Vol.:(0123456789) MRS Advances https://doi.org/10.1557/s43580-021-00192-0 1 3 ORIGINAL PAPER Electrospun silk fbroin using aqueous and formic acid solutions Maria Vallejo‑Martinez 1,2  · Melissa Puerta 1  · Adriana Restrepo‑Osorio 1,2 Received: 13 September 2021 / Accepted: 22 November 2021 © The Author(s), under exclusive licence to The Materials Research Society 2021 Abstract Silk fbroin is a polymer of interest thanks to its ability to be transformed into diferent structures, such as fbers. The elec- trospun technique can produce micro and nanofbers, presenting advantages like high superfcial area and porosity. However, this polymer needs to be dissolved into a liquid solution using solvents. This study evaluates the efect of formic acid and water as solvents on the silk fbroin electrospun fbers morphology, chemical structure, and thermal properties. In this case, silk fbroin was obtained from silk fbrous wastes. The results suggest that the morphology obtained from both solutions has a similar fber diameter. Electrospun silk fbers using formic acid solution present a relatively high porosity and recrystallization enthalpy. In contrast, the percentage of crystallinity and degradation temperature were higher in samples with aqueous solu- tion. This indicates that the aqueous process allows higher structural ordering, improving the thermal stability for the fbers. Introduction Silk is a protein fber produced by a variety of insects, including silkworms like Bombyx mori. Its silk is com- posed of two proteins, silk fbroin (SF) (70–75%) and silk sericin (25–30%) [1]. SF is usually obtained from silkworm cocoons, which can be used for other purposes like silk textiles. Nevertheless, SF can also be obtained from silk fbrous wastes as raw material with relatively low-cost [2, 3], namely silk fbroin from wastes (SFw). SF is versatile polymer due to the diferent forms it can be manufactured, such as powder, gels, flms, foams, and nanofbers, making it useful on several applications [4]. This versatility combined with its outstanding properties such as biocompatibility, per- meability, thermal stability, and degradation, makes the SF a promising material for diferent applications [5–7] such as textiles [8–10], food packaging [11], wound dressings [12], fltration media [13], and medical materials [4, 14, 15]. Several techniques are used to transform the SF into diferent forms for its fnal application. The electrospinning technique, for instance, allows producing SF fbers with diameters in the range of micrometers down to tens nanom- eters as a function of its processing conditions, giving high specifc surface area and high porosity to the fnal material. These properties improve its capability to use it in these applications mentioned above [6]. It is possible to electrospun SF on an aqueous solution (AQ) or use organic solvents such as formic acid (FA). AQ solution systems with SF stands out due to their null toxicity compared to FA systems, but it has lower stability in solu- tion. For this reason, external mechanical force or storage conditions could induce molecular aggregation, precipita- tion, and SF gelation in AQ systems [16]. In contrast, FA and SF system produce transparent solutions, prevent aggrega- tion formation, and allow longer storage time than AQ [17]. Also, FA as solvent helps to control the viscosity during the SF electrospinning processing [18]. SFw fbers’ properties, manufactured through the electrospun process using AQ and FA as solvents, is still been studied in order to establish the diferences between both solvent systems. In this work, defect-free electrospun fbers of SFw, were manufactured and characterized. The samples morphology, chemical structure, and thermal behavior were evaluated. Scanning Electron Microscopy (SEM), Attenuated Total Refectance Fourier Transform Infrared Spectroscopy (FTIR-ATR), and Temperature Modulated Diferential Scanning Calorimetric (TM-DSC) were implemented, respectively, to compare the efect of the solvent system in the electrospun SFw fbers. * Adriana Restrepo-Osorio adriana.restrepo@upb.edu.co 1 Grupo de Investigación Sobre Nuevos Materiales (GINUMA), Semillero de Investigación en Textiles (SI Textil), Universidad Pontifcia Bolivariana, Circular 1 # 70-01, Medellín, Colombia 2 Facultad de Ingeniería Textil y Nanotecnología, Escuela de Ingenierías, Universidad Pontifcia Bolivariana, Circular 1 # 70-01, Medellín, Colombia