urea as cross-linker by in situ free-radical polymerization [15]. The hydrogel showed

excellent improvement in electrical conductivity up to 0.572 S cm⁻¹ that can be con­

sidered a promising material for nanoelectronic devices.

Platinum nanoparticles (PtNPs)–doped conductive PANI hydrogel enabled the

transduction of signals for electrochemical sensing of glucose [16]. An electronically

conductive channel allowed efficient charge transfer for sensitive determination of

analyte with fast response time. Graphene- and CNT-based materials were engaged as

reinforcing filler during the preparation of hydrogel composites for enhancing the

electrical conductivity and mechanical properties. A conducting biocompatible chitosan-

lactic acid hydrogel composite using graphene as filler material improved the mechan­

ical strength and conductivity of hydrogels [17]. Reduced graphene nanosheets

containing biocompatible UV cross-linked methacrylated chitosan (rGO /ChiMA) hy­

drogels produced conducting 3D-printable scaffolds with good cell adhesion and bio­

degradable and cytocompatible properties, which can be beneficial. A polyacrylamide

(PAM)–based conductive hydrogel with partially reduced graphene oxide/fully re­

duced graphene oxide (pGO/rGO) using polydopamine (PDA) solution was prepared

by controlling the reaction time. The pGO introduced PDA–pGO–PAM hydrogel ex­

hibited the overall highest extension ratio, good toughness (4280 J/m²), and conductivity

(0.08 S/cm) with respect to the unreduced GO and rGO incorporated. The unreduced GO

filler forms strong non-covalent interactions with PDA and PAM and also exhibited

extremely low conductivity. On the other hand, rGO incorporated PDA–rGO–PAM

exhibits good conductivity (0.1 S/cm) but low extension ratio (λ = 20). Thus the con­

ductive PDA–pGO– PAM hydrogels with high stretchability, self-healablility, and self-

adhesiveness potential pave a way as a cell stimulator and implantable bioelectronics for

human body (Figure 18.2) [18]. While rGO-containing polyacrylamide, r(GO/PAAm)

hydrogel was developed by using mild chemical reduction of GO/PAAm hydrogel in

aqueous L-ascorbic acid solution. The r(GO/PAAm) hydrogel exhibited high relative

stiffness with a Young’s modulus of about 50 kPa. The conductive rGO within the hy­

drogel network significantly enhanced the electrical and mechanical properties of

the hydrogel. The electrical stimulation of C2C12 myoblasts with r(GO/PAAm) hy­

drogels for seven days greatly enhanced the proliferation and differentiation of myo­

blasts compared to unreduced hydrogels (GO/PAAm) [19]. As a result, soft and

conductive r(GO/PAAm) hydrogels will be useful material for skeletal muscle tissue

engineering scaffolds. PEDOT-CNT encapsulated fibrin hydrogel-coated electrodes

were designed to record somatosensory induced potentials into a rat cortex through the

deflection of multi-whisker [20]. The nanocoating significantly enhanced the electrical

conductivity of microelectrode with two orders of magnitude and proved significant for

neural recordings. Further, poly(2-hydroxyethyl methacrylate) (pHEMA)-encapsulated

PEDOT-PSS-CNT microspheres for neural stimulation and high-quality signal recording

in the rat cortex were used [21]. Fractal carbon nanotube (CNT) network tailored gelatin

methacrylate (GelMA) hydrogels were found apt for seeding neonatal rat cardiomyo­

cytes onto the conductive CNTs-GelMA hydrogels as functional cardiac patches.

CNT–GelMA hydrogels greatly enhanced the electrical signal propagation and syn­

chronous cellular excitability of cardiomyocytes cultured on it. The incorporation of

small amounts of CNTs into gelatin-chitosan-based hydrogel supports cardiomyocyte

function and helps to attain the electrical conductivity of beating rate of the hearts [22].

Tissue-engineered scaffolds with the combined fascinating properties of CNTs improved

the cardiovascular defect repairs.

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Bioelectronics