Piezoionics Reading List - Early Works
The scientific basis for piezoionics is fundamentally based on force-induced ion transport carrying electricity. This phenomenon—the movement of charged particles under external driving forces—was established by pioneering scientists starting two centuries ago. Alessandro Volta (1745–1827) provided the foundation with the voltaic pile, proving chemical energy could generate steady electrical flow. Humphry Davy (1778–1829) subsequently showed that electrical forces drive chemical constituents during electrolysis, while Michael Faraday (1791–1867) identified this ionic mobility within solid-state lattices. The quantitative framework was refined by Johann Wilhelm Hittorf (1824–1914), who introduced ionic transport numbers, and Svante Arrhenius (1859–1927), who theorized electrolytic dissociation. Finally, Walther Nernst (1864–1941) mathematically linked chemical and electrical gradients. These discoveries provide the physical laws essential to piezoionics, where mechanical stress serves as the primary driving force to redistribute ions and generate a potential.
In the recent decades, the theoretical groundwork was established by Nobel laureate P. G. de Gennes and colleagues, whose 2000 model described the mechanoelectric coupling in ionic gels. However, it was not until the early 2020s that the field gained significant momentum, with pioneering experimental demonstrations in hydrogels and ionic polymers unlocking its potential for self-powered sensing and biointerfaces.
The following reading list captures the seminal works from this critical emergence period (2022-2025), highlighting the progression from molecular simulation and material innovation to advanced device architectures for wearables, robotics, and neuromodulation.
1. Mechanoelectric effects in ionic gels
P. G. de Gennes, K. Okumura, M. Shahinpoor, K. J. Kim
Europhysics Letters, 2000, 50(4), 513-518. (DOI)
This foundational paper provides the first compact theoretical framework for mechanoelectric coupling in ionic gels based on linear irreversible thermodynamics. It establishes the theoretical underpinnings for the entire field of soft, ionic actuators and sensors by deriving Onsager relations that couple electric fields, pressure gradients, and ionic/water fluxes. The proposed methodology uses a two-force, two-flux model to elegantly describe both the direct (electric field → deformation) and inverse (deformation → electric field) effects in static conditions. This elegant formalism is significant as it explains the operation of ionic polymer-metal composite (IPMC) actuators and predicts the piezoionic effect, laying the groundwork for decades of subsequent research into energy-harvesting ionotronics and soft robotics.
2. Molecular simulations of the piezoionic effect
V. Triandafilidi, S. G. Hatzikiriakos, J. Rottler
Soft Matter, 2018, 14, 5350-5360. (DOI)
This study employs coarse-grained molecular dynamics simulations to investigate the molecular origins of the piezoionic effect in polyelectrolyte gels. By modeling a slab geometry with two gels of different ionization degrees, the work demonstrates that a pressure gradient spontaneously arises, leading to the buildup of a Nernst–Donnan potential at the interface—a reverse methodology to experimental piezoionic sensing. The simulations reveal three distinct regimes governed by counterion condensation, which depend on the Bjerrum length relative to the spacing between backbone charges. The Nernst–Donnan potential scales linearly with temperature and, crucially, with the lateral pressure difference between the gels, providing a fundamental molecular-level explanation for the linear relationship between applied mechanical stress and generated electrical potential in piezoionic materials.
3. Piezoionic mechanoreceptors: Force-induced current generation in hydrogels
Y. Dobashi, D. Yao, Y. Petel, T. N. Nguyen, M. S. Sarwar, Y. Thabet, C. L. W. Ng, E. S. Glitz, G. T. M. Nguyen, C. Plesse, F. Vidal, C. A. Michal, J. D. W. Madden
Science, 2022, 376(6592), 502-507. (DOI)
This study presents hydrogels that transduce pressure into ionic currents via the piezoionic effect, mimicking biological mechanoreceptors. By exploiting differences in cationic and anionic mobilities within hydrogel matrices, the sensors generate high charge densities (up to 80 mC/cm³) and tunable transient responses (from milliseconds to hundreds of seconds). The work demonstrates a piezoionic skin with built-in Donnan potentials and successful peripheral nerve stimulation in rodent models using the self-generated currents. These findings establish piezoionic materials as a promising platform for self-powered, ultrasoft neural interfaces and biomimetic sensing.
