Abstract
The rapid advances in human-friendly and wearable photoplethysmography (PPG) sensors have facilitated the continuous and real-time monitoring of physiological conditions, enabling self-health care without being restricted by location. In this paper, we focus on state-of-the-art skin-compatible PPG sensors and strategies to obtain accurate and stable sensing of biological signals adhered to human skin along with light-absorbing semiconducting materials that are classified as silicone, inorganic, and organic absorbers. The challenges of skin-compatible PPG-based monitoring technologies and their further improvements are also discussed. We expect that such technological developments will accelerate accurate diagnostic evaluation with the aid of the biomedical electronic devices.
Highlights
Owing to stable device operation under a high tensile strain of 35%. Owing to their low flexural their lowepidermal flexural rigidity, epidermal optoelectronic devices were positioned on the rigidity, optoelectronic devices were positioned on the wrist
Additional work on the integration of highly flexible near-infrared organic light-emitting diodes (LEDs) and organic photodetectors photodetectors (OPDs) will allow the practical implementation of all organic-based conformal PPG sensors
Note that the figure 8-shaped OPD wraps around red and green OLEDs in operation. (c) PPG signals, SpO2 values, and heart rate obtained from various body parts. (d) Comparison of the power consumption of R and G light sources of oximetry sensors: †, discrete optical elements integrated on a PCB substrate with the edge-to-edge distance between elements being 2 mm (=PO1); ‡, a commercially available reflective pulse oximetry head
Summary
The demand for wearable electronic devices to monitor physiological conditions has increased exponentially in recent years [1,2,3,4]. The skin-interfaced wearable devices have the advantage of allowing the continuous monitoring of various physiological data as comfortably as possible. Despite the recent advances in wearable sensor technology for clinical applications, the following challenges still remain: (i) skin irritation due to friction between the skin and device; (ii) insufficient conformal adhesion with a complex skin surface owing to the rigidity. A brief overview of the operational mechanism and its applications of PPG sensors is first presented, followed by recent progress and technological developments of skin-compatible materials to obtain accurate and stable lightsensing performance and mechanical durability. We highlight current challenges and possible future research directions for multifunctional PPG sensors
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