A testing device and method for biological soft tissue composite stiffness

Abstract

The present application provides a kind of biomass soft tissue composite rigidity testing device and method, it includes test platform;Weight, weight acceleration sensor is installed on the top of weight;Drop hammer impact device, including hammer head, impact sensor is installed on the bottom of hammer head;Data acquisition system, with weight acceleration sensor and impact sensor are connected;Data processing system, with the data acquisition system is connected, according to the excitation load, time and response displacement data of data acquisition system transmission calculation the viscoelastic parameter of biomass soft tissue sample.The present application utilizes drop hammer to realize high strain rate impact loading under very short time, simulates the dynamic stress environment of soft tissue under real physiological conditions, and can be loaded to biological soft tissue by changing drop hammer release height, especially can handle the viscoelastic behavior under large deformation condition.

Description

Technical Field

[0001] This invention relates to the field of biological tissue technology, and specifically to a testing device and method for the composite stiffness of biomass soft tissue. Background Technology

[0002] Human soft tissues, such as muscles, skin, fat, and blood vessels, possess highly complex structures and functions. These soft tissues play multiple important roles in daily life, such as providing support, protecting organs, participating in movement, and regulating body temperature. Due to their structural complexity and functional diversity, soft tissues exhibit significant anisotropy and highly nonlinear mechanical behavior. The mechanical properties of soft tissues depend not only on their inherent material properties but are also influenced by various factors such as cell structure, tissue arrangement, and physiological conditions. The evaluation of the mechanical properties of biological soft tissues is an important research direction, crucial for understanding their physiological functions and pathological changes.

[0003] Soft tissues are inherently fragile and have high water content, exhibiting highly heterogeneous structures and complex mechanical characteristics such as highly nonlinear mechanical responses, significant time dependence, and anisotropy. Viscoelasticity can be summarized as their most prominent feature, representing an important manifestation of soft tissue response to external forces and reflecting the energy storage and dissipation mechanisms within the tissue. Although viscoelastic testing is crucial in the study of soft tissue mechanical properties, limitations such as the accuracy of testing equipment, time resolution, complexity of loading conditions, and difficulty in sample preparation affect the accuracy and reliability of test results. Therefore, there is an urgent need to develop novel devices and methods that can overcome these limitations and provide high-precision, high-resolution viscoelastic testing to advance the development of biomedical engineering and related fields.

[0004] Currently, there are three main methods for evaluating the viscoelastic mechanical properties of biological soft tissues. One is the Ramp-Hold test, a classic viscoelastic testing method. It involves applying a constant rate of strain loading (Ramp), then holding the strain or stress constant (Hold) and observing the stress relaxation and creep process. However, this method is time-consuming, requires long-term stable data recording, and its accuracy may be limited for very small or very large strain ranges. Furthermore, it cannot simulate the behavior of soft tissues under dynamic conditions and is only suitable for static or quasi-static analysis. The second method is the cyclic loading method, which measures the hysteresis and stress-strain relationship of soft tissues by applying repeated loading and unloading cycles. This method is suitable for studying the viscoelastic behavior of soft tissues under cyclic loading. However, this method is limited by the need for complex loading equipment and control systems to ensure precise control of the loading and unloading process. Data processing is also complex, especially under high-frequency cycling, requiring high sampling rates and data processing capabilities, which may introduce material fatigue effects and affect the accuracy of the test results. Thirdly, dynamic thermomechanical analysis measures the energy storage stiffness (energy storage part) and loss stiffness (energy dissipation part) of a material by applying periodic dynamic strain or stress, and is applicable to the viscoelastic analysis of various materials. Its limitations lie in the complexity and expense of the equipment, the high technical requirements for operation, its applicability only to small deformation conditions, its inability to handle viscoelastic behavior under large deformation conditions, its limited frequency range, and its inability to fully simulate dynamic behavior under all physiological conditions.

