Bingze He, Yao Guo, Guang-Zhong Yang

Cyborg and Bionic Systems 2025: 0417.

Abstract

Precision-controlled microscale manipulation tasks—including neural probe implantation, ophthalmic surgery, and cell membrane puncture— often involve minimally invasive membrane penetration techniques with real-time force feedback to minimize tissue trauma. This imposes rigorous design requirements on the corresponding miniaturised instruments with robotic assistance. This paper proposes an integrated piezoelectric module (IPEM) that combines high-frequency vibration-assisted penetration with real-time in-situ force sensing. The IPEM features a compact piezoelectric actuator integrated with a central tungsten probe, generating axial micro-vibration (4652 Hz) to enable smooth tissue penetration while simultaneously measuring contact and penetration forces via the piezoelectric effect.   

Extensive experiments were conducted to validate the effectiveness and efficacy of the pro-posed IPEM. Both static and dynamic force sensing tests demonstrate the linearity, sensitivity(9.3 mV/mN), and accuracy (MAE < 0.3mN, MAPE < 1%) of the embedded sensing unit. In gelatin phantom tests, the module reduced puncture and insertion forces upon activation of vibration. In vivo experiments in mouse brains further confirmed that the system could reduce penetration resistance (from an average of 11.67mN without vibration to 7.8mN with vibration, decreased by 33%) through the pia mater and accurately mimic the electrode implantation-detachment sequence, leaving a flexible electrode embedded with minimal trauma.

This work establishes a new paradigm for smart surgical instruments by integrating a com-pact actuator-sensor design with real-time in-situ force feedback capabilities, with immediate applications in brain-machine interfaces and microsurgical robotics.

Introduction and Methods

In this study, we propose a novel integrated piezoelectric module (IPEM) based on a piezo electric ceramic element designed specifically for bio-membrane puncture and insertion applications. By leveraging the inverse piezoelectric effect, we induce high-frequency axial vibrations at the probe tip to assist membrane rupture and reduce insertion resistance. Simultaneously, using the direct piezoelectric effect, we measure the generated charge response during tissue interaction, enabling real-time force sensing without additional hardware. As illustrated in Fig.1(c), the system has potential applications in various biomedical procedures, including tumor tissue biopsy, corneal puncture surgery, flexible neural electrode implantation, single-cell puncture and so on. This dual-functionality design addresses several key challenges in existing systems:1) Reduced Penetration Force: Axial micro-vibrations enhance rupture efficiency and re-duce peak insertion forces, while maintaining low transverse displacement to preserve accuracy and minimize off-axis trauma.2) Accurate in-situ Force Monitoring: The same piezoelectric element serves as a charge-based force sensor, capturing puncture events and insertion resistance profiles in real time, even during high-frequency operation.3) Compact and Minimalist Architecture: By avoiding external sensors, bulky load cells, or separate vibration modules, the device offers an integrated, lightweight platform suitable for small-scale biomedical procedures.

Key Results and Conclusions

This study introduces a novel piezoelectric penetration system that integrates vibration-assisted actuation with in-situ force sensing, addressing key challenges in low-damage, high-precision im-plantation tasks for bio-interfacing applications. The system was designed to minimize insertion force through axial high-frequency vibration while simultaneously enabling direct measurement of puncture and insertion forces via the direct piezoelectric effect. Through a series of experiments including static calibration, dynamic force tracking, gelatin phantom tests, and in vivo mouse brain penetration, the system demonstrated the following characteristics. High linearity and sensitivity in force sensing, achieving an R2 of 0.9998 in static calibration and real-time tracking accuracy com-parable to commercial sensors; Effective force reduction during vibration-assisted penetration, with clear reductions in peak puncture force, insertion force, and withdrawal resistance. In vivo experiments conducted on anesthetized mice confirmed that turning on vibration reduced the maximum insertion force by 33% compared to that without vibration. The system shows robust performance across various loading conditions, maintaining low error rates under both sinusoidal and abrupt force input profiles. Functional demonstration of electrode implantation shows that the probe can successfully mimick the process of pia mater penetration, cortical insertion, electrode release, and probe withdrawal with force sensing throughout.

