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Materials Science in Additive Manufacturing Materials for 3D-printed electrodes

physiological activities and improving human health [6-8] . specific wavelength of light beams and stacking multiple
In traditional rigid electrodes, hard metal materials with layers to prepare 3D structures . It can prepare high-
[25]
good electrical conductivity are mostly used as conductors. precision flexible electrodes with printing accuracy down to
However, the shortcomings of these electrodes, such as the micron level [26,27] . Direct-ink-writing (DIW) can utilize
poor adherence to the human body and propensity to mechanical or pneumatic pressure to extrude and shape
cause skin and tissue contusion, make long-term stable highly viscous or solid–liquid mixed ink materials, which
human monitoring a challenging endeavor [9-11] . Thus, it is is suitable for the preparation of large flexible electrodes
of utmost importance to develop flexible electrodes with in vitro [28-31] . Compared to DIW printing or digital light
stable electrical conductivity, excellent tissue adhesion, processing (DLP)-based 3D printing, fused deposition
and good biocompatibility, which also possess the ability modeling (FDM) printing requires lower material fluidity
to prevent mechanical damage to tissues. These flexible and eliminates the need for post-processing, such as
electrodes can be utilized in various medical applications, drying or freeze-drying [32-34] . It simplifies the printing
such as brain-computer interface, signal monitoring, process and maintains the mechanical properties of
[12]
and tissue regeneration and repair [13-15] . Nevertheless, the the material, allowing more materials to be used in the
preparation of flexible electrodes with properties such as manufacture of wearable devices and bionic electronic
high sensitivity, high adhesion, small size, high specific skin products [35,36] . Electrospinning can obtain nanoscale
capacity, long cycle life, and excellent human compatibility fibers by applying a voltage to the needle and collector
is still a great challenge [16,17] . and using static field forces to pull out the polymer-
Compared with traditional manufacturing technologies, based liquid, which is advantageous for the preparation
3D printing is an additive manufacturing technology of multichannel, stretchable, and flexible electrodes [37-39] .
that transforms digital models into physical models Inkjet printing (IJP) creates patterned thin films or stacked
with complex shapes [18-21] . With the advantages of high 3D structures on media by spraying nano-sized solutions,
resolution, fast printing speed, and low cost, 3D printing which can be used to prepare miniature, multichannel
provides a new strategy for preparing personalized, high flexible electrodes, or arrays for sensitive acquisition of
[40-42]
precision, and multichannel flexible electrodes [22-24] . electrical signals . The rapid development of different
Several studies have applied 3D printing technology to 3D printing technologies in recent years has provided
prepare flexible electrodes for use in medical applications additional strategies for preparing flexible electrodes.
(Figure 1). Light-curing 3D printing is a printing However, the lack of advanced materials limit the medical
[43]
technology that scans photosensitive materials with a applications of 3D-printed flexible electrodes . Materials
used to prepare flexible medical electrodes need to be
conductive, biocompatible, ductile, and stable [44,45] . To
advance the development of conductive materials in 3D
printing, various strategies for the preparation of flexible
electrodes have emerged, as shown in Figure 2.
This article provides an overview of recent research
advances in materials used for 3D-printed flexible
electrodes, including metallic materials, carbon-based
materials, conductive polymers, and other materials
(Figure 1). Through intensive efforts in improving 3D
printing technology and material properties, as well as
combining multiple materials, a range of flexible medical
electrodes with good performance has been created,
displaying great application prospects in medicine, such
as physiological signal acquisition, biochips, soft robotics,
tissue regeneration, and biosensors.

2. Metallic materials
Metallic materials are known for their good ductility,
thermal conductivity, and electrical conductivity.
Electrodes made with metallic materials, such as gold,
Figure 1. Materials and 3D printing technologies for flexible medical
electrodes. (The middle image was generated by an AI tool, while other silver, and platinum, have a wide range of applications
images were created using BioRender.com.) for neural recordings, typically seen in animal studies

Volume 2 Issue 4 (2023) 2 https://doi.org/10.36922/msam.2084