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Agarwala
electrically conductive scaffold for muscle and 3 Methods of Fabrication
nerve tissues . Sasaki et al. reported the fabrication 3.1 Traditional approaches
[44]
of the hydrogel-based devices with high electrically
conductivity using a combination of chemical Several approaches have been taken to synthesize
polymerization and electropolymerization of conducting hydrogels depending on the nature
PEDOT and polyurethane (PU) . Mechanically of the additive and hydrogel matrix. The most
[45]
strong conducting hydrogels composed of PAAM common method for aqueous compatible
and PEDOT-PSS was synthesized through the conducting materials is to simply mix with
construction of a special double-network (sDN) the hydrogel components aided by ultrasonic
structure . PAA has been polymerized with both energy or heating. However, there are five other
[46]
PPy and PEDOT resulting in pH responsive and gel main approaches that have been identified in
with high mechanical strength, respectively [47,48] . the literature to synthesize conducting hydrogel
Experimenting with a different class of materials, composites with uniform distribution, as shown
in Figure 2. These includes hydrogel monomers
copper phthalocyanine-3,4′,4″,4‴-tetrasulfonic with cross-linkers and nanoparticles gelated
acid tetrasodium salt (CuPcTs) was added to together ; physically embedding nanoparticles
[50]
PPy through a supramolecular self-assembly into hydrogel matrix after gelation ; reactive
[51]
approach . The steric and electrostatic nanoparticle formation aided by the hydrogel
[49]
interactions between CuPcTs and PPy favored the network where nanoparticle precursors are loaded
self-assembly of PPy chains, which promotes the in the gel ; cross-linking using nanoparticles to
[52]
1D growth of PPy and resulted in the formation of form hydrogels ; and hydrogel formation using
[53]
interconnected nanofibers. nanoparticles, polymers, and other molecules .
[54]
A

B

C

D

E

Figure 2. Schematic diagram depicting various approaches to synthesize conducting hydrogel: (A)
hydrogel monomers with cross-linkers and nanoparticles gelated together; (B) physically embedding
nanoparticles into hydrogel matrix after gelation; (C) reactive nanoparticle formation aided by the hydrogel
network where nanoparticle precursors are loaded in the gel; (D) cross-linking using nanoparticles to
form hydrogel; and (E) hydrogel formation using nanoparticles, polymers, and other molecules.

International Journal of Bioprinting (2020)–Volume 6, Issue 2 5