Dialysis machine blood flow measurement method based on MEMS flow sensor

Abstract

The invention belongs to the field of micro electro mechanical systems and biomedical engineering, and discloses a dialysis machine blood flow measuring method based on an MEMS flow sensor. An MEMS flow sensor is installed on the side wall of the dialysis machine catheter; the MEMS flow sensor comprises a flow detection module and a signal transmission module which are connected in sequence; the flow detection module converts the flow into an electric signal; under the impact of blood, the cilium clusters generate mechanical deformation to drive the PVDF piezoelectric film layer to deform, so that electric polarization is generated; the electric signal is wirelessly transmitted to external equipment through the signal transmission module for data processing, and the blood drawing rate of the dialysis machine is obtained. The method is different from a previous method for measuring the blood flow through an ultrasonic Doppler effect detection method or spiral CT angiography, the purpose of detecting the blood flow in the dialysis process is achieved, so that the dialysis blood flow is better and accurately controlled in real time, and the problem that the actual blood flow is different from the set blood flow in clinic can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the fields of microelectromechanical systems and biomedical engineering, and particularly relates to a method for measuring the blood flow rate of a dialysis machine based on a MEMS flow sensor. Background Art

[0002] Sensor technology has very broad application prospects in many fields such as automotive electronics, industrial manufacturing, and network communication due to its advantages of miniaturization, strong stability, and low energy consumption. Especially in the medical field, with the continuous progress of medical technology, sensor technology plays an increasingly important role in the prevention, diagnosis, and treatment of diseases.

[0003] The blood flow rate, that is, the amount of blood passing through the dialysis machine per unit time, affects the toxin clearance efficiency, the service life of the dialyzer, and the patient's comfort, and is a key factor affecting dialysis efficiency and patient safety. Controlling the blood flow rate is crucial for ensuring the adequacy of dialysis treatment and optimizing the patient's quality of life. Currently, the blood flow rate detection methods used clinically include ultrasonic Doppler effect detection method and spiral CT angiography. The patent application document with the application number 201810005469.2 discloses a Doppler blood flow velocity imaging method and system based on ultrasonic channel data, which can separately estimate the blood flow velocity through the channel data corresponding to different array elements, and then improve the signal-to-noise ratio of the blood flow signal and further improve the accuracy of blood flow velocity estimation by means of angle phase alignment and superposition, but it cannot accurately label and distinguish the blood vessel area, which is not conducive to the auxiliary diagnosis of the exact condition. The patent with the application number 202010063353.1 discloses a spectral blood flow detection method based on the color spectral diagram of ultrasonic Doppler, which can accurately label and distinguish the blood vessel area, but still needs to be analyzed based on the spectrogram and cannot achieve real-time detection. In fact, in clinical applications, the situation where the set blood flow rate of the dialysis machine is not equal to the actual blood flow rate often occurs. Therefore, it is particularly important to achieve real-time control of the blood flow rate during dialysis on the premise of ensuring the detection accuracy.

[0004] Kidney disease failure seriously endangers national health. Therefore, ensuring the dialysis treatment effect is of great significance for treating kidney-related diseases and has broad prospects. The present invention provides a novel detection method for doctors and patients, which can realize the real-time control of the blood flow rate during dialysis. How to improve the detection accuracy and achieve high-volume production of this product with high integration while meeting the diagnostic safety is a new research topic. Summary of the Invention

[0005] In view of the above analysis, the present invention designs a method for measuring the blood flow rate of a dialysis machine based on a MEMS flow sensor. The MEMS flow sensor is installed on the dialysis machine catheter and mainly consists of a flow detection module and a signal transmission module. The flow detection module on the MEMS flow sensor converts the flow rate into an electrical signal, and then wirelessly transmits the signal to an external receiving instrument through the signal transmission module, so that data processing can be carried out to realize the real-time control of the blood extraction rate of the dialysis machine.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for measuring the blood flow rate of a dialysis machine based on a MEMS flow sensor is as follows: Install the MEMS flow sensor on the side wall of the dialysis machine catheter; the MEMS flow sensor includes a flow detection module and a signal transmission module 4, which are connected in sequence; the flow detection module converts the flow rate into an electrical signal; the electrical signal is wirelessly transmitted to an external device for data processing through the signal transmission module 4 to obtain the blood flow rate of the dialysis machine.