[0005] Therefore, the existing technologies described above have the following main technical problems in testing and analyzing the viscoelastic mechanical properties of biological soft tissues: First, traditional viscoelastic testing techniques have long testing times and are not suitable for the extremely short response time of biological soft tissues under high-speed impacts; second, traditional loading devices apply loading rates below medium strain rates to soft tissues and are not suitable for the complex dynamic responses of biological soft tissues under high-speed impacts; third, existing testing techniques that match the viscoelastic characterization theory of soft tissues are only applicable to linear assumptions and are not suitable for data analysis and processing over a large strain range. Summary of the Invention

[0006] This invention addresses the technical problems of existing technologies in testing and analyzing the viscoelastic mechanical properties of biological soft tissues, which are unsuitable for the extremely short response time and complex dynamic response of biological soft tissues under high-speed impact, and are also unsuitable for analyzing data with a large strain range. Therefore, it provides a device and method for testing the composite stiffness of biomass soft tissues.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A testing device for the composite stiffness of biomass soft tissue includes: a testing platform for placing a biomass soft tissue sample; a weight placed on the biomass soft tissue sample on the testing platform, with a weight acceleration sensor mounted on top of the weight; an impact device located directly above the testing platform, with an impact sensor mounted on bottom of the impact device; a data acquisition system connected to the weight acceleration sensor and the impact sensor, recording excitation load and response acceleration data, as well as time data, and obtaining response displacement data by performing a second integral on the response acceleration data; and a data processing system connected to the data acquisition system, calculating the viscoelastic parameters of the biomass soft tissue sample based on the excitation load, time, and response displacement data transmitted by the data acquisition system.

[0009] The impact device is a hammer head, and it is also equipped with a height-adjustable clamp, with the hammer head clamped below the clamp.

[0010] The drop hammer impact device is equipped with a series of replaceable hammers of different weights.

[0011] The weight completely covers the biomass soft tissue sample.

[0012] The Young's modulus of the weight is greater than or equal to 100 GPa.

[0013] The mass of the weight is 5000-10000g, and the vertical drop between the hammer and the weight is 0.05-1 meter.

[0014] The data acquisition system employs high-frequency sampling, with a sampling frequency of... It is 3-4 MHz.

[0015] The time for applying impact force to the biomass soft tissue sample is less than 2 milliseconds.

[0016] The biomass soft tissue composite stiffness testing method based on the aforementioned testing device includes: placing a biomass soft tissue sample on the testing platform and pressing it with the weight, releasing the hammer head of the drop hammer impact device, and the data processing system calculating the viscoelastic parameters of the biomass soft tissue sample according to the excitation load, time, and response displacement data transmitted by the data acquisition system, using the following method: the time-domain discrete signal of the excitation force. F ( n and response displacement x ( n The discrete-time signal of ) is represented as:

[0017] ;

[0018] in t nIt represents the time corresponding to each sampling point; n =0,1,2,…, N -1, N This represents the number of sampling points;

[0019] Perform Fourier transform on the time-domain discrete signals of excitation force and response displacement to convert the data from the time domain to the frequency domain:

[0020] ;

[0021] F ( k ) and X ( k These are the frequency components of the excitation force and the response displacement in the frequency domain, respectively. k For frequency index, k =0,1,2,…, N -1; k With angular frequency The relationship is The force frequency components and displacement frequency components at the corresponding angular velocities are obtained by expressing them in terms of angular frequency:

[0022] ;

[0023] With dynamic softness As a transfer function, it can be expressed in complex function form as follows:

[0024] ;

[0025] Calculate the three viscoelastic parameters of the biological tissue, with the energy storage stiffness as follows: The loss stiffness is , The loss factor is equal to the loss modulus divided by the energy storage modulus; that is, the ratio of the loss modulus to the energy storage modulus. For the excitation frequency, It is the natural frequency of a single-degree-of-freedom system. It is the system damping ratio. r It is the ratio of the excitation frequency to the natural frequency. It is dynamic stiffness, obtained by fitting data.

