Flexible pressure sensor for intracranial pressure monitoring

Abstract

A flexible pressure sensor for intracranial pressure monitoring, comprising a pressure sensitive diaphragm, an upper inner electrode, a lower inner electrode, a flexible wrapping encapsulation layer, an upper outer electrode and a lower outer electrode, the upper and lower inner electrodes are respectively arranged on the upper and lower sides of the pressure sensitive diaphragm, the flexible wrapping encapsulation layer forms a sealed cavity in which the pressure sensitive diaphragm, the upper inner electrode and the lower inner electrode are wrapped, the upper and lower outer electrodes are respectively arranged on the upper and lower sides of the flexible wrapping encapsulation layer, the upper and lower parts of the flexible wrapping encapsulation layer are respectively provided with conductive holes, and the upper and lower inner electrodes are respectively connected to the upper and lower outer electrodes through the corresponding conductive holes; the outer surface of the flexible pressure sensor is covered with a layer of biocompatible material. The packaging structure design of the flexible pressure sensor has better biocompatibility and packaging conformability, and the device has high monitoring sensitivity and fast response speed.

Description

TECHNICAL FIELD

[0001] The present application relates to pressure sensors, in particular to a flexible pressure sensor that can be used for intracranial pressure monitoring. BACKGROUND

[0002] Most brain lesions such as intracranial hemorrhage, brain tumor, brain abscess, etc. can cause intracranial blood pressure changes, and the size of intracranial pressure is an important basis for doctors to make clinical diagnosis and propose accurate treatment plans. Monitoring of intracranial pressure can reflect the patient's condition to the doctor in a timely manner. However, intracranial pressure is different from atmospheric pressure and belongs to micro-pressure, which is not easy to monitor.

[0003] In actual clinical practice, there are generally four methods for monitoring intracranial pressure: (a) ventricle method (b) subdural space, subarachnoid space catheterization method (c) epidural method (d) lumbar puncture method. Among them, the ventricle method is the most accurate measurement method, has the highest accuracy and has been used since the earliest time, and has been called the "gold standard" for intracranial pressure monitoring. A catheter with a pressure detection sensor and a drainage device is implanted in the intracranial space of a patient, and intracranial decompression is achieved by using external ventricular drainage. However, most of the current pressure monitoring devices use silicon-based sensors, which have poor biocompatibility, general conformability when performing external encapsulation of the catheter, and high risk, which can easily cause intracranial infection of the patient and damage to the surrounding brain tissue. The processing precision of the pressure sensor used for intracranial pressure monitoring has high requirements, the cost is high, and there are certain difficulties in biological encapsulation.

[0004] It should be noted that the information disclosed in the above background section is only for understanding the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0005] The main purpose of the present application is to overcome the defects of the above background technology, and to provide a flexible pressure sensor that can be used for intracranial pressure monitoring.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

[0007] A flexible pressure sensor for intracranial pressure monitoring, comprising a pressure sensitive film, an upper inner electrode, a lower inner electrode, a flexible wrapping encapsulation layer, an upper outer electrode and a lower outer electrode, the upper inner electrode and the lower inner electrode are respectively arranged on the upper and lower sides of the pressure sensitive film, the flexible wrapping encapsulation layer forms a sealed cavity wrapping the pressure sensitive film, the upper inner electrode and the lower inner electrode, the upper outer electrode and the lower outer electrode are respectively arranged on the upper and lower sides of the flexible wrapping encapsulation layer, the upper and lower parts of the flexible wrapping encapsulation layer are respectively provided with conductive holes, the upper inner electrode is connected with the upper outer electrode through the conductive hole of the upper part of the flexible wrapping encapsulation layer, and the lower inner electrode is connected with the lower outer electrode through the conductive hole of the lower part of the flexible wrapping encapsulation layer; the outer surface of the flexible pressure sensor is covered with a biocompatible material layer.

[0008] Further,

[0009] The pressure sensitive film is a mixed material of polydimethylsiloxane (PDMS) and multi-walled carbon nanotubes (MWCNT).

[0010] The pressure sensitive film is obtained by fully mixing a dispersion liquid obtained by ultrasonic dispersion of multi-walled carbon nanotubes and a dispersion liquid obtained by ultrasonic dispersion of PDMS monomers, and adding a curing agent for curing.

