Magnetic control system for sensing mechanical characteristics of organoid

Abstract

The invention discloses a magnetic control system for sensing mechanical characteristics of an organoid, and relates to the field of organoid operation. The invention aims to solve the problems that an existing microscopic biological structure mechanical characteristic measuring system is insufficient in working space, small in applied force, low in precision, poor in flexibility and difficult to meet the requirement for mechanical characteristic measurement of organoids in biomedical research. An execution module is of an octupole magnetic tweezers structure and is used for executing mechanical actions of a magnetic control system on the similar organs; the visual feedback module is used for tracking and positioning the magnetic beads in the execution module through a microscope camera; the electric control module is used for supplying power to eight magnetic poles of the eight-pole magnetic tweezers structure; and the controller is used for controlling the expected control current of the electric control module according to a driving target.

Description

Technical Field

[0001] The present invention belongs to the field of organoid manipulation, and in particular relates to a magnetic control system for organoid manipulation. Background Art

[0002] Organoids have the advantages of miniaturization, easy cultivation, and ability to simulate the structure and function of real organs. They have been widely used in the fields of regenerative medicine and pharmaceutical research. Currently, a variety of tumor organoids have been produced for anti-cancer research. The mechanical properties of organoids are closely related to their development and behavior, tissue homeostasis, and disease progression. Accurately measuring the mechanical properties of organoids has guiding significance for regulating cell activity, predicting fate, monitoring homeostasis, preventing tumor deterioration, and exploring cancer therapies.

[0003] Current systems for measuring the mechanical properties of microscopic biological structures include atomic force microscopes, optical tweezers systems, and magnetic tweezers systems. Among them, atomic force microscopes cannot measure deeply into tissues due to the tethered nature of their probes, making it difficult to achieve a more comprehensive measurement of biological tissues, and the materials of the indenter and substrate will greatly affect the measurement accuracy. Optical tweezer systems use laser beams to manipulate particles, and because high laser power can damage tissues, they are usually used to test cells or subcellular structures. Traditional magnetic tweezers technology can measure the mechanical properties of larger biological structures, but its working space is generally small, the force output to micron-sized particles is small, and the particle movement pattern is limited, making it difficult to achieve measurement operations on organoids.

[0004] In summary, existing systems for measuring the mechanical properties of microscopic biological structures can test biological structures at the cell scale, but they are difficult to meet the needs of measuring the mechanical properties of organoids in biomedical research. Summary of the invention

[0005] The present invention aims to solve the problems of existing microscopic biological structure mechanical property measurement systems, such as insufficient working space, small force, low precision, and poor flexibility, which make it difficult to meet the needs of organoid mechanical property measurement in biomedical research. A magnetic control system for sensing the mechanical properties of organoids is now provided.

[0006] A magnetic control system for sensing the mechanical properties of organoids, comprising: an execution module, a visual feedback module, an electric control module and a controller;

[0007] The execution module is an octapole magnetic tweezers structure, which is used to execute the mechanical action of the magnetic control system on the organoid;

[0008] The visual feedback module is used to track and locate the magnetic beads in the execution module through a microscope camera;

[0009] The electric control module is used to supply power to the eight magnetic poles of the octupole magnetic tweezers structure;

[0010] The controller is used to control the desired control current of the electric control module according to a driving target.

[0011] Furthermore, the above-mentioned execution module includes two layers of magnetic tweezers platforms and magnetic beads that are mirror-imaged, each layer of the magnetic tweezers platform includes four magnetic pole pieces, the four magnetic pole pieces are evenly arranged in a circle, and the magnetic field generated by the eight magnetic pole pieces is used to drive the movement of the magnetic beads.

[0012] Furthermore, each layer of the magnetic tweezers platform further includes: a magnetic yoke and a magnetic pole piece fixing plate, the magnetic yoke is connected to the magnetic pole piece fixing plate via a coil core, and the four magnetic pole pieces are each fixed to the magnetic pole piece fixing plate via a magnetic pole piece fixer.

