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Device-assisted practice for instrument learning has been widely used by professional and amateur musicians to improve their learning efficiency. This study fabricates a novel self-powered and flexible player-interactive patch for guitar-learning assistance based on a piezoelectric T-ZnO/PVDF film. The system consists primarily of three parts: a flexible piezoelectric T-ZnO/PVDF film for pressure sensing, a signal processing module for analyzing the sensed signal, and light-emitting diode (LED) indicators for visualizing guitar performance. The sensing film can be conformably fixed on a guitar and can convert the mechanical energy generated by pressing a finger on a string into a piezoelectric signal without any external power supply. The output voltage of the film can act as a sensing signal for guitar performance, and both the response and recovery times are short. As fingers press on different strings, a series of piezoelectric signals are generated and transferred to the signal processing module, subsequently lighting up LEDs of different colors. The actions of the fingers during guitar playing are reflected by the corresponding LED indicators. The proposed system can help players adjust their posture and rhythm in real time, thus improving their playing technique. This study demonstrates the potential application of self-powered sensing systems in musical instrument learning assistance.

Bone traumatic injuries, enduring a prolonged healing process since it involves a series of bio events, becomes gradually challenging with increasing aging population. The integration of a home-based therapy strategy with emerging microelectronic technology holds promise for optimizing the whole long-term healing process of bone defect. Given the bioelectric properties of bone, utilizing biomedical electronics to providing external electric field (EF) is preferred for physical therapy strategies. Our study provides a wireless implantable bone-electronic interface (IBEI) based on ultrasonic-driven battery-free piezoelectric technology. The IBEI without percutaneous leads can effectively complete the process of converting ultrasonic signals into electric signals and finally into biological signals for bone repair. This system is miniatured, battery-free, wireless, controllable, biocomfortable and biosafe with high osteogenic efficiency. For the underlying mechanism, the EF can activate multicellular synergistic osteogenesis and up-regulate the Ca2+/CaMKIIα/CREB signal pathway in osteogenesis effector cells. The IBEI aligns with the future trajectory of home-based medicine, presenting a commendable therapy pattern for doctor-patient collaboration and offering a novel perspective in the realm of physical therapy.

Piezoelectric shunt damping is promising in vibration suppression of thin structures. A Low-power direct adaptive synchronized switch damping on voltage (LDA-SSDV) circuit is designed to solve the stability problem of the SSDV without additional vibration strength monitoring devices. Based on the linear relationship between the maximum piezovoltage and the values of series voltage sources, we use simple envelope detectors and resistive voltage dividers to control the voltage sources. And the voltage sources are activated during the switching events for saving energy. The experimental results show that the LDA-SSDV circuit has a stable operation and similar vibration suppression level compared to SSDV.

The amalgamation of high-sensitivity gas sensors with neural electrical stimulation technology stands as a compelling solution for eliciting behavioral responses in the presence of low-level hazardous gases. The utilization of battery-powered or coil-based configurations introduces spatiotemporal limitations, encompassing constrained experimental durations due to battery life or the necessity to confine subjects to specific locales for wireless power transmission. In this study, we present an advanced wireless neural modulator, meticulously engineered for behavioral intervention in unrestricted environments. This device integrates a solar-powered unit, gas sensor, brain stimulation signal management system, and a neurostimulation electrode. The solar energy utilization eliminates the necessity for battery replacements and local range limitations. The surface of the solar cells is treated with a superhydrophobic coating, enhancing performance in outdoor settings by mitigating surface contamination issues inherent in traditional solar cells. This innovation guarantees continuous, long-term, on-demand operational capacity, ensuring uninterrupted power supply to the system. Experimentation revealed extended locomotor activity in mice, induced by stimulation of the periaqueductal gray (PAG) brain region, for up to thirty minutes. These results underscore the significant potential of our technology for spatially and temporally unrestricted neuromodulatory applications, offering a viable strategy to alleviate the detrimental effects of hazardous gas exposure on physiological functions.

