Mechanical properties of silk fibroin–microcrystalline cellulose composite films

Silk fibroin–microcrystalline cellulose (cellulose whisker) composite films with varied compositions were prepared by casting mixed aqueous solution/suspensions of the two components. Silk fibroin was dissolved in 10M LiSCN followed by dialysis; a cellulose whisker suspension was prepared by sulfuric acid hydrolysis of tunicate cellulose. Macroscopically homogeneous films were obtained at all mixing ratios. While the Young's modulus of the composite films showed a linear, additive dependence on the mixing ratio, the tensile strength and ultimate strain showed a maximum at a 70–80% cellulose content, reaching five times those of fibroin‐alone or cellulose‐alone films. At the same mixing ratio, infrared spectra of the composite films showed a shift of the amide I peak from 1654 to 1625 cm^?1, indicating the conformational change of fibroin from a random coil to a β structure (silk II) at the whisker–matrix interface. This change seems to be induced by contact of fibroin molecules with a highly ordered surface of cellulose whisker. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3425–3429, 2002     

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     

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     

凝固条件对纤维素/丝素蛋白纤维相形态及性能的影响

蛋白质纤维具有光滑柔顺、透气吸湿等优点,然而天然蛋白纤维产量有限。再生蛋白纤维的制备通常采用与其它成纤高分子接枝或共混的方法,有利于提高再生蛋白纤维的断裂强度。选用同为天然高分子的纤维素为基体,以共溶剂溶解纤维素与蛋白质,进而纺丝成形制得力学性能满足要求的纤维素/丝素蛋白共混纤维。为了探究凝固剂组成对纤维素/丝素蛋白共混纤维相形态及性能的影响,选用水、乙醇、乙醇/1-丁基-3-甲基咪唑氯盐([BMIM]Cl)等作为凝固剂。研究发现:乙醇作为凝固剂时,纤维素与丝素蛋白能很好地同时凝固;而当在乙醇凝固浴中加入适量的[BMIM]Cl径向均匀分散。通过对凝固剂组成的调控能有效提升纤维的力学强度。     

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     

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     

棉织物丝素/TiO_2生态功能整理

用丝素蛋白整理棉织物,研究丝素蛋白降解时间及浓度对整理后棉织物性能的影响,确定最佳的丝素降解时间和浓度。在此基础上与TiO2复配,研究整理剂中TiO2含量对棉织物性能和结构的影响。结果表明:最佳丝素蛋白降解时间为120min,丝素浓度(质量分数)为1.63%;此时将丝素与TiO2复配,当TiO2质量分数为0.35%时,可使织物折皱回复角比纯丝素整理提高8.68%,紫外防护系数达到42.9,抗紫外性能达到二级。X射线衍射分析表明,丝素蛋白整理可降低棉纤维的结晶度,并使棉纤维由纤维素Ⅰ向纤维素Ⅱ转变,而TiO2整理可提高棉纤维的结晶度。     

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     

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.     

Silk fibroin composite membranes for application in corneal regeneration

The ordered microstructure of the corneal stroma determines the transparency of the cornea. The difficulty of constructing three‐dimensional corneal tissue mainly lies in the reconstruction of the corneal stroma. This article reports propionamide/silk fibroin composite membrane materials for use in corneal regeneration. X‐ray diffraction is used to explore the structure of the composite fibroin membrane. Propionamide acts as a crosslinking agent and inhibits the formation of larger crystal grains controlling the crystallization process. Corneal stromal cells are seeded on sterilized composite films. Propionamide/fibroin membranes with different blending proportions exhibit stable transparency and good cell compatibility. The results demonstrate that composite fibroin membranes are suitable potential materials for use in corneal stromal cell proliferation and repair. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42407.     

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     

Self-assembled silk fibroin particles: Tunable size and appearance

Silk fibroin had various applications especially outstanding for drug delivery due to its protein component, biocompatibility and biodegradability. In this paper, silk fibroin particles were prepared via self-assembly. Their sizes and appearances could be modified by adjusting of volume ratios among poly vinyl alcohol (PVA), silk fibroin and ethanol. Regular silk particles were formed in PVA solution when the volume ratio of silk to ethanol ranged from 2 to 20. Preparation pathways could be concluded as 1) mixing ethanol with silk fibroin solution, 2) blending the silk fibroin/ethanol solution with PVA, 3) freezing the ternary solution for 48 h and collection of silk fibroin particles via thaw and centrifugation. Silk particles with various appearances were also obtained by addition of concentrated PVA solution. Silk particles reported have potential as drug delivery carriers in a variety of biomedical applications.     

Preparation of non-woven mats from all-aqueous silk fibroin solution with electrospinning method

In the present study, we successfully prepared non-woven mats from stable regenerated silk fibroin aqueous solution at high concentration. Scanning electronic microscope (SEM) was used to observe the morphology of the fibers. The structure of the fibers was characterized using Fourier transform infrared (FTIR), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The mechanical tests were also performed. In the as-spun fibers, silk fibroin was present in a random coil conformation, the stress and strain at break were 0.82 MPa and 0.76%, respectively, while after methanol treatment, the silk fibroin was transformed into a β-sheet-containing structure, the stress and strain at break increased to 1.49 MPa and 1.63%, respectively. This study provided an option for the electrospinning of silk fibroin without using organic solvent or blending with any other polymers, which may be important in tissue engineering scaffold preparation.     

