Device and method for testing composite stiffness of biomass soft tissue

Abstract

The invention provides a device and a method for testing the composite stiffness of a biomass soft tissue. The device comprises a testing platform, the top of the weight is provided with a weight acceleration sensor; the drop hammer impact device comprises a hammer head, and an impact sensor is mounted at the bottom of the hammer head; the data acquisition system is connected with the weight acceleration sensor and the impact sensor; and the data processing system is connected with the data acquisition system and is used for calculating viscoelastic parameters of the biomass soft tissue sample according to the excitation load, time and response displacement data transmitted by the data acquisition system. According to the invention, impact loading with a high strain rate in an extremely short time is realized by using the drop hammer, a dynamic stress environment of soft tissue under a real physiological condition is simulated, loading of biological soft tissue can be realized by changing the release height of the drop hammer, and especially the viscoelastic behavior under a large deformation condition can be processed.

Description

Technical Field

[0001] The invention relates to the technical field of biological tissues, and in particular to a testing device and method for composite stiffness of biomass soft tissues. Background Art

[0002] Human soft tissues, such as muscles, skin, fat, and blood vessels, have highly complex structures and functions. These soft tissues play a variety of important roles in daily life, such as providing support, protecting organs, participating in sports, and regulating body temperature. Due to the complexity of their structure and the diversity of their functions, soft tissues exhibit significant anisotropy and highly nonlinear mechanical behavior. The mechanical properties of soft tissues not only depend on their inherent material properties, but are also affected by multiple 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, which is of great significance for understanding their physiological functions and pathological changes.

[0003] Soft tissues are fragile and have a high water content. They are highly heterogeneous in structure and exhibit complex mechanical characteristics such as highly nonlinear mechanical response, significant time dependence, and anisotropy. Viscoelasticity can summarize its most significant characteristics. It is an important manifestation of soft tissue response to external forces and reflects the energy storage and dissipation mechanism inside the tissue. Although viscoelastic testing is crucial in the study of soft tissue mechanical properties, the accuracy and reliability of the test results are affected by limitations such as the accuracy of the test equipment, time resolution, complexity of loading conditions, and difficulty in sample preparation. Therefore, it is urgent to develop a new device and method that can overcome the above limitations and provide high-precision and high-resolution viscoelastic testing to promote the development of biomedical engineering and related fields.

[0004] At present, there are three main methods for evaluating the viscoelastic mechanical properties of biological soft tissues. One is the Ramp-Hold test, which is a classic viscoelastic test method that applies a constant rate of strain loading (Ramp), then keeps the strain or stress constant (Hold) and observes the relaxation and creep process of stress. However, its test time is long and requires long-term stable data recording. For very small or very large strain ranges, the accuracy of the test results may be limited, and it cannot simulate the behavior of soft tissues under dynamic conditions. It is only suitable for static or quasi-static analysis. The second is the cyclic loading method, which measures the hysteresis phenomenon 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. This method is limited by the need for complex loading equipment and control systems to ensure precise control of the loading and unloading process, and the data processing is complex, especially under high-frequency cycles, the sampling rate and data processing capabilities require high requirements, which may introduce material fatigue effects and affect the accuracy of the test results. The third is the dynamic thermomechanical analysis method, which measures the storage stiffness (energy storage part) and loss stiffness (energy consumption part) of the material by applying periodic dynamic strain or stress, and is applicable to the viscoelastic analysis of a variety of materials. Its limitations are that the equipment is complex and expensive, the operation technology requirements are high, and it is only applicable to small deformation conditions, and cannot handle viscoelastic behavior under large deformation conditions. The frequency range is limited and cannot fully simulate the dynamic behavior under all physiological conditions.

[0005] Therefore, the above existing technologies have the following technical problems in the process of testing and analyzing the viscoelastic mechanical properties of biological soft tissues: first, the traditional viscoelastic testing technology has a long testing time and is not suitable for the extremely short response time of biological soft tissues under high-speed impact; second, the loading speed of traditional loading equipment for soft tissues is below the medium strain rate, which is not suitable for the complex dynamic response of biological soft tissues under high-speed impact; third, the existing testing technology that matches the viscoelastic characterization theory of soft tissues is only applicable to linear assumptions and is not applicable to data analysis and processing over a large strain range. Summary of the invention

[0006] The present invention solves the technical problems that the prior art is not suitable for the extremely short response time and complex dynamic response of biological soft tissue under high-speed impact, and is not suitable for analyzing data in a large strain range when testing and analyzing the viscoelastic mechanical properties of biological soft tissue, and further provides a testing device and method for the composite stiffness of biomass soft tissue.

