乙二醇缩水甘油醚改性丝素蛋白研究

采用聚乙二醇400与环氧氯丙烷合成聚乙二醇缩水甘油醚(PEGO)并对丝素蛋白(SF)进行改性,采用红外光谱、X射线衍射、差式量热扫描、扫描电镜和物理性能测试对共混膜的结构和性能进行表征,表明PEGO的加入使得丝素蛋白从silkⅠ结构向silkⅡ构象转变,而当m(PEGO)∶m(SF)>50%的时候,共混膜的二级结构却呈现相反变化。共混膜的含水量由共混膜的表面粗糙度和亲水性决定,在m(PEGO)∶m(SF)<50%时,其含水量随粗糙度增加而减少;在m(PEGO)∶m(SF)>50%时,随着PEGO的增加,SF/PEGO共混膜的含水量增加。当m(PEGO)∶m(SF)=50%时,共混膜SP50具有最好的热稳定性和良好的机械性能。     

Structure and properties of silk fibroin/carboxymethyl chitosan blend films

The secondary structure of silk fibroin (SF) and the compatibility of the two components were associated with the carboxymethyl chitosan (CMCS) content in SF/CMCS blend films. A rather complete conformation transition of SF from random coil to β-sheet occurred after adding 5% CMCS into the SF film, and the blend film exhibited a high crystallinity and a good compatibility. The conformation of SF changed from β-sheet to α-helix when blending 10% CMCS. When the CMCS content was up to 15%, the conformation of SF in blend films showed a transformation from β-sheet to a random coil and their crystallinities decreased evidently; accordingly, there was a two-phase separation structure for the blend films containing 15% CMCS or more. However, the intermolecular interaction between the two polymers still existed in blend film with 15% CMCS or more. The blend films with 5–10% CMCS content showed the lower moisture absorption, swelling capacity, and solubility in water. These properties of blend films increased when adding CMCS more than 15%.     

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