Soft Graspers for Safe and Effective Tissue Clutching in Minimally Invasive Surgery.

Surgical graspers must be safe, not to damage tissue, and effective, to establish a stable contact for operation. For conventional rigid graspers, these requirements are conflicting and tissue damage is often induced. We thus proposed novel soft graspers, based on morphing jaws that increase contact area with clutching force. We introduced two soft jaw concepts: DJ and CJ. They were designed (using analytical and numerical models) and prototyped (10 mm diameter, 10 mm span). Corresponding graspers were obtained by integrating the jaws into a conventional tool used in the dVRK surgical robotics platform. Morphing performance was experimentally characterized. Jaw-tissue interaction was quantitatively assessed through damage indicators obtained from ex vivo tests and histological analysis, also comparing DJ, CJ and dVRK rigid jaws. Soft graspers were demonstrated through ex vivo tests on dVRK. Ex vivo tests and related analysis were devised/performed with medical doctors. Design goal was achieved for both soft jaws: by morphing, contact area exceeded by 20-30% the maximum area allowed by encumbrance specifications to rigid jaws. Experimental characterization was in good agreement with model predictions (error ≈ 4%). Damage indicators showed differences amongst DJ, CJ and dVRK jaws (ANOVA p-value  =  0.0005): damage was one order of magnitude lower for soft graspers (each pairwise comparison was statistically significant). We proposed and demonstrated soft graspers potentially less harmful to tissue than conventional graspers. Beyond minimally invasive surgery, the proposed concepts and design methodology can foster the development of graspers for soft robotics.