Printed (bio-)sensors for medical diagnostics are the single-use disposable key components for test strips, wearables for the monitoring of biomolecules and electrodes for electrocardiography- (ECG) and electroencephalography- (EEG) measurements. The widespread and increasing availability of such devices results in a corresponding increase in the volume of waste, much of it non-recyclable, especially when used in homecare settings. Therefore, it is of utmost importance to develop environmentally sustainable solutions in alignment with the requirements of the In-Vitro Diagnostics and Medical Device Regulations (IVDR and MDR). As an example, we present here the development of additive manufacturing to fabricate microneedle electrodes in an environmentally sustainable and economically viable fashion based on renewable materials.
Metallized microneedle electrodes have been demonstrated as valid alternative to well-established wet electrodes for ECG and EEG measurements. The advantage of microneedles primarily lies in their drastically reduced skin-electrode impedance. By eliminating the need for skin preparation and/or the application of electrolytic gels, microneedle-based dry electrodes result in superior user comfort as well as signal quality and long-term stability. This is particularly relevant for specialty ECG and EEG applications such as long-term monitoring. Our approach is the implementation of the printing of materials based on lignin via projection-microstereolithography (PµSL). Lignin is the second-most abundant natural polymer and accumulating as byproduct of cellulose production. The goal is to achieve sub-100 µm feature sizes, biocompatibility, and spatially controlled electrical conductivity. As well, a high-resolution PµSL system is developed and used as manufacturing platform. The system is designed to permit hybrid printing of two different materials (conductive and insulating) and incorporates a cleaning process of 3D-printed structures before switching from one material to the next one. This enables the direct fabrication and usage of the printed microneedles for ECG- and EEG measurements without requiring further post-processing (such as metal evaporation), which usually implies a high energy consumption and the use of metals with high environmental impact.

Giorgio C. MUTINATI, PhD, after his degree in physics, specialized in micro- and nanotechnology and solid-state electronics. After seven years at the R&D departments of semiconductor industries, he joined AIT Austrian Institute of Technology in 2010. His research activities as senior research engineer and project manager focus on printing technologies for the realization of electrochemical biosensors.