Sunghoon Hur

In the native extracellular matrix, collagen fibrils regulate stem cell fate and tissue regeneration by modulating the number of serial kinks via intramolecular kinking and unkinking, which affects integrin ligation. However, biomimetic materials composed solely of multi‐kink‐bearing molecules for dynamic regulation of ligand exposure remain limited. In this study, we designed materials composed solely of liganded multiple kink‐bearing molecules with a tunable number of kink points (mono‐kink, tri‐kink, and penta‐kink molecules), including flexible linkers and densely packed via intermolecular interactions, are designed. Near‐infrared‐upconverted ultraviolet light and visible light induce multiple kinking and unkinking of liganded multiple kink‐bearing molecules conjugated to upconversion nanoparticle‐coated materials, inducing kinked and unkinked states, respectively. Tri‐kinking and unkinking mediate the effective regulation of ligand masking and exposure, respectively, by modulating intermolecular interactions, while mono‐kink and penta‐kink molecules continuously expose the ligands regardless of their kinking/unkinking state. Tri‐unkinking cyclically stimulates integrin ligation and focal adhesion‐mediated stem cell mechanotransduction and differentiation in vivo, which are inhibited by tri‐kinking. This study presents a newly developed reversibly switchable multi‐kink molecule‐conjugated surface for dynamic regulation of ligand exposure and stem cell responses, providing a useful modality for regulating cell–material interactions and stem cell fate in vivo.

While hydrogen peroxide (H ₂ O ₂ ) serves as a pivotal reagent across biomedical and environmental domains, its centralized production conflicts with the demand for on‐demand, spatially confined delivery. Ultrasound‐driven piezocatalysis directly converts mechanical energy into surface chemistry through piezoelectric polarization without electrodes or photons, enabling oxidant generation precisely where and when needed. Despite progress, the field lacks a unified framework connecting its mechanistic foundations, acoustic physics, and application potential. We systematically examine the two dominant mechanistic models; energy band theory and the screening charge effect, and discuss the H ₂ O ₂ pathway. The physical role of ultrasound is examined beyond its conventional treatment, distinguishing between pressure‐driven deformation and cavitation‐induced impulsive stress as distinct modes of energy transfer. Rather than a compilation of materials, we outline design strategies through which heterojunction engineering, geometric dimensionality, crystal structure modulation, and surface functionalization enhance charge separation and catalytic H ₂ O ₂ yield. Furthermore, we highlight applications ranging from cancer immunotherapy and implant infection control to environmental remediation. Crucially, its wireless and light‐free operation enables deployment in deep‐tissue and enclosed scenarios inaccessible to photocatalytic or electrochemical systems. Finally, this review establishes a clear framework for the rational design of next‐generation piezocatalysts.

Vat photopolymerization-based 3D printing is an emerging platform for fabricating high-performance piezoelectric ceramic–polymer composites with precise structural control. 3D printing processing of piezoelectric composites critically depends on the optimization of the interfacial chemistry and compatibility between ceramic fillers and polymer matrices. Specifically, the use of materials with excellent piezoelectric properties, an optimal formulation combined with dispersants and silane coupling agents that enhance uniform particle dispersion and strong interfacial adhesion, enables high ceramic loading at low viscosity critical for defect-free printing and facilitates the fabrication of high-performance piezoelectric composites. Structurally, architectural designs such as lattices and metamaterials enable localized stress concentration and anisotropic strain distribution, amplifying piezoelectric responses. Simulation-based materials and structural designs can also predict piezoelectric properties and bridge the gap between experiments and performance. Moreover, controlling the rheological properties and curing behavior is critical for achieving high-resolution, defect-free prints. This review highlights the synergistic roles of material design, structural architecture, and processing control in enhancing the electromechanical coupling of 3D-printed piezoelectric composites, thereby offering new pathways for advanced piezoelectric composite additive manufacturing applications.

Conventional electromagnetic generators are limited to low‐power applications owing to their mechanical complexity, bulky design, and reduced efficiency at small scales. Their performance is further hindered by the resistive torque according to Lenz's law, which makes them unsuitable for low‐load environments. To overcome these challenges, we propose a novel in‐wheel direct‐current piezoelectric generator (DC‐PG), which enables efficient power generation with zero resistive torque and does not require rectification. The system leverages continuous in‐phase polarization during rotation to deliver a stable low‐ripple DC output with minimal energy loss. Integrated into a suitcase wheel without adding weight or volume, the DC‐PG achieved a peak power of 4.28 mW under realistic conditions (20 kg load, 3–5 km/h), surpassing conventional AC‐based piezoelectric systems. It successfully powered a wireless Internet of things (IoT) location sensor, charging a 5 V capacitor in 134 s. This compact rectification‐free generator is a viable solution for small‐scale power generation and self‐powered IoT applications. Its high‐efficiency performance and elimination of electromagnetic resistance open new possibilities for energy autonomy in low‐speed, low‐load environments.

Wireless power transfer (WPT) technologies enable the remote transmission of electric charges without galvanic connections, offering promising applications in biomedical and environmental fields. Recent advancements in ultrasound‐driven triboelectric nanogenerators (US‐TENGs) address key technical challenges such as safety, deep penetration, compatibility, and tunability, enabling efficient electricity generation within biological tissues and fluidic environments. The emergence of US‐TENGs represents a pivotal advancement in WPT, particularly for powering rechargeable implantable bioelectronic systems, as well as battery‐free and self‐powered devices for biotherapy, and underwater energy transfer and communications. This review discusses the potential of US‐TENGs to enhance wireless energy harvesting in medical and environmental fields, emphasizing their integration and design with booster, flexible, biocompatible, and biodegradable materials to develop mechanically adaptive, efficient, stable, and minimally invasive systems. Roadmaps for various energy transfer applications of US‐TENGs are presented to show recent progress. Finally, the necessary developments for the classified functionalities are discussed to address remaining challenges.

Energy harvesting has drawn growing interest as a reliable power source for IoT applications, with piezoelectric materials notable for their high sensitivity and straightforward integration. Their robust mechanical‐electrical coupling also makes them ideal for harnessing environmental vibrations or mechanical motions. Still, standard piezoelectric harvesters inherently produce alternating current (AC), necessitating complex rectification steps and leading to substantial energy loss. This work introduces a direct current (DC) harvesting method that employs a novel in‐phase polarization strategy, enabling a stable, continuous DC output. This approach surpasses prior attempts that offered only low or pulsed DC signals, achieving an open‐circuit voltage of 33.44 V and a short‐circuit current of 3.72 mA with a size of 7.5 cm ² . A prototype generator demonstrated a maximum power output of 29.73 mW. Moreover, this design is both miniaturizable and scalable, broadening its potential deployment across diverse sectors. Its practical value was exemplified by directly powering CO ₂ electrolysis, where it achieveds a Faradaic efficiency of 86.22%, underscoring the method's ability to circumvent AC‐based inefficiencies and pave the way for more effective, sustainable energy solutions.