[0013] Furthermore, the execution module further comprises a support structure, wherein the support structure comprises: a vertical fine-tuning screw of the magnetic tweezers platform, a horizontal fine-tuning screw of the magnetic tweezers platform, an upper base and a base;

[0014] The two layers of magnetic tweezers platforms are fixed to the upper base and the base respectively through fixers. The vertical fine-tuning screw of the magnetic tweezers platform and the horizontal fine-tuning screw of the magnetic tweezers platform are located on the upper base and are used to adjust the position of the magnetic tweezers platform on the upper base. The upper base is fixed to the base through a platform connecting column.

[0015] Furthermore, the visual feedback module can realize the tracking and positioning of the magnetic beads through the following steps:

[0016] S1: Adjust the microscope camera to focus on the magnetic beads and select the magnetic beads in the picture, and obtain the clarity reference value of the selected picture;

[0017] S2: Use the microscope camera to sample the current magnetic beads and obtain a target image containing the magnetic beads;

[0018] S3: using the CSRT algorithm to track the magnetic beads and obtain the XY axis coordinates of the magnetic beads in the target image;

[0019] S4: binarizing the target image, and then using the Laplace gradient method to calculate the image clarity under the current sampling;

[0020] S5: Determine whether the clarity exceeds 90% of the clarity reference value. If so, use the Z-axis coordinate of the focal plane of the current microscope camera lens as the Z-axis coordinate of the magnetic bead. Otherwise, execute S6;

[0021] S6: Determine whether the clarity is higher than the image clarity at the last sampling. If yes, move the focus point in the direction of the current microscope camera movement with a fixed step length, and then return to S3. Otherwise, move the focus point in the opposite direction of the current microscope camera movement with a fixed step length, and then return to S3.

[0022] The plane where the XY axes are located is the plane where the target image is located, and the Z axis is perpendicular to the plane where the XY axes are located.

[0023] Furthermore, the above-mentioned electric control module includes: 8 constant voltage switching power supplies, 1 amplifier circuit power supply, 8 constant current source modules and a push-pull amplifier circuit;

[0024] The PWM signal output end of the controller is connected to the PWM signal input end of the push-pull amplifier circuit. The amplifier circuit power supply is used to excite the push-pull amplifier circuit to amplify the input PWM signal into a PWM signal with the same frequency and duty cycle. The PWM signal output end of the push-pull amplifier circuit is respectively connected to the control ends of 8 constant current source modules, and the 8 constant voltage switching power supplies respectively power the 8 constant current source modules.

[0025] Furthermore, the controller controls the desired control current of the electric control module according to the driving target through the following steps:

[0026] SA: Determine the current working mode. In the precise force application mode, execute SB1. In the motion control mode, execute SC1.

[0027] The precise force application mode is to control the magnetic beads to perform a short-distance impact motion, and the motion control mode is to control the magnetic beads to perform a long-distance movement;

[0028] SB1: Calculate the magnetic field strength-current coefficient matrix of the execution module according to the actual position r of the magnetic bead and the magnetic field intensity gradient-current coefficient matrix Then execute SB2;

[0029] SB2: According to the magnetic field strength-current coefficient matrix and the magnetic field intensity gradient-current coefficient matrix Calculate the actual magnetic field force F, and then execute SB3;

[0030] SB3: Compare the actual magnetic field force F under the current with the expected magnetic field force F d The goal is to minimize the relative error of , and determine whether the actual magnetic field force F under the current current meets the goal. If so, the current current is the desired control current. Otherwise, the current vector I is optimized using the differential evolution algorithm, and then SB2 is returned.

[0031] SC1: According to the actual position r of the magnetic bead and the expected position r d Construct the objective function and obtain the desired control current.

[0032] Furthermore, the above magnetic field intensity-current coefficient matrix And the magnetic field intensity-current coefficient matrix for gradient They are:

[0033]

[0034] Where i = 1, 2, ..., 8, μ0 is the vacuum permeability, k q is the proportionality coefficient, r p =[r p,1 ,r p,2 ,...,r p,8 ],r p,i is the position vector of the i-th magnetic pole tip, I 3×3 is a 3rd order unit matrix, 1 3×3 is a 3×3 matrix with all elements being 1, Represents a tensor product.

