Experimental device and method for measuring swimming characteristics of algae cells in shear flow

Abstract

The invention discloses an experimental device and method for measuring the swimming characteristics of algae cells in shear flow. The experimental device comprises an air pressure source, a pressure pump, a liquid storage bottle, a flow meter, a micro-channel and a waste liquid bottle which are connected in sequence, the method comprises the following steps: determining average flow according to experimental working conditions to produce stable shear flow, shooting an algae cell movement track image sequence, obtaining the distribution of the migration velocity V of algae cells through the observed algae cell movement track, calculating the distribution of the flow velocity Vflow of the algae cells in combination with an analytical method, and calculating the flow velocity Vflow of the algae cells according to the distribution of the flow velocity Vflow of the algae cells. And calculating to obtain the algae cell swimming characteristics in the shear flow, wherein the algae cell swimming characteristics comprise the self swimming speed Vs and the angular speed omega. According to the device and the method, high-precision measurement of the movement behavior of the algae cells in the shear flow is realized, an experimental method and an analytical method are combined, the defect that swimming characteristics such as swimming speed and angular speed of the algae cells cannot be obtained in previous researches is overcome, and technical support is provided for development of micromechanics in a more detailed micro-scale.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental hydraulics, and particularly relates to an experimental device and method for measuring the swimming characteristics of algal cells in a shear flow. Background Art

[0002] Currently, the problems of water environmental pollution and water ecological damage caused by algal blooms are becoming increasingly prominent. Therefore, clarifying the swimming characteristics of algal cells is of great significance for understanding the migration, aggregation, and distribution laws of algae, and further predicting the occurrence and development processes of algal blooms. Flagellate algal blooms are a phenomenon that widely occurs in river-type reservoirs and bays. They can move by driving their own flagella. This movement is not only related to their own dynamic characteristics but also significantly affected by external flow conditions.

[0003] Shear flows widely exist in natural and artificial environments. From ocean turbulence to river flows, and then to liquid circulation in bioreactors, all contain significant shear effects. Therefore, precisely observing the movement of algal cells in a shear flow is crucial for revealing the interaction between water flow and microalgae movement. The swimming characteristics of algal cells mainly include swimming speed, angular velocity, etc. Currently, in a shear flow environment, using micro-scale experiments to observe the swimming characteristics of algal cells is still immature, and there are no corresponding research results in China. Therefore, how to measure the swimming characteristics of algal cells in a shear flow is a technical problem that urgently needs to be solved at present. Summary of the Invention

[0004] The purpose of the present invention is to provide an experimental device and method for measuring the swimming characteristics of algal cells in a shear flow to solve the above technical problems.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention discloses an experimental device for measuring the swimming characteristics of algal cells in a shear flow. The experimental device includes a gas pressure source, a pressure pump, a liquid storage bottle, a flowmeter, a microchannel, and a waste liquid bottle connected in sequence. The gas pressure source and the pressure pump, as well as the pressure pump and the liquid storage bottle, are connected through connecting pipes. The liquid storage bottle and the flowmeter, the flowmeter and the inlet of the microchannel, and the outlet of the microchannel and the waste liquid bottle are connected through conduits. The device further includes a fluorescence microscope and a high-speed camera connected to each other. The high-speed camera is installed under the stage of the fluorescence microscope, and the microchannel is arranged on the stage of the fluorescence microscope. The gas pressure source is used to provide a basic pressure for the pressure pump. The pressure pump is used to output a set constant pressure to create an internal and external pressure difference in the liquid storage bottle. The liquid storage bottle is airtight and contains an algal cell solution. Under the action of the internal and external pressure difference, the algal cell solution is transported to the microchannel through the conduit to form a shear flow. The flowmeter is used to monitor the flow rate pumped by the pressure pump in real time. The microchannel is used to form a shear flow. The waste liquid bottle is used to collect the waste algal cell solution flowing out of the outlet of the microchannel. The fluorescence microscope is used to create a fluorescence field environment, induce the algal cells to generate characteristic fluorescence signals, and simultaneously magnify the microscopic image and filter out other stray light. The high-speed camera is used to capture the image sequence of the algal cells in the shear flow.