[0011] The flexible wrapping encapsulation layer is made of FEP material.

[0012] The biocompatible material layer is poly-p-xylylene.

[0013] The upper surface of the pressure sensitive film is formed with an array of pyramid-shaped microstructure protrusions.

[0014] The outer surface of the pyramid-shaped microstructure is subjected to gold plating treatment.

[0015] The outer surface of the pyramid-shaped microstructure has a chromium plating layer and a gold plating layer covering the chromium plating layer.

[0016] The upper inner electrode, the lower inner electrode, the upper outer electrode and the lower outer electrode are copper foils, and the conductive holes are filled with conductive silver paste.

[0017] The flexible pressure sensor is encapsulated in a ring shape after being bent as a whole.

[0018] The present application has the following beneficial effects:

[0019] The present application provides a flexible pressure sensor which can be used for intracranial pressure monitoring, and the packaging structure design has high biocompatibility, is convenient to be placed on the inner wall or outer wall of a catheter, interacts gently with the surrounding tissue in the intracranial, and reduces the risk of infection and other injuries. As a flexible pressure monitoring device, it has better biocompatibility and packaging conformability compared with traditional pressure sensors. In a preferred scheme, a pressure sensitive film of a polydimethylsiloxane doped multi-walled carbon nanotube nanomaterial is used, and a pyramid-shaped microstructure is formed on the surface of the film, which can greatly improve the monitoring sensitivity of the device. In a further preferred scheme, gold plating treatment is further performed on the outer surface of the pyramid-shaped microstructure, which can improve the conductivity of the device, strengthen the contact conduction between the film and the inner electrode, and on the other hand, can reduce the viscoelasticity between the film and the electrode, and accelerate the response speed of the device. The present application can more efficiently, safely and accurately monitor the intracranial pressure of a patient, and is also beneficial to reduce the production difficulty of the intracranial pressure drainage catheter, and is convenient for the application of related implantable medical devices. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A preparation flowchart of the pressure sensitive film in an embodiment of the present application.

[0021] Figure 2 A schematic diagram of the pressure sensitive film with a pyramid microstructure in an embodiment of the present application.

[0022] Figure 3 A structure schematic diagram of the pressure sensitive film and the upper and lower layer inner electrodes in an embodiment of the present application.

[0023] Figure 4 A packaging cross-sectional schematic diagram of the flexible pressure sensor in an embodiment of the present application.

[0024] Figure 5 A schematic diagram of the flexible pressure sensor packaging in an embodiment of the present application is annular.

[0025] Figure 6 A characteristic diagram of the flexible pressure sensor in an embodiment of the present application in a low pressure area.

[0026] Figure 7 A minimum resolution and response time diagram of the flexible pressure sensor in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The embodiments of the present application are described in detail below. It should be emphasized that the following description is only exemplary, and is not intended to limit the scope of the present application and its applications.

[0028] It is to be noted that when an element is referred to as being "fixed" or "set" on another element, it can be directly on the other element or indirectly on the other element, with one or more intervening elements. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or indirectly connected to the other element, with one or more intervening elements. Additionally, connections can be for either a securing action or a coupling or communicating action.

[0029] It is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, specify relative positions or orientations based on the orientations or positions shown in the drawings, and are used for convenience of description and simplification of description only, and thus cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus cannot be understood as limiting the present application.

[0030] In addition, the terms "first", "second", "third", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0031] Referring to Figures 2 to 4 The embodiment of the present application provides a flexible pressure sensor which can be used for intracranial pressure monitoring, comprising a pressure sensitive film 5, an upper layer inner electrode 1, a lower layer inner electrode 6, a flexible wrapping packaging layer 4, an upper layer outer electrode 2 and a lower layer outer electrode 7, the upper layer inner electrode 1 and the lower layer inner electrode 6 are respectively arranged on the upper and lower sides of the pressure sensitive film 5, the flexible wrapping packaging layer 4 forms a sealed cavity in which the pressure sensitive film 5, the upper layer inner electrode 1 and the lower layer inner electrode 6 are wrapped, the upper layer outer electrode 2 and the lower layer outer electrode 7 are respectively arranged on the upper and lower sides of the flexible wrapping packaging layer 4, the upper part and the lower part of the flexible wrapping packaging layer 4 are respectively provided with conductive holes, the upper layer inner electrode 1 is connected to the upper layer outer electrode 2 through the conductive hole in the upper part of the flexible wrapping packaging layer 4, and the lower layer inner electrode 6 is connected to the lower layer outer electrode 7 through the conductive hole in the lower part of the flexible wrapping packaging layer 4; the outer surface of the flexible pressure sensor is covered with a biocompatible material layer.

