Micro-fluidic chip system for simulating cartilage mechanics loading environment

Abstract

The invention discloses a micro-fluidic chip system for simulating a cartilage mechanical loading environment, and belongs to the technical field of biological micro-fluidic chips. A micro-fluidic chip and a peripheral system are designed according to a biomechanical principle and a micro-fluidic chip technology, and a real cartilage microstructure and a mechanical environment can be simulated. The micro-fluidic chip simulates a real cartilage structure and is used for providing internal synovial fluid pressure. The peripheral system provides a controllable external mechanical environment, internal synovial fluid pressure and external three-dimensional mechanical loading of the chip are controlled through PID feedback, a platform is provided for researching a synergistic effect mechanism of the internal synovial fluid pressure and the external three-dimensional mechanical loading, and the peripheral system can also observe diffusion movement of internal nano-particles in the mechanical environment in real time. The system provides an experimental platform for researching the influence and mechanism of mechanical stimulation on OA cartilage cell functions, avoids the defects of ethical problems and individual differences in previous animal experiments, is simpler and more convenient to operate, lower in cost and shorter in experimental period, and provides a scientific basis for researching the influence of mechanical loading on cartilage repair.

Description

Technical Field

[0001] The present invention belongs to the technical field of cell biomechanics experimental devices. It is an experimental device that combines biomechanical principles with microfluidic chip technology to simulate the real cartilage microstructure and mechanical environment. Specifically, it is a microfluidic chip system for simulating the mechanical loading environment of cartilage. Background Art

[0002] Osteoarthritis (OA) is a common degenerative joint disease, known as the "immortal cancer". Data show that the incidence is becoming younger and younger. Early diagnosis of OA is difficult to achieve, and articular cartilage damage is often present when patients are diagnosed. Because articular cartilage lacks blood vessels, nerves and lymphatic tissue, and contains a small number of cells, cartilage damage often cannot repair itself and gradually induces degenerative changes, leading to irreversible damage or even necrosis. In view of this, cartilage damage repair is crucial for OA treatment.

[0003] Increased oxidative stress and complex inflammatory environment are important factors in the development of OA. Excessive secretion of reactive oxygen species in OA cartilage can cause oxidative damage, trigger an inflammatory signal cascade, and aggravate cartilage damage. Direct injection of steroid drugs into the joint cavity can effectively relieve inflammatory response, inhibit cartilage matrix degradation, and promote cartilage repair, but there are problems such as too fast clearance, systemic toxicity, and frequent administration. Nanotechnology has shown great potential in improving drug treatment effects and reducing adverse reactions. However, in practical applications, nanoparticles will only work when they are transported to the vicinity of chondrocytes, so their transport in cartilage is particularly important. On the one hand, articular cartilage is mainly composed of low-density chondrocytes and their secreted extracellular matrix (ECM). ECM is composed of collagen and proteoglycans, presenting a dense collagen fiber network. This non-uniform dense network structure will limit the diffusion of nanoparticles. In addition, chondrocytes are sparsely distributed, and the transport of nanoparticles to chondrocytes actually presents long-distance confined transmission characteristics. On the other hand, the mechanical loading at the joint caused by normal human activities will drive the flow of synovial fluid in the cartilage. At the same time, chondrocytes sense mechanical stimuli such as compression, stretching, and shear, thereby affecting the transport of nanoparticles.

[0004] In recent years, the anti-inflammatory, anti-oxidative and cell proliferation and differentiation effects of nanoparticles in promoting cartilage repair and related biological mechanisms have been systematically understood, but the analysis of these effects and mechanisms is mainly based on different types of animal OA model experiments. The daily activities of animals always impose dynamic loads on articular cartilage, and the individual differences are significant. At the same time, dynamic loads in animal experiments may cause mechanobiological effects, but the relevant mechanisms are still unclear. Compared with animal models, in vitro models can effectively eliminate individual differences, facilitate the control of experimental conditions, are easy to operate, low-cost, have a short experimental cycle and avoid ethical disputes. They have significant advantages in quantitatively studying the effects of mechanical loading on chondrocyte function. In recent years, microfluidic chips have become an ideal platform for in vitro simulation of various biological tissues, organs and cell microenvironments due to their miniaturized structure, refined fluid manipulation, easy integration, easy optical detection, and good biological adaptability. In view of this, it is urgent to develop a microfluidic chip system for simulating the mechanical loading environment of cartilage. Summary of the invention

