Intracranial pressure sensor based on split-ring resonator structure, monitoring system and method

Abstract

The invention provides an intracranial pressure sensor based on a split-ring resonator structure, a monitoring system and a monitoring method, and belongs to the technical field of medical instruments. The intracranial pressure sensor is composed of a substrate, an interdigital capacitor-split resonant ring structure and a micro-channel pressure conversion structure. Intracranial pressure acts on the micro-channel film to drive the gallium-indium eutectic alloy to displace, the interdigital capacitance is modulated in real time, resonant frequency deviation is caused, and 0.47 MHz / kPa high-sensitivity pressure monitoring is achieved. The monitoring system comprises an intracranial pressure sensor, an in-vitro radio frequency read-write device and a data processing terminal, and the intracranial pressure can be continuously monitored in real time for a long time. Compared with an existing intracranial pressure detection means, the intracranial pressure sensor based on the split-ring resonator structure, the monitoring system and the monitoring method have the advantages that high sensitivity, high stability, good repeatability and excellent wireless readability are achieved on the basis that an integrated chip is not needed, and a better solution is provided for high-precision minimally invasive intracranial pressure monitoring.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical devices, in particular to an intracranial pressure sensor based on an open resonant ring structure, a monitoring system and a method. BACKGROUND

[0002] Intracranial pressure is a key biomechanical parameter for maintaining the normal physiological function of the central nervous system. Under various pathological conditions of the nervous system such as craniocerebral injury, brain tumor, and hydrocephalus, abnormal elevation of intracranial pressure is a common and dangerous complication that can directly lead to decreased cerebral perfusion pressure, cerebral ischemia and hypoxia, and even cause fatal brain herniation. Therefore, continuous and real-time monitoring of intracranial pressure in high-risk patients is of great clinical significance for guiding clinical intervention, evaluating treatment effect, and improving patient prognosis.

[0003] Currently, the techniques for monitoring intracranial pressure in clinical practice mainly fall into two categories: invasive monitoring and non-invasive monitoring. Invasive monitoring techniques, such as direct measurement through an external ventricular drainage tube or a subdural probe, are considered the "gold standard" for monitoring. They have the advantages of accurate and reliable measurement results and the ability to achieve continuous monitoring. However, the invasive nature of these techniques inevitably carries a higher risk of complications, including intracranial hemorrhage, central nervous system infection, probe blockage or displacement, etc., limiting their long-term application and causing additional pain and risk to patients.

[0004] In contrast, non-invasive monitoring techniques, such as transcranial Doppler ultrasound and optic nerve sheath diameter ultrasound measurement, have attracted attention due to their safe and convenient operation. However, these techniques generally have limitations such as insufficient measurement accuracy, susceptibility to operator subjectivity, and inability to achieve continuous and uninterrupted monitoring. They are usually only used as an auxiliary screening or trend assessment tool and cannot replace the central role of invasive monitoring in critical care management. Therefore, there is an urgent need for a new type of intracranial pressure monitoring solution that can bridge the gap between existing technologies, i.e., a monitoring technology that is minimally invasive, highly accurate, highly stable, and can achieve long-term continuous operation.

[0005] With the development of wireless radio frequency identification technology and micro-electromechanical system technology, passive wireless implantable sensors provide a promising technical path to solve the above problems. Passive sensors do not require internal batteries and are powered and data read by external radio frequency energy, with advantages such as small size, long life, and good biocompatibility. However, wireless radio frequency sensors for intracranial pressure detection still have problems such as complex structure and poor long-term implant stability.

[0006] Therefore, how to design a new sensing structure and transduction mechanism, develop a passive wireless pressure sensor without integrated circuit chip, with higher sensitivity, better stability and biocompatibility, to meet the needs of minimally invasive, long-term, precise intracranial pressure monitoring, is the technical problem to be solved in the current field. SUMMARY

[0007] The purpose of the present application is to provide an intracranial pressure sensor based on an open resonant ring structure, a monitoring system and a method, which has high sensitivity, high stability, good repeatability and excellent wireless readability without integrated chip, providing a better solution for high-precision minimally invasive intracranial pressure monitoring.

