Medical device

Abstract

This guide wire 10 (medical device) comprises a long core 1, cylindrical bodies 2 provided on the outer side of the core 1, a hydrophilic coat layer 61 formed of a first coating material and disposed on the outer peripheral surface of the cylindrical bodies 2, and a hydrophobic coat layer 62 formed of a second coating material and disposed on the radially outer side the hydrophilic coat layer 61. The hydrophilic coat layer 61 is configured to be capable of absorbing water. In the presence of a liquid, the hydrophilic coat layer 61 swells and is exposed on the outer surface of the hydrophobic coat layer 62. Such a guide wire 10 has good operability despite having a simple structure.

Description

medical devices

[0001] The present disclosure relates to medical devices.

[0002] Conventionally, medical devices such as guidewires have been used to guide catheter-like medical instruments inserted into tubular organs of the human body, such as blood vessels and digestive organs, to target sites. Guidewires are inserted into internal lumens from the outer surface of the body and are used by inserting them to the target site in order to guide a combined device, such as a catheter or an intracorporeal indwelling device, to the target site within the lumen. Because the internal lumen from the outer surface to the target site is often bent or branched, guidewires are required to have sufficient lubricity to smoothly advance within the lumen and sufficient rotational tracking ability to sensitively respond to the operator's manipulation.

[0003] A guidewire is known that improves lubricity and ensures rotational followability by coating the outer surface of the guidewire with a hydrophilic resin that reduces the coefficient of dynamic friction. For example, Patent Document 1 discloses that a hydrophilic coating layer is formed on the outer surface of a guidewire that includes a metal core wire and a coil body.

[0004] Special Publication No. 2003-500116

[0005] If a hydrophilic coating layer is formed on the outer surface of the guidewire as in Patent Document 1, the outer surface of the guidewire becomes sticky when used in combination with a therapeutic device such as a catheter or intracorporeal indwelling device in a location where the surrounding moisture decreases, such as a bent portion of a blood vessel. Because there is a concern that such a sticky outer surface may affect operability, there is a demand for a guidewire with surface properties that provide better operability with a simple structure.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a medical device that has a simple structure but is easy to operate.

[0007] In order to achieve the above object, the present disclosure provides a medical device (Disclosure 1) comprising an elongated core, a cylindrical body provided on the outside of the core, a hydrophilic coating layer formed of a first coating material and disposed on the outer surface of the cylindrical body, and a hydrophobic coating layer formed of a second coating material and disposed radially outside the hydrophilic coating layer, wherein the hydrophilic coating layer is configured to be water-absorbent.

[0008] According to this disclosure (Disclosure 1), by disposing a hydrophobic coating layer on the outside of the hydrophilic coating layer, the outer surface of the medical device is prevented from becoming sticky even when the surrounding moisture decreases due to the presence of a concomitant device, etc., and the static friction coefficient is reduced. On the other hand, by configuring the hydrophilic coating layer to be water-absorbent, liquid reaches the inside of the hydrophobic coating layer from the outer surface, causing the hydrophilic coating layer to swell and improve the hydrophilicity of the outer surface of the medical device, thereby realizing a medical device with good operability despite its simple structure.

[0009] In the above disclosure (Disclosure 1), an opening communicating with the outer surface of the hydrophilic coating layer may be formed in the hydrophobic coating layer (Disclosure 2).

[0010] According to this disclosure (Disclosure 2), a liquid is supplied to the hydrophilic coating layer through the opening, causing the hydrophilic coating layer to swell. The hydrophilic coating layer swelled by the supplied liquid is exposed to the outside of the hydrophobic coating layer through the opening, thereby improving the hydrophilicity of the outer surface of the medical device.

[0011] In the above disclosures (Disclosures 1 and 2), it is preferable that the hydrophilic coating layer swells and is exposed on the outer surface of the hydrophobic coating layer in the presence of a liquid (Disclosure 3).

[0012] In the above disclosure (Disclosure 1), an intermediate layer formed of the first coating material and the second coating material may be provided between the hydrophilic coating layer and the hydrophobic coating layer (Disclosure 4).

[0013] According to this disclosure (Disclosure 4), the hydrophilic coating layer is configured to be water-absorbent, so that liquid reaches the inside of the hydrophobic coating layer from the outer surface, and the intermediate layer containing components of the first coating material, which is a hydrophilic coating material, and the hydrophilic coating layer swell, improving the hydrophilicity of the outer surface of the medical device, thereby realizing a medical device that is easy to operate despite its simple structure.

