Electro-assisted printing of soft hydrogels via controlled electrochemical reactions

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.

Integrated silicon microfluidic chip for picoliter-scale analyte segmentation and microscale printing for mass spectrometry imaging

“…EHD-assisted printing 22 enables fine tuning of the droplet detachment since it relies on additional electrostatic force, 33 σ E = 2π r 2 ε 0 E c 2 (where r is the droplet radius, ε 0 is the air permittivity, and E c is the electric field strength), that changes the force balance at the nozzle tip ( Fig. 3A ).…”

“…19 To transfer droplets onto a MALDI substrate while preserving their chronological order, various deposition techniques have been reported including contact printing, 20 as well as contactless approaches including electrospray deposition 21 and electrohydrodynamic (EHD) assisted printing. 22 Contact printing enables deposition 13 or formation 23 of picoliter to femtoliter droplets by passing a waterfront through an array of prepatterned hydrophilic sites. Among contactless methods, electrospray ionization has been used to introduce picoliter-scale segmented analytes for MS analysis; 10,19 however, when used for deposition on a MALDI substrate, analytes are aerosolized and ionized in the electrosprayed jet 24 which significantly increases the spread of printed patterns and lowers MS sensitivity.…”

Advances in the Translation of Electrochemical Hydrogel‐Based Sensors

“…[ 18 ] Novel techniques can use potentiostatic methods of electrofabrication or electroassisted techniques of controllable electrochemical reactions. [ 19 ] These methods provide exceptional spatiotemporal control directly on the surface of the electrode, thereby allowing for improved processability and high adhesion. To ensure that the hydrogel mimics the physical, biological, and mechanical properties of biological tissue while retaining the electrochemical properties necessary for sensor sensitivity, a thorough material characterization should be investigated in a standardized manner.…”

Multifunctional Antifreezing Organogel Polyelectrolyte for a Flexible Supercapacitor

“…With the continuous progress and development of wearable electronic technology, flexible electronic products with the characteristics of portability, wearability, collapsibility, miniature, and lightweight have been paid more and more attention. − As we know, in lots of energy storing devices, flexible solid-state supercapacitors have become one of the most hopeful flexible energy storage devices due to their large specific capacitance, rapid charging and discharging properties, wonderful stability, and excellent mechanical properties. − The rational design of electrode or electrolyte materials − and the optimization of device configuration have become the direction of development to build high-performance flexible supercapacitors (FSCs). Conductive gels with intrinsic flexibility, significant mechanical recycling, and remarkable ionic conductivity can not only be used as ideal materials for FSC electrolytes − but also have considerable applications in tissue engineering, drug delivery, water treatment, bioengineering, and many other fields. Last decade, various types of gel electrolytes have emerged as prospective candidates for FSCs, such as hydrogels, organic gels, ionic liquid gels, redox-active gels, and so forth, which have been diffusely applied in supercapacitors.…”

“…7−10 The rational design of electrode or electrolyte materials 11−13 and the optimization of device configuration 14 have become the direction of development to build high-performance flexible supercapacitors (FSCs). Conductive gels with intrinsic flexibility, significant mechanical recycling, and remarkable ionic conductivity can not only be used as ideal materials for FSC electrolytes 15−17 but also have considerable applications in tissue engineering, 18 drug delivery, 19 water treatment, 20 bioengineering, 21 and many other fields. Last decade, various types of gel electrolytes have emerged as prospective candidates for FSCs, such as hydrogels, 22 organic gels, 23 ionic liquid gels, 24 redox-active gels, 25 and so forth, which have been diffusely applied in supercapacitors.…”