Microfluidic device for endothelialization evaluation of tissue engineering valve
By combining biomechanics and microfluidic chip technology, a microfluidic device was designed to accurately simulate the shear force of aortic valve endothelial cells, solving the problems of complexity and high cost in existing endothelialization assessment, and realizing efficient endothelial cell assessment and research.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2025-04-18
- Publication Date
- 2026-05-19
AI Technical Summary
Existing in vitro assessment devices for tissue-engineered valve endothelialization cannot accurately simulate complex real aortic hemodynamic signals, cannot replicate the accurate shear force distribution on tissue-engineered valve endothelial cells, and are complex to operate, costly, and subject to ethical controversies.
Combining biomechanical principles with microfluidic chip technology, a microfluidic device was designed to accurately simulate the shear force of endothelial cells on the aortic valve through a PID control system and integrate a signal acquisition and processing system to achieve precise evaluation and research of endothelial cells.
It enables efficient and low-cost in vitro evaluation of tissue-engineered valve endothelialization, accurately simulates the real hemodynamic environment, provides an efficient experimental platform, and supports valve performance evaluation and optimization.
Smart Images
Figure CN224258649U_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of cell mechanobiology experimental devices for health and rehabilitation engineering, and relates to a microfluidic device for evaluating the endothelialization of tissue-engineered valves. Background Technology
[0002] Heart valve disease is a common condition that can generally cause any of the four types of heart valves to malfunction, primarily due to stenosis or regurgitation, and can only be treated surgically or via catheter intervention. Clearly, any heart valve disease alters its hemodynamic properties, and the goal of treatment is to restore blood flow to a healthy state. Currently, two types of surgical artificial valves are available: mechanical valves and bioprosthetic valves. Mechanical valves are very durable and can be used in artificial hearts; however, their main drawback is the formation of blood clots due to non-physiological hemodynamics. On the other hand, bioprosthetic valves mimic the function of natural valves, thus eliminating the need for long-term anticoagulation, but their limited durability compared to mechanical valves is currently difficult to overcome.
[0003] Tissue-engineered heart valves (TEHVs) are a novel type of heart valve replacement developed in recent years, representing the future direction of valve development. Utilizing advanced biotechnology and materials science principles, they culture the patient's own cells or tissues on a specific scaffold to form a bioactive valve. The structure of a tissue-engineered valve is essentially the same as a normal heart valve, offering better hemodynamic characteristics compared to mechanical valves. Tissue-engineered valves are bioactive, growing and developing alongside the body, making them less prone to degeneration and decay, and highly durable, effectively avoiding the need for secondary surgery. This characteristic is a significant advantage over bioprosthetic valves (such as porcine aortic valves and bovine pericardial bioprosthetic valves), as bioprosthetic valves have a relatively short lifespan, generally between 10 and 20 years, and may require secondary surgery due to degenerative changes. Furthermore, the internal and surface cellular components of tissue-engineered valves are identical to those of normal valves and are autologous cells, therefore they are non-immunogenic. Post-implantation anticoagulation therapy is unnecessary, avoiding the bleeding risks and other complications associated with anticoagulation treatment.
[0004] Endothelialization refers to the process of seeding a layer of endothelial cells onto the inner surface of a valve scaffold to provide an anticoagulant surface and maintain normal valve function. Endothelial cells have functions such as antithrombotic activity, prevention of platelet adhesion, prevention of leukocyte adhesion, and inhibition of smooth muscle cell proliferation. Lack of endothelial coverage or loss of endothelial cell function are the main causes of aging and calcification in tissue-engineered valves, and represent a key challenge in the clinical translation of tissue-engineered valves. However, endothelialization of tissue-engineered valves is a complex process involving multiple factors, including endothelial cell proliferation, dynamic blood flow, regulation of biochemical factor concentrations, and the influence of valve material properties. Furthermore, clinical and in vivo experiments face bottlenecks such as complex operation, high cost, long cycles, and ethical controversies. Therefore, there is an urgent need to develop a highly efficient and low-cost in vitro evaluation device for endothelialization of tissue-engineered valves.
