CN103674829A - Measuring method and measuring platform for biomechanical performance parameters of in vitro corneas - Google Patents

Abstract

The invention relates to a measurement method and a measurement platform for isolated corneal biomechanical performance parameters. The measurement method includes: first, fixing a corneal sample, and spraying powder; second, continuously applying pressure to deform the corneal sample, and recording the pressure value; third, recording the distance between the powder particles distance change; 4. Calculate the three-dimensional deformation of each area on the surface of the cornea sample; 5. Calculate the biomechanical performance parameters through the general constitutive equation. The measurement platform includes an installation platform on which a corneal fixation device is installed. One end of the inner cavity is provided with a clamping end for clamping the cornea sample, the other end of the inner cavity is connected with a pressure device, and the front end of the cornea fixation device is provided with a shooting device, the pressure device is connected with a pressure sensor, and the pressure device is connected with the pressure sensor. The pressure of the corneal sample is monitored, and the deformation of the corneal sample is recorded by the shooting equipment, so as to realize the measurement of the regional difference of the corneal constitutive parameters, and provide a reference for the diagnosis and treatment of related corneal diseases.

Description

A method and platform for measuring biomechanical performance parameters of isolated cornea

technical field

The invention relates to a measurement method and a measurement platform for isolated corneal biomechanical performance parameters, in particular to a measurement method and a measurement platform for corneal biomechanical performance that can measure regional differences in corneal constitutive parameters.

Background technique

Keratoconus is a relatively common ophthalmic disease in clinical practice, which can produce highly irregular myopic astigmatism and different degrees of visual impairment. The incidence rate in European and American countries is 0.01%~0.05%, and in Japan is 0.07%~0.08%, but there is still no epidemic in my country. learning information. As an important biological attribute, the biomechanical properties of the cornea can directly affect the shape of the cornea, and then affect the refractive state and optical imaging quality of the cornea. Studies have shown that the occurrence and development of keratoconus are closely related to the changes in the regional biomechanical properties of the cornea. Most of the pathological changes occur in the lower temporal part of the cornea, with thinner thickness and weaker mechanical properties. occur. The biomechanical properties of corneal tissue are often described quantitatively using constitutive parameters, and the measurement results have a wide range of fluctuations, which are closely related to the experimental platform. The isolated corneal expansion test platform basically continues the ellipsoid shape of the cornea, maintains the structural integrity of the cornea, and maintains its physiological stress mode. It is a measurement method that is relatively close to the physiological state of the cornea. However, the existing isolated corneal expansion test platform still has the disadvantage that the measurement area is small and cannot provide regional differences in the distribution of biomechanical properties of the whole cornea.

Contents of the invention

In order to solve the problem that the existing corneal biomechanical performance measurement platform cannot measure the regional difference distribution of corneal biomechanical performance, the present invention provides a measurement method and measurement platform for isolated corneal biomechanical performance, which can measure the regional difference of corneal constitutive parameters, Provide reference for the diagnosis and treatment of related corneal diseases.

The technical scheme adopted in the present invention is: a kind of measurement method of the biomechanical property parameter of isolated cornea, it comprises the following steps:

1. Fix the corneal sample on the corneal fixation device, and spray opaque powder that does not chemically react with the cornea on the corneal sample;

2. Control the pressure change in the corneal fixation device through the syringe pump device, apply continuous pressure to deform the corneal sample, and record the pressure value through the pressure sensor;

3. The distance between the powder particles sprayed on the corneal sample is changed when the corneal deformation is recorded by the shooting equipment;

4. Calculate the three-dimensional deformation of each area on the surface of the corneal sample through digital speckle technology;

5. Through the pressure value obtained in step 2 and the deformation data of the corneal sample, the general constitutive equation is used to calculate the biomechanical performance parameters of each area of the isolated cornea. The general constitutive equation is

                                                                             

A measurement platform for biomechanical performance parameters of an isolated cornea, which includes an installation platform, on which a corneal fixation device for fixing corneal samples is fixedly installed, and an inner cavity is provided in the corneal fixation device, and the inner cavity One end of the inner cavity is provided with a clamping end for clamping the corneal sample, the other end of the inner cavity is connected with a pressure device containing a pressure medium, and the front end of the corneal fixing device is provided with a photographing device for recording the deformation of the corneal sample. The pressure device is connected with the pressure sensor.

