Wearable medical sensors that can monitor biosignals have the potential to transform healthcare - they encourage healthy living by providing individuals feedback on personal vital signs and enable facile implementation of both in-hospital and in-home health monitoring. To date, fabrication of wearable medical sensors heavily relies on conventional semiconductor vacuum-processing, which is expensive and has limited large-area scalability. Taking advantage of the unique manufacturing capabilities of printed electronics, we can now design wearables that are soft, lightweight, and skin-like. These soft and conformable sensors significantly improve the signal-to-noise ratio (SNR) by establishing high-fidelity sensor-skin interfaces.
In this talk, I will discuss different printing techniques for fabricating wearable medical sensors and highlight two sensing modalities: bioelectronic and biophotonic. For bioelectronic sensing, I will focus on flexible inkjet-printed gold electrodes, and their applications in bioimpedance spectroscopy, electrocardiography (ECG), and electromyography (EMG). For biophotonic sensing, I will present our work on printed biophotonic sensors for blood and tissue oximetry that will include an all-organic optoelectronic sensor, which accurately measures pulse rate and oxygenation via transmission-mode pulse oximetry. Since transmission-mode oximetry can only be performed at the extremities of the body and requires a pulsatile arterial blood signal - printed, organic, reflection-mode oximeters will be discussed. The design, sensing methodology, and fabrication of a flexible sensor array composed of organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) will be shown, which senses reflected light from tissue to determine oxygen saturation. Finally, a key enabling technology for wearables - flexible hybrid electronics (FHE) will be presented. I will focus on the implementation of FHE in an integrated multi-sensor platform, where soft sensors are interfaced with hard silicon-based integrated circuits for wearable health monitoring.