For both professional and amateur athletes, perspiration analysis technique is considered as a powerful tool for real-time monitoring the athletes’ physiological status during sports. This study presents an innovative self-powered wireless sweat-analysis patch worn on the skin for real-time monitoring chloride concentration and pH levels in perspiration. The patch consists of two main components: self-powered unit and sensing unit. The power unit, made of piezoelectric ceramic materials, converts mechanical energy during exercise into electrical energy to drive the whole system. The sensing unit has the functions of sampling and analyzing the sweat, and wireless communication. Through an exactly designed hydrophobic and hydrophilic composite microchannel structure, sweat is effectively guided to the storage chamber. The colorimetric fabrics embedded in the chamber respond to the presence of chloride ions and pH levels in the sweat, producing a color-changing reaction. Color sensors above the fabrics detects these color changes for analyzing the sweat, while Near Field Communication (NFC) technology wirelessly transmits this information to outside mobile devices or data-collection cloud. This system not only provides a new avenue for real-time monitoring of athletes’ health status but also offers a scientific basis for adjusting training plans.

Optimal orthodontic forces need to be applied to induce appropriate biological and mechanical reactions in the periodontium, thus leading to proper tooth movements, while excessive orthodontic forces could harm the tooth roots and periodontal tissues during treatment. However, estimating orthodontic forces currently relies on clinical experience, lacking objective data and analysis; thus monitoring the in-vivo orthodontic force is essential to reducing side effects and improving orthodontic treatment. Unfortunately, in-vivo orthodontic force sensor systems are currently not available, and in-vitro ones are mostly bulky and costly. Here, we report a battery-free and wireless orthodontic force sensing system (BWS) designed for in-vivo, contactless, and real-time measurement of the orthodontic force. We developed a 915MHz far-field RF energy harvesting system to power the intraoral BWS, and achieved an in vivo wireless measurement distance of 220mm. This system allows in-vivo orthodontic force monitoring at anytime and anywhere, so it can be applied to improve clinical treatments and orthodontic research. Besides, in vivo experiments demonstrate that the system can harvest a voltage of 2V even at a 350mm distance, which highlights the device's potential to serve as a versatile platform for monitoring various oral environmental parameters through different sensors.

Cancer is a growing global health concern, and photodynamic therapy (PDT) has emerged as a promising technology with minimal side effects for cancer treatment. Miniaturized PDT devices that offer a flexible and convenient strategy for the low-dose delivery of light or drugs are needed to replace invasive optical fibers. Here, we present a self-powered, wireless, and detachable drug/light injector that conforms to the properties of metronomic PDT for cancer treatment. The device comprises a semi-invasive pedestal with a micro light emitting diode (μ-LED) and a syringe needle, and a detachable actuator that contains a drug reservoir, a thermally-driven pump, and a wireless control circuit. The two parts are magnetically attracted to each other, and the detachable actuator can be conveniently replaced or refilled with drugs. The device can be wirelessly controlled to deliver on-demand dosages of drugs and light into the tumor under the skin. Additionally, we further demonstrate that the device can in principle be partially self-powered using body motion energy upon connection to different piezoelectric nanogenerators. In-vitro and in-vivo experiments on mice have demonstrated the feasibility of the device's therapeutic regimen for implementing metronomic PDT. The average volume of tumors in the treatment group was reduced by 57.4 % compared to the control group. This device has potential applications in future clinical cancer treatment and can expand the scope of self-powered systems for biomedical engineering.

Hypertension, a common cardiovascular disorder characterized by elevated blood pressure levels, is conventionally managed using pharmacological interventions to achieve optimal blood pressure control. In this study, a novel self-powered, biocompatible brain probe is presented as a potential long-term and remote approach to blood pressure regulation. The device consists of a piezoelectric transducer, an electronic module, brain stimulating electrodes, and a drug microneedle array. As the resonator, the piezoelectric transducer is embedded in resonant structure within resin shell, enabling the harvesting of acoustic energy from smartphone audio tone without any external power sources. By programming specific audio signals, the resonator can be activated, and the electronic module can output corresponding electrostimulation signals on demand. Implanted brain stimulating electrodes in the ventrolateral periaqueductal grey matter (vlPAG) of rats can be wirelessly controlled by the smartphone, resulting in a significant reduction in blood pressure of approximately 20 mmHg. The device's drug microneedle array, located beneath the pedestal of device, can deliver antibiotics percutaneously to prevent post-surgical infections, indicating a biocompatible approach for long-term hypertension treatment. This novel, self-powered and wireless treatment has significant potential for clinical hypertension therapy and may broaden the scope of self-powered techniques for telemedicine and brain-machine interfaces.