[0035] Furthermore, according to the magnetic field intensity-current coefficient matrix and the magnetic field intensity gradient-current coefficient matrix Calculate the actual magnetic field force F, including:

[0036]

[0037] Among them, k m is the proportional coefficient of the magnetization of the magnetic bead, and I is the current vector formed by the currents of the coils connected to the magnetic poles.

[0038] Furthermore, the above-mentioned actual position r of the magnetic bead and the expected position r d Construct the objective function J(k) to obtain the desired control current, including:

[0039]

[0040] Where, e(k) = r(k) - r d (k) is the position tracking error at time k, e(k+n|k) and u(k+n|k) represent the tracking error and expected control current at time k+n predicted at time k, respectively, N is the maximum number of prediction steps, Q and W are both positive definite matrices given by the user, which are used to weight the tracking error and current control amount, respectively.

[0041] The magnetic control system for sensing the mechanical properties of organoids proposed in the present invention can realize the measurement of the mechanical properties of three-dimensional multicellular biological structures such as organoids, and has the following advantages over existing methods:

[0042] High efficiency: The magnetic tweezers device has eight closely arranged magnetic poles, which generate a large magnetic force, can drive the magnetic beads to move quickly, and has the possibility of controlling the simultaneous measurement of multiple magnetic beads, with high measurement efficiency. Organoids and other samples are kept in liquid culture medium for a short time, and improving measurement efficiency helps to improve the accuracy of measurement data.

[0043] Large working space: The proposed magnetic tweezers structure and current configuration algorithm can give full play to the ability of the coil to generate magnetic field or magnetic field gradient. The working space of the magnetic beads is significantly improved, and the working space is large enough to accommodate organoids with a diameter of 300 microns for operation.

[0044] High control accuracy: The dual-mode control algorithm adopted can be optimized for trajectory tracking and precise force application scenarios respectively, achieving high-precision control to meet experimental needs.

[0045] Wide range of applications: The designed glass culture dish can accommodate most samples with complex spatial structures at the hundred-micron level. At the same time, it has a dish cover to ensure the closedness of the culture and testing process to avoid contamination.

[0046] By utilizing the magnetic tweezers system of the present invention with high efficiency, high output, high precision, large working space and wide application range, the mechanical properties of three-dimensional biological tissues can be characterized more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the overall structure discrete state of the execution module;

[0048] Figure 2 It is a schematic diagram of the structural parameters of the culture dish;

[0049] Figure 3 Schematic diagrams of the structure of the execution module under four viewing angles, including (a) isometric view, (b) top view, (c) bottom view, and (d) side view;

[0050] Figure 4 It is a structural diagram of the electric control module;

[0051] Figure 5 Flowchart for object tracking and autofocus;

[0052] Figure 6 This is the control flow chart of the controller. DETAILED DESCRIPTION

[0053] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0054] Reference Figures 1 to 6Specifically describing this embodiment, a magnetic control system for sensing the mechanical properties of organoids described in this embodiment includes: an execution module, an electric control module, a visual feedback module and a controller.

[0055] like Figure 1 and Figure 3 As shown, the execution module as a whole is composed of an upper magnetic tweezers platform, a lower magnetic tweezers platform and a supporting structure. The upper and lower magnetic tweezers platforms have the same structure, and each magnetic tweezers platform includes: a magnetic yoke 1, a magnetic pole piece fixing plate 2, a coil core 3, four magnetic pole pieces 8 and four magnetic pole piece fixers 10.

[0056] The yoke 1 is pressed from silicon steel sheets, and the yoke 1 is connected to the pole piece fixing plate 2 through the coil core 3. The four pole pieces 8 correspond to the four pole piece holders 10 respectively, and the pole piece holders 10 are used to fix the corresponding pole pieces 8 on the pole piece fixing plate 2. The four pole pieces 8 are evenly arranged in a circular shape. The pole piece 8 is cut from a 0.1 mm thick silicon steel sheet into a sharp angle, and the tip angle is less than 10°. The sharp pole piece 8 has a higher magnetic permeability and can generate a larger magnetic field gradient.

