Electrochemically Induced Deposition of a Polysaccharide Hydrogel onto a Patterned Surface

Abstract

Hydrogels are increasingly considered for creating three-dimensional structures in miniaturized devices, yet few techniques exist for creating such hydrogel structures. We report a new approach for creating hydrogels using the amine-containing polysaccharide chitosan. Specifically, electrodes are immersed into a slightly acidic chitosan solution and a voltage is applied to promote the proton-consuming hydrogen evolution reaction at the cathode surface. This reaction leads to a high localized pH in the vicinity of the cathode surface, and if this localized pH exceeds about 6.3, then chitosan becomes insoluble and deposits at the cathode surface. As the current density is increased, the region of high pH is expected to extend further from the cathode surface into the bulk solution. Using moderately high current densities (50 A/m 2 ), we observed that chitosan deposited as a thick hydrogel. Measurements of the water content confirmed that the deposited chitosan was a hydrogel. To suggest the potential utility, we deposited a chitosan hydrogel on a patterned surface to create a channel. Because of chitosan's pH-dependent solubility, this channel could be "disassembled" by mild acid treatment. We envision that electrochemically-induced deposition of chitosan-based hydrogels may offer interesting opportunities for the integration of biological systems into miniaturized devices.

Transient charge-masking effect of applied voltage on electrospinning of pure chitosan nanofibers from aqueous solutions

“…Chitosan becomes insoluble and forms a hydrogel on the cathode surface when it is attracted to the surface and then crosses a certain threshold of pH in the solution. In previous studies, the voltage applied during the electrodeposition of chitosan was limited to 0.5-2.5 volts [19][20][21]. Our results suggest the following model.…”

“…At pH values higher than 6.3, a reduction in the number of deprotonated amino groups renders chitosan insoluble in aqueous solutions. Using this sensitivity to pH, chitosan can be deposited onto a cathode surface even from an acidic solution in response to an applied voltage [19][20][21]. A pH gradient is generated in the chitosan solution (spreading concentrically from the cathode surface) when a voltage is applied to the electrodes.…”

Electrochemical Synthesis of Nitro-Chitosan and Its Performance in Chromium Removal

“…The process is reversible and on increasing pH higher than 6.3, protonated chitosan deprotonates and precipitates. As reported previously by this group [13] as well as in work by Fernendes et al [14], a localized zone of high pH is created near a cathode held at sufficiently negative potential in water, a method utilized in this process to electrochemically deprotonate protonated chitosan and form deposits on the steel substrate. Stainless steel is chosen as an electrode as it is inexpensive, easy to use, and does not corrode at cathodic potentials.…”

Chitosan Electrodeposition for Microrobotic Drug Delivery

“…This value could be further optimized by tuning the different variables of the electrodeposition process. Longer process times or higher current densities [ 30 ] introduce voids and imperfections and reduce the reproducibility of the measurements but have the potential to increase loading to hundreds of μ g cm − 2 . The concentration of the electrolytes in the bath can also infl uence the fi lm structure and composition.…”

“…[ 26 ] However, only electrodeposition provides the unique ability to create three-dimensional structures of various size and shape at a low cost, [ 27 , 28 ] and can conformally coat structures using local pH gradients on negatively charged electrodes. While the mechanism of formation has been proved and investigated, [29][30][31] only a few applications actually exploit this technique. To date, biosensor platforms have been developed by co-deposition with nanoparticles [ 32 ] or proteins, [ 33 ] but no full drug delivery devices have been designed.…”