Wasp-inspired needle insertion with low net push force

This paper outlines the development of a four-part needle prototype inspired by the ovipositor of parasitic wasps. In the wasp ovipositor, three longitudinal segments called valves move reciprocally to gain depth in the substrate. It has been suggested that serrations located along the wasp ovipositor induce a friction difference between moving and anchoring valves that is needed for this reciprocal motion. Such an anchoring mechanism may not be desired in a medical setting, as serrations can induce tissue damage. Our aim was to investigate whether a multipart needle can penetrate tissue phantom material with near-zero net push force while using needle parts devoid of surface gripping textures or serrations. Accordingly, a four-part needle prototype was developed and tested in gelatine substrates. The performance of the prototype was assessed in terms of the degree of slipping of the needle with respect to the gelatine, with less slip implying better performance. Slip decreased with decreasing gelatine concentration and increasing offset between the needle parts. Motion through gelatine was achieved with a maximum push force of 0.035 N. This study indicates the possibility of needle propagation into a substrate with low net push force and without the need of serrations on the needle surface.