Zhuomin Zhang

Biomolecular piezoelectrics offer promising alternatives to ceramics for transient electronics and medical devices due to their intrinsic biocompatibility and biodegradability. Among them, β‐glycine exhibits high piezoelectricity, but its practical applications are severely limited by its inherent rigidity and its rapid destabilization in water‐rich environments. Here, we present a multi‐length‐scale engineering strategy that integrates molecular phase selection and stabilization with crystalline alignment and mesoscale composite design. β‐glycine crystals are incorporated as discrete inclusions within a continuous soft hydrophobic Poly(ε‐caprolactone) (PCL) matrix and co‐assembled with racemic DL‐methionine (DLM) to stabilize the piezoelectric β‐phase. A dual‐nozzle electrohydrodynamic spraying printing (DESP) method enables synchronized assembly, phase selection, and controlled orientation. The resulting 0–3 composites exhibit improved flexibility (469 MPa) and a high piezoelectric coefficient (175 mV m/N). The composites maintain β‐phase stability for over two months in aqueous environments, compared to rapid dissolution within seconds or phase transformation within hours for bare crystals. This work establishes a general framework for stabilizing metastable molecular piezoelectrics within flexible matrices for long‐term bio‐integrated applications interfacing with soft living systems.

Piezoionic hydrogels are emerging as innovative smart materials for integrating biological and electronic functionalities in sensors, energy harvesters, and medical devices. However, a clear understanding of the relationship between mechanical microstructures and directional ion transport remains elusive. A significant limitation of existing hydrogel electronics is their ultralow voltage response. To address this knowledge gap, we systematically analyze the influence of structural characteristics on the electrical response of piezoionic hydrogels and introduce a material property termed "tortuosity." Guided by this concept, we develop an artificial ion pump (AIP) hydrogel, characterized by low tortuosity in ion transport pathways and anisotropic deformability, attributed to its modified surface polarity and aligned porous structure. The reduced tortuosity factor (reduced to 35%) provides ordered pathways for ion transportation, reducing random diffusion in the matrix and enhancing directional ion transport efficiency. Simultaneously, the aligned porous structure concentrates stress during mechanical deformation, improving stress transfer and amplification within the hydrogel. This promotes the relative displacement of mobile ions, thereby enhancing the piezoionic effect. Consequently, the new AIP hydrogel achieved over 20 times higher coefficient compared to its unoptimized counterpart. These findings provide valuable insights into the structure-performance correlation in piezoionic materials. What's more, in the peripheral nerve regulation experiment in mice, the AIP hydrogel generator demonstrated the ability to synchronize with physiological rhythms while effectively regulating neural activity. This capability highlights potential applications in implant devices for self-powered sensing and electrical stimulation.

The piezoelectric effect enables the conversion between electrical and mechanical energy, making it essential across various fields. While synthetic piezoelectric ceramics and polymers are extensively utilized in electronics and biomedicine, their inherent rigidity, fragility, processing challenges, toxicity, and nondegradability limit their potential. In contrast, piezoelectric biomaterials offer a promising alternative for biomedical fields because of their natural biocompatibility, biodegradability, and environmental friendliness. However, weak piezoelectricity and challenges in large-scale fabrication hinder their applications. This paper critically reviews recent advances in piezoelectric biomaterials, focusing primarily on design strategies and manufacturing methods. We first summarize the principles, advantages, and categories of a variety of piezoelectric biomaterials. Next, we explore computational studies, highlight emerging approaches in molecular engineering and manufacturing, and examine their cutting-edge applications in bioelectronics and biomedicine. Additionally, we evaluate the effectiveness of various design and manufacturing approaches in enhancing piezoelectric performance, outlining their respective advantages and limitations. Finally, we discuss key challenges and provide insights into computational modeling, fabrication techniques, characterization methods, and biomedical applications to guide future research.

The thickness of film materials is a critical factor influencing properties such as energy density, optical performance, and mechanical strength. However, the long-standing challenge of the intrinsic thermodynamic limit on maximum thickness often leads to detrimental cracking, compromising these desirable properties. In this study, we present an approach called the stress-eliminated liquid-phase fabrication (SELF) method. The SELF method eliminates the need for substrates to support the precursor solution used for film fabrication. We harness the intrinsic surface tension of the solution by confining it within specifically designed grids in a framework, forming suspended liquid bridges. This technique enables fabrication of crack-free ceramic films within a broad thickness range from 1 to 100 μm. Furthermore, the fabricated PZT films exhibit a high piezoelectric coefficient (d₃₃) of 229 pC N⁻¹. The customizable grids not only offer design freedom for film topologies but also facilitate the fabrication of diverse film arrays without the need for destructive cutting processes. Moreover, the freestanding nature of these films enhances their adaptability for MEMS processing, and the “capillary bridge” topology allows the PZT films to be used in ultrasound focusing transmitter, providing possibilities in the medical imaging.

Shaping of ceramics is crucial. Current techniques cannot easily and rapidly shape ceramics without weakening their properties, especially for piezoceramics. We present an ultrafast ceramic shaping method that leverages thermomechanical fields to deform and sinter ceramic powder compacts into complex-shaped ceramics. The shape-forming process hinges on: (1) the implementation of a precise thermal field to activate optimal deformability, and (2) the application of sufficient mechanical loads to guide deformation. We employ a programmable carbon-felt Joule heater that concurrently function as mechanical carriers, effectively transferring applied loads to the ceramic powder compacts. Using this ultrafast shaping and sintering (USS) method, we fabricate barium titanate (BT) piezoceramics in twisted shape, arch shape and with micropatterns. The USS method is energy-friendly (requiring approximately 1.06 kJ mm⁻³) and time-efficient (in several minutes level). Overall, the USS method offers an effective solution for shaping ceramics and extends them to 3D geometries with enhanced versatility.

