Cell Adhesion Governs Cardiac Signal Fidelity in Printed Organic Transistors

A study from researchers at the Istituto Italiano di Tecnologia (IIT), Istituto Auxologico Italiano IRCCS, Politecnico di Milano, and the University of Milano-Bicocca has overturned a central assumption in organic bioelectronics: that higher electrical performance directly translates to better biological signal recording.

Published in Advanced Science in 2026, the paper demonstrates that in electrolyte-gated polymer transistors used to record cardiac action potentials from human heart cells, how well the cells physically adhere to the polymer surface matters more than the transistor’s electrical gain.

Science Made Simple

An action potential is the electrical signal a heart cell produces every time it contracts — a brief, characteristic voltage spike that researchers use to assess whether a cell is healthy, drug-affected, or diseased.
To capture these signals without puncturing the cell, scientists grow heart cells directly on thin polymer films connected to miniature transistors. Think of the polymer as a landing pad: the better the cells grip it, the more faithfully the transistor picks up their signal.

This study found that a polymer with ten times the electrical conductance of its rival still produced poorer, more distorted recordings — because the cells didn’t adhere to it as well. Getting the landing pad right mattered more than boosting the transistor’s amplifying power.

Two Polymers on One Chip

The IIT-led team printed two conducting polymers side by side on the same transistor array — poly(3-hexylthiophene-2,5-diyl) (P3HT), a well-established material for bioelectronic devices, and p(g2T-TT), a newer glycolated polymer with transconductance values more than ten times higher. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were cultured across both halves simultaneously, making the polymer type the only experimental variable.

Electrically, p(g2T-TT)-based organic electrochemical transistors (OECTs) were the clear winner. But when it came to recording cardiac action potential waveforms, the result was reversed: P3HT-based electrolyte-gated field-effect transistors consistently reproduced the full action potential shape typical of ventricular cardiomyocytes, while p(g2T-TT)-based devices mostly produced attenuated, distorted signals. Over 90% of signals from P3HT devices showed accurate action potential morphology; only around 8% of those from p(g2T-TT) devices did the same.

Cell Adhesion as the Deciding Factor

To understand why, the team examined cell-substrate bonding using immunofluorescence staining for vinculin — a protein that anchors cells to surfaces through structures called focal adhesions. Cells on P3HT showed significantly more peripheral vinculin expression, indicating stronger, better-organised adhesion. On p(g2T-TT), vinculin pooled near the cell nucleus instead, a pattern associated with weak cell-substrate contact.

The researchers also ruled out device response speed as the cause: even when p(g2T-TT) OECTs were redesigned to match the switching speed of P3HT devices, signal fidelity remained poor. Surface characterisation provided the underlying explanation. P3HT films are hydrophobic and smooth (RMS roughness 0.7–0.9 nm), while p(g2T-TT) films are hydrophilic and rougher (3.7–4.8 nm). Critically, the ethylene glycol side chains that give p(g2T-TT) its high ionic conductance also act as an antifouling surface, reducing the protein adsorption that cells rely on to form a strong mechanical grip.

What This Means for Drug Screening and Disease Modelling

Extracting precise action potential durations and repolarisation parameters from hiPSC-CMs is critical for in vitro cardiac safety testing and disease modelling. The degraded, field-potential-like waveforms that the higher-performing p(g2T-TT) devices produced cannot reliably yield these parameters. The study’s conclusion is direct: optimising surface chemistry, topography, and protein adsorption behaviour at the cell-device interface must be treated as an equal design priority to electrical performance when developing organic bioelectronic recording platforms.

Platinum Wire as the Gate Electrode

Throughout all electrical measurements, a platinum wire gate electrode — 99.99+% purity, 0.5 mm diameter, supplied by Advent Research Materials — was immersed in the cell culture medium to complete the transistor circuit.

Platinum’s electrochemical stability, inertness in physiological saline, and established biocompatibility make it the standard choice for this role in electrolyte-gated organic transistor research, providing a consistent reference potential during long-duration recordings of spontaneously beating cardiomyocytes.

Source: Zemignani GZ et al. Beyond Transconductance: Cell-Polymer Coupling Determines Fidelity in Action Potential Recording via Electrolyte-Gated Polymer Transistors. https://doi.org/10.1002/advs.202520122