| Background: With the advent of the Da Vinci surgical robot,surgery has entered the robot era.Da Vinci robot has been widely used in gastrointestinal surgery.However,one obvious disadvantage of Da Vinci robot is lack of force feedback.In this circumstance,surgeons can not accurately control the force in the clamping process,which leads to uncertainty and increases the risk of tissue damage in surgery.Furthermore,as the most commonly used surgical forcep,dentate forcep cause stress concentration in the clamping process and easily lead to tissue damage.However,these problems have not been well solved at present.Our research was conducted from two parts: firstly,we analyzed the mechanism of tissue damage in the clamping process,and then try to solve tissue damage through two different countermeasures.Objective:(1)To research the biomechanical change of intestinal tract during the clamping process.(2)To determine the stress threshold and time threshold of tissue damage under the microscope.(3)Countermeasure one:developing a new interface with low damage morphology and excellent friction performance to indirectly reduce the force load and the tissue damage during the clamping process.(4)Countermeasure two: developing a new surgical robot with force feedback to directly solve the tissue damage caused by the lack of feedback in Da Vinci surgical robot.Methods:(1)Through biomechanical testing machine,the loadingunloading,strain creep and stress relaxation tests were performed using small and large intestines removed from four pigs.Each test was repeated4 times respectively and the stress,strain and time were recorded.The stress-strain,strain-time,stress-time curve were established and analyzed.(2)The small and large intestines of 10 live pigs were clamped under different pressures(small intestine: 0/30/40/50/60/70/80 k Pa;large intestine:0/40/60/80/100/120/140 k Pa)and duration time(5/10/20/30s)and then marked.The tissues were removed for pathological examinations after five hours.The tissue damage was quantified by three indicators: the number of neutrophil cells,the number of CD4+T cells and the expression of Occludin protein in the mucosa,and then tissue damage score was calculated based on the above three indicators.The tissue damage thresholds of pressure and time were determined according to the damage score.(3)According to the principle of strong adhesion of tree frog,we designed five biomimetic interfaces with different pillar-textured micronano structures using polydimethylsiloxane(PDMS).Different concentrations of surfactant was added to modify the hydrophilia.Then,the biocompatibility of the interfaces were evaluated using the extracting liquid method according to the standard of GB/T 16886.5-2017 for biological evaluation of medical devices.Finally,the friction properties of five interfaces were tested using single-side sliding mode,and the parameters of interface was optimized by orthogonal experimental design.(4)After analyzing the key technology and structure,a new integrated surgical robot with force feedback was developed.In order to evaluate the effect of force feedback,the force ratio of master-slave manipulators of five medical students were analyzed in the clamping process through the simulation box experiments(fixed-point clamping,linear motion,circular motion).At the same time,the five medical students were trained and the clamping force of the slave manipulators was compared before,during and after training.The learning curve of the clamping force were compared between the new integrated robot and the "Micro hand S" robot.Results:(1)In the loading-unloading test,the stress-strain curve showed a nonlinear relationship;In the creep test,the strain increased with time,especially in the first 20 s,and then gradually slowed down.The strain increment was lagrest in the first 40s(83.7% for small intestine,82.0% for large intestine).In the stress relaxation test,the stress decreased with time,decreasing rapidly in the first 20s(82.8% for small intestine,76.8% for large intestine),and then gradually slowed down.(2)After the intestinal tissue was clamped under the above pressure and time,no visible damage was observed.However,microscopic damage did exist: the number of neutrophil cells increased,the number of CD4+T lymphocytes and the expression of tight junction protein Occludin decreased.When the clamping force≥50k Pa,tissue damage score of small intestine significantly increased(-2.898±1.248 vs.-0.165±0.614,P<0.001);tissue damage score of large intestine significantly increased when clamping force≥80k Pa(-2.728±0.874 vs.-0.032±0.871,P<0.001).At the pressure threshold of 50 k Pa,when clamping time increased form 5s to 20 s,tissue damage score of small intestine significantly increased(-1.827±1.274 vs.0.904±1.645,P<0.01).For large intestine,tissue damage score significantly increased when clamping time≥20s at the pressure threshold of 80 kpa compared with 5s(-1.818±1.182 vs.3.171±0.481,P<0.001).(3)We developed five PDMS microstructural interfaces based on the tree frog toe pads.The results of hydrophilic modification showed that contact angle decreased with the increase of surfactant concentration.The results of biocompatibility experiment showed that no obvious toxicity was found when the surfactant concentration was less than 3.0%.Therfore,the concentration of 3% was adopted.The results of friction experiments showed that hexagonal surface(mean friction coefficient 0.33±0.04),and then circle(0.30±0.05),square(0.27±0.02),rhomboid(0.26±0.05),triangle(0.25±0.03).The friction coefficient of the hexagonal interface was significantly higher than that of conventional stainless steel interface(0.33±0.04 vs.0.22±0.02,P<0.001).(4)The results of the simulation box experiments showed that the new integrated robot initially has force feedback effect,especially when the clamping force was more than 5N.Compared with the "Micro hand S" robot,the clamping force of the slave manipulator for the integrated robot was lower before,during and after training,respectively(P<0.05),but still higher than that of the traditional forcep(P<0.05).In addition,the maximum clamping force of the integrated robot(Fmax),overcome the learning curve after 17-24 times of training,which was significantly shorter than the 29-40 times for “Micro hand S” robot.Conclusion:(1)The creep and stress relaxation properties of intestinal tissue during the clamping process decrease with clamping time.In both creep and stress relaxation tests,pressure plays a key role and time plays a secondary role.(2)The pressure threshold of tissue damage under the microscope was50 k Pa for small intestine and 80 k Pa for large intestine,respectively.Under pressure thresholds,the time threshold was 20 s for small intestine,30 s for large intestine.(3)We developed a hexagonal pillar-textured biomimetic interface using the material of PDMS.This new interface exhibits excellenct biological compatibility,which not only produce low tissue damage,but also can effectively increase friction force.(4)Our team successfully developed a new type of integrated surgical robot with force feedback,which can significantly reduce the clamping force and be helpful to reduce the tissue damage. |
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