Electro-assisted printing of soft hydrogels via controlled electrochemical reactions

Aruã Clayton Da Silva,Ivan Rusev Minev,Junzhi Wang

doi:10.1038/s41467-022-29037-6

Aruã Clayton Da Silva, Ivan Rusev Minev + Show 1 more

Open Access

https://doi.org/10.1038/s41467-022-29037-6

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Abstract

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.

Highlights

Hydrogels underpin many applications in tissue engineering, cell encapsulation, drug delivery and bioelectronics
While two electrodes are sufficient to trigger electrochemical reactions, selecting which reactions occur and controlling their rate is challenging because electrode potentials are uncertain
We further demonstrate polymerisation of a hybrid system where the conductive polymer PEDOT is polymerised alongside alginate

Summary

Introduction

Hydrogels underpin many applications in tissue engineering, cell encapsulation, drug delivery and bioelectronics. They can be patterned by casting the pre-gel solution in moulds or for hydrogels that are already formed, direct ink writing (extrusion) or lithography may be employed Despite these promising developments, the integration of well-defined hydrogel systems in devices remains a challenge. The integration of well-defined hydrogel systems in devices remains a challenge This is because hydrogel formation requires precise control over polymerisation reactions that determine the physical and biological properties of the material. While two electrodes are sufficient to trigger electrochemical reactions (e.g., electrolysis), selecting which reactions occur and controlling their rate is challenging because electrode potentials are uncertain When producing biomaterials such as hydrogels, poor control over gelation reactions may have implications on the biodegradation, mechanical, electrical or biochemical properties of the material

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