Journal
SOFT MATTER
Volume 8, Issue 26, Pages 6897-6905Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c2sm25783a
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Funding
- NIH [DE017207, EB003210, EB002520]
- AFOSR
- Ministry of Education and Science of Serbia [OI 174028, III 41007]
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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) approximate to 4 surrounded by pH(silk-solution) approximate to 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 (2 mA and 3 mA) 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.
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