The clamping end includes a clamping end bottom part and a clamping end top part adapted thereto.

The inner cavity is also provided with a first exhaust valve for exhaust.

The photographing equipment includes a camera holder and a high-speed camera.

There are two high-speed cameras arranged at the front end of the corneal fixation device at intervals of 5-10 degrees.

The pressure device adopts a syringe pump device.

The pressure device uses phosphate buffer as the pressure medium.

The opaque powder used in the second step that does not chemically react with the cornea is carbon powder.

The beneficial effects of the present invention are: the pressure monitoring of the corneal sample is carried out by the pressure device and the pressure sensor, and the deformation of the corneal sample is recorded by the photographing equipment, so as to realize the measurement of the regional differences of the corneal constitutive parameters, and provide reference for the diagnosis and treatment of related corneal diseases .

Description of drawings

Fig. 1 is the front view of the present invention.

Figure 2 is a side view of the present invention.

Fig. 3 is a schematic structural view of the corneal fixation device of the present invention.

Detailed ways

Embodiments of the present invention will be further described below in conjunction with accompanying drawings:

A method for measuring biomechanical performance parameters of an isolated cornea, comprising the following steps:

1. Fix the corneal sample on the corneal fixation device, and spray opaque powder that does not chemically react with the cornea on the corneal sample;

2. Control the pressure change in the corneal fixation device through the syringe pump device, apply continuous pressure to deform the corneal sample, and record the pressure value through the pressure sensor;

3. The distance change between the powder particles sprayed on the corneal sample when the corneal deformation is recorded by the shooting equipment;

4. Calculate the three-dimensional deformation of each area on the surface of the corneal sample through digital speckle technology;

The digital speckle technology, also known as digital image correlation technology, uses a mathematical correlation method to analyze the data of a digital image of a pattern surface under load (randomly distributed speckle points on the surface of an object are recorded in the digital image), that is, using digital The gray value pattern of the image is used to accurately determine the deformation (displacement). It is different from interferometric methods (such as laser holography and electronic speckle method). The range can be arbitrarily specified and so on. If combined with a high-magnification microscope or a scanning electron microscope with a loading device, deformation measurements at the micron or nanometer scale can also be performed.

The key problem of digital speckle technology to measure deformation is to perform correlation calculation on two speckle fields (reference speckle field before deformation and speckle field after deformation). Select the sub-area that can reflect the displacement information to be measured on the speckle image, and then use the sub-area of the same size to perform correlation search in the deformed correlation area to find the position of the largest correlation point, and the coordinate displacement difference between the two points The value is the deformation displacement of the point to be measured.

When the corneal sample undergoes pressure deformation, the opaque powder on the surface that does not react chemically with the cornea passes through the imaging device and is continuously recorded into a digital picture format. Select the reference image and the target image, and use the compiled digital correlation calculation software to perform correlation calculations on the designated area to obtain the deformation distribution. The deformation field can be obtained through the visualization software, and the strain field distribution can be obtained through numerical differentiation. According to the accuracy of the imaging system of the shooting equipment And the speed of image acquisition, the digital speckle correlation method can go deep into the micron or even nanometer scale on the spatial scale, and can cover the deformation measurement from the quasi-static to the dynamic range in terms of speed, and the continuous use of multiple shooting devices can perform three-dimensional deformation measurement , to achieve the purpose of calculating the three-dimensional deformation of each area on the surface of the corneal sample through digital speckle technology.