[0057] The supporting structure includes: a vertical fine-tuning screw 4 of the magnetic tweezers platform, a horizontal fine-tuning screw 5 of the magnetic tweezers platform, an upper base 6, a fixer 7, a platform connecting column 11 and a base 12.

[0058] The upper magnetic tweezers platform is fixed to the upper base 6 by a fixture 7, and its position can be adjusted at the micron level through the vertical fine-tuning screw 4 and the horizontal fine-tuning screw 5 of the magnetic tweezers platform as needed, thereby reducing the impact of assembly errors. The upper base 6 is fixed to the base 12 of the magnetic tweezers device through the platform connecting column 11, so that the upper structure of the magnetic tweezers can be more conveniently separated from the lower structure, which is convenient for the addition and liquid replacement of biological tissues or magnetic beads. The magnetic pole pieces 8 of the upper and lower magnetic tweezers platforms are staggered. There is a gap in the center of the lower magnetic pole piece fixing plate 2, into which a micro glass culture dish 9 with a diameter of 4 mm and a thickness of 1 mm can be placed. Unlike a glass slide, the glass culture dish 9 can hold biological tissues with complex three-dimensional structures and provide better protection. The glass culture dish 9 is equipped with a dish cover to isolate external contamination. The specific parameters of the culture dish are as follows: Figure 2 shown.

[0059] This embodiment uses eight magnetic pole pieces 8 to form an octupole magnetic tweezers structure, which has the following effects: 1. The magnetic field generated by the magnetic control system in the working space is larger; 2. There are many current parameters, and the success rate of solving the expected current according to the expected force is improved, which improves the flexibility of the system in operation; 3. The magnetic pole distribution has good symmetry, and the system's ability to generate magnetic fields can be fully utilized in special directions commonly used in experiments such as along the coordinate axis, thereby generating a greater magnetic field force.

[0060] The above execution modules can be directly integrated on an inverted microscope, and the system image feedback is realized through the microscope camera. The visual feedback module of the magnetic control system has object tracking and autofocus functions. The specific workflow is as follows: Figure 5 As shown, including:

[0061] S1: The microscope camera focuses on the magnetic beads and selects the beads in the picture to obtain a clarity reference value of the selected picture.

[0062] S2: Use the microscope camera to sample the current magnetic beads and obtain a target image containing the magnetic beads.

[0063] S3: Use the CSRT algorithm to track the magnetic beads and obtain the XY axis coordinates of the magnetic beads in the target image.

[0064] S4: binarizing the target image, and then using the Laplace gradient method to calculate the image clarity under the current sampling.

[0065] S5: Determine whether the clarity exceeds 90% of the clarity reference value. If so, it means that the current focal plane of the microscope camera lens is located at the Z-axis position where the magnetic bead is located, and then obtain the Z-axis coordinates of the magnetic bead. Otherwise, execute S6.

[0066] S6: Determine whether the clarity is higher than the clarity obtained by the last sampling. If so, move the focus point in the current direction with a fixed step size, and then return to S3. Otherwise, move the focus point in the opposite direction of the current direction with a fixed step size, and then return to S3.

[0067] The controller can calculate the expected coil current based on the current working mode, user instructions, current position of the magnetic beads and other information, and convert the instruction signal into the excitation current of the input coil through the power amplifier module to drive the movement of the magnetic beads. The movement of the magnetic beads includes two working modes, namely the precise force mode and the motion control mode. The precise force mode is to control the magnetic beads to perform a short-distance and low-speed impact movement on the organoids, and the motion control mode is to control the magnetic beads to move quickly and over a long distance in a liquid environment.

