Device and method for measuring displacement and strain of inner surface of tissue

Abstract

The invention discloses a tissue inner surface displacement and strain measurement device and method, and the device comprises a simulated tissue which comprises a bionic polymer, a connecting liquid, and a to-be-measured tissue; the space between the to-be-detected tissue and the bionic polymer is filled with connecting liquid and then packaged; the loading device comprises an impact rod and a transmission rod, the impact rod is arranged at one end of the simulated tissue, and the transmission rod is arranged at the other end of the simulated tissue; the feature making tool is used for making two speckles randomly distributed on the two curved surfaces, the two speckles are transparent under natural light and present two different colors under illumination with a certain bandwidth, and the imaged curved surface picture has high contrast; the calibration tool is used for calibrating internal parameters and external parameters of the camera; and the data processing module is used for calculating the displacement and strain mechanical quantity of the acquired image and correcting a calculation result. The device solves the problems that when a contact impact object is measured, the measurement object and the impact object shield each other, the internal mechanical response of the object is difficult to capture, and the distortion error of the observation object is large.

Description

Technical Field

[0001] The present invention belongs to the technical field of the intersection of biomechanics and photogrammetry, and specifically relates to a device and method for measuring displacement and strain of the inner surface of a tissue. Background Art

[0002] At present, the precise measurement technology and characterization methods of internal full-field mechanical parameters have always been a common "bottleneck" problem that restricts the development and safe service of major engineering materials and structures. Traditional mechanical experiments have many measurement methods for the mechanical behavior of the surface of the structure, but there is always a lack of suitable means for the measurement and characterization of internal mechanical parameters. This is one of the weak links in the field of solid mechanics and a century-old problem that solid mechanics scientists urgently need to solve. The current technical means revolve around internal imaging methods such as advanced light sources such as X-ray and neutron imaging, as well as spectral mechanics methods represented by micro-Raman, micro-fluorescence, and THz wave time-domain spectroscopy for mechanical testing and characterization of composite structure interface problems.

[0003] Understanding the mechanical effects of external forces (such as impact forces) on biological tissues is crucial for preventing, diagnosing, and treating tissue injuries. The mechanical response of biological tissues after impact is an interdisciplinary field involving multiple disciplines such as biomechanics, materials science, and medicine. By deeply studying the mechanical response of tissues after impact, researchers hope to improve the design of safety protection devices, optimize athletes' protective equipment to reduce the incidence of injuries, and develop more effective rehabilitation programs to improve the quality of life of patients. However, general biological tissues are composed of components such as water, cells, and matrix, and their mechanical properties are nonlinear, anisotropic, and time-dependent. There are limitations in using traditional mechanical models to describe their mechanical responses, which poses certain challenges to studying the mechanical mechanisms of biological tissues after stress. Therefore, researchers have tried to use finite element simulations, biomechanical experiments such as dynamic mechanical analysis (DMA), micro compression tests, and imaging techniques (such as MRI and CT) to evaluate the mechanical properties of tissues, hoping to predict and verify the behavior of tissues under stress, but there are technical bottlenecks in the real-time measurement of the full-surface displacement and deformation of internal tissues. Summary of the invention

[0004] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a device and method for measuring the displacement and strain of the inner surface of a tissue, so as to solve the problems in the prior art of measuring contact and impact objects, such as the mutual obstruction of the measured object and the impact object, the difficulty in capturing the internal mechanical response of the object, and the large distortion error of the observed object.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A tissue inner surface displacement and strain measurement device of the present invention comprises: a loading device, a simulated tissue, a feature making tool, a calibration tool and a data processing module;

[0007] The simulated tissue includes a biomimetic polymer, a connecting liquid and a tissue to be tested; the tissue to be tested is assembled with the biomimetic polymer, and the connecting liquid is filled between the two to form a whole package;

[0008] A loading device, comprising an impact rod (impact force applying part) and a transmission rod (supporting part), wherein the impact rod is placed at one end of the simulated tissue and the transmission rod is placed at the other end of the simulated tissue; the loading device is used to generate force and act on the simulated tissue;

[0009] Feature creation tool, used to create two types of speckles randomly distributed on two surfaces. The two types of speckles are transparent under natural light and present two different colors under a certain bandwidth of light. The image of the surface after imaging has high contrast.

[0010] Calibration tool, used to calibrate the internal and external parameters of the camera;

[0011] The data processing module is used to calculate the displacement and strain mechanical quantities of the acquired images.

