Self-propelling needles: From biological inspiration to percutaneous interventions

During percutaneous interventions, medical needles are inserted through the skin inside the body to collect diagnostic samples or to inject substances in a minimally invasive manner. However, when the target to be reached is located deep inside the body, needle insertion becomes challenging: the needle should be long enough to reach the target, thin (diameter lower than 1 mm) to limit tissue damage, and preferably steerable in order to move around obstructing anatomical structures. No needle currently used in medical practice combines all these characteristics: slender (i.e., long-and-thin) needles are susceptible to buckling, and steerable mechanisms require space, inhibiting miniaturization. In nature, such needles exist. Some species of parasitic wasps use their slender ovipositor to puncture, advance and steer through solid substrates, such as fruits or wood. These wasps use a push-pull mechanism to advance their ovipositor through the substrate without buckling. Translating that mechanism into a technical system might help to solve the current challenges with medical needles. Accordingly, this thesis aimed to design, develop, and evaluate a new ovipositor-inspired ultra-thin (i.e., submillimetre diameter) and long needle that can self-propel through solid substrates. A series of needles were developed that combined morphological and functional features inspired by the ovipositor of parasitic wasps. The proposed bio-inspired needle design and mechanism of motion hold great promise to improve accuracy and safety during delicate percutaneous procedures and to perform those that are not yet possible.