[0068] (1) Accurate force application mode

[0069] The magnetic beads are magnetized in the magnetic field to generate magnetic moment. Since the magnetic beads are extremely small and have superparamagnetism, the magnetic moment of the magnetic beads is consistent with the direction of the magnetic field outside the magnetic beads, and the amplitude is proportional. According to the force formula of an object with magnetic moment in a magnetic field, the magnetic bead is subject to the magnetic force F, that is, the magnetic field force as shown in formula (1):

[0070]

[0071] Where B is the external magnetic field strength of the magnetic bead, represents the gradient, is the gradient of the external magnetic field strength (3×3 matrix), d is the magnetic moment generated by the magnetization of the magnetic beads, k m is the proportional coefficient of the magnetization of the magnetic bead, d = k m B.

[0072] The magnetic pole piece made of silicon steel sheet has high magnetic permeability, and the sharp angle configuration at its end makes the magnetic flux lines concentrate at the tip to enter the working space. Therefore, the magnetic field generated by a single magnetic pole in the working space is approximately the same as the magnetic field generated by the ideal magnetic charge, which can be approximately calculated by equations (2) and (3):

[0073]

[0074] in, is the magnetic scalar potential, μ0 is the vacuum magnetic permeability, r is the magnetic bead position vector, r p is the position vector of the magnetic pole tip, and q is the equivalent magnetic charge. As for the size of q, it can be known from the linearity of Maxwell's equations that it is proportional to the coil current I, that is, q = k q I. Proportional coefficient k q The error in theoretical calculation is relatively large and can be calibrated in experiments.

[0075] When the eight coils of the magnetic tweezers device are all energized, the superposition theorem shows that the magnetic field in the working space is expressed as:

[0076]

[0077]

[0078] Among them, r p,i is the position vector of the i-th magnetic pole tip, I i is the current flowing through the ith coil, is the BI coefficient matrix of the i-th magnetic pole, B i is the magnetic field strength of the ith magnetic pole.

[0079] Writing formula (4) in matrix form gives formula (6):

[0080]

[0081] Where I is the vector of current parameters, is the BI coefficient matrix of the magnetic tweezers device, which is only related to the magnetic bead position r when the positions of the magnetic poles are fixed.

[0082] right Taking the gradient, we can get Coefficient Matrix The expression of each block is shown in formula (7):

[0083]

[0084] Among them, I 3×3 is a 3rd order unit matrix, 1 3×3 is a 3×3 matrix with all elements being 1, Represents a tensor product.

[0085] When solving the current according to the expected force, the relative error between the magnetic field force under the current current and the expected force is taken as the objective function J I ,Right now:

[0086]

[0087] Among them, in the precise force application mode, the expected force F d Input by the user through the operation interface.

[0088] The desired current can be obtained by iteratively optimizing the vector I composed of current parameters using the differential evolution algorithm.

[0089] (2) Motion control mode

[0090] In motion control mode, the controller adopts MPC control algorithm. The control object model is as follows:

[0091] The magnetic beads are affected by magnetic force, viscous resistance, thermal fluctuation, buoyancy and gravity in the working space. The motion equation of the magnetic beads is as follows:

[0092]

[0093] Where m is the mass of the magnetic bead, is the acceleration of the magnetic bead, F is the magnetic force on the magnetic bead, and F η is the fluid viscosity force on the magnetic beads, F buoyance is the buoyancy of the magnetic bead, G is the gravity of the magnetic bead, and f thermal is the force of thermal disturbance on the magnetic bead. In the workspace, the thermal disturbance on the magnetic bead can be modeled as white noise, which is relatively small and can be ignored. In addition, since the mass of the magnetic bead is extremely small, its inertia term can be ignored. At the same time, the buoyancy and gravity of the magnetic beads in the working space are basically offset, so the motion equation of the magnetic beads can be simplified to formula (10):

[0094] F+F η =0 (10),

[0095] According to Stokes viscous drag formula: Where η is the fluid viscosity, R is the radius of the magnetic bead, is the speed of the magnetic bead. Substituting into formula (10), we can get:

[0096]

[0097] Given Substituting into equations (1)(5)(6)(7), we can obtain that the magnetic force on the bead at r = 0 is F = k I u, where is the current control quantity, a, b, c are the additional currents of I4 and I6, I2 and I8, I1 and I5 respectively, I m is a current parameter that can be set by the user, k I is obtained from the calculation and k m , k q ,I m The related constants.

