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International Journal of Bioprinting 3D-printed bioelectronic devices

Figure 4. 3D-printed bionic devices. (A) 3D-printed electronic skin with an integrated sensor for accurate stimulus identification of hair growth.
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Reproduced with permission from American Chemical Society . Copyright © 2022 American Chemical Society. (B) 3D-printed flexible photodetector
fabricated on a curved surface. Reproduced with permission from Wiley. Copyright © 2018 Wiley.
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applications such as contact lenses or bionic eyes. Arrays to ensure adaptation to curved tissue surfaces. An
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of quantum-dot-based light-emitting diodes and organic inkjet-printed stretchable conductor was developed
photodetectors have been fabricated through layer-by- using a PEDOT:PSS/ PEO polymer blend to achieve
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layer deposition on nonflat substrates, achieved through high elasticity. This device has shown potential as
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the direct deposition of inks on curved surfaces via DIW a wearable sensor patch, particularly for recording
(Figure 4B). photoplethysmography (PPG) and electrocardiography
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Furthermore, 3D printing technology allows the (ECG). In another study, a highly stretchable conductive
direct interweaving of biological materials with electronic polymer composed of PEDOT:PSS nanofibers and PVA
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components in multiple dimensions. This integration was 3D-printed via DIW to fabricate a strain sensor.
not only mimics the functions and external appearance This strain sensor was integrated with electronic skin
but also replicates the mechanical properties of specific to identify hand gestures and has been applied to a soft
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organs. For example, a 3D cyborg ear has been created gripper for object manipulation (Figure 5A).
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by directly integrating cells and hydrogels with electronic Not only can the materials be modified but the
components. A chondrocyte-seeded alginate hydrogel structure of the devices can also be designed to enhance
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was 3D-printed via extrusion-based printer to recreate their functionality. For example, auxetic structures with a
the complex anatomical geometry of the human ear, and negative Poisson’s ratio have been used to fabricate flexible
a silver nanoparticle-infused coil antenna was printed strain sensors to increase the sensing performance.
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to receive signals with frequencies beyond the normal A skin-inspired gradient porous-structure sensor was
audible range. developed to achieve high sensitivity and stability. In
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4.3. Health monitoring devices both studies, 3D printing technique offered a high degree
Extensive research efforts are underway in the field of of design flexibility and fabrication efficiency.
wearable electronic devices, with a focus on sensing, Implantable monitoring devices have introduced new
diagnosing, and predicting health conditions through opportunities for directly recording biological signals.
advanced human-machine interfaces. Through the The multi-material and high-resolution DIW capability
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precise fabrication of intricate structures and incorporation enabled the fabrication of flexible and highly conductive
of flexible electronic materials, 3D printing has enhanced soft neural probes without the need for post-assembly and
the sensitivity and specificity of biosensors. Various multi-step procedures (Figure 5B). The 3D-printed soft
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3D-printed biosensors such as wearable ultraviolet neural probe was implanted in the dorsal hippocampus of
sensors, strain-insensitive temperature sensors, and the mice to monitor neural activity under freely moving
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conformal strain and humidity sensors have shown high conditions. Recently, an implantable vascular electronic
responsivity, good stability, and robust performance even system with aerosol jet-printed soft pressure sensors and
after repeated bending cycles. a multi-material inductive stent was developed for wireless
When designing wearable applications, mechanical monitoring of hemodynamics (Figure 5C). In this study,
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flexibility and stretchability are critical considerations 3D printing allowed for the rapid fabrication of pressure
Volume 10 Issue 6 (2024) 103 doi: 10.36922/ijb.4139