[0026] The advantages of the testing device and method for biomass soft tissue composite stiffness described in this invention are:

[0027] The biomass soft tissue composite stiffness testing device of this invention utilizes a drop hammer to achieve high strain rate impact loading in an extremely short time, simulating the dynamic stress environment of soft tissue under real physiological conditions. Moreover, the loading of biological soft tissue can be achieved by changing the drop hammer release height, especially capable of handling viscoelastic behavior under large deformation conditions. The biomass soft tissue composite stiffness testing device and method of this invention form a stable and accurate mechanical analysis method, which can quickly measure and record the mechanical response of soft tissue under instantaneous impact force, reduce testing time, and improve the timeliness and accuracy of data. The testing device of this invention, in which biological soft tissue and a weight together constitute a "single-degree-of-freedom system," has the technical advantage of not only generating high strain rate impacts but also having controllable impact energy. By changing the height of the impact device, stress environments under different physiological conditions can be simulated. For example, smaller impacts are used to simulate mild mechanical stress, while larger impacts are used to simulate the situation when soft tissue is subjected to strong external forces. Especially under high strain rates (i.e., higher drop height), the testing device can capture the large deformation behavior that occurs instantaneously in soft tissue, thereby better characterizing the mechanical properties of soft tissue under complex physiological environments. This is crucial for the accuracy and adaptability of the testing device.

[0028] In this application, the mass of the weight is large enough to negligibly account for the weight of the soft tissue sample, and the Young's modulus is large enough to treat it as a rigid body that will not deform, thus avoiding the influence of the weight's own deformation on the experimental results. This ensures the response time of the single-degree-of-freedom system and the transmission process of the impact force. The length and width of the weight ensure that its contact surface corresponds to the stress surface of the soft tissue, thereby ensuring that the impact force is evenly distributed on the tissue and reducing local stress concentration. This is particularly important for testing large areas of soft tissue, as it can better simulate the stress state of the tissue under real physiological conditions. The height can affect the distribution of applied pressure, ensuring that the depth of impact force transmission is appropriate, thereby more accurately simulating the overall stress response of the soft tissue. Compared to traditional testing devices that can typically only measure the storage modulus and loss modulus of a single sample taken from a specific site, the testing device in this application can test the overall mechanical properties of the entire organ. The test results obtained are closer to the actual physiological state of biological tissues, providing more comprehensive and accurate mechanical parameters for the study of the mechanical behavior of the entire organ, such as organ transplantation or medical device design, which helps to improve the reliability and applicability of experimental results. From the perspective of test operation, it also avoids the operation of cutting samples from the whole organ, reduces the error caused by sample processing, improves test efficiency, and reduces the need for repeated testing of a single sample.

[0029] To make the technical solution of the biomass soft tissue composite stiffness testing device and method of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0030] like Figure 1 The diagram shown is a structural schematic of the biomass soft tissue composite stiffness testing device of the present invention.

[0031] like Figure 2 The figure shown is a graph illustrating the relationship between the excitation load applied to biological soft tissue by the impact device of the present invention and time during the impact excitation phase.

[0032] like Figure 3 The figure shown is a graph illustrating the relationship between the excitation load applied to biological soft tissue by the impact device of the present invention and time during the complete phase.

[0033] like Figure 4 The figure shows the relationship between acceleration and time for a single-degree-of-freedom system during the impact excitation phase.

[0034] like Figure 5 The figure shows the relationship between acceleration and time for a single-degree-of-freedom system during the decay phase.

[0035] like Figure 6 The figure shows the relationship between acceleration and time for a single-degree-of-freedom system during the complete phase.

[0036] like Figure 7 The figure shows the response displacement versus time relationship of a single-degree-of-freedom system during the excitation phase.

[0037] like Figure 8 The figure shows the response displacement versus time of a single-degree-of-freedom system during the complete phase.

[0038] like Figure 9 As shown Figure 3 Load amplitude-frequency relationship diagram transformed from time domain to frequency domain;

[0039] like Figure 10 As shown Figure 8 Displacement amplitude-frequency relationship graph transformed from time domain to frequency domain;

[0040] like Figure 11 The image shows the amplitude-frequency graph of the frequency response function of a single-degree-of-freedom system.

[0041] like Figure 12 The figure shows the variation of energy storage stiffness of biological soft tissue samples with frequency.

[0042] like Figure 13 The figure shows the variation of loss stiffness of biological soft tissue samples with frequency.

[0043] like Figure 14 The figure shows the variation of the loss factor of a biological soft tissue sample with frequency.

