Page 302 - IJB-9-1

International Journal of Bioprinting 3D printable conductive composite inks for biocompatible electrodes

due to its self-healing behavior . When the electrode peek was recorded in real-time to analyze the drug’s effect
[76]
is exposed to the surrounding circumstances, it suffers on the engineered tissue.
from current leakage, protein fouling, and corrosion,
thus reducing the electrode’s efficiency and lifecycle [22,77] . 6. Future applications
The passivation by encapsulating the electrode prevents Electrical stimulation has been adopted as a promising
direct contact with outer environments, decreasing the technique for controlling cell behavior. It has been mainly
[78]
threat of damage to the electrode and tissue . Electrodes applied to neuronal, cardiac, and muscular tissues that
can be used either for electrically stimulating the tissues show spontaneous electrical activity. Recently, electrical
or sensing the electrical properties of tissues. Mature stimulation has been applied to other tissues, such as skin,
cardiomyocyte shows spontaneous beating behavior and and in bone regeneration, accelerating the healing process
electrical signals related to the calcium ion transient . by elevating cell proliferation and enhancing antimicrobial
[79]
Asulin et al. fabricated a cardiac patch with built-in properties [81,82] . Furthermore, with increasing studies
electronics that can sense signals and stimulate the tissue about the relationship between endocrine cells and the
at the same time . The serpentine electrode was printed innervation of neurons, the response of pancreatic β-cells
[71]
with PDMS ink with 45 wt% graphite filler that has a [83]
conductivity of around 30 S/m. The serpentine structure to electrical stimulation has been explored . Various tissue
was selected to reduce the destruction of the electrode by types, signal transduction pathways, and ion transients
contraction or elongation. The electrode was embedded should be further studied and the electrode integrated cell
in PDMS with the surfactant for the hydrophilic property culture platform can be a major tool for investigating cells’
and the cell-laden omentum-based hydrogel surrounds responses.
the entire structure. Six electrodes were embedded except The versatility of the material and the extrusion-based
for the two ends for the contact and two electrodes printing process potentiates the application for complex
were completely exposed to apply an electric field to circuits for drug delivery induced by electrical fields.
the engineered tissue. After 7 days of culturing cardiac A drug delivery device is composed of complex circuit
cells derived from induced pluripotent stem cells, connecting sensors, electrical sources, and electrodes .
[84]
the extracellular potential signals were verified to be In addition, removing the need to replace, new batteries
similar to those of neonatal ventricular cardiomyocytes. during surgery has prompted the conception of wireless
Furthermore, electrical stimulation of 1 or 2 Hz, 7 V, designs that transport energy through electromagnetic
50 ms-long pulses were applied. The contraction of waves [85,86] . Sun et al., showed that the 3D circuit design can
the engineered tissue synchronized with the electrical be directly printed, demonstrating its ability to fabricate
stimulation proved the ability to control the tissue. intricate circuits . In summary, 3D printing technology
[87]
The electrodes can also be used as strain gauges, as and conductive ink may contribute to the fabrication
the strain affects the distance between the fillers . The of a closed-loop drug delivery device that mimics the
[80]
embedded strain gauge minimizes the reaction with homeostatic regulation of human body , paving the way
[84]
the media and the signal noise. Lind et al. printed an for a new generation of therapeutic devices.
embedded strain gauge with TPU ink dispersed with 25
wt% carbon black fillers (CB: TPU) . The Microgroove Acknowledgments
[72]
PDMS layer was printed above for the biocompatible Not applicable.
environment and alignment of cardiomyocytes. The
polyamide ink dispersed with silver flake fillers (Ag: PA) Funding
was printed afterward for contact between the strain This work was supported by the MSIT (Ministry of
gauge and the wire. As the THF solvent was left inside the
CB: TPU ink, the viscosity was dependent on the solvent Science, ICT), Korea, under the High-Potential Individuals
evaporation and did not show shear-thinning behavior. Global Training Program (No. IITP-2021-0-01517)
Meanwhile, Ag: PA ink has tan δ < 1 at low strain and tan supervised by the IITP (Institute for Information and
δ > 1 at high strain, showing high printability and fidelity Communications Technology Planning and Evaluation),
when stacked. The conductivity of the CB: TPU ink was and the NRF (National Research Foundation of Korea)
84.1 S/m, while the conductivity of the Ag: PA ink was grant funded by the Ministry of Science and ICT (MSIT)
around 1.53∙10 S/m. As cardiomyocyte maturates, the (No. 2021R1A2C2004981).
6
tissue contracts and rolls up the entire platform, leading Conflict of interest
to the relative resistance change in the strain gauge. The
value and the frequency of the relative resistance change The authors declare no known conflicts of interest.

Volume 9 Issue 1 (2023) 294 https://doi.org/10.18063/ijb.v9i1.643