Design and Mechanics of Active Needles: A Review

Steerable needles have been extensively studied in the medical robotics society for the past two decades, evolving from passive needles to active ones that enable independent motion at their distal tip via robotics technology. Extensive design and actuation options have been proposed for the more capable active needles, followed by a few studies on their path-planning and control techniques; however, no commercial systems are available for the clinical environment yet despite their clear benefit, i.e., improved steerability and versatility compared to the other existing types of needles. This paper reviews the state-of-the-art steerable needle studies to identify research gaps and aims to deepen understanding the mechanics of active needles in soft tissue, which is critical for design optimization, precise control, and preoperative planning but currently remains unclear. To simplify the analysis, this review suggests separating the mechanics of an active needle into two parts: one for each of the tip and the shaft, where the shaft can be understood similarly to the passive needle whose mechanics has been thoroughly studied compared to the active one. Therefore, investigating the tip mechanics, including tissue properties, tip loadings, and tip kinematics, can lead to the complete understanding of active needle mechanics, the next challenges.