[0098] Considering that the magnetic field force F is an odd function of the magnetic bead position r, the even terms of its Taylor expansion are all zero. A relatively accurate result can be obtained by performing a first-order Taylor expansion of F at r = 0, u = 0, and then:

[0099]

[0100] in, k T is obtained from the calculation and k m , k q ,I m The related constants.

[0101] Substituting equation (12) into equation (11), we can obtain the differential equation of the motion of the magnetic bead:

[0102]

[0103] The magnetic bead dynamics equation is discretized with T as the period to design the digital control system. The discretized magnetic bead state equation is equation (14):

[0104] r(k+1)=[(6πηRI3+k T TK)r(k)+(k I TI3)u(k)] / 6πηR (14),

[0105] Among them, I3 is a third-order unit matrix, r(k+1) and r(k) are the magnetic bead position vectors at time k+1 and k respectively.

[0106] Take A c =(6πηRI3+k T TK) / 6πηR,B c =(k I TI3) / 6πηR, equation (14) is simplified to:

[0107] r(k+1)=A c r(k)+Bc u(k) (15),

[0108] Among them, A c and B c It is called the discrete state matrix, from which the state equation of the controlled object of the system is obtained.

[0109] The user specifies the desired position r of the magnetic bead through the operation interface d When , the MPC control algorithm optimizes the current control variable u using the objective function shown in formula (16):

[0110]

[0111] Where, e(k) = r(k) - r d (k) is the tracking error at time k, e(k+n|k) and u(k+n|k) represent the tracking error and current control value at time k+n predicted at time k, respectively, N is the maximum prediction step number of the MPC control algorithm, Q and W are positive definite matrices that can be given by the user, which are used to weight the tracking error and current control value, respectively.

[0112] The objective function is the weighted sum of the tracking error and the predicted value of the current control amount. According to the MPC algorithm, the optimal current control amount that minimizes the tracking error and current control amount in the next N steps can be calculated. according to The expected current I can be calculated d .

[0113] The specific process of the control law calculation thread is as follows:

[0114] SA: Determine the current working mode. In the precise force application mode, execute SB1. In the motion control mode, execute SC1. SB1: Calculate the BI coefficient matrix of the execution module according to the actual position r of the magnetic bead. as well as Coefficient Matrix

[0115] SB2: Calculate the actual magnetic field force F:

[0116]

[0117] Among them, k m The proportional coefficient of the magnetization of the magnetic bead, I is the current vector formed by the currents of each coil connected to the magnetic pole.

[0118] SB3: Compare the actual magnetic field force F under the current with the expected magnetic field force F d The goal is to minimize the relative error.

[0119] SB4: Determine whether the actual magnetic field force F under the current meets the target. If so, the current current is the desired control current. Otherwise, the current vector I is optimized using the differential evolution algorithm, and then returns to SB2.

[0120] SC1: According to the actual position r of the magnetic bead and the expected position r d Construct the objective function and obtain the desired current control quantity.

[0121] like Figure 4 As shown, the electric control module includes 8 D-50F24 24V switching power supplies 13, 1 D-50B 5V switching power supply 14, 8 OPA549 constant current source modules 15, a frame with vents 16 and a push-pull amplifier circuit, wherein the push-pull amplifier circuit is composed of 8 2SJ532 P-channel MOS tubes and 8 10N65 N-channel MOS tubes. The 24V switching power supply 13 is located on the upper layer of the frame 16, and the 8 D-50F24 24V switching power supplies 13 correspond to the 8 OPA549 constant current source modules 15 one by one and are used to power the corresponding OPA549 constant current source modules 15. The D-50B 5V switching power supply 14 powers the push-pull amplifier circuit and amplifies the command voltage signal.