[0032] In a preferred embodiment, the pressure sensitive film 5 is a mixed material of polydimethylsiloxane (PDMS) and multi-walled carbon nanotubes (MWCNT).

[0033] As Figure 1In the preparation process shown, in a preferred embodiment, the pressure-sensitive film 5 is obtained by mixing a dispersion liquid of multi-walled carbon nanotubes ultrasonically dispersed with a dispersion liquid of PDMS monomers ultrasonically dispersed, and adding a curing agent to cure.

[0034] In a preferred embodiment, the flexible wrapping encapsulation layer 4 is FEP material.

[0035] In a preferred embodiment, the biocompatible material layer is poly-p-xylylene.

[0036] Referring to Figures 2 to 4 In a preferred embodiment, the upper surface of the pressure-sensitive film 5 is formed with an array of protrusions of pyramid-shaped microstructures 51.

[0037] In a more preferred embodiment, the outer surface of the pyramid-shaped microstructure 51 is gold-plated.

[0038] In a more preferred embodiment, the outer surface of the pyramid-shaped microstructure has a chromium plating layer and a gold plating layer 3 covering the chromium plating layer.

[0039] The upper-layer inner electrode 1, the lower-layer inner electrode 6, the upper-layer outer electrode 2, and the lower-layer outer electrode 7 are copper foils, and the conductive holes are filled with conductive silver paste.

[0040] Referring to Figure 5 In an embodiment, the flexible pressure sensor is encapsulated in a ring shape after being bent as a whole.

[0041] Compared with conventional pressure sensors, the encapsulation structure design of the flexible pressure sensor for intracranial pressure monitoring provided by the embodiments of the present application has better biocompatibility and encapsulation conformability, is convenient to place on the inner wall or outer wall of a catheter, interacts gently with the surrounding tissues in the cranium, and reduces the risk of infection and other damage. In a preferred embodiment, the pressure-sensitive film of polydimethylsiloxane doped with multi-walled carbon nanotube nanomaterials, and the pyramid-shaped microstructures formed on the surface of the film, can greatly improve the monitoring sensitivity of the device. In a further preferred embodiment, the outer surface of the pyramid-shaped microstructure is gold-plated, which can improve the conductivity of the device, strengthen the contact and conduction between the film and the inner electrode, and reduce the viscoelastic properties between the film and the electrode, thereby accelerating the response speed of the device. The present application can more efficiently, safely, and accurately monitor the intracranial pressure of a patient, and is also beneficial to reducing the production difficulty of an intracranial pressure drainage catheter and facilitating the application of related implantable medical devices.

[0042] The specific embodiments of the present application are further described below.

[0043] The basic principle of the pressure monitoring device used in the present application is the piezoresistive effect. When the material detects pressure, it will cause the deformation of the device, thereby changing the resistance of the device, and converting it into a response to force. The materials used in the device are flexible materials, which have excellent bending and stretching properties, and have extremely high biocompatibility.

[0044] (1) Preparation of pressure sensitive material

[0045] PDMS (polydimethylsiloxane) has good biocompatibility, but it is an insulating material itself. In order to make it have good stable conductivity, multi-walled carbon nanotube conductive nanomaterial is added to PDMS. The dispersion liquid of multi-walled carbon nanotubes obtained by ultrasonic treatment of a cell crusher is mixed with the PDMS monomer dispersion liquid prepared by ultrasonic treatment, and a curing agent is added to form a conductive mixture, and finally a pressure sensitive material with conductivity is obtained. The preparation process of the pressure sensitive material is as shown in Figure 1

[0046] (2) Preparation of pressure sensitive film and its microstructure

[0047] In order to improve the sensitivity and monitoring range of the sensitive material, a pressure sensitive film with pyramid microstructure is prepared using the pressure sensitive material. When pressure acts on the pressure sensitive film, the deformation of the pyramid-shaped microstructure is the largest, and the change of the measured resistance value is also the most obvious, which improves the sensitivity of the sensor.