[0005] The design purpose of the present invention is to provide a microfluidic chip for three-dimensional culture of chondrocytes and simulation of mechanical loading, which can be used to reproduce the real cartilage stress deformation and synovial fluid flow. The present invention cleverly combines the principles of biomechanics with microfluidic chip technology, connects the control system, mechanical loading device, and microfluidic chip, and constructs a microfluidic three-dimensional culture model and peripheral system. The real-time and precise control of mechanical loading is achieved through the PID control system, and mechanical stimuli such as compression, stretching, and shearing are applied to the chondrocyte culture area. At the same time, the microscopic flow of synovial fluid in the cartilage tissue is driven to simulate the real stress conditions and dynamic hydraulic environment of chondrocytes, which is used to analyze and study the influence of mechanical loading on the function of OA chondrocytes.

[0006] The technical solution of the present invention is as follows:

[0007] A microfluidic chip system for simulating a cartilage mechanical loading environment, comprising a microfluidic chip and a peripheral system;

[0008] The microfluidic chip comprises a lower layer PDMS1-1 and an upper layer PDMS1-2; the upper layer PDMS1-2 is adhered to the upper surface of the lower layer PDMS1-1; the upper layer PDMS1-2 is internally etched with vertically arranged inlet holes a1-3, inlet holes b1-5, inlet holes c1-7, outlet holes a1-4, outlet holes b1-6 and outlet holes c1-8, and a microfluidic channel 1-9 arranged horizontally in the middle, one end of the microfluidic channel 1-9 is connected to the inlet holes a1-3, inlet holes b1-5 and inlet holes c1-7, and the other end is connected to the outlet holes a1-4, outlet holes b1-6 and outlet holes c1-8, the inlet holes a1-3 correspond to the outlet holes a1-4, the inlet holes b1-5 correspond to the outlet holes b1-6, and the inlet holes c1-7 correspond to the outlet holes c1-8.

[0009] The microfluidic channel 1-9 is provided with a row of microcolumn arrays 2-3, dividing the internal space of the microfluidic channel 1-9 into two parts, namely channel a2-1 and channel b2-2; the two ends of channel a2-1 are respectively connected to the inlet hole a1-3, the inlet hole b1-5 and the outlet hole a1-4, the outlet hole b1-6, and the two ends of channel b2-2 are respectively connected to the inlet hole c1-7 and the outlet hole c1-8; the inlet hole b1-5 is located between the inlet hole a1-3 and the inlet hole c1-7, and the The outlet hole b1-6 is located between the outlet hole a1-4 and the outlet hole c1-8, and the edges of the connection between the inlet hole b1-5 and the outlet hole b1-6 and the channel a2-1 are flush with the microcolumn array 2-3; the inlet hole a1-3, the inlet hole b1-5, the inlet hole c1-7, the outlet hole a1-4, the outlet hole b1-6 and the outlet hole c1-8 all pass through the entire upper layer PDMS1-2, and the external catheter is inserted into the hole from the opening on the upper surface of the upper layer PDMS1-2 to input or output liquid.

[0010] The inlet holes a1-3 and the outlet holes a1-4 respectively input and output synovial fluid, and the inlet holes b1-5 and the outlet holes b1-6 respectively input and output uncross-linked hydrogel solutions containing nanoparticles and chondrocytes; at the same time, the synovial fluid and the hydrogel solution are respectively input at the same flow rate into the inlet holes a1-3 and the inlet holes b1-5. Due to the effect of surface tension, the synovial fluid and the hydrogel solution are automatically divided into two parallel immiscible liquid flows in the microfluidic channel a2-1. When the solution just flows out from the outlet holes a1-4 and the outlet holes b1-6, the input is stopped, and the two liquids exist in parallel in the microfluidic channel a2-1. Then, the hydrogel solution is cured and cross-linked, so that the hydrogel solution is cured in the channel a2-1. In subsequent simulations, the synovial fluid is continuously injected from the inlet hole a1-3, so that the synovial fluid flows in the space of the channel a2-1 after the cured hydrogel solution is removed.

