Foam dressing shape optimization method based on multi-physics field coupling numerical simulation

Abstract

The invention provides a foam dressing shape optimization method based on multi-physics field coupling numerical simulation. The foam dressing shape optimization method comprises the following steps that 1, a head model, a skull model and a skin tissue model of a patient are obtained; 2, calculating and simulating based on a fluid-solid-heat multi-physics field coupling model; and 3, topological optimization: optimizing the structure by adopting a level set method, and gradually changing the topology of the structure by evolving a level set function. According to the foam dressing shape obtained after simulation, harm to the human body can be reduced to the minimum, stress concentration caused by manual cutting is avoided, and pressure sores are avoided to the maximum extent.

Description

Technical Field

[0001] The present invention provides a method for optimizing the shape of a foam dressing based on multi - physical - field coupling numerical simulation, belonging to the technical field of medical devices. Background Art

[0002] The prevention of pressure injury (PI) has become a difficult and key point in geriatric care. Pressure ulcers are mainly local injuries caused by the combined action of pressure and shear force on the skin and subcutaneous tissues; the appearance of pressure ulcers not only causes long - term pain to patients, but also increases the treatment pressure of hospitals.

[0003] Generally, it is considered that using foam dressings can disperse pressure and reduce shear force, thereby effectively reducing the incidence of PI. Currently, foam dressings are widely used in the medical care process. However, the process of empirically using foam dressings is too cumbersome, and nurses need to cut out corresponding dressing shapes according to experience. Since making dressings takes a lot of time, it will delay the overall treatment progress of patients. Moreover, the cut - out foam dressings cannot ensure close fit with the patient's skin, and may also cause stress concentration and aggravate pressure ulcers. At the same time, the influence of the shape of internal cavities in the dressing on the diffusion of skin humidity and heat of patients is not considered, resulting in problems such as too high skin humidity and temperature in patients, and cannot effectively prevent the generation of pressure ulcers. Especially for the elderly, due to their weak cardiovascular function and dull pain sensation, they are extremely prone to pressure ulcers during nursing, leading to a series of difficult - to - solve problems. Therefore, there is an urgent need to propose a scientific dressing customization method. Summary of the Invention

[0004] In view of the above - mentioned technical problems, the present invention proposes an automatic dressing shape optimization method based on multi - physical - field coupling numerical simulation of dressings around foam dressings. The optimized foam dressing shape of the present invention can be generated by 3D printing, which can reduce material waste and control costs compared with the cutting method.

[0005] The present invention performs simulation calculations on the surface of the three - dimensional shape of the patient's head to optimize the foam dressing shape. It realizes the simulation calculation of physical quantities during the bone - muscle - dressing - tissue contact process, and reveals the variation laws of indicators such as pressure, shear force, temperature, and humidity. This method has the characteristics of fast speed, high precision, and low cost compared with obtaining foam dressings by manual cutting. Only need to obtain the CT data of the head in advance, generate the corresponding three - dimensional model of the head, perform pressure simulation calculations on the surface of the three - dimensional shape of the head, and optimize the shape of the dressing, thereby maximizing the dispersion and reduction of the pressure on the patient's head during the nursing process. The foam dressing obtained through precise calculation can effectively reduce the generation of pressure ulcers.

[0006] The specific technical solution is as follows: A method for optimizing the shape of a foam dressing based on multi-physics field coupling numerical simulation, comprising the following steps: Step 1: Obtain the head, skull, and skin tissue models of the patient; Generate a high-precision three-dimensional model of the patient's head through a circumferential video of the patient's head. After obtaining the three-dimensional head model, use 3D-gan technology to generate the corresponding skull and facial skin tissue models from the three-dimensional head model. After importing the models into Meshlab for preprocessing, then import them into COMSOL for the next step.

[0007] Step 2: Calculate and simulate based on the fluid-structure-thermal multi-physics field coupling model; Based on the models obtained in the first step, establish fluid domain and solid domain models. After importing into COMSOL, perform mesh division on the skull, head tissues, and dressings, and adjust according to physical properties to ensure mesh refinement in key areas; then set material properties, including the materials of head tissues and dressings;

[0008] Set the control equations. The fluid is set as an incompressible gas and is controlled by the Navier-Stokes equation. The conservation equation of the solid part is derived from Newton's second law, and the control equation for the change in the solid domain is controlled by the linear equilibrium equation. The temperature domain transformation uses the heat equation. Define the fluid-structure and heat conduction boundary conditions and initial conditions, including fluid inlet and outlet boundaries, heat flux boundaries, temperature boundaries as fixed temperatures, displacement boundaries as fixed displacements, and stress boundaries.

