Surface Characterization of As-Spun and Supercontracted Nephila clavipes Dragline Silk

Benoit Faugas, Michael S. Ellison, Delphine Dean, Marian S. Kennedy

Department of Bioengineering, Clemson University, Clemson, USA..
Department of Materials Science & Engineering, Clemson University, Clemson, USA;.

DOI: 10.4236/jsemat.2013.33A004                

Abstract

Dragline spider silks have relatively high mass-based mechanical properties (tensile strength, elongation to break and rupture energy) and are environmentally responsive (supercontraction). In order to produce new synthetic fibers with these properties, many research groups have focused on identifying the chemical composition of these fibers and the structure of the fiber core. Since each fiber also has an outer skin, our study will provide a detailed understanding of the silk surface morphology, the response of the surface morphology to environmental conditions and processing variables, and also determine if the silk surface has a definitive patterning of charged amino acids. Specifically, by using force microscopy and functionalized nanoparticles, the present study examines 1) how the silk surface (topography, average roughness) is altered due to prior mechanical loading (viz. reeling speed), 2) alterations in morphology due to environmental conditions (supercontraction, storage time), and 3) the negatively and positively charged regions along with the surface using both force and nanoparticle mapping. Roughness data taken on dragline silk collected from Nephila clavipes spiders revealed that the surface comprised both smooth (5 nm RMS) and rough (65 nm RMS) regions. Supercontracted silk (from immersion in0.01 MPBS during AFM testing) showed higher surface roughness values compared to spider silk tested in the air, indicating that the surface might be reorganized during supercontraction. No correlation was found between surface roughness and neither collection speed nor aging time for the as-spun or supercontracted fiber, demonstrating the surface stability of the dragline silk over time in terms of roughness. Both the force microscopy and the nanoparticle methods suggested that the density of negatively charged amino acids (glutamic acid, aspartic acid) was higher than that of the positively charged amino acids (lysine, asparagine, and histidine).

Keywords

Spider Dragline Silk; Surface Roughness; Supercontraction; Amino Acids; AFM; Force Microscopy; Na-noparticles

Conflicts of Interest

The authors declare no conflicts of interest.

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