[0014] In the above disclosures (Disclosures 1 and 4), the second coating material may contain one or more polar solvents selected from the group consisting of lower chain alcohols, lower alkyl ethers, acetone, halogen-containing solvents, and lower alkylamines (Disclosure 5).

[0015] According to this disclosure (Disclosure 5), after coating a hydrophilic coating layer, in the process of coating a hydrophobic coating layer on the outer peripheral surface of the hydrophilic coating, the polar solvent contained in the hydrophobic coating layer partially dissolves the outer surface of the hydrophilic coating layer and becomes compatible with a part of the hydrophobic coating layer, thereby intentionally forming an intermediate layer.

[0016] In the above disclosures (Disclosures 4 and 5), an opening communicating with the outer surface of the intermediate layer may be formed in the hydrophobic coating layer (Disclosure 6).

[0017] According to this disclosure (Disclosure 6), a liquid is supplied to the intermediate layer through the opening, or to the hydrophilic coating layer via the intermediate layer, causing the intermediate layer and the hydrophilic coating layer to swell. Furthermore, the intermediate layer and the hydrophilic coating layer swelled by the supplied liquid are exposed to the outside of the hydrophobic coating layer through the opening, thereby improving the hydrophilicity of the outer surface of the medical device.

[0018] In the above disclosures (Disclosures 4 and 5), it is preferable that at least one of the intermediate layer and the hydrophilic coating layer swell and be exposed on the outer surface of the hydrophobic coating layer in the presence of a liquid (Disclosure 7).

[0019] According to the present disclosure, it is possible to provide a medical device that has a simple structure and good operability.

[0020] While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments and is not to be limited to the disclosed exemplary embodiments.

[0021] A guidewire 10 according to an embodiment of the present disclosure will be described below with reference to the drawings. The guidewire 10 is an example of a medical device according to the present disclosure and is used when inserting a combined device such as a catheter or an intracorporeal indwelling device into a blood vessel, digestive organ, or the like. The distal end of the guidewire 10 is the side that is inserted into the body, and the proximal end of the guidewire 10 is the side that is manipulated by a surgeon such as a doctor. The present disclosure is not limited to the embodiments described below, and the described embodiments are merely examples for illustrating the technical features of the present disclosure. The shapes and dimensions shown in the drawings are shown solely to facilitate understanding of the contents of the present disclosure and do not accurately reflect the actual shapes and dimensions. The present disclosure can also be applied to medical devices other than guidewires.

[0022] As used herein, the term "distal side" refers to the axial direction of the guidewire, in which the guidewire advances toward the target site. The term "proximal side" refers to the axial direction of the guidewire, in the opposite direction from the distal side. The term "distal" refers to the distal end of any component or component, and the term "proximal end" refers to the proximal end of any component or component. The term "distal portion" refers to the portion of any component or component that includes the distal end and extends from the distal end toward the proximal end to the middle of the component, and the term "proximal end" refers to the portion of any component or component that includes the proximal end and extends from the proximal end toward the distal end to the middle of the component. In FIG. 1 , the left side of the illustration is the "distal side" that is inserted into the body, and the right side is the "proximal side" that is operated by the operator.

[0023] 1 is a longitudinal cross-sectional view showing the structure of a guidewire 10 according to this embodiment. The guidewire 10 comprises an elongated core 1 and a tubular body 2 provided on the outside of the core 1. A distal tip 3 is provided at the distal end of the guidewire 10, joining the core 1 and the tubular body 2, and a fixing portion 4 is provided at the proximal end of the tubular body 2, fixing the core 1 and the tubular body 2 together.

[0024] The core 1 is an elongated member that serves as the shaft of the guidewire 10. As shown in FIG. 1 , the core 1 has a small diameter section 11 on the distal end side and a large diameter section 13 on the proximal end side, with a tapered section 12 between the small diameter section 11 and the large diameter section 13, the outer diameter of which decreases from the proximal end side to the distal end side. The core 1 can be formed from materials such as, but not limited to, stainless steel alloys (SUS302, SUS304, SUS316, etc.), superelastic alloys such as Ni-Ti alloys, piano wire, nickel-chromium alloys, cobalt alloys, and tungsten. The core 1 may also be formed from other known materials as long as they prevent the core 1 itself from breaking and allow the distal end to rotate.

[0025] The thin-diameter portion 11 has a flattened shape (having a substantially elliptical cross section) obtained by, for example, pressing a cylindrical material. The thick-diameter portion 13 has a cylindrical shape with a constant outer diameter from the tip to the base. The tapered portion 12 has a truncated cone shape with an outer diameter that gradually increases from the tip to the base, connecting the thin-diameter portion 11 and the thick-diameter portion 13.