[0008] The flow detection module mainly consists of a cilia cluster 7, a top electrode 9, a polyvinylidene fluoride PVDF piezoelectric film layer 6, a bottom electrode 10, and a silicon-based bottom layer 8;

[0009] The cilia cluster 7 is adhered to the polyvinylidene fluoride PVDF piezoelectric film layer 6 through its circular bottom surface for detecting changes in the blood flow rate in the dialysis machine; under the impact of blood, the cilia cluster 7 generates mechanical deformation and drives the polyvinylidene fluoride PVDF piezoelectric film layer 6 to deform; the deformation of the polyvinylidene fluoride PVDF piezoelectric film layer 6 generates polarization, separating positive charges and negative charges, so that opposite-polarity and equal-magnitude electric charges are generated on its upper surface and lower surface, thereby forming an electric potential difference; the electric potential difference is processed and transmitted to an external receiving instrument through the signal transmission module 4 to obtain an electrical signal; the electric potential difference takes the negative polarity grounded as the reference zero potential, and the positive polarity potential correspondingly becomes an electrical signal whose voltage changes in real time with the deformation of the polyvinylidene fluoride PVDF piezoelectric film layer 6.

[0010] One surface of the polyvinylidene fluoride PVDF film is directly in contact with the bottom electrode 10 to form a connection, and the other surface is directly in contact with the top electrode 9 to form a connection.

[0011] The cilia cluster 7 is distributed in a circular array, and the cilia it contains are cylindrical, and the ratio of the height to the diameter is required to be in the range of 10 to 20.

[0012] The cilia of the cilia cluster 7 are made of SU-8 glue cilia. As a polymer material, SU-8 glue has good mechanical properties, high chemical stability, and is harmless to human cells. And SU-8 glue is a non-brittle material and will not break into the blood during dialysis, meeting the medical standards.

[0013] The signal transmission module 4 is powered by the power supply battery 1 and receives the electrical signals generated by the polyvinylidene fluoride piezoelectric film layer 6. The interior of the signal transmission module 4 mainly consists of a signal amplification circuit, a signal filtering circuit, an analog-to-digital conversion circuit, and a Bluetooth module, which are connected in sequence. The metal wire a2 serves as the positive electrode and the metal wire b3 serves as the negative electrode to receive power supply.

[0014] The signal amplification circuit is connected to the metal wire c5 and the metal wire d11, and is used to amplify the electrical signals generated by the flow rate detection module. The electrical signals achieve voltage amplification through the energy provided by the DC power supply.

[0015] The signal filtering circuit is used to filter the high-frequency signal noise that may be generated in the flow rate detection module and the environment, and retain the flow rate signals collected by the flow rate detection module.

[0016] The analog-to-digital conversion circuit adopts a successive approximation type ADC circuit, which is used to convert the amplified and filtered voltage analog signals into digital signals, and send the data to the Bluetooth module in accordance with the universal asynchronous receiver / transmitter protocol.

[0017] The blood flow rate of the dialysis machine is calculated based on the electrical signal U obtained by the external receiving instrument according to the following formula:

[0018]

[0019] K is the characteristic coefficient representing the blood flow rate in the dialysis machine catheter and the stress received by the polyvinylidene fluoride PVDF piezoelectric film layer 6; C is the amplification coefficient of the signal amplification circuit; t is the thickness of the polyvinylidene fluoride PVDF piezoelectric film layer 6; g 33 is the piezoelectric coefficient of the polyvinylidene fluoride PVDF material; υ is the blood flow rate in the dialysis machine catheter; S is the cross-sectional area of the catheter.