[0011] The inlet hole c1-7 and the outlet hole c1-8 respectively input and output the chondrocyte culture solution, and the micro-column array 2-3 guides the chondrocyte culture solution to flow along the channel b2-2, while ensuring that it does not flow into the channel a2-1, while providing nutrients for the cells.

[0012] The peripheral system is used to generate mechanical stimuli such as compression, tension, shearing, etc. applied to the chondrocyte culture area and observe the confined movement of nanoparticles therein, including an external three-dimensional mechanical loading device, an internal hydraulic measurement and control device and a particle tracking measurement device; wherein, the three-dimensional mechanical loading device includes a PID computer 3-1, a three-dimensional bidirectional stepping motor 3-2, a three-dimensional mechanical loading fixture 3-3 and a flexible deformable pressure sensor 3-4; the internal hydraulic measurement and control device includes a PID computer 3-1, a flow rate pump 3-5 and a flow sensor 3-6; the particle tracking measurement device includes an inverted fluorescence microscope 3-7, an EMCCD camera 3-8 and a computer 3-9.

[0013] The three-dimensional bidirectional stepper motor 3-2 is connected to the three loading rods of the three-dimensional mechanical loading fixture 3-3, and the three loading rods apply mechanical loading to the microfluidic chip from the x, y, and z directions respectively; the initial value and the initial waveform are input into the PID computer 3-1, and the PID computer 3-1 outputs different mechanical signals to the three-dimensional bidirectional stepper motor 3-2 after calculation, and the three-dimensional bidirectional stepper motor 3-2 controls the loading rods to realize the mechanical loading of the microfluidic chip by the three-dimensional mechanical loading fixture 3-3 (the x and y axial loading rods of the three-dimensional mechanical loading fixture 3-3 can realize precise and controllable extension and contraction, and the size of the z-axial loading rod is basically consistent with the size of the cartilage hydrogel part, and the cartilage hydrogel part of the chip can be shear-loaded); a flexible deformable pressure sensor 3-4 is attached to the upper surface of the microfluidic channel a2-1 of the microfluidic chip, and the flexible deformable pressure sensor 3-4 can detect the force exerted on the cartilage-like structure part (i.e., the microfluidic channel a2-1) in real time, and feed back the data to the PID computer. Through this set of feedback processes, the microfluidic chip can be realized. The hydrogel cartilage part in the chip is compressed, stretched and sheared to achieve different mechanical stimulations; the flow pump 3-5 is connected to the inlet hole a1-3, the flow sensor 3-6 is connected to the outlet hole a1-4, the initial flow rate of the flow pump 3-5 and the initial value of the synovial fluid flow rate control by the PID computer 3-1 are set in the PID computer 3-1, the flow sensor 3-6 measures the flow rate of the synovial fluid in the channel a2-1 of the microfluidic channel 1-9 and feeds it back to the PID computer 3-1, and after calculation A new signal is sent to the flow pump 3-5 to measure and control the flow rate; the light source of the inverted fluorescence microscope 3-7 is placed directly above the microfluidic chip, and the inverted fluorescence microscope 3-7 observes the confined transport of nanoparticles in the cartilage hydrogel. The inverted fluorescence microscope 3-7 is connected to the EMCCD camera 3-8, and the inverted fluorescence microscope 3-7 transmits the observation results to the EMCCD camera 3-8, and the EMCCD camera 3-8 transmits the taken photos to the computer 3-9, so as to realize the observation of nanoparticles and collect images.

