| Micro-water jet(medical water jet)technology can be used as a surgical separation instrument for cutting and separating human tissues,etc.It has high flexibility,selective and protective resection of tissues,no thermal damage,and low intraoperative blood loss,short operation time and other advantages.Therefore,this technique is widely used in orthopedics,ophthalmology,trauma surgery and other surgical operations.At present,there are still some problems with the micro-water jet technology,such as poor jet bunching and unstable pressure.In addition,the micro-water jet has no relatively mature theoretical system for the processing of human tissue materials with high toughness and elastic body,and lacks corresponding experimental research.So,this article takes the pig liver closest to human liver tissue as the research object,and optimizes the structure size of the micro-water jet nozzle to establish a stress-strain constitutive model.And used in the process of micro-water jet impact on pig liver material,to obtain the pig liver tissue material destruction threshold.The experimental verification of the jet parameters on pig liver tissue and vascular disruption.It provides theoretical data for the application of micro-water jet technology in medicine.The main research work of this paper is as follows:Firstly,numerical simulation of the internal and external flow field of the micro-water jet nozzle and optimization of its internal structure size.Theoretical analysis of the flow state of micro-water jet fluid,determination of fluid properties,determination of fluid flow governing equation.The computational fluid dynamics software Fluent is used to numerically simulate the distribution of mico-water jets inside and outside the nozzle.The distribution of pressure field and velocity field of jet flow inside and outside the nozzle was obtained.The influence of the internal structure of the cone-shaped nozzle,such as the shrinkage angle,the length of the straight segment and the nozzle length,on the jet velocity was analyzed.The best combination to obtain the internal structure size parameters of the nozzle is: shrink angle ?=13 °,straight line length I=0.2 mm,nozzle length L=2.0 mm.By introducing transition fillets to improve the jet beam concentrating and enhance the jet stability,the research shows that the optimal transition ratio for transition fillets is 0.3.Secondly,establish a stress-strain constitutive model of pig liver.The effects of strain rate and loading direction on the mechanical properties of pig liver tissues were studied through quasi-static uniaxial tensile experiments on porcine liver parenchyma.It is obtained that the average elastic modulus of pig liver tissue was 0.27 MPa,and the failure strain occurred at 55-65%.An improved SHPB device is used to measure the dynamic compression mechanical response of pig liver tissue,and an incompressible visco-hyperelastic constitutive equation based on exponential and third-order Yeoh's high strain rate is established.Thirdly,numerical simulation of the process of erosion of pig liver tissue by micro-water jet.The Ansys/Ls-Dyna software is used to numerically simulate the cutting process of porcine liver tissue by introducing an incompressible visco-hyperelastic constitutive model to analyze the deformation and damage process of porcine liver tissue material during water jet processing,and obtain the failure threshold of material separation and destruction Jet pressure value.Fourthly,experimental study on the mechanism of removing liver tissue material from micro-water jet processing.The above-mentioned optimized design nozzle is installed on a self-made micro water jet processing equipment,and a micro water jet processing pig liver experiment is carried out to verify the numerical simulation results.The experimental results show that the simulation results have the same trend as the experimental results and the values are close.Therefore,the constitutive model and simulation method established are reasonable and feasible.By analyzing the influence of jet pressure on the mechanism of pig liver tissue removal,it is found that there is a region with a large strain value under the impact of micro-water jets on the surface of pig liver.The higher the impact pressure,the greater the amount of material bulging in the impact area.When it reaches 3.39 MPa,the highest stress in the impact area exceeds the yield limit,and the pig liver material is damaged.Experimental studies on the damage of blood vessels in tissues when micro-water jets cut pig livers,the results show that: when the jet pressure is 4 MPa,0.8 mm diameter vessels can be retained;when the jet pressure is 5 MPa,1.0 mm diameter vessels can be retained;When the pressure exceeds 6 MPa,there is a certain damage to blood vessels with a diameter of 1.2 mm.The above research results provide theoretical references and data support for the technical promotion of micro-water jet technology in medicine. |
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