Flexible force sensors rely on soft elastomers and stretchable conductors to conform to curved surfaces and convert mechanical loads into electrical signals. However, the intrinsically nonlinear and coupled mechanical responses of soft materials make it difficult to simultaneously achieve high sensitivity, broad dynamic range, and long-term stability. In this Review, microstructural architecture is identified as a primary design variable governing force-to-electrical transduction beyond material composition alone. A unified structural framework is established to connect uniaxial force sensing and triaxial force sensing through the deliberate regulation of deformation modes and load-transfer pathways. Porous, micropatterned, and hierarchical structures are examined for their roles in amplifying and stabilizing pressure-induced responses in uniaxial sensing, whereas distributed arrays and multilayer heterogeneous designs are analyzed for their abilities to enable directional discrimination, signal reconstruction, and normal-shear force decoupling in triaxial sensing. By comparing structure-mediated behaviors across major transduction mechanisms, general design principles are identified for improving sensitivity, linearity, and force decoupling, while the growing integration of structural engineering with data-driven signal reconstruction is also highlighted. This perspective provides a rational foundation for the design of next-generation wearable electronics and robotic tactile systems.

Piezoelectric materials are essential for electronics but suffer from thermal instability, especially lead-free alternatives to lead zirconate titanate (PZT). The absence of quantitative thermal stability metrics has hindered progress. In this work, we introduce a new index, denoted as "S-d", which accounts for both the operating temperature range and the central operating temperature, allowing for a comprehensive assessment. Applying this criterion, we found that the commercial PZT-4 material exhibits the highest thermal stability among the ceramics tested, confirming its reputation as the industry standard. Notably, we developed a new lead-free piezoelectric ceramic based on bismuth ferrite that achieved a stable piezoelectric coefficient at 38-247 degrees C; the corresponding S-d value (173) exceeds that (163) of commercial PZT-8 (20-232 degrees C). Further analysis revealed that reducing the concentration of point defects improved its electrical homogeneity and reduced conductivity, leading to enhanced thermal stability. This work provides a new evaluation framework that can accelerate the development of thermally stable lead-free piezoelectric materials. The implications of this research extend beyond piezoelectrics, as the S-d index could find broader application in the characterization of other functional oxides.

Microsurgical anastomosis demands ultra-high precision, but inherent manufacturing tolerances in robotic systems cause geometric errors. These deviations induce distal positioning offsets, jeopardizing surgical safety. This paper proposes a dedicated microanastomosis robot featuring a position-orientation decoupled architecture, integrating a three-axis translational stage and a dual-triangular RCM mechanism. To enhance absolute positioning accuracy and eliminate RCM point drift, a comprehensive kinematic error correction model is established. The Levenberg-Marquardt (LM) algorithm is utilized for parameter identification and active error compensation. Experimental results demonstrate that by effectively eliminating RCM point deviation, the proposed strategy reduces the dynamic spatial trajectory tracking error by 91.2% (to 55 μm), thereby strictly satisfying the stringent constraints for microanastomosis.

Quasi-static magnetic localization offers advantages in eliminating geomagnetic interference and compatibility with magnetic actuation. However, existing systems that rely on high-frequency magnetic fields (>= 1000 Hz) often require high sampling rates, which increase the communication bandwidth demands and power consumption in wireless applications. This article presents a wireless electromagnetic tracking system (WEMTS) that operates at ultra-low frequencies (210 Hz), specifically designed for hardware-constrained medical devices like capsule robots. The WEMTS hardware consists of two main components: three external coil groups and a wireless sensor module (WSM) that integrates a three-axis magnetic sensor and an RF transmitter. A multilateration-based sequential pose estimation method is implemented for the 6-DoF localization of the WSM, improving convergence stability and computational efficiency. Experimental results show that WEMTS achieves static localization accuracy of 3.09 +/- 0.99 mm in position and 2.21 +/- 0.62(degrees) in orientation, and dynamic tracking errors of 3.23 +/- 1.05 mm and 2.67 +/- 0.89 degrees at 5 mm/s within a 400 mm & times; 200 mm & times; 300 mm workspace. To validate practical applicability, the WSM was integrated into a vibrating capsule and successfully tracked in real time inside an ex vivo porcine colon. The proposed WEMTS allows precise and robust tracking, effectively addressing the challenges posed by hardware-constrained medical devices.