[0008] To achieve the above purpose, the present application provides an intracranial pressure sensor based on an open resonant ring structure, comprising:

[0009] a substrate;

[0010] an interdigital capacitor-open resonant ring structure disposed on the substrate, the interdigital capacitor-open resonant ring structure being composed of an open resonant ring and an interdigital capacitor replacing the open gap of the open resonant ring;

[0011] a micro-channel pressure conversion structure bonded directly above the interdigital capacitor, the micro-channel pressure conversion structure being internally sealed and filled with a conductive liquid metal;

[0012] The intracranial pressure sensor is a passive wireless intracranial pressure sensor, configured to drive the conductive liquid metal to displace when external pressure acts on the micro-channel pressure conversion structure, change the coverage area of the interdigital capacitor, modulate the equivalent dielectric constant of the interdigital capacitor, cause the resonant frequency of the interdigital capacitor-open resonant ring structure to shift, and realize passive wireless pressure monitoring.

[0013] Preferably, the conductive liquid metal is a gallium-indium eutectic alloy, wherein the content of gallium is 75.5±0.5 atomic percent, and the content of indium is 24.5±0.5 atomic percent.

[0014] Preferably, the substrate is made of polydimethylsiloxane, and after curing, the Young's modulus is 1.0-3.0 MPa, and the Shore A hardness is 30-60; the effective thickness of the substrate is 100-500 μm.

[0015] Preferably, the interdigital capacitor-open resonant ring structure is made by the following process:

[0016] forming a mask on the substrate by photolithography;

[0017] The chromium adhesion layer and the gold conductive layer are sequentially deposited by magnetron sputtering; wherein the thickness of the chromium adhesion layer is 5-50nm, the thickness of the gold conductive layer is 20-200nm, and the ratio of the thickness of the chromium adhesion layer to the thickness of the gold conductive layer is between 1:5 and 1:4;

[0018] The mask is removed to form a metallized resonant structure;

[0019] The conductive liquid metal is infiltrated into the interdigital capacitance area.

[0020] Preferably, the micro-channel pressure conversion structure is manufactured by using a light-cured printing process to make a mold and using polydimethylsiloxane for film pouring.

[0021] Preferably, the substrate and the micro-channel pressure conversion structure are bonded by oxygen plasma treatment, and the process parameters of the oxygen plasma treatment are as follows: power is 100-500W, processing time is 30-300s, working gas pressure is 10-100Pa, and oxygen flow is 5-50sccm.

[0022] Preferably, the pressure sensing sensitivity of the intracranial pressure sensor is 0.47MHz / kPa.

[0023] The application also provides an intracranial pressure monitoring system, comprising:

[0024] The intracranial pressure sensor based on the open resonant ring structure as described above is used for implanting in an intracranial region to be measured.

[0025] An external radio frequency reading and writing device is used for transmitting a sweep excitation signal to the intracranial pressure sensor and receiving a resonant response signal.

[0026] A data processing terminal is internally provided with a pressure-frequency conversion algorithm, which converts the resonant frequency into an intracranial pressure value in real time, and the conversion algorithm converts the resonant frequency f0 into the intracranial pressure P value based on the following formula:

[0027]

[0028] Wherein, S C represents the sensitivity coefficient of the capacitor to the pressure, L' represents the total length of the liquid column in the micro-channel, C offset represents the capacitance value under normal pressure.

[0029] Preferably, the external radio frequency reading and writing device is a vector network analyzer or a special radio frequency transceiver module, the working frequency band of the external radio frequency reading and writing device is 1-6GHz, and the output power is 1-100mW.

[0030] The application also provides an intracranial pressure monitoring method, which utilizes the intracranial pressure monitoring system as described above, and comprises the following steps:

[0031] Step S1, implanting the intracranial pressure sensor into an intracranial region to be measured;

[0032] Step S2, using an in-vitro radio frequency read-write device, transmitting a sweep excitation signal to the area where the intracranial pressure sensor is located;

[0033] Step S3, the in-vitro radio frequency read-write device receives the resonant response signal of the intracranial pressure sensor and determines its current resonant frequency;

[0034] Step S4, according to the pressure-frequency conversion algorithm, the resonant frequency is converted into the intracranial pressure value and output.

[0035] Therefore, the intracranial pressure monitoring system and method based on the above-mentioned open resonant ring structure intracranial pressure sensor have the following beneficial technical effects:

[0036] (1) Passive wireless, high safety: The sensor proposed in the present application does not need to be built-in battery or any physical cable, and works through wireless radio frequency energy coupling, which fundamentally eliminates the risk caused by battery depletion, circuit failure or cable breakage / infection, greatly improving the long-term safety and reliability of implantable monitoring.

