Insertion force in manual and robotic corneal suturing

Background: Due to differences in corneal grafting microsurgery between manual and robotic suturing, new challenges have arisen in testing the insertion force and torque of corneal tissue acting on suturing needles in order to guarantee successful completion of surgical procedures. Methods: In order to measure the force during the insertion operation, from the needle entering the cornea through the entry point until the puncturing of the exit point along the circular trajectory, a force measurement system was established, including fresh porcine cornea, a corneal-suturing robot, a circular needle, a micro-forceps manipulator with a force transducer, a computer with a data acquisition board and a medical microscope. The force values in the needle coordinate frames were obtained on the basis of a sensor coordinate frame through D-H coordinate transformation, and an index is proposed here to evaluate the insertion performance. Experiments on both manual and robotic suturing were carried out for comparison. Results: The scale and changes of the needle insertion force were obtained using two different suturing methods. The maximal tangent force in robotic suturing is a little larger than in manual suturing, and the maximal resultant force in robotic suturing is somewhat smaller. Although the difference is not very significant, robotic suturing performs in a more stable way. Moreover, the performance evaluation index M_dmax (the maximum of square root of the quadratic sum of torque components M_OX and M_OY) in robotic suturing is much smaller than that in manual suturing. Conclusions: The force measurement system has been verified to be feasible through experimentation. Compared with conventional manual surgery, robotic suturing has some advantages: more stable suturing, smaller distortion torque and fewer invasions to the corneal tissue, showing that its application in minimally invasive surgery is practical.