Additive and digital manufacturing of transient sensors and bioelectronics

Transient electronics have emerged as a promising class of devices, capable of breaking down without harmful side effects to their environment. They have tremendous potential as bioresorbable electronics for temporary applications in the human body, and as disposable or biodegradable eco-friendly devices. However, transient materials are challenging to pattern, due to their sensitivity to heat, humidity and solvents. Additive manufacturing techniques can help solve this challenge, and allow for large-area fabrication of electronics on sensitive substrates with a reduced environmental footprint. Moreover, their adaptability enables the fast prototyping and customization of electronic devices. In this thesis, several advances in printed transient electronics are presented, leading to devices integrating sensing functions for biomechanical, environmental and biochemical monitoring.Firstly, a novel two-step sintering process for screen-printed zinc is introduced. Combining electrochemical and photonic methods results in unprecedented conductivity (5.6·10^6 S/m). The process is compatible with bioresorbable substrates such as polylactic acid (PLA) and polyvinyl alcohol (PVA). The degradation of zinc on PLA is studied, demonstrating exceptional electrical stability in air. Fully bioresorbable implantable pressure capacitive sensors are fabricated, using (poly(octamethylene maleate (anhydride) citrate); POMaC) as a soft dielectric. The integration of these sensors into a chipless wireless configuration as well as a power receiver is also demonstrated.Next, we fabricate bioresorbable and ecoresorbable temperature sensors enabled by the zinc hybrid sintering process, respectively on PLA and paper. The influence of photonic sintering parameters on the temperature coefficient of resistance (TCR) is carefully studied to enhance the stability and linearity of sensor responses to temperature changes, leading to a TCR of 0.00316 1/°C. The use of a degradable beeswax encapsulant offers protection against the interference of humidity allowing the sensors to operate reliably from -20°C to 40°C. As a next study, we fabricate organic electrochemical transistors (OECTs) from degradable materials, fully by printing on a PLA substrate. Highly electrically conductive zinc interconnects are integrated with a water-resistant carbon-shellac composite as contacts and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to form the channel of the transistor. The disposable OECTs are evaluated as bio-chemical sensors for ion and glucose detection, exhibiting sensitivity to ion concentration changes in the order of 10 %/dec and a limit of detection of 5 µM for glucose.Lastly, we explore the 3D digital printing of customizable transient bioelectronics using direct ink writing. A meticulous process optimization enables the printing of 3D structures using UV-curable POMaC pre-polymer ink. Flexible conductive patterns made of carbon-shellac ink are embedded in POMaC constructs. We demonstrate fully 3D printed capacitive sensors capable of detecting pressures up to 1500 kPa and strain sensors that operate for axial deformations of up to 20%. Electrode arrays with impedance below 10 kOhm at 1 kHz offer potential applications in transient neuromuscular interfaces. In conclusion, this research advances the printing of transient electronics, opening new avenues for post-surgical monitoring, regeneration applications, and sustainable electronics.