[0037] (2) Good biocompatibility and flexibility: The sensor body is made of flexible materials such as PDMS, which has better mechanical properties and soft brain tissue, can effectively reduce the mechanical stimulation and inflammatory reaction to the surrounding tissue after implantation, improve the biocompatibility, and reduce the discomfort of patients.

[0038] (3) High sensitivity and high stability: The displacement of conductive liquid metal in the micro-channel is used to modulate the interdigital capacitor, and then the resonant frequency is changed, which has high sensitivity. At the same time, the open resonant ring structure as a mature resonator has stable frequency response and strong anti-interference ability, which ensures the accuracy of the monitoring data.

[0039] (4) Simple structure, easy to miniaturize and mass produce: The structure design of the sensor is simple, which can be manufactured by mature micro-nano processing technology (such as photolithography, soft lithography, 3D printing, etc.), easy to realize miniaturization to reduce the implantation trauma, and low cost, with the potential for large-scale production.

[0040] (5) Long-term continuous monitoring: Due to its passive and high stability characteristics, the sensor can realize long-term, continuous and real-time bedside or home monitoring of intracranial pressure after implantation. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a structural schematic diagram of the intracranial pressure monitoring system of the present application;

[0042] Figure 2 is an exploded view of the intracranial pressure sensor;

[0043] Figure 3 This is a schematic diagram of the operation of an intracranial pressure sensor;

[0044] Figure 4 The curve of the sensor's S11 parameter changing with pressure;

[0045] Figure 5 The curve showing the change of the sensor's resonant center frequency with pressure;

[0046] Figure 6 Ten repeatability analyses were performed on the sensor.

[0047] Figure Labels

[0048] 100. Intracranial pressure sensor; 110. Substrate; 120. Interdigitated capacitor-open resonant ring structure; 131. Microfluidic channel; 132. Gallium indium eutectic alloy; 133. PDMS thin film; 134. PDMS thin film encapsulation; 200. External radio frequency reading and writing device; 210. Radio frequency reading and writing coil; 300. Data processing terminal. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0050] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0051] Example 1

[0052] like Figure 1 As shown, an intracranial pressure monitoring system includes an intracranial pressure sensor (implantable pressure-capacitance sensor) 100, an external radio frequency reader / writer 200, and a data processing terminal 300. The intracranial pressure sensor 100 is implanted in a target area within the cranium to sense changes in intracranial pressure in real time. The external radio frequency reader / writer 200 communicates wirelessly with the intracranial pressure sensor 100, providing it with energy and reading its resonant frequency data. The data processing terminal 300 receives and analyzes data from the external radio frequency reader / writer 200, converting the frequency information into readable pressure values ​​for display and storage.

[0053] like Figure 2 As shown, the intracranial pressure sensor 100 is the core sensing unit of this invention, and its overall design is a passive, chip-free system. The intracranial pressure sensor 100 mainly consists of a substrate (flexible biocompatible substrate) 110 and an interdigital capacitor-open resonant ring structure (IDC-SRR) 120 constructed on the substrate 110.

[0054] The substrate 110 is made of polydimethylsiloxane (PDMS) with a Young's modulus of 1.0-3.0 MPa and a Shore A hardness of 30-60 after curing, and an effective thickness of 100-500 μm.

[0055] The interdigital capacitor-open resonant ring structure 120 is formed by replacing the open gap part of the traditional open resonant ring with an interdigital capacitor structure with higher capacitance density and higher sensitivity to changes in the dielectric environment. The structure is made on the substrate 110 by standard photolithography micro-nano processing and magnetron sputtering phase deposition process. The ring part of the open resonant ring determines the basic inductance of the sensor, and the interdigital capacitor part serves as the core variable capacitance unit.

[0056] The interdigital capacitor-open resonant ring structure 120 is formed by the following process:

[0057] A mask is formed on the substrate 110 by photolithography, which includes: spin-coating a layer of positive photoresist S813 on the cleaned PDMS substrate surface, with a thickness of 1-10 μm; then, patterning the photoresist by a mask plate and ultraviolet (UV) exposure; then, developing the exposed or unexposed areas by S813 developer to form a mask of the desired interdigital capacitor-open resonant ring pattern, and post-baking to enhance the adhesion and stability of the mask;

