The magnetoelastic effect—the variation of the magnetic properties of a material under mechanical stress—is usually observed in rigid alloys, whose mechanical modulus is significantly different from that of human tissues, thus limiting their use in bioelectronics applications. Here, we observed a giant magnetoelastic effect in a soft system based on micromagnets dispersed in a silicone matrix, reaching a magnetomechanical coupling factor indicating up to four times more enhancement than in rigid counterparts. The results are interpreted using a wavy chain model, showing how mechanical stress changes the micromagnets’ spacing and dipole alignment, thus altering the magnetic field generated by the composite. Combined with liquid-metal coils patterned on polydimethylsiloxane working as a magnetic induction layer, the soft magnetoelastic composite is used for stretchable and water-resistant magnetoelastic generators adhering conformably to human skin. Such devices can be used as wearable or implantable power generators and biomedical sensors, opening alternative avenues for human-body-centred applications. Micromagnets dispersed in a polymer matrix are used to realize a soft magnetoelastic generator with high magnetomechanical coupling factor, used for wearable and implantable power generation and sensing applications.

Giant magnetoelastic effect in soft systems for bioelectronics.

From every heartbeat to every footstep, human beings dissipate energy all the time. Researchers are trying to harvest energy from the human body and convert it into electricity, which can be supplied to electronic medical devices closely related to human health. Such an energy recycling form is currently a research hotspot in the fields of energy harvesting and bioelectronics. This review firstly summarizes the distribution and characteristics of three primary energy sources contained in the human body, including thermal energy, chemical energy, and mechanical energy. Afterwards, the applicable energy harvesting technologies and corresponding working mechanisms for different energy sources are introduced. Some typical demos and practical applications of each type of human body energy harvesting technology are also presented. Specifically, the advantages and critical issues of different energy harvesting technologies are summarized, and corresponding promising solutions are also provided. Besides, the interaction strategies between various energy harvesting devices and the human body are summarized from the aspects of wearable and implantable applications. Finally, the concept of a self-powered closed-loop bioelectronic system (SCBS) is put forward for the first time, which organically combines portable electronic devices, implantable electronic medical devices, energy harvesting devices, and the human body. The prospect of symbiosis between the SCBS and the human body is provided. The demands and future development trends of the SCBS are also discussed.

Recent progress in human body energy harvesting for smart bioelectronic system

The development of flexible piezoelectric nanogenerators has experienced rapid progress in the past decade and is serving as the technological foundation of future state-of-the-art personalized healthcare. Due to their highly efficient mechanical-to-electrical energy conversion, easy implementation, and self-powering nature, these devices permit a plethora of innovative healthcare applications in the space of active sensing, electrical stimulation therapy, as well as passive human biomechanical energy harvesting to third party power on-body devices. This article gives a comprehensive review of the piezoelectric nanogenerators for personalized healthcare. After a brief introduction to the fundamental physical science of the piezoelectric effect, material engineering strategies, device structural designs, and human-body centered energy harvesting, sensing, and therapeutics applications are also systematically discussed. In addition, the challenges and opportunities of utilizing piezoelectric nanogenerators for self-powered bioelectronics and personalized healthcare are outlined in detail.

Piezoelectric nanogenerators for personalized healthcare.

Strategies toward harvesting energy from water movements are proposed in recent years. Reverse electrowetting allows high efficiency energy generation, but requires external electric field. Triboelectric nanogenerators, as passive energy harvesting devices, are limited by the unstable and low density of tribo-charges. Here, a charge trapping-based electricity generator (CTEG) is proposed for passive energy harvesting from water droplets with high efficiency. The hydrophobic fluoropolymer films utilized in CTEG are pre-charged by a homogeneous electrowetting-assisted charge injection (h-EWCI) method, allowing an ultrahigh negative charge density of 1.8 mC m-2 . By utilizing a dedicated designed circuit to connect the bottom electrode and top electrode of a Pt wire, instantaneous currents beyond 2 mA, power density above 160 W m-2 , and energy harvesting efficiency over 11% are achieved from continuously falling water droplets. CTEG devices show excellent robustness for energy harvesting from water drops, without appreciable degradation for intermittent testing during 100 days. These results exceed previously reported values by far. The approach is not only applicable for energy harvesting from water droplets or wave-like oscillatory fluid motion, but also opens up avenues toward other applications requiring passive electric responses, such as diverse sensors and wearable devices.