With the continuous increase in the incidence rate of respiratory diseases, the importance of pulmonary function tests (PFTs) in early diagnosis and disease monitoring has become increasingly prominent. This article proposes a high-sensitivity, wide-range flow sensor based on fiber Bragg grating (FBG) for pulmonary function testing. The sensor consists of two cylindrical covers and an internal flexible differential lever structure. By replacing rigid hinges with flexible hinges, it achieves airflow thrust amplification and differential strain measurement, effectively enhancing sensitivity and suppressing temperature effects. The sensor structure has been verified through structural optimization and finite-element simulation, resulting in high sensitivity. Simulation results show that the sensor exhibits excellent static and dynamic performance within the range of 0-12 L/s, with an average sensitivity of 877.2 pm/(L & centerdot;s(-1)) and a safety factor greater than 3. A calibration experiment was conducted, and a quartic polynomial fitting was applied, which reduced the maximum fitting error to 5% and yielded an average resolution of 1.4 mL/s. Dynamic performance testing and temperature-decoupling experiments further verify its dynamic accuracy and insensitivity to temperature. Finally, by comparing the PFT data from six healthy subjects with those from a commercial spirometer, the average errors for key parameters, including forced vital capacity (FVC), FEV1, and peak expiratory flow (PEF), were all below 3%, demonstrating the feasibility and accuracy of the sensor in clinical PFTs.

This paper introduces a novel fiber Bragg grating (FBG)-based sensor for measuring 4-D forces and torque during percutaneous puncture with high sensitivity, high accuracy, and low inter-dimensional coupling. The sensor comprises serially configured sensing units: an annular-guided-structure-based axial force sensing unit and a radial force and torque sensing unit employing a spoke-type structure, effectively reducing coupling between axial and radial forces/torque measurements. The axial guiding structure evolves from classical flexible parallelogram modules, transforming them through reversed coupling and symmetric arrangement into an annular configuration to achieve enhanced axial sensitivity and cross-axis decoupling. The spoke-type structure adopts a three-spoke configuration and incorporates optimized cantilever beam dimensions to improve torque measurement sensitivity while balancing multi-directional sensitivity values. The sensor utilizes five FBG fibers in a dual-point mounting configuration to achieve high sensitivity and prevent chirping failure. Finite element analysis and optimization were conducted to validate and enhance the sensor's comprehensive performance. Calibration experiments have been implemented, revealing the sensor's high-resolution capabilities with values of 0.26 mN, 0.21 mN, 1.8 mN, and 2.7 mNmm within +1.5 N for Fx, +1.5 N for Fy, 0-6 N for Fz, and +30 Nmm for Tz. This sensor exhibits a maximum crosstalk of 3.64% among 3-D forces and 5.53% among forces and torque. Experimental validation with silicone phantom and ex vivo tissues confirmed the sensor's superior accuracy and clinical potential, with maximum root mean square error values of 33 mN (7.24%), 20 mN (4.69%), 79 mN (1.02%), and 194 mNmm (3.38%), respectively.

Transbronchial lung biopsy (TBLB) has increasingly been recognized as a clinically significant procedure for the early diagnosis and treatment of lung cancer. However, the complex anatomical anatomy and narrow bronchial pathways present substantial challenges for conventional bronchoscopy, demanding exceptional surgical expertise, skills, and meticulous precision. To address these limitations, robot-assisted bronchoscopic systems integrated with flexible continuum bending sections and advanced sensing technologies have been developed to enable dexterous access and ensure safe tissue interaction. This review systematically examines the recent advancements in robot-assisted bronchoscopic systems and classifies them into two primary categories based on actuation mechanisms: tendon-driven and magnetic-driven approaches. The innovative mechanical designs, intelligent sensing techniques, control strategies, clinical progress, and current limitations of these robotic systems have been critically analyzed and summarized. Furthermore, the evolutionary trends of flexible bronchoscopic robots suitable for TBLB have been outlined, and the remaining challenges and potential technical solutions

This work introduces a novel compact 7-degree-of freedom (7-DOF) microsurgical robot with position-orientation decoupling capacity for microvascular anastomosis. The proposed system employs a modular architecture combining a proximal displacement platform for 3D small-stroke translation and a distal compact remote center of motion (RCM) mechanism for wide range orientation adjustment. This design meets the workspace requirements for microvascular anastomosis, requiring extensive orientation adjustments with minimal positional movement and reducing the system footprint. The parasitic motion reverse self-compensation method has been developed for motorized surgical instruments, effectively reducing operational resistance to improve precision. Theoretical analysis has been performed on both the RCM mechanism and motorized surgical instruments, and kinematics-based parameter optimization and data-driven calibration have been conducted to enhance superior performance. A prototype has been constructed, and its experimental validation demonstrated that the system achieved repeatability of 11.24 ± 2.31 μm (XY) and 12.46 ± 4.48 μm (YZ), and absolute positioning accuracy of 29.80 ± 12.27 μm (XY) and 37.02 ± 19.47 μm (YZ), meeting super-microsurgical requirements. Experiments that include needle-threading and stamen peeling tasks demonstrate the robot's superior dexterity and manipulation capabilities.

