Experiment Study On Interaction Behavior Between Minimally Invasive Surgical Suture Needle And Soft Tissue

Surgical suture is a time-consuming, a litter complex and challenging task. Surgeons always have the problem that there exist insufficient space and degree of motion in the process of suture, especially for larger wounds and must be deal with at once, which will cause the surgeons produce serve fatigue. These problems will greatly lower the seamed-efficiency and rise the risk of injury of organ. Consequently, the realization of the stitching automation technology is imminent, it can be automatically surgical suture instead of a doctor, and can improve suture efficiency and reduce the risk of injury. The stitching automation technology calls the robot identify the needle force in suture for a perfect stitching path planing. In addition, the needle deformation, bend and even break are also a common matter, so it is not enough to require doctor to acquire adequate suture skills, they should also understand the interaction between suture needle and tissue, which has a practical and guiding significance for needle design and selection.After a comprehensive review of abundant literature at home and abroad, The bio-mechanical tests relate to needle insertion were conducted in a 1-DOF electronic universal material testing machine (HY0580), porcine liver/skin, rabbit large/small intestine and liver were chosen as experimental sample for acupuncture experiment. The needle-tissue interaction behavior and the factors which influence the interaction were analyzed. By designing MATLAB program, we built the nonlinear model among needle force, insertion displacement and insertion velocity in the first insertion stage. Some basic rules of needle-tissue interaction are revealed. Main conclusions are as follows:1. The insertion can be divided into two stages. The before-puncture stage was called first stage, the main force was contributed by the tissue to the needle tip, which was called stiffness force. The after-puncture stage was the second stage, the needle force was composed of cutting force and friction force between needle and its surrounding tissue. The force in the puncture moment was called puncture force, and it was closely related to the condition of acupuncture. The puncture force and time were decreased with the rising velocity; The needle with triangle cross-section tip and larger size showed higher puncture force than that with round cross-section and smaller one under the same experimental condition. The puncture force and stiffness force for porcine skin was roughly ten times than the porcine liver, rabbit large/small intestine and liver. The research indicated that different ways of insertion will obtain different interaction results.2. There existed consanguineous relationship among stiffness force, insertion deformation and insertion velocity in the first stage. By designing MATLAB program based on least square method, we built the nonlinear model among the above three parameters, the residual value was about 0.012, which showed a relative good fit result. Besides, we compared the difference between several groups of measured data and the fitted value calculated by the nonlinear model to verify roughly the accuracy of the model.3. Established energy equilibrium equation of the two stages, and then a special experimental scheme was given to calculate the energy dissipation in the process of needle puncturing its surrounding tissue. The rising insertion rate, the more energy consumption; For the same velocity and diameter, the needle with triangle cross-section tip showed higher energy dissipation than that with round cross-section; For the same velocity and cross-section shape, larger size showed bigger energy dissipation than that with smaller one.4. Based on crack propagation criterion and Kelvin contact model, we demonstrated the validity of the relevant experiment results.