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Issue 26, 2012
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Ion electrodiffusion governs silk electrogelation

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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 pHgel ≈ 4 surrounded by pHsilk-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 (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.

Graphical abstract: Ion electrodiffusion governs silk electrogelation

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Publication details

The article was received on 03 Apr 2012, accepted on 08 May 2012 and first published on 28 May 2012

Article type: Paper
DOI: 10.1039/C2SM25783A
Soft Matter, 2012,8, 6897-6905

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    Ion electrodiffusion governs silk electrogelation

    N. Kojic, M. J. Panzer, G. G. Leisk, W. K. Raja, M. Kojic and D. L. Kaplan, Soft Matter, 2012, 8, 6897
    DOI: 10.1039/C2SM25783A

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