[0048] In preparation, first, a pyramid-shaped microstructure with a side length of 50 microns is etched on a silicon wafer using a wet etching technique, and the conductive mixture obtained in step (1) is poured on the silicon wafer with microstructure, and a conductive pressure sensitive film 5 with a thickness of 0.5 mm is prepared using a uniform glue machine, and the surface has a pyramid-shaped microstructure 51, as shown in Figure 2

[0049] As shown in Figure 3 , the pressure sensitive film 5 and the upper and lower two layers of inner electrodes 1, 6 form a "sandwich" structure, and the inner electrode is, for example, a 25 μm thick copper foil, and the middle layer is the pressure sensitive film 5. When pressure acts, the "sandwich" structure will bend, and the pressure sensitive film 5 in the middle layer will change greatly in resistance under the action of pressure, and the pressure value can be obtained by measuring the corresponding electrical signal.

[0050] (3) Microstructure surface treatment

[0051] ​​The outer surface of the pyramid-shaped microstructure 51 is gold-plated. Electron beam evaporation can be used. The gold-plating can improve the conductivity of the device and strengthen the contact between the thin film and the electrode. It can also reduce the viscoelasticity between the thin film and the inner electrode and accelerate the response speed of the device. Preferably, 10 nm of chromium is plated first, and then 50 nm of gold is plated, which can achieve better adhesion.

[0052] (4) Device packaging

[0053] The outer surface of the device is wrapped with FEP material to form a flexible wrapping encapsulation layer 4, which ensures that the device can work stably in a liquid environment and has good biocompatibility. The flexible wrapping encapsulation layer 4 of the FEP material also has good flexibility and a Young's modulus smaller than that of human muscle tissue, which will not scratch the muscle tissue. The "sandwich" structure is placed between the flexible wrapping encapsulation layers 4 of the FEP material, the flexible wrapping encapsulation layer 4 is excavated to form a circular through hole and filled with conductive silver paste 2, and the inner electrodes 1, 6 of the sensor are led out to the outside and connected to the outer electrodes 2, 7 (such as micron-level conductive copper adhesive tape) arranged on the outside of the flexible wrapping encapsulation layer 4. The FEP materials on both sides can be bonded together by using a hot press to form a sealed cavity, achieving the purpose of sealing the pressure-sensitive thin film 5 and the inner electrodes 1, 6. The packaging cross-sectional view is shown in Figure 4 .

[0054] A layer of parylene is deposited on the outer surface of the pressure sensor after overall encapsulation with FEP material, so that the entire device has good biocompatibility and can be implanted intracranially for pressure measurement. Parylene is a polymer with excellent performance, strong electrical insulation, chemical inertness, permeation resistance, and hydrolysis resistance, as well as good biocompatibility, making it an ideal biocompatible packaging material.

[0055] Since all the materials used are flexible, the overall encapsulated pressure sensor can be bent at a large angle. In one embodiment, the pressure sensor is packaged in a ring shape, as shown in Figure 5 , with a length of only 7 mm, which can be placed on the inner wall or outer wall of a medical rubber catheter as needed.

[0056] Actual index test

[0057] Linearity test:

[0058] Figure 6The flexible pressure sensor of the embodiment is shown in a low pressure area characteristic. In a clinical index, <2.00KPa is a normal physiological range, 2.00KPa-2.70KPa belongs to mild intracranial pressure increase, 2.70KPa-5.50KPa belongs to moderate intracranial pressure increase, and when the intracranial pressure changes more than 5.50KPa, it belongs to moderate intracranial pressure increase, which needs emergency treatment of a clinician. According to this standard test device of the application, it can be seen from Figure Five that the device has good linear monitoring characteristics within 0-10KPa, which meets the use requirements of the intracranial pressure monitoring device.