4. Piezoionic sensors based on formulated PEDOT:PSS and Aquivion® for ionic polymer–polymer composites
A. Adjaoud, G. T. M. Nguyen, L. Chikh, S. Péralta, L. Trouillet-Fonti, N. Uguen, M.-D. Braida, C. Plesse
Smart Materials and Structures, 2022, 31(7), 075012. (DOI)
This work develops ionic polymer–polymer composites (IP2Cs) as piezoionic sensors using the commercially available Aquivion® perfluorinated membranes and formulated PEDOT:PSS electrodes. By tuning electrode properties through solvent annealing and additive formulation (ionic liquids, polar solvents, Aquivion®), the study demonstrates that mechanical properties of the electrodes are more critical than electronic conductivity for sensing performance. The optimal sensor, fabricated via drop-casting, achieves a voltage output of up to 2.9 mV under ±2% strain, with performance influenced by the Aquivion® membrane grade and the manufacturing process. This work highlights the potential of fully organic, soft piezoionic sensors for robotic and medical applications, emphasizing the importance of electrode–hydrogel interfacial design.
5. Ultrasensitive multi-degree-of-freedom piezoionic sensor via synergistic hydrogel-ion interactions
Y. Fang, H. Ouyang, Y. Cheng, Y. Zhou, L. Shi, J. Sun, G. W. Ho, R. Wang
Nature Communications, 2026, 17, 893. (DOI)
This work reports a soft, piezoionic, multi-degree-of-freedom (SPIM) flex-sensor for self-powered, high-fidelity body motion capture. It achieves a record-high piezoionic flex-sensitivity of 3.2 mV/degree by synergistically integrating zwitterionic dipole-ion interactions (to form fast ion channels) and size-induced steric hindrance from bulky organic anions (to amplify cation/anion transport imbalance). The sensor features a square prism-shaped hydrogel fiber with two pairs of symmetric nanomesh electrodes, enabling it to decouple and distinguish complex multi-degree of freedom joint motions (flexion/extension, abduction/adduction, circumduction). Its significance is demonstrated in metaverse applications, including creating a digital-twin of free-pose hand motions and enabling intuitive single-joint VR control, paving the way for next-generation wearable interfaces for biomechanics and immersive VR/AR.
6. Liquid metal nanoparticles physically hybridized with cellulose nanocrystals initiate and toughen hydrogels with piezoionic properties
P. Rahmani, A. Shojaei, T. Sakorikar, M. Wang, Y. Mendoza-Apodaca, M. D. Dickey
ACS Nano, 2024, 18(1), 1136-1150. (DOI)
This paper’s novelty lies in using cellulose nanocrystal-coated liquid metal (LM-CNC) as a multifunctional component that simultaneously initiates polymerization, acts as a physical cross-linker, and toughens the hydrogel, all without molecular initiators. It contributes to piezoionics by providing a robust, easily fabricated material platform where post-soaking in NaCl introduces high ionic conductivity and a clear piezoionic current from anion-dominant transport. The PAA/LM-CNC/NaCl hydrogel architecture is significant for its combination of extreme stretchability (~2000%), high toughness (~1.8 MJ/m³), efficient self-healing (~90%), and a self-powered touch response (~30 µA). This work demonstrates that high-performance mechanical and piezoionic properties can be integrated into a single, simple-to-synthesize material, paving the way for durable, self-powered wearable sensors and touch panels.
