Page 11 - IJB-10-2

International Journal of Bioprinting PEDOT/PSS-based sensors

and ion transport capabilities along with desirable The second strategy entails the introduction of
biological features such as biocompatibility, adhesion, and ionic species into the hydrogel network to synthesize
antibacterial properties. These remarkable attributes have conductive hydrogels, either during the gel synthesis
7
bestowed conductive hydrogels a myriad of applications, process or through post-synthesis doping methods.
encompassing drug delivery systems, tissue engineering, The presence of conductive ions within the hydrogel
electronic skins, biosensors, supercapacitors, and flexible establishes an interconnected pathway for the movement
wearable electronic devices. In addition, conductive of charge carriers, facilitating their migration throughout
8
hydrogels are poised to play a pivotal role in the realm the material. The conductive ions, acting as mobile
of flexible and wearable electronic devices due to their charge carriers, enable the hydrogel to conduct electricity
inherent conductivity, enabling seamless integration with effectively and pave the way for applications in various
wearable technologies. As a rising star in materials science, fields, including flexible electronics, bioelectronics, and
9
conductive hydrogels hold immense promise in reshaping smart sensors, among others.
the future of sensor industries and bridging the gap between The third strategy involves introducing conductive
electronic systems and biological entities. Their ongoing polymer into a hydrogel matrix to obtain polymer
development promises to unlock innovative and cutting- electronic conductive hydrogel. Conductive polymers
edge applications, ushering in a new era of possibilities. belong to a class of high polymers capable of generating
Over the past few decades, significant progress a positive response to electric current signals and achieve
has been made in the development of various types of electrical conductivity through their own conjugated
conductive hydrogels. These can generally be classified structures or ionizable ions along the molecular chains.
into three main categories, according to the different types The recognition of this field’s significance is evident from
of conductive media integrated into the hydrogel matrix. the 2000 Nobel Prize in Chemistry awarded in celebration
The first category involves incorporating conductive of the birth and evolution of conductive polyacetylene.
particles such as metal nanoparticles and carbon-based By linking the structural units within polymers, these
nanomaterials into the hydrogel to form electronically materials can harness the π-π conjugated structure
conductive hydrogels. In these hydrogels, conductivity present within large molecular chains or utilize ionizable
ions along the chains to facilitate the free movement of
arises from the directed movement of free electrons within charge carriers. Consequently, they acquire electrical
these embedded conductive particles. This results in the conductivity. In this strategy, the conductive properties of
formation of a percolating particle network, effectively the polymer are retained within the hydrogel, rendering
enhancing both the electrical conductivity and mechanical it an efficient solid-state conductor for electronic charge
properties of the hydrogel. For example, the conductive transport. Since the discovery of conductive polyacetylene,
10
hydrogel synthesized by oxidized tannic acid-modified numerous other conductive polymer materials have
AuNPs and chitosan hydrogel matrix with a dynamic Schiff been developed, including polyaniline, polypyrrole, and
base reaction shows electrical conductivity ranging from poly(3,4-ethylenedioxythiophene) (PEDOT). However,
1 to 1.4 mS/cm. It also effectively alleviates the irregular a noteworthy challenge arises with many conductive
discharge of nerve cells in the intracerebral projection polymer materials. They tend to be challenging to
area, leading to improved motor function recovery and dissolve, or in some cases, entirely insoluble in water due
reduced histological neurodegeneration in rats with to their high molecular weights and the hydrophobic
11
Parkinson’s disease. Regardless of these achievements, nature of their organic constituents. As a result, when
certain attributes of this material type limit its applications, attempting to prepare conductive hydrogels using the
such as the high cost of noble metal conductive materials. doping method, the solubility issue can lead to difficulties
Additionally, metals are susceptible to corrosion in in achieving uniform incorporation of the conductive
humid environments, and it thus leads to a degradation components into the hydrogel matrix. This non-uniform
in the electrical performance of the conductive hydrogel distribution within the gel structure significantly
biomaterials. Carbon-based nanomaterials, such as carbon compromises the electrical conductivity of the conductive
nanotubes (CNTs), graphene oxide (GO), and carbon fibers, hydrogel. The typical strategy for achieving water-
14
have emerged as highly promising conductive materials due soluble conductive polymers is to complex them with
to high electrical conductivity, environmental stability, and other hydrophilic molecules. For example, PEDOT, a
good biocompatibility, making them excellent alternatives derivative of polythiophene, is inherently insoluble in
12
to metallic nanoparticles. However, the low dispersibility water due to its hydrophobic nature. However, PEDOT
13
in solution and high cost of CNTs and GO also limit their can be doped with hydrophilic poly(styrene sulfonate)
practical applications in large-scale production. (PSS) to form PEDOT:PSS electrostatic complex. This
15
Volume 10 Issue 2 (2024) 3 doi: 10.36922/ijb.1725