This paper applies bootstrap methods to LM tests (including LM-lag test and LM-error test) for spatial dependence in panel data models with fixed effects, and removes fixed effects based on orthogonal transformation method proposed by Lee and Yu (2010). The consistencies of LM tests and their bootstrap versions are proved, and then some asymptotic refinements of bootstrap LM tests are obtained. It shows that the convergence rate of bootstrap LM tests is O((NT)−2) and that of fast double bootstrap LM tests is O((NT)−5/2). Extensive Monte Carlo experiments suggest that, compared to aysmptotic LM tests, the size of bootstrap LM tests gets closer to the nominal level of signifiance, and the power of bootstrap LM tests is higher, especially in the cases with small spatial correlation. Moreover, when the error is not normal or with heteroskedastic, asymptotic LM tests suffer from severe size distortion, but the size of bootstrap LM tests is close to the nominal significance level. Bootstrap LM tests are superior to aysmptotic LM tests in terms of size and power.

Humans have evolved to walk highly efficiently to conserve energy, making it challenging to develop assistive and energy-harvesting devices for walking. Herein, we report a heel pad-based assistance device for walking that not only optimizes the energetic economy of walking and prevents plantar fasciitis but also harvests energy from heel impact. Our footwear-embedded device improves the walking economy by offering shock absorption and walking assistance, while simultaneously providing energy-harvesting functions. We demonstrate that the use of our device reduces the activation of the gastrocnemius and soleus muscles during the foot strike by 5.8 ± 1.0 % and 4.1 ± 0.6 %, respectively. The collisional energy conserved from the impact at the touchdown is transformed into 3.8 ± 0.3 watts of electrical power (mean ± SEM). Compared with walking in normal shoes, the energy savings with the device imply that walking endurance could be increased by as much as 10 % without extra effort from the wearer. Our findings demonstrate the potential of the heel pad-based device that enhances the energy economy of walking and human bipedal locomotion.

The neural regulation that is tele-controlled remotely by medical professionals or artificial intelligence (AI) agents can meet the requirement of rapid, precise, personalized intervention and optimize the allocation of medical resources. Here, we develop a new self-powered wireless mini-invasive brain probe for remote intelligent neuroregulation. The probe can be wirelessly powered and controlled by cellphone audio tones (through piezoelectric effect) with the assistance of AI cellphone video analysis. The probe consists of a biocompatible pedestal integrated with implanting stimulation electrodes connected to embedded magnets and a magnetically coupled custom-designed signal-intensifying resonator integrated with a piezoelectric powered signal modulation circuit. A programmed audio tone functions as the wireless power source, and it can be tele-transmitted remotely from other cellphones with desired neural stimulation protocols. Combined with AI-enabled video monitoring of the epileptic tremor, we show that the probe can relieve the seizure events in the epileptic mice, and the therapeutic effect is confirmed by in-vivo electroencephalography and free-moving scenario. The multi-functionality of versatility, AI-assistance, wireless power transfer, and tele-transmission of the cellphone-interacted brain probe opens the possibility for remote precision neural modulation.

Wrist-worn smart devices such as smartwatches and wristbands are rapidly penetrating our daily life for health, security and fashion purposes. However, the battery-powered wearables have a limited lifetime and need to be frequently recharged, which degrades user experience and further poses environmental problems. Inspired by the structure of the woodpecker’s head, this paper reports a bionic two-layer band piezoelectric energy harvester for self-powered smartwatches and wristbands. An inner band and an outer band of the harvester mimic two branches of the hyoid bone of the woodpecker. The energy harvesting unit employs a piezoelectric array structure. A finite element analysis is conducted to identify the optimal positions of piezoelectric patches in the array and an improved rectifier circuit is developed to manage the multiple AC inputs. We design two operation modes, i.e., movement mode and impact mode, to accommodate energy harvesters in different human activities. A maximum power output of 15.41 mW is achieved in experiments when tapping the prototype, corresponding to an equivalent power density of 1049.01 μW/cm3, around five times higher than previous wrist-worn harvesters. The design demonstrates its capability of continuously powering a watch and a screen during a normal walking process. The concept of shifting from the watch body to watch bands provides the design of energy harvesters a larger space and higher user-friendliness, which, fused with the piezoelectric array method, shows the potential to merge the gap of the power generation of energy harvesters and the power consumption of wrist wearables.