Research On Grasping Behavior Of The Interface Between MIS Grasper And Soft Tissue

Minimally Invasive Surgery (MIS) is a widespread new technique with various advantages than traditional open surgical operation during the past few decades, which assembles new instruments, microelectronics, new materials and automation. However, there are two hindrances in the progress of the more advanced, intelligent and widespread MIS: one is lack of tissue response database of tissue-tool for surgical simulations and training surgeons, the other is lack of biomechanical model for researching intelligent surgical robotics system.In this paper, we studied creep behavior of porcine liver under indentation with laparoscopic grasper and the grasping stability during tissue traction by laparoscopic grasper based on surgical simulation manipulation. The creep tests were conducted by using a microcomputer control electronic universal material testing machine (HY0580, Shanghai Hengyi Testing Machine Co., Ltd., China). And the indenter was one of the jaws of a laparoscopic grasper to simulate the real process of minimally invasive surgery. The creep characteristic of liver behaves time-dependent, load-dependent and strongly loading velocity-dependent due to its nonlinear viscoelastic characteristics and hysteresis characteristics. These creep behavior might also be associated with the deformation, migration and biochemical reaction of the liver cells, and a creep process model revealed from microstructure was shown in this description.Meanwhile, an UMT series multi-specimen Biomedical Micro-Tribometer (UMT-Ⅱ, Bruker Corporation, American) was used for the investigation of grasping stability with minor modifications. A test prototype with one-sided parallel grasper clamping-sliding on tissue was performed. Several factors:(Ⅰ) bio-surface liquids, (II) pull angles, and (III) surface profile types which influenced the grasping stability of MIS grasper during tissue traction operation were investigated in three separate experiments. The moist surface of large intestine could decrease the friction coefficient due to its bio-surface microstructure, and then reduce the grasping efficiency. The resistance forces present peak values with the pull angle of 15°t all applied clamp forces. The grasper with teeth surface could enhance the resistance force between grasper and tissue and the grasper with wedged teeth shown the best grasping stability.The results would be the basis for designing new, atraumatic, non-slip surgical instruments. Meanwhile, it could provide some suggestions for surgical manipulation skills in MIS.