Robotic prostheses and powered exoskeletons are novel assistive robotic devices for modern medicine. Muscle activity sensing plays an important role in controlling assistive robotics devices. Most devices measure the surface electromyography (sEMG) signal for myoelectric control. However, sEMG is an integrated signal from muscle activities. It is difficult to sense muscle movements in specific small regions, particularly at different depths. Alternatively, traditional ultrasound imaging has recently been proposed to monitor muscle activity due to its ability to directly visualize superficial and at-depth muscles. Despite their advantages, traditional ultrasound probes lack wearability. In this paper, a wearable ultrasound (US) transducer, based on lead zirconate titanate (PZT) and a polyimide substrate, was developed for a muscle activity sensing demonstration. The fabricated PZT-5A elements were arranged into a 4 × 4 array and then packaged in polydimethylsiloxane (PDMS). In vitro porcine tissue experiments were carried out by generating the muscle activities artificially, and the muscle movements were detected by the proposed wearable US transducer via muscle movement imaging. Experimental results showed that all 16 elements had very similar acoustic behaviors: the averaged central frequency, −6 dB bandwidth, and electrical impedance in water were 10.59 MHz, 37.69%, and 78.41 Ω, respectively. The in vitro study successfully demonstrated the capability of monitoring local muscle activity using the prototyped wearable transducer. The findings indicate that ultrasonic sensing may be an alternative to standardize myoelectric control for assistive robotics applications.

Re-poling of unexpected partially depoled piezoelectric materials conventionally needs to be first fully depoled through annealing above their Curie temperature to revive piezoelectric performances. Here, we investigated de-poling and re-poling of Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystals under electric fields at room temperature. We found that alternating current electric fields with amplitudes near the coercive field at low frequencies (<10 Hz) can be employed to successfully depolarize poled crystals at room temperature. We also demonstrated a reversible polarization switching process with a relaxor-PbTiO₃ single crystal ultrasound transducer without device performance degradations. This experimental observation is supported by phase-field simulation, showing that alternating current electric fields can readily induce de-poling at room temperature, while direct current electric fields induce a transient depoled state only within an uncontrollable short period of time. The findings suggest new strategies for unprecedented in-device tailoring of the polarization states of ferroelectric materials.

To address the need for high-resolution imaging in lung nodule detection and overcome the limitations of the shallow imaging depth associated with high-frequency ultrasound and the complex structure of lung tissue, we successfully integrated 50 MHz ultrasound transducers with 18-gauge biopsy needles. Featuring a miniaturized size of 0.6 × 0.5 × 0.5 mm³, the 50 MHz micromachined 1-3 composite transducer was tested to perform mechanical scanning of a nodule within a lung-tissue-mimicking phantom in vitro. The high-frequency transducer demonstrated the ability to achieve imaging with an axial resolution of 30 μm for measuring nodule edges. Moreover, the integrated biopsy needle prototype exhibited high accuracy (1.74% discrepancy) in estimating nodule area compared to actual dimensions in vitro. These results underscore the promising potential of biopsy-needle-integrated transducers in enhancing the accuracy of endoscopic ultrasound-guided fine needle aspiration biopsy (EUS-FNA) for clinical applications.

Functional electrical stimulation (FES) is a vital method in neurorehabilitation used to reanimate paralyzed muscles, enhance the size and strength of atrophied muscles, and reduce spasticity. FES often leads to increased muscle fatigue, necessitating careful monitoring of the patient’s response. Ultrasound (US) imaging has been utilized to provide valuable insights into FES-induced fatigue by assessing changes in muscle thickness, stiffness, and strain. Current commercial FES electrodes lack sufficient US transparency, hindering the observation of muscle activity beneath the skin where the electrodes are placed. US-compatible electrodes are essential for accurate imaging and optimal FES performance, especially given the spatial constraints of conventional US probes and the need to monitor muscle areas directly beneath the electrodes. This study introduces specially designed body-conforming US-compatible FES (US-FES) electrodes constructed with a silver nanowire/polydimethylsiloxane (AgNW/PDMS) composite. We compared the performance of our body-conforming US-FES electrode with a commercial hydrogel electrode. The findings revealed that our US-FES electrode exhibited comparable conductivity and performance to the commercial one. Furthermore, US compatibility was investigated through phantom and in vivo tests, showing significant compatibility even during FES, unlike the commercial electrode. The results indicated that US-FES electrodes hold significant promise for the real-time monitoring of muscle activity during FES in clinical rehabilitative applications.

Precise and time-efficient sensing of tremor dynamics is essential for developing personalized, adaptive stimulation strategies for movement disorders such as Parkinson’s Disease (PD) and Essential Tremor (ET). Existing modalities—such as inertial measurement units (IMUs) and surface electromyography (EMG)—lack muscle specificity and are prone to stimulation artifacts. To address these limitations, we fabricated and applied a Wearable Ultrasound Sensing (WUS) system, featuring dual flexible 64- element transducer arrays with center frequency of 6 MHz conformed over the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles for simultaneous antagonist muscle monitoring. A machine learning (ML) pipeline was introduced to estimate tissue displacement (TD) from raw ultrasound signals. Across three participants and multiple trials, the WUS system achieved tremor frequency detection within 10 %variation relative to commercial B-mode and IMU sensors, and met statistical equivalence thresholds based on two one-sided test (TOST) analysis. The TD estimation models demonstrated high predictive accuracy, with overall Pearson correlation coefficients between predicted and actual values ranging from 0.88 to 0.97, normalized RMSE values below 10 %, and offline model building times under 800 seconds. Compared to classical B-mode speckle tracking, the proposed WUS-ML pipeline reduced offline model building time by 75 % (from 3095 sec to 792 sec). In real-time performance tests, it reduced frame-level latency from 3700 ms to 17 ms and achieved effective processing rates exceeding 50 Hz, well above the Nyquist threshold for tremor analysis. These results demonstrate the feasibility of dual-array wearable ultrasound for accurate, low-latency tremor tracking and lay the groundwork for future closed-loop afferent stimulation systems in both clinical and at-home environments.

Cancer immunotherapy offers a promising long-term treatment for solid tumors by activating the immune system, but side effects and systemic toxicity limit its broad clinical translation. While intratumoral delivery addresses these limitations, elevated stiffness within solid tumors continues to hinder both intracellular and extracellular delivery. Here, a novel therapeutic platform, the Precision Ultrasound-Localized Sonoporation-Equipment (PULSE), is presented to enable spatiotemporally controlled, ultrasound-mediated gene and drug delivery for intratumoral immunotherapy. The PULSE incorporates forward and sideward-looking miniaturized ultrasound transducers, integrated into either a 7-French catheter (cPULSE) or a 16-gauge needle (nPULSE), to minimally invasively sonicate a centimeter-sized tumor. Following the design, prototyping, and characterization of PULSE, its dual capability for intracellular and extracellular delivery is demonstrated through comprehensive in vitro cell-based sonoporation tests and phantom-based drug penetration tests. Luciferase assays (activity: ~10 ⁴ RLU/μg level) in the cell studies confirm significantly enhanced gene transfection with cPULSE, while increased dye diffusion (width: ~1 cm level) in the phantom tests validates improved perfusion with nPULSE. The reported PULSE shows promise for spatiotemporally precise, controlled, and localized therapeutic delivery in early-stage tumors for intratumoral immunotherapy.