[0012] Furthermore, the data processing module includes an image acquisition unit, a three-dimensional point cloud reconstruction unit, a point cloud correction processing unit, and a full-field displacement and strain calculation unit;

[0013] An image acquisition unit, used for acquiring image data of simulated tissue;

[0014] A three-dimensional point cloud reconstruction unit is used to respectively perform three-dimensional reconstruction on two curved surfaces of the bionic polymer and the tissue to be tested by using limit constraints, and the influence of the bionic polymer on the imaging of the tissue to be tested is ignored in the reconstruction process;

[0015] A point cloud correction processing unit, which uses calibration parameters and the three-dimensional point cloud of the biomimetic polymer to correct the point cloud of the tissue to be tested point by point;

[0016] The full-field displacement and strain calculation unit is used to calculate the first-order and second-order derivatives of the bionic polymer and the point cloud coordinates of the tissue to be tested on the time axis.

[0017] Furthermore, the loading device is a device that generates mechanics, such as a universal testing machine, a Hopkinson bar, etc.

[0018] Furthermore, the bionic polymer is a transparent substance and is produced by 3D printing after scanning the three-dimensional contour of the original structure.

[0019] Furthermore, the connection liquid is a transparent solution of food coloring and water, which has a strong light-transmitting property, and the refractive index of the transparent solution is the same as that of the biomimetic polymer.

[0020] Furthermore, the tissue to be tested is a hydrogel material made from biological original tissue or simulated tissue.

[0021] Furthermore, the calibration tool is a calibration plate of known size commonly used in computer vision.

[0022] Furthermore, the image acquisition unit acquires image data through two color cameras.

[0023] A method for measuring displacement and strain of the inner surface of a tissue according to the present invention is based on the above device and comprises the following steps:

[0024] 1) Encapsulating the simulated tissue: spraying a fluorescent blue solution on the surface of the tissue to be tested, spraying a fluorescent red solution on the surface of the biomimetic polymer, then filling the space between the biomimetic polymer and the tissue to be tested with a connecting liquid, and sealing the biomimetic polymer with glue to encapsulate the simulated tissue;

[0025] 2) System calibration and preliminary morphology measurement: The three-dimensional point cloud of the speckle on the surface of the biomimetic polymer and the speckle on the surface of the tissue to be measured is calculated by the three-dimensional DIC method. The calculated morphology of the tissue to be measured contains distortion and is a distorted point cloud. The three-dimensional point cloud of the speckle on the surface of the biomimetic polymer calculated by the three-dimensional DIC method is t n The coordinate value at the moment is {Ψ n |(X i Y i Z i ),i=1,2,…,m};

[0026] 3) Real-time calibration of the refractive distortion of the simulated tissue inner surface: real-time correction of the biomimetic polymer surface equation f of the simulated tissue under test by transparent 3D DIC data n (x,y,z,Ψ n )=0, (x, y, z) are Cartesian coordinates, the refraction points of the distorted point cloud light on the polymer surface equation are calculated, and the intersection points of the distorted light are recalculated, which are the corrected points.

[0027] 4) The full-field displacement and strain of the tissue are calculated for the corrected tissue point cloud morphology, which is used to calculate the first-order and second-order derivatives of the bionic polymer and the measured tissue point cloud coordinates on the time axis.

[0028] Furthermore, the fluorescent blue solution is sprayed on the surface of the tissue to be tested to form randomly distributed droplets. The droplets adhere to the surface of the tissue to be tested, follow the movement and deformation of the tissue to be tested, and are recorded by a color camera, showing a black and white high-contrast speckle pattern (SP) on the image. The speckle pattern (SP) is used for digital image correlation (DIC) measurement to record the movement and deformation information of the droplets under the action of external force, so as to characterize the mechanical response of the tissue.

[0029] Furthermore, the bionic polymer is obtained by scanning the three-dimensional contour of the original structure (such as the exocranium of the skull structure) and is manufactured as a transparent material by 3D printing.

[0030] Furthermore, the fluorescent red solution is sprayed on the surface of the bionic polymer to form randomly distributed droplets. The droplets adhere to the surface of the bionic polymer, follow the movement and deformation of the bionic polymer, are recorded by a color camera, and appear as speckles with black and white intensity contrast on the image, which is used for real-time measurement of the morphology of the bionic polymer after being subjected to force.

