Implantable Smart Stent with Nanomembrane Soft Sensors for Wireless Monitoring of Hemodynamics

Abstract

Cardiovascular diseases, including hypertension and atherosclerosis, account for over 30% of deaths worldwide. To diagnose and monitor these diseases, hemodynamic parameters, such as pressures, flow rates, and flow resistances, are measured. Current measurement techniques include expensive imaging processes and repetitive invasive catheterizations. These methods provide a narrow view of hemodynamics that may fail to capture significant abnormalities and may be inaccurate due to patient discomfort. Continuous monitoring would offer distinct advantages for clinical and research applications. However, implantable hemodynamic sensors are lacking due to stringent mechanical and electrical requirements. Wireless communication through tissue is required for noninvasive monitoring, but narrow blood vessels (<5 mm-diameter) with tortuous geometries prevent the use of conventional rigid electronic components. Additionally, implantable vascular sensors should be compatible with conventional catheter deployment procedures, which require mechanical stability under crimping, sheath introduction, and expansion. The only commercially available implantable sensor is a bulky, rigid package restricted for blood pressure monitoring in larger vessels. Existing research works are severely limited by short wireless communication distances and fragile designs.Here, we introduce a low-profile, wireless biosensor system comprised of an inductive medical stent and capacitive pressure sensor. The smart stent is designed and fabricated to maximize inductance to achieve functional readout distances, while maintaining its medical purpose. Analytical and experimental study optimizes the stent design for wireless communication via inductive coupling. The low-profile capacitive sensor is fabricated via aerosol jet printing, an additive manufacturing process. The sensor employs a microstructured PDMS layer as the dielectric of a highly flexible parallel-plate structure to achieve high pressure sensitivity (6 fF/mmHg). Experimental study optimizes the printed PDMS structures to maximize sensitivity. The capacitive sensor is integrated with the inductive stent to form an LC circuit with a resonant frequency dependent on pressure. The device is experimentally proven to be readily expandable by balloon catheter to allow for compatibility with existing catheter and stent placement procedures. The low-profile biosensor system is also shown to minimize disruption to normal hemodynamics compared to available commercial devices. Quantitative analysis of transient sensor signals identifies resonant frequency to allow for wireless monitoring of hemodynamics. Sensor functionality is displayed in mock blood vessels with pulsatile flow, which will enable continuous, wireless monitoring of hemodynamics throughout the vascular system. Figure 1