Fig. 1: Schematic illustration of the proposed vibration-assisted puncture and in-situ force sensing system.

(a): A 6-DOF robotic arm integrated with a microscope and a piezoelectric puncture module enables precise manipulation and real-time observation of soft tissue penetration. (b): The piezoelectric component simultaneously provides axial vibration for membrane puncture and real-time in-situ force sensing based on piezoelectric coupling. (c): The system has potential applications in various biomedical procedures, including tumor tissue biopsy, corneal puncture surgery, flexible neural electrode implantation, and single-cell puncture.

Fig. 2: Working principle and structural design of the integrated piezoelectric puncture and sensing system.

(a): Schematic comparison of the puncture process with and without axial vibration, including three stages: pre-puncture (contact compression), puncture (membrane rupture), and post-puncture (insertion into tissue). (b): Exploded view of the piezoelectric actuator-sensor integration, consisting of a substrate, an actuating PZT, and a sensing PZT, clamped together by a ring and coated with silver electrodes.(c1)-(c2):Working mechanism of the piezoelectric sensor: (c1) under no external load, no voltage is generated;(c2) under external force while the actuator applies a sinusoidal voltage.(d):Signal flow and circuit design for vibration driving and force sensing. The upper loop represents the actuation path using a DAC and power amplifier, while the lower loop shows the sensing path using a charge amplifier, lowpass filter, and ADC for real-time acquisition of force signals.

Fig. 3: (a) Experimental setup for vibration performance testing. The IPEM is mounted on a precision 3D stage and actuated via a sinusoidal signal. A laser Doppler vibrometer (LDV) is aligned to measure out-of-plane displacement at the probe tip. (b) Finite element analysis (FEA) simulation results showing the first six vibration modes of the IPEM structure. The first natural frequency (f1 =4665Hz) corresponds to dominant axial mode, while higher-order modes exhibit increasing degrees of radial and torsional deformation. (c) Experimental frequency response obtained by sweeping the excitation frequency while measuring vibration amplitude using LDV. A sharp resonance peak appears near 4.6kHz. (d) Real-time vibration amplitude in axial and lateral directions at resonance. The axial amplitude reaches ±9.6 µm under 80 V sinusoidal excitation, while lateral amplitude remains below ±3.1 µm. (e) Displacement-voltage hysteresis loop of the IPEM at the resonant frequency. (f): Infrared thermograph before vibration, showing IPEM (upper red area, max 27.6◦C) and gelatin phantom (lower blue area, center 24.1◦C); (g): Infrared thermograph after 10 minutes of vibration with 5 mm probe insertion, showing IPEM-probe junction (max 28.1◦C) and phantom center (24.2◦C), with a temperature rise of 0.5◦C and 0.1◦C respectively.

Fig. 4: (a) Experimental setup showing a 6-degree-of-freedom (6-DOF) robotic arm applying programmable contact forces via a spring mechanism. The integrated piezoelectric module (IPEM)and a commercial force sensor are mounted in series at the arm’s end-effector to enable synchronous measurement and validation. (b) Static calibration curve of the IPEM, showing excellent linearity between the applied force and output voltage with a coefficient of determination R2 = 0.9998and slope of 9.3 mV/mN. (c1) Force signals recorded by the IPEM and commercial sensor under sinusoidal loading. (c2) Time-domain error under sinusoidal loading, showing peak-to-peak error below ±0.5mN. (c3) Histogram of sinusoidal tracking errors, approximating a normal distribution centered near 0 with narrow spread. (d1) Force signals recorded by the IPEM and commercial sensor under square-wave loading. (d2) Time-domain error under square-wave loading, with transient error peaks during sharp transitions. (d3) Histogram of square-wave tracking errors, showing larger spread due to dynamic overshoot.

Fig. 5: (a); Sequential photographs of the puncture process in gelatin phantom; (b): Insertion force with and without vibration; (c): The distance of the probe moves during the puncture process. All scale bars: 500 µm.

Fig. 6: (a): Photographs of insertion stages in live tissue; (b): Insertion force with and without vibration; (c): The distance of the probe moves during the puncture process. All scale bars: 200 µm.

https://spj.science.org/doi/10.34133/cbsystems.0417