Composite piezoelectric negative pressure dressing and preparation method thereof

Abstract

The invention relates to a composite piezoelectric negative pressure dressing and a preparation method thereof, and belongs to the field of medical dressings. The preparation method comprises the following steps: S1, dissolving collagen in acetic acid to obtain a collagen solution, and carrying out a freeze-drying process to obtain collagen sponge; s2, PVDF powder and ZnO nanoparticles are dissolved in an organic solvent, and a PVDF / ZnO solution is obtained; s3, placing an injector filled with the PVDF / ZnO solution in an electrostatic spinning machine, fixing the collagen sponge on a collecting wheel of the electrostatic spinning machine, and covering the collagen sponge with the PVDF / ZnO nanofibers through an electrostatic spinning method to form a composite piezoelectric dressing; s4, covering the top layer of the composite piezoelectric dressing with a semi-permeable membrane, and meanwhile, connecting a drainage tube to form a negative pressure system, so as to obtain the composite piezoelectric negative pressure dressing. The composite material disclosed by the invention has good biocompatibility. The response of the nanofiber membrane is more sensitive, and the controllable negative pressure strength enables the nanofiber membrane to have excellent stability and more excellent piezoelectric property.

Description

Technical Field

[0001] The invention relates to the field of medical dressings, and more specifically to a composite piezoelectric negative pressure dressing and a preparation method thereof. Background Art

[0002] The skin is the first line of defense for the human body, protecting human health and preventing the invasion of pathogens. After traumatic injury, exogenous infection, diabetic ulcer or surgery, the skin's self-healing ability is severely impaired, accompanied by heavy bleeding and exudate, requiring ideal wound dressings for timely wound management to avoid prolonged exposure of the wound.

[0003] The wound healing process includes four stages: hemostasis, inflammation, proliferation, and remodeling. The hemostasis stage is the first stage of wound healing, and it is necessary to reduce blood loss as much as possible and maintain blood supply to the wound. The inflammatory stage is based on the release of vascular endothelial growth factor and other factors at the wound during the hemostasis stage, which recruits a large number of neutrophils and lymphocytes, causing an inflammatory response. Neutrophils and lymphocytes can clear pathogens and release tumor necrosis factor and interleukin-6 at the same time. The third stage is the proliferation stage, during which a large number of growth factors are released at the wound to promote angiogenesis, collagen deposition, elastin synthesis, cell migration and proliferation, and granulation tissue formation. In the final remodeling stage, capillaries degenerate, macrophages apoptosis, wound scar formation, and the tensile strength of the wound increases.

[0004] During wound treatment, wound dressings cover the damaged area to maintain a moist wound environment and appropriate body temperature, provide physical protection and prevent microbial invasion, and relieve pain. Ideal wound dressings need to have good biocompatibility and antibacterial ability to avoid excessive inflammatory response in chronic wounds. Common wound dressings include film dressings, hydrogel dressings, foam dressings, and bioprotein sponges. Collagen is an important component of the extracellular matrix and is essential for wound closure and tissue integrity. Common chronic wounds such as diabetic foot ulcers are prone to produce a large amount of exudate. Negative pressure drainage technology can be used to remove effusion and necrosis in the tissue to prevent the spread of infection. Controllable negative pressure intensity can maintain blood circulation, promote granulation tissue regeneration, and accelerate the wound healing rate.

[0005] The piezoelectric effect is a phenomenon in which the crystal structure of a material changes due to external mechanical pressure or tension in the absence of an external electric field, the charge center in the crystal structure shifts, a molecular dipole moment is generated, and an electric potential difference is generated. PVDF is one of the most common piezoelectric polymers and has good biocompatibility. Its crystal structure has a great influence on its piezoelectric properties, among which the β phase can produce excellent piezoelectric properties. The high voltage electric field during the electrospinning process can promote the formation of the β phase in the PVDF solution to enhance its piezoelectric ability. Composite ZnO nanoparticles have a certain antibacterial effect while enhancing the piezoelectric response. Under the action of the negative pressure system, the composite piezoelectric film can generate sustainable piezoelectric voltage and current when under pressure, and the generated bioelectric stimulation signal can trigger a cascade reaction, promote cell proliferation and migration, orderly collagen deposition, angiogenesis, and upregulate the expression of various growth factors related to wound healing.

