Heart Sensor Grows With Tissue to Measure Both Mechanical, Electrical Data

April 04, 2024 by Jake Hertz

In contrast to current cardiac sensors, which can only measure mechanical or electrical data in bulky form factors, the new one-atom-thin device measures both.

Researchers from the University of Massachusetts (UMass) Amherst and the Massachusetts Institute of Technology (MIT) recently introduced a bioelectronic mesh system integrated with graphene sensors to monitor the heart.


A novel bioelectric mesh

A novel bioelectric mesh. Image used courtesy of UMass Amherst

This study, published in Nature, adds to the body of biometric sensing research that focuses particularly on sensors embedded in the body to monitor the function of specific vital organs in real time. The mesh system from UMass Amherst and MIT can simultaneously measure the physical movement of lab-grown human cardiac tissue cells and their electrical signals. Because the system can grow with the heart cells, the researchers could monitor how the heart's electrical and mechanical functions vary over time or in response to new drug therapies. 


Graphene Mesh System Measures Mechanical and Electrical Heart Data

The researchers designed their system to comprehensively track multimodal excitation-contraction dynamics within cardiac microtissues (CMTs). Scientists prefer CMTs for heart research because they closely simulate in-vivo conditions. However, because of their three-dimensional complexity, these tissues can be challenging to monitor. Furthermore, researchers must monitor electrical and mechanical activity simultaneously to understand cardiac function and drug effects.

The UMass Amherst and MIT team embedded graphene sensors in a mesh to mimic tissue's softness and dimensions, so it could be stably integrated into the CMTs. With this approach, the system captured the action potential and strain induced by cellular contractions directly within the tissue environment. Such dual-functionality is critical for accurately mapping the intricacies of cardiac excitation-contraction coupling, a vital aspect often missed in traditional single-modality sensing approaches.


The device concept and fabrication

The device concept and fabrication. Image used courtesy of Nature

The device consists of a multilayer construction, including monolayer graphene synthesized using chemical vapor deposition, patterned onto an ultra-flexible ribbon substrate. This configuration minimally disrupts the tissue and precisely monitors localized cellular activities. The graphene transistors at the core of this system are extremely sensitive to both electrical signals (with a maximal transconductance of ~2.2 ± 0.4 mS/V) and mechanical deformation (indicated by a gauge factor of ~82 ± 24).

The team then validated the system's efficacy by tracking the maturation process within CMTs, assessing the effects of pharmacological agents, and modeling diseases. The sensor system detected subtle changes in tissue response to different drugs, making it potentially useful for drug screening and cardiotoxicity testing. By capturing both electrical and mechanical heart data, the system provides more holistic data on heart functionality, including real-time tracking of EC dynamics, detailed assessments of tissue maturation, and drug responses.


The Merits of Graphene for Biometric Monitoring

This study is one of many in recent years that relies on graphene electronics for biometric sensing. In such use cases, graphene is extremely sensitive and quickly responsive to biological and chemical stimuli. Graphene's high surface area-to-volume ratio and excellent conductivity enable it to detect minute changes in electrical signals caused by physiological activities, such as heart rate, glucose levels, and neural activity. This allows graphene-based biosensors to precisely monitor health conditions in real time, paving the way for early diagnosis and personalized medicine.


Potential for graphene-based sensors in health monitoring

Potential for graphene-based sensors in health monitoring. Image used courtesy of Frontiers

Because graphene is extremely flexible and strong, researchers often use it to develop wearable and implantable sensors that conform to the body's contours. Users can comfortably wear these devices for continuous health monitoring without them interfering with their daily activities. Flexible graphene sensors can integrate into textiles or directly adhere to the skin, offering a non-invasive way to track vital signs and physical activity.

Graphene is also an appealing material for biometric sensing because of its biocompatibility. It interfaces with biological tissues without eliciting adverse reactions, making it suitable for long-term implantable devices that monitor internal physiological processes or support tissue regeneration and healing.


A First Cardiac Sensor of Its Kind

Current cardiac sensors can only measure mechanical activity (the pumping of blood through the body) or the electrical signals that control that activity—but not both. The UMass Amherst and MIT graphene sensor uniquely monitors movement and charge in a slim form factor that doesn't impinge on heart tissue function. The researchers attribute the system's size to its graphene array, only one atom thick. The graphene-based mesh is electrically conductive, sensing electrical charges pulsing through the heart, and piezoresistive, increasing in electrical resistance as the cardiac tissue beats and stretches. 

This study received the support of the Army Research Office, the U.S. National Science Foundation, the National Institutes of Health, the Semiconductor Research Corporation, the Link Foundation, and UMass Amherst's Institute for Applied Life Sciences.