[0122] The 8-way GPIO pins of the STM32F103 single-chip microcomputer output PWM signal are connected to the PWM signal input end of the push-pull amplifier circuit. Under the DC excitation provided by the 5V switching power supply 14, the push-pull amplifier circuit amplifies the 3.3V peak-to-peak PWM signal of the STM32 output to a 5V peak-to-peak PWM signal of the same frequency and duty cycle, and the signal is respectively input to the control end of 8 constant current source modules 15. The voltage output end of the 24V switching power supply 13 located in the upper layer of the framework is connected to the DC voltage input end of the constant current source module 15, which is powered and stimulates it to output a DC current (proportional coefficient is 1A:1V) that is proportional to the average value of the control end voltage. The constant current source module 15 is located in the lower layer of the framework 16 and can dissipate heat through the vents during operation. The electric control module can output eight-way excitation currents of up to 5A. The constant current source module 15 can theoretically output up to 8 excitation currents of up to 8 maximum 8A.

[0123] In summary, this embodiment can accurately output a sufficiently large magnetic field force while ensuring a large working space by introducing multiple magnetic poles, coordinating the relative positions of the magnetic poles and designing a suitable current control scheme, and give full play to the high flexibility of non-tethered systems such as magnetic tweezers systems. In addition, a special micro-glass culture dish can be placed in the center of the magnetic tweezers device. Compared with glass slides, the culture dish can hold larger multicellular biological samples such as organoids with complex three-dimensional spatial structures. In response to different measurement needs of users, the system has two working modes: magnetic bead position control mode and precise force output mode. The two modes use different algorithms to solve the magnetic pole coil current, which can measure mechanical properties more efficiently and accurately for different scenarios.

[0124] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A magnetic control system for sensing the mechanical properties of organoids, characterized in that: include: Execution module, visual feedback module, electronic control module and controller; The execution module is an octapole magnetic tweezers structure, which is used to execute the mechanical action of the magnetic control system on the organoid; The visual feedback module is used to track and locate the magnetic beads in the execution module through a microscope camera; The electric control module is used to supply power to the eight magnetic poles of the octupole magnetic tweezers structure; The controller is used to control the desired control current of the electric control module according to a driving target.

2. A magnetic control system for sensing the mechanical properties of organoids according to claim 1, characterized in that: The execution module comprises two layers of magnetic tweezers platforms and magnetic beads that are mirror-imaged to each other, each layer of the magnetic tweezers platform comprises four magnetic pole pieces (8), the four magnetic pole pieces (8) are evenly arranged in a circle, and the magnetic field generated by the eight magnetic pole pieces (8) is used to drive the movement of the magnetic beads.

3. A magnetic control system for sensing the mechanical properties of organoids according to claim 2, characterized in that: Each layer of the magnetic tweezers platform further comprises: a magnetic yoke (1) and a magnetic pole piece fixing plate (2); the magnetic yoke (1) is connected to the magnetic pole piece fixing plate (2) via a coil core (3); and each of the four magnetic pole pieces (8) is fixed to the magnetic pole piece fixing plate (2) via a magnetic pole piece fixer (10).

4. A magnetic control system for sensing the mechanical properties of organoids according to claim 3, characterized in that: The execution module also includes a support structure, which includes: a vertical fine-tuning screw (4) of the magnetic tweezers platform, a horizontal fine-tuning screw (5) of the magnetic tweezers platform, an upper base (6) and a base (12); The two layers of magnetic tweezers platforms are fixed to an upper base (6) and a base (12) respectively through a fixer (7); the vertical fine-tuning screw (4) and the horizontal fine-tuning screw (5) of the magnetic tweezers platform are located on the upper base (6) and are used to adjust the position of the magnetic tweezers platform on the upper base (6); the upper base (6) is fixed to the base (12) through a platform connection column (11).

