Spider silk is a particularly promising material for its outstanding strength, elasticity, and biocompatibility. Since the surface properties of a biomaterial are the key to control the interactions that occur when it is exposed to biological environments, understanding of the surface features of spider silk could provide insight into new opportunities for its application in biomedical fields.

In this work, the influence of selective solvent (90% methanol aqueous solution) treatment on surface properties of three kinds of spider silk proteins was studied. Proteins were obtained from the major ampullate gland of N. clavipes, recombinant MaSp2 from E. coli and recombinant MaSp2 from goat's milk. The surface properties of the proteins were investigated by Atomic Force Microscope (AFM), Scanning Electron Microscopy (SEM) and Contact Angle analysis. The AFM analysis revealed that the native silk is very smooth (RMS roughness 8-12 nm) both before and after treatment with 90% methanol, the recombinant silks are found to be very rough before methanol treatment (RMS roughness 49-82 nm), but after treatment with methanol they became smooth (RMS roughness 11-26 nm). These results are consistent with the surface wettability behavior. The native spider silk initially was more hydrophobic (contact angle above 100 degrees) than the recombinant silks whose contact angles were similar. However, after methanol treatment, the contact angles of the films of the three sources of spider silk proteins converged (around 55 degrees). The experimental data indicate that the surface structure and wettability of the three spider silks were initially different, but methanol treatment produced films with reduced variance in surface properties.