5. Calculate the biomechanical performance parameters of each region of the isolated cornea through the general constitutive equation between the pressure value obtained in step 2 and the deformation of the corneal sample.

The relationship between stress and strain is called constitutive relationship, and its function equation is constitutive equation, which is used to describe the biomechanical properties or material properties of biological tissues, and the parameter components of the equation are called constitutive parameters.

The Ogden equation is selected as the general constitutive equation of corneal tissue,

。

.

As material constants, the constitutive parameters α and μ represent the strain hardening exponent and the shear modulus, respectively, which jointly determine the shape of the stress-strain curve that can be described by the equation. Each area of the corneal sample uses the Ogden equation to set the biomaterial properties separately, and the deformation data of each area of the cornea obtained by the digital speckle technique is used as the target value. The convergence rule is the simulated deformation of each area of the corneal sample at each pressure segment and the digital speckle technique The root mean square (RMS) of the actual deformation is the smallest. With the help of optimization software and finite element analysis software, the calculation results of the constitutive parameters α and μ that can accurately describe the mechanical relationship of corneal tissue in each area are obtained through repeated iterative calculations, so that the in vitro Biomechanical performance parameters of the various regions of the cornea.

As shown in Fig. 1 and Fig. 2, a kind of measuring platform of the biomechanical performance parameter of isolated cornea, it comprises installation platform, and the corneal fixation device that is used for fixing corneal sample is fixedly installed on the described installation platform, in the described cornea fixation device An inner cavity 12 is provided, one end of the inner cavity 12 is provided with a clamping end for clamping a corneal sample, the other end of the inner cavity is connected to a pressure device containing a pressure medium, and the front end of the corneal fixation device is set for The pressure device is connected with the pressure sensor for the photographing equipment for recording the deformation of the corneal sample.

The clamping end includes a clamping end bottom part 10 and a clamping end top part 9 adapted thereto, and the corneal sample 5 comprising part of the annular scleral tissue is placed on the clamping end bottom part 10, and then passed through the clamping end Hold the end top part 9 to fix it, and the middle of the clamping end bottom part 10 and the clamping end top part 9 has an aperture that is the same as the diameter of the cornea sample 5 to expose the cornea sample 5, and the clamping end top part 9 and The clamping bottom part 10 fixes the corneal sample 5 by clamping the sclera tissue surrounding it, and the aperture on the clamping bottom part 10 communicates with the inner cavity 12 for injection pressure of the pressure device to deform the corneal sample 5 .

The inner cavity 12 is also provided with a first exhaust valve 11 for exhausting the air in the inner cavity.

The photographing device includes a camera holder 2 and a high-speed camera 3, and multiple photographing devices can be used for three-dimensional deformation measurement, so as to achieve the purpose of calculating the three-dimensional deformation of each area of the corneal sample surface through digital speckle technology.

There are two high-speed cameras 3 arranged at the front end of the cornea fixing device 1 at intervals of 5-10 degrees.

The pressure device adopts a syringe pump device 4 . The syringe pump device 4 uses a phosphate buffer as the pressure medium, and the phosphate buffer is formed by mixing powder with water, and its main components are anhydrous sodium dihydrogen phosphate, anhydrous disodium hydrogen phosphate and sodium chloride. A solution is formed by adding water, and the pH value of the phosphate buffer solution is between 7.4-7.6.

