Finite-Element Model of the Silk Electrogelation Process

Abstract

Driven by the desire to fulfill major needs for medical adhesives that fully degrade with time, adhere to wet tissues, control bleeding, and are mechanically durable with controlled drug-release capabilities, our group has discovered a unique new material called “e-gel”. The e-gel forms during a process called electrogelation, when a low-voltage direct-current field causes a sol-gel transition in an aqueous silk protein solution. The e-gel is fully biocompatible and exhibits exceptional adhesive properties, both to tissue and synthetic surfaces (including water environments) and can also be re-dissolved into solution by reversal of electrical polarity. Furthermore, small shear forces induce structural alignment of silk proteins resulting in the irreversible transition to the gel state. To help elucidate the underlying mechanisms governing e-gel formation and growth we have developed a finite element model of the electrogelation process. The model examines how the dynamics of the pH field, caused by electrolysis of water, controls e-gel growth. The pH field is variable during electrogelation due to the interplay of positive H+ ions generated at the e-gel forming (+) electrode and the negative OH- ions formed at the opposite (-) electrode. The acidic pH propagates from the positive electrode and induces a gradual transition of the silk protein to the gel state. Our ion electro-diffusion model has been experimentally verified and provides the ability to predict, for a given set of conditions (e.g. strength of the current, geometry of the setup) the growth of the e-gel from the positive toward the negative electrode, including its final, steady-state length. The model is adaptable and can serve as a platform for more intricate, multiscale models that would couple conformational changes of silk proteins with macro-scale ion and protein transport.