[0031] Furthermore, the connection liquid is a biocompatible transparent solution, and its refractive index is consistent with that of the biomimetic polymer. It is a mixture of edible pigment and water, and has the functions of filling the gap between the biomimetic polymer and the tissue, eliminating 3D printing errors, reducing light scattering caused by medium changes, and increasing light transmittance, which is conducive to helping the blue light emitted by the fluorescent blue speckle to be fully captured by the color camera.

[0032] Furthermore, the modified biomimetic polymer surface equation of the simulated tissue to be tested is specifically: the three-dimensional reconstructed point cloud {Ψ n |(X i Y i Z i ), i = 1, 2, ..., m}, as the truth point of the biomimetic polymer surface equation, and substitute it into the initial equation f 0 (x,y,z,Ψ 0 )=0 to optimize and obtain the optimized biomimetic polymer equation f n (x,y,z,Ψ n )=0.

[0033] Furthermore, in step 3), any point B of the distorted point cloud is calculated 1v (X B1v, Y B1v, Z B1v ) in the biomimetic polymer surface equation f n (x,y,z,Ψ n )=0, denoted as (x 1 ,y 1 ,z1 )、(x 2 ,y 2 ,z 2 ) to derive the direction vector of light refracted from the biomimetic polymer medium to the air, specifically:

[0034]

[0035] Among them, t x ,t y ,t z They are the three components of the camera external parameter translation vector t, obtained by camera calibration, and the surface is at the intersection coordinate (x 1 ,y 1 ,z 1 )、(x 2 ,y 2 ,z 2 )’s normal vector n 1 、n 2 From the surface equation f n (x,y,z,Ψ n )=0 is given.

[0036] Furthermore, in the step 3), the intersection of the distorted light rays is recalculated, i.e., the corrected point, and the stereoscopic vision imaging model in the three-dimensional digital image correlation method is corrected in real time; specifically, the refraction law is used to calculate the corrected refracted light rays, and then the refracted light rays are subjected to beam adjustment to solve the points without distortion after correction; the point cloud is traversed to obtain the corrected tissue point cloud morphology.

[0037] Beneficial effects of the present invention:

[0038] In the present invention, the gap between the tissue to be tested and the biomimetic polymer is filled with an optically transparent liquid, which can reduce the refraction and scattering of light between different substances; the assembled biomimetic polymer and the tissue to be tested simulate the real biological tissue structure; they are placed under a loading device, and under a certain bandwidth of light, the tissue to be tested in the biomimetic polymer can be captured in real time.

[0039] The present invention can solve the problem that the bionic polymer structure in the prior art has light refraction distortion due to its irregular curved surface shape. This distortion is coupled with the real-time deformation measurement of the bionic polymer outer surface, and the general correction method is difficult to solve the real morphology and deformation information of the internal tissue. Based on the measuring device of the present invention, a method for real-time correction of the skull surface equation of transparent experimental data is proposed for correction of internal tissue model distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0041] Figure 2 This is a schematic diagram of the material simulating the cross-section of the brain in the present invention;

[0042] Figure 3 A schematic diagram of simulated cranial brain structure and characteristic markings in the present invention;

[0043] Figure 4a This is a schematic diagram of simulating tissue distortion correction in the present invention;

[0044] Figure 4b Schematic diagram of the calculation grid and refraction points for simulating the polymer surface (simulating the outer surface of the tissue) in the present invention. DETAILED DESCRIPTION

[0045] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0046] Reference Figures 1 to 3 As shown, a tissue inner surface displacement and strain measurement device of the present invention, in the example, simulates the brain, comprises: loading devices B1 and B2, a simulated brain S, a feature making tool M1, a calibration tool, color cameras C1, C2 and a computer;

[0047] The loading device is a Hopkinson bar that produces an impact effect. B1 is an impact bar used to produce an impact and is placed at the front end of the simulated skull S being impacted. B2 is a transmission bar and is placed at the rear end of the simulated skull S being impacted. The impact device realizes in-situ impact of the skull sample.

[0048] The simulated skull S comprises a skull 10, a skull-brain connection fluid 20 and a brain tissue 30, wherein the skull 10 is a transparent bionic polymer, which is made by scanning the three-dimensional contour of a real skull and then using 3D printing, or by mold forming; the brain tissue 30 is made by filling a mold with materials such as biological original tissue or brain tissue-mimicking hydrogel; the skull-brain connection fluid 20 is filled between the brain tissue and the skull, and the skull-brain connection fluid 20 is a biocompatible transparent solution, and its refractive index is consistent with the refractive index of the bionic polymer used in the skull, both of which are η e .