[0007] Furthermore, the inlet, outlet of the microchannel and the conduit are all connected through Luer connectors.

[0008] Furthermore, the microchannel is of a cuboid structure, with a length of 5 cm, a width of 600 μm, and a height of 150 μm. The microchannel is cast with PDMS material or etched with silicon material.

[0009] The present invention also discloses a method for measuring the swimming characteristics of algal cells in a shear flow. The method includes the following steps:

[0010] Step 1: Prepare an algal cell solution with a certain concentration, connect the experimental device and check the airtightness of the experimental device.

[0011] Step 2: Adjust the position of the microchannel so that the center of the shooting frame of the high-speed camera corresponds to the center position of the microchannel, and at the same time, the front and rear wall surfaces of the microchannel are parallel to the long border of the shooting frame.

[0012] Step 3: Determine the average flow rate according to the experimental conditions, set the pressure in the liquid storage bottle using the pressure pump, and continuously adjust its pressure magnitude according to the flow rate monitored by the flowmeter in real time until the measured flow rate remains stable and is consistent with the required average flow rate to create a stable shear flow.

[0013] Step 4: First, use a high-speed camera to take an image in a bright field environment to calibrate the front and rear walls of the microchannel, which correspond to the upper and lower boundaries of the captured image respectively; then turn off the light source and take a sequence of images in a fluorescent field environment. Each set of experimental recording time is five minutes, and the experiment is repeated many times until the number of effective algae cell movement trajectories reaches tens of thousands;

[0014] Step 5: Process the captured image sequence, set the diameter and brightness thresholds to identify algae cells, extract the coordinate data of the algae cell movement trajectory, and remove the trajectory outside the observation area according to the calibrated upper and lower boundaries of the captured image, and only retain the trajectory within the observation area;

[0015] Step 6: Obtain the distribution of the migration velocity V of the algae cells by observing the movement trajectory of the algae cells, and calculate the algae cell flow velocity V by combining the analytical method. flow The distribution of the algae cells in the shear flow is then calculated to obtain the swimming characteristics, including their own swimming speed V s and angular velocity ω; specifically comprising the following steps:

[0016] Step 61, calculate the migration velocity component of the algae cells: according to the position coordinates of the algae cell movement trajectory observed in the experiment, except for the first point which uses forward difference and the last point which uses backward difference, the other points on the trajectory are calculated using the central difference format to obtain the migration velocity component V of the algae cells at different positions on each trajectory. x 、V y :

[0017] First point:

[0018]

[0019] One last point:

[0020]

[0021] Other points:

[0022]

[0023] Where: x, y are the coordinates of the algae cells, and their subscripts represent the coordinates of different points, μm; V x 、V y are the migration velocity components, respectively, and their subscripts represent the migration velocity components at different points, μm / s; Δt is the time interval between adjacent points on the trajectory, s;

[0024] Step 62, calculate the flow velocity distribution of algae cells: In the shear flow environment, the flow velocity at different positions in the width direction of the microchannel has a component V in the y direction of 0 and a component V in the x direction of 0. flow_xObtained by an analytical method, the calculation formula is:

[0025]

[0026]

[0027] In the formula: a and b are respectively half of the width and height of the microchannel, in μm; is the pressure, in Kgμm -1 s -2 ; μ is the dynamic viscosity of the liquid, in Kgμm -1 s -1 ; i is the index variable for series summation; Q is the average flow rate, in μm 3 / s;

[0028] Step 63: Calculate the self-swimming speed of the algal cells and its components: The migration speed V of the algal cells in the shear flow is divided into two parts. One is the self-swimming speed V s , that is, the swimming speed actively generated by the algal cells through flagellar drive. The other is the flow-following speed V flow , that is, the water flow velocity at the position where the algal cells are located; The migration speed V is the superposition of the self-swimming speed V s , the flow-following speed V flow , that is:

[0029] V = V s + V flow (6)

[0030] In the formula: The units of V, V s , V flow are all in μm / s;

[0031] According to the migration speed of the algal cells and the flow-following speed at their positions, calculate the self-swimming speed V s of the algal cells and its components V s_x , V s_y , and the calculation formulas are as follows:

[0032] V s_x = V x - V flow_x (7)

[0033] V s_y = V y (8)

[0034]

