Ovipositor-Inspired Needle with Mechanical Stroke Adjustment

Abstract

Miniaturizing needle diameter has improved patient comfort, reduced tissue damage, and lowered infection risk; however, it also increases the risk of buckling. In nature, certain wasp species have evolved slender, buckling-resistant organs known as ovipositors, which have inspired the development of bio-inspired medical needles. Despite their potential, the needle segments of ovipositor-inspired needles often suffer from high slip in ex vivo tissue. We hypothesize this is mainly due to connective tissue layers causing reciprocating segments to elastically deform tissue without cutting it, preventing needle propagation. To address this challenge, we established design requirements for a needle system capable of adapting to varying tissue stiffness and toughness while minimizing slip in layered tissues. Three functions were defined: transmission, stroke adjustment, and connective tissue perforation. Solutions to each were developed and integrated into concept designs. Among these, the Planar Cam Design emerged as most promising. It features a translationally symmetric cam transmission, a variable-length bar linkage for stroke adjustment, and a vibrating needle for perforating connective tissue layers. The design was fabricated and tested through two experiments: the perforation and stroke adjustment experiments, aimed at evaluating the effectiveness of the vibrating needle and the stroke control mechanism, respectively. Results from the perforation experiment suggest vibration does not significantly improve performance in layered phantom tissues. In contrast, the stroke adjustment experiment indicates that optimal stroke length varies with tissue stiffness, validating the utility of the mechanism. These findings bring ovipositor-inspired needle designs a step closer to practical clinical implementation.