Piezoelectric biomaterials hold a pivotal role in the progression of bioelectronics and biomedicine, owing to their remarkable electromechanical properties, biocompatibility, and bioresorbability. However, their technological potential is restrained by certain challenges, including precise manipulation of nanobiomolecules, controlling their growth across nano-to-macro hierarchy, and tuning desirable mechanical properties. We report a high-speed thermal-electric driven aerosol (TEA) printing method capable of fabricating piezoelectric biofilms in a singular step. Electrohydrodynamic aerosolizing and in situ electrical poling allow instantaneous tuning of the spatial organization of biomolecular inks. We demonstrate TEA printing of β-glycine/polyvinylpyrrolidone films, and such films exhibit the piezoelectric voltage coefficient of 190 × 10 ⁻³ volt-meters per newton, surpassing that of industry-standard lead zirconate titanate by approximately 10-fold. Furthermore, these films demonstrate nearly two orders of magnitude improvement in mechanical flexibility compared to glycine crystals. We also demonstrate the ultrasonic energy harvesters based on the biofilms, providing the possibility of wirelessly powering bioelectronics.

Implantable medical devices (IMDs), like pacemakers regulating heart rhythm or deep brain stimulators treating neurological disorders, revolutionize healthcare. However, limited battery life necessitates frequent surgeries for replacements. Ultrasound power transfer (UPT) emerges as a promising solution for sustainable IMD operation. Current research prioritizes implantable materials, with less emphasis on sound field analysis and maximizing energy transfer during wireless power delivery. This review addresses this gap. A comprehensive analysis of UPT technology, examining cutting‐edge system designs, particularly in power supply and efficiency is provided. The review critically examines existing efficiency models, summarizing the key parameters influencing energy transmission in UPT systems. For the first time, an energy flow diagram of a general UPT system is proposed to offer insights into the overall functioning. Additionally, the review explores the development stages of UPT technology, showcasing representative designs and applications. The remaining challenges, future directions, and exciting opportunities associated with UPT are discussed. By highlighting the importance of sustainable IMDs with advanced functions like biosensing and closed‐loop drug delivery, as well as UPT's potential, this review aims to inspire further research and advancements in this promising field.

The intriguing biomineralization process in nature endows the mineralized biological materials with intricate microarchitected structures in a facile and orderly way, which provides an inspiration for processing ceramics. Here, we propose a simple and efficient manufacturing process to fabricate cellular ceramics in programmed cell-based 3D configurations, inspired by the biomineralization process of the diatom frustule. Our approach separates the ingredient synthesis from architecture building, enabling the programmable manufacturing of cellular ceramics with various cell sizes, geometries, densities, metastructures, and constituent elements. Our approach exploits surface tension to capture precursor solutions in the architected cellular lattices, allowing us to control the liquid geometry and manufacture cellular ceramics with high precision. We investigate the geometry parameters for the architected lattices assembled by unit cells and unit columns, both theoretically and experimentally, to guide the 3D fluid interface creation in arranged configurations. We manufacture a series of globally cellular and locally compact piezoceramics, obtaining an enhanced piezoelectric constant and a designed piezoelectric anisotropy. This bioinspired, surface tension-assisted approach has the potential to revolutionize the design and processing of multifarious ceramic materials for structural and functional applications in energy, electronics and biomedicine.

Nanoparticles, films, and patterns are three critical piezoelectric elements with widespread applications in sensing, actuations, catalysis and energy harvesting. High productivity and large-area fabrication of these functional elements is still a significant challenge, let alone the control of their structures and feature sizes on various substrates. Here, we report a fast and versatile electrostatic disc microprinting, enabled by triggering the instability of liquid-air interface of inks. The printing process allows for fabricating lead zirconate titanate free-standing nanoparticles, films, and micro-patterns. The as-fabricated lead zirconate titanate films exhibit a high piezoelectric strain constant of 560 pm V⁻¹, one to two times higher than the state-of-the-art. The multiplexed tip jetting mode and the large layer-by-layer depositing area can translate into depositing speeds up to 10⁹ μm³ s⁻¹, one order of magnitude faster than current techniques. Printing diversified functional materials, ranging from suspensions of dielectric ceramic and metal nanoparticles, to insulating polymers, to solutions of biological molecules, demonstrates the great potential of the electrostatic disc microprinting in electronics, biotechnology and beyond.

Low-resistance contact has long been pursued in the two-dimensional (2D) electronic/optoelectronic device community. Still, an economy-efficient method highly compatible with the conventional 2D device fabrication process in laboratory remains to be explored. Herein, we report a plasma-optimized contact strategy for high-performance PdSe2 nanoflake-based field-effect transistors (FETs). Selenium vacancies created by air plasma can introduce p-type doping in the contact area, thus optimizing the device performance. The effect of plasma treatment on PdSe2 nanoflake is corroborated by high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy spectrum, atomic force microscopy, and Kelvin probe force microscopy. The PdSe2 FET with plasma-optimized contact exhibits significantly improved field-effect carrier mobilities, current on/off ratios, and reduced contact resistance than that without plasma treatment fabricated from the same PdSe2 nanoflake. Moreover, this strategy has also been proven effective to prepare high-performance FETs based on 2D WSe2 and MoSe2 nanoflakes, further demonstrating its application prospect.