| Medical waterjet separation technology combines waterjet technology with medical engineering to be used in surgery.Clinical practice shows that it has significant advantages such as fine separation,flat incision,clear vision,and low bleeding.Based on the above advantages,as one of the channels for constructing a precise surgical system,medical waterjet technology is facing the challenge of intelligence and refinement.However,at present,the action mechanism and dynamic evolution mechanism of high-speed waterjet impacting on soft tissues are still blank,there is a lack of theoretical research,experimental analysis methods,and optimization paths that closely connect application requirements and equipment characteristics between medical clinical needs and waterjet separation equipment.This dissertation started from the characteristics of micro-scale waterjet flow force distribution and bio-soft tissue mechanical response characteristics,through theoretical analysis,experimental design,observation discrimination,numerical analysis,index quantification and other methods,studied the mechanism of high-speed micro-scale waterjet impacting and separating the bio-soft tissue,constructed a medical waterjet separating soft tissue test platform based on the direct-driven pump,revealed the law of waterjet flow force evolution during the separation process,established the numerical analysis theory and method of the impact process,and formed an optimized path for clinical indicators.The main research contents and results are as follows:(1)Aiming at the impact mechanism of waterjet impact on soft tissue and the basic constraint conditions of medical waterjet force parameters,the power transmission and distribution of micro-scale waterjet were studied,and the basic constraints of the exit parameters of micro-scale waterjet generators under clinical operation were established.The typical stress stages and critical fracture force thresholds during soft tissue separation are analyzed,and a biomechanical explanation of the clinical advantages of soft tissue destruction by waterjet is proposed.Based on the dynamic deformation characteristics of soft tissues,a dynamic mechanical interaction model of soft tissue destruction by waterjet is constructed.An energy conversion model of the waterjet impacting on soft tissue was established,and the splashing behavior was studied in combination with the momentum conservation relationship.The results show that when the soft tissue deformation angle reaches 0.4466?,the radius of the water hammer action area is the largest,which is extend to the entire waterjet section.This critical value is beyond the strain range of general biological materials,so the water hammer action zone is almost impossible to cover the entire waterjet section.Increasing the waterjet impacting velocity and diameter can prolong the action time of the water hammer,making the action range of the water hammer closer to the diameter of the cross section of the waterjet.The splash range after the impact of the waterjet and soft tissue is not only related to the waterjet impacting velocity,but also to the tangent angle of the soft tissue surface and the waterjet incident angle.(2)To meet the experimental observation needs of medical waterjet separating soft tissues,the structure design and control scheme of the direct-driven waterjet pump and nozzle was carried out to form a medical waterjet separation soft tissue observation platform.Based on this platform,experimental research was conducted to verify the matching interval of the exit parameters of the waterjet generating device.According to the compression,tensile,and indentation mechanical tests of biological materials under large impact rates,a method for preparing gelatin samples that can cover the mechanical properties of porcine liver was determined.The results show that the energy conversion efficiency of the conical nozzle is higher than that of the cylindrical nozzle,the energy loss of the conical nozzle under the same pressure is smaller,and the pressure stability of the conical nozzle is better.The length of the initial segment of the high-speed waterjet formed by the test bench is less than 14 mm.The impact distance adjustment in this range meets the requirements of clinical applications.8%,10%,and 12% of the gelatin mass fraction ratio can basically cover the mechanical behavior difference between the two materials of porcine liver and gelatin.Gelatin samples can replace porcine liver for dynamic observation of separation process.(3)In order to numerically reproduce the response process of soft tissue under high-speed waterjet impact,based on the smooth particle hydrodynamics(SPH)-finite element(FEM)numerical calculation method,a micro-scale waterjet impingement gelatin separation calculation model was established.Then,the impact pressure control interval that forms the separation effect is obtained.Comparison of stress-strain distribution and separation efficiency of soft tissue with three clinical operating modes of vertical impact,oblique invasion,and moving failure.The results show that the stress in the object is continuously transmitted in the axial and radial directions during the vertical impact of the waterjet,and the range of stress concentration is spindle-shaped.The radial effect of the waterjet force creates a larger range of radial stress concentration.The horizontal momentum component of the oblique intrusion process makes the radial range of the impact object destruction wider.When the waterjet moves and impacts,as the waterjet moving speed increases,the damage depth decreases,and the length of the separation surface slightly increases.However,the reduction proportion in damage depth is lower than the increase proportion in movement speed.(4)In order to find out the dynamic and static changes of the soft tissue separation effect and verify the accuracy of the numerical calculation method.The relationship between impact pressure,impact distance and moving speed and static separation efficiency was analyzed.The dynamic separation efficiency of gelatin under high-speed waterjet impact was studied.The evolution law of waterjet flow force and its influencing factors during the separation process were deduced.A typical process of dynamic deformation of soft tissue under high-speed waterjet impact is proposed.Based on the RBF neural network and the adjacent average method,the elastic potential energy storage and release frequency and amplitude were quantified by prediction and reduction,which establishes a theoretical basis for the numerical study of the dynamic deformation process of soft tissue separation process.The results show that there are differences in the optimal separation pressure range for different soft tissues.The influence of the impact distance on the separation efficiency is the smallest,and the proportional increase of the waterjet's moving speed will not cause the corresponding damage depth to proportional decrease inversely.The impact separation depth is dynamically fluctuating,during which the elastic potential energy of the soft tissue is alternately stored and released.Under the same impact condition,the elastic potential energy storage and release process of the tissue with large elastic modulus during impact separation is more intense,and its utilization of waterjet flow energy is lower.(5)Facing the concerns in clinical practice,a clinical evaluation index of medical waterjet separating soft tissue and the quantitative method of non-measurement indicators were proposed.A multi-objective optimization model for clinical indicators was established,and the analysis of main factors for dynamic regulation in clinical applications was carried out.The results show that,within the scope of clinical involvement,impact pressure is the main factor in the dynamic optimization of clinical indicators,impact distance and moving speed are secondary factors,and different adjustment paths should be adopted for different adjustment needs.The dissertation has 84 figures,14 tables and 165 references. |
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