Development of the bending mechanism for forceps with least-incision transformable end-effector mechanism for endoscopic surgery: Development of the operating interface and in vivo experiment

In endoscopic surgery, smaller incisions produce good clinical results for patients. Therefore, there is increasing demand for thinner instruments for endoscopic surgery. However, the small size of the end-effectors limits the functionality of the instruments. To solve this problem, we developed a least-incision transformable end-effector (LITE) with a mechanism to transform from a linear shape into a large end-effector after being inserted into the body. However, the linear shape and thus fewer degrees of freedom sometimes makes surgeons use these forceps in an undesirable manner, which can cause complications during surgery. Therefore, this paper proposes a bending mechanism that can be mounted onto forceps that use the LITE mechanism. We conducted in vivo experiments to evaluate the usefulness of this forceps. The developed bending forceps had a diameter of 8 mm with a 1-DOF bending mechanism. This link mechanism is comprised of one joint and two frames and enables the LITE forceps to be bent to one side by 45° upon pulling of a wire. We confirmed that our developed prototype can smoothly perform bending and grasping motions. The grasping force under bending conditions of 0°-45° was at least 3.8 N. The extent of change in the 45° bending angle was 2.8° ± 0.2° or 19.4° ± 1.2° for loads of 1.96 and 3.92 N, respectively, applied to the tip of the forceps. An in vivo experiment was performed on a pig was under simulated surgery conditions to evaluate the usefulness of the developed prototype. We confirmed that transformation, removal, grasping and bending motions could be performed in vivo.