title: Ion Electrodiffusion Governs Silk Electrogelation.
abstract: Silk electrogelation involves the transition of an aqueous silk fibroin solution to a gel state (E-gel) in the presence of an electric current. The process is based on local pH changes as a result of water electrolysis - generating H(+) and OH(-) ions at the (+) and (-) electrodes, respectively. Silk fibroin has a pI=4.2 and when local pH<pI, E-gel forms. An experimental system was constructed that allowed the measurement of E-gel growth and pH distribution for an applied current. To explain the observed rectangular pH profile of pH(gel)~4 surrounded by pH(silk-solution)~10, a finite-element ion electrodiffusion model was developed. The model relies on electrodiffusion of the generated H(+) and OH(-) ions. Initially, inputs into the model were the measured E-gel and voltage curves. The governing ion electrodiffusion equations were solved and the calculated pH matched the experimental pH profile, indicating that ion electrodiffusion dictates local pH changes and E-gel growth. Furthermore, the model predicted the constant currents (2mA and 3mA) necessary for two hypothetical E-gel growth curves and these results were then validated experimentally. The model thus shows how ion electrodiffusion governs the electrogelation process and also provides predictable outcomes for fundamental and practical E-gel applications.
authors: Department of Biomedical Engineering, Tufts University, Medford MA, 02155.
authors: Nikola
authors: N
authors: Kojic
authors: Matthew J
authors: MJ
authors: Panzer
authors: Gary G
authors: GG
authors: Leisk
authors: Waseem K
authors: WK
authors: Raja
authors: Milos
authors: M
authors: Kojic
authors: David L
authors: DL
authors: Kaplan