[0059] Response characteristics and pressure resolution:

[0060] Figure 7 The minimum resolution and response time of the flexible pressure sensor of the embodiment are shown. The response characteristics of the device are detected by a weight removal experiment. A button cell with a weight of 2.03g (bottom diameter of 11.52mm) is placed, and the flexible pressure sensor can obviously perceive, and the calculated pressure value is about 195Pa. According to the existing clinical medical detection judgment intracranial pressure increase standard, it can meet the monitoring standard. At the same time, the pressure response time of the flexible pressure sensor is checked. The LCR bridge is used to test in the MED (sampling time is 90ms) mode, and the response time of the sensor is less than 200ms, which can fully meet the medical measurement conditions.

[0061] The flexible pressure sensor for intracranial pressure measurement of the application has better biological interaction characteristics than the traditional silicon-based pressure sensor, and is safer in the application of intracranial (implantable) pressure monitoring instruments. The packaging structure design of the flexible sensor solves the application problem of the implantable flexible device, and can be conformable according to the different shape requirements of the instrument. It is convenient, simple and easy to batch process, and has a broad prospect in the field of micro devices, and has great advantages in the field of medical instruments. The flexible device application scheme proposed in the application can greatly improve the utilization rate of micro flexible devices, facilitate integration, and can also be applied to various implantable medical instruments.

[0062] The background part of the application can include background information about the problems or environment of the application, and is not necessarily a description of the prior art. Therefore, the content included in the background art part is not an admission by the applicant of the prior art.

[0063] The above further describes the present application in conjunction with specific / preferred embodiments, and cannot be deemed to limit the specific implementation of the present application to these descriptions. For those skilled in the art to which the present application belongs, without departing from the concept of the present application, they can make several substitutions or variations to the described embodiments, and these substitutions or variations shall be deemed to fall within the protection scope of the present application. In the description of the present application, the description of the terms "an embodiment", "some embodiments", "a preferred embodiment", "an example", "a specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the case of no mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples. Although the embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A flexible pressure sensor for intracranial pressure monitoring, characterized in that, The device comprises a pressure-sensitive film, an upper inner electrode, a lower inner electrode, a flexible encapsulation layer, an upper outer electrode, and a lower outer electrode. The pressure-sensitive film is a hybrid material of polydimethylsiloxane (PDMS) and multi-walled carbon nanotubes (MWCNTs). A pyramidal array of microstructures is formed on the upper surface of the pressure-sensitive film. The upper and lower inner electrodes are respectively disposed on the upper and lower sides of the pressure-sensitive film. The flexible encapsulation layer forms a sealed cavity encapsulating the pressure-sensitive film, the upper inner electrode, and the lower inner electrode. The upper and lower outer electrodes are respectively disposed on the upper and lower sides of the flexible encapsulation layer. Conductive holes are provided in the upper and lower parts of the flexible encapsulation layer. The upper inner electrode is connected to the upper outer electrode through the conductive holes in the upper part of the flexible encapsulation layer, and the lower inner electrode is connected to the lower outer electrode through the conductive holes in the lower part of the flexible encapsulation layer. The flexible pressure sensor is bent and encapsulated into a ring shape, with its outer surface covered by a biocompatible material layer.

2. The flexible pressure sensor as described in claim 1, characterized in that, The pressure-sensitive film is obtained by thoroughly mixing a dispersion of multi-walled carbon nanotubes obtained by ultrasonic dispersion with a dispersion of PDMS monomers obtained by ultrasonic dispersion, and then adding a curing agent for curing.

3. The flexible pressure sensor as described in any one of claims 1 to 2, characterized in that, The flexible encapsulation layer is made of FEP material.

4. The flexible pressure sensor as described in any one of claims 1 to 2, characterized in that, The biocompatible material layer is parylene.

5. The flexible pressure sensor as described in any one of claims 1 to 2, characterized in that, The outer surface of the pyramid-shaped microstructure was gold-plated.

6. The flexible pressure sensor as described in claim 5, characterized in that, The outer surface of the pyramid-shaped microstructure has a chromium plating layer and a gold plating layer covering the chromium plating layer.

7. The flexible pressure sensor as described in any one of claims 1 to 2, characterized in that, The upper inner electrode, the lower inner electrode, the upper outer electrode, and the lower outer electrode are all made of copper foil, and the conductive holes are filled with conductive silver paste.

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