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A stiffness-tunable soft actuator inspired by helix for medical applications

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International Journal of Computer Assisted Radiology and Surgery Aims and scope Submit manuscript

Abstract

Purpose

This paper introduces the stiffness-tunable soft actuator (STSA), a novel device that combines a silicone body with a thermoplastic resin structure (TPRS). The STSA’s design allows for the variable stiffness of soft robots, significantly increasing their potential for use in medical scenarios such as minimally invasive surgeries (MIS). By adjusting the stiffness of the STSA, it is possible to enhance the robot’s dexterity and adaptability, making it a promising tool for performing complex tasks in narrow and delicate spaces.

Methods

The stiffness of the STSA can be modulated by altering the temperature of the TPRS, which has been inspired by the helix and is integrated into the soft actuator to achieve a broad range of stiffness modulation while maintaining flexibility. The STSA has been designed with both diagnostic and therapeutic functions in mind, with the hollow area of the TPRS serving as an instrument channel for delivering surgical instruments. Additionally, the STSA features three uniformly arranged pipelines for actuation by air or tendon, and can be expanded with more functional chambers for endoscopy, illumination, water injection, and other purposes.

Results

Experimental results show that the STSA can achieve a maximum 30-fold stiffness tuning, providing a significant improvement in load capacity and stability when compared to pure soft actuators (PSAs). Of particular importance, the STSA is capable of achieving stiffness modulation below 45 °C, thereby ensuring a safe entry into the human body and creating an environment conducive to the normal operation of surgical instruments such as endoscope.

Conclusion

The experimental findings indicate that the soft actuator with TPRS can achieve a broad range of stiffness modulation while retaining flexibility. Moreover, the STSA can be designed to have a diameter of 8–10 mm, which satisfies the diameter requirements of a bronchoscope. Furthermore, the STSA has the potential to be utilized for clamping and ablation in a laparoscopic scenario, thereby demonstrating its potential for clinical use. Overall, these results suggest that the STSA has significant promise for use in medical applications, particularly in the context of minimally invasive surgeries.

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Acknowledgements

The authors acknowledge supports from National Key Research and Development Program of China (2022YFC2405200), National Natural Science Foundation of China (82027807, U22A2051), Beijing Municipal Natural Science Foundation (7212202), Institute for Intelligent Healthcare, Tsinghua University (2022ZLB001), and Tsinghua-Foshan Innovation Special Fund (2021THFS0104).

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Authors and Affiliations

  1. Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, 100084, China

    Shangqi Dai, Chengquan Hu, Longfei Ma, Xinran Zhang, Hui Zhang & Hongen Liao

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Dai, S., Hu, C., Ma, L. et al. A stiffness-tunable soft actuator inspired by helix for medical applications. Int J CARS 18, 1625–1638 (2023). https://doi.org/10.1007/s11548-023-02902-5

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