A Needle Biopsy-Inspired Method for Rapid Mechanical Characterization of Soft Tissue

Mechanical characterization of soft tissue provides critical insights for disease diagnosis, treatment planning, and regenerative medicine. However, existing techniques are limited by time-consuming procedures and restricted measurement regions, often limited to the sample surface. To address these limitations, we propose a needle biopsy-inspired method for rapid mechanical characterization of soft tissue across deep tissue regions. The proposed system employs a highly flexible 0.6 mm-diameter magnetic catheter composed of polydimethylsiloxane (PDMS) and neodymium–iron–boron (NdFeB), which can deflect under an external magnetic field. By inserting the catheter into tissue using a puncture mechanism and analyzing its deflection, tissue stiffness can be quantified rapidly without the need for time-consuming sample preparation or experimental procedures. Since the catheter interacts with tissue along its insertion path, the mechanical property is characterized across a tissue region, rather than confined to the tissue surface. The system was calibrated through deflection measurements in air and agar gels, followed by validation in ex vivo mouse brain tissue. The measured brain stiffness of 2644.3 ± 107.73 Pa was consistent with reference values reported in the literature for mouse brain cortex, demonstrating its feasibility for mechanical characterization of biological tissues. This study serves as a foundational step toward expanding the medical potential of magnetic soft continuum catheters for future tissue characterization applications in biomedical and clinical settings. Note to Practitioners—This paper was motivated by the challenge of rapidly characterizing the mechanical properties of soft tissues without extensive sample preparation and without restricting measurements to the tissue surface. Existing methods are often time-consuming and mainly provide surface-level information, which limits their practical utility when deeper tissue regions are of interest. This paper proposes a needle-biopsy-inspired mechanical characterization method based on a thin magnetic soft continuum catheter. The catheter is inserted into tissue through a puncture mechanism and deflected by an external magnetic field, and tissue stiffness is then estimated from the resulting catheter deformation. Because the catheter interacts with tissue along its insertion path, the method enables characterization over a tissue region rather than only at the surface. Experimental results in agar gels and ex vivo mouse brain tissue demonstrate the feasibility of this concept. This study suggests a potential new role for magnetic soft continuum catheters beyond manipulation and navigation, namely as tools for tissue mechanical characterization. In the future, this rapid measurement approach may support biomedical research and clinical workflows that require fast assessment of tissue mechanical properties, and may be integrated with robotic platforms for minimally invasive diagnostic and therapeutic applications.