Device and method for measuring mechanical properties of biological tissues

Abstract

The invention relates to a device for measuring mechanical properties of biological tissues and a testing method, belongs to the technical field of performance testing, and solves the problems of easiness in sliding, non-uniform deformation, even damage and inaccurate testing data during testing in the prior art. The biological tissue mechanical property measuring device comprises a clamp system and a water bath system, the clamp system comprises clamping assemblies which are symmetrically arranged; the two clamping assemblies are oppositely arranged in the stretching direction. And the clamp system is arranged in the water bath system. The defect that an existing clamp cannot conveniently test the mechanical property of the biological tissue under the water bath condition is overcome, water bath equipment and the clamp are creatively designed in an integrated mode, and meanwhile the sample clamping convenience is improved under the condition that the test precision is met.

Description

Technical Field

[0001] The invention relates to the technical field of performance testing, and in particular to a device and a testing method for measuring the mechanical properties of biological tissues. Background Art

[0002] In the measurement of mechanical properties of biological tissues, the design and performance of the clamping system are crucial to the accuracy, repeatability and operability of the test results. Biological tissues are usually soft, elastic and irregular in shape, which makes traditional clamping devices face many challenges in application. Traditional clamping systems often have uneven pressure when applying pressure, especially when clamping softer or complex-shaped tissues, which can easily lead to excessive pressure in local areas, while other areas may be subjected to less pressure. This uneven pressure can cause biological tissues to slip, deform unevenly or tear locally during the test, affecting the accuracy of mechanical property measurement. In addition, traditional clamping devices cannot provide uniform support for irregularly shaped biological tissues, especially when the tissues have asymmetric shapes or more complex geometric forms, which often leads to unstable clamping, and the tissues may shift or deform during the test, thereby interfering with the experimental results. In addition, due to the softness and high hydration of biological tissues, traditional clamping systems may not effectively prevent the tissues from slipping or shifting due to insufficient friction or uneven contact surfaces during the measurement process, which in turn causes uneven stress distribution and affects the reliability and repeatability of the measurement data. At the same time, the existing clamping device is not easy to disassemble and quick enough, resulting in poor convenience of the experiment. Therefore, developing a clamping system that can provide a stable, accurate and convenient clamping system is of vital importance to improve the accuracy, reliability and experimental repeatability of the measurement of mechanical properties of biological tissues. Summary of the invention

[0003] In view of the above problems, the present invention provides a device and a testing method for measuring the mechanical properties of biological tissues, in order to solve the problems of easy sliding, uneven deformation, even damage and inaccurate test data during testing in the prior art. The present invention provides a biological tissue mechanical property measurement device, comprising a fixture system and a water bath system; The clamp system includes symmetrically arranged clamping components; two sets of clamping components are arranged opposite to each other along the stretching direction; The fixture system is set in the water bath system.

[0004] Optionally, the clamping assembly includes a clamping arm base, a clamping arm and a clamping arm cover; the clamping arm is arranged at the end of the clamping arm base; and the clamping arm cover is arranged at the end of the clamping arm.

[0005] Optionally, a retainer is also included; the clamping arms of the two sets of clamping assemblies are connected via the retainer.

[0006] Optionally, a fixing member is included above the base of the clamping arm for connecting to an external force input device.

[0007] Optionally, a groove is further provided at the base of the clamping arm; the clamping arm comprises a magnet and a protrusion, and the clamping arm is connected to the groove in the clamping arm via the magnet and the protrusion.

[0008] Optionally, the clamping arm is provided with a sample clamping platform.

[0009] Another embodiment of the present invention further discloses a method for measuring the mechanical properties of biological tissues, which uses the aforementioned biological tissue mechanical properties measuring device to perform measurements, and the specific steps are as follows: Step 1. Install the biological tissue on a biological tissue mechanical property measurement device, apply external force to the biological tissue, and collect force-time and displacement-time images; Step 2. Based on the force-time and displacement-time images, obtain the material parameters of the complete nonlinear viscoelasticity of the biological tissue. The specific steps are as follows: Obtain tissue strain and stress based on force-time and displacement-time images; Based on the strain and stress of the tissue, a material parameter comparison model of the fully nonlinear viscoelastic mechanical properties of biological tissues is constructed, and the expression is: (1) In the formula, represents the strain of the tissue at time t Stress in biological tissues under Indicates integration time The strain corresponding to the time is: is the integration time; is the initial stress; is the nonlinear relaxation modulus; in, , the expression is: (2) In the formula, and are the steady-state modulus corresponding to the biological tissue strain at time t and the time constant The corresponding strain modulus; Represents the natural base; Among them, the steady-state modulus corresponding to the strain and the time constant The corresponding strain modulus expression is: (3) In the formula, and is the material parameter of biological tissue; represents the strain of the tissue at time t; Apply the above stress ( ) and strain ( ) image and equations (1), (2) and (3) to obtain the material parameters of the nonlinear viscoelasticity of biological tissues .