[0014] Furthermore, the channel a2-1 and channel b2-2 are both straight channels, the total length of the straight channel is L, the entire channel depth is H, the width of the channel a2-1 is W1, and the width of the channel b2-2 is W2; the channel a2-1 is a cubic flat structure, and the length L, width W1, and height H of the channel a2-1 meet the following conditions: H<W1 and H<L. (The width W1, W2 and length L are in the millimeter order, and the height H is in the micrometer order. The synovial fluid in the microfluidic channel can exhibit laminar flow characteristics.) Since the height of the channel a2-1 is much smaller than the width and length, and at the same time, the Reynolds number of the flow in the chamber is very low, satisfying the quasi-steady flow assumption, the shear stress τ formula in the channel a2-1 can be simplified to:

[0015]

[0016] Wherein, μ is the fluid viscosity, W and H are the width and height of channel a2-1. Therefore, the shear stress τ loaded on the cartilage hydrogel is proportional to the fluid flow Q(t) flowing through channel a2-1, and the shear stress can be quantitatively controlled by controlling the flow Q(t).

[0017] Furthermore, the PID computer 3-1 uses a PID algorithm to achieve precise real-time control of mechanical loading. The formula used to adjust the relationship between PID parameters and output is:

[0018]

[0019] Among them, e(t) is the deviation, that is, the difference between the set value and the actual output value, u(t) is the output voltage, dt is the time change, K p is the proportionality coefficient, K i is the integration coefficient, K d It is the differential coefficient. Adjusting these three parameters makes PID control more accurate and rapid.

[0020] Beneficial effects of the present invention: The present invention provides a set of microfluidic chips for cartilage, which can not only perform mechanical loading, but also realize the measurement and control of internal joint synovial pressure, and at the same time can observe the confined transport of nanoparticles therein; the device of the present invention combines microfluidic technology with biomechanics, reproduces the real mechanical environment of cartilage in the body, and quantitatively measures and controls external mechanical loading, such as tensile force, compressive force and shear force, etc., as well as the internal liquid pressure, so as to better perform variable regulation and quantitative analysis, study the synergistic effect of internal and external forces, and the confined transport of internal nanoparticles; the device of the present invention avoids the ethical issues and individual differences in previous animal experiments, is simpler to operate, has lower cost, and a shorter experimental cycle, and realizes quantitative research on the impact of mechanical loading on chondrocytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of the microfluidic chip used for simulating cartilage model in the present invention.

[0022] Figure 2 It is a top view of the microfluidic channel design.

[0023] Figure 3 Schematic diagram of the simulation device used to study the mechanical loading environment of cartilage.

[0024] In the figure: 1-1 lower layer PDMS; 1-2 upper layer PDMS; 1-3 inlet hole a; 1-4 outlet hole a; 1-5 inlet hole b; 1-6 outlet hole b; 1-7 inlet hole c; 1-8 outlet hole c; 1-9 microfluidic channel; 2-1 channel a; 2-2 channel b; 2-3 microcolumn array; 3-1 PID computer; 3-2 three-dimensional bidirectional stepper motor; 3-3 three-dimensional mechanical loading fixture; 3-4 flexible deformable pressure sensor; 3-5 flow rate pump; 3-6 flow sensor; 3-7 inverted fluorescence microscope; 3-8 EMCCD camera; 3-9 computer. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be further described below in conjunction with specific embodiments and drawings.

[0026] like Figure 1-3 As shown, a microfluidic device for simulating cartilage mechanical loading environment of the present invention is shown, and the microfluidic device for simulating cartilage mechanical loading comprises a lower layer PDMS1-1 and an upper layer PDMS1-2, and the upper layer PDMS1-2 is bonded to the lower layer PDMS1-1. PDMS is made of prepolymer A glue and crosslinking agent B glue. Before chip manufacturing, the ratio of prepolymer A glue and crosslinking agent B glue is pre-tested to select the most suitable ratio for mechanical loading, so as to ensure appropriate elastic deformation under mechanical loading. The upper layer PDMS 1-2 is etched with vertically arranged inlet holes a1-3, inlet holes b1-5, inlet holes b1-7, outlet holes a1-4, outlet holes b1-6 and outlet holes c1-8, as well as a microfluidic channel 1-9 arranged horizontally in the middle. The microfluidic channel 1-9 is connected to inlet holes a1-3, inlet holes b1-5 and inlet holes c1-7 on the left, and to outlet holes a1-4, outlet holes b1-6 and outlet holes c1-8 on the right, and each inlet hole corresponds to an outlet hole.