This paper proposes a novel 4-DoF Remote Center of Motion (RCM) mechanism based on a serial-parallel hybrid architecture, denoted as (2-RRRRR-RR)+C. Featuring an overconstrained configuration, the design is specifically engineered to enhance structural stiffness and improve metrological accuracy. The parallel module consists of two orthogonally arranged planar branch chains integrated with a circular-arc branch that effectively suppresses parasitic motion, while the serial end-effector incorporates a specialized decoupled cylindrical gear assembly. This architecture achieves fully decoupled 4-DoF motion, significantly bolstering the safety and reliability of the surgical robot system. A physical prototype was developed and subjected to comprehensive kinematic modeling, Jacobian analysis, and singularity assessments. Furthermore, dimensional optimization based on the Local Transmission Index (LTI) was implemented to maximize motion/force transmission efficiency and workspace volume. Experimental investigations validate an expansive orientational workspace, supporting full 360° axial rotation within a 100° conical envelope, alongside a 100 mm translational range. Metrological evaluations yielded average absolute and repeatable positioning errors of 58.52 μm and 25.77 μm, respectively. The average Remote Center of Motion (RCM) deviation and tilt errors were quantified at 33.34 μm and 0.085°, confirming high-fidelity precision. Finally, simulated nasal cavity-probing tasks demonstrated an average target-point transition time of 71 seconds. These outcomes underscore the potential of the proposed mechanism for robotic endonasal skull base surgery, offering compatibility with relevant surgical instruments and enabling precise manipulation in confined surgical environments.

This paper introduces a wearable fiber Bragg grating (FBG)-based sensor for high-sensitivity radial artery pulse waveform acquisition. To address the weak amplitude of radial artery pulse signals and the limited sensitivity of conventional force/displacement-based sensors, a compliant two-stage lever amplification mechanism with flexure hinges is designed to convert pulse-induced forces into uniform tensile strain on a suspended FBG. Finite element analysis is performed to evaluate structural performance and optimize key structural parameters. The fabricated sensor is experimentally calibrated using a commercial six-axis F/T sensor, achieving a sensitivity of 3130 pm/N, a resolution of 0.32 mN, and a measurement range of 0–2 N. Dynamic force loading and radial crosstalk experiments verify the sensor’s dynamic measurement accuracy. Human subject experiments demonstrate that the proposed sensor can acquire high-fidelity radial pulse waveforms with amplitudes up to 300 pm and resolve up to 3 characteristic peaks. Frequency-domain analysis further confirms its capability to extract heart rate information. It also shows close agreement with a commercial ECG monitor with a maximum error of 0.8%. These results demonstrate the feasibility of the proposed sensor for high-resolution radial pulse waveform acquisition.

Continuum robots employed in flexible gastrointestinal endoscopy require the capability of transitioning between the flexible and the rigid states. Phase-change-material-based variable stiffness (VS) methods exhibit a significant stiffness change ratio but are typically time-consuming. Besides, these materials are commonly fabricated into simplistic cylindrical or tubular structures and subsequently integrated with continuum joints, overlooking the impact of the intrinsic structural characteristics of the VS module on stiffness modulation and bending performance. To maintain the combination of motion flexibility and operation stability, this work presents a stiffness-tunable sheath inspired by a multi-layer wave spring structure, which is fabricated utilizing thermoplastic material. A water-based active heating/cooling method is employed, wherein the circulation of hot/cold water through silicone tubes helically wound around the exterior of the VS sheath enables rapid thermal regulation. Structural parameters selection of the VS sheath based on the orthogonal design method has been performed to enhance its stiffness in a rigid state and reduce the maximum stress during 90° flexion in a flexible state. Experimental results indicate that the proposed VS sheath can achieve a stiffness change ratio of up to 16.5 times within 30s. After being integrated with a continuum joint, the sheath demonstrates an average positioning error of 1.48mm within a ±90° bending range in a flexible state, without structural compromise or interference with the continuum joint’s bending. In the rigid state, the proposed design can resist 400g external payload with a deflection of less than 6mm. The efficacy of this design has been validated through ex-vivo experiments conducted on a porcine stom