[0049] A fluorescent blue solution is sprayed with a spray gun to form randomly distributed droplets on the surface of the brain tissue 30. The droplets can adhere to the surface of the brain tissue and move with the movement of the brain tissue. They are recorded by a color camera and appear as black and white high-contrast speckle pattern (SP) 301 on the image. They are used for digital image correlation (DIC) measurement to record the movement and deformation information of the droplets under the action of impact force, so as to characterize the impact mechanical response of the brain tissue.

[0050] The brain connecting fluid 20 is filled between the brain tissue and the skull. The fluid is a mixture of edible pigment and water. The fluid has the functions of filling the gap 201 between the skull and the brain tissue, compensating for the 3D printing error of the skull, reducing the light scattering caused by the change from the speckle 301 to the skull medium, and increasing the light transmittance, which is beneficial to help the blue light emitted by the speckle 301 to be fully captured by the color camera.

[0051] In a preferred example, the skull 10, the cranial-brain connecting fluid 20, and the brain tissue 30 are bonded and sealed with polymer glue.

[0052] In the preferred example, considering the non-planar characteristics of the cranial material, the imaging of the speckle 301 will be refracted and distorted, and the distorted surface is the unknown outer surface of the skull, which will be deformed under the action of external force. In order to track the deformation in real time, a fluorescent red solution is sprayed on the outer surface of the skull to form randomly distributed fluorescent red speckles 101. The fluorescent blue speckle 301 and the fluorescent red speckle 101 are colorless and transparent, and only emit blue and red light respectively under the irradiation of ultraviolet light.

[0053] Reference Figure 4a As shown, the refractive distortion of the brain is calibrated in real time; standard calibration tools such as the chessboard calibration board are placed at the simulated brain position, and the color cameras C1 and C2 are given by Zhang's calibration method, where the relative external parameters are the rotation matrix R and the translation vector t; the world coordinate system OX is established w Y w Z w. , the coordinate origin is located at the optical center of the color camera C1, and the coordinate of the optical center of the color camera C1 is O 1 (0,0,0), the optical center coordinate of color camera C2 is O 2 (t x ,t y ,y z ), the translation vector t of C2 relative to C1; then synchronously collect speckle images of the skull surface and brain tissue. Based on stereo vision and limit constraints, reconstruct the reference time t of the fluorescent red speckle 101 and the fluorescent blue speckle 301 0 The three-dimensional point cloud (before impact) is Ψ 0 ,Ω 0 , the surface equation of the 3D printed skull surface is f(x,y,z)=0, which is corrected to the equation f in the camera world coordinate system 0 (x,y,z,Ψ 0 )=0, (x, y, z) are Cartesian coordinates. Figure 4a to Figure 4b As shown, after the impact, the fluorescent red speckle 101 and the fluorescent blue speckle 301 are reconstructed at any time t n The three-dimensional point cloud (after impact) is 1011Ψ n 、3012V n Among them, point cloud 1011Ψn The surface equation f(x, y, z) = 0 calculated by DIC for the fluorescent red speckle 101 is corrected to f n (x,y,z,Ψ n )=0; the three-dimensional point cloud reconstructed by the calibration data and the fluorescent blue speckle 301 is 3012V n , the point cloud contains the air refractive index η a The refractive index η of the skull 10 and the cranial brain connecting fluid 20 is e The refraction distortion caused by the difference; the distorted three-dimensional point cloud 3012V n Correction is performed to obtain the real world coordinates of the speckle on the surface of brain tissue 3011Ω n .

[0054] The calibration method is as follows:

[0055] 1) Calculate the three-dimensional point cloud of the skull polymer surface speckle by three-dimensional DIC, with m grid points 1011, and the grid points are at t n The coordinate value at the moment is {Ψ n |(X i Y i Z i ),i=1,2,…,m};

[0056] 2) The surface equation of the skull speckle at any time after the impact is corrected by the grid point 1011; {Ψ n |(X i Y i Z i ),i=1,2,…,m} into f n (x,y,z,Ψ n ), use the Gauss-Newton iteration method to solve the optimization problem of the following formula (1), and obtain the function f of the grid correction after impact n (x,y,z,Ψ n )=0:

[0057]

[0058] 3) Performing 3D reconstruction according to the pinhole imaging model by 3D DIC, calculating the 3D point cloud s distorted grid points 3012V of the fluorescent blue speckle 301 on the surface of the brain tissue 30 n ;

