Biocomposite membranes of sodium alginate and silk fibroin fibers for biomedical applications

Biocomposite membranes from biodegradable and biocompatible natural polymers were prepared from sodium alginate solution reinforced with silk fibroin fibers in several fiber content by casting and solvent evaporation. The properties of these biocomposites were investigated by scanning electron microscopy, swelling test, water vapor transmission, mechanical and thermal analyses, and cytotoxicity test. A biocomposite with uniform fiber dispersion and good fiber–matrix interaction was obtained through the incorporation of fibroin fibers in the alginate membrane, even though the fibers were used without any surface treatment to enhance the interfacial adhesion. The incorporation of fibroin fibers improved the tensile strength and also provided a new property to the alginate, that is, the resistance to tear. Moreover, the use of silk fibroin fibers in polymeric composites can result in a material with adequate characteristics for application in the biomaterial field, especially as wound dressings, because of its nontoxic effect to cells, flexibility, and resistance to tear. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3451–3457, 2013     

Immobilization of silk fibroin on the surface of PCL nanofibrous scaffolds for tissue engineering applications

Poly(?‐caprolactone) (PCL) is explored in tissue engineering (TE) applications due to its biocompatibility, processability, and appropriate mechanical properties. However, its hydrophobic nature and lack of functional groups in its structure are major drawbacks of PCL‐based scaffolds limiting appropriate cell adhesion and proliferation. In this study, silk fibroin (SF) was immobilized on the surface of electrospun PCL nanofibers via covalent bonds in order to improve their hydrophilicity. To this end, the surface of PCL nanofibers was activated by ultraviolet (UV)–ozone irradiation followed by carboxylic functional groups immobilization on their surface by their immersion in acrylic acid under UV radiation and final immersion in SF solution. Furthermore, morphological, mechanical, contact angle, and Attenuated total reflection‐ Fourier transform infrared (ATR‐FTIR) were measured to assess the properties of the surface‐modified PCL nanofibers grafted with SF. ATR‐FTIR results confirmed the presence of SF on the surface of PCL nanofibers. Moreover, contact angle measurements of the PCL nanofibers grafted with SF showed the contact angle of zero indicating high hydrophilicity of modified nanofibers. In vitro cell culture studies using NIH 3T3 mouse fibroblasts confirmed enhanced cytocompatibility, cell adhesion, and proliferation of the SF‐treated PCL nanofibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46684.     

Chitosan/silk fibroin composite scaffolds for wound dressing

Three‐dimensional (3D) chitosan/silk fibroin (CS/SF) porous composite scaffolds have been prepared by simply coating a thin layer of CS onto spunlaced SF scaffolds via hydrogen‐bonding assembly technique, and they were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and mechanical property measurements. The results show that porous scaffolds have a pore diameter around 50–200 μm, and improved mechanical property compared with SF, resulting from strong intermolecular hydrogen bonding interactions between CS and SF, together with the maintained β‐sheet structure of SF. The medical and biological properties of the composite scaffolds were further evaluated. The results demonstrate that they possess good biocompatibility and a broad spectrum of antimicrobial properties. The in vivo animal experiments show that the composite scaffolds promote skin regeneration of rats without any teratogenic effect and inflection, thus they are very promising in the application of wound dressings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42503.     

A novel silk fibroin/sodium alginate hybrid scaffolds

Porous silk fibroin/sodium alginate hybrid scaffolds were prepared through lyophilization method. Hybrid scaffolds were characterized for morphological and functional properties related to different mixture ratios between silk fibroin and sodium alginate. The silk fibroin/sodium alginate hybrid scaffolds showed a thin‐layer structure and much more irregular rod‐like structure appeared at the layer surface after adding 50% sodium alginate. The results of wide‐angle X‐ray diffraction and Fourier transform infrared analysis confirmed that the crystal structure of silk fibroin was not influenced by adding the different contents of sodium alginate, exhibiting the random coil structure in the hybrid scaffolds. The thermal behavior of the hybrid scaffolds exhibited major change with containing 30% sodium alginate or more. The porosity of the scaffolds varied between 92 and 94% with a favorable compressive modulus and stress. The mechanical properties results depicted the hybrid scaffolds containing 10% sodium alginate, with a porosity of 94.0 ± 0.10%, attained the highest compressive modulus and stress for 41 ± 6 and 44 ± 3 kPa, respectively. In addition, mineralization results showed hydroxyapatite crystal growing on the surface of the scaffold. This hybrid biomaterial should offer new and important options to the needs related to biomineralization and tissue engineering, in general. POLYM. ENG. SCI., 54:129–136, 2014. © 2013 Society of Plastics Engineers     