[0009] Create a fluid-structure-thermal coupling relationship. At the fluid-structure coupling interface, satisfy the equality or conservation of the fluid and solid stress (t), displacement (d), heat flux (q), and temperature (T) variables, that is, satisfy the following 4 equations, with the subscript f representing the fluid and the subscript s representing the solid;

[0010] Introduce the Newton iteration method to use full coupling. The solver starts from the initial state and then applies Newton iteration until a convergent solution is obtained, and its pressure distribution, temperature gradient, and water vapor transmission rate are obtained.

[0011] Step 3: Topological optimization; The structure is optimized by the level set method. By evolving the level set function, the topology of the structure is gradually changed. First, the design variables are initialized, and the flow resistance coefficient, heat conduction coefficient, and elastic modulus obtained in the previous step are updated. The objective function is determined. According to medical standards, the heat dissipation capacity, humidity diffusion capacity, and pressure distribution that the dressing needs to achieve are determined respectively. Minimizing the strain is used as the objective function. The energy dissipation of the flow field is constrained. The flow velocity field, temperature field, and displacement field at the current iteration step are obtained, and then the values of the objective function and each constraint function at the current iteration step are calculated. The sensitivities of the energy dissipation constraint, average temperature target, and structural compliance constraint are calculated respectively, and the sensitivity information is used to update the design variables. Gradient descent optimization iteration is used. When the objective function and constraints meet the preset convergence conditions, the optimization is stopped, and the shape optimization result of the foam dressing is obtained.

[0012] The shape of the foam dressing obtained by simulation in the present invention can minimize the harm to the human body, avoid stress concentration caused by manual cutting, and maximize the prevention of pressure ulcers. Brief Description of the Drawings

[0013] Figure 1 is a flow chart of the present invention; Figure 2 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 1 s in the embodiment; Figure 3 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 2 s in the embodiment; Figure 4 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 4 s in the embodiment; Figure 5 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 5 s in the embodiment; Figure 6 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 7 s in the embodiment; Figure 7 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 10 s in the embodiment; Figure 8 Schematic diagram of the optimization of the dressing structure for heat dissipation as the target at 14 s in the embodiment; Figure 9 Schematic diagram of the minimum strain energy of the foam dressing structure in the embodiment. Detailed Embodiments

[0014] The specific technical solutions of the present invention are described in conjunction with the embodiments.

[0015] As Figure 1 shown, the method for optimizing the shape of the foam dressing based on multi-physics field coupling numerical simulation includes the following steps: First step, obtain the head, skull, and skin tissue models of the patient.

[0016] The technology of forming a three-dimensional human body surface through human body video mapping has been mature. A high-precision three-dimensional model of the patient's head can be generated through the circumferential video of the patient's head. After obtaining the three-dimensional head model, the 3D-gan technology can be used to generate corresponding skull and facial skin tissue models based on the three-dimensional head model. After importing the model into Meshlab for preprocessing, it is then imported into COMSOL for the next step.

[0017] Step 2: Calculation and simulation based on the fluid-structure-thermal multi-physics field coupling model.

[0018] Based on the model obtained in the first step, fluid domain and solid domain models are established. After importing into COMSOL, mesh generation is performed on the skull, head tissues, and dressings, and adjustments are made according to physical properties to ensure mesh refinement in key areas, such as the edges of the dressings.

[0019] Subsequently, material properties are set, including the materials of head tissues and dressings. Since this embodiment mainly simulates heat conduction, humidity diffusion, and pressure distribution between the dressing and the skin, the density, elastic modulus, thermal conductivity, specific heat capacity, porosity, air permeability, etc. of the materials need to be considered key points.

[0020] Set the governing equations. Fluid flow should follow the physical conservation laws. The basic conservation laws include the law of conservation of mass, the law of conservation of momentum, and the law of conservation of energy. In this invention, the fluid is regarded as an incompressible gas and is controlled by the Navier-Stokes equation. The conservation equation of the solid part can be derived from Newton's second law, and the governing equation for the change of the solid domain is controlled by the linear equilibrium equation. The temperature domain transformation uses the heat equation. Define the fluid-structure and heat conduction boundary conditions and initial conditions, including fluid inlet and outlet boundaries, heat flux boundaries, temperature boundaries as fixed temperatures, displacement boundaries as fixed displacements, and stress boundaries.

[0021] Create a fluid-structure-thermal coupling relationship. Fluid-structure coupling follows the most basic conservation principle. Therefore, at the fluid-structure coupling interface, variables such as fluid and solid stress (t), displacement (d), heat flux (q), and temperature (T) should satisfy equality or conservation, that is, the following 4 equations are satisfied (subscript f represents fluid, subscript s represents solid).

[0022] In this invention, the fluid motion mainly considers the process of skin moisture diffusion in the foam dressing, so the flow resistance coefficient is used to represent it. Heat transfer mainly considers the heat transfer of skin temperature through the foam dressing and is described by the thermal conductivity. And solid mechanics analysis mainly considers the relationship between stress and strain of solid materials under unidirectional tension or compression and is described by Young's modulus.