[0035] Step 64: Calculate the angular velocity of the algal cells: According to the components of the swimming speed of the algal cells, calculate its movement direction θ, and the calculation formula is:

[0036]

[0037] According to the movement directions of each algal cell trajectory at different times, calculate the change in the movement direction of the algal cell, and the angular velocity ω of the algal cell can be obtained. The calculation method is as follows: except for the first point using forward difference and the last point using backward difference, central difference format is used to calculate other points on the trajectory:

[0038] The first point:

[0039]

[0040] The last point:

[0041]

[0042] Other points:

[0043]

[0044] In the formula: θ is the movement direction of the algal cell, in rad; ω is the angular velocity of the algal cell, in rad / s; the subscripts represent the movement directions and angular velocities of different points;

[0045] Step 65, measure the swimming characteristics of algal cells: According to the analysis of a large number of algal cell movement trajectories, statistically calculate the self-swimming speed and angular velocity of algal cells at different positions in the width direction of the microchannel, and perform averaging to obtain the distribution of the self-swimming speed and angular velocity of algal cells in the width direction of the microchannel, that is, the measurement of the swimming characteristics of algal cells at different shear rates is achieved.

[0046] Furthermore, the concentration of the algal cell solution configured in step 1 is 1.2×10 5 cells / ml.

[0047] Furthermore, the determination criteria for valid algal cell movement trajectories in step 4 are:

[0048] 1) The recorded duration of the algal cell movement trajectory is greater than 10 s;

[0049] 2) The recorded trajectory does not include trajectories of stationary cells and trajectories of impurities adhering to certain areas.

[0050] Furthermore, the diameter threshold in step 5 is set according to the type of algal cell, and different types of algal cells have different sizes; the brightness threshold is set according to the wavelength, intensity, and exposure time of the laser.

[0051] Furthermore, the large number of algal cell movement trajectories in step 65 is at least 10,000 or more algal cell movement trajectories.

[0052] The beneficial effects of the present invention are as follows: The beneficial effects of the present invention are reflected in the following aspects:

[0053] 1. The present invention uses a pressure pump to create a shear flow. The pressure pump drives the stable flow of the algal solution based on the internal and external pressure difference of a sealed liquid storage bottle by outputting a constant pressure, achieving pulse-free fluid delivery. Compared with the commonly used syringe pump, the pressure pump has higher precision and better stability, thus ensuring the reliability of the shear flow environment in the experiment. In addition, the pressure pump is also connected to a non-contact and highly sensitive flowmeter, enabling real-time monitoring of the flow rate change during the experiment and allowing appropriate adjustment of the output pressure of the pressure pump;

[0054] 2. The present invention obtains the distribution of the migration velocity V of algal cells from the observed movement trajectories of algal cells, and combines analytical methods to calculate the distribution of the flow velocity V of algal cells along the flow, and then calculates the self-swimming velocity V flow of algal cells and the angular velocity ω, realizing the measurement of the swimming characteristics of algal cells; s and angular velocity ω, realizing the measurement of the swimming characteristics of algal cells;

[0055] 3. The present invention realizes the high-precision measurement of the movement behavior of algal cells in a shear flow, combines experimental methods with analytical methods, fills the gap in the previous research that cannot obtain the swimming characteristics such as the self-swimming velocity and angular velocity of algal cells, and provides technical support for the development of microbial hydraulics at a more detailed microscopic scale.

[0056] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a schematic structural diagram of the experimental device;

[0058] Figure 2 is a schematic structural diagram of the microchannel;

[0059] Figure 3 is a partial trajectory diagram of the movement of algal cells observed in Example 1;

[0060] Figure 4 is a distribution diagram of the migration velocity component V of algal cells in Example 1 x ;

[0061] Figure 5 is a distribution diagram of the self-swimming velocity component V of algal cells in Example 1 s_x ;

[0062] Figure 6 is a distribution diagram of the self-swimming velocity component V of algal cells in Example 1 s_y ;

[0063] Figure 7 is a distribution diagram of the angular velocity ω of algal cells in Example 1.

