Mechanism of anodic electrodeposition of calcium alginate

Abstract

Stimuli-responsive polysaccharides that can undergo a sol-gel transition in response to localized electrical signals provide a unique opportunity to electroaddress biological components at device interfaces. Most polysaccharide electroaddressing mechanisms use electrochemical reactions to generate pH gradients that can locally neutralize the polysaccharide and induce its reversible sol-gel transition to form a hydrogel film adjacent to the electrode surface. The calcium-responsive polysaccharide alginate is an exception; it may electrodeposit without requiring extreme pH gradients and thus may provide a means to electroaddress pH-sensitive biological components. Here, we use a novel device to characterize the mechanism for the anodic electrodeposition of a calcium alginate hydrogel. This device consists of a transparent fluidic channel with built-in sidewall electrodes that allows Ca-alginate electrodeposition to be directly measured by non-destructive optical and spectroscopic methods. We hypothesize a 3-step mechanism for calcium-alginate electrodeposition: (i) water is electrolyzed to locally generate protons (or hydronium ions); (ii) these protons are consumed by reacting with suspended CaCO 3 particles and this ''buffering'' reaction generates a gradient in soluble Ca 2+ ; and (iii) the locally generated Ca 2+ ions interact with alginate to induce its sol-gel transition. We verified this electrodeposition mechanism using pH-responsive dyes to observe the local pH gradients during gel formation, Ca 2+ indicator dyes to observe the Ca 2+ gradient, and in situ Raman spectroscopy to demonstrate a strong interaction between soluble Ca 2+ and alginate. Importantly, these results demonstrate electrodeposition without the need for a substantial pH excursion from neutrality. Thus, calcium alginate appears especially well-suited for electroaddressing labile biological components for applications in biosensors, biofabrication and BioMEMS.

Yeast-based Biochemical Oxygen Demand Sensors Using Gold-modified Boron-doped Diamond Electrodes

“…The strength of the gel depends on the alginate composition and the cross-linker ions, which is added during the polymerization process. 16 However, since the electrochemical technique was affected by material diffusion to the electrode surface, the thickness of the film becomes an important factor. The influence of the film thickness was investigated using a total number of 2.56 × 10 8 R. mucilaginosa cells, which are immobilized in various film thicknesses.…”

“…Ca 2+ ), alginate turns to gel formation through the crosslink carboxylate groups in the G-block of alginate, which leads to the formation of alginate macromolecular chain crosslinking. [16][17][18] In addition to this unique gel formation, the flexible structure and highly adsorbent of the gel establishes it as a suitable matrix to immobilize yeast, enzyme, and living cells. 16 Therefore, it was expected that no extreme change occurrs on R. mucilaginosa Y-181 when it is being immobilized as well as during storage after immobilization.…”

“…[16][17][18] In addition to this unique gel formation, the flexible structure and highly adsorbent of the gel establishes it as a suitable matrix to immobilize yeast, enzyme, and living cells. 16 Therefore, it was expected that no extreme change occurrs on R. mucilaginosa Y-181 when it is being immobilized as well as during storage after immobilization. 16 The result demonstrated that although the BOD sensor with immobilized R. mucilaginosa shows less sensitivity and less satisfactory LOD, however a better reproducibility of the current responses as well as better resistance from the influence of copper presence were observed.…”

“…Alginate, natural polysaccharide abundant in the cell walls of brown algae, is a linear copolymer composed of pattern blocks of homopolymeric regions of β-(1 → 4)-linked D-mannuronic acid (M) and α-(1 → 4)-linked L-guluronic acid (G). 16 With divalent cations (e.g. Ca 2+ ), alginate turns to gel formation through the crosslink carboxylate groups in the G-block of alginate, which leads to the formation of alginate macromolecular chain crosslinking.…”

Light-Addressable Electrodeposition of Magnetically-Guided Cells Encapsulated in Alginate Hydrogels for Three-Dimensional Cell Patterning

“…Recently, a biocompatible polysaccharide of sodium alginate, which can form a calcium alginate gel in the presence of calcium ions (Ca 2+ ), is widely used to entrap and immobilize prokaryotes and eukaryotic cells in 3D hydrogel structures [3][4][5]. Among these fabrication methods to form alginate hydrogels, electroaddressing is an attractive technique due to its ability to deposit alginate hydrogels [6][7][8][9][10][11][12][13] at specific addresses and in specific shapes with a controllable pattern on the preformed metal thin-film electrode surfaces. Payne et al [8,11] reported the electroaddressing of calcium alginate hydrogels, with the ability to entrap viable cell populations within the electrodeposited films.…”