Engineers have developed a new way to monitor how tiny lab-grown human heart tissues beat—by effectively “listening” to the ripples they create. The team has created a wireless, noninvasive sensing platform that can biomechanically measure how strongly the miniature heart tissues, known as cardiac organoids, beat in real time. The research could help accelerate drug development, improve disease modeling and reduce reliance on animal testing, offering a more human-relevant way to study how the heart works.

Cardiac organoids are 3D clusters of human heart cells grown in a laboratory that are used to evaluate the safety and efficacy of new drugs prior to clinical trials, as well as study disease. While they don’t replicate the full structure of a human heart, they mimic key behaviors, especially how heart muscles contract when drugs are administered.

They are increasingly seen as a powerful alternative to animal models, which often fail to fully capture how human biology works.

To treat or manage various heart, gastrointestinal and neurological conditions, including arrhythmias, heart block, gastroparesis, epilepsy and some nerve injuries, doctors rely on a technique known as electrical stimulation. Electrical stimulation entails the delivery of small electrical pulses to target locations to prompt the activation of nerves, muscles or organs.

Many existing approaches for delivering electrical stimulation rely on electronic devices that are permanently or temporarily implanted inside the body. These devices can sometimes fail, cause adverse effects and might need to be surgically removed.

Researchers at Northwestern University, Sungkyunkwan University and other institutes recently developed a new implantable and bioresorbable system that could be used to electrically stimulate specific organs, muscles or nerves inside the body. This stimulator, presented in a paper published in Nature Electronics, could gradually disappear after a treatment is complete, so it would not need to be surgically extracted.

When living cells grow, divide or respond to drugs, they give off tiny amounts of heat that offer information about what the cells are doing. But because these heat signals are so vanishingly small, they have traditionally been impossible to measure directly. Researchers in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a calorimeter—a device that measures the heat transfer between a living system and its environment—that can detect metabolic heat signals on the order of 100 picowatts, or trillionths of a watt, in living cells.

The device is the most sensitive of any comparable bio-calorimeter to date. The new “pico-calorimeter” can track the metabolism of small populations of bacteria in real time, as well as monitor how bacterial growth changes in response to different antibiotics.

The work is from the lab of Joost Vlassak, the Abbott and James Lawrence Professor of Materials Engineering, and was carried out by Harvard associate Juanjuan Zheng, a former postdoctoral researcher in Vlassak’s lab. The research is published in the Proceedings of the National Academy of Sciences.