(J-395) Flexible Biophotonic Oximetry for Continuous Non-invasive Cardiac Monitoring

Introduction:: Continuous non-invasive monitoring of tissue oxygenation levels (Hemoglobin oxygen saturation levels based on the relative amount of hemoglobin that carries oxygen), is essential for cardiac monitoring, disease diagnosis as well as for follow-up of therapeutic interventions, especially in older populations. Tissue hypoxia, due to a relative imbalance between oxygen supply and consumption levels, is not only associated with cardiovascular disorders including Atherosclerosis, Vascular Remodeling or Heart Failure, but also can serve as a key risk factor for pathogenesis of Thrombosis (venous or arterial) [1,2]. Flexible epidermal electronics for health-monitoring include conformal, substrate integrated high-density electronics that can easily be subjected to considerable bending or stretching without any resulting damage or loss of electrical and/or structural integrity. The components are assembled either by direct embedding or using additively deposited isotropic conductive adhesives. Silicone elastomers (DOWSIL™ 3-4207) used as encapsulants help provide additional stress relief for interconnections under applied displacements as well as provide adequate protection from moisture and other environmental contaminants [3].

Materials and Methods:: The low form factor/footprint (weight < 2g & thickness < 3mm) biophotonic device prototype is fabricated on a flexible Polyimide substrate with components mounted or embedded on the substrate (Fig.1) patterned using a CO2 Laser (M-300 Laser Engraving and Cutting System by Universal Laser Systems, Inc). The bridge connections are screen-printed using silver-elastomer composites (CI – 4040) and cured twice at 120℃ for 10 minutes. The assembled device is then encapsulated (Dowsil™ 4207 Dielectric Tough Gel Kit) and cured at room temperature for 4 hours.

Verification of the prototype is performed using Peel, Thickness, Tensile tests as well as functional validation of Oxygen Saturation levels measured at 670 nm and 850 nm.


Results, Conclusions, and Discussions:: The results of the study show that the Photodiode is able to detect and discern between levels of Oxygen Saturation (75% and 99%) which can serve as a vital marker for functional oxygen transport as seen in various disease states. Photodiode voltage outputs are proportional to the Oxygen Saturation level.The biophotonic sensor prototype is used to demonstrate state of the art embedded-chip technology, with both embedded light sources (LEDs) as well as photodetectors in the flex package that provides a flat surface for the device-skin interface allowing intimate contact of the photonic components with the skin and a large signal to noise ratio allowing detection at lower LED and detector power [3]. Embedding allows integration of additional components into smaller volumes thus allowing vertical three-dimensional integration of multilayer packages with power harvesting.


Acknowledgements (Optional): :

References (Optional): : [1] Abe H, Semba H, Takeda N. The Roles of Hypoxia Signaling in the Pathogenesis of Cardiovascular Diseases. J Atheroscler Thromb. 2017 Sep 1;24(9):884-894.

[2] Ninivaggi M, de Laat M, Lancé MM, Kicken CH, Pelkmans L, Bloemen S, Dirks ML, van Loon LJ, Govers-Riemslag JW, Lindhout T, Konings J, de Laat B. Hypoxia Induces a Prothrombotic State Independently of the Physical Activity. PLoS One. 2015 Oct 30;10(10):e0141797.

[3] Hassan A, Soroushiani S, Abdal A, Sayeed SYB, Lin W-C, Pulugurtha MR. Embedded-Component Planar Fan-Out Packaging for Biophotonic Applications. IEEE Open Journal of Nanotechnology. 2022; 3: 52-60.