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

[0008] A test device for composite stiffness of biomass soft tissues comprises: a test platform for placing biomass soft tissue samples; a weight placed on the biomass soft tissue samples on the test platform, with a weight acceleration sensor installed on the top of the weight; an impact device located directly above the test platform, with an impact sensor installed on the 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 secondary integral calculation 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 samples according to the excitation load, time and response displacement data transmitted by the data acquisition system.

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

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

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

[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 head and the weight is 0.05-1 meter.

[0014] The data acquisition system adopts high-frequency sampling, and the sampling frequency f s 3-4Mhz.

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

[0016] The biomass soft tissue composite stiffness test method based on the test device comprises: placing the material soft tissue sample on the test platform and pressing the weight, releasing the hammer head of the drop hammer impact device, and the data processing system calculates 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 in accordance with the following method: the time domain discrete signal F(n) of the excitation force and the time domain discrete signal of the response displacement x(n) are expressed as:

[0017] F(n)=F(t n ),x(n)=x(t n );

[0018] where t n is the time corresponding to each sampling point; n = 0, 1, 2, ..., N-1, N is the number of sampling points;

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

[0020]

[0021] F(k) and X(k) are the frequency components of the excitation force and response displacement in the frequency domain, respectively. k is the frequency index, k = 0, 1, 2, ..., N-1; the relationship between k and the angular frequency ω is ω = 2πkf s , expressed in angular frequency, the force frequency component and displacement frequency component at the corresponding angular velocity are obtained:

[0022]

[0023] Dynamic Flexibility As a transfer function, it is expressed in complex function form as:

[0024]

[0025] Calculate the three viscoelastic parameters of biological tissues, the energy storage stiffness is The loss stiffness is η(ω) is the loss factor, which is equal to the loss modulus / storage modulus, that is, the ratio of the loss modulus to the storage modulus; where ω is the excitation frequency, ω n is the natural frequency of the single degree of freedom system, ζ is the system damping ratio, r is the ratio of the excitation frequency to the natural frequency, and k(ω) is the dynamic stiffness, which is obtained by fitting the data.

[0026] The device and method for testing the composite stiffness of biomass soft tissues of the present invention have the following advantages:

[0027] The testing device for the composite stiffness of biomass soft tissue described in the present invention uses a drop hammer to achieve impact loading with a high strain rate in an extremely short time, simulating the dynamic stress environment of soft tissue under real physiological conditions, and can load biological soft tissue by changing the release height of the drop hammer, especially being able to handle viscoelastic behavior under large deformation conditions. The testing device and method for the composite stiffness of biomass soft tissue described in the present 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 test time, and improve the timeliness and accuracy of data. The test device in the present invention, the biological soft tissue and the heavy object together constitute a "single degree of freedom system", and its technical effect is that the design of the test device is not only to generate high strain rate impact, but also to adjust the impact energy. By changing the height of the impact device, the stress environment under different physiological conditions can be simulated. For example, a smaller impact is used to simulate mild mechanical stress, while a larger impact is used to simulate the situation when the soft tissue is subjected to strong external force. Especially under high strain rates (i.e., a higher drop weight release height), the test device can capture the instantaneous large deformation behavior of the soft tissue, thereby better characterizing the mechanical properties of the soft tissue under complex physiological environments, which is crucial to the accuracy and adaptability of the test device.

[0028] In this application, the mass of the weight is large enough to ignore the weight of the soft tissue sample, and the Young's modulus is large enough to be regarded as a rigid body that will not deform, so as to avoid the deformation of the weight itself affecting the experimental results, ensuring 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 make its contact surface correspond to the force surface of the soft tissue, thereby ensuring that the impact force is evenly distributed on the tissue and reducing local stress concentration. This is especially important for testing large areas of soft tissue, because it can better simulate the stress state of the tissue in a real physiological environment, and the height can affect the distribution of the applied pressure, ensuring that the depth of the impact force transmission is appropriate, thereby more accurately simulating the overall force response of the soft tissue. Compared with traditional testing devices that can usually only measure the storage modulus and loss modulus of a single sample taken from a specific part, the testing device in the present application can test the overall mechanical properties of the entire organ, and the obtained test results are closer to the actual physiological state of the biological tissue, providing more comprehensive and accurate mechanical parameters for the study of the overall mechanical behavior of the organ, such as organ transplantation or medical equipment design, which helps to improve the credibility and applicability of the 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] In order to make the technical solution of the testing device and method for composite stiffness of biomass soft tissue described in the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] like Figure 1 Shown is a schematic structural diagram of the testing device for composite stiffness of biomass soft tissues according to the present invention;

