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Journal of Visualized Experiments www.jove.com

Copyright 2013 Creative Commons Attribution-NonCommercial License May 2013 | 75 | e50492 | Page 1 of 10

Video Article

Air Filter Devices Including Nonwoven Meshes of Electrospun Recombinant

Spider Silk Proteins

Gregor Lang, Stephan Jokisch, Thomas Scheibel

Biomaterials Research Group, University of Bayreuth

Correspondence to: Thomas Scheibel at Thomas.Scheibel@fiberlab.de

URL: http://www.jove.com/video/50492

DOI: doi:10.3791/50492

Keywords: Bioengineering, Issue 75, Biochemistry, Chemistry, Materials Science, Molecular Biology, Cellular Biology, Proteins, Nanotechnology,

materials (general), materials handling, nanodevices (mechanical), structural analysis, spider silk, electrospinning, microfibers, nonwoven, filter,

mesh, biomaterials

Date Published: 5/8/2013

Citation: Lang, G., Jokisch, S., Scheibel, T. Air Filter Devices Including Nonwoven Meshes of Electrospun Recombinant Spider Silk Proteins. J. Vis.

Exp. (75), e50492, doi:10.3791/50492 (2013).

Abstract

Based on the natural sequence ofAraneus diadematus Fibroin 4 (ADF4), the recombinant spider silk protein eADF4(C16) has been engineered.

This highly repetitive protein has a molecular weight of 48kDa and is soluble in different solvents (hexafluoroisopropanol (HFIP), formic acid and

aqueous buffers). eADF4(C16) provides a high potential for various technical applications when processed into morphologies such as films,

capsules, particles, hydrogels, coatings, fibers and nonwoven meshes. Due to their chemical stability and controlled morphology, the latter can

be used to improve filter materials. In this protocol, we present a procedure to enhance the efficiency of different air filter devices, by deposition

of nonwoven meshes of electrospun recombinant spider silk proteins. Electrospinning of eADF4(C16) dissolved in HFIP results in smooth fibers.

Variation of the protein concentration (5-25% w/v) results in different fiber diameters (80-1,100 nm) and thus pore sizes of the nonwoven mesh.

Post-treatment of eADF4(C16) electrospun from HFIP is necessary since the protein displays a predominantly -helical secondary structure in

freshly spun fibers, and therefore the fibers are water soluble. Subsequent treatment with ethanol vapor induces formation of water resistant,

stable -sheet structures, preserving the morphology of the silk fibers and meshes. Secondary structure analysis was performed using Fourier

transform infrared spectroscopy (FTIR) and subsequent Fourier self-deconvolution (FSD).

The primary goal was to improve the filter efficiency of existing filter substrates by adding silk nonwoven layers on top. To evaluate the influence

of electrospinning duration and thus nonwoven layer thickness on the filter efficiency, we performed air permeability tests in combination with

particle deposition measurements. The experiments were carried out according to standard protocols.

Video Link

The video component of this article can be found at http://www.jove.com/video/50492/

Introduction

Due to their combination of strength and extensibility, spider silk fibers can absorb more kinetic energy than most other natural or synthetic

fibers1. Furthermore, unlike most synthetic polymeric materials silk materials are nontoxic and biocompatible and cause no allergic reaction

when incorporated2,3

. Putative health risks can be prevented by using spider silk. These features make spider silk highly attractive for a variety

of medical and technical applications. Since spiders can't be farmed due to their cannibalistic behavior, biotechnological methods have been

developed to produce spider silk proteins, both cost-efficiently and in sufficient quantities4.

The recombinant silk protein eADF4(C16) has been engineered based on the natural sequence ofAraneus diadematus Fibroin 4 (ADF4).

eADF4(C16) has a molecular weight of 48kDa5

and is soluble in various solvents (hexafluoroisopropanol (HFIP)6, formic acid

7and aqueous

buffers)8. eADF4(C16) can be processed into different morphologies such as films

9, capsules

8, particles

10, hydrogels

11, coatings

7, fibers

12

and nonwoven meshes6. Due to their chemical stability, the latter provide high potential in filter applications.

Here, we present a protocol to fabricate air filter devices including a nonwoven mesh of electrospun recombinant spider silk proteins.

Electrospinning or electrostatic spinning is a technique typically employed for producing polymer fibers with diameters in the range of 10 nm -10

m13

, and nonwoven meshes have already been investigated for filter applications14

. In the past, electrospinning has been successfully applied

for processing of regenerated15

as well as recombinantly produced16

spider silk proteins. Typically a high electric voltage (5-30 kV) is applied

to a syringe and a counter electrode (0-20 kV) placed in a distance of 8-20 cm. The strong electrostatic field induces repulsive forces within the

charged solution. If the surface tension is exceeded, a Taylor cone is formed, and a thin jet erupts from the tip17,18

. After formation, bending

instabilities occur within the jet causing further stretching as the solvent evaporates, and a solid fiber is formed. Finally, the fiber is randomly

deposited on the counter electrode as a nonwoven mesh19

. Fiber properties like diameter and surface topology (smooth, porous) are mainly

dependent on solution parameters such as concentration, viscosity, surface free energy and the solvent's intrinsic electrical conductivity and

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