[0020] Furthermore, a simulation model is constructed through COMSOL software, and different flow conditions are set for fluid-structure interaction simulation. A data set with the independent variable and the dependent variable being the flow rate and stress respectively can be obtained. Based on this data set, the K value can be fitted, and in specific implementation, the K value can be corrected according to the actual test results.

[0021] Both the top electrode 9 and the bottom electrode 10 are made of Pt / Ti composite materials.

[0022] The top electrode 9 is connected to the signal transmission module through the metal wire c5.

[0023] The bottom electrode 10 is connected to the signal transmission module through the metal wire d11.

[0024] The materials of the metal wire a2, the metal wire b3, the metal wire c5, and the metal wire d11 can be selected from Au or Ag.

[0025] The successive approximation ADC circuit is based on the successive approximation algorithm. Its core is to gradually narrow the numerical range of the input voltage analog signal through the dichotomy method, and finally determine the digital representation of the input signal. Further, the successive approximation ADC circuit has the characteristics of high speed, low power consumption and moderate resolution, and is widely used in the field of sensor interfaces.

[0026] The Bluetooth module supports the Bluetooth 5.3 version and is used to wirelessly transmit digital signals to other external receiving instruments that support the Bluetooth module to achieve data communication.

[0027] The overall MEMS flow sensor is encapsulated with the biocompatible material polyimide, which can protect the MEMS flow sensor from being corroded by blood, and at the same time avoid the MEMS flow sensor itself from causing damage to human cells or causing rejection reactions of the body.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) Different from the previous methods of detecting blood flow by ultrasonic Doppler effect detection method or spiral CT angiography measurement, the present invention can achieve the purpose of detecting blood flow during dialysis, so as to better control the dialysis blood flow in real time and accurately, and can effectively solve the problem that the actual blood flow is different from the set blood flow in clinical practice.

[0030] (2) The manufacturing materials used in the present invention are all biocompatible materials, which are non-toxic and harmless to the human body and will not affect human health on the premise of ensuring performance.

[0031] (3) The present invention uses a Bluetooth module as a signal transmission means, which can provide a data transmission interface for devices such as external receiving instruments. Under the condition that the connection permission is controllable, doctors, patients and their families can view the blood flow data. Brief Description of the Drawings

[0032] Figure 1 It is a design schematic diagram of the MEMS flow sensor.

[0033] Figure 2 It is a schematic diagram of the internal structure disassembly of the MEMS flow sensor.

[0034] Figure 3 It is a schematic diagram of the internal signal processing flow of the signal transmission module.

[0035] Figure 4 It is a schematic diagram of the program for the external receiving instrument at the signal receiving end to process data.

[0036] In the figure: 1. Power supply battery; 2. Metal wire a; 3. Metal wire b; 4. Signal transmission module; 5. Metal wire c; 6. Polyvinylidene fluoride (PVDF) piezoelectric film layer; 7. Cilia cluster; 8. Silicon-based substrate; 9. Top electrode; 10. Bottom electrode; 11. Metal wire d; 12. Silicon dioxide layer; 13. Silicon pores. Detailed implementation mode

[0037] A method for measuring the blood flow rate of a dialysis machine based on a MEMS flow sensor. The following combines the technical solutions and the attached Figures 1-4 Describe in detail the specific embodiments of the present invention.

[0038] A manufacturing method for the MEMS flow sensor specifically includes the following steps:

[0039] (1) First, adopt the thermal oxidation method, keep the oxidation temperature at about 1000 °C, and form a silicon dioxide layer 12 on the upper surface of the silicon-based substrate 8;

[0040] (2) Sputter a Pt / Ti composite material on the silicon dioxide layer 12 to form the bottom electrode 10;

[0041] (3) Use laser cutting technology to cut a PVDF film of appropriate size to make a polyvinylidene fluoride (PVDF) piezoelectric film layer 6, and bond it to the bottom electrode 10;

[0042] (4) Coat a photoresist on the polyvinylidene fluoride (PVDF) piezoelectric film layer 6, and after development, sputter Ti / Pt to form the top electrode 9;