[0064] In the figure: 1. Pressure pump; 2. Pneumatic source; 3. Liquid storage bottle; 4. Flowmeter; 5. Microchannel; 6. Luer connector; 7. Conduit; 8. Waste liquid bottle. Detailed implementation manner

[0065] The present invention discloses an experimental device and method for measuring the swimming characteristics of algal cells in a shear flow. As Figure 1 shown, the experimental device includes a pneumatic source 2, a pressure pump 1, a liquid storage bottle 3, a flowmeter 4, a microchannel 5, and a waste liquid bottle 8 that are connected in sequence. The pneumatic source and the pressure pump, and the pressure pump and the liquid storage bottle are both connected by connecting pipes. The liquid storage bottle and the flowmeter, the flowmeter and the inlet of the microchannel, and the outlet of the microchannel and the waste liquid bottle are all connected by conduits 7. The inlet and outlet of the microchannel and the conduits are all connected by Luer connectors 6. The device also includes a fluorescence microscope and a high-speed camera that are connected. The high-speed camera is installed under the stage of the fluorescence microscope, and the microchannel is arranged on the stage of the fluorescence microscope. The pneumatic source provides a basic pressure for the pressure pump; the pressure pump outputs a set constant pressure to create an internal and external pressure difference in the liquid storage bottle; the liquid storage bottle is a closed type with an algal cell solution inside. Under the action of the internal and external pressure difference, the algal cell solution is transported to the microchannel through the conduit to form a shear flow; the flowmeter is used to monitor the flow rate pumped by the pressure pump in real time; the microchannel is the area where the algal solution flows, and cooperates with the pressure pump to create a stable and accurate shear flow; the waste liquid bottle is used to collect the waste algal cell solution flowing out of the outlet of the microchannel; the fluorescence microscope is used to create a fluorescence field environment, induce the algal cells to generate characteristic fluorescence signals, and synchronously magnify the microscopic image and filter out other stray light; the high-speed camera is used to capture the image sequence of the algal cells in the shear flow.

[0066] As Figure 2 shown, the microchannel is a cuboid structure with a length of 5 cm, a width of 600 μm, and a height of 150 μm; the microchannel is generally cast with PDMS material or etched with silicon material.

[0067] The present invention also discloses a method for measuring the swimming characteristics of algal cells in a shear flow. The method includes the following steps:

[0068] Step 1: Prepare an algal cell solution with a certain concentration, connect the experimental device and check the airtightness of the experimental device;

[0069] Step 2: Adjust the position of the microchannel so that the center of the shooting frame of the high-speed camera corresponds to the center position of the microchannel, the observation area is in the middle of the inlet and outlet of the channel, and at the same time, the front and rear wall surfaces of the microchannel are parallel to the long border of the shooting frame;

[0070] Step 3, determine the average flow rate (or shear rate) according to the experimental conditions, use a pressure pump to set the pressure in the liquid storage bottle, and continuously adjust the pressure according to the real-time flow rate monitored by the flow meter until the measured flow rate remains stable and consistent with the required average flow rate, so as to produce a stable shear flow;

[0071] Step 4: First, use a high-speed camera to take an image in a bright field environment to calibrate the front and rear walls of the microchannel, which correspond to the upper and lower boundaries of the captured image, respectively; then turn off the light source and take a sequence of images in a fluorescent field environment. Each set of experiments is recorded for five minutes; repeat the experiment many times until there are tens of thousands of effective algae cell movement trajectories. Generally speaking, the shooting frame rate is 100 frames, that is, 30,000 images are taken for each set of experiments.

[0072] Specifically, the effective algae cell motion trajectory refers to the long-term algae cell motion trajectory in the observation area, which can reflect the normal movement of algae cells in shear flow. The following conditions must be met:

[0073] 1) The duration of recording the trajectory of algal cells is greater than 10 seconds (the duration can be adjusted according to the specific experimental conditions);

[0074] 2) The recorded trajectories do not include the trajectories of algae cells with weak mobility (such as stationary trajectories) and the trajectories of algae cells that are misidentified (such as trajectories of impurities adhering to certain areas).

[0075] Step 5: Use the trackmate open source program to process the recorded image sequence, set appropriate diameter and brightness thresholds to identify algae cells, extract the coordinate data of the algae cell movement trajectory, and remove the trajectory outside the observation area according to the calibrated upper and lower boundaries of the captured image, and only retain the trajectory within the observation area;

[0076] The diameter threshold is set according to the algae cell type, and different types of algae cells have different sizes. The brightness threshold is set according to the laser band, strength and exposure time.