The corneal fixation device 1 is assembled in the center of the installation platform, and the front surface of the cornea sample 5 is sprayed with powder. The powder is black powder that does not chemically react with the cornea sample. The opaque powder used in the second step does not chemically react with the cornea. The powder is carbon powder, because there are no characteristic points on the surface of the corneal sample, it is difficult to identify. But if the black powder is sprayed, the distance between the powder particles on the surface of the corneal sample can be found to change during the deformation process, and the deformation can be calculated by digital speckle technology. The cornea sample 5 is fixed between the clamping end top part 9 and the clamping end bottom part 10 in the cornea fixing device 1, with the center of the cornea fixing device 1 as the center of the circle, and the high-speed camera 3 is set at a specific angle (5-10 degrees apart from each other) ) are distributed in front of the cornea and fixed on the camera fixing frame 2 . The syringe pump device 4 contains phosphate buffer solution, and one end of the cross hose 7 is connected to the cornea fixation device 1 , and the other end of the cross hose 7 is connected to the pressure sensor 6 . After exhausting through the second exhaust valve 8 connected to the cross hose 7, the syringe pump device 4 changes the pressure in the corneal fixation device 1 by slowly injecting phosphate buffer solution, so that the cornea deforms; the pressure sensor 6 records the cornea in real time. The pressure in the fixing device 1 changes, and the high-speed camera 3 distributed in front of the cornea takes pictures of the corneal morphology changes in real time during the pressure change process. The three-dimensional deformation of each area of the corneal surface is calculated by digital speckle technology, and then the biomechanical performance parameters of each area of the isolated cornea are calculated according to the quantitative relationship between the applied pressure and the corneal deformation, which provides a reference for the diagnosis and treatment of related corneal diseases.

The embodiments described above in conjunction with the accompanying drawings are only preferred implementations of the present invention, rather than limiting the protection scope of the present invention. Any improvement made based on the spirit of the present invention should fall within the protection scope of the present invention. the

Claims (9)

1. a measuring method for isolated cornea biomechanical property parameter, is characterized in that: it comprises the following steps:

One, cornea sample is fixed on corneal fixture, and on cornea sample, spray opaque and not with the powder of cornea generation chemical reaction;

Two, the pressure of controlling in corneal fixture by pressure apparatus changes, and exerts pressure continuously and makes cornea sample generation deformation, and record force value by pressure transducer;

While three, adopting capture apparatus to record cornea deformation, be sprayed at the change of distance between the powder particle on cornea sample;

Four, by the three-dimensional deformation in each region of digital speckle technique computes cornea sample surface;

Five, by force value and the cornea sample deformation data that obtain in step 2, adopt general constitutive equation to calculate the biomechanical property parameter in each region of isolated cornea, described general constitutive equation is

。

2. the measuring table of an isolated cornea biomechanical property parameter, it comprises mounting platform, it is characterized in that: on described mounting platform, fixed installation is for the corneal fixture of immobilizing corneal sample, in described corneal fixture, be provided with inner chamber, one end of described inner chamber is provided with the bare terminal end for holding angle membrane sample, the other end of described inner chamber is connected with the pressure apparatus that has pressure medium, described corneal fixture front end is provided for recording the capture apparatus of cornea sample deformation, and described pressure apparatus is connected with pressure transducer.

3. the measuring table of isolated cornea biomechanical property parameter according to claim 2, is characterized in that, described bare terminal end comprises bare terminal end bottom parts and suitable bare terminal end top part with it.

4. the measuring table of isolated cornea biomechanical property parameter according to claim 2, is characterized in that, is also provided with the first row air valve for exhaust on described inner chamber.

5. the measuring table of isolated cornea biomechanical property parameter according to claim 2, is characterized in that, described capture apparatus comprises camera fixed mount and high speed camera.

6. the measuring table of isolated cornea biomechanical property parameter according to claim 5, is characterized in that, described high speed camera is two, and apart 5-10 degree is arranged in corneal fixture front end.

7. the measuring table of isolated cornea biomechanical property parameter according to claim 2, is characterized in that, described pressure apparatus adopts syringe pump apparatus.

8. according to the measuring table of the isolated cornea biomechanical property parameter described in claim 2 or 7, it is characterized in that, described pressure apparatus adopts phosphate buffer as pressure medium.

9. the measuring table of isolated cornea biomechanical property parameter according to claim 1, is characterized in that, adopt in described step 2 opaque and be not carbon powder with the powder of cornea generation chemical reaction.

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