[0005] Currently, there are few existing in vitro evaluation devices for tissue-engineered valves, and they are all based on macroscopic in vitro flow culture chambers to fix the valve leaflets within the reaction chamber and ensure that endothelial cells adhere firmly to the surface of the tissue-engineered valve without detachment. Examples include a pulsatile flow culture device for cardiac tissue-engineered valves (patent number: CN200320129429.8) and a flat-plate flow reaction chamber for dynamic culture of tissue-engineered valves (patent number: CN202120468435.4). However, these devices can only realize simple hemodynamic signals and cannot realize complex and realistic aortic hemodynamic signals, making it difficult to replicate the accurate spatiotemporal distribution of shear forces on the endothelial cells of tissue-engineered valves. The development of microfluidic chip technology provides an effective experimental platform for accurately simulating the extracellular hemodynamic microenvironment and observing and detecting the interaction between the cellular microenvironment and cells. At the same time, microfluidic chips have advantages such as requiring small sample volumes, easy integration, easy optical detection, and good biocompatibility, making them an ideal experimental platform for reproducing the arterial hemodynamic microenvironment in the in vivo circulatory system. However, an in vitro evaluation device for tissue-engineered valves based on microfluidic chips has not yet been developed. Utility Model Content
[0006] The purpose of this invention is to provide a microfluidic chip for endothelialization and simulated mechanical loading of tissue-engineered valves. This chip can reproduce the distribution of shear forces in real aortic valve endothelial cells, enabling precise evaluation of tissue-engineered valve endothelialization. This invention innovatively introduces microfluidic chip technology to accurately simulate the biological effects of shear forces on endothelial cells in human aortic valves, predicting the endothelialization performance of tissue-engineered valve endothelial cells in human aortic valves, thereby providing strong technical support for valve performance evaluation and optimization.
[0007] This invention ingeniously combines biomechanical principles with microfluidic chip technology, connecting a control system, a mechanical loading device, and a microfluidic chip to construct a microfluidic endothelial cell culture chamber and peripheral system. Through a PID control system, it achieves real-time and precise control of blood flow in the aortic valve, generating shear stress applied to the culture area of tissue-engineered valve endothelial cells to simulate the actual stress conditions of tissue-engineered valve endothelial cells, and is used to analyze and study the influence of mechanical loading on tissue-engineered valve endothelial cells.
[0008] The technical solution of this utility model is as follows:
[0009] A microfluidic device for evaluating endothelialization of tissue-engineered valves includes a microfluidic chip, peripheral devices, and a signal acquisition and processing system and a feedback system.
[0010] The microfluidic chip includes a microfluidic chip channel, a microfluidic chip inlet, and a microfluidic chip outlet. The microfluidic chip channel is a groove structure etched inside the microfluidic chip, serving as a cell culture chamber. Both the microfluidic chip inlet and outlet are connected to the cell culture chamber, forming a fluid dynamics loop. A tissue-engineered valve is fixed on the upper surface of the cell culture chamber, and endothelial cells are located on the lower surface of the tissue-engineered valve. The cell culture chamber simulates the wall shear stress signal in the in vivo aortic valve endothelial hemodynamic microenvironment.
[0011] The peripheral devices provide power flow to the microfluidic chip and include a liquid reservoir, an air pump, and a fluid loading device. The fluid loading device is connected to the liquid reservoir via a pipeline, and the air pump pumps the fluid from the fluid loading device into the liquid reservoir. The liquid reservoir is connected to the inlet and outlet of the microfluidic chip via pipelines to form a fluid circulation loop. Fluid is supplied to the cell culture chamber through the inlet of the microfluidic chip and flows out through the outlet of the microfluidic chip.
[0012] The aforementioned signal acquisition, processing, and feedback system is used for the acquisition, processing, and feedback of hemodynamic signals and intracellular biological and chemical signals on the microfluidic chip. It includes a flow sensor, a fluorescence microscope, a CCD, and an industrial control computer. The flow sensor, fluorescence microscope, and CCD are all connected to the industrial control computer. The flow sensor acquires flow signals from the inlet and outlet of the microfluidic chip. The fluorescence microscope and CCD camera are combined to detect dynamic images of the biological response of tissue-engineered valve endothelial cells. The acquired images are sent to the industrial control computer, which processes them to generate control commands, precisely controlling the fluid loading device to generate wall shear stress signals within the cell culture chamber on the microfluidic chip, reflecting the hemodynamic microenvironment of real aortic tissue-engineered valve endothelial cells.
