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International Journal of Bioprinting 3D-printed bioelectronic devices

anatomically accurate pre-surgical models, implantable 3D printing, such as design flexibility, cost-effectiveness,
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devices, biosensors, 7–10 and multifunctional tissue and rapid prototyping, and personalized fabrication. Finally,
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organ models. 11–13 we address the current challenges of 3D-printed
bioelectronics, including device structures and materials,
The growing interest in personalized health monitoring
and feedback therapy underscores the need to integrate suggesting future directions for bioelectronic applications.
electronics into biomedical devices. Despite significant 2. 3D printing technologies
advancements in conventional microfabrication, 3D
printing emerges as an innovative technology that offers According to the International Organization for
enhanced design flexibility for fabricating constructs within Standardization, 3D printing techniques can be categorized
a shorter fabrication time at a lower cost. This technology into seven different types. Here, we describe three types
enables electronics to be deposited on the 3D surface of of 3D printing methods (inkjet-based printing, vat
a device or fully 3D-printed with other components of photopolymerization-based printing, and extrusion-based
the device. The direct deposition of electronic materials printing) that provide high precision, biocompatibility,
on devices using inkjet- or extrusion-based 3D printing and minimal post-processing, allowing for bioelectronic
allows complex patterning, even on moving freeform fabrication. Each printing method has its advantages and
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surfaces. Fully 3D-printed electronics enable the real- limitations, as summarized in Table 1.
time interweaving of electronic materials with biological
components. Various 3D printing techniques have been 2.1. Material jetting
used to fabricate bioelectronic devices, demonstrating Material jetting method, which ejects ink droplets
the versatility and potential of 3D printing in advancing from nozzles onto a substrate, is characterized by high
bioelectronic devices. fabrication speed, low cost, and high printing resolution.
Its low material usage makes it suitable for fabricating
The design and materials of bioelectronic devices need large objects. 22,23 There are two conventional methods for
to be carefully considered to establish a stable interface generating energy at the nozzles for ink ejection: thermal
between the device and the body. Considering the 3D and piezoelectric inkjet methods (Figure 1A). Thermal
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structure and motion of the human body, many types of inkjet printing applies thermal energy to generate air
bioinspired structures have been introduced. 15–17 These bubbles within the print head, creating a pressure pulse
structures have provided enhanced device stability and that produces and pushes ink droplets. 25,26 Due to its
functionality for specific applications. Moreover, the fast printing speed, low cost, and wide availability, this
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development of electrically conductive materials that method has been used to fabricate various electronic
exhibit printability and biocompatibility has improved the devices, such as inorganic quantum-dot light-emitting
functionality and biointegration capabilities of devices. 18,19 diodes (QD-LEDs), 3D structure of conductive
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Mechanical flexibility and robustness are also critical for hydrogel, 29 neuromorphic transistors, 30 field-effect
ensuring device stability and reliability. 20 transistors, and fully printed capacitors. However,
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The convergence of 3D printing technologies, electronic during ink jetting, the thermal and mechanical stresses
materials, and medical imaging techniques has paved the generated at the nozzle can cause damage to materials,
way for developing a wide range of bioelectronic devices. inaccurate droplet direction, non-uniform droplet size,
Moreover, advances in signal processing techniques have and nozzle clogging. 33–37 Vaporizable and thermally stable
further enhanced the development of biomedical sensors, materials should be used to avoid printing errors. In a
wearables, and multifunctional biomedical platforms for piezoelectric inkjet printing system, voltage is applied to
real-time monitoring of physiological signals. Recently, the piezoelectric actuator to generate a mechanical pulse
artificial intelligence (AI) has been applied to enhance the that creates ink droplets. 38,39 Using a piezoelectric inkjet
capabilities and functionalities of these devices, offering printer, it is relatively easy to control the size of the ink
improved data analysis, predictive analytics, and adaptive droplets and the jetting direction. Moreover, a broader
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responses for medical applications. 21 range of materials, including thermally sensitive materials,
can be used because the printer does not apply high
This review aims to describe recent progress in the 41
3D printing of bioelectronic devices. First, different temperatures to materials.
types of 3D printing techniques and electronic materials For inkjet printing, ink properties such as viscosity
widely used in the fabrication of bioelectronic devices and surface tension must be considered to generate ink
are introduced. We then explore recent advancements droplets. Inks with low viscosity (under 20 mPa·s) are
in 3D-printed bioelectronic devices across various capable of creating droplets without excessive force. For
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biomedical applications, highlighting the advantages of example, materials with low viscosity, such as AgNO ,
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Volume 10 Issue 6 (2024) 96 doi: 10.36922/ijb.4139