[0059] 4) Set 3D point cloud 3012V n Any distortion point B 1v (X B1v, Y B1v, Z B1v ) and the surface equation at R 1 , R 2, calculate the refracted light L of the air medium corresponding to the distortion point 1 With L 2 , that is, the refracted light O 1 R 1 , O 2 R 2 ; Due to O 1 R 1 , O 2 R 2 With O 1 B 1v , O 2 B 1v The direction vector is the same, the refracted light L 1 With L 2 The solution of is transformed into the solution of ray O 1 B 1v , O 2 B 1v The intersection problem with the outer surface of the skull where the speckle fluorescent red speckle 101 is located, that is, solving Figure 4a The distortion point B is shown in 1v Corresponding to the light refraction point R on the outer surface of the skull 1 , R 2 . R 1 (x 1 ,y 1 ,z 1 ), R 2 (x 2 ,y 2 ,z 2 )'s coordinates are as follows Figure 4a and Figure 4b Where 1012 is obtained by formula (2) and (3) as follows:

[0060]

[0061] Among them, t x ,t y ,t z They are the three components of the camera external parameter translation vector t;

[0062] Further, R 1 , R 2 Normal vector n of the position 1 、n 2 The surface equation f n (x,y,z,Ψ n ) = 0 gives;

[0063] 5) Calculate the normal vector n 1 、n 2 , respectively with L 1 , L 2 Angle, denoted as β 1With β 2 ; Set the refractive index of air to η a =1, according to the law of refraction, calculate the refracted light L 1 , L 2 The refraction angle θ in the skull 10 and the cranial-brain connection fluid 20 1 With θ 2 , as shown in formula (4)(5):

[0064] θ 1 = arcsin(sinβ 1 / η e ) (4)

[0065] θ 2 = arcsin(sinβ 2 / η e ) (5);

[0066] Solve for the refraction point R 1 , R 2 and the direction of the refracted light θ 1 With θ 2 , and further solve the light L by bundle adjustment method 1 ', L 2 '.

[0067] 6) Using the bundle adjustment method, solve the ray L 1 'With L 2 'The intersection point B, that is, the distortion point B 1v The three-dimensional coordinates of the brain tissue surface after correction;

[0068] Repeat steps 4) to 6) to traverse all the speckle real world coordinates of the brain tissue 3011Ω n .

[0069] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A device for measuring displacement and strain of tissue inner surface, characterized in that: include: Loading devices, simulated tissues, feature making tools, calibration tools and data processing modules; The simulated tissue includes a biomimetic polymer, a connecting liquid and a tissue to be tested; the tissue to be tested is assembled with the biomimetic polymer, and the connecting liquid is filled between the two to form a whole package; A loading device, comprising an impact rod and a transmission rod, wherein the impact rod is placed at one end of the simulated tissue and the transmission rod is placed at the other end of the simulated tissue; the loading device is used to generate force and act on the simulated tissue; Feature creation tool, used to create two types of speckles randomly distributed on two surfaces. The two types of speckles are transparent under natural light and present two different colors under a certain bandwidth of light. The image of the surface after imaging has high contrast. Calibration tool, used to calibrate the internal and external parameters of the camera; The data processing module is used to calculate the displacement and strain mechanical quantities of the acquired images.

2. The tissue inner surface displacement and strain measurement device according to claim 1, characterized in that: The data processing module includes an image acquisition unit, a three-dimensional point cloud reconstruction unit, a point cloud correction processing unit, and a full-field displacement and strain calculation unit; An image acquisition unit, used for acquiring image data of simulated tissue; A three-dimensional point cloud reconstruction unit is used to respectively perform three-dimensional reconstruction on two curved surfaces of the bionic polymer and the tissue to be tested by using limit constraints, and the influence of the bionic polymer on the imaging of the tissue to be tested is ignored in the reconstruction process; A point cloud correction processing unit, which uses calibration parameters and the three-dimensional point cloud of the biomimetic polymer to correct the point cloud of the tissue to be tested point by point; The full-field displacement and strain calculation unit is used to calculate the first-order and second-order derivatives of the bionic polymer and the point cloud coordinates of the tissue to be tested on the time axis.

3. The tissue inner surface displacement and strain measurement device according to claim 1, characterized in that: The bionic polymer is a transparent substance and is produced by 3D printing after scanning the three-dimensional contour of the original structure.

4. The tissue inner surface displacement and strain measurement device according to claim 1, characterized in that: The connecting liquid is a transparent solution of food coloring and water, has strong light transmission performance, and the refractive index of the transparent solution is the same as that of the biomimetic polymer.

