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Nanogenerators for Biomechanical Energy Harvesting and Biomedical Applications
The nanogenerator is a technology that converts micro- or nano-scale mechanical energy into electricity. A nanogenerator utilizes nanostructured functional materials as building blocks to generate electricity from physical displacement via the piezoelectric or triboelectric effect. Human body is a rich source of biomechanical energy. Many regular body motions, such as muscle stretching, breathing, heart beating, blood pressure fluctuation, etc. provide versatile selections for energy harvesting by nanogenerators, enabling self-powered operation of wearable and implantable biomedical devices.

Our research in this category focuses on the development of wearable and implantable nanogenerators. Our specific research directions are:

•  Developing implantable or wearable nanogenerators with desired biocompatibility, flexibility and conformality on different muscle and skin surfaces.

•  Developing nanogenerators for harvesting energy from heart beats to serve as a sole power source for implant pacemakers.

•  Developing nanogenerator-driven electrostimulation devices for therapeutic treatments, such as vagus nerve stimulation, skin wound recovery, and hair regeneration.

Novel piezoelectric materials and enhanced properties

The piezoelectric phenomenon depicts a coupling between mechanical displacement and electric polarization. It has been applied in many different areas, such as sensors, energy transducers, and actuators since its discovery century ago. Currently, novel applications of piezoelectric materials placed new requirements on the materials properties, such as nano-structuring, three-dimensional configuration, flexibility, biocompatibility, and multi-property coupling.

Our research in this category focuses on the development of novel piezoelectric and composites with new dimensionality, geometry, and the study of multiple coupling properties. Our specific research directions are:

•  Synthesizing 2D piezoelectric materials, such as ZnO and characterizing its size-related piezoelectric polarization at the nanometer scale, particularly due to the flexoelectric enhancement.

•  Developing flexible piezoelectric and ferroelectric materials and composites with tunable mechanical modulus that matches that of body tissues.

•  Designing and fabricating 3D piezoelectric and ferroelectric geometry by additive manufacturing.

•  Developing biocompatible or biodegradable piezoelectric materials from biomaterials.

•  Studying the coupling effects between piezoelectric polarization and electrochemical processes (piezotronics).

Two-dimensional (ultrathin) oxide nanomaterials

Since the discovery of graphene, the family of 2D materials has been rapidly expanded toward a broad range of materials including transition metal dichalcogenides, Mxenes, MOFs, oxides and pure organics. Thus far, study of 2D nanostructures are largely focused on naturally layered materials, i.e. the van der Waals (vdW) solids. Nevertheless, most binary oxides have three dimensional lattices. It is extremely challenging to form 2D geometry of this group of materials to enable the intriguing 2D-related properties.

The ionic layer epitaxy (ILE) technique developed in our group offers an ideal solution to the synthesis of 2D structure from materials with 3D lattices, such as oxides and metals. Their new 2D geometry brings many new or enhanced physical and chemical properties. Our research in this category focuses on the growth and property characterization of new 2D materials beyond vdW solids, particularly from oxide materials. Specific research directions include:

•  Understanding the growth mechanism and geometry control of 2D materials by ILE.

•  Studying novel physical (e.g. electronic, ferromagnetic, and piezoelectric) properties related to the ultrathin structure of 2D oxide materials.

•  Developing of 2D materials from electrocatalytic materials to improve their electrochemical performance and preserve precious elements.

•  Studying the intermediate phase evolution of amorphous oxide materials by atomic layer deposition to develop stable nanolayers for catalyst protection.

Our thanks to Jenny Morber for text editing jennymorber.com

Professor Xudong Wang's Nanoscience and Nanotechnology Group
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