Significantly Reinforced Composite Fibers Electrospun from Silk Fibroin/Carbon Nanotube Aqueous Solutions Hui Pan, † Yaopeng Zhang,* ,† Yichun Hang, † Huili Shao, † Xuechao Hu, † Yuemin Xu,* ,‡ and Chao Feng ‡ † State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, P. R. China ‡ Department of Urology, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai 200233, P. R. China * S Supporting Information ABSTRACT: Microcomposite fibers of regenerated silk fibroin (RSF) and multiwalled carbon nanotubes (MWNTs) were successfully prepared by an electrospinning process from aqueous solutions. A quiescent blended solution and a three-dimensional Raman image of the composite fibers showed that functionalized MWNTs (F-MWNTs) were well dispersed in the solutions and the RSF fibers, respectively. Raman spectra and wide-angle X-ray diffraction (WAXD) patterns of RSF/F-MWNT electrospun fibers indicated that the composite fibers had higher β-sheet content and crystallinity than the pure RSF electrospun fibers, respectively. The mechanical properties of the RSF electrospun fibers were improved drastically by incorporating F-MWNTs. Compared with the pure RSF electrospun fibers, the composite fibers with 1.0 wt % F-MWNTs exhibited a 2.8-fold increase in breaking strength, a 4.4-fold increase in Young’s modulus, and a 2.1-fold increase in breaking energy. Cytotoxicity test preliminarily demonstrated that the electrospun fiber mats have good biocompatibility for tissue engineering scaffolds. ■ INTRODUCTION Bombyx mori silk produced by silkworms with exceptional mechanical properties and luster has been used in textiles for thousands of years in human history. As well-known, silk fibroin offers a series of properties including mechanical superiority and biocompatibility. It also shows great potential applications in blood vessel engineering, 1 drug delivery, 2 and porous silk scaffolds. 3,4 Furthermore, electrospinning possesses a unique superiority that enables the development of protein-based biomaterials. The diameter of electrospun fibers is in nano- or microscale. 5−8 As a result, the materials produced by the electrospinning process exhibit greatly outstanding oxygen and water vapor permeability. Accompanying their biocompatibility, degradability, and processability, electrospun regenerated silk fibroin (RSF) fibers have been investigated widely for their potential applications in tissue engineering. 9−14 To date, most nano/micro silk fiber mats are prepared from hash or toxic solvents, such as formic acid, 15−19 hexafluor- oisopropanol (HFIP), 20,21 and hexafluoroacetone (HFA). 7 The residual solvents in the fibers are very likely harmful to the growth of cells. Therefore, our group and other researchers replaced the organic solvent with water and prepared electrospun RSF fibers from aqueous solutions. 5,6,22−27 However, the mechanical properties of the mats were still very poor for application. Normally, there are two ways to reinforce the RSF mats. One is to treat the electrospun RSF mats by methanol or ethanol, in which the RSF fibers experience some structure transition and crystalline trans- formation. 5,6,19 The other way is to add a reinforcing agent into the spinning dope to prepare composite fibers. Carbon nanotubes (CNTs), as typical reinforcing agents with out- standing mechanical properties, 28,29 have successfully enhanced numbers of polymers, such as polypropylene, 30 polyamide 6, 31 polyacrylonitrile, 32,33 and so on. 34−37 Due to their exceptional Young’s modulus and strength, CNTs might also be used to reinforce electrospun RSF fibers. Ko et al. 18 utilized CNTs and tried to reinforce the electrospun RSF nano/microfibers from formic acid solution, and the mechanical properties of as-spun composite mats were not improved as expected. Only post- treatment with alcohol can make a significant modification on their mechanical properties. 19,38 CNTs are not only a reinforcing agent but also a crucial functionalizing agent because of their high electrical conductivity. 39−42 In this study, MWNTs were employed as reinforcing agents to modify the electrospun RSF fibers from aqueous solution. The dispersion of MWNTs in RSF solutions and electrospun fibers was investigated. In addition, the morphology, structure, and mechanical properties of the electrospun fibers and the biocompatibility of electrospun composite mats were examined. ■ EXPERIMENTAL METHODS 2.1. Preparation of RSF/F-MWNT Electrospinning Dope. Cocoons of B. mori (produced in Tongxiang, China) were treated twice with 0.5 wt % Na 2 CO 3 aqueous solution at Received: June 7, 2012 Revised: August 1, 2012 Published: August 10, 2012 Article pubs.acs.org/Biomac © 2012 American Chemical Society 2859 dx.doi.org/10.1021/bm300877d | Biomacromolecules 2012, 13, 2859−2867
Significantly Reinforced Composite Fibers Electrospun from Silk Fibroin/Carbon Nanotube Aqueous Solutions
May 16, 2023
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