[0013] The beneficial effects of this utility model are:
[0014] This invention facilitates experiments on the interaction between hemodynamic signals and tissue-engineered valve endothelial cells under real extracellular physiological conditions. It accurately and completely replicates the hemodynamic microenvironment of real aortic tissue-engineered valve endothelial cells, with higher integration, fewer consumables, and real-time observation and acquisition of cellular mechanobiological responses. It provides an efficient and powerful experimental platform for studying the quantitative relationship between hemodynamic signals and the mechanobiological mechanisms of tissue-engineered valve endothelial cells.
[0015] This novel device integrates advanced computational fluid dynamics (CFD) simulation technology, microfluidic chips, and biomedical engineering technology, enabling in vitro simulation, precise evaluation, and in-depth analysis of the mechanobiology of tissue-engineered valve endothelial cells, providing scientific basis and technical support for the treatment of valvular diseases. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of a microfluidic chip.
[0017] Figure 2 This is a schematic diagram of a cross-section of a cell culture chamber.
[0018] Figure 3 This is a structural diagram of a microfluidic chip-level in vitro simulated circulatory system.
[0019] In the figure: 1-1 Microfluidic chip inlet hole; 1-2 Microfluidic chip outlet hole; 1-3 Upper PDMS; 1-4 Lower PDMS; 1-5 Tissue-engineered valve; 1-6 Endothelial cells; 1-7 Microfluidic chip channel; 2-1 Air pump; 2-2 Fluid loading device; 2-3 Reservoir; 2-4 Microfluidic chip; 2-5 Microfluidic chip inlet flow sensor; 2-6 Microfluidic chip outlet flow sensor; 2-7 Fluorescence microscope; 2-8 CCD camera; 2-9 Industrial control computer. Detailed Implementation
[0020] The technical solution of this utility model will be further described below with reference to specific embodiments and accompanying drawings.
[0021] A microfluidic device and method for evaluating endothelialization of tissue-engineered valves. The system consists of three basic units: The first basic unit is a microfluidic chip that simulates the wall shear stress signal in the in vivo aortic valve endothelial hemodynamic microenvironment within a cell culture chamber, including the cell culture chamber and the tissue-engineered valve, forming a multi-element hydrodynamic loop. The second basic unit is peripheral equipment providing power flow to the microfluidic chip, including a reservoir, an air pump, and a fluid loading device. The reservoir is connected to the inlet and outlet of the microfluidic chip to form a fluid circulation loop, and the air pump is connected to the reservoir via the fluid loading device. The third basic unit is a system for acquiring, processing, and feeding back hemodynamic signals and intracellular biological and chemical signals on the microfluidic chip, including sensors, a fluorescence microscope, a CCD, and an industrial control computer. Signals are transmitted to the industrial control computer via the sensor or fluorescence microscope and CCD, where they are processed to generate control commands that precisely control the fluid loading device to generate wall shear stress signals within the target aortic tissue-engineered valve endothelial hemodynamic microenvironment on the cell culture chamber of the microfluidic chip.
[0022] The cell culture chamber on the microfluidic chip, such as Figure 2 As shown. A cell culture chamber is formed by separating upper and lower layers of PDMS with flattened cubic channels using a tissue-engineered valve. The lower cell culture chamber is connected to the circulatory pathway. The length of the culture chamber is L. c Width W c and height H c Satisfy: H c < <W c And H c < <L c When the fluid is driven by pressure, the tissue-engineered valve is stretched, and the endothelial cells cultured on the tissue-engineered valve at the top of the lower culture chamber are subjected to wall shear stress τ. w The role of (t). Since the height of the cell culture chamber is much smaller than its width and length, the Reynolds number Re and the Womersley number α within the cell culture chamber satisfy Re << 1 and α << 1, satisfying the quasi-steady assumption. Further assuming that the tissue-engineered valve undergoes small deformation after being stretched, the wall shear stress τ borne by the endothelial cells is... w (t) should satisfy:
[0023]
[0024] In the formula, η is the viscosity of the cell culture medium, and q(t) is the volumetric flow rate through the cell culture chamber. Therefore, the magnitude of the shear stress τ applied to the endothelial cells of the tissue-engineered valve is directly proportional to the flow rate q(t) of the fluid flowing through the channel. The magnitude of the shear stress can be quantitatively controlled by controlling the flow rate q(t).
