The core of the work is a technical answer to a long-standing problem in preclinical drug testing. Cardiomyocytes, the contractile cells of the heart, respond to pharmacological agents in vivo within minutes, and those responses are strongly influenced by the dynamic delivery of the drug through the bloodstream. Conventional two-dimensional cultures and static three-dimensional constructs cannot replicate these fluid flow kinetics, which limits how well they predict what will happen in a patient. The Mera system, developed by Hooke Bio, is designed to address this by supporting long-term culture and functional analysis of three-dimensional cardiac spheroids built from human induced pluripotent stem cell-derived cardiomyocytes together with cardiac fibroblasts, the supporting cells that help give heart tissue its structure and signaling environment.

Architecturally, Mera is ambitious. The platform is designed to accommodate up to 640 spheroids per run across a modular layout, integrating automated imaging, automated fluid handling, and user-friendly software, all operating under tightly controlled physiological conditions of 37 degrees Celsius and 5 percent carbon dioxide. Flow rates are tunable between zero and 12.5 milliliters per minute, a range intended to mimic the perfusion conditions cells would experience inside the body. In the study now published, however, the researchers deliberately worked at a smaller experimental scale, using up to 18 spheroids per condition, and they are explicit that full-scale throughput and parallelisation remain to be validated in future work. That honesty about scale matters, because throughput claims in the organ-on-a-chip field have often outpaced what has actually been demonstrated.

The biological building blocks of the assay are spheroids, tiny spherical aggregates of cells that self-organize into tissue-like structures. Combining cardiomyocytes with cardiac fibroblasts in three dimensions is known to improve the maturation and tissue-like features of such constructs, and the spheroid format offers a practical compromise between physiological relevance and the numbers needed for statistically meaningful drug testing. Inside Mera, these spheroids are perfused with medium while an automated imaging system tracks their beating. Because the contraction of cardiomyocytes produces visible motion, beat rate can be quantified from video, giving a functional readout that changes in real time as drugs flow past the cells.

To validate the platform, the team turned to a pharmacopoeia of cardiac pharmacology. Verapamil, a calcium channel blocker, slows the heart by reducing calcium entry into cardiomyocytes; isoproterenol, a beta-adrenergic agonist, accelerates beating by mimicking the sympathetic nervous system’s fight-or-flight signals; calcium chloride increases the calcium available to the contractile machinery; and propranolol, a beta-blocker, dampens adrenergic stimulation. Under dynamic flow in Mera, all four drugs produced real-time, reversible modulation of the spheroids’ beat rate. Crucially, the researchers observed recovery following drug-induced suppression, meaning that when the drug was washed out by the flowing medium, the cells resumed their baseline rhythm. That reversibility is a key indicator that the observed effects reflect genuine pharmacology rather than irreversible damage to the tissue.

The quantitative output of these experiments also passed a demanding test. Dose-response studies on the platform yielded IC50 values, the concentrations at which a drug produces half of its maximal effect, that were consistent with values reported in the scientific literature. Matching known potency benchmarks is one of the strongest arguments that a new in vitro system is behaving in a physiologically meaningful way rather than generating artifacts. The team also assessed how much the platform’s measurements varied from run to run and from spheroid to spheroid, finding that system variability was comparable to a temperature-controlled reference platform. That comparison supports the use of standard statistical analysis on Mera’s data, an unglamorous but essential requirement for any technology that hopes to influence regulatory decisions.

One of the most consequential framing devices in the paper is the concept of a new approach methodology, or NAM, a term increasingly used by regulators to describe non-animal testing strategies that can inform safety assessment. Cardiac toxicity has historically been a leading cause of drug withdrawal and of costly late-stage clinical failures, and current testing relies heavily on animal models that often translate poorly to humans, alongside in vitro systems that lack the dynamics of the bloodstream. By enabling dynamic drug exposure, automated analysis, and human-cell-based tissue, Mera is positioned as a candidate NAM for cardiac drug response testing. The researchers are careful, however, to note what the platform does not yet do: incorporation of contractility measurements, which capture the force of each beat, and electrophysiological readouts, which capture the electrical signals that coordinate the rhythm, will be an important next step toward supporting its use in predictive cardiac safety assessment.

The technical significance of adding flow deserves emphasis, because it changes more than just the delivery of drugs. Perfusion continuously refreshes nutrients and oxygen, removes metabolic waste, and subjects cells to shear stress, all of which influence how stem cell-derived cardiomyocytes mature and behave. It also eliminates a subtle but well-documented problem in microfluidic devices: certain small molecules are absorbed by the silicone polymer commonly used to fabricate chips, distorting the effective drug concentration that cells actually experience. Dynamic, controlled perfusion with automated fluid handling gives experimenters a much firmer grip on the dose that reaches the tissue, which in turn makes dose-response curves and derived potency values more trustworthy.

The study also reflects a broader shift in how organ-on-a-chip technologies are being engineered. Early microphysiological systems were often bespoke devices built by academic labs, powerful as proofs of concept but difficult to operate, hard to reproduce, and impractical for the throughput that pharmaceutical screening demands. Mera’s design philosophy runs in the opposite direction: modular architecture, automated imaging and fluidics, and software intended to be usable by operators who are not microfluidics specialists. The authors acknowledge the financial support of Ireland’s Disruptive Technologies Innovation Fund and the European Innovation Council, and they are transparent that all authors are or were employees of Hooke Bio, the company that developed the system, with some holding shares or stock options. That commercial stake does not invalidate the data, but it is the kind of disclosure that readers weighing the technology’s maturity should keep in view.

What emerges from the study is a platform that has demonstrated, at modest scale, that human cardiac spheroids can be cultured long-term under physiologically relevant flow and interrogated with clinically important drugs in real time. The reversible beat-rate responses, the literature-consistent IC50 values, and the reproducibility relative to a reference platform together make a credible case that Mera captures something genuinely physiological about how the human heart responds to pharmacological challenge. The road ahead is clearly mapped by the authors themselves: scaling to the full 640-spheroid capacity, adding force and electrical measurements, and validating the system against a wider panel of compounds, including known cardiotoxins. If those steps succeed, the vision is a future in which a drug’s effects on the human heartbeat can be measured in a perfused, human-cell model before it ever reaches a patient, replacing some animal studies with experiments that are faster, more human, and conducted entirely under glass.

Subject of Research: A microphysiological system for assessing human cardiomyocyte beat-rate responses to drugs under dynamic flow

Article Title: Functional assessment of cardiac beat dynamics under dynamic flow: insights from the Mera microphysiological system

Article References: Almeida, N., Sum-Coffey, V., Costello, P., Madden, C., Devitt, S., Mukkunda, S. R., Keshava, B. B., Sunil, S., Riley, L. G., Deely, S., de Benedictis, C. A., Lyons, M., & Cliffe, F. E. (2026). Functional assessment of cardiac beat dynamics under dynamic flow: insights from the Mera microphysiological system. Biomedical Microdevices, 28(4), Article 70. https://doi.org/10.1007/s10544-026-00839-5

Image Credits: AI Generated

DOI: 10.1007/s10544-026-00839-5

Keywords: microphysiological system, heart-on-a-chip, cardiomyocytes, cardiac toxicity, drug testing, organ-on-a-chip, microfluidics, induced pluripotent stem cells, beat rate, new approach methodology, cardiac spheroids, pharmacology