Mechanistic Analysis and Control of Electro-Fabrication with Soft Matter: Polysaccharide Self-Assembly with Electrochemically Produced Metal Ions

Electro-fabrication is an emerging additive manufacturing approach that includes a variety of mechanisms and crosslinking chemistries to induce the self-assembly- of soft matter. Within electro-fabrication techniques, anodic electro-fabrication is of great interest, because it can use the electrode as a sacrificial source of metal ions for the controlled formation of chelated hydrogels. However, it remains challenging to understand how the various solution conditions (e.g., buffer capacity, ligands) and imposed voltages must be controlled to achieve the chelation and sol-gel transition. Herein, a comprehensive thermodynamics-based framework is built to guide the selection of conditions for the self -assembly of polysaccharide hydrogels by crosslinking with transition metal ions generated via corrosion. This methodology is demonstrated through real-time spectro-electrochemical monitoring and employed for the electro-fabrication of chitosan hydrogels chelated with Au3+, Ag+, Cu2+, and Pd2+, and alginate hydrogels chelated with Cu2+. The presented guidelines are intended to extend the capabilities of the controlled fabrication of assemblies crosslinked with metal ions, opening new horizons for unprecedented materials design with precisely tailored structures and functions. Pourbaix diagrams are employed as a framework to attain control on the electro-fabrication of polysaccharide hydrogels chelated with metal-ions. These thermodynamic phase diagrams describe the interplay between the metal source, polysaccharide, electrolyte, imposed voltages, pH, and ligand chemistry. This approach offers a practical solution for the unambiguous determination of the experimental conditions required for the electro-fabrication of chelated hydrogels.image