[0025] Furthermore, the industrial control computer uses a PID algorithm to achieve precise real-time control of mechanical loading. The formula used when adjusting the PID parameters and output relationship is as follows:
[0026]
[0027] In the formula, e(t) is the deviation, i.e., the difference between the set value and the actual output value, u(t) is the output voltage, dt is the time change, and K... P It is the proportionality coefficient, K i It is the integral coefficient, K d These are the derivative coefficients. Adjusting these three parameters makes PID control more precise and faster.
[0028] The fluidic circuit on the microfluidic chip discharges gas into the reservoir via a fluid loading device. Due to the pressure change, an equal amount of liquid is discharged. The liquid enters the chip through the inlet and exits through the outlet, returning to the reservoir for recycling. The design of the fluid dynamics circuit on the microfluidic chip must ensure that the wall shear stress borne by the endothelial cells cultured on the tissue-engineered valve at the top of the cell culture chamber is equal to the wall shear stress τ of the aortic valve endothelial microenvironment. w (t) The waveforms are consistent.
[0029] The fluid loading device uses a programmable air pump manufactured by Elveflow. Based on the LabVIEW platform, a related program is written to generate a target arterial endothelial microenvironment flow rate waveform q(t) in the cell culture chamber of the microfluidic chip. Thus, according to equation (1), the endothelial cells on the tissue-engineered valve at the top of the cell culture chamber bear the wall shear stress τ. w The role of (t).
[0030] The fluid flow rate waveform and shear stress waveform of the target artery endothelial microenvironment can be obtained through computational fluid dynamics (CFD) simulation technology.
[0031] The signal acquisition and processing system and feedback control system mentioned above are as follows: Figure 3 As shown, the signal acquisition and processing system includes an inverted fluorescence microscope, a CCD industrial camera, and a flow sensor, used to monitor and acquire the flow waveform q(t) at the input and output ends of the cell culture chamber in real time, reflecting the actual state of the mechanobiological response of cells within the microfluidic chip cell culture chamber. The acquired signals are fed back to the industrial control computer, which further adjusts the fluid loading device to quantitatively control the changes in wall shear stress and flow signal acting on the cyclic simulation system, ultimately generating the real human wall shear stress τ in the microfluidic chip cell culture chamber. w The role of (t). In addition, the dynamic process of the mechanobiological response of aortic valve endothelial cells was detected, recorded and saved to an industrial control computer by microscopy combined with a CCD camera.
[0032] like Figure 1 and Figure 2 As shown, this utility model discloses a microfluidic device for accurately simulating tissue-engineered valve endothelialization. The microfluidic device comprises an upper PDMS1-3 and a lower PDMS1-4, which are bonded together. The PDMS is composed of prepolymer A and crosslinking agent B. Before chip fabrication, a preliminary experiment is conducted to determine the optimal ratio for mechanical loading, ensuring appropriate elastic deformation under mechanical loading. Vertically arranged inlet holes 1-1 and outlet holes 1-2 are etched inside the upper PDMS1-3. The cell culture chamber on the microfluidic chip is as follows... Figure 2 As shown, tissue-engineered valves 1-5 separate the upper and lower layers of PDMS to form cell culture chambers 1-7, and endothelial cells 1-6 are cultured on the tissue-engineered valves.
[0033] like Figure 3 The diagram shows a microfluidic chip system for accurately simulating tissue-engineered valve endothelialization according to this invention. The microfluidic chip system includes a microfluidic chip, a peripheral system (air pump 2-1, fluid loading device 2-2, and reservoir 2-3), a signal acquisition and processing system, and a feedback system (inlet flow sensor 2-5, outlet flow sensor 2-6, fluorescence microscope 2-7, CCD camera 2-8, and industrial computer 2-9). The peripheral system is used to generate shear stress applied to the aortic tissue-engineered valve cell culture area and observe its effect on the endothelial cells.