[0006] In the prior art, the patent with application number 202110499780.9 and publication date May 8, 2021, and the invention name "A wound dressing based on piezoelectric effect and its preparation method" discloses a wound dressing based on piezoelectric effect and its preparation method. In this technical solution, packaging materials, electrodes, piezoelectric materials, substrates and adhesives are combined together, and electrodes are sputtered on the surface of the piezoelectric material to obtain a wound dressing with electrodes. When the human body moves, the piezoelectric material generates electric charges that act on the wound to achieve electrical stimulation, promote the proliferation of fibroblasts, etc., and shorten the healing time. However, the method of generating electric charges through human body movement may cause unstable electrical stimulation during use, and the wound healing effect is limited.

[0007] Therefore, designing a negative pressure dressing that can provide a template and has antibacterial and stable piezoelectric response has good application prospects and needs to be studied urgently. Summary of the invention

[0008] In view of the problems existing in the prior art, the purpose of the present invention is to provide a collagen sponge template for the regeneration of new tissue. The surface of the collagen sponge is covered with a PVDF / ZnO nanofiber membrane, so that the composite collagen sponge can produce a piezoelectric effect, and also gives the collagen sponge antibacterial properties. At the same time, the controllable negative pressure value makes the piezoelectric effect more stable. The piezoelectric effect causes a cascade reaction in the wound site, promotes cell proliferation and migration, and orderly deposits collagen, thereby improving the wound healing rate.

[0009] In order to solve the above problems, the present invention proposes a composite piezoelectric negative pressure dressing and a preparation method thereof. The technical solution of the present invention is as follows:

[0010] On one hand, the present invention provides a composite piezoelectric negative pressure dressing, which is composed of a PVDF / ZnO nanofiber piezoelectric film, a collagen sponge layer and a negative pressure drainage layer.

[0011] Another aspect of the present invention provides a method for preparing a composite piezoelectric negative pressure dressing, comprising the following steps:

[0012] S1. Preparation of collagen sponge: dissolving collagen in an acetic acid solution to obtain a collagen solution; pre-freezing at -60°C to -80°C for 12 to 24 hours, freeze-drying in a freeze dryer for 40 to 72 hours, and performing vacuum heat cross-linking treatment to obtain the collagen sponge;

[0013] S2. Preparation method of PVDF / ZnO solution: PVDF powder and ZnO nanoparticles are added simultaneously into a beaker containing one or more organic solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, acetone and tetrahydrofuran, the obtained mixed solution is sealed, subjected to strong ultrasonic stirring for 30 to 60 minutes, and then placed in a water bath at 40°C to 60°C and subjected to magnetic stirring for 4 to 12 hours to obtain a uniform PVDF / ZnO spinning solution;

[0014] S3. Preparation method of composite piezoelectric dressing: fix the collagen sponge on the collecting wheel of the electrospinning machine, and cover the PVDF / ZnO nanofibers on the collagen sponge by electrospinning to form a composite piezoelectric dressing;

[0015] S4. Cover the top layer of the composite piezoelectric dressing with a semipermeable membrane and connect the drainage tube to form a negative pressure system to obtain a composite piezoelectric negative pressure dressing.

[0016] Furthermore, the porosity of the collagen sponge layer is 60% to 90%, and the pore size is 50 to 200 μm; the porosity of the PVDF / ZnO nanofiber piezoelectric membrane is 50% to 80%, and the pore size is 20 to 150 μm.

[0017] Furthermore, in step S1, the collagen is derived from one of pig tendon, bovine Achilles tendon and fish skin, the molecular weight of the collagen is 100-550 kDa, the collagen mass fraction is 0.5%-10%, and the acetic acid concentration is 0.5%-5% of the collagen solution.

