Flexible and stretchable electronic systems have generated significant interest as a new class of bioelectronics, providing models to study biological species and electronics interactions. A wide range of applications is available to use these devices, including epidermal sensors, smart sutures, artificial electronic muscles, implantable medical devices, and artificial skin. Electronic platforms’ proper functioning is directly linked to reliable electrical performance under several loading conditions and deformations within all these applications. Bioprinters can enable fast and straightforward fabrication of these electronic systems, providing a platform that is ready to use as soon as it is printed, requiring no post-processing. 1 2 3D printing electronic systems is an attractive alternative to conventional technologies as it enables the fabrication of flexible devices at a low cost. 3
To illustrate, in bioelectronic devices that interface with tissues, such as an electrocardiograph (ECG), properties such as flexibility and biocompatibility are desirable to maintain personal and conformal contact as the device can adapt to the movements of tissue and body. Flexibility allows neat electrode contact to skin and tissue, and biocompatibility prevents electrodes from reacting with biological fluids and living tissues. 1 4 With the emergence of novel printing methods and soft materials, wearable electronics systems are transitioning from rigid modalities based on metals and plastics to soft form factors, offering more comfort and seamless integration with the skin. 5 6
Kwon et al. developed a fully printed hybrid electronic system. By merging additive manufacturing with machine learning they printed flexible electronics that are versatile, multi-class human-machine interfaces. The leading technology of this approach uses functionalized conductive graphene with improved biocompatibility, anti-oxidation, and solderability, which allows for a flexible wireless circuit and a high-fidelity recording of muscle activity. 5
A 3D-printed ear prosthesis fabricated by polyvinylidene fluoride (PVDF) printing process was developed to serve as an alternative to a hearing aid. The device’s performance is based on the nervous system’s electrical stimulation to extend the area of sensory perception. Initially, the ear prosthesis is designed in 3D computer graphics software and then printed using a 3D printing process of PVDF. Due to changes of the permittivity of PVDF in response to temperature and pressure variations, the material has the ability to generate an electrical response that is proportional to these stimuli. 7 This is an attractive technology that allows the patient to recover the functionality and appearance of a natural ear.
Figure 2: a -Human ear created with a 3D CAD program. b- Ear prosthesis printed from PVDF. 8
REFERENCES
1. Shin, S. R. et al. A Bioactive Carbon Nanotube-Based Ink for Printing 2D and 3D Flexible Electronics. Adv. Mater. 28, 3280–3289 (2016).
2. Agarwala, S., Lee, J. M., Yeong, W. Y., Layani, M. & Magdassi, S. 3D Printed Bioelectronic Platform with Embedded Electronics. MRS Advances vol. 3 3011–3017 (2018).
3. Ahn, B. Y. et al. Omnidirectional Printing of Flexible, Stretchable, and Spanning Silver Microelectrodes. Science vol. 323 1590–1593 (2009).
4. Khan, Y. et al. Bioelectronic Interfaces: Inkjet-Printed Flexible Gold Electrode Arrays for Bioelectronic Interfaces (Adv. Funct. Mater. 7/2016). Advanced Functional Materials vol. 26 981–981 (2016).
5. Kwon, Y.-T. et al. All-printed nanomembrane wireless bioelectronics using a biocompatible solderable graphene for multimodal human-machine interfaces. Nat. Commun. 11, 3450 (2020).
6. Khan, Y. et al. Flexible Hybrid Electronics: Direct Interfacing of Soft and Hard Electronics for Wearable Health Monitoring. Advanced Functional Materials vol. 26 8764–8775 (2016).
7. Suaste-Gómez, E., Rodríguez-Roldán, G., Reyes-Cruz, H. & Terán-Jiménez, O. Developing an Ear Prosthesis Fabricated in Polyvinylidene Fluoride by a 3D Printer with Sensory Intrinsic Properties of Pressure and Temperature. Sensors vol. 16 332 (2016).