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Charge Trapping‐Based Electricity Generator (CTEG): An Ultrarobust and High Efficiency Nanogenerator for Energy Harvesting from Water Droplets

Flexible self-charging power sources

The low output current density of piezoelectric nanogenerators (PENGs) severely restricts their application for ambient mechanical energy harvest. This has been a key challenge in the development of PENG. Here, to conquer this, based on a piezoelectric material with high piezoelectric coefficient (Sm-PMN-PT), a new design of PENG with a three-dimensional intercalation electrode (IENG) is proposed. By creating many boundary interfaces inside the piezoelectric material, the total amount of surface polarization charges increased, which contributes to an increased current density. The IENG can output a maximum peak short-circuit current of 320 μA, and the corresponding current density 290 μA cm−2 is 1.93 and 1.61 times the record values of PENG and triboelectric nanogenerator (TENG), respectively. It can also charge a 1 μF capacitor from 0 V to 8 V in 21 cycles, and the equivalent surface charge density 1690 μC m−2 is 1.35 times the record value of TENG. Increasing the output current density is the key challenge for nanogenerators. Here, a new piezoelectric nanogenerator with a three-dimensional intercalation electrode is developed to reach 290 μA cm−2 by creating and utilizing many boundary interfaces.

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Enhancing the current density of a piezoelectric nanogenerator using a three-dimensional intercalation electrode.

Highly sensitive strain sensors based on piezotronic tunneling junction

The output current from a triboelectric nanogenerator (TENG) primarily depends on the amount of triboelectric charge existing on the friction layer. The triboelectric charge capacity and charge-driving ability of the friction layer are the key parameters for enhancing the output performance of a TENG. In this paper, we developed a new TENG with a multigap-structured friction layer. The presence of these gaps creates additional contacts between the friction layers, which can induce additional separated triboelectric charges and increased output charge quantity. Moreover, because of these gaps, the TENG generates more output current pulses for each driving cycle, which implies that the frequency of the output current can be several times the driving frequency. In one driving cycle, a generic TENG without any gaps in the friction layer generates 2 current pulses and a unit area charge quantity per cycle (UCQC) value of 0.23 nC cm−2, while a TENG with seven gaps in the friction layer can generate around 14 current output pulses and UCQC value of 294 nC cm−2, which is 1.18 times the value of the record one. This work can contribute toward a rapid increase in TENG performance, thereby accelerating its applications.

Increasing the output charge quantity of triboelectric nanogenerators via frequency multiplication with a multigap-structured friction layer

Harvesting energy from the surrounding environment, particularly from human body motions, is an effective way to provide sustainable electricity for low-power mobile and portable electronics. To get adapted to the human body and its motions, we report a new fiber-based triboelectric nanogenerator (FTNG) with a coaxial double helix structure, which is appropriate for collecting mechanical energy in different forms. With a small displacement (10 mm at 1.8 Hz), this FTNG could output 850.20 mV voltage and 0.66 mA m−2 current density in the lateral sliding mode, or 2.15 V voltage and 1.42 mA m−2 current density in the vertical separating mode. Applications onto the human body are also demonstrated: the output of 6 V and 600 nA (3 V and 300 nA) could be achieved when the FTNG was attached to a cloth (wore on a wrist). The output of FTNG was maintained after washing or long-time working. This FTNG is highly adaptable to the human body and has the potential to be a promising mobile and portable power supply for wearable electronic devices.

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Coaxial double helix structured fiber-based triboelectric nanogenerator for effectively harvesting mechanical energy

Globally, bladder cancer (BLC) is one of the most common cancers and has a high recurrence and mortality rate. Current clinical diagnostic approaches are either invasive or inaccurate. Here, we report on a cost-efficient, artificially intelligent chemiresistive sensor array made of polyaniline (PANI) derivatives that can noninvasively diagnose BLC at an early stage and maintain postoperative surveillance through ″smelling″ clinical urine samples at room temperature. In clinical trials, 18 healthy controls and 76 BLC patients (60 and 16 at early and advanced stages, respectively) are assessed by the artificial olfactory system. With the assistance of a support vector machine (SVM), very high sensitivity and accuracy from healthy controls are achieved, exceeding those obtained by the current techniques in practice. In addition, the recurrences of both early and advanced stages are diagnosed well, with the effect of confounding factors on the performance of the artificial olfactory system found to have a negligible influence on the diagnostic performance. Overall, this study contributes a novel, noninvasive, easy-to-use, inexpensive, real-time, accurate method for urine disease diagnosis, which can be useful for personalized care/diagnosis and postoperative surveillance, resulting in saving more lives.

Tao Du

Papers

Enhancing the current density of a piezoelectric nanogenerator using a three-dimensional intercalation electrode.

Highly sensitive strain sensors based on piezotronic tunneling junction

Increasing the output charge quantity of triboelectric nanogenerators via frequency multiplication with a multigap-structured friction layer

Coaxial double helix structured fiber-based triboelectric nanogenerator for effectively harvesting mechanical energy

Artificially Intelligent Olfaction for Fast and Noninvasive Diagnosis of Bladder Cancer from Urine.