Micromechanical Investigations on Films made of Recombinant Spider Silk Proteins and Silk Fibroin
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1062-NN06-08
Micromechanical Investigations on Films made of Recombinant Spider Silk Proteins and Silk Fibroin Frauke Junghans1, Udo Conrad2, Andreas Heilmann1, and Uwe Spohn1 1 Biological Materials and Interfaces, Fraunhofer Institute for Mechanics of Materials, WalterHülse-Strasse 1, Halle (Saale), Germany 2 Institute of Plant Genetics and Crop Plant Research, Leibniz Institute, Corrensstrasse 3, Gatersleben, Germany *Corresponding author: [email protected], Tel. 049 345 55 89 123, Fax 049 345 55 89 101 ABSTRACT Films made of a recombinant spider silk protein and silk fibroin were prepared by spincoating and casting. Therefore the solubility of these substances was investigated in hexafluoroisopropanol, ionic liquids and concentrated salt solutions. The roughness and the thickness of the protein films were determined by the Atomic Force Microscopy (AFM) and by mechanical profilometry. The micromechanical behaviour was investigated by acoustic impedance analysis using a quartz crystal microbalance (QCMB) as well as by microindentation. Films with thickness less than 350 nm revealed an almost ideal elastic behaviour in the range of 5 to 75 MHz. At a higher film thickness the half-band-half width increases considerably and the films show a viscoelastic behaviour with a considerable dissipation. The relative humidity significantly influences the mechanical behaviour of protein films. Hence the microhardness and the ability of water adsorption were determined in dependence on the relative humidity.
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INTRODUCTION
The outstanding mechanical properties, e.g. extreme strength and toughness combined with high elasticity, of natural silk fibres from spiders [1–3] and from silk worms [4,5] are well-known. The degummed silk of Bombyx mori (B.m.) shows a moderate and subsiding foreign body response supporting cell attachment and growth, e.g. of bone marrow stromal cells and osteoblasts [6]. These promising effects and the mechanical properties of the fibres recommend this material for coating of implants and scaffold materials which can be used for tissue engineering of tendons, ligaments, cartilage and bone [7,8]. The first aim of this work was the preparation of protein films from recombinant spider silk protein SO1-100xELP expressed from tobacco plants [9,10] and the comparison of their mechanical properties with those films analogously prepared from the silk fibroin of Bombyx mori. The protein SO1-100xELP is a fusion protein consisting of a spidroin like protein sequence and an elastin like protein (ELP) sequence 100xELP [11]. The amino acid sequence SO1 is highly homologous to the repetitive portion of spidroin 1 of the spider Nephila clavipes [9]. The 100xELP was designed according to Meyer and Chilkoti [12]. The SO1-100xELP protein was isolated and purified from the transformed leafs of the tobacco plant Nicotiana tabacum cv. SNN as described by Scheller and Conrad [11].
Both silk proteins had to be purified and dissolved in hexafluoroisopropanol (HFIP), ionic liquids or concentrated salt solutions to g
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