[0027] like Figure 2 As shown, the microfluidic channel 1-9 in the present invention includes a channel a2-1, a channel b2-2 and a row of microcolumn arrays 2-3 in the middle, the two ends of the channel a2-1 are respectively connected to the inlet hole a1-3, the inlet hole b1-5 and the outlet hole a1-4, the outlet hole b1-6, and the two ends of the channel b2-2 are respectively connected to the inlet hole c1-7 and the outlet hole c1-8.

[0028] like Figure 3As shown, it is a diagram of a microfluidic chip system for simulating the mechanical loading environment of cartilage according to the present invention, and the microfluidic chip system includes a microfluidic chip, a peripheral system (external three-dimensional mechanical loading device, internal hydraulic measurement and control device, and particle tracking measurement device). The peripheral system is used to generate mechanical stimuli such as compression, tension, and shear applied to the chondrocyte culture area and observe the confined motion of the nanoparticles therein. Among them, the three-dimensional mechanical loading device includes a PID computer 3-1, a three-dimensional bidirectional stepping motor 3-2, a three-dimensional mechanical loading fixture 3-3, and a flexible deformable pressure sensor 3-4; the internal hydraulic measurement and control device includes a PID computer 3-1, a flow rate pump 3-5, and a flow sensor 3-6; the particle tracking measurement device includes an inverted fluorescence microscope 3-7, an EMCCD camera 3-8, and a computer 3-9.

[0029] The specific design, processing and use steps of the microfluidic device for simulating mechanical loading of a cartilage microfluidic chip of the present invention are as follows:

[0030] Step 1: Conduct a preliminary experiment on the PDMS material ratio. Both layers of PDMS need to have a suitable elastic modulus. Verify the following ratio: the volume ratios of PDMS prepolymer A glue and cross-linking agent B glue are 10:1, 8:1 and 6:1 respectively. The smaller the ratio of prepolymer A glue to cross-linking agent B glue, the greater the elasticity of PDMS and the easier it is to deform. Select the most suitable ratio for mechanical loading through preliminary experiments to ensure that the chip can have appropriate elastic deformation under mechanical loading.

[0031] Step 2: Design a microfluidic chip. The inlet hole a1-3 and outlet hole a1-4 of the microfluidic chip are both circular holes with a diameter of 2 mm, the inlet hole b1-5 and outlet hole b1-6 are both circular holes with a diameter of 1 mm, and the inlet hole c1-7 and outlet hole c1-8 are both circular holes with a diameter of 3 mm. The above holes are all through holes of the upper layer PDMS; channel a2-1 is 10 mm long and 2 mm wide, and channel b2-1 is 10 mm long and 750 μm wide. All channels and chamber structures on the chip are made of PDMS using standardized micromachining methods and are permanently bonded and sealed with the clean lower layer PDMS to form a transparent PDMS chip with good biocompatibility. The etching height of all microfluidic channels is 150 μm.

[0032] Step 3: Based on the design in step 1, a microfluidic chip is made. The microfluidic chip can be processed using standard soft lithography and laser engraving techniques. In the device structure made of polydimethylsiloxane (PDMS) material, a 150 μm thick polyimide film is cut using a laser engraving machine and attached to a silicon wafer. Place the silicon wafer in a glass dish, pour in the prepared PDMS solution, then let it stand in a vacuum for 20 minutes to remove bubbles, put it in a drying oven, bake it at 80°C for 90 minutes to solidify the PDMS, then take out the glass dish, and after the temperature drops, separate the PMDS from the mold to obtain a PMDS with a microfluidic channel structure, cut off the PDMS with the microfluidic channels used, use a puncher to punch through the channel inlet and outlet, and after cleaning, bond the PDMS to the clean lower layer PDMS through a plasma cleaner, heat it at 120°C for 15-20 minutes to make it more firmly bonded, then insert the catheter into the hole punched on the chip, and evenly apply glue at the junction of the catheter and the hole to prevent leakage. After applying the glue, place the chip in a drying oven and bake it at 80°C for one night. Finally, connect the catheter and the flow pump together. At this point, the preparation of the device is completed.

