Electro-assisted printing of soft hydrogels via controlled electrochemical reactions

Despite the widespread use of hydrogels, methods offering improved control over gelation mechanisms and patterning are still sought for. Here, the authors explore potentiostatic control in electrochemical-chemical-chemical reactions on chitosan, alginate and alginate/PEDOT composite systems which allows selection of covalent and ionic gelation mechanisms as well as the growth rate of the hydrogel. Hydrogels underpin many applications in tissue engineering, cell encapsulation, drug delivery and bioelectronics. Methods improving control over gelation mechanisms and patterning are still needed. Here we explore a less-known gelation approach relying on sequential electrochemical-chemical-chemical (ECC) reactions. An ionic species and/or molecule in solution is oxidised over a conductive surface at a specific electric potential. The oxidation generates an intermediate species that reacts with a macromolecule, forming a hydrogel at the electrode-electrolyte interface. We introduce potentiostatic control over this process, allowing the selection of gelation reactions and control of hydrogel growth rate. In chitosan and alginate systems, we demonstrate precipitation, covalent and ionic gelation mechanisms. The method can be applied in the polymerisation of hybrid systems consisting of more than one polymer. We demonstrate concomitant deposition of the conductive polymer Poly(3,4-ethylenedioxythiophene) (PEDOT) and alginate. Deposition of the hydrogels occurs in small droplets held between a conductive plate (working electrode, WE), a printing nozzle (counter electrode, CE) and a pseudoreference electrode (reference electrode, RE). We install this setup on a commercial 3D printer to demonstrate patterning of adherent hydrogels on gold and flexible ITO foils. Electro-assisted printing may contribute to the integration of well-defined hydrogels on hybrid electronic-hydrogel devices for bioelectronics applications.

Automated summary

In this study, the authors explore a new approach to control gelation mechanisms and patterns using electrochemical-chemical-chemical reactions. By oxidizing the ionic species and/or molecules in solution at a specific electric potential, an intermediate species is generated and reacts with macromolecules to form hydrogels. This method allows for the selection of gelation reactions and control of hydrogel growth rate, and has been demonstrated for patterning hydrogels on gold and flexible ITO foils using a commercial 3D printer.