[0077] Step 6: Obtain the distribution of the migration velocity V of the algae cells by observing the movement trajectory of the algae cells, and calculate the algae cell flow velocity V by combining the analytical method. flow The distribution of the algae cells in the shear flow is then calculated to obtain the swimming characteristics, including their own swimming speed V s and angular velocity ω; specifically comprising the following steps:

[0078] Step 61, calculate the migration velocity component of the algae cells: according to the position coordinates of the algae cell movement trajectory observed in the experiment, except for the first point which uses forward difference and the last point which uses backward difference, the other points on the trajectory are calculated using the central difference format to obtain the migration velocity component V of the algae cells at different positions on each trajectory. x, V y :

[0079] The first point:

[0080]

[0081] The last point:

[0082]

[0083] Other points:

[0084]

[0085] where: x and y are the coordinates of the algal cells, and their subscripts represent the coordinates of different points, μm; V x , V y are the migration velocity components respectively, and their subscripts represent the migration velocity components of different points, μm / s; Δt is the time interval between adjacent points on the trajectory, s.

[0086] Step 62, calculate the advection velocity distribution of the algal cells: In the shear flow environment, the component of the advection velocity in the y direction at different positions in the width direction of the microchannel is 0, and the component in the x direction is V flow_x obtained by an analytical method, and the calculation formula is:

[0087]

[0088]

[0089] where: a and b are respectively half of the width and height of the microchannel, μm; is the pressure, Kgμm -1 s -2 ; μ is the dynamic viscosity of the liquid, Kgμm -1 s -1 ; i is the index variable for series summation; Q is the average flow rate, μm 3 / s.

[0090] Step 63, calculate the self-swimming speed of the algal cells and its components: The migration speed V of the algal cells in the shear flow is divided into two parts. One is the self-swimming speed V s , that is, the swimming speed actively generated by the algal cells through flagellar drive. The other is the advection speed V flow , that is, the water flow movement speed at the position where the algal cells are located; the migration speed V is the superposition of the self-swimming speed V s , the advection speed V flow , that is:

[0091] V = V s + V fl ow (6)

[0092] Where: V, V s , V flow are both in μm / s.

[0093] Calculate the self-swimming speed V s of the algal cells and its components V s_x , V s_y according to the migration speed of the algal cells and the advection speed at their locations. The calculation formula is as follows:

[0094] V s_x = V x - V flow_x (7)

[0095] V s_y = V y (8)

[0096]

[0097] Step 64. Calculate the angular velocity of the algal cells: Calculate its movement direction θ according to the components of the swimming speed of the algal cells. The calculation formula is:

[0098]

[0099] Calculate the change in the movement direction of the algal cells based on the movement directions of each trajectory of the algal cells at different times, and then the angular velocity ω of the algal cells can be obtained. The calculation method is the same as that for calculating the speed. Except for using forward difference for the first point and backward difference for the last point, central difference format is used for other points on the trajectory:

[0100] The first point:

[0101]

[0102] The last point:

[0103]

[0104] Other points:

[0105]

[0106] Where: θ is the movement direction of the algal cells, in rad; ω is the angular velocity of the algal cells, in rad / s; the subscripts represent the movement directions and angular velocities of different points.

[0107] Step 65, Measuring the swimming characteristics of algal cells: Since the water flow velocity in the width direction is parabolic, the shear rates at different positions in the width direction are different. According to the analysis of a large number of algal cell movement trajectories (at least more than 10,000), the self-swimming speed and angular velocity of algal cells at different positions in the width direction of the microchannel are statistically analyzed and averaged to obtain the distribution of the self-swimming speed and angular velocity of algal cells in the width direction of the microchannel, that is, the measurement of the swimming characteristics of algal cells under different shear rates is realized.

[0108] Example 1

[0109] This example is an application example of the above method.

[0110] The concentration of the algal cell solution configured in this example is 1.2×10 5 cells / ml, and the type of algal cells used is Heterosigma akashiwo, with a cell diameter of about 10 μm. In this example, taking the shear flow with an average flow rate of 9×10 6 μm 3 / s as an example, the swimming characteristics of algal cells are measured now.

