How Electric Field Remodels the Nanofibril Structure of Chitosan Hydrogels: the Role of Dewetting During Electro-Assembly.

Electrofabrication has emerged as a versatile technique for creating complex functional materials from self-assembling biopolymers such as chitosan and collagen; however, a molecular-level understanding of electric cueing remains lacking. Here we investigate how a mild electric field (similar in magnitude to that imposed on biological membranes) remodels the nanofibril structure of chitosan hydrogels using all-atom molecular dynamics simulations. The simulations revealed a mechanism of active dewetting, in which the electric field enhances fibrillar order and induces compaction along the sheet-stacking direction through expulsion of water and stabilization of the hydrogen-bond network within and between fibril sheets. This mechanism provides a physical basis for a recent experimental observation that electrodeposited chitosan hydrogel film undergoes vertical contraction. The electric field-induced dewetting between amphiphilic chitosan sheets is reminiscent of but fundamentally different from the classic dewetting phenomenon for purely hydrophobic systems, which has been intensively studied by both theoretical and experimental communities in the past. Using active dewetting to control microstructures has implications for tailored engineering of functional materials such as artificial bones and tissues based on self-assembling chitosan.