[0058] A chromium adhesion layer and a gold conductive layer are deposited in sequence by magnetron sputtering; the chromium adhesion layer has a thickness of 5-50 nm, the gold conductive layer has a thickness of 20-200 nm, and the ratio of the thickness of the chromium adhesion layer to the thickness of the gold conductive layer is between 1:5 and 1:4. The magnetron sputtering process parameters include: plasma pretreatment of the PDMS substrate surface before deposition; the cavity vacuum degree is less than 5.0×10 -5 Pa; high-purity argon gas is used as the working gas, with a working pressure of 0.1-1.0 Pa; direct current (DC) sputtering is used, with a chromium target sputtering power of 50-200 W and a gold target sputtering power of 100-400 W; the substrate temperature is controlled between 25-80°C during deposition;

[0059] The mask is removed to form a metallized resonant structure; the mask removal step uses a lift-off process, which includes immersing the substrate with the deposited metal layer in acetone, dissolving and peeling off the photoresist mask and the metal layer above it with the aid of ultrasonic or mechanical stirring, thereby accurately forming a metallized structure of the interdigital capacitor-open resonant ring on the substrate 110, followed by isopropanol and deionized water cleaning and drying;

[0060] The conductive liquid metal is infiltrated into the interdigital capacitor region, and the infiltration step includes: mixing the conductive liquid metal with a NaOH solution with a concentration of 0.1-1.0 M to remove the oxide layer on the surface of the liquid metal; then, the treated conductive liquid metal is applied to the surface of the gold layer of the interdigital capacitor region by means of dripping, coating, etc., and finally the PDMS is coated on the infiltrated liquid metal, and the PDMS film is spin-coated at a speed of 1000 rpm for 30 s to form a uniform thickness of the PDMS film package 134 to prevent liquid metal leakage. A deformable liquid metal electrode can be formed in the interdigital capacitor region.

[0061] The sensing principle is: the external pressure (such as intracranial pressure) acting on the micro-channel pressure conversion structure 130 causes its elastic deformation, which drives the conductive liquid metal to displace in the micro-channel pressure conversion structure 130. Since the micro-channel 131 is located above the interdigital capacitor, the displacement of the conductive liquid metal will directly change the coverage of the underlying interdigital capacitor electrode, thereby significantly modulating the equivalent dielectric constant and capacitance value of the interdigital capacitor, and ultimately leading to a measurable change in the resonant frequency of the entire interdigital capacitor-open resonant ring structure 120.

[0062] The micro-channel pressure conversion structure 130 is made of polydimethylsiloxane (PDMS) material with high biocompatibility and good elasticity. The structure contains a sealed micro-channel 131 inside, and the micro-channel 131 is filled with liquid metal with good conductivity and fluidity, preferably gallium-indium eutectic alloy 132, with a gallium content of 75.5±0.5 atomic percent and an indium content of 24.5±0.5 atomic percent, chemical symbol GaIn, melting point of gallium-indium eutectic alloy 132 is 15.5-16℃, and its dynamic viscosity at 25℃ is about 1.9mPa·s, density of 6.3g / cm 2 , and thermal conductivity of 38w / (m.k) at 99.99% purity, electrical conductivity of 3.3×10 6 S / m. The structure is tightly combined with the PDMS film package 134 by plasma bonding and accurately aligned above the interdigital capacitor region of the interdigital capacitor-open resonant ring structure 120, which greatly enhances the sensitivity of the sensor to the displacement of the conductive liquid metal. The PDMS film 133 on the top is directly in contact with the intracranial environment as a pressure sensing film.

[0063] As Figure 3As shown, the working principle of the intracranial pressure monitoring system is as follows: when the external intracranial pressure P changes, the pressure acts on the PDMS elastic film 133 of the micro-channel pressure conversion structure 130, causing the PDMS film 133 to deform; the deformation will extrude the gallium-indium eutectic alloy 132 in the sealed micro-channel 131, driving the liquid metal gallium-indium eutectic alloy 132 to displace in the micro-channel 131; since the micro-channel 131 is accurately aligned with the below interdigital capacitor-open resonant ring structure 120, the displacement of the gallium-indium eutectic alloy 132 will directly change its coverage length and area above the interdigital capacitor (IDC) electrode fingers; as a conductor, the change of the position of the gallium-indium eutectic alloy 132 will significantly change the electric field distribution of the IDC region, thereby modulating the equivalent dielectric constant of the IDC, and further causing the equivalent capacitance C of the IDC to change; according to the resonant frequency formula Since the equivalent inductance L of the SRR is basically constant after the structure is fixed, the change of the equivalent capacitance C will directly cause the resonant frequency of the entire sensor to shift; the radio frequency reading and writing coil 210 in the external radio frequency reading and writing device 200 is coupled with the implanted pressure-capacitance sensor 100 through a magnetic field and continuously monitors the resonant frequency of the sensor through a wireless way, and the data processing terminal 300 has a built-in pressure-frequency conversion algorithm, which converts the resonant frequency f0 into an intracranial pressure value in real time, and the conversion algorithm converts the resonant frequency f0 into an intracranial pressure value P in real time based on the following formula:

[0064]

[0065] wherein S C represents the sensitivity coefficient of the capacitor to the pressure, L' represents the total length of the liquid column in the micro-channel, C offset represents the capacitance value under normal pressure.