[0010] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention makes up for the defect that the existing fixture cannot conveniently perform the mechanical property test of biological tissue under water bath conditions. It innovatively integrates the water bath equipment and the fixture into a design, and at the same time improves the convenience of sample clamping while ensuring the test accuracy; (2) The present invention innovatively divides sample clamping into two steps to ensure the integrity of the sample clamping process and reduce the difficulty of sample clamping: a magnetic fixed clamping fixture is designed. When clamping the sample, the upper and lower clamp platforms can be removed from the upper and lower clamp arms. The distance between the upper and lower clamp platforms is maintained by a magnetic retainer, which is convenient for the experimenter to transfer the sample from the dissection table to the clamp platform. After the sample is stably clamped by the clamp cover through a thread, the upper and lower clamp platforms are fixed to the upper and lower clamp arms by magnetic attraction. The magnetic attraction force can meet the requirement of stable clamping during the experiment and is convenient for the experimenter to install or remove the clamp platform; (3) In order to meet the requirements of the test being carried out in a water bath and to record the changes of the sample during the test process through a high-speed camera, the water bath of the present invention uses a transparent 3D printing material.

[0011] (4) The measuring device of the present invention pays special attention to the convenience and accuracy of clamping, and can firmly fix various biological tissues and reduce errors introduced by improper operation. It ensures the stability of biological tissues during the test and the accuracy of test data, providing reliable experimental guarantee for mechanical property measurement. In addition, this device that is easy to install on mechanical instruments greatly improves the efficiency of the experiment, allowing experimenters to quickly complete the installation and alignment of biological tissues, facilitating repeated tests or multi-sample measurements. This is particularly important for experimental scenarios that require a large number of sample measurements, and can also avoid damage to tissues caused by traditional clamping systems during repeated installation. This technology not only improves the convenience of experimental operations, but also ensures the stability and accuracy of mechanical property test data, providing strong support for research in fields such as tissue engineering and rehabilitation engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a front view of the biological tissue mechanical property measuring device of the present invention; Figure 2 is a schematic diagram of a fixture system of the present invention; Figure 3 It is a schematic diagram of a water bath system of the present invention; Figure 4 It is a schematic diagram of the magnetic connection between the clamping arm base and the clamping arm of the present invention; Figure 5 It is a schematic diagram of the disassembly of the retainer and the clamping arm cover plate of the present invention; Figure 6 is a schematic diagram of the magnetic connection between the retainer and the clamping arm of the present invention; Figure 7 It is a schematic diagram of the retainer and the clamping arm as a whole of the present invention.

[0013] Reference numerals: 1-clamping arm base, 2-clamping arm, 3-clamping arm cover, 4-holder, 5-solution reservoir, 6-positioning ear, 7-sensor connection seat. DETAILED DESCRIPTION

[0014] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. In addition, the present invention can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0015] A specific embodiment of the present invention, as Figure 1-Figure 7 , discloses a device for measuring the mechanical properties of biological tissues, including a clamp system and a water bath system.

[0016] Further, see Figure 2 The clamping system includes symmetrically arranged clamping assemblies; two groups of clamping assemblies are arranged opposite to each other along the stretching direction; the clamping assembly includes a clamping arm base 1, a clamping arm 2 and a clamping arm cover 3; the clamping arm 2 is arranged at the end of the clamping arm base 1; the clamping arm cover 3 is arranged at the end of the clamping arm 2; The clamping arms 2 of the two clamping assemblies are connected by a retainer 4 .

[0017] Furthermore, the retainer 4 is disposed on a side of the clamping arm 2 .

