Harvesting biomechanical energy in vivo is an important route in obtaining sustainable electric energy for powering implantable medical devices. Here, we demonstrate an innovative implantable triboelectric nanogenerator (iTENG) for in vivo biomechanical energy harvesting. Driven by the heartbeat of adult swine, the output voltage and the corresponding current were improved by factors of 3.5 and 25, respectively, compared with the reported in vivo output performance of biomechanical energy conversion devices. In addition, the in vivo evaluation of the iTENG was demonstrated for over 72 h of implantation, during which the iTENG generated electricity continuously in the active animal. Due to its excellent in vivo performance, a self-powered wireless transmission system was fabricated for real-time wireless cardiac monitoring. Given its outstanding in vivo output and stability, iTENG can be applied not only to power implantable medical devices but also possibly to fabricate a self-powered, wireless healthcare monitoring system.

The low utilization of active sites and sluggish reaction kinetics of MoSe severely impede its commercial application as electrocatalyst for hydrogen evolution reaction (HER). To address these two issues, the first example of introducing 1T MoSe and N dopant into vertical 2H MoSe /graphene shell/core nanoflake arrays that remarkably boost their HER activity is herein described. By means of the improved conductivity, rich catalytic active sites and highly accessible surface area as a result of the introduction of 1T MoSe and N doping as well as the unique structural features, the N-doped 1T-2H MoSe /graphene (N-MoSe /VG) shell/core nanoflake arrays show substantially enhanced HER activity. Remarkably, the N-MoSe /VG nanoflakes exhibit a relatively low onset potential of 45 mV and overpotential of 98 mV (vs RHE) at 10 mA cm with excellent long-term stability (no decay after 20 000 cycles), outperforming most of the recently reported Mo-based electrocatalysts. The success of improving the electrochemical performance via the introduction of 1T phase and N dopant offers new opportunities in the development of high-performance MoSe -based electrodes for other energy-related applications.

Piezoelectric biomaterials are intrinsically suitable for coupling mechanical and electrical energy in biological systems to achieve in vivo real-time sensing, actuation, and electricity generation. However, the inability to synthesize and align the piezoelectric phase at a large scale remains a roadblock toward practical applications. We present a wafer-scale approach to creating piezoelectric biomaterial thin films based on γ-glycine crystals. The thin film has a sandwich structure, where a crystalline glycine layer self-assembles and automatically aligns between two polyvinyl alcohol (PVA) thin films. The heterostructured glycine-PVA films exhibit piezoelectric coefficients of 5.3 picocoulombs per newton or 157.5 × 10−3 volt meters per newton and nearly an order of magnitude enhancement of the mechanical flexibility compared with pure glycine crystals. With its natural compatibility and degradability in physiological environments, glycine-PVA films may enable the development of transient implantable electromechanical devices.

Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase- and morphology-modulated N-doped MoSe /TiC-C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC-C nanorod arrays serve as the backbone for MoSe nanosheets to form high-quality MoSe /TiC-C shell/core arrays. Impressively, continuous phase modulation of MoSe is realized on the MoSe /TiC-C arrays. Except for the pure 1T-MoSe and 2H-MoSe , mixed (1T-2H)-MoSe nanosheets are achieved in the N-MoSe by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer HSe bond length, and diminished bandgap endow N-MoSe /TiC-C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N-MoSe /TiC-C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm , and a small Tafel slope of 32 mV dec . Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.

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Current bioelectronics are facing a paradigm shift from old-fashioned unrecyclable materials to green and degradable functional materials with desired biocompatibility. As an essential electromechanical coupling component in many bioelectronics, new piezoelectric materials are being developed with biodegradability, as well as desired mechanical and electromechanical properties for the next generation implantable and wearable bioelectronics. In this review, we provide an overview of the major advancements in biodegradable piezoelectric materials. Different natural (such as peptide, amino acids, proteins, cellulose, chitin, silk, collagen, and M13 phage) and synthetic piezoelectric materials (such as polylactic acid) are discussed to reveal the underlying electromechanical coupling mechanism at the molecular level, together with typical approaches to the alignment of orientation and polarization to boost their electromechanical performance. Meanwhile, in vivo and in vitro degradation manners of those piezoelectric materials are summarized and compared. Representative developments of typical electronic prototypes leveraging these materials are also discussed. At last, challenges toward practical applications are pointed out together with potential research opportunities that might be critical in this new materials research area.

Wearable and implantable electroceuticals (WIEs) for therapeutic electrostimulation (ES) have become indispensable medical devices in modern healthcare. In addition to functionality, device miniaturization, conformability, biocompatibility, and/or biodegradability are the main engineering targets for the development and clinical translation of WIEs. Recent innovations are mainly focused on wearable/implantable power sources, advanced conformable electrodes, and efficient ES on targeted organs and tissues. Herein, nanogenerators as a hotspot wearable/implantable energy-harvesting technique suitable for powering WIEs are reviewed. Then, electrodes for comfortable attachment and efficient delivery of electrical signals to targeted tissue/organ are introduced and compared. A few promising application directions of ES are discussed, including heart stimulation, nerve modulation, skin regeneration, muscle activation, and assistance to other therapeutic modalities.

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