[0111] Using the above experimental device to observe the movement trajectories of algal cells, as Figure 3 shown, are some randomly selected trajectories. The circles in the figure are the initial positions of the trajectories. The set diameter threshold is 12 pixel, and the brightness threshold is 20. Figure 4 is the distribution map of the migration speed component V x of algal cells measured by the experimental method. Figure 5 、 Figure 6 are the distribution maps of the self-swimming speed components V s_x 、V s_y of algal cells obtained by the above method respectively. Figure 7 is the distribution map of the angular velocity ω of algal cells obtained by the above method.

[0112] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those of ordinary skill in the art should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. An experimental device for measuring the swimming characteristics of algal cells in a shear flow, characterized in that, The experimental device comprises an air pressure source, a pressure pump, a liquid storage bottle, a flow meter, a microchannel and a waste liquid bottle which are connected in sequence, wherein the air pressure source and the pressure pump, and the pressure pump and the liquid storage bottle are connected via connecting pipes, and the liquid storage bottle and the flow meter, the flow meter and the inlet of the microchannel, and the outlet of the microchannel and the waste liquid bottle are connected via conduits, and the device also comprises a connected fluorescence microscope and a high-speed camera, wherein the high-speed camera is installed below the stage of the fluorescence microscope, and the microchannel is arranged on the stage of the fluorescence microscope; the air pressure source is used to provide a basic pressure for the pressure pump; and the pressure pump is used to output a set constant pressure to create an internal and external pressure difference in the liquid storage bottle; The liquid storage bottle is sealed and contains algae cell solution. Under the action of the internal and external pressure difference, the algae cell solution is transported to the microchannel through the catheter to form a shear flow. The flowmeter is used to monitor the flow rate pumped in by the pressure pump in real time; the microchannel is used to form a shear flow; the waste liquid bottle is used to collect the algae cell waste solution flowing out of the microchannel outlet; the fluorescence microscope is used to create a fluorescence field environment, induce the algae cells to generate characteristic fluorescence signals, and simultaneously realize microscopic image amplification and filter out other stray light; the high-speed camera is used to capture the image sequence of the algae cells in the shear flow.

2. The experimental device for measuring the swimming characteristics of algal cells in a shear flow according to claim 1, characterized in that, The inlet and outlet of the microchannel are connected to the catheter via a Luer connector.

3. An experimental device for measuring the swimming characteristics of algal cells in a shear flow according to claim 1, characterized in that, The microchannel is a rectangular parallelepiped structure with a length of 5 cm, a width of 600 μm and a height of 150 μm; the microchannel is cast with PDMS material or etched with silicon material.