[0044] The attached figures are labeled as follows:

[0045] 1-Test platform; 2-Weight; 3-Weight acceleration sensor; 4-Impact device; 5-Impact sensor; 6-Data acquisition system. Detailed Implementation

[0046] This embodiment provides a testing device for the composite stiffness of biomass soft tissue, such as... Figure 1 As shown, the testing device includes a testing platform 1 for placing a biomass soft tissue sample. In this embodiment, the biomass soft tissue sample tested by the testing device is a whole pig kidney. A weight 2 is placed on the biomass soft tissue sample on the testing platform 1. In a preferred embodiment, the weight 2 has a Young's modulus ≥100 GPa. Specifically, the weight 2 is made of steel and completely covers the biomass soft tissue sample. In this embodiment, the weight 2 weighs 10000g, and its length, width, and height are 14cm, 8cm, and 5cm, respectively. The weight 2 completely covers the biomass soft tissue sample, constructing a single degree of freedom (SDOF) system. A weight accelerometer 3 is installed on the weight 2. In this embodiment, the weight accelerometer 3 is adhered to the weight 2. The testing device also includes an impact device 4 that can be dropped from a height. The impact device 4 includes a clamp and a hammer head suitable for clamping below the clamp. The hammer head is located directly above the testing platform 1. An impact sensor 5 is installed at the bottom of the hammer head. Also, as a preferred embodiment, the hammer head in this embodiment is equipped with a series of hammer heads of different masses. Clamping different hammer heads below the clamp can be used to assist in providing different impact forces. A data acquisition system 6 is connected to the weight acceleration sensor 3 and the impact sensor 5. The data acquisition system 6 records excitation load and time data and calculates response displacement data. In addition, a data processing system is provided, connected to the data acquisition system 6, to calculate the viscoelastic parameters of the biomass soft tissue sample based on the data transmitted by the data acquisition system 6. In this embodiment, the sampling frequency of the data acquisition system is 4MHz.

[0047] The testing method based on the biomass soft tissue composite stiffness testing device described in this embodiment includes the following steps:

[0048] The drop hammer height is set through the operating system to ensure stable lifting and accurate release of the hammerhead to apply impact force to the bio-soft tissue composite system. In this embodiment, the impact time of the drop hammer on the weight 2 is less than 2 milliseconds. During the impact, the excitation load is captured by the impact sensor 5, and the response acceleration is captured by the acceleration sensor attached to the weight 2. Based on the load magnitude applied to the bio-soft tissue composite system by the drop hammer and the acceleration of the bio-soft tissue composite system, the load-time relationship curve of the drop hammer applied to the bio-soft tissue composite system is obtained through experimental testing device analysis, see [link to experimental device]. Figure 2 , Figure 3 The acceleration-time relationship curve of the biological tissue complex system is shown in the figure. Figure 4 , Figure 5 , Figure 6 .

[0049] In this embodiment, the response displacement of the bio-soft tissue composite system applied by the falling hammer is obtained by performing a quadratic integration on the response acceleration data of the bio-soft tissue composite system. The calculation result is as follows: Figure 7 and Figure 8 As shown.

[0050] In this embodiment, the method for calculating the three viscoelastic parameters of biological tissue is as follows:

[0051] Discrete-time signal of excitation force F ( n and response displacement x ( n The discrete-time signal of ) is represented as:

[0052] ;

[0053] in t n It represents the time corresponding to each sampling point; n =0,1,2,…, N -1, N This represents the number of sampling points;

[0054] Perform Fourier transform on the time-domain discrete signals of excitation force and response displacement to convert the data from the time domain to the frequency domain:

[0055] ;

[0056] F ( k ) and X ( k These are the frequency components of the excitation force and the response displacement in the frequency domain, respectively. k For frequency index, k =0,1,2,…, N -1;k With angular frequency The relationship is The force frequency components at the corresponding angular velocities are obtained by expressing them in terms of angular frequency, such as... Figure 9 As shown, and the displacement frequency component, as Figure 10 As shown:

[0057] ;

[0058] With dynamic softness As a transfer function, such as Figure 11 As shown, it can be expressed in complex function form as follows:

[0059] ;

[0060] Calculate the three viscoelastic parameters of the biological tissue, where the energy storage stiffness is... The loss stiffness is ; The loss factor is equal to the loss modulus divided by the energy storage modulus; where For the excitation frequency, It is the natural frequency of a single-degree-of-freedom system. It is the system damping ratio, and r is the ratio of the excitation frequency to the natural frequency. It is dynamic stiffness, obtained by fitting data to determine frequency-dependent dynamic stiffness. The calculation results in this embodiment are as follows: Figures 12-14 As shown.