Water sorption,membrane potentials,and ion permeability of styrene-grafted Bombyx mori silk fibroin membrane

Characterization of styrene-grafted Bombyx mori silk fibroin membrance was investigated. It was revealed from the water sorption and ¹H nuclear magnetic resonance (NMR) measurements that the amounts of water adsorbed on the silk fibroin membranes decreased by the styrene grafting and the states of water adsorbed on the styrene-grafted silk fibroin membranes were not homogeneous; the presence of two components of water adsorbed on the membranes at 60% relative humidity was observed. In addition, the fraction of the fast component decreased with increasing styrene grafting. The membrane potentials increased with increasing of the grafting. The KCl permeability of the membrane strongly depends on the degree of styrene grafting.     

Chitosan‐finished Antheraea mylitta silk fibroin nonwoven composite films for wound dressing

In this study, we aimed to produce nonwoven wound‐dressing films made of Antheraea mylitta (tasar) silk fibroin by a solution‐casting method. These nonwoven films were finished with chitosan solutions of different concentrations ranging from 0.75 to 2% w/v with a pad–dry method to fabricate nonwoven composite films. Chitosan‐finished tasar fibroin nonwoven composite films (CMTFFs) showed higher mechanical and dynamic mechanical properties as compared to nonwoven tasar fibroin. The physical, structural, and thermal properties of the films were investigated. The hemocompatibility, cytocompatibility, and biodegradation tests showed that the CMTFF was a promising material for use as a wound dressing. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44341.     

Fabrication and characterization of silk fibroin/poly(ethylene glycol)/cellulose nanowhisker composite films

The flexible and transparent composite films were fabricated by a mixture of silk fibroin (SF), poly(ethylene glycol), and mulberry cellulose nanowhiskers (CNWs). The CNWs were uniformly dispersed in the matrix when its content was as high as 12 w/w%. The tensile properties of composite films generally depended on the nanowhisker content, but significantly improved when compared to the pure SF film. DMA analysis revealed that the alpha transition temperature increased gradually with the increase of nanowhisker content, probably due to the formation of interactions between the nanowhiskers and the SF molecular chains, leading to the mobility reduction of the amorphous SF. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

丝素/羧甲基壳聚糖共混膜的结构与性能

利用丝素(SF)与羧甲基壳聚糖(CMCS)共混制取不同比例的SF/CMCS共混膜。研究了CMCS诱导的丝素构象转变行为,测试了共混膜的吸湿性、透湿性和保水性。当CMCS的质量分数为5%时,共混膜中丝素的构象以β-折叠为主;当CMCS的质量分数为10%时,共混膜中丝素的构象由β-折叠向α-螺旋发生转变;当CMCS的质量分数达到15%时,共混膜中丝素的构象向无规卷曲发生转变。当CMCS质量分数小于15%时,共混膜中SF与CMCS具有良好的相容性,溶胀度较小,吸湿性随CMCS含量的增加而迅速降低。     

Study on secondary structural transition of nano‐TiO2 modified silk fibroin composite films by two‐dimensional Raman correlation spectroscopy and solid‐state 13C‐NMR spectroscopy

By a sol–gel processing, the nano‐TiO₂/silk fibroin (SF) composite films were prepared. One‐dimensional (1D) Raman, two‐dimensional (2D) correlation Raman spectroscopy, and ¹³C cross‐polarization magic‐angle‐spinning nuclear magnetic resonance (¹³C CP‐MAS NMR) were used to characterize the structural evolution of SF as the nano‐TiO₂ content increased from 0 to 0.4 wt%. The experimental data demonstrated that the secondary structures in the pure SF film and nano‐TiO₂/silk fibroin (SF) composite films were random coil, α‐helix and β‐sheet structures. The nano‐TiO₂ particles formed in the SF films might induce partial structural transitions from random coil and Silk I (α‐helix) to Silk II (β‐sheet). The transition identified by 2D‐Raman correlation spectra was the following order: silk I‐like structure, silk I (α‐helical structure), Silk II‐like structure, and Silk II (β‐sheet structure). POLYM. COMPOS., 36:121–127, 2015. © 2014 Society of Plastics Engineers     

Surface modification of textile material through deposition of regenerated silk fibroin

Regeneration of silk fibroin from calcium chloride/ethanol/water solution is of high interest to shape biomaterial based products for medical and technical application. In this study a continuous process for surface modification of cellulose or polyamide fibers by regenerated fibroin deposits has been investigated. The decomposition of the fibroin‐calcium complex was initiated by addition of K₂CO₃ followed by a methanol rinse. Reactive Blue 19 labeled fibroin was used to monitor the deposition of fibroin on the substrates by colour measurement. The fibroin deposits on the fabric were characterized by microscopy, N‐content, calcium, and protein content. Stiffness and surface resistivity of modified fabrics were determined as representative physical parameters. The reduced mobility of fibers increased fabric stiffness. Surface resistivity of treated samples was reduced by a factor of 10 to 100, which gives an example for the potential of the technique as coating for man‐made fiber textiles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45098.     

丝素蛋白/聚丙烯酸共混膜仿生合成羟基磷灰石

将丝素蛋白(SF)与聚丙烯酸(PAA)共混,制备丝素蛋白/聚丙烯酸(SF/PAA)共混膜;然后将此共混膜进行改性及矿化处理后,放置于(37±0.5)℃人体仿生液中24h,诱导合成丝素蛋白/羟基磷灰石(SF/HA)复合材料.利用傅里叶红外(FTIR)、X-射线衍射(XRD)、环境扫描电镜(ESEM)以及X射线能谱(EDX...