[0034] The specific implementation of the microfluidic device of this invention for accurately simulating the endothelialization of tissue-engineered valves is as follows:
[0035] Step 1: Conduct a preliminary experiment on the formulation of PDMS materials. Both layers of PDMS need to have a suitable elastic modulus. Verify the following formulation: the volume ratio of PDMS prepolymer A to crosslinker B is 10:1, 8:1 and 6:1 respectively. The smaller the ratio of prepolymer A to crosslinker B, the greater the elasticity of PDMS and the easier it is to deform. Select the most suitable formulation for mechanical loading through the preliminary experiment to ensure that the chip can have appropriate elastic deformation under mechanical loading.
[0036] Step 2: Design a "sandwich" microfluidic chip. The inlet hole 1-1 and outlet hole 1-2 of the microfluidic chip are both 2 mm diameter circular holes, which are through-holes in the upper PDMS layer; the cell culture chamber height H... c Width W c and length L cThe microfluidic channels are 0.5 mm, 10 mm, and 15 mm in diameter, respectively, and the viscosity η of the cell culture medium is typically 0.001 Pa·s. All channels and chambers of the microfluidic chip are fabricated using standardized microfabrication methods. The chip material is PDMS, which is bonded and sealed to a clean glass slide to form a transparent, biocompatible glass PDMS chip. All microfluidic channels are etched to a height of 150 μm.
[0037] Step 3: Based on the design in Step 1, fabricate the microfluidic chip. The microfluidic chip can be processed using standard soft lithography and laser engraving techniques. In the device structure made of polydimethylsiloxane (PDMS) material, a 150μm thick polyimide film is cut using a laser engraving machine and attached to the silicon wafer. The silicon wafer was placed in a glass dish, and the prepared PDMS solution was poured in. It was then allowed to stand in a vacuum for 20 minutes to remove air bubbles. The dish was then placed in a drying oven and baked at 80°C for 90 minutes to solidify the PDMS. Afterward, the glass dish was removed, and the PDMS was separated from the mold after cooling, yielding a PMDS with a microfluidic channel structure. The PDMS with the microfluidic channels was cut off, and the inlet and outlet of the channels were punched using a punch. After cleaning, the PDMS and the clean lower layer of PDMS were sandwiched together using a plasma cleaner, and the tissue-engineered valve was bonded together. Heating at 120°C for 15-20 minutes further solidified the bond. The catheter was then inserted into the punched hole on the chip, and adhesive was evenly applied at the junction of the catheter and the hole to prevent leakage. After applying the adhesive, the chip was placed in a drying oven and baked at 80°C overnight. Finally, the catheter and the fluid loading device were connected together, completing the device fabrication.
[0038] Step 4: Place the fabricated microfluidic chip in water to remove air bubbles. After removing all air bubbles from the channel, place it in a high-temperature and high-pressure sterilizer for sterilization. After sterilization, store the microfluidic chip in a clean bench for later use.
[0039] Step 5: Passage the primary cultured aortic valve endothelial cells into EGM medium (Lonza Benelux) specifically for endothelial cells. Passages 2-5 are used for experiments. During experiments, endothelial cells are seeded onto the lower surface of the tissue-engineered valve within the microarray cell culture chamber, coated with Fibronection, ensuring cell adhesion and confluence exceeding 90%. Figure 1 As shown.
[0040] Step Six: Acquire the shear force waveform of the aortic valve under normal human conditions using fluid dynamics (CFD) simulation technology as the shear force waveform of the aortic tissue-engineered valve. Calculate the target flow waveform and input it into the industrial control computer to set the proportional coefficient K in the three-dimensional mechanical loading PID control. p1 Integral coefficient K i1Differential coefficient K d1 The initial values are output to a high-precision fluid loading device 2-2, which precisely controls the air pump 2-1 to achieve compression, tension, and shear forces on the microfluidic chip. The microfluidic chip feeds back the inlet and outlet flow rates to the inlet flow sensor 2-5 and the outlet flow sensor 2-6. The flow sensors can accurately detect the flow rate on the microfluidic chip and transmit the flow signal back to the industrial control computer in real time. The industrial control computer calculates the initial value and error signal, and recalculates the input using the PID calculation formula to achieve closed-loop real-time control. If the returned flow signal is unsuitable, the proportional coefficient K can be manually adjusted in a timely manner. p1 Integral coefficient K i1 Differential coefficient K d1 This is to achieve rapid, accurate, and high signal-to-noise ratio reproduction of the target's mechanical signals.