[0026] The cylindrical body 2 is wound around the core 1 so as to cover the outer periphery of the small-diameter portion 11, the tapered portion 12, and a portion of the large-diameter portion 13 of the core 1. The cylindrical body 2 may be a single coil formed by spirally winding a single wire with a circular cross section into a cylindrical shape, or a hollow stranded coil formed by twisting together multiple wires into a cylindrical shape. The cylindrical body 2 may be formed by combining a single coil and a hollow stranded coil. The cylindrical body 2 may be formed from, for example, a stainless steel alloy (SUS302, SUS304, SUS316, etc.), a superelastic alloy such as a Ni-Ti alloy, a radiolucent alloy such as piano wire, a nickel-chromium alloy, or a cobalt alloy, or a radiopaque alloy such as gold, platinum, tungsten, or an alloy containing these elements (e.g., a platinum-nickel alloy), but is not limited thereto. The cylindrical body 2 may also be formed from known materials other than those mentioned above. In this embodiment, the entire cylindrical body 2 is formed as a single member using the same material, and its outer diameter is constant from the tip to the base end.

[0027] A distal tip 3 is formed at the distal end of the guide wire 10 (i.e., the distal end of the core 1) to join the core 1 and the tubular body 2. The distal tip 3 is formed of a metal solder such as silver solder, gold solder, zinc, a Sn—Ag alloy, or a Au—Sn alloy, and this metal solder fastens the distal end of the core shaft 1 to the distal end of the tubular body 2. The distal tip 3 may also be formed of an adhesive such as an epoxy adhesive, and the distal end of the core 1 and the distal end of the tubular body 2 may be fastened together by the adhesive.

[0028] A fixing portion 4 is formed at the base end of the cylindrical body 2, fixing the core 1 to the cylindrical body 2. The fixing portion 4 is formed of a metal solder such as silver solder, gold solder, zinc, a Sn—Ag alloy, or a Au—Sn alloy, and the base end of the cylindrical body 2 is fixed to the large diameter portion 13 of the core 1 by this metal solder. The fixing portion 4 may be formed of an adhesive such as an epoxy adhesive, and the large diameter portion 13 of the core 1 and the base end of the cylindrical body 2 may be fixed by the adhesive.

[0029] Two joints 5a and 5b are formed inside the cylindrical body 2 to join the tapered portion 12 of the core 1 to the cylindrical body 2. The joints 5a and 5b are formed of a metal solder such as silver solder, gold solder, zinc, an Sn—Ag alloy, or an Au—Sn alloy, and the tapered portion 12 of the core 1 is fixed to the cylindrical body 2 by this metal solder. The joints 5a and 5b may be formed of an adhesive such as an epoxy adhesive, and the tapered portion 12 of the core 1 and the cylindrical body 2 may be fixed to each other by the adhesive.

[0030] A first coating layer 6 is formed on the outer peripheral surface of the guidewire 10 excluding the proximal end of the thickened portion 13 of the core 1, i.e., the outer peripheral surface from the distal tip 3 to the tubular body 2, the fixing portion 4, and the thickened portion 13 of the core 1. A second coating layer 7, which is separate from the first coating layer 6, is formed on the outer peripheral surface of the proximal end of the thickened portion 13 of the core 1.

[0031] The second coating layer 7 is formed of a hydrophobic resin material, and examples of the hydrophobic resin material include fluorine-based resins such as polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and FEP, as well as silicone. By coating the outer peripheral surface of the base end of the core 1 with such a hydrophobic resin material, the area where the first coating layer 6 is formed can be reduced, thereby improving the operability of the operator.

[0032] 2 is a partially enlarged explanatory diagram showing the structure of the first coating layer 6 formed on the guidewire 10, and shows an enlarged view of the structure of the portion X in FIG. 1. The first coating layer 6 has a laminated structure in which a hydrophilic coating layer 61 disposed on the outer peripheral surface of the tubular body 2 and a hydrophobic coating layer 62 disposed radially outward of the hydrophilic coating layer 61 are laminated.

[0033] The hydrophilic coating layer 61 is formed of a hydrophilic coating material (first coating material). Examples of hydrophilic coating materials include solutions of nonionic hydrophilic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyacrylamide, polymethylacrylamide, poly(2-hydroxyethyl methacrylate), and poly(N-hydroxyethylacrylamide); anionic hydrophilic polymers such as polyacrylic acid, sodium polyacrylate, polymethacrylic acid, polymaleic acid, carboxymethyl cellulose, hyaluronic acid, and poly(2-acrylamido-2-methylpropanesulfonic acid); and cationic hydrophilic polymers such as polyethyleneimine, polyallylamine, and polyvinylamine. The hydrophilic coating layer 61 can be formed by a known coating formation method, such as by applying the hydrophilic coating material to the outer peripheral surface from the distal tip 3 to the cylindrical body 2, the fixing portion 4, and the thick-diameter portion 13 of the core 1.