[0018] Furthermore, in step S1, the cross-linking temperature of the collagen sponge is 95 to 130° C., and the cross-linking time is 24 to 48 hours.

[0019] Furthermore, in step S1, the thickness of the collagen sponge is 1 to 15 mm.

[0020] Furthermore, in step S2, the mass fraction of PVDF powder is 5% to 30%, the mass fraction of ZnO nanoparticles is 5% to 20% of the mass fraction of PVDF powder, and the particle size is 20 to 150 nm.

[0021] Furthermore, in step S2, the thickness of the PVDF / ZnO nanofiber membrane is 0.5 to 5 mm.

[0022] Furthermore, in step S3, the needle diameter is 0.15 mm to 1 mm, the spinning solution ejection speed is 0.5 mL / h to 10 mL / h, the collector is a rotatable and grounded wheel with a rotation speed of 50 r / min to 800 r / min, and a voltage of 10 kV to 30 kV is connected to the spinning head.

[0023] Furthermore, in step S4, the negative pressure value is -80 to -120 mmHg, the negative pressure working time is 2 to 8 minutes, and the stop working time is 1 to 5 minutes.

[0024] Technical effects and advantages of the present invention:

[0025] 1. A composite piezoelectric negative pressure dressing prepared by the present invention, wherein the collagen sponge layer can stimulate the wound site to recruit fibroblasts, etc., provide a template for the regeneration of new tissue, and can provide a buffering effect for the wound site; the collagen sponge is softer in texture and can evenly transmit the negative pressure to the wound surface; the composite PVDF nanofiber membrane has good biocompatibility and piezoelectric properties, and doping with ZnO can enhance the piezoelectric properties while having a certain antibacterial effect, so the composite piezoelectric dressing has good biocompatibility.

[0026] 2. A composite piezoelectric negative pressure dressing prepared by the present invention generates a piezoelectric effect in the PVDF / ZnO nanofiber piezoelectric film by means of negative pressure. When the nanofiber film is subjected to pressure, it can produce a greater degree of deformation, making the nanofiber film more sensitive to response. The controllable negative pressure strength makes it have excellent stability and better piezoelectric performance. At the same time, the high-speed rotating collection wheel is conducive to the orientation of the fibers. The high orientation of the fibers will cause the orientation of the β phase, thereby generating a higher piezoelectric response. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the preparation process of the composite piezoelectric dressing provided by the present invention;

[0028] Figure 2 A schematic diagram of the structure of the composite piezoelectric negative pressure dressing provided by the present invention;

[0029] Figure 3 The piezoelectric curves of the composite piezoelectric dressings at different ZnO contents;

[0030] Figure 4 The positive peak voltage diagram of the composite piezoelectric dressing at different ZnO contents;

[0031] The reference numerals are as follows: 1. semipermeable membrane; 2. PVDF / ZnO nanofiber piezoelectric membrane; 3. collagen sponge layer. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0034] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0035] See also Figure 1 to Figure 2 As shown, the present invention provides a composite piezoelectric negative pressure dressing and a preparation method thereof, comprising the following steps:

[0036] A composite piezoelectric negative pressure dressing and a preparation method thereof, characterized in that the composite piezoelectric dressing consists of a PVDF / ZnO nanofiber piezoelectric film, a collagen sponge layer and a negative pressure drainage layer.

[0037] A composite piezoelectric negative pressure dressing and a preparation method thereof, characterized in that the steps include:

[0038] S1. Preparation of collagen sponge: dissolving collagen in an acetic acid solution to obtain a collagen solution; pre-freezing at -60°C to -80°C for 12 to 24 hours, freeze-drying in a freeze dryer for 40 to 72 hours, and performing vacuum heat cross-linking treatment to obtain the collagen sponge;

[0039] S2. Preparation method of PVDF / ZnO solution: PVDF powder and ZnO nanoparticles are added simultaneously into a beaker containing one or more organic solvents selected from N-dimethylformamide, N,N-dimethylacetamide, acetone and tetrahydrofuran, the mixed solution is sealed, subjected to strong ultrasonic stirring for 30 to 60 minutes, and then placed in a water bath at 40°C to 60°C and subjected to magnetic stirring for 4 to 12 hours to obtain a uniform PVDF / ZnO spinning solution;

