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

The assay combines two complementary technologies. The first is a microelectrode array (MEA) that records the electrical activity of networks of human induced pluripotent stem cell (hiPSC) neurons. These cultures, supplied by Fujifilm Cellular Dynamics, consist of roughly 68 percent glutamatergic neurons, 17 percent GABAergic neurons and 15 percent astrocytes, a carefully controlled ratio designed to mimic key features of human brain circuitry. After 21 to 25 days in culture, the neurons form functional networks whose spikes and bursts can be monitored before and after compound exposure using an Axion Biosystems Maestro instrument. The second component is a panel of human ion channel assays, run on automated patch clamp electrophysiology platforms, that measures how potently a drug inhibits channels long associated with seizure biology, including sodium channels such as NaV1.1, NaV1.2 and NaV1.6, potassium channels such as Kv7.2 and Kv7.3, GABA receptors, NMDA receptors and nicotinic acetylcholine receptors.

To interpret the data, the researchers quantified changes in a defined set of MEA parameters, including mean firing rate, burst frequency, network burst frequency, the number of spikes per burst and the mean inter-spike interval within bursts. Changes were categorized as no change (0 to 29 percent), moderate change (30 to 49 percent) or high change (greater than 50 percent), thresholds grounded in the typical variability of vehicle controls and historical datasets with known seizurogenic drugs. Crucially, the team then compared in vitro effect concentrations with human or animal exposure data, asking whether the concentrations that perturbed neuronal networks in the dish resembled the concentrations actually circulating in patients or test animals.

The benchmark for validation was amoxapine, an antidepressant with a well-documented incidence of clinical seizures. In the MEA assay, amoxapine produced visible disruption of firing patterns at 1 micromolar, marked changes at 3 micromolar and intense changes at 10 micromolar, with burst frequency and network burst frequency rising in a clear concentration-dependent manner. Strikingly, these effects began within the human therapeutic plasma concentration range of 0.57 to 1.91 micromolar, providing direct evidence that the dish-based readout can align with clinically relevant exposures. The ion channel panel reinforced the picture: amoxapine showed high-potency inhibition of nine seizure-related targets, including NaV1.1, Kv1.1, Kv4.2, the GABA alpha1 beta2 gamma2 receptor and the nicotinic alpha2 beta4 receptor, with medium-potency hits at Kv7.2 and NMDA1/1.

The first case study applied the assay during lead optimization, the stage where medicinal chemists select which chemical series to advance. Five lead series, tested at 30 micromolar, produced sharply divergent profiles. Compound A showed no changes in any MEA parameter and was judged the safest lead to progress. Compounds B, C, D and E showed progressively concerning alterations in network burst frequency and inter-spike intervals, with compound E displaying the most severe perturbations. This kind of ranking, the authors argue, allows seizurogenic risk to be designed out of a molecule before animals, resources and years of development time are spent, offering a human-relevant alternative to zebrafish larval assays and rat hippocampal brain slices, both of which have struggled with throughput and translation to patients.

The second case study tackled a problem that had brought an entire project to a standstill: convulsions observed in dogs during the good laboratory practice toxicology studies required before first-in-human trials, with no seizures seen in rats tested in parallel. Metabolic analysis revealed a species difference. Humans and rats shared one predominant metabolite, while dogs produced a different metabolite that was only minor in the other species. When the parent drug, the human and rodent metabolite, and the dog-specific metabolite were run through the assay, the results were decisive. The parent compound and the human-relevant metabolite were essentially clean, while the dog metabolite produced a clear seizurogenic phenotype at 100 micromolar, disrupting burst frequency, spikes per burst and, most notably, the mean inter-spike interval. The dog metabolite also showed a high-potency hit at the NMDA 1/2A receptor, with an IC50 of 19.3 micromolar, whereas the other two compounds had no ion channel hits at all. The conclusion was that the canine convulsions stemmed from a dog-specific metabolite unlikely to pose a comparable risk to humans.

The third case study compared two clinical candidates, X and Y, to guide prioritization. Candidate Y displayed a potent seizurogenic signature at 3 and 10 micromolar, concentrations overlapping its clinical maximum plasma concentration of 5 micromolar, and at higher doses it completely disintegrated synchronous firing, rendering the raster plots unreadable. Candidate X, by contrast, was clean at its clinical Cmax of 1 micromolar, with only scattered changes appearing above 10 micromolar. The data clearly identified X as the lower-risk candidate. In a fourth case study, the team directly tested in vitro to in vivo translation using compound B, for which animal exposure data existed. The compound left MEA parameters untouched up to 10 micromolar, matching the absence of nervous system signs in animals at total plasma concentrations up to 38 micromolar, but produced marked changes at 100 micromolar, mirroring convulsions seen in vivo at plasma concentrations of 148 to 297 micromolar.

The authors are candid about limitations. The case studies come from client work, so the compounds are anonymous and the datasets limited. Changes in MEA parameters could in principle reflect generalized network perturbation rather than seizure liability specifically, although the researchers note that non-specific effects produce a different fingerprint and that their benchmark validation set represents an industry standard for seizure detection. A formal decision framework and refined exposure metrics, including unbound brain concentrations that are difficult to measure, remain works in progress. The work is therefore described as hypothesis-generating, a starting point for defining the context of use that regulators increasingly demand from new approach methodologies.

Nevertheless, the regulatory timing is favorable. A recent FDA Center for Drug Evaluation and Research review has emphasized the potential of new approach methodologies, and proposals to modernize the ICH S7A safety pharmacology guideline call for greater use of secondary pharmacology, integrated risk assessment and weight-of-evidence approaches. The authors propose that the MEA assay could be framed as a tool for assessing whether small molecule candidates alter human neuronal excitability, while the ion channel panel assesses perturbations of neuronal channel function, together supporting compound prioritization and first-time-in-human submissions. By analogy with the hERG cardiac channel assay, which transformed arrhythmia screening two decades ago, a potent ion channel IC50 would serve as an alert for further investigation rather than an automatic stop.

Looking ahead, the team is developing structure-activity relationship models to predict unwanted ion channel activity in silico, potentially allowing predicted metabolites to be evaluated computationally before any laboratory work begins. For projects where brain penetration can be avoided, that remains the simplest route to eliminating seizure risk; for central nervous system programs, where brain exposure is essential, the focus shifts to selectivity between the intended target and off-target channel effects. What the iLAseizure case studies demonstrate, above all, is that human cells in a dish can now speak with surprising authority about a risk that has historically only revealed itself in convulsing animals or, tragically, in patients.

Subject of Research: An in vitro seizure liability assay using human induced pluripotent stem cell neurons and ion channel panels to predict drug-induced seizure risk in drug discovery and development.

Article Title: Implementation of the In Vitro Seizure Liability Assay (iLAseizure) in Drug Discovery and Development: Mechanism of Action Case Studies

Article References: Rockley, K., Roberts, R., Jennings, H., Jones, K., Maizières, M.-A., & Morton, M. (2026). Implementation of the In Vitro Seizure Liability Assay ( iLA seizure ) in Drug Discovery and Development: Mechanism of Action Case Studies. Pharmacology Research & Perspectives, 14(5), Article e70317. https://doi.org/10.1002/prp2.70317

Image Credits: AI Generated

DOI: 10.1002/prp2.70317

Keywords: seizure liability, drug discovery, hiPSC neurons, microelectrode array, ion channels, new approach methodology, safety pharmacology, neurotoxicity, MEA assay, drug-induced seizures, ICH S7A, in vitro to in vivo translation