Influence of the protocol used for fibroin extraction on the mechanical properties and fiber sizes of electrospun silk mats Salvador D. Aznar-Cervantes a , Daniel Vicente-Cervantes a , Luis Meseguer-Olmo b , José L. Cenis a , A. Abel Lozano-Pérez a, ⁎ a Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA), Department of Biotechnology, La Alberca (Murcia), CP 30150, Spain b Hospital Universitario Virgen de la Arrixaca, Unidad de Cirugía Ortopédica e Ingeniería de Tejido Óseo, El Palmar (Murcia), CP 30120, Spain abstract article info Article history: Received 14 May 2012 Received in revised form 2 January 2013 Accepted 3 January 2013 Available online xxxx Keywords: Bombyx mori Silk fibroin Electrospinning Fibroin solubilization Mechanical properties Silk fibroin (SF) was regenerated using three of the most common protocols described in the bibliography for the dissolution of raw SF (LiBr 9.3 M, CaCl 2 50 wt.% or CaCl 2 :EtOH:H 2 O 1:2:8 in molar ratio). The integrity of regenerated SF in aqueous solution was analyzed by SDS-PAGE and different profiles of degradation were ob- served depending on the protocol used. This fact was found to affect also the aqueous solubility of the freeze dried protein. These different SFs were used to produce electrospun mats using SF solutions of SF 17 wt.% in 1,1,1,1′,1′,1′-hexafluoro-2-propanol (HFIP) and significant differences in fiber sizes, elongation and ultimate strength values were found. This work provides a global overview of the manner that different methods of SF extraction can affect the properties of electrospun SF-mats and consequently it should be considered depending on the use they are going to be made for. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Silk produced by Bombyx mori is formed by the combination of a fibrilar protein, named fibroin, and a glue-like protein, named sericin, which represents about 25–30 wt.% of the cocoon mass [1]. Silk fibroin is composed of three proteinaceous components: the heavy chain (350 kDa) fibroin (H-chain), the light chain (25 kDa) fibroin (L-chain) and P25 protein. The molar ratios of these three components are 6:6:1 respectively. The first one is hydrophobic and responsible of the forma- tion of β-sheet structures, the second one is more hydrophilic and elas- tic and both of them are linked by a disulfide bond, meanwhile the P25 protein gives integrity to the complex [2]. Several protocols have been developed for dissolution of SF with the common point of using solvents capable to break the hydrogen bond-stacks of β-sheets (as concentrated solutions of salts, strong acids or ionic liquids). SF materials are highly biocompatible and can be processed in different formats such as capsules, films, 3D-sponges, hydrogels, nanoparticles or micro- and nanofibers produced by electrospinning [3]. Silk fibroin has been widely studied for tissue engineering appli- cations in the repair of blood vessels [4], skin [5], bone [6] and carti- lage [7], among many others. Electrospinning is a technique that enables the making of nanofiber-based scaffolds with applications in a wide variety of fields as filtration equipments [8], catalysts, electronic devices and tissue engineering [9]. A typical electrospinning setup consists of three components: a high voltage supplier, a capillary needle, and a collec- tor of dry fibers. During electrospinning, an electric potential is applied to a pendent droplet of polymer solution suspended from a needle, usually delivered with a syringe pump or by gravitational force [10]. Repulsive forces produced by like charges in the solution as well as the attractive forces between the fluid and the collector work together to exert tensile forces on the solution. Surface tension and viscoelastic forces of the polymer solution retain the hemispher- ical shape of the suspended droplet, while the electric force pulls the droplet away from the capillary [11]. The development of the Taylor cone occurs when the applied voltage is increased beyond a critical value, where the electrostatic forces balance out the surface tension of the droplet at the tip of the capillary. Finally, a fiber jet ejects from the apex of the cone and accelerates towards the grounded collector [12]. Since the first patent was issued by Formhals in 1934 [13] and mostly after 1998 a great number of works related with electrospinning have been developed [14] and published applying this technique to different polymer solutions. Silk fibroin is a biomaterial apt for being processed by electro- spinning. Numerous types of electrospun silk matrices, alone or in combination with other biomaterials, have been developed in the last years. Park et al. produced chitin/silk fibroin blend fibers [15], col- lagen/silk fibroin solutions in HFIP were electrospun by Yeo et al. [16]. Electrospun fibroin mats can also be functionalized with diverse li- gands or components. Li et al. linked covalently bone morphogenetic protein-2 (BMP-2) into silk fibroin nanofibers [17] and our group Materials Science and Engineering C xxx (2013) xxx–xxx ⁎ Corresponding author. Tel.: +34 968368584. E-mail address: abel@um.es (A.A. Lozano-Pérez). MSC-03793; No of Pages 6 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.01.001 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec Please cite this article as: S.D. Aznar-Cervantes, et al., Mater. Sci. Eng., C (2013), http://dx.doi.org/10.1016/j.msec.2013.01.001