This article presents a novel fiber Bragg grating (FBG)-based sensor for precise 2-degree-of-freedom (DoF) ankle angle monitoring. The proposed sensor primarily comprises two symmetric torsion springs, a planar spring, and three FBG-embedded optical fibers. Symmetric torsion springs are used to measure plantarflexion/dorsiflexion (PF/DF) rotation, while a planar spring targets inversion/eversion (INV/EVE) motion, effectively minimizing cross-axis interference due to their distinct stiffness characteristics. Crucially, the sensor's high in-plane compliance accommodates the physiological shift of the ankle's rotation center, enabling enhanced wearing comfort. Moreover, a symmetric differential fiber configuration compensates for rotation-axis variations and ensures high measurement accuracy. Structural optimization was conducted to maximize sensitivity and minimize crosstalk. Experimental results demonstrate high sensitivities of 37.09 pm/degrees (PF/DF) and 224.70 pm/degrees (INV/EVE) over ranges of +/- 55 degrees and +/- 23 degrees, respectively. The structural decoupling is validated by a low maximum crosstalk of 3.56%. Furthermore, the sensor maintains accuracy against rotation center offsets, with sensitivity deviations kept below 2.8% under a 2-mm misalignment. Dynamic tests at 50 degrees/s and 300 degrees/s yielded maximum root-mean-square errors (RMSEs) of 2.47 degrees and 1.27 degrees for PF/DF and INV/EVE, respectively. Finally, on-body validation, including seated range-of-motion (ROM) tests, squat-to-stand exercises, and level walking, confirmed the sensor's ability to capture high-fidelity kinematic profiles for rehabilitation applications.

In-pipe swimming robots (ISRs) are essential for inspecting and maintaining urban water supply networks. However, existing ISRs often face limitations in maneuverability and environmental sensing due to size constraints, which reduces their efficiency and reliability when navigating complex or narrow pipelines. In this article, we develop a compact ISR with a diameter of 7.8 cm, a length of 12.9 cm, and a density similar to water for autonomous navigation through narrow pipelines. The ISR incorporates four propellers for maintaining attitude and depth, and two tail propellers for horizontal movement. It is equipped with a pressure sensor, an inertial measurement unit, and a camera to perceive depth, attitude, acceleration, and the pipeline environment. An onboard embedded computer manages estimation, mapping, and planning tasks. For stable yaw and depth control, a double-loop proportional-integral-derivative (PID) controller is implemented. To enable autonomous inspections despite limited perception, we propose a reactive navigation method that leverages visual landmarks (forks, T-turning, T-direct, L-turning, and Up/Down-turning) together with a preloaded topological map and path. The robot utilizes visual algorithms to determine its relative position within the pipeline and complete autonomous inspections in a custom-built pipeline. Experimental results demonstrate the effectiveness of the proposed algorithms and approaches.

WEEE and RoHS regulations impose strict restrictions on lead content in electronics, whereas many accelerometers used in automotive, aerospace, and consumer electronics currently rely on lead-based piezoceramics. To address this challenge, we design and develop a novel lead-free compressive-mode accelerometer based on BCZT (Barium Calcium Zirconate Titanate). Environmentally friendly BCZT ceramics were synthesized in this work. The freshly poled BCZT ceramics exhibited an initial maximum piezoelectric coefficient of 350 pC/N, as measured immediately after poling. After storage and thermal cycling associated with temperature-coefficient characterization, the stabilized room-temperature decreased to 281.96 pC/N, which is consistent with the commonly observed aging and domain-relaxation behavior of poled ferroelectric ceramics. Subsequently, we designed a new compressive-mode accelerometer featuring a symmetric dual-element configuration integrated with a charge-amplifier read-out circuit. Through systematic material-structure-circuit co-optimization, our BCZT-based accelerometer achieved a voltage sensitivity of 10.61 mV/(m/s2) with an output error of <= 2% and +/- 7.08%FS linearity. Within the investigated operating temperature range of 24 degrees C-70 degrees C, decreased from 281.96 to 261.25 pC/N, corresponding to a 7.34% reduction. This research demonstrates that BCZT serves as a high-performance, lead-free alternative for conventional piezoelectric sensing materials, offering enhanced stability and precision for dynamic measurement applications.

