www.nature.com/scientificreports OPEN Electrospinning over Solvent Casting: Tuning of Mechanical Properties of Membranes Received: 16 November 2017 Kajal Ghosal1, Aniruddha Chandra2, Praveen G.1, Snigdha S.1, Sudeep Roy3, Accepted: 1 March 2018 Christian Agatemor4, Sabu Thomas1 & Ivo Provaznik3,5 Published: xx xx xxxx We put forth our opinion regarding the enhanced plasticity and modulation of mechanical properties of polymeric flms obtained through electrospinning process in this article. In majority of the pharmaceutical, biomedical, and packaging applications, it is desirable that polymer based matrices should be soft, fexible, and have a moderate toughness. In order to convert infexible and brittle polymers, adjuvants in the form of plasticizers are added to improve the fexibility and smoothness of solvent casted polymer flms. However, many of these plasticizers are under scrutiny for their toxic efects and environmental hazards. In addition, plasticizers also increase the cost of end products. This has motivated the scientifc community to investigate alternate approaches. The changes imparted in membrane casted by electrospinning were tried to be proved by SEM, Mechanical property study, DSC and XRD studies. We have showed dramatic improvement in fexibility of poly(ε-caprolactone) based nanofber matrix prepared by electrospinning method whereas solvent casting method without any plasticizer produced very brittle, infexible flm of PCL. Modulation capacity of mechanical properties is also recorded. We tried to support our opinion by citing several similar fndings available in the open literature. The electrospinning method helps in plasticization and in tuning mechanical properties. Polymers, be it synthetic, semi-synthetic, or natural, have gained wide attention in diferent technology sectors. Tey are used in various forms, such as solid flms, thin matrices, nanofber mats or patches, hydrogel flms etc.1,2. All these polymer forms are obtained from their original bulk form afer appropriate modifcation of mechanical properties3,4. Further modifcation is ofen needed depending on the target application. One such important modifcation, especially for pharmaceutical, biomedical, and packaging industries, is to increase the fexibility of the polymer flms through incorporation of plasticizer. As the plasticity of a polymer flm turns out to be one of the most crucial fabrication points, similarly mechanical properties of flms should also be considered during diferent applications. Polymeric flms that are widely used as coatings over solid pharmaceutical dosage forms to improve their appearance and mechanical strength, to prevent them from dusting, chipping, and cracking, and to modify release of active ingredients from formulations are taken care of. In their basic form, these flm coatings are ofen hard, brittle, and have lower ductility. Proper adjuvants are added during the manufacturing process to overcome these limitations. Several investigators have confrmed the utility of polymeric flm as a drug delivery carrier to avoid hepatic frst pass metabolism and to reduce side efects related with other dosage forms. Systems that involve drug admin- istration through adhesive bases, e.g., transdermal systems, bioadhesive vaginal flms, sublingual or buccal flms, wound dressing flms, are all primarily comprised of polymer flms that contain drugs. Further, using flms as carrier attains some other goals such as enhancing bioavailability, realizing controlled/sustained and/or targeted drug release, minimizing drug dosage, and elevating patient compliance. Of course all the goals are accomplished only when conformability criterion for these thin flms is compiled during formulation, i.e. they are strong and fexible enough for practical use. 1Center for Nanoscience and Nanotechnology, Mahatma Gandhi University, Priyadarshini Hill, Kottayam, 686560, Kerala, India. 2Electronics and Communication Engineering Department, National Institute of Technology, Durgapur, 713209, West Bengal, India. 3Department of Biomedical Engineering, Faculty of Electrical Engineering and Communication, Brno University of Technology, Brno, Czech Republic. 4School of Engineering and Applied Sciences, Harvard University, 52 Oxford Street, Cambridge, MA, 02138, USA. 5Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic. Correspondence and requests for materials should be addressed to K.G. (email: [email protected]) or I.P. (email: [email protected]) SCIENTIFIC REPORTS | (2018) 8:5058 | DOI:10.1038/s41598-018-23378-3 1 www.nature.com/scientificreports/ without Plasticizer with Plasticizer Young’s % Young’s UTS % Elongation Modulus UTS Elongation Modulus Polymer Plasticizer (MPa) at break (MPa) (MPa) at break (MPa) Application PVA 7 Sorbitol 14.36 61.23 75.9 5.36 110.81 22.6 Vaginal flm Controlled drug release Eudragit RS PO8 Citric Acid 4.46 — 760 1.00 117.11 520 flm Transdermal drug HPMC9 TEC 83.3 8.5 891.1 76.7 107.0 516.9 delivery Chitosan and Transdermal drug Glycerol 4.56 44 — 4.5 65 — Carbopol10 delivery Zein11 Glycerol — — — 24 0.029 1480 Drug release flm PMVE/MA12 Glycerol 18.23 1.68 24.07 4.73 14.72 1.14 Bioadhesive patch PMVE/MA13 PEG 10000 — — — 31.02 478.43 9.32 Bioadhesive flm Pressure sensitive PVP-PEGDA-PEG14 PG 0.135 42.5 — 0.09 75 — adhesive HPC and EC15 PG 10.51 15.51 70.06 7.82 26.62 30.07 Buccal flm TEC 8.5 2.6 472.4 5.1 178.5 70.0 Drug release flm Soluplus16 PPG 13.4 25.9 326.2 6.8 119.6 121.1 Glycerin 10.5 47.3 279.1 4.7 195.5 77.5 Plasticizer at low level Plasticizer at high level % Young’s % Young’s Polymer Plasticizer UTS UTS Application Elongation Modulus Elongation Modulus (MPa) (MPa) at break (MPa) at break (MPa) HPMC17 PEG 5.96 106 2.1 4.96 242 0.56 Oral fast dissolving flm Soluplus16 PEG 8.8 66.4 196.0 0.37 461 1.4 Drug release flm HPC18 PEG 400 7.83 51.42 — 6.99 55.91 — Vaginal flm PMVE/MA12 Glycerol 4.73 14.72 1.14 2.02 36.54 0.04 Bioadhesive patch Starch19 Glycerol 17.5 1.3 2120 1.2 5.6 26 Bioadhesive flm Cashew gum and Glycerol 5.35 0.78 710 1.81 59 3 Biotechnology/packaging CMC20 Table 1. Efect of plasticizer on fexibility of diferent polymer flms. Ref.7. Garg et al.8. Schilling et al.9. Limpongsa et al.10 Silva et al.11 Singh et al.12 Moss et al.13 Singh et al.14 Dana et al.15 Alanazi et al.16 Lim et al.17 Pandey et al.18 Dobaria et al.19 Rechia et al.20 Britto et al. Abbreviations used - UTS: ultimate tensile strength, PVA: poly vinyl alcohol, HPMC: hyrdoxy propyl methyl cellulose, PMVE/MA: (poly) methylvinyl ether/ maleic anhydride, PVP: polyvinyl pyrrolidone, PEGDA: poly(ethylene glycol) diacrylate, PEG: polyethylene glycol, HPC: hydroxypropyl cellulose, EC: ethyl cellulose, PG: propylene glycol, TEC: triethyl citrate, PPG: polypropylene glycol, CMC: carboxy methyl cellulose. Polymeric flms have gained attention of the biomedical community as well5. Biomedical device construction is challenging because it is difcult to fabricate devices that are both biocompatible and portable6. Moreover, majority of the conventional biomedical devices lack fexibility which is of serious concern if they are to be worn or implanted to the patient body. Te rigidity can be overcome with biopolymer based matrix or thin flms. Te flms are biodegradable and this aspect is an added advantage. Polymer flms, either in membrane or in matrix forms, can contribute hugely in packaging, optical lenses, touch screens, foldable sensors, and each of these domains has their own set of plasticity and mechanical property requirements. In pharmaceutical, biomedical, and packaging industries there is a demand for fexible flms. Tis requirement is fulflled through incorporation of polymer specifc plasticizers such as phtalates, trimellitates, adipates, sebacates, glycols, polyethers and alkyl citrates. In fact for the mentioned target applications plasticizers have become a very important additive in polymer systems, and modifcation of plasticity with plasticizer forms an integral part during fabrication irrespective of the flm fabrication or matrix formation process. Table 1 sum- marizes how the plasticity of several solvent-cast polymer flms is modifed with the introduction of plasticizer. Te cells (in Table 1) with no entries represent values that are either not calculated or could not be determined due to very brittle nature of flm7–20. In this paper, for the frst time we have investigated and reported potential of electro-spinning method (Fig. 1) over solvent casting method to fabricate polymeric membrane with enhanced fexibility and plasticity. We have systematically evaluated the phenomena by thorough investigation of electrospun and solvent casted membrane. We hypothesize that the mechanical properties and plasticity of electrospun polymer nanofbers will be infu- enced by the fabrication method. In this study, we employed scanning electron microscopy technology to eval- uate the consequence of electrospinning method on morphology of spun fbers as well as on the morphology of solvent casted membrane. Te change in mechanical properties and fexibility were also studied. How the fber alignment itself change the mechanical properties of fber, were studied. XRD, DSC were employed to support the potentiality of electrospinning process. SCIENTIFIC REPORTS | (2018) 8:5058 | DOI:10.1038/s41598-018-23378-3 2 www.nature.com/scientificreports/ Figure 1. Electrospinning apparatus set-up and nanofber mesh. Results Surface Morphology. Electrospinning is extensively used to develop fber of high tensile strength, which is desirable in applications that need lightweight but durable materials. Te ability to align and control fber diame- ter makes this technique highly attractive. Here, we prepared three electrospun membranes with diferent kinds of alignment using a rotating mandrel. For simplicity, we designated membrane with uni-directionally aligned fbers as aligned, those randomly aligned as random, and those with aligned fbers overlaid on a randomly aligned as a bilayer. Tese diferences tuned the morphology and size of the fber because the aligned consisted of uniformly sized fbers that mainly ranged from 5–8 µm.