[0018] Furthermore, a stud hole is designed on the top of the clamping arm base 1 for connecting with an external force input device, and a groove is also provided on the clamping arm base 1; see Figure 4 The clamping arm 2 includes a circular magnet (diameter 5 mm, thickness 3 mm) and a protrusion, and the clamping arm 2 is connected to the groove in the clamping arm 1 through the circular magnet and the protrusion; see Figure 5 The clamping arm 2 is provided with a sample clamping platform. When in use, the end of the sample is placed on the sample clamping platform, the clamping arm cover 3 is covered on the sample clamping platform on the sample, and then the clamping arm 2 and the clamping arm cover 3 are fixedly connected to clamp the end of the sample.

[0019] Furthermore, the width of the sample clamping platform is not less than 6 mm; in order to firmly clamp the sample on the clamping platform, the clamping arm 2 is designed with threaded holes to install the clamping arm cover 3.

[0020] Furthermore, the retainer 4 connects the upper and lower symmetrical clamping components together by magnetic attraction, such as Figure 6 As shown, the circular magnet used is 4mm in diameter and 2mm in thickness.

[0021] Further, Figure 3 The water bath system comprises a solution pool 5, a positioning ear piece 6 and a sensor connecting seat 7.

[0022] Preferably, the box body is a transparent box body.

[0023] Furthermore, the positioning ear piece 6 is used to fix the sensor connection socket 7 to the bottom of the box body.

[0024] The design of the transparent box body of the present invention is not only convenient for observing the experiment, but also conducive to using a high-speed camera to record the complete experimental process; the positioning ear piece 6 and the sensor connecting seat 7 facilitate the connection of the entire biological tissue mechanical properties measurement device with the sensor and then stably fix it on the measurement platform.

[0025] A major advantage of the device of the present invention is that each component can be quickly disassembled, which facilitates the transfer of the mounted biological tissue sample from the dissection table to the clamp system and then connects it to the sensor and external force input device to achieve the effect of accurately measuring the mechanical properties of the biological tissue.

[0026] Another aspect of the present invention further discloses a method for measuring the mechanical properties of biological tissues, which is performed using the aforementioned biological tissue mechanical properties measuring device, and the specific steps are as follows: Step 1. Install the biological tissue on the biological tissue mechanical properties measurement device and apply external force to the biological tissue; collect force-time ( Ft ) and sample tissue displacement-time images (WLt ); First, remove the clamping arm base 1 of a clamping assembly of the clamping system; install a stud on the external force input device; connect the external force input device to the stud hole in the clamping arm base 1 through a stud bolt; Fix the clamping arm base 1 of another set of clamping components in the transparent solution pool 5 by transparent glue, and connect the sensor to the sensor connecting seat 7 through the screw hole at the bottom of the sensor connecting seat 7; Install the entire water bath system including the solution pool 5, the positioning ear piece 6 and the sensor connection seat 7 on the measurement platform equipped with the sensor; like Figure 7As shown, the upper and lower symmetrical clamping arms 2, clamping arm cover plates 3 and retainers 4 in the two sets of clamping assemblies are moved to the dissection table as a whole; like Figure 5 As shown, remove the retainer 4 and the clamping arm cover 3, place the two ends of the biological tissue sample to be tested on the sample clamping platforms of the two clamping arms 2 symmetrically located above and below, and firmly fix the clamping arm cover 3 to the clamping arm 2 by screws to clamp the two ends of the biological tissue sample to be tested, ensuring that the biological tissue to be tested will not escape from the clamping system during the experiment.

[0027] The holder 4 is then used to connect the upper and lower symmetrical clamping arms 2 and the clamping arm cover plate 3 in the two sets of clamping assemblies. The existence of the holder 4 ensures that the biological tissue to be measured will not be separated from the clamp system during the transfer from the dissection table to the measurement platform. The upper and lower symmetrical clamping arms 2, the clamping arm cover plate 3 and the holder 4 are moved to the measurement platform. The clamping arm base 1 and the circular magnet of the clamping arm 2 and the protrusion of the clamping arm 2 and the recess in the clamping arm base 1 are used to achieve a tight connection with the upper clamping arm base 1. Similarly, the connection between the lower clamping arm and the clamping arm cover plate and the clamping arm base is achieved, so that the biological tissue is installed on the biological tissue mechanical property measurement device.

[0028] Remove holder 4 and add 37 Physiological saline is used to simulate the in vivo environment to maintain the physiological activity of the biological tissue sample to be tested. An external force input device is used to apply force to the upper clamping arm base 1 of the clamping device in the vertical direction to stretch and relax the biological tissue. At the same time, the sensor at the bottom is connected to the external software to output the mechanical image.