静电纺丝素蛋白组织工程支架的增强改性研究进展

常规静电纺丝法制得的丝素蛋白纤维毡的力学性能较差,不能很好地满足人体对生物组织工程支架的要求。为了提高丝素蛋白组织工程支架的力学性能,对丝素蛋白纤维毡进行增强改性是目前研究的热点。文章简要介绍了丝素蛋白的结构和性能及其在组织工程领域的应用研究,重点总结了提高静电纺丝素蛋白纤维毡力学性能的3种方法,即后处理、添加增强组分以及制备取向纳米纤维。     

Characterization of PLLA scaffolds for biomedical applications

The porosity and pore size distribution of three-dimensional scaffolds have direct implications on their biomedical applications (tissue engineering, drug delivery, and wound dressing). Accordingly, in this paper, a fast, facile, and conservative method relying on low-field nuclear magnetic resonance (LF-NMR) for the evaluation of mean pore size and pore size distribution of polymeric scaffolds is reported. The applicability of the technique is demonstrated on poly-L-lactic acid scaffolds fabricated using the thermal induced phase separation. Results obtained through LF-NMR are successfully compared to scanning electron microscope and X-ray microcomputed tomography micrographs.     

Mechanical modeling of silk fibroin/TiO2 and silk fibroin/fluoridated TiO2 nanocomposite scaffolds for bone tissue engineering

Biocompatible and biodegradable three-dimensional scaffolds are commonly porous which serve to provide suitable microenvironments for mechanical supporting and optimal cell growth. Silk fibroin (SF) is a natural and biomedical polymer with appropriate and improvable mechanical properties. Making a composite with a bioceramicas reinforcement is a general strategy to prepare a scaffold for hard tissue engineering applications. In the present study, SF was separately combined with titanium dioxide (TiO₂) and fluoridated titanium dioxide nanoparticles (TiO₂-F) as bioceramic reinforcements for bone tissue engineering purposes. At the first step, SF was extracted from Bombyx mori cocoons. Then, TiO₂ nanoparticles were fluoridated by hydrofluoric acid. Afterward, SF/TiO₂ and SF/TiO₂-F nanocomposite scaffolds were prepared by freeze-drying method to obtain a porous microstructure. Both SF/TiO₂ and SF/TiO₂-F scaffolds contained 0, 5, 10, 15 and 20 wt% nanoparticles. To evaluate the efficacy of nanoparticles addition on the mechanical properties of the prepared scaffolds, their compressive properties were assayed. Likewise, the pores morphology and microstructure of the scaffolds were investigated using scanning electron microscopy. In addition, the porosity and density of the scaffolds were measured according to the Archimedes’ principle. Afterward, compressive modulus and microstructure of the prepared scaffolds were evaluated and modeled by Gibson–Ashby’s mechanical models. The results revealed that the compressive modulus predicted by the mechanical model exactly corresponds to the experimental one. The modeling approved the honeycomb structure of the prepared scaffolds which possess interconnected pores.

     

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     

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     

Structures,mechanical properties and applications of silk fibroin materials

For centuries, Bombyx mori silkworm silk fibroin has been used as a high-end textile fiber. Beyond textiles, silk fibroin has also been used as a surgical suture material for decades, and is being further developed for various emerging biomedical applications. The facile and versatile processability of silk fibroin in native and regenerated forms makes it appealing in a range of applications that require a mechanically superior, biocompatible, biodegradable, and functionalizable material. In this review, we describe the current understandings of the constituents, structures, and mechanical properties of silk fibroin. Following that, we summarize the strategies to bring its mechanical performance closer to that of spider dragline silk. Next, we discuss how functionalization endows silk fibroin with desired functionalities and also the effects of functionalization on its mechanical properties. Finally, from the mechanical point of view, we discuss various matrices/morphologies of silk fibroin, and their respective applications in term of functionalities, mechanical properties and performance.     