5. The tissue inner surface displacement and strain measurement device according to claim 1, characterized in that: The tissue to be tested is a hydrogel material made of biological original tissue or simulated tissue.

6. A method for measuring displacement and strain of the inner surface of a tissue, based on the device according to any one of claims 1 to 5, characterized in that: The steps are as follows: 1) Encapsulating the simulated tissue: spraying a fluorescent blue solution on the surface of the tissue to be tested, spraying a fluorescent red solution on the surface of the biomimetic polymer, then filling the space between the biomimetic polymer and the tissue to be tested with a connecting liquid, and sealing the biomimetic polymer with glue to encapsulate the simulated tissue; 2) System calibration and preliminary morphology measurement: The three-dimensional point clouds of the speckle on the surface of the biomimetic polymer and the surface of the tissue to be measured are calculated using the three-dimensional DIC method. The calculated morphology of the tissue to be measured contains distortion and is a distorted point cloud; The three-dimensional point cloud of the biomimetic polymer surface speckle calculated by the three-dimensional DIC method is n The coordinate value at the moment is {Ψ n |(X i Y i Z i ),i=1,2,…,m}; 3) Real-time calibration of the refractive distortion of the simulated tissue inner surface: real-time correction of the biomimetic polymer surface equation f of the simulated tissue under test by transparent 3D DIC data n (x,y,z,Ψ n )=0, (x, y, z) are Cartesian coordinates, calculate the refraction point of the distorted point cloud light on the polymer surface equation, and recalculate the intersection point of the distorted light, which is the corrected point; 4) The full-field displacement and strain of the tissue are calculated for the corrected tissue point cloud morphology, which is used to calculate the first-order and second-order derivatives of the bionic polymer and the measured tissue point cloud coordinates on the time axis.

7. The method for measuring displacement and strain of the inner surface of tissue according to claim 6, characterized in that: The fluorescent blue solution is sprayed on the surface of the tissue to be tested to form randomly distributed droplets. The droplets adhere to the surface of the tissue to be tested, follow the movement and deformation of the tissue to be tested, and are recorded by a color camera. Black and white high-contrast speckles appear on the image, which are used for digital image correlation measurement, record the movement and deformation information of the droplets under the action of external forces, and are used to characterize the mechanical response of the tissue.

8. The method for measuring displacement and strain of the inner surface of tissue according to claim 6, characterized in that: The fluorescent red solution is sprayed on the surface of the biomimetic polymer to form randomly distributed droplets. The droplets adhere to the surface of the biomimetic polymer, follow the movement and deformation of the biomimetic polymer, are recorded by a color camera, and show black and white intensity contrast speckles on the image, which are used for real-time measurement of the morphology of the biomimetic polymer after being subjected to force.

9. The method for measuring displacement and strain of the inner surface of tissue according to claim 6, characterized in that: The modified biomimetic polymer surface equation of the simulated tissue to be tested is specifically: the three-dimensional reconstructed point cloud {Ψ n |(X i Y i Z i ),i=1,2,…,m}, as the truth point of the bionic polymer surface equation, the initial equation f0(x,y,z,Ψ0)=0 is substituted for optimization to obtain the optimized bionic polymer equation f n (x,y,z,Ψ n )=0.

10. The method for measuring displacement and strain of the inner surface of tissue according to claim 9, characterized in that: In step 3), any point B of the distorted point cloud is calculated. 1v (X B1v, Y B1v, Z B1v ) in the biomimetic polymer surface equation f n (x,y,z,Ψ n )=0, recorded as (x1, y1, z1), (x2, y2, z2) to derive the direction vector of light refracted from the bionic polymer medium to the air, specifically: Among them, t x ,t y ,t z They are the three components of the camera external parameter translation vector t, which are obtained by camera calibration. The normal vectors n1 and n2 of the surface at the intersection coordinates (x1, y1, z1) and (x2, y2, z2) are given by the surface equation f n (x,y,z,Ψ n ) = 0 gives; In the step 3), the intersection of the distorted light rays is recalculated, i.e., the corrected point, and the stereoscopic vision imaging model in the three-dimensional digital image correlation method is corrected in real time; specifically, the corrected refracted light rays are calculated using the law of refraction, and then the refracted light rays are subjected to beam adjustment to solve the corrected point without distortion; the point cloud is traversed to obtain the corrected tissue point cloud morphology.

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