[0029] Step 2. Based on force-time ( Ft ) and displacement (sample tissue width and length)-time images (WLt ), obtain the thickness variation of biological tissue and the material parameters that characterize the complete nonlinear viscoelasticity of biological tissue .

[0030] First, obtain the initial length of the biological tissue , initial width and initial thickness ; Furthermore, the initial length of biological tissue is the initial distance between the upper and lower clamping arms, the initial width and initial thickness It can be defined by using a double blade used for dissection. (For example, the double blade used in this experiment cuts out the initial width of the biological tissue. and initial thickness 2mm in all) Then, based on the force-time ( Ft) and sample tissue displacement-time images (LWt ), obtain the thickness change and stress of biological tissue ( ) and strain ( )image.

[0031] Specifically, the holder 4 and the magnetic attraction method of the measuring device of the present invention can be adjusted according to the experimental needs to obtain the initial length of the experiment that meets the needs of the experiment. W and thickness T The change in tissue width was recorded by high-speed camera during the experiment and the Wt Image measurement width variation , and then use the displacement-time image measured above to obtain the Poisson's ratio at time t ,in represents the width change at time t, Indicates the initial width, represents the length change at time t, represents the initial length. Assuming that the material is isotropic, Get the thickness change at time t ,in, represents the length change at time t, Indicates the initial length, Indicates the initial thickness.

[0032] Furthermore, the strain of the tissue at time t , represents the length of the sample organization time t, represents the initial length. The vertical stress at time t is ， in, , F represents the force at time t; S represents is the force area at time t, represents the sample tissue thickness at time t. The experimentally measured stress ( ) and strain ( )image.

[0033] Furthermore, based on the stress ( ) and strain ( ) image, and construct a material parameter comparison model of the fully nonlinear viscoelastic mechanical properties of biological tissues, expressed as: (1) In the formula, represents the strain corresponding to time t Stress in biological tissues under Indicates integration time The strain corresponding to the time is: is the integration time; is the initial stress; is the nonlinear relaxation modulus; Further, , the expression is: (2) In the formula, and are the steady-state modulus corresponding to the biological tissue strain at time t and the time constant The corresponding strain modulus; Represents the natural base.

[0034] Furthermore, the time constant Used to capture the main viscoelastic properties of tissues during extension-relaxation loading.

[0035] Furthermore, the steady-state modulus corresponding to the strain and the time constant The corresponding strain modulus expression is: (3) In the formula, and is the material parameter of biological tissue; represents the strain of the tissue at time t.

[0036] Furthermore, applying the above stress ( ) and strain ( ) image and equations (1), (2) and (3) to obtain the material parameters of the nonlinear viscoelasticity of biological tissues .

[0037] It is understood that the material parameters of the nonlinear viscoelasticity of biological tissues are Material parameters of biological tissues and composition.

[0038] Furthermore, the least square error is used as the optimization objective function to minimize the error between the stress predicted by the material parameter model of the fully nonlinear viscoelastic mechanical properties of biological tissues and the experimental data.

[0039] Specifically, the sum of squared errors is used as the objective function: The sum of squared errors is used to evaluate the error, and the specific expression is:

[0040] in, is the actual stress measured in the experimental data, The stress is predicted by a fully nonlinear viscoelastic material parameter model of the mechanical properties of biological tissues. The optimization process is performed by adjusting the material parameters To minimize the sum of square errors and obtain the optimal material parameters The lsqnonlin function in MATLAB software is used to perform nonlinear least squares optimization. It finds the optimal solution by minimizing the objective function. Initially, an initial material parameter is given. , which is usually an estimated initial guess (e.g., [1 1 1 1 1 1 1 1 1]). The lsqnonlin function then continuously adjusts the material parameters , calculate the sum of squared errors for each iteration and update the parameters according to minimizing the objective function .

[0041] Furthermore, in order to improve the accuracy, the present invention uses a weighted error function to process the influence of errors at different time points on the optimization of the material parameter model of the fully nonlinear viscoelastic mechanical properties of the final biological tissue. The weighted function assigns different weights to different time points, which can make the errors at certain specific time points more important. The expression of the weighted function is:

[0042] in, represents the weighting function; , , , There are 4 time constants.

[0043] Furthermore, the expression of weighted root mean square error is:

[0044] in, is the number of sample points collected. This weighted error is used in the error calculation to ensure that the fit is more accurate at certain time points. In addition, an integration method is used to calculate the stress response of the material. The time integration is used to simulate the change of viscoelastic stress. Specifically, the stress contribution at each time point is calculated and the total stress is accumulated by numerical integration.