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     

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。     

Cell-culture compatible silk fibroin scaffolds concomitantly patterned by freezing conditions and salt concentration

The morphology of freeze-dried silk fibroin 3D-scaffolds was modified by varying both the NaCl concentration and the freezing temperature of the silk fibroin solution prior to lyophilization. Scanning electron micrographs showed that slow freezing at −22 °C generated sponge-like interconnected porous networks, whereas fast freezing at −73 °C formed stacked leaflet structures. The presence of millimolar NaCl (50–250 mM) increased the porosity of the scaffolds and generated small outgrowths at their surface, depending on the freezing regime. Our results suggest that the morphological differences seen between the materials likely depend on ice and NaCl hydrate crystal nucleation and growth mechanisms. Infrared spectroscopy and X-ray diffraction analyses revealed that the salt concentration and freezing conditions induced no structural changes in fibroin. The seeding of P19 embryonic carcinoma cells showed that the presence of salt and freezing conditions influenced the cell distribution into the scaffolds, with salt addition increasing the access of cells to deeper regions.     

Electrowriting of silk fibroin: Towards 3D fabrication for tissue engineering applications

Electrowriting (EW) successfully combines the principles of two widely studied biofabrication techniques; 3D printing and electrospinning, and is capable of producing complex architectures, with submicron resolutions. However, the EW process so far is limited mainly to thermoplastic polymers of synthetic origin such as poly ε-caprolactone. Herein we demonstrate the EW of silk fibroin (SF) on an in-house build setup to identify the compatibility of water-based SF ink with EW. More specifically, we optimized the SF ink composition and investigated the effect of EW process parameters including ink concentration, collector translation speed, applied voltage, and distance between nozzle and collector on filament orientation and diameter. During SF ink preparation, control over the silk degumming process and ink concentration enabled modulation of rheology and surface tension properties of SF inks. We envision that the EW of hydrophilic SF will offer a new class of material structures with biological properties akin to natural systems.     

Magnetic silk fibroin composite nanofibers for biomedical applications: Fabrication and evaluation of the chemical,thermal, mechanical,and in vitro biological properties

Magnetically responsive polymer composites have great potential for use in diverse biomedical applications. In this study, composite biomaterials consisting of silk fibroin (SF) and superparamagnetic iron oxide nanoparticles (SPIONs) were fabricated by the electrospinning method. Two different methods were employed to incorporate the SPIONs into the SF nanofibers. In the first encapsulation method (M1), SPIONs (1.0, 3.0, and 5.0 wt%) were initially included in the electrospinning solution. In the second dip-coating method (M2), electrospun SF nanofiber mats were immersed in the aqueous suspensions of SPIONs (10, 30 and 50% v/v). Then, the pure and composite silk fibroin composite mats were comparatively evaluated for their morphological, chemical, magnetic, mechanical and in vitro biological properties, by using a number of methods including SEM, TEM, FTIR, XRD, EDS, VSM, TGA, mechanical tensile tests, as well as by indirect in vitro cytotoxicity and in vitro hemocompatibility analyses. Overall findings suggested that, while M1 nanofiber mats could be a suitable candidate for use in tissue engineering as a magnetically responsive cytocompatible scaffold, the M2 nanofiber mats perhaps could be more appropriate as an interface for triggering the in vitro stem cell differentiation and/or biosensor applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48040.     

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.     

丝素/羧甲基壳聚糖复合材料的制备及其在丝绸文物加固中的应用

为了对脆弱丝绸文物进行保护修复，延长其寿命，本研究以丝素蛋白（SF）、羧甲基壳聚糖（CMCS）为原料，谷氨酰胺转氨酶为交联剂，制备丝素/羧甲基壳聚糖复合材料（SF/CMCS），并将其应用于老化丝绸加固保护。选用傅里叶变换红外光谱（FT-IR）、X-射线衍射仪（XRD）、测色配色分光光度计、扫描电镜（SEM）及伺服高低温控制拉伸机对老化丝绸加固前后效果进行表征。结果表明，与老化丝绸相比，SF/CMCS加固丝绸的颜色无明显变化，物理机械性能有明显提升，抗张强度和断裂伸长率分别提升了379.12%、14.12%%，且有一定的抗菌性。     

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     

Study on porous silk fibroin materials. I. Fine structure of freeze dried silk fibroin

Silk fibroin solution was prepared by dissolving the silk fibroin in triad solvent CaCl₂ · CH₃CH₂OH · H₂O. In this article we tested and analyzed the state of frozen silk fibroin solution and fine structure of freeze dried porous silk fibroin materials. The results indicated that the glass transition temperature of frozen silk fibroin solution ranges from −34 to −20°C, and the initial melting temperature of ice in frozen solution is about −8.5°C. When porous silk fibroin materials are prepared by means of freeze drying, if freezing temperature is below −20°C, the structure of silk fibroin is mainly amorphous with a little silk II crystal structure, and if freezing temperature is above −20°C, quite a lot of silk I crystal structure forms. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2185–2191, 2001     

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