[0040] S3. Preparation method of composite piezoelectric dressing: fix the collagen sponge on the collecting wheel of the electrospinning machine, and cover the PVDF / ZnO nanofibers on the collagen sponge by electrospinning to form a composite piezoelectric dressing;

[0041] S4. Cover the top layer of the composite piezoelectric dressing with a semipermeable membrane and connect the drainage tube to form a negative pressure system to obtain a composite piezoelectric negative pressure dressing.

[0042] Preferably, the porosity of the collagen sponge layer is 60% to 90%, and the pore size is 50 to 200 μm; the porosity of the PVDF / ZnO nanofiber piezoelectric membrane is 50% to 80%, and the pore size is 20 to 150 μm.

[0043] Preferably, in step S1, the collagen is derived from one of pig tendon, bovine Achilles tendon and fish skin, the molecular weight of the collagen is 100-550 kDa, the collagen mass fraction is 0.5%-10%, and the acetic acid concentration is 0.5%-5% of the collagen solution.

[0044] Preferably, in step S1, the cross-linking temperature of the collagen sponge is 95 to 130° C., and the cross-linking time is 24 to 48 hours.

[0045] Preferably, the thickness of the collagen sponge in step S1 is 1 to 15 mm. If the thickness of the collagen sponge is too small, the buffering effect is not obvious; if the thickness of the collagen sponge exceeds 15 mm, the electrostatic spinning effect on its surface is not good.

[0046] Preferably, in step S2, the mass fraction of PVDF powder is 5% to 30%, the mass fraction of ZnO nanoparticles is 5% to 20% of the mass fraction of PVDF powder, and the particle size is 20 to 150 nm. If the mass fraction of PVDF is lower than 5%, the solution viscosity is too small, the electric field force on the spinning solution is much greater than the surface tension, and the fiber is too thin; if the mass fraction of PVDF is higher than 30%, the solution viscosity is too large, it is easy to clog the needle, which is not conducive to the formation of fibers during electrospinning; if the mass fraction of ZnO nanoparticles is greater than 20%, it is not conducive to the formation of β phase in PVDF fiber, thereby affecting the piezoelectric response.

[0047] Preferably, in step S2, the thickness of the PVDF / ZnO nanofiber membrane is 0.5-5 mm. If the thickness of the nanofiber is too small, the piezoelectric response is weak.

[0048] Preferably, in step S3, the needle diameter is 0.15 mm to 1 mm, the spinning solution ejection speed is 0.5 mL / h to 10 mL / h, the collector is a rotatable and grounded wheel with a rotation speed of 50 r / min to 800 r / min, and a voltage of 10 kV to 30 kV is connected to the spinning head. The collector has a high rotation speed and good fiber orientation; when the voltage value is lower than 10 kV or higher than 30 kV, fibers cannot be formed.

[0049] Preferably, in step S4, the negative pressure value is -80 to -120 mmHg, the negative pressure working time is 2 to 8 minutes, and the stop working time is 1 to 5 minutes. When the negative pressure value is too low, it is not conducive to local blood circulation; when the negative pressure value is too high, it will cause tissue ischemia; at the same time, the intermittent negative pressure working mode can promote blood circulation and granulation tissue regeneration in the wound site.

[0050] The following is a further description of a composite piezoelectric negative pressure dressing and a preparation method thereof according to the present invention in conjunction with specific embodiments:

[0051] Example 1

[0052] This embodiment prepares a composite piezoelectric negative pressure dressing and a preparation method thereof, comprising the following steps:

[0053] S1. Preparation of collagen sponge: dissolving collagen in acetic acid solution to obtain collagen solution; pre-freezing at -60°C for 12 hours, freeze drying in a freeze dryer for 40 hours, and performing vacuum heat cross-linking treatment to obtain the collagen sponge;