[0045] The entire optimization process: Initial material parameters are obtained at the beginning Then, use the lsqnonlin function to calculate and update the material parameters Substitute into (1) to calculate the new stress prediction. After each update, calculate , and check Is it less than the preset tolerance? If the error is small enough, the algorithm is considered to have converged; otherwise, it continues to iterate until the error threshold is met (such as ) or reaches the maximum number of iterations. Finally, the optimization process obtains the optimal material parameters , these parameters minimize the error between the stress predicted by the model and the experimental data.

[0046] Step 3. Replace the biological tissue sample and conduct a secondary test; Take out the upper and lower symmetrical clamping arm 2 and the clamping arm cover 3 as a whole, unscrew the clamping arm 2 and the clamping arm cover 3, take out the biological tissue sample on the fixture installation platform, and then connect the upper and lower symmetrical clamping arm 2 with the holder 4, replace the new biological tissue sample and perform the experiment of the new sample in the above installation process. In this way, the repeatability of the measurement of the mechanical properties of biological tissues is achieved, and the experimental efficiency is greatly improved.

[0047] Step 4. Disassemble the device: Take out the upper and lower symmetrical clamping arm 2 and the clamping arm cover 3 as a whole, unscrew the clamping arm 2 and the clamping arm cover 3, take out the biological tissue sample on the clamp mounting platform, clean the clamp mounting platform, and tighten the screws again. Connect the upper and lower symmetrical clamping arm 2 with the retainer 4, and then take out the clamping arm base 1 connected to the external force input device and the water bath device equipped with the clamping arm base.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A biological tissue mechanical properties measuring device, characterized in that: Includes fixture system and water bath system; The clamp system includes symmetrically arranged clamping components; two sets of clamping components are arranged opposite to each other along the stretching direction; The fixture system is set in the water bath system.

2. The biological tissue mechanical properties measuring device according to claim 1, characterized in that: The clamping assembly comprises a clamping arm base, a clamping arm and a clamping arm cover plate; the clamping arm is arranged at the end of the clamping arm base; and the clamping arm cover plate is arranged at the end of the clamping arm.

3. The biotissue mechanical properties measuring device according to claim 2, characterized in that: The utility model also comprises a retainer; the clamping arms of the two sets of clamping assemblies are connected through the retainer.

4. The biological tissue mechanical properties measuring device according to claim 3, characterized in that: The upper part of the clamping arm base includes a fixing piece for connecting with an external force input device.

5. The biological tissue mechanical property measuring device according to claim 3, characterized in that: The base of the clamping arm is also provided with a groove; the clamping arm comprises a magnet and a protrusion, and the clamping arm is connected with the groove in the clamping arm through the magnet and the protrusion.

6. The biological tissue mechanical property measuring device according to claim 3, characterized in that: The clamping arm is provided with a sample clamping platform.

7. A method for measuring mechanical properties of biological tissues, using the biological tissue mechanical properties measuring device according to any one of claims 1 to 6 for measurement, the specific steps being as follows: Step 1. Install the biological tissue on a biological tissue mechanical property measurement device, apply external force to the biological tissue, and collect force-time and displacement-time images; Step 2. Based on the force-time and displacement-time images, obtain the material parameters of the complete nonlinear viscoelasticity of the biological tissue. The specific steps are as follows: Obtain tissue strain and stress based on force-time and displacement-time images; Based on the strain and stress of the tissue, a material parameter comparison model of the fully nonlinear viscoelastic mechanical properties of biological tissues is constructed, and the expression is: (1) In the formula, represents the strain of the tissue at time t Stress in biological tissues under Indicates integration time The strain corresponding to the time is: is the integration time; is the initial stress; is the nonlinear relaxation modulus; in, , the expression is: (2) In the formula, and are the steady-state modulus corresponding to the biological tissue strain at time t and the time constant The corresponding strain modulus; Represents the natural base; Among them, the steady-state modulus corresponding to the strain and the time constant The corresponding strain modulus expression is: (3) In the formula, and is the material parameter of biological tissue; represents the strain of the tissue at time t; Apply the above stress ( ) and strain ( ) image and equations (1), (2) and (3) to obtain the material parameters of the nonlinear viscoelasticity of biological tissues .

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