5. A magnetic control system for sensing the mechanical properties of organoids according to claim 1, 2, 3 or 4, characterized in that: The visual feedback module realizes tracking and positioning of the magnetic beads through the following steps: Adjust the microscope camera to focus on the magnetic beads and select the magnetic beads in the picture, and obtain the clarity reference value of the selected picture; The microscope camera is used to sample the current magnetic beads and obtain a target image containing the magnetic beads; Using the CSRT algorithm to track the magnetic beads and obtain the XY axis coordinates of the magnetic beads in the target image; Binarizing the target image, and then using the Laplace gradient method to calculate the image clarity under current sampling; Determine whether the clarity exceeds 90% of the clarity reference value. If so, use the Z-axis coordinate of the focal plane of the current microscope camera lens as the Z-axis coordinate of the magnetic bead. Otherwise, determine whether the clarity is higher than the image clarity at the last sampling. If so, move the focus point in the direction of the current microscope camera movement with a fixed step length, and then re-track the position coordinates of the magnetic bead. Otherwise, move the focus point in the opposite direction of the current microscope camera movement with a fixed step length, and then re-track the position coordinates of the magnetic bead. The plane where the XY axes are located is the plane where the target image is located, and the Z axis is perpendicular to the plane where the XY axes are located.

6. A magnetic control system for sensing the mechanical properties of organoids according to claim 1, 2, 3 or 4, characterized in that: The electric control module includes: 8 constant voltage switch power supplies, 1 amplifier circuit power supply, 8 constant current source modules and a push-pull amplifier circuit; The PWM signal output end of the controller is connected to the PWM signal input end of the push-pull amplifier circuit. The amplifier circuit power supply is used to excite the push-pull amplifier circuit to amplify the input PWM signal into a PWM signal with the same frequency and duty cycle. The PWM signal output end of the push-pull amplifier circuit is respectively connected to the control ends of 8 constant current source modules, and the 8 constant voltage switching power supplies respectively power the 8 constant current source modules.

7. A magnetic control system for sensing the mechanical properties of organoids according to claim 1, 2, 3 or 4, characterized in that: The controller controls the desired control current of the electric control module according to the driving target through the following steps: In the precise force application mode, the magnetic field strength-current coefficient matrix of the execution module is calculated according to the actual position r of the magnetic bead. and the magnetic field intensity gradient-current coefficient matrix According to the magnetic field intensity-current coefficient matrix and the magnetic field intensity gradient-current coefficient matrix Calculate the actual magnetic field force F; compare the actual magnetic field force F under the current with the expected magnetic field force F d The goal is to minimize the relative error of , and determine whether the actual magnetic field force F under the current current meets the goal. If so, the current current is the desired control current. Otherwise, the current vector I is optimized using the differential evolution algorithm, and then the actual magnetic field force F is recalculated. In motion control mode, the actual position r of the magnetic bead is compared with the expected position r. d Construct an objective function to obtain the desired control current; The precise force application mode is to control the magnetic beads to perform a short-distance impact motion, and the motion control mode is to control the magnetic beads to move a long distance.

8. A magnetic control system for sensing mechanical properties of organoids according to claim 7, characterized in that: The magnetic field strength-current coefficient matrix And the magnetic field intensity-current coefficient matrix for gradient They are: Where i = 1, 2, ..., 8, μ0 is the vacuum permeability, k q is the proportionality coefficient, r p =[r p,1 ,r p,2 ,...,r p,8 ],r p,i is the position vector of the i-th magnetic pole tip, I 3×3 is a 3rd order unit matrix, 1 3×3 is a 3×3 matrix with all elements being 1, Represents a tensor product.

9. A magnetic control system for sensing mechanical properties of organoids according to claim 8, characterized in that: The magnetic field intensity-current coefficient matrix and the magnetic field intensity gradient-current coefficient matrix Calculate the actual magnetic field force F, including: Among them, k m is the proportional coefficient of the magnetization of the magnetic bead, and I is the current vector formed by the currents of the coils connected to the magnetic poles.

10. The magnetic control system for sensing the mechanical properties of organoids according to claim 7, characterized in that: According to the actual position r of the magnetic bead and the expected position r d Construct the objective function J(k) to obtain the desired control current, including: Where, e(k) = r(k) - r d (k) is the position tracking error at time k, e(k+n|k) and u(k+n|k) represent the tracking error and expected control current at time k+n predicted at time k, respectively, N is the maximum number of prediction steps, Q and W are both positive definite matrices given by the user, which are used to weight the tracking error and current control amount, respectively.

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