Study On The Damage Mechanisms Of Soft Tissues In The Processes Of Natural Orifice Devices Inserting And Clamping

Both natural orifice transluminal endoscopic surgery and gastrointestinal endoscopic treatment are cutting-edge technologies combining the latest engineering technology and medical technology.In the courses of these surgeries,the surgical instruments are operated by surgeons to insert into the abdominal cavity or chest cavity through various natural cavities such as mouth,esophagus,stomach,colon,rectum,etc.,and then probe,clamp,drag,suture and excise organs or tissues with 2D real-time images.Due to the lack of haptic devices in most of these minimally invasive surgical instruments,surgeons are unable to accurately perceive the contact,friction,and clamping actions between the surgical instruments and soft tissues.Thus,inappropriate operations,including excessive pushing force during inserting operation and excessive clamping force during holding operation,can easily cause tissue damage and various postoperative complications.In this study,the interaction behavior between natural orifice instruments and soft tissues during inserting and clamping operations was investigated based on the experimental study,pathological analysis and cell morphology analysis.The effects of mechanical parameter,lubrication medium and device configuration on the mechanical properties and damage mechanisms of rabbit liver and intestinal tissues were explored.Through establishing pathological grading system,the degree of damage to these soft tissues was quantitatively evaluated.According to the results,the thresholds of safe operating parameters were proposed to prevent rabbit liver and intestinal tissues from severe damage.Main conclusions are drawn as follows:The effects of normal force,sliding speed and lubrication condition on the friction characteristics and trauma responses of in vivo small intestine and large intestine of rabbits were investigated by simulating the insertion process of gastroenteroscope.Results showed that the traumas(namely,hyperemia,hemorrhage,breakages of collagen fiber and elastic fiber,and damages of F-actin and ?-Tubulin),strongly depended on mechanical parameters and lubrication conditions.With the increase of loading force,a greater amount ofdeformation was accumulated in the front end of endoscope along the direction of movement,which resulted in the increases in maximum static friction force and friction coefficient.The increased friction coefficient eventually exacerbated the trauma degree of the tested tissue.Besides,as sliding velocity increased,the elastic deformation energy increased,which enhanced the friction coefficient and trauma degree.When the lubricants of Normal Saline,Hyaluronic Acid and Calf Serum were added respectively,the wettability of the tissue mucosa gradually improved,which decreased simultaneously elastic deformation and amount of accumulated displacement.As a result,the maximum static friction force,the friction coefficient and the damage degree of tissue reduced in turn.For rabbit small intestine and large intestine tissues,the safety thresholds of loading force and sliding velocity were 0.2 N and 0.2 mm/s,respectively;Compared with Normal Saline,Calf Serum and Hyaluronic Acid lubricants had better effects in reducing friction and preventing trauma.Moreover,the effects of loading speed,clamping force and duration time on the damage degrees of solid and tubular organs such as rabbit liver,small intestine and large intestine,were studied by simulating the clamping action with laparascopic grasper.Inflammatory cell infiltration,hyperemia and hemorrhage appeared in all tissues after compression testing;In addition,capsule rupture occurred in the liver,while breakage between the serosa and muscularic layers,and destruction of mucosa layer appeared in the small intestine and large intestine.With the increases of the loading speed,clamping force and duration time,the strain,or the deformation of these tissues increased,leading to the increase of tissue damage degree and the decrease of tissue viscoelasticity.For each tissue,there are safety parameter thresholds that can avoid severe clamping injury.Finally,the safety of laparascopic graspers with four different configurations in the processes of clamping soft tissues including liver,small intestine and large intestine was evaluated quantitatively by means of experimental research,finite element simulation and pathological analysis.Results showed that both stress concentration and seriouse damage occurred in these tissues when contacted with the edge of the jaw;Increasing the radius ofcurvature of the jaw edge and the curvature of the tooth tip could decrease the stress concentration and deformation in the tested tissue,and then reduce the tissue damage that has been caused by clamping.Therefore,a design concept of the grasper configuration for safe operation is proposed.In-depth exploration of tissue damage mechanisms under the actions of friction and clamping by using surgical instruments in this study not only can provide theoretical basis and basic data for prevention and treatment of tissue damage in the clinic,but also contribute to theoretical research of tissue injury that has been induced by mechanical stress stimulation.This helps to improve the efficiency and safety of minimally invasive surgeries such as natural orifice transluminal endoscopic surgeries.