[0023] If the initial conditions selected during the calculation are poor, problems such as non-convergence or very slow convergence may occur. The present invention introduces the Newton iteration method with full coupling. The solver will start from an initial guess and then apply Newton iteration until a converged solution is obtained, and its pressure distribution, temperature gradient, and water vapor transmission rate are obtained.

[0024] Step 3: Topological optimization.

[0025] Since the present invention needs to optimize the cavity structure inside the foam dressing, the level set method is used to optimize the structure, and the topology of the structure is gradually changed by evolving the level set function.

[0026] First, initialize the design variables and update the flow resistance coefficient, heat conduction coefficient, and elastic modulus obtained in the previous step. Determine the objective function. According to medical standards, the heat dissipation capacity, humidity diffusion capacity, and pressure distribution that the dressing needs to achieve can be determined respectively.

[0027] The present invention takes minimizing strain as the objective function. Since the mechanical energy of the fluid is converted into heat energy during the diffusion process due to factors such as internal friction (viscous force) or turbulence, resulting in insufficient heat dissipation capacity of the dressing, it is necessary to constrain the energy dissipation of the flow field.

[0028] Obtain the velocity field, temperature field, and displacement field at the current iteration step, and then calculate the values of the objective function and each constraint function at the current iteration step.

[0029] Calculate the sensitivities of the energy dissipation constraint, average temperature target, and structural compliance constraint respectively. The sensitivity information is used to update the design variables.

[0030] Use gradient descent to optimize the iteration. When the objective function and constraints meet the preset convergence conditions, stop the optimization, and the shape optimization result of the foam dressing can be obtained.

[0031] The structural optimization process of the foam dressing with the optimal heat dissipation at 1s, 2s, 4s, 5s, 7s, 10s, and 14s is respectively as Figures 2 to 8 ; the structural strain energy of the foam dressing is minimized as Figure 9 .

Claims

1. A foam dressing shape optimization method based on multi-physics field coupling numerical simulation, characterized in that: The following steps are involved: The first step is to obtain the patient's head, skull and skin tissue models; Generate a high-precision 3D model of the patient's head through the patient's head surround video; after obtaining the 3D model of the head, use 3D-gan technology to generate the corresponding skull and facial skin tissue models through the 3D model of the head; import the model into Meshlab for preprocessing, and then import it into COMSOL for the next step; The second step is calculation and simulation based on the fluid-solid-heat multi-physics field coupling model; Based on the model obtained in the first step, the fluid domain and solid domain models are established; after importing into COMSOL, the skull, head tissue and dressing are meshed and adjusted according to the physical properties to ensure the mesh refinement of key areas; then the material properties are set, including the materials of the head tissue and dressing; Step 3: Topology optimization; The level set method is used to optimize the structure, and the topology of the structure is gradually changed by evolving the level set function.

2. The foam dressing shape optimization method based on multi-physical field coupling numerical simulation according to claim 1 is characterized in that: The second step is specific The process includes: (1) Setting the control equation; The fluid is treated as an incompressible gas and is controlled by the Navier-Stokes equations. The conservation equations of the solid part are derived from Newton's second law, and the control equations of the solid domain changes are controlled by the linear equilibrium equations. The heat equation is used for temperature domain transformation. The fluid-solid and heat conduction boundary conditions and initial conditions are defined, including the fluid inlet and outlet boundaries, the heat flux boundary, the temperature boundary as a fixed temperature, the displacement boundary as a fixed displacement, and the stress boundary. (2) Create fluid-solid-thermal coupling relationship; At the fluid-solid coupling interface, the fluid and solid stress t, displacement d, heat flow q, and temperature T variables are equal or conserved, that is, the following four equations are satisfied, where subscript f represents fluid and subscript s represents solid; The Newton iteration method is introduced to use full coupling. The solver starts with an initial guess and then applies Newton iteration until a converged solution is obtained to obtain its pressure distribution, temperature gradient, and water vapor permeability.

3. The foam dressing shape optimization method based on multi-physical field coupling numerical simulation according to claim 1 is characterized in that: The third step specifically includes the following processes: First, initialize the design variables and update the flow resistance coefficient, thermal conductivity coefficient and elastic modulus obtained in the previous step; Determine the objective function and determine the heat dissipation capacity, moisture diffusion capacity and pressure distribution that the dressing needs to achieve based on medical standards; Take minimizing strain as the objective function; constrain the energy dissipation of the flow field; obtain the velocity field, temperature field and displacement field under the current iteration step, and then calculate the values ​​of the objective function and each constraint function under the current iteration step; The sensitivity of energy dissipation constraint, average temperature target and structural flexibility constraint are calculated respectively, and the sensitivity information is used to update the design variables; Using gradient descent optimization iteration, when the objective function and constraints meet the preset convergence conditions, the optimization is stopped to obtain the shape optimization result of the foam dressing.

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