Printed Wearable Electronics for Healthcare

Additive manufacturing (AM) routes, in particular direct writing (DW) non-contact techniques from liquid precursors (inks) are currently gaining a great deal of interest within the research community and industrial sector, due to the benefits provided in terms of the allowed design freedom, architectural flexibility and industrial scalability. The latter is sustained by relatively small investments and fabrication costs, while guaranteeing the rapid prototyping of desired artifacts. Based on current trends, these technologies have a strong impact in the context of flexible/bendable and conformable electronic devices. They typically require simple manufacturing steps combined with a wide range of printable materials, low cost, reduced waste and fine features. Among DW non-contact techniques, Ink-jet Printing (IJP) and Aerosol Jet Printing (AJP) have been massively employed during the last decade to implement several electronic devices, including biosensors. AJP technology exploits the ink atomization through two processes, i.e. the ultrasonic and the pneumatic atomization, allowing the material deposition over flat and curved substrates [1]. The ability to atomize liquid precursors by two different processes largely increases the range of printable materials (viscosity range between 1 and 1000 cPs), thus exceeding one of the major limitations of IJP techniques. This contribution shows the use of AJP technique to develop applications in bioelectronics. The first example shows a comprehensive characterization of PEDOT:PSS deposition based on a systematic analysis of the overspray effect, which is aimed at preliminary spotting the proper deposition parameters for minimizing defects and short circuits between near patterns. It is then shown the voltage amplifying capability for small amplitude time-varying signals of a fully printed planar organic transistors, consisting of printed Silver electrodes (source, drain and gate), a PEDOT:PSS active layer deposited using the best deposition parameters from the previous analysis, and a passivation layer for interconnections made of NEA 121, all layers being printed on a flexible Kapton substrate [2]. The second example will report the development of an electrochemical biosensor for the detection in biological fluids of the interleukin 6 (IL-6), a cytokine associated to potential inflammation states. IL-6 detection is based on the antigen-antibody selective binding, including the EDC-NHS chemistry to drive the formation of a self-assembled monolayer (SAM). An ink based on Thermally Exfoliated Graphene Oxide (TEGO) is developed and used to cover the working electrode of a Screen Printed Electrode (SPE). TEGO directly provides a defective surface (i.e. presence of oxygenated species, such as carboxyl and carbonyl groups) available for antibody anchoring, hence avoiding time and cost consuming post deposition processes [3]. Electrochemical Impedance Spectroscopy (EIS) was used to access the detection of IL-6 in real saliva samples, while a measurement protocol involving single SPEs for each IL-6 concentration and providing reproducible measurements, has been adopted to assess a calibration curve showing a Limit of Detection (LoD) falling with in IL-6 physiological range (units of pg/ml). References [1] E. Secor, “Principles of aerosol jet printing,” Flex. Print. Electron 3, 035002 (2018). [2] G. Tarabella, “Aerosol Jet Printing of PEDOT:PSS for large area flexible electronics,” Flex. Print. Electron 5, 014005 (2020). [3] K. Parate, “Aerosol-Jet-Printed Graphene Immunosensor For Label-Free Cytokine Monitoring in Serum” ACS Appl. Mater. Interfaces 12, 7, 8592-8603 (2020).