[0033] Step 4: Place the prepared microfluidic chip in water to evacuate the air bubbles. After all the bubbles in the channel are exhausted, place it in a high-temperature and high-pressure sterilizer for sterilization. The sterilized microfluidic chip is placed in an ultra-clean bench for future use.

[0034] Step 5: Place the sterilized microfluidic chip in step 3 in a glass dish, and use two 1 ml syringes to simultaneously input synovial fluid (synovial fluid is a 2% hyaluronic acid (HA) solution) and uncross-linked hydrogel solution containing chondrocytes and nanoparticles (nanoparticles are polystyrene particles with a particle size of 200 nm, cells are chondrocytes that have been passaged more than four times after thawing, and hydrogel is a solution of azide-modified sodium alginate (ALG-BAT) mixed with collagen (COL)) into the inlet holes a1-3 and a1-5. The two solutions are slowly injected into the microfluidic chip at the same flow rate. In the fluidic channel a2-1, observe whether there is any solution flowing out from the outlet holes a1-4 and b1-6 during input. When liquid just starts to flow out, stop inputting both liquids at the same time. Due to the effect of surface tension, the two liquids will exist in parallel in the front and back of the microfluidic channel a2-1. The hydrogel solution is then cured and cross-linked at 37°C. After curing, synovial fluid is injected into the inlet hole a1-3 and culture fluid is injected into the inlet hole c1-7 again. The cells are then placed in a cell culture incubator and the temperature in the cell culture incubator is maintained at 37°C. The gas in the incubator is 95% air and 5% CO2 and cultured for 48 hours.

[0035] Step 6: Collect the compression, stretching and shearing waveforms of the cartilage during normal human movement as the compression, stretching and shearing waveforms of the target cartilage, calculate the target flow waveform, and input it into the PID computer 3-1 to set the proportional coefficient K in the three-dimensional mechanical loading PID control. p1 , integral coefficient K i1 , differential coefficient K d1 The initial value of the output signal is sent to the high-precision three-dimensional bidirectional stepper motor 3-2. The three-dimensional bidirectional stepper motor 3-2 controls the three loading rods of the three-dimensional mechanical loading fixture 3-3 to achieve compression, tension and shear force on the microfluidic chip. The microfluidic chip feeds back the force to the flexible deformable pressure sensor 3-4. The flexible deformable pressure sensor 3-4 can accurately detect the three-dimensional mechanical size of the microfluidic chip and transmit the mechanical signal back to the PID computer 3-1 in real time. The PID computer 3-1 calculates the initial value and the error signal, and recalculates the input quantity through the PID calculation formula (2) to achieve closed-loop real-time control. If the returned mechanical signal is not appropriate, the proportional coefficient K can be adjusted manually in time. p1 , integral coefficient K i1 , differential coefficient K d1 , in order to reproduce the target mechanical signals quickly, accurately and with high signal-to-noise ratio.

[0036] Step 7: After adjusting each peripheral mechanical load as described in step 5, set the proportional coefficient K in the flow rate PID control of PID computer 3-1 p2 , integral coefficient K i2 , differential coefficient K d2 The initial value of the pressure sensor a1-3 is set, and the initial flow rate of the flow pump 3-5 is set. The flow pump 3-5 delivers synovial fluid of a certain flow rate from the inlet hole a1-3. The flow sensor 3-6 detects the synovial fluid flow rate flowing out of the outlet hole a1-4 and feeds the signal back to the PID computer 3-1. The PID computer 3-1 recalculates and outputs a new value to achieve the effect of closed-loop control of hydraulic pressure, and realizes the detection and control of the synovial fluid flow rate and hydraulic signal under different peripheral mechanical loading conditions. The control program flow is roughly the same as step four. At this point, the coordinated control of peripheral mechanical loading and internal hydraulic control can be achieved, and the parameters can be flexibly adjusted according to specific experimental requirements. For example, after the peripheral mechanical loading is stable, the type and size of the peripheral force are fixed, and only the liquid flow rate is adjusted to achieve the experimental effect of accurate quantitative measurement and control of the mechanical environment of the cartilage.