7. Ultrafast underwater self-healing piezo-ionic elastomer via dynamic hydrophobic-hydrolytic domains
Z. Kong, E. Boahen, D. Kim, F. Li, J. Kim, H. Kweon, S. Kim, H. Choi, J. Zhu, W. Ying, D. Kim
Nature Communications, 2024, 15, 2129. (DOI)
This work presents a molecularly engineered self-healing piezo-ionic elastomer (MESHPIE) that achieves ultrafast autonomous self-healing and high-pressure sensing in both ambient and aquatic environments. It advances the piezoionics field by integrating hydrophobic C–F groups and hydrolytic boronate ester bonds into a polyurethane matrix, creating a synergistic dynamic domain that repels bulk water while allowing minimal water ingress to accelerate bond reformation. This results in record self-healing speeds (9.1 µm/min in air, 13.3 µm/min underwater) and high efficiencies (~90%). The C–F groups also enable a "trap-and-release" ion-pumping mechanism via ion-dipole interactions, yielding a highly sensitive piezo-ionic pressure sensor (18.1 kPa⁻¹). Its significance is demonstrated in underwater robotics and tactile interfaces, where the material enables visual signal transmission via LED modulation upon impact, showcasing its potential for durable, water-resistant soft electronics and human-machine interfaces.
8. Piezoionic elastomers by phase and interface engineering for high-performance energy-harvesting-electronics
W. Zhu, B. Wu, Z. Lei, P. Wu
Advanced Materials, 2024, 36(11), 2313127. (DOI)
This work introduces a novel piezoionic elastomer that uniquely employs a microphase-separated structure with a bridging intermediate phase to resolve the classic trade-off between high voltage output and high current/stretchability in soft energy harvesters. It advances the field by achieving a record piezoionic coefficient (~6.0 mV/kPa) and power density (1.3 µW/cm³) for stretchable ionic materials. The methodology integrates ionic liquids and ionic plastic crystals within a PVDF-HFP matrix, where the hard phases concentrate stress for voltage while the soft/intermediate phases facilitate ion transport for current. This architecture enables simultaneous high toughness, self-healing, and sensitive acoustic/pressure sensing, paving the way for robust, high-performance ionotronic systems for human-machine interaction and self-powered sensing.
9. Bilayer piezoionic sensors for enhanced detection of dynamic, static, and directional forces with self-healing capabilities
Y. Kim, G. Lim, H. Cho, J. Kim, J. Kim, J. Yeom, D. Kang, H. Lee, D. Lim, S. Kim, H. Ko
Nano Energy, 2024, 127, 109749. (DOI)
This work introduces a novel bilayer piezoionic sensor that uniquely integrates self-healing, directional force detection, and simultaneous static/dynamic sensing into a single self-powered device. It advances the field by resolving the classic trade-off between self-powered dynamic sensing (piezoelectric/triboelectric) and static force detection, offering a versatile alternative to conventional e-skin. The methodology uses a bilayer structure of crosslinked PVDF-HFP elastomer and EMIM TFSI ionic liquid, where the internal interface acts as an ion-accumulation layer to amplify polarization. This architecture enhances the output voltage (~95 mV), enables fast response (30 ms), and provides ~100% self-healing via ion-dipole interactions. Its significance lies in enabling robust, multi-modal tactile perception for applications like Braille readers and texture discrimination, paving the way for durable, all-in-one iontronic skins for robotics and human-machine interfaces.
10. Intercellular ion-gradient piezoheterogated biphasic gel for ultrahigh iontronic generation
W. Chen, S. Zhang, A. Zhang, H. Liu, Z. Wu, L. Zhai, X. Dong, Z. Xu, Z. Zhao, L. Wen
Journal of the American Chemical Society, 2024, 146(50), 35478-35487. (DOI)
This work presents a bioinspired, biphasic gel that achieves record-high piezoionic power by mimicking the ion-gradient and selective transport mechanisms of electric eels. It significantly advances the field by demonstrating a power density of 150 W/m³, far exceeding previous piezoionic systems (<80 W/m³). The material is a microphase-separated gel consisting of cationic hydrogel compartments (acting as electric cells) within an oleophilic organogel matrix, creating multiple heterointerfaces that impose distinct energy barriers for cation vs. anion transport. This architecture, combined with stable, internally confined ion gradients, generates ultrahigh and sustained ionic flux. Its significance lies in enabling direct, efficient abiotic–biotic interfacing, as demonstrated by a piezoionic neuromodulation device that successfully regulates rodent blood pressure via vagus nerve stimulation.