[0031] like Figure 2 The figure shows the relationship between the excitation load and time applied to the biological soft tissue by the impact device of the present invention during the impact excitation stage;

[0032] like Figure 3 The figure shows the relationship between the excitation load and time applied to the biological soft tissue by the impact device of the present invention in the complete stage;

[0033] like Figure 4 Shown is the corresponding acceleration-time diagram of the single-degree-of-freedom system during the impact excitation stage;

[0034] like Figure 5 Shown is the corresponding acceleration versus time graph of a single degree of freedom system in the decay phase;

[0035] like Figure 6 Shown is the corresponding acceleration versus time graph for the single degree of freedom system in the complete stage;

[0036] like Figure 7 The figure shows the relationship between the response displacement and time of the single degree of freedom system during the excitation stage;

[0037] like Figure 8 Shown is the response displacement versus time graph of the single degree of freedom system in the complete stage;

[0038] like Fig. 9 Shown Figure 3 Load amplitude-frequency relationship diagram converted from time domain to frequency domain;

[0039] like Fig.10 Shown Figure 8 The displacement amplitude-frequency relationship diagram converted from time domain to frequency domain;

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

[0041] like Fig.12 Shown is a graph showing the variation of energy storage stiffness of biological soft tissue samples with frequency;

[0042] like Fig.13 Shown is a graph showing the loss stiffness of biological soft tissue samples as a function of frequency;

[0043] like Fig.14 Shown is a graph showing the variation of loss factor of biological soft tissue samples with frequency;

[0044] Wherein, the accompanying drawings are marked as follows:

[0045] 1-test platform; 2-weight; 3-weight acceleration sensor; 4-impact device; 5-impact sensor; 6-data acquisition system. DETAILED DESCRIPTION

[0046] This embodiment provides a test device for the composite stiffness of biomass soft tissue, such as Figure 1 As shown, the test device includes a test platform 1 for placing a biomass soft tissue sample. The biomass soft tissue sample tested by the test device in this embodiment is a whole pig kidney. A weight 2 is placed on the biomass soft tissue sample on the test platform 1. As a preferred embodiment, the Young's modulus of the weight 2 in this embodiment is ≥100GPa. This embodiment specifically adopts a steel weight 2, and the weight 2 fully covers the biomass soft tissue sample. In this embodiment, the weight 2 is 10000g, and the length, width and height of the weight 2 are 14cm, 8cm and 5cm respectively. The size of the weight 2 completely covers the biomass soft tissue sample to construct a single degree of freedom system (SDOF). A weight acceleration sensor 3 is installed on the weight 2. The weight acceleration sensor 3 in this embodiment is adhered to the weight 2. The test device is also provided with an impact device 4 that can fall from a height, and the impact device 4 includes a fixture and a hammer head that is suitable for clamping under the fixture, and the hammer head is located directly above the test platform 1. An impact sensor 5 is installed at the bottom of the hammer head. Also as a preferred embodiment, the hammer head described in this embodiment is provided with a series of hammer heads of different masses, and different hammer heads are clamped under the fixture, which 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, and the data acquisition system 6 records the excitation load and time data, and calculates the response displacement data. In addition, a data processing system is also provided, and the data processing system is connected to the data acquisition system 6, and the viscoelastic parameters of the biomass soft tissue sample are calculated according to 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 of the testing device for the composite stiffness of biomass soft tissue described in this embodiment comprises the following steps:

[0048] The height of the drop hammer is set by the drop hammer operating system to ensure the stable lifting of the drop hammer and the accurate release of the hammer head to apply impact force to the biological 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 process, 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; according to the load size and acceleration of the biological soft tissue composite system applied by the drop hammer to the biological soft tissue composite system, the load-time relationship curve of the drop hammer applied to the biological soft tissue composite system is obtained through the experimental test device analysis, see Figure 2 , Figure 3 , and the acceleration-time relationship curve of the biological tissue composite system, see Figure 4 , Figure 5 , Figure 6 .

[0049] In this embodiment, the response displacement of the biological soft tissue composite system applied by the drop hammer is obtained by calculating the response acceleration data of the biological soft tissue composite system and performing secondary integration. The calculation result is as follows: Figure 7 and Figure 8 shown.