[0054] S2. Preparation method of PVDF / ZnO solution: PVDF powder and ZnO nanoparticles are added to a mixed organic solvent of N,N-dimethylformamide / acetone at the same time, the obtained mixed solution is sealed, subjected to strong ultrasonic stirring for 30 minutes, and then placed in a 40° C. water bath for magnetic stirring for 4 hours to obtain a uniform PVDF / ZnO spinning solution;

[0055] S3. Preparation method of composite piezoelectric dressing: fix the collagen sponge on the collecting wheel of the electrospinning machine, and cover the PVDF / ZnO nanofibers on the collagen sponge by electrospinning to form a composite piezoelectric dressing;

[0056] S4. Cover the top layer of the composite piezoelectric dressing with a semipermeable membrane and connect the drainage tube to form a negative pressure system to obtain a composite piezoelectric negative pressure dressing.

[0057] Wherein, collagen is derived from pig tendon, the molecular weight of collagen is 100kDa, the mass fraction of collagen is 5%, and the concentration of acetic acid is 0.5% of the collagen solution. In step S1, the cross-linking temperature of the collagen sponge is 105°C, and the cross-linking time is 24h. In step S1, the thickness of the collagen sponge is 5mm. In step S2, the mass fraction of PVDF powder is 10%, and in step S2, the thickness of the PVDF / ZnO nanofiber membrane is 1mm.

[0058] In step S3, the needle diameter is 0.6 mm, the spinning solution ejection speed is 0.5 mL / h, the collector is a rotatable and grounded wheel with a rotation speed of 800 r / min, and a voltage of 15 kV is connected to the spinning head.

[0059] The schematic diagram of the composite piezoelectric dressing structure prepared in this embodiment is as follows: Figure 2 As shown, the composite piezoelectric dressing is placed on a test platform, and the two poles of the composite piezoelectric dressing are connected to an oscilloscope. The positive probe of the oscilloscope is connected to the upper pole of the dressing, and the grounding probe is connected to the lower pole of the dressing. Directly above the composite piezoelectric dressing is a catheter, which is fixed by an iron frame. The oscilloscope is used to record the potential difference between the two poles of the composite piezoelectric dressing during the impact of the small ball, that is, the open circuit voltage of the composite piezoelectric dressing. The composite piezoelectric dressing prepared in Example 1 of the present application was tested. When the mass fraction of ZnO was 0%, the positive peak voltage value of the composite piezoelectric dressing was 3.28V.

[0060] Examples 2 to 5

[0061] The difference between Examples 2 to 5 and Example 1 is that in step S2, the mass fraction of ZnO nanoparticles is different, and the other steps are basically the same as Example 1, which will not be repeated here. The different settings of the ZnO mass fraction of Examples 1 to 5 are shown in Table 1. The thickness of the piezoelectric nanofiber membrane prepared by the PVDF spinning solution containing ZnO mass fractions of 0%, 5%, 10%, 15% and 20% is within 1±0.1mm, and the positive peak voltage value of the prepared composite piezoelectric dressing is shown in the following table.

[0062] Table 1 The mass fraction of ZnO nanoparticles in Examples 1 to 5 and the positive peak voltage values ​​of the composite piezoelectric dressings prepared under the corresponding conditions

[0063] project Mass fraction of ZnO nanoparticles (%) Positive peak voltage(V) Example 1 0 3.28 Example 2 5 4.24 Example 3 10 8.6 Example 4 15 2.36 Example 5 20 1.44