[0061] The testing device in this embodiment enables testing of the entire kidney, which can obtain the overall energy storage modulus and loss modulus of the kidney, reflecting the overall mechanical behavior of the organ.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the claims.

Claims

1. A method for testing the composite stiffness of biological soft tissue, characterized in that, The testing method is based on a testing device for the composite stiffness of biological soft tissue. The testing device includes: a testing platform for placing the biological soft tissue sample; a weight placed on the biological soft tissue sample on the testing platform, with a weight acceleration sensor mounted on top of the weight; an impact device located directly above the testing platform, with an impact sensor mounted on its bottom; a data acquisition system connected to the weight acceleration sensor and the impact sensor, recording excitation load and response acceleration data, as well as time data, and obtaining response displacement data by performing a quadratic integration on the response acceleration data; and a data processing system connected to the data acquisition system, calculating the viscoelastic parameters of the biological soft tissue sample based on the excitation load, time, and response displacement data transmitted by the data acquisition system. The testing method includes: placing a biological soft tissue sample on the testing platform and pressing it with the weight, releasing the impact device, and the data processing system calculating the viscoelastic parameters of the biological soft tissue sample based on the excitation load, time, and response displacement data transmitted by the data acquisition system. Discrete-time signal of excitation force F ( n and response displacement x ( n The discrete-time signal of ) is represented as: ； in t n It represents the time corresponding to each sampling point; n =0,1,2,…, N -1, N This represents the number of sampling points; Perform Fourier transform on the time-domain discrete signals of excitation force and response displacement: ； F ( k ) and X ( k These are the frequency components of the excitation force and the response displacement in the frequency domain, respectively. k For frequency index, k =0,1,2,…, N -1; k With angular frequency The relationship is , The sampling frequency of the data acquisition system is used; the force frequency component and displacement frequency component at the corresponding angular velocity are obtained by expressing them as angular frequency. ； With dynamic softness As a transfer function, it can be expressed in complex function form as follows: ； Calculate the three viscoelastic parameters of the biological tissue, with the energy storage stiffness as follows: The loss stiffness is , The loss factor is equal to the loss modulus divided by the energy storage modulus; where For the excitation frequency, It is the natural frequency of a single-degree-of-freedom system. It is the system damping ratio. r It is the ratio of the excitation frequency to the natural frequency. It is dynamic stiffness, obtained by fitting data.

2. The method for testing the composite stiffness of biological soft tissue according to claim 1, characterized in that, The impact device is a hammer head, and it is also equipped with a height-adjustable clamp, with the hammer head clamped below the clamp.

3. The method for testing the composite stiffness of biological soft tissue according to claim 2, characterized in that, The impact device is equipped with a series of replaceable hammers of different weights.

4. The method for testing the composite stiffness of biological soft tissue according to claim 3, characterized in that, The weight completely covers the biological soft tissue sample.

5. The method for testing the composite stiffness of biological soft tissue according to claim 4, characterized in that, The Young's modulus of the weight is greater than or equal to 100 GPa.

6. The method for testing the composite stiffness of biological soft tissue according to claim 5, characterized in that, The mass of the weight is 5000-10000g, and the vertical drop between the hammer and the weight is 0.05-1 meter.

7. The method for testing the composite stiffness of biological soft tissue according to claim 6, characterized in that, The data acquisition system employs high-frequency sampling, with a sampling frequency of... It is 3-4 MHz.

8. The method for testing the composite stiffness of biological soft tissue according to claim 7, characterized in that, The time for applying the impact force to the biological soft tissue sample is less than 2 milliseconds.

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