[0037] Step 8: After adjusting and stabilizing the mechanical environment of the microfluidic chip according to steps 5 and 6, the flow of nanoparticles is observed under transient conditions through an inverted fluorescence microscope 3-7, and the EMCCD camera captures video images at a shooting rate of n frames / second, and the images can be observed and collected on the screen of the computer 3-9.

Claims

1. A microfluidic chip system for simulating the mechanical loading environment of cartilage, characterized in that: The microfluidic chip system for simulating the mechanical loading environment of cartilage comprises a microfluidic chip and a peripheral system; The microfluidic chip comprises a lower PDMS layer (1-1) and an upper PDMS layer (1-2); the upper PDMS layer (1-2) is adhered to the upper surface of the lower PDMS layer (1-1); the upper PDMS layer (1-2) is internally etched with vertically arranged inlet holes a (1-3), inlet holes b (1-5), inlet holes c (1-7), outlet holes a (1-4), outlet holes b (1-6) and outlet holes c (1-8), and a microfluidic channel arranged horizontally in the middle. Channel (1-9), one end of the microfluidic channel (1-9) is connected to inlet hole a (1-3), inlet hole b (1-5), and inlet hole c (1-7), and the other end is connected to outlet hole a (1-4), outlet hole b (1-6), and outlet hole c (1-8), inlet hole a (1-3) corresponds to outlet hole a (1-4), inlet hole b (1-5) corresponds to outlet hole b (1-6), and inlet hole c (1-7) corresponds to outlet hole c (1-8); The microfluidic channel (1-9) is provided with a row of microcolumn arrays (2-3), dividing the internal space of the microfluidic channel (1-9) into two parts, namely channel a (2-1) and channel b (2-2); the two ends of channel a (2-1) are respectively connected to the inlet hole a (1-3), the inlet hole b (1-5) and the outlet hole a (1-4), the outlet hole b (1-6); the two ends of channel b (2-2) are respectively connected to the inlet hole c (1-7) and the outlet hole c (1-8); the inlet hole b (1-5) is located between the inlet hole a (1-3) and the inlet hole c (1-7); The outlet hole b (1-6) is located between the outlet hole a (1-4) and the outlet hole c (1-8), and the edges of the connection between the inlet hole b (1-5) and the outlet hole b (1-6) and the channel a (2-1) are flush with the micro-pillar array (2-3); the inlet hole a (1-3), the inlet hole b (1-5), the inlet hole c (1-7), the outlet hole a (1-4), the outlet hole b (1-6) and the outlet hole c (1-8) all penetrate the entire upper layer PDMS (1-2), and an external catheter is inserted into the hole from the opening on the upper surface of the upper layer PDMS (1-2) to input or output liquid; The inlet holes a (1-3) and the outlet holes a (1-4) are used to input and output synovial fluid, respectively; the inlet holes b (1-5) and the outlet holes b (1-6) are used to input and output a hydrogel solution containing uncrosslinked nanoparticles and chondrocytes, respectively; at the same time, the synovial fluid and the hydrogel solution are respectively input at the same flow rate into the inlet holes a (1-3) and the inlet holes b (1-5), and due to the effect of surface tension, the synovial fluid and the hydrogel solution are automatically in the microfluidic channel a (2-1). It is divided into two parallel immiscible liquid flows, and when the solution just flows out from the outlet hole a (1-4) and the outlet hole b (1-6), the input is stopped, and the two liquids exist in parallel in the microfluidic channel a (2-1). Then, the hydrogel solution is solidified and cross-linked, so that the hydrogel solution is solidified in the channel a (2-1). In the subsequent simulation, the synovial fluid is continuously injected from the inlet hole a (1-3), so that the synovial fluid flows in the space in the channel a (2-1) where the solidified hydrogel solution is removed; The inlet hole c (1-7) and the outlet hole c (1-8) are used to input and output the chondrocyte culture solution respectively, and the micro-column array (2-3) guides the chondrocyte culture solution to flow along the channel b (2-2), while ensuring that the chondrocyte culture solution does not flow into the channel a (2-1), and provides nutrients for the cells; The peripheral system is used to generate mechanical stimulation such as compression, stretching, shearing, etc. applied to the chondrocyte culture area and observe the confined movement of the nanoparticles therein, and includes an external three-dimensional mechanical loading device, an internal hydraulic measurement and control device, and a particle tracking measurement device; wherein the three-dimensional mechanical loading device includes a PID computer (3-1), a three-dimensional bidirectional stepping motor (3-2), a three-dimensional mechanical loading fixture (3-3), and a flexible deformable pressure sensor (3-4); the internal hydraulic measurement and control device includes a PID computer (3-1), a flow rate pump (3-5), and a flow sensor (3-6); the particle tracking measurement device includes an inverted fluorescence microscope (3-7), an EMCCD camera (3-8), and a computer (3-9); The three-dimensional bidirectional stepper motor (3-2) is connected to three loading rods of a three-dimensional mechanical loading fixture (3-3), and the three loading rods apply mechanical loading to the microfluidic chip from three directions of x, y and z respectively; the initial value and the initial waveform are input into a PID computer (3-1), and the PID computer (3-1) outputs different mechanical signals to the three-dimensional bidirectional stepper motor (3-2) after calculation, and the three-dimensional bidirectional stepper motor (3-2) controls the loading rods to realize the mechanical loading of the microfluidic chip by the three-dimensional mechanical loading fixture (3-3); a flexible deformable pressure sensor (3-4) is attached to the upper surface of the microfluidic channel a (2-1) of the microfluidic chip, and the flexible deformable pressure sensor (3-4) can detect the force exerted on the cartilage-mimicking structure part, i.e., the microfluidic channel a (2-1), in real time, and feed back the data to the PID computer, and through the feedback process, the compression, stretching and shearing of the hydrogel cartilage part in the chip are realized, so as to realize different mechanical stimulations; the flow rate pump (3-5) is connected to the inlet hole a (1- 3), the flow sensor (3-6) is connected to the outlet hole a (1-4), the initial flow rate of the flow pump (3-5) and the initial value of the PID computer (3-1) for controlling the synovial fluid flow rate are set in the PID computer (3-1), the flow sensor (3-6) measures the flow rate of the synovial fluid in the channel a (2-1) of the microfluidic channel (1-9) and feeds it back to the PID computer (3-1), and after calculation, a new signal is sent to the flow pump (3-5), so as to achieve the measurement and control of the flow rate Control: The light source of the inverted fluorescence microscope (3-7) is placed directly above the microfluidic chip, the inverted fluorescence microscope (3-7) observes the confined transport of nanoparticles in the cartilage hydrogel, the inverted fluorescence microscope (3-7) is connected to the EMCCD camera (3-8), the inverted fluorescence microscope (3-7) transmits the observation results to the EMCCD camera (3-8), and the EMCCD camera (3-8) transmits the taken photos to the computer (3-9), thereby realizing the observation of nanoparticles and collecting images.