[0066] Example Two

[0067] The embodiment provides a performance verification method for the intracranial pressure sensor 100 in Example One.

[0068] First, the intracranial pressure sensor 100 is prepared. On the flexible PDMS substrate 110, the interdigital capacitor-open resonant ring structure 120 of chromium film and gold film material is prepared by photolithography and magnetron sputtering deposition process. At the same time, a mold is made by using light-cured printing technology, and the pressure conversion structure with the micro-channel pressure conversion structure 130 is prepared by pouring PDMS. After the two parts are treated by oxygen plasma, they are accurately aligned and irreversibly bonded. Finally, the gallium-indium eutectic alloy 132 is accurately injected into the micro-channel through a micro-needle tube, and the port is sealed with PDMS.

[0069] Secondly, an in vitro test system was built. The system includes a push gauge for applying and precisely controlling pressure, and a vector network analyzer (VNA) for wirelessly reading and writing the resonant frequency of the sensor, with a working frequency range of 1-6 GHz and an output power of 1-100 mW. The prepared intracranial pressure sensor 100 was placed on the test platform, and the test antenna of the VNA was coupled within a distance of 10 cm from the intracranial pressure sensor 100.

[0070] Subsequently, performance tests were carried out. The intracranial pressure sensor 100 was subjected to gradient pressure in the range of 0 kPa to 318 kPa by the push gauge. At each pressure point, the S11 parameter curve of the sensor was recorded using the vector network analyzer, and the resonant frequency point was determined, and the test results are shown in Figure 4 and Figure 5 .

[0071] The test results show that within the above pressure test range, the resonant frequency of the sensor increases linearly from 4.6 GHz when no pressure is applied to 4.75 GHz as the pressure increases, and the total resonant frequency offset (frequency deviation) reaches 150 MHz. By linear fitting analysis of the pressure-frequency data, the pressure sensing sensitivity of the sensor is as high as 0.47 MHz / kPa, and the linear correlation coefficient R 2 value reaches 0.96, indicating excellent linear response. At the same pressure point, the maximum deviation of the resonant frequency of the sensor is less than 0.5% in repeated measurements, showing good stability and repeatability, and the repeated measurement results of the sensor are shown in Figure 6 .

[0072] It is worth noting that the contents not elaborated in the present application are all prior art and are well known to those skilled in the art.

[0073] Therefore, the intracranial pressure sensor, monitoring system and method based on the open resonant ring structure described above are used. By combining the innovative IDC-SRR with the liquid metal microfluidic technology, the pressure change is efficiently converted into resonant frequency shift. Its passive, chipless and wireless characteristics, combined with the excellent biocompatibility of the material, make it particularly suitable for minimally invasive implantation and long-term continuous intracranial pressure monitoring.

[0074] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or equivalently replaced, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. An intracranial pressure sensor based on an open resonant ring structure, characterized in that, The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure.

2. The open resonant ring structure based intracranial pressure sensor of claim 1, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure.

3. The open resonant ring structure based intracranial pressure sensor of claim 1, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure.

4. The open resonant ring structure based intracranial pressure sensor of claim 1, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure.

5. The open resonant ring structure based intracranial pressure sensor of claim 1, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure.

6. The open resonant ring structure based intracranial pressure sensor of claim 1, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure.

7. The open resonant ring structure based intracranial pressure sensor of claim 1, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure.

8. An intracranial pressure monitoring system, characterized by The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. where S C represents the sensitivity coefficient of the capacitance to the pressure, L' represents the total length of the liquid column in the microfluidic channel, C offset represents the capacitance value under normal pressure.

9. The intracranial pressure monitoring system of claim 8, wherein, The application relates to an intracranial pressure sensor based on an open resonant ring structure.

10. A method of intracranial pressure monitoring, characterized in that, The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. The application relates to an intracranial pressure sensor based on an open resonant ring structure. 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