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

[0051] The time-domain discrete signal F(n) of the excitation force and the time-domain discrete signal x(n) of the response displacement are expressed as:

[0052] F(n)=F(t n ),x(n)=x(t n );

[0053] where t n is the time corresponding to each sampling point; n = 0, 1, 2, ..., N-1, N is the number of sampling points;

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

[0055]

[0056] F(k) and X(k) are the frequency components of the excitation force and response displacement in the frequency domain, respectively. k is the frequency index, k = 0, 1, 2, ..., N-1; the relationship between k and the angular frequency ω is ω = 2πkf s , expressed in angular frequency, the force frequency components at the corresponding angular velocity are obtained, such as Fig. 9 As shown, and the displacement frequency component, as Fig.10 As shown:

[0057]

[0058] Dynamic Flexibility As a transfer function, Fig.11 As shown, it can be expressed in complex function form as:

[0059]

[0060] Calculate the three viscoelastic parameters of biological tissue, among which the storage stiffness is The loss stiffness is η(ω) is the loss factor, which is equal to loss modulus / storage modulus; where ω is the excitation frequency, ω n is the natural frequency of the single degree of freedom system, ζ is the system damping ratio, r is the ratio of the excitation frequency to the natural frequency, k(ω) is the dynamic stiffness, and the frequency-dependent dynamic stiffness k(ω) is obtained by fitting the data; the calculation results in this embodiment are as follows Figure 12-14 shown.

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

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the claims.

Claims

1. A test device for composite stiffness of biomass soft tissue, characterized in that: include: A testing platform for placing biomass soft tissue samples; A weight is placed on the biomass soft tissue sample on the test platform, and a weight acceleration sensor is installed on the top of the weight; An impact device is located directly above the test platform, and an impact sensor is installed at the bottom of the impact device; A data acquisition system is connected to the weight acceleration sensor and the impact sensor, records the excitation load and response acceleration data, as well as time data, and obtains response displacement data by performing a secondary integral calculation on the response acceleration data; The data processing system is connected to the data acquisition system and calculates 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.

2. The test device for composite stiffness of biomass soft tissue according to claim 1, characterized in that: The impact device is a hammer head, and is also provided with a height-adjustable clamp, and the hammer head is clamped under the clamp.

3. The test device for composite stiffness of biomass soft tissue according to claim 2, characterized in that: The drop hammer impact device is provided with a series of replaceable hammer heads of different weights.

4. The test device for composite stiffness of biomass soft tissue according to claim 3, characterized in that: The weight completely covers the biomass soft tissue sample setup.

5. The test device for composite stiffness of biomass 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 test device for composite stiffness of biomass soft tissue according to claim 5, characterized in that: The mass of the weight is 5000-10000g, and the vertical drop between the hammer head and the weight is 0.05-1 meter.

7. The test device for composite stiffness of biomass soft tissue according to claim 6, characterized in that: The data acquisition system adopts high-frequency sampling, and the sampling frequency f s 3-4Mhz.

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

9. A biomass soft tissue composite stiffness testing method based on the testing device of claim 1, characterized in that: include: The biomass soft tissue sample is placed on the test platform and pressed with the weight, and the impact device is released. The data processing system calculates 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: The time-domain discrete signal F(n) of the excitation force and the time-domain discrete signal x(n) of the response displacement are expressed as: F(n)=F(t n ),x(n)=x(t n ); where t n is the time corresponding to each sampling point; n = 0, 1, 2, ..., N-1, N is the number of sampling points; Perform Fourier transform on the discrete time-domain signals of the excitation force and response displacement: F(k) and X(k) are the frequency components of the excitation force and response displacement in the frequency domain, respectively. k is the frequency index, k = 0, 1, 2, ..., N-1; the relationship between k and the angular frequency ω is ω = 2πkf s , f s is the sampling frequency of the data acquisition system; the force frequency component and displacement frequency component under the corresponding angular velocity are obtained by expressing them in angular frequency: Dynamic Flexibility As a transfer function, it is expressed in complex function form as: Calculate the three viscoelastic parameters of biological tissues, the energy storage stiffness is The loss stiffness is η(ω) is the loss factor, which is equal to loss modulus / storage modulus; where ω is the excitation frequency, ω n is the natural frequency of the single degree of freedom system, ζ is the system damping ratio, r is the ratio of the excitation frequency to the natural frequency, and k(ω) is the dynamic stiffness, which is obtained by fitting the data.

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