[0041] Step 7: After adjusting and stabilizing the mechanical environment of the microfluidic chip as in Step 6, observe the flow of nanoparticles under transient conditions using an inverted fluorescence microscope 2-7. The CCD camera acquires video images at a shooting rate of n frames per second, and the images can be observed and acquired on the screen of the industrial control computer 2-9.
Claims
1. A microfluidic device for evaluating endothelialization of tissue-engineered valves, characterized in that, The microfluidic device for evaluating endothelialization of tissue-engineered valves includes a microfluidic chip, peripheral devices, and a signal acquisition and processing system and a feedback system. The microfluidic chip includes a microfluidic chip channel, a microfluidic chip inlet, and a microfluidic chip outlet. The microfluidic chip channel is a groove structure etched inside the microfluidic chip, serving as a cell culture chamber. Both the microfluidic chip inlet and outlet are connected to the cell culture chamber, forming a fluid dynamics loop. A tissue-engineered valve is fixed on the upper surface of the cell culture chamber, and endothelial cells are located on the lower surface of the tissue-engineered valve. The cell culture chamber simulates the wall shear stress signal in the in vivo aortic valve endothelial hemodynamic microenvironment. The peripheral devices provide power flow to the microfluidic chip and include a liquid reservoir, an air pump, and a fluid loading device. The fluid loading device is connected to the liquid reservoir via a pipeline, and the air pump pumps the fluid from the fluid loading device into the liquid reservoir. The liquid reservoir is connected to the inlet and outlet of the microfluidic chip via a pipeline to form a fluid circulation loop, providing fluid to the cell culture chamber through the microfluidic chip inlet and flowing out through the microfluidic chip outlet. The aforementioned signal acquisition, processing, and feedback system is used for the acquisition, processing, and feedback of hemodynamic signals and intracellular biological and chemical signals on the microfluidic chip. It includes a flow sensor, a fluorescence microscope, a CCD, and an industrial control computer. The flow sensor, fluorescence microscope, and CCD are all connected to the industrial control computer. The flow sensor acquires flow signals from the inlet and outlet of the microfluidic chip. The fluorescence microscope and CCD camera are combined to detect dynamic images of the biological response of tissue-engineered valve endothelial cells. The acquired images are sent to the industrial control computer, which controls a fluid loading device to generate wall shear stress signals within the cell culture chamber of the microfluidic chip, reflecting the hemodynamic microenvironment of real aortic tissue-engineered valve endothelial cells.
2. The microfluidic device for evaluating endothelialization of tissue-engineered valves according to claim 1, characterized in that, Cell culture chamber length L c Width W c and height H c Satisfy: H c < <W c And H c < <L c ; Wall shear stress τ borne by endothelial cells w (t) should satisfy: In the formula, η is the viscosity of the cell culture medium, and q(t) is the volumetric flow rate through the cell culture chamber. The magnitude of the shear stress τ loaded on the endothelial cells of the tissue-engineered valve is proportional to the flow rate q(t) of the fluid flowing through the channel. The magnitude of the shear stress can be quantitatively controlled by controlling the flow rate q(t).
3. The microfluidic device for evaluating endothelialization of tissue-engineered valves according to claim 1, characterized in that, The industrial control computer uses a PID algorithm to achieve precise real-time control of mechanical loading. The formula used when adjusting the PID parameters and output relationship is as follows: In the formula, e(t) is the deviation, i.e., the difference between the set value and the actual output value, u(t) is the output voltage, dt is the time change, and K... P It is the proportionality coefficient, K i It is the integral coefficient, K d These are the derivative coefficients. Adjusting these three parameters makes PID control more precise and faster.
4. The microfluidic device for evaluating endothelialization of tissue-engineered valves according to claim 1, characterized in that, The fluid circuit on the microfluidic chip discharges gas into the storage tank through a fluid loading device. Due to the pressure change, an equal amount of liquid is discharged. The liquid enters the chip through the inlet of the microfluidic chip, leaves the chip through the outlet of the microfluidic chip, and returns to the storage tank for recycling.
5. A microfluidic device for evaluating endothelialization of tissue-engineered valves according to claim 1, characterized in that, The fluid loading device employs a programmable air pump.