This work presents a novel rolling driving principle (RDP) for stick-slip actuators to achieve high motion consistency, inspired by the rack-and-pinion mechanism. This RDP utilizes a symmetrical driving structure and tangential contact to realize the pure rolling motion between the stator and the slider, requiring just a single lead zirconate titanate (PZT). This configuration ensures a consistent bidirectional driving process with a constant contact force, which improves both motion consistency and linearity. Based on this RDP principle, a linear stick-slip actuator incorporating an isosceles trapezoidal flexible mechanism (ITFM) has been implemented. The corresponding driving principle, operating principle, and the RDP’s advantages have been analyzed and revealed. Design optimization was performed to investigate the optimal structural parameters of the ITFM. The superior performance of the proposed RDP-type actuator was experimentally verified across both high- and low-frequency ranges. The results indicate that the presented design exhibits forward and reverse output speed values of 0.410 and 0.417 mm/s at 10 Hz with linear correlation coefficients of 0.99969 and 0.99962, indicating an excellent motion consistency with a velocity difference ratio of 1.96%. When working at 560 Hz, the presented actuator reaches 37.73 and 34.99 mm/s for the forward and reverse output speed, yielding high linearity values of 0.99999 and 0.99999 due to the tiny speed fluctuation, and maintains a reasonable motion consistency with a velocity difference ratio of 7.54%. Finally, an RDP-type actuator-based magnetic resonance imaging (MRI)-compatible microsurgical instrument was proposed and prototyped, which enables opening–closing motions and cutting motions for intraoperative MRI surgical applications.

This paper presents a wrist rehabilitation robot based on a 3R spherical linkage and proposes a multimodal human–robot interaction (HRI) control method integrating surface electromyography (sEMG) and force sensing. The proposed robot provides three degrees of freedom (DoFs) of posture adjustment for wrist rehabilitation training and incorporates a 6-axis force sensor to establish an interactive rehabilitation platform. A variable admittance control strategy is further developed using fuzzy rules. In this strategy, sEMG signals are used to characterize muscle activation and active participation, while interaction force/torque information reflects the current mechanical interaction state. Based on these multimodal inputs, the admittance damping parameter is adjusted online. Experimental results show that the proposed method can identify different training states, including active exertion, abnormal spasticity, muscle weakness, and interaction discomfort. Compared with the fixed admittance controller, the physical-signal-based admittance controller, and the physiological-signal-based variable admittance controller, the proposed controller increases muscle activation by 5.88%, 4.79%, and 1.07% of the full-scale range, respectively, thereby demonstrating superior effectiveness in promoting active participation.

Capsule robot can reach the focus area of gastrointestinal tract by oral administration to perform medical functions, which provides an important way to realize painless and non-invasive diagnosis and treatment of gastrointestinal diseases and improve patient compliance. In this work, we introduce a novel capsule robot designed for gastric biopsy and multi-drug delivery. The robot incorporates an innovative “roulette wheel-like” internal switching mechanism, which is controlled by two independent motors. One DC motor governs the inner chamber, enabling free switching between biopsy and drug delivery, and the other motor actuates a pusher to deploy the biopsy needle or expel drugs. Different types and quantities of biopsy and drug delivery modules can be adapted by designing different container cavities. Furthermore, a permanent magnet is installed at the back end of the robot for active motion control, and multi-degree-of-freedom motion is realized by using gradient magnetic field on the commercial magnetic control platform. In vitro validation studies demonstrate the capsule robot's successful execution of complete biopsy and drug delivery procedures in both liquid-free and liquid environment. This platform furnishes a viable solution for capsule robots intended for gastric biopsy and drug delivery, exhibiting considerable potential for practical implementation.

The clinical endoluminal flexible instruments exhibit limited degrees of freedom (DOFs) and operational dexterity, making reorientation or repositioning challenging during the complex flexible endoscopic procedure, particularly in endoscopic submucosal dissection (ESD). This work presents a novel 5-DOF miniature flexible instrument for dual-armed upper gastrointestinal endoscopic robots with only 2.6 mm in diameter. It employs a continuum bending section featuring interlocking discrete joints and superelastic NiTi driving rods to achieve high dexterity, accurate positioning with inconspicuous motion hysteresis, and sufficient loading/clamping capacities. The design enables 360 degrees unrestricted distal independent rotation of the forceps, unlike the entire rotation of typical flexible instruments. The central forceps movement slightly impacts the overall positioning accuracy of the instrument with a crosstalk error of less than 1 mm. Kinematic parameter calibration improves the instrument's motion accuracy, achieving an average distal positioning error of 1.56 mm within +/- 100 degrees in the 2-D plane and 2.29 mm in 3-D space. The distal loading stiffness is 0.29 N/mm and the clamping force exceeds 0.8 N, providing adequate tissue interaction forces during ESD procedures. The modularized instrument prompts the seamless integration of diverse surgical tools, ultimately establishing a dual-armed endoscopic robot. Ex-vivo experiments have been performed to verify its effectiveness in ESD procedures.