Continuous Heart Volume Monitoring by Fully Implantable Soft Strain Sensor

Abstract

Cardiothoracic open-heart surgery has revolutionized the treatment of cardiovascular disease, the leading cause of death worldwide. After the surgery, hemodynamic and volume management can be complicated, for example in case of vasoplegia after endocarditis. Timely treatment is crucial for outcomes. Currently, treatment decisions are made based on heart volume, which needs to be measured manually by the clinician each time using ultrasound. Alternatively, implantable sensors offer a real-time window into the dynamic function of our body. Here it is shown that a soft flexible sensor, made with biocompatible materials, implanted on the surface of the heart, can provide continuous information of the heart volume after surgery. The sensor works robustly for a period of two days on a tensile machine. The accuracy of measuring heart volume is improved compared to the clinical gold standard in vivo, with an error of 7.1 mL for the strain sensor versus impedance and 14.0 mL versus ultrasound. Implanting such a sensor would provide essential, continuous information on heart volume in the critical time following the surgery, allowing early identification of complications, facilitating treatment, and hence potentially improving patient outcome.

Materials, Electrical Performance, Mechanisms, Applications, and Manufacturing Approaches for Flexible Strain Sensors

“…Flexible and wearable electronics have recently attracted wide attention due to their great potential applications in real-time human health monitoring systems (e.g., detection of human motions [1][2][3][4], heart-beat [5,6], blood pressure [7][8][9], and beyond [10][11][12]), humanmachine interfaces [13][14][15] (e.g., flexible sensors work as a medium and dialogue interface for the transmission and exchange of information between humans and machines), and implantable devices [6,[16][17][18]] (e.g., transmit the sense of skin touch information to the brain by using electronic skin, and prosthesis was controlled by the cerebral cortex with 3D microelectrodes, etc.). The synchronized delivery and control of the signal from human body to detector or actuator are convenient, expeditious, effective, and accurate compared with traditional rigid conducting and semiconducting materials based on smart devices [19,20].…”

Recent Advances in Printing Technologies of Nanomaterials for Implantable Wireless Systems in Health Monitoring and Diagnosis

“…Reproduced with permission. [ 63 ] Copyright 2020, Wiley‐VCH GmbH. c) Fully implantable symbiotic pacemaker based on an implantable triboelectric nanogenerator, whereby nanostructured polytetrafluoroethylene thin film improved output performance.…”

“…Figure 3b shows a flexible piezo‐resistive strain sensor, made up of nanostructured Au–TiO 2 in PDMS, working as an implantable heart monitoring device. [ 63 ] Upon deformation of the composite sensor, the number of electrical contacts between Au‐TiO 2 nanowires changes, which generated a resistance change that can be correlated to the filling volume in the range of 6% to 15% strain. The nanostructure showed resistance strain sensor functionality, designed to smoothly conform to the heart wall due to its small size and flexibility, which is not obtained by conventional bulky sensors.…”

Soft Electronics Based on Stretchable and Conductive Nanocomposites for Biomedical Applications

“…C) Resistive strain sensor for continuous LV monitoring. [ 84 ] i) Continuous monitoring of the LV volume of a porcine heart with a resistive strain sensor based on Au‐TiO 2 NWs. ii) After calibration the, the strain sensor was able to continuously measure changes in volume.…”

“…Dual and co‐workers fabricated a soft resistive strain sensor with AuTiO 2 NWs and tested it in an acute porcine in vivo study. [ 84 ] The strain sensor was sutured on the apex of the heart (Figure 6C,i). Subsequently, the changes in resistance were compared to changes in volume measured by “electric impedance,” a method only available for animal studies.…”