2. A microfluidic chip system for simulating cartilage mechanical loading environment according to claim 1, characterized in that: The synovial fluid is hyaluronic acid with a mass fraction of 2%; the uncrosslinked hydrogel solution containing nanoparticles and chondrocytes, the nanoparticles are polystyrene particles with a particle size of 200nm, the cells are chondrocytes that have been passaged more than four times after thawing, and the hydrogel is a solution of azide-modified sodium alginate mixed with collagen.

3. A microfluidic chip system for simulating cartilage mechanical loading environment according to claim 1 or 2, characterized in that: The channel a (2-1) and channel b (2-2) are both straight channels, the total length of the straight channel is L, the depth of the entire channel is H, the width of the channel a (2-1) is W1, and the width of the channel b (2-2) is W2; the channel a (2-1) is a cubic flat structure, and the length L, width W1, and height H of the channel a (2-1) meet the following conditions: H<W1 and H<L; wherein the width W1, W2 and length L are in the millimeter order, and the height H is in the micrometer order.

4. A microfluidic chip system for simulating cartilage mechanical loading environment according to claim 3, characterized in that: The shear stress τ formula in channel a (2-1) is simplified to: Wherein, μ is the fluid viscosity, W and H are the width and height of channel a(2-1); the magnitude of shear stress can be quantitatively controlled by controlling the flow rate Q(t).

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