4. A method for measuring the swimming characteristics of algal cells in a shear flow based on the experimental device described in claim 1, characterized in that, The method comprises the following steps: Step 1: prepare algae cell solution of a certain concentration, connect the experimental device and check the air tightness of the experimental device; Step 2: Adjust the position of the microchannel so that the center of the frame shot by the high-speed camera corresponds to the center of the microchannel, and the front and rear walls of the microchannel are parallel to the long frame of the frame shot; Step 3, determine the average flow rate according to the experimental working conditions, use a pressure pump to set the pressure in the liquid storage bottle, and continuously adjust the pressure according to the real-time flow rate monitored by the flow meter until the measured flow rate remains stable and consistent with the required average flow rate, so as to produce a stable shear flow; Step 4: First, use a high-speed camera to take an image in a bright field environment to calibrate the front and rear walls of the microchannel, which correspond to the upper and lower boundaries of the captured image respectively; then turn off the light source and take a sequence of images in a fluorescent field environment. Each set of experimental recording time is five minutes, and the experiment is repeated many times until the number of effective algae cell movement trajectories reaches tens of thousands; Step 5: Process the captured image sequence, set the diameter and brightness thresholds to identify algae cells, extract the coordinate data of the algae cell movement trajectory, and remove the trajectory outside the observation area according to the calibrated upper and lower boundaries of the captured image, and only retain the trajectory within the observation area; Step 6: Obtain the distribution of the migration velocity V of algal cells from the observed movement trajectories of algal cells, and calculate the distribution of the flow velocity V of algal cells with the analytical method, and then calculate the swimming characteristics of algal cells in the shear flow, including the self-swimming velocity V flow and the angular velocity ω; specifically, the following steps are included: s and the angular velocity ω; specifically, the following steps are included: Step 61. Calculate the migration velocity components of algal cells: Based on the position coordinates of the movement trajectories of the algal cells observed in the experiment, except for the first point using forward difference and the last point using backward difference, central difference format is used to calculate the other points on the trajectory, and thus the migration velocity components V x and V y at different positions of the algal cells on each trajectory can be obtained. First point: One last point: Other points: where: x and y are the coordinates of the algal cells, and their subscripts represent the coordinates of different points, in μm; V x , V y are the migration velocity components respectively, and their subscripts represent the migration velocity components of different points, in μm / s; Δt is the time interval between adjacent points on the trajectory, in s; Step 62, calculate the advection velocity distribution of algal cells: In a shear flow environment, the y-component of the advection velocity at different positions in the width direction of the microchannel is 0, and the x-component V flow_x is obtained by an analytical method, and the calculation formula is: Where: a and b are respectively half of the width and height of the microchannel, in μm; is the pressure, in Kgμm -1 s -2 ; μ is the dynamic viscosity of the liquid, in Kgμm -1 s -1 ; i is the index variable for summing the series; Q is the average flow rate, in μm 3 / s; Step 63: Calculate the self-swimming speed of algal cells and its components. The migration speed V of algal cells in a shear flow is divided into two parts. One is the self-swimming speed V s , which is the swimming speed actively generated by the algal cells through flagellar drive. The other is the flow velocity V flow , which is the water flow velocity at the location of the algal cells. The migration speed V is the superposition of the self-swimming speed V s and the flow velocity V flow , that is: V = V s +V flow (6) Where: V, V s , V flow are all in the unit of μm / s; Calculate the self-swimming speed V of algal cells based on the migration speed of algal cells and the advection speed at their locations s and its components V s_x , V s_y , and the calculation formula is as follows: V s_x = V x -V flow_x (7) V s_y = V y (8) Step 64, calculate the angular velocity of the algae cell: calculate the moving direction θ according to the component of the swimming velocity of the algae cell, and the calculation formula is: According to the movement directions of each algal cell trajectory at different times, calculate the change in the movement direction of the algal cell, and the angular velocity ω of the algal cell can be obtained. The calculation method is as follows: except for the first point using forward difference and the last point using backward difference, central difference format is used to calculate other points on the trajectory: The first point: The last point: Other points: In the formula: θ is the movement direction of the algal cell, in rad; ω is the angular velocity of the algal cell, in rad / s; the subscript represents the movement direction and angular velocity of different points; Step 65, measure the swimming characteristics of algal cells: According to the analysis of a large number of algal cell movement trajectories, statistically calculate the self-swimming speed and angular velocity of algal cells at different positions in the width direction of the microchannel, and perform averaging to obtain the distribution of the self-swimming speed and angular velocity of algal cells in the width direction of the microchannel, that is, the measurement of the swimming characteristics of algal cells at different shear rates is realized.

5. A method for measuring the swimming characteristics of algal cells in a shear flow according to claim 4, characterized in that, The concentration of the algal cell solution configured in Step 1 is 1.2×10 5 cells / mL.

6. The method for measuring the swimming characteristics of algal cells in a shear flow according to claim 4, wherein The determination criteria for effective algal cell movement trajectories in step 4 are: 1) The recorded duration of the algal cell movement trajectory is greater than 10 s; 2) The recorded trajectory does not include stationary trajectories and trajectories of impurities adhering to certain areas.

7. A method for measuring the swimming characteristics of algal cells in a shear flow according to claim 4, characterized in that, The diameter threshold in step 5 is set according to the type of algal cell, and different types of algal cells have different sizes; the brightness threshold is set according to the wavelength band, intensity, and exposure time of the laser.

8. A method for measuring the swimming characteristics of algal cells in a shear flow according to claim 4, characterized in that The large number of algal cell movement trajectories in step 65 refers to at least more than 10,000 algal cell movement trajectories.

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