Electrodeposition of a Biopolymeric Hydrogel: Potential for One-Step Protein Electroaddressing

Abstract

The electrodeposition of hydrogels provides a programmable means to assemble soft matter for various technological applications. We report an anodic method to deposit hydrogel films of the aminopolysaccharide chitosan. Evidence suggests the deposition mechanism involves the electrolysis of chloride to generate reactive chlorine species (e.g., HOCl) that partially oxidize chitosan to generate aldehydes that can couple covalently with amines (presumably through Schiff base linkages). Chitosan's anodic deposition is controllable spatially and temporally. Consistent with a covalent cross-linking mechanism, the deposited chitosan undergoes repeated swelling/deswelling in response to pH changes. Consistent with a covalent conjugation mechanism, proteins could be codeposited and retained within the chitosan film even after detergent washing. As a proof-of-concept, we electroaddressed glucose oxidase to a side-wall electrode of a microfabricated fluidic channel and demonstrated this enzyme could perform electrochemical biosensing functions. Thus, anodic chitosan deposition provides a reagentless, single-step method to electroaddress a stimuli-responsive and biofunctionalized hydrogel film.

Chitosan to Connect Biology to Electronics: Fabricating the Bio-Device Interface and Communicating Across This Interface

“…Physical and chemical evidence support the anodic deposition mechanism of Figure 11a [131]. For instance, anodically deposited films were observed to swell (but not dissolve) under acidic conditions-consistent with expectations of a covalently-crosslinked hydrogel network.…”

“…Recently, an anodic mechanism was reported to electrodeposit a covalently crosslinked chitosan film [131]. In contrast to cathodic electrodeposition, anodic deposition (i) results from chemical (vs. physical) interactions; (ii) is irreversible; and (iii) relies on chitosan's ability to be partially oxidized [132].…”

“…For our anodic deposition studies, we prepared solutions by dissolving chitosan in acetic acid (and not HCl). We believe the choice of acid is important because acetic acid serves as a buffer to maintain a pH ≈ 5 adjacent to the anode and this is near the optimum pH for the HOCl species [131]. …”

Electrochemical quartz crystal microbalance study of polyelectrolyte film growth under anodic conditions

“…In the case of LbL thin film assembly, the construction of films by alternately adsorbing positively-and negatively-charged polyelectrolytes has been investigated using optical waveguide lightmode spectroscopy (OWLS) or ellipsometry with indium tin oxide (ITO) as the substrate [6,11,12,14,15] van Tassel et al have also reported the continuous adsorption of a polyelectrolyte under an applied anodic potential [7] via a similar adsorption process for both strongly-and weaklycharged polymers [8,16], and hypothesized that the film growth mechanism changes during the process [8], resulting in a different orientation of the polymer chains (secondary structure). The assembly of thin films of chitosan by anodic electrodeposition has also recently been reported [17]. At first glance, such 4 of 27 observations are counterintuitive, as the positively-charged polymers should be electrophoretically attracted to the cathode, rather than the anode.…”

Electrodeposited Gels Prepared from Protein Alloys

“…In an earlier example, electrodeposition paints with protonated ammonium groups were shown to recognize the local pH increase at the cathode. These polymer electrolytes switched from soluble to an insoluble state, and subsequently formed a precipitation layer on the surface [13]. Direct blending of silk with tropoelastin (equal volume at 2 wt%), however, failed to show an electrochemical response (up to an applied electric field strength of ~2 × 10 3 V/m), as the total charges on the two types of proteins cancelled each other out to a significant extent.…”