[0064] In summary, the present invention proposes a composite piezoelectric negative pressure dressing and a preparation method thereof, by preparing a porous collagen sponge, and then covering the surface thereof with a PVDF / ZnO nanofiber membrane. Among them, the collagen sponge is used as a template, and the PVDF / ZnO nanofiber membrane is covered on the surface of the collagen sponge through an electrostatic spinning process to form a composite piezoelectric dressing. A semipermeable membrane is attached to the surface of the prepared composite piezoelectric dressing, and a drainage tube is connected at the same time to form a negative pressure system. By combining electrospinning with negative pressure drainage, the liquid absorption of the piezoelectric dressing is improved, the exudate of chronic wounds is reduced, and the inflammatory response is alleviated, which effectively solves the problem of chronic wounds being difficult to heal caused by the unstable piezoelectric effect and poor absorption of exudate in the piezoelectric dressing prepared by the prior art; the high-speed rotation of the collecting wheel during electrospinning is conducive to the high orientation of the fibers, promotes the formation of the β phase, and enhances the piezoelectric effect. In the above process, by adjusting the thickness of the collagen film, the voltage of the electrospinning, the negative pressure value of the negative pressure drainage and other parameter conditions during the preparation process, a composite piezoelectric negative pressure dressing with stable piezoelectric effect, the ability to stimulate cell migration and proliferation, promote collagen deposition and have antibacterial effect can be obtained.

[0065] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A composite piezoelectric negative pressure dressing, characterized in that: The composite piezoelectric dressing consists of a PVDF / ZnO nanofiber piezoelectric film, a collagen sponge layer and a negative pressure drainage layer.

2. A method for preparing a composite piezoelectric negative pressure dressing, characterized in that: The steps include: S1. Preparation of collagen sponge: dissolving collagen in an acetic acid solution to obtain a collagen solution; pre-freezing at -60°C to -80°C for 12 to 24 hours, freeze-drying in a freeze dryer for 40 to 72 hours, and performing vacuum heat cross-linking treatment to obtain the collagen sponge; S2. Preparation method of PVDF / ZnO solution: PVDF powder and ZnO nanoparticles are added simultaneously into a beaker containing one or more organic solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, acetone and tetrahydrofuran, the obtained mixed solution is sealed, subjected to strong ultrasonic stirring for 30 to 60 minutes, and then placed in a water bath at 40°C to 60°C and subjected to magnetic stirring for 4 to 12 hours to obtain a uniform PVDF / ZnO spinning solution; S3. Preparation method of composite piezoelectric dressing: fix the collagen sponge on the collecting wheel of the electrospinning machine, and cover the PVDF / ZnO nanofibers on the collagen sponge by electrospinning to form a composite piezoelectric dressing; S4. Cover the top layer of the composite piezoelectric dressing with a semipermeable membrane and connect the drainage tube to form a negative pressure system to obtain a composite piezoelectric negative pressure dressing.

3. The method for preparing a composite piezoelectric negative pressure dressing according to claim 1, characterized in that: The porosity of the collagen sponge layer is 60% to 90%, and the pore size is 50 to 200 μm; the porosity of the PVDF / ZnO nanofiber piezoelectric film is 50% to 80%, and the pore size is 20 to 150 μm.

4. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In step S1, the collagen is derived from one of pig tendon, bovine Achilles tendon and fish skin, the molecular weight of the collagen is 100-550 kDa, the collagen mass fraction is 0.5%-10%, and the acetic acid concentration is 0.5%-5% of the collagen solution.

5. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In the step S1, the cross-linking temperature of the collagen sponge is 95 to 130° C., and the cross-linking time is 24 to 48 hours.

6. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In the step S1, the thickness of the collagen sponge is 1 to 15 mm.

7. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In the step S2, the mass fraction of PVDF powder is 5%-30%, the mass fraction of ZnO nanoparticles is 5%-20% of the mass fraction of PVDF powder, and the particle size is 20-150 nm.

8. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In the step S2, the thickness of the PVDF / ZnO nanofiber membrane is 0.5-5 mm.

9. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In step S3, the needle diameter is 0.15 mm to 1 mm, the spinning solution ejection speed is 0.5 mL / h to 10 mL / h, the collector is a rotatable and grounded wheel with a rotation speed of 50 r / min to 800 r / min, and a voltage of 10 kV to 30 kV is connected to the spinning head.

10. The method for preparing a composite piezoelectric negative pressure dressing according to claim 2, characterized in that: In step S4, the negative pressure value is -80 to -120 mmHg, the negative pressure working time is 2 to 8 minutes, and the stop working time is 1 to 5 minutes.

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