[0043] (5) Dry-etch silicon pores 13 on the silicon-based substrate 8;

[0044] (6) Coat SU-8 photoresist on the top electrode 9, and after the development process, make a high aspect ratio SU-8 cilia cluster;

[0045] (7) Bond the power supply battery 1, metal wire 2a, metal wire 3b, metal wire 5c, metal wire 11d, and signal transmission module 4 on the silicon-based substrate 8, so that the potential difference generated by the polyvinylidene fluoride (PVDF) piezoelectric film layer 6 can be transmitted to the signal transmission module 4 via the metal wire;

[0046] (8) Use polyimide (PI) to perform overall packaging on the MEMS flow sensor;

[0047] The MEMS flow sensor manufactured according to the above steps needs to be sterilized and disinfected in accordance with medical standards, and then bonded to the inner side wall of the dialysis machine catheter.

[0048] A method for measuring the blood flow rate of a dialysis machine based on a MEMS flow sensor. The processing and subsequent analysis process of the electrical signal are as follows:

[0049] (1) The potential difference takes the negative - polarity grounded as the reference zero potential, and the positive - polarity potential correspondingly becomes an electrical signal whose voltage changes in real - time with the deformation of the polyvinylidene fluoride (PVDF) piezoelectric film layer 6.

[0050] (2) The electrical signal enters the signal amplification circuit in the signal transmission module 4 to achieve the amplification of the signal amplitude and power.

[0051] (3) The amplified electrical signal passes through the signal filtering circuit in the signal transmission module 4, and a low - pass filter is used to filter out the high - frequency Gaussian thermal noise caused by environmental factors and other factors in the electrical signal.

[0052] (4) The filtered electrical signal passes through the analog - to - digital conversion circuit ADC, samples and quantizes the continuous analog signal into a discrete digital signal, and sends the data to the Bluetooth module according to the Universal Asynchronous Receiver / Transmitter (UART) protocol.

[0053] (5) The Bluetooth module transmits the discrete digital signal data to the external receiving instrument according to the communication protocol of the Bluetooth 5.3 version.

[0054] (6) After the external receiving instrument receives the data, it first converts the data into a floating - point format, then converts the data to the blood flow rate of the dialysis machine, and finally performs a Kalman filtering operation on the data.

[0055] (7) The blood flow rate data of the dialysis machine collected in chronological order is aggregated. An existing display interface can be externally connected to plot the aggregation result on the screen and display the real - time blood flow rate data.

[0056] By constructing a simulation model through COMSOL software and setting different flow conditions for fluid - structure interaction simulation, a data set with the independent variable and the dependent variable being the flow rate and stress respectively can be obtained. Based on this data set, the K value can be fitted, and in specific implementation, the K value can be corrected according to the actual test results.

[0057] Certainly, the present invention is not limited to the above examples. The technical features not described in the present invention can be realized by or adopted from the prior art, and will not be elaborated here. The above embodiments are only used to illustrate the technical solutions of the present invention and are not limitations to the present invention. The present invention has been described in detail with reference to the preferred embodiments. Those of ordinary skill in the art should understand that any changes, modifications, additions, or substitutions made by those of ordinary skill in the art within the scope of the essence of the present invention do not depart from the purpose of the present invention and should also fall within the scope of the protection of the claims of the present invention.

Claims

1. A method for measuring blood flow in a dialysis machine based on a MEMS flow sensor, characterized in that: The MEMS flow sensor is installed on the side wall of the dialysis machine catheter; the MEMS flow sensor comprises a flow detection module and a signal transmission module (4), which are connected in sequence; the flow detection module converts the flow size into an electrical signal; The electrical signal is wirelessly transmitted to an external device for data processing via a signal transmission module (4) to obtain the blood flow of the dialysis machine.

2. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 1, characterized in that: The flow detection module is mainly composed of a ciliary cluster (7), a top electrode (9), a polyvinylidene fluoride (PVDF) piezoelectric film layer (6), a bottom electrode (10) and a silicon substrate layer (8); The ciliary cluster (7) is adhered to the polyvinylidene fluoride (PVDF) piezoelectric film layer (6) through its circular bottom surface, and is used to detect changes in blood flow rate in the dialysis machine; under the impact of blood, the ciliary cluster (7) produces mechanical deformation and drives the polyvinylidene fluoride (PVDF) piezoelectric film layer (6) to deform; the polyvinylidene fluoride (PVDF) piezoelectric film layer (6) deforms to produce electric polarization, separates positive charges and negative charges, and generates charges of opposite polarity and equal magnitude on its upper and lower surfaces, thereby forming an electric potential difference; the electric potential difference is processed by the signal transmission module (4) and transmitted to an external receiving instrument to obtain an electric signal; One surface of the polyvinylidene fluoride (PVDF) film directly contacts the bottom electrode (10) to form a connection, and the other surface directly contacts the top electrode (9) to form a connection.

3. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 2, characterized in that: The cilia clusters (7) are distributed in a circular array, and the cilia contained therein are cylindrical, and the ratio of height to diameter is required to be in the range of 10 to 20.

4. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 2, characterized in that: The ciliary material of the ciliary cluster (7) is SU-8 gel ciliary material.

5. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 1, characterized in that: The signal transmission module (4) is powered by a power supply battery (1) and receives an electrical signal generated by a polyvinylidene fluoride piezoelectric film layer (6); the interior of the signal transmission module (4) is mainly composed of a signal amplification circuit, a signal filtering circuit, an analog-to-digital conversion circuit and a Bluetooth module, which are connected in sequence; the metal wire a (2) serves as a positive electrode and the metal wire b (3) serves as a negative electrode to receive power; The signal amplifying circuit is connected to the metal wire c (5) and the metal wire d (11) and is used to amplify the electrical signal generated by the flow detection module; the electrical signal is voltage-amplified by the energy provided by the DC power supply; The signal filtering circuit is used to filter the high-frequency signal noise that may be generated by the flow detection module and the environment, and retain the flow signal collected by the flow detection module; The analog-to-digital conversion circuit adopts a successive approximation ADC circuit, which is used to convert the amplified and filtered voltage analog signal into a digital signal, and send the data to the Bluetooth module in accordance with the universal asynchronous receiver-transmitter protocol.

6. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 5, characterized in that: The blood flow of the dialysis machine is calculated based on the electrical signal U obtained by the external receiving instrument according to the following formula: K is a characteristic coefficient representing the blood flow rate in the dialysis machine catheter and the stress on the polyvinylidene fluoride PVDF piezoelectric film layer (6); C is the amplification factor of the signal amplification circuit; t is the thickness of the polyvinylidene fluoride PVDF piezoelectric film layer (6); g 33 is the piezoelectric coefficient of polyvinylidene fluoride (PVDF) material; v is the blood flow in the dialysis machine catheter; S is the cross-sectional area of ​​the catheter.

7. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 5, characterized in that: The top electrode (9) and the bottom electrode (10) are both Pt / Ti composite materials; The top electrode (9) is connected to the signal transmission module via a metal wire c (5); The bottom electrode (10) is connected to the signal transmission module via a metal wire d (11).

8. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 5, characterized in that: The metal wire a (2), the metal wire b (3), the metal wire c (5), and the metal wire d (11) may be made of Au or Ag.

9. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 5, characterized in that: The successive approximation ADC circuit is based on a successive approximation algorithm, the core of which is to gradually reduce the numerical range of the input voltage analog signal through binary division, and finally determine the digital representation of the input signal.

10. The method for measuring blood flow of a dialysis machine based on a MEMS flow sensor according to claim 1, characterized in that: The MEMS flow sensor is encapsulated as a whole using biocompatible polyimide material, which protects the MEMS flow sensor from being corroded by blood and prevents the MEMS flow sensor itself from causing damage to human cells or causing a rejection reaction in the body.

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