A research team at the Center for Neuroscience Imaging Research (CNIR) within the Institute for Basic Science (IBS), together with Sungkyunkwan University (SKKU), has developed a new class of ultra-thin, flexible bioelectronic material that can seamlessly interface with living tissues. The researchers introduced a novel device called THIN (Transformable and Imperceptible Hydrogel-Elastomer Ionic-Electronic Nanomembrane). THIN is a membrane just 350 nanometers thick that transforms from a dry, rigid film into an ultra-soft, tissue-like interface upon hydration.

Biological tissues – especially vital organs such as the heart, brain, and muscles – are soft, curved, and constantly in motion. Even the thinnest existing bioelectronic devices can feel foreign, leading to poor adhesion, inflammation, and unstable signal acquisition. While ultrathin flexible devices have been developed, most still require adhesives, rigid packaging, or mechanical supports, particularly for dynamic tissues such as the heart or brain.

This challenge inspired the team to ask a simple but compelling question:

“What if a device could become soft, sticky, and shape-adapting only when it touches tissue – like magic?”

That question led to the development of THIN, a transformable, substrate-free nanomembrane that self-adheres to wet tissue without sutures, adhesives, or external pressure. By exploiting hydration-triggered swelling, THIN self-adheres without sutures or external pressure even on microscopically folded or highly curved surfaces, which allows it to maintain long-term contact with the tissue.

The nanomembrane is specifically engineered by design to be “soft when wet” and “robust when dry”. THIN consists of two layers – the first being a mussel-inspired, tissue-adhesive hydrogel (catechol-conjugated alginate; Alg-CA), and the second being a high-performance semiconducting elastomer, P(g2T2-Se).

Together they form a freestanding bilayer only 350 nm thick – nearly a thousand times thinner than a human hair. The device’s bending stiffness decreases over a million-fold (to 9.08 × 10⁻⁵ GPa·μm⁴) when hydrated, allowing it to wrap around surfaces with curvature radii below 5 μm – so soft that it becomes mechanically imperceptible to tissue.

When dry, the hydrogel layer is rigid (1.35 GPa), enabling easy handling and direct semiconductor coating. Upon hydration, it softens dramatically (0.035 GPa) and curls spontaneously, forming natural, gentle adhesion to the target organ surface.

The selenophene-based polymer P(g2T2-Se) achieves a record µC* (mobility × capacitance product) of 1,034 F·cm⁻¹·V⁻¹·s⁻¹, roughly 3.7 times higher than conventional stretchable materials. This high ionic-electronic coupling enables organic electrochemical transistors (OECTs) built on THIN to amplify biological signals with remarkable stability even during stretching or motion.

In animal experiments, THIN-OECTs instantly adhered to rodent hearts, muscles, and brain cortices, recording epicardial electrograms (EGM), electromyograms (EMG), and electrocorticograms (ECoG) with high fidelity. The devices remained stable and biocompatible for over four weeks, showing no inflammation or tissue damage after long-term implantation.

“Our THIN-OECT platform acts like a nano-skin – it is invisible to the body, mechanically imperceptible, and yet electrically powerful,” said Prof. SON Donghee, corresponding author of the study. “It opens new possibilities for chronic brain-machine interfaces, cardiac monitoring, and soft neuroprosthetics.”

Unlike conventional bioelectronic systems that depend on elastomeric substrates or adhesives, THIN is substrate-free, freestanding, and operational at the nanoscale. Its mechanical imperceptibility and autonomous adhesion make it suitable for stable signal acquisition from dynamic tissues without interference or foreign-body sensation.

Because THIN amplifies electrophysiological signals directly at the contact site, it eliminates bulky external amplifiers, paving the way for next-generation implantable, wearable, and injectable medical devices.

“By combining transformability, self-adhesion, and record-high ionic-electronic performance, THIN sets a new standard for bioelectronics that truly belong inside the body,” Prof. Son added.

Future work will focus on multichannel, wireless-capable THIN arrays for closed-loop neuroprosthetics, brain-machine interfaces, and rehabilitation robotics, as well as injectable or bioresorbable versions for minimally invasive clinical use.

The findings of this research have been published in Nature Nanotechnology.

Figure 1. Mechanically transformable and imperceptible hydrogel-elastomer adhesive bilayer (THIN) transistor based on an ion-electron conducting nanomembrane for bio-signal amplification
The IBS Center for Neuroscience Imaging has developed a free-standing ion-electron conducting nanomembrane (THIN) that retains structural integrity without external support. When implemented as an organic electrochemical transistor (OECT), the THIN device adapts conformally to curved biological tissues by absorbing bodily fluids and enables real-time on-site amplification of subtle bio-signals for precise in vivo monitoring.

Figure 2. Self-adaptive conformability of THIN for imperceptible tissue integration
The IBS Center for Neuroscience Imaging has demonstrated that THIN can stretch under hydration without cracking, conform to tissue surfaces with micron-scale curvature radii, and adhere tightly to microstructured surfaces via mussel-inspired interfacial chemistry. Upon exposure to bodily fluids, THIN asymmetrically swells, leading to a reduction in contact area and an upward shift of the center of mass as the nanomembrane curls. This swelling-induced transformation enables spontaneous and rapid self-adhesion to curved tissue surfaces. The same mechanism ensures stable and robust conformal contact even under dynamic cardiac motion. Unlike devices with elastomeric substrates, THIN exhibits ultralow mechanical stiffness and deforms together with the tissue, enabling long-term, durable integration.

Figure 3. THIN-based organic electrochemical transistor (OECT) interface for real-time amplification and monitoring of bio-signals
THIN-based organic electrochemical transistor (OECT) developed by the IBS Center for Neuroscience Imaging was applied to the heart, anterior tibialis muscle, and cerebral cortex of rats. The device conformally adheres to dynamic and soft tissues – including beating heart, twitching TA muscles, and the delicate brain surface – and enables real-time amplification and monitoring of subtle physiological signals across diverse in vivo environments.

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