[0034] The hydrophobic coating layer 62 is formed of a hydrophobic coating material (second coating material). Examples of hydrophobic coating materials include a silicone coating material such as a medical-grade silicone solution, silicone, and fluorine-based resins such as polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and FEP. The hydrophobic coating layer 62 can be formed by a known coating formation method, such as by applying the hydrophobic coating material on top of the hydrophilic coating layer 61.

[0035] The hydrophobic coating material (second coating material) may contain one or more polar solvents selected from the group consisting of lower chain alcohols, lower alkyl ethers, acetone, halogen-containing solvents, and lower alkylamines. Examples of lower chain alcohols include chain alkyl alcohols having 1 to 6 carbon atoms, such as methanol, ethanol, n-propanol, i-propanol (IPA), n-butanol, sec-butanol, t-butanol, n-pentanol, and n-hexanol. Examples of lower alkyl ethers include chain or cyclic alkyl ethers having 1 to 6 carbon atoms, such as dimethyl ether, diethyl ether, tetrahydrofuran, and 1,4-dioxane. Furthermore, examples of halogen-containing solvents include chain alkyls having 1 to 6 carbon atoms and containing 1 to 4 halogen atoms such as fluorine, bromine, iodine, etc. Examples of chain alkyls having 1 to 6 carbon atoms and containing 1 to 4 halogen atoms include chloroform, dichloromethane, carbon tetrachloride, etc. Examples of lower alkylamines include chain alkylamines having 1 to 6 carbon atoms, such as dimethylamine, methylamine, diethylamine, ethylamine, i-propylethylamine, and i-propylamine.

[0036] When the hydrophobic coating layer 62 is made of, for example, a silicone coating material, the hydrophobic coating layer 62 is configured to be liquid permeable. Specifically, the hydrophobic coating layer 62 has openings formed therein that communicate with the outer surface of the hydrophilic coating layer 61. In the presence of a liquid, the hydrophilic coating layer 61 swells as the liquid is supplied to the hydrophilic coating layer 61 through the openings. The hydrophilic coating layer 61 swells with the supplied liquid and is exposed to the outside of the hydrophobic coating layer 62 through the openings, thereby improving the hydrophilicity of the outer surface of the guidewire 10.

[0037] The state in which the hydrophobic coating layer 62 has openings may be realized, for example, by forming the hydrophobic coating layer 62 in a mesh-like shape, or by local gaps, cracks, perforations, etc. that are naturally formed in the process of forming the hydrophobic coating layer 62, or by forming the hydrophobic coating layer 62 by a known coating formation method and then performing some kind of surface treatment on the hydrophobic coating layer 62.

[0038] In this guidewire 10, the hydrophobic coating layer 62 is disposed on the outside of the hydrophilic coating layer 61, which prevents the outer surface of the guidewire 10 from becoming sticky even when the surrounding moisture content decreases, thereby reducing the static friction coefficient. On the other hand, the hydrophobic coating layer 62 is configured to be liquid permeable, which allows liquid to reach the inside of the hydrophobic coating layer 62 from the outer surface, causing the hydrophilic coating layer 61 to swell and improving the hydrophilicity of the outer surface of the guidewire 10. This results in a guidewire 10 that is easy to operate despite its simple structure.

[0039] In general, when a hydrophilic coating layer is disposed on the outermost layer of a medical device such as a guidewire, the dynamic friction coefficient is small but the static friction coefficient is large. On the other hand, when a hydrophobic coating layer is disposed on the outermost layer of a medical device such as a guidewire, the dynamic friction coefficient is large but the static friction coefficient is small. In the guidewire 10 of this embodiment, in which the hydrophobic coating layer 62 is disposed on the outer side of the hydrophilic coating layer 61, the presence of the hydrophobic coating layer 62 on the outermost layer has the effect of reducing the static friction coefficient, and the swelling of the hydrophilic coating layer 61 improves the hydrophilicity of the outer surface of the guidewire 10 (partial leaching of the hydrophilic coating layer 61 from the hydrophobic coating layer 62) has the effect of reducing the dynamic friction coefficient, thereby realizing a guidewire with good operability that combines these two contradictory properties.

[0040] While the guidewire according to the present disclosure has been described above with reference to the drawings, the present disclosure is not limited to the above-described embodiment and various modifications are possible. For example, in the above-described embodiment, the core 