Abstract
A silk fibroin gel system (e-gel), formed with weak electric fields, has potential utility in medical materials and devices. The mechanism of silk e-gel formation was studied to gain additional insight into the process and control of the material properties. Silk fibroin nanoparticles with sizes of tens of nanometers, composed of metastable conformations, were involved in e-gel formation. Under electric fields the nanoparticles rapidly assembled into larger nano- or microspheres with size range from tens of nanometers to several microns. Repulsive forces from the negative surface charge of the acidic groups on the protein were screened by the local decrease in solution pH in the vicinity of the positive electrode. By controlling the formation and content of silk fibroin nanoparticles e-gels could be formed even from low concentration silk fibroin solutions (1%). When e-gel formation was reversed to the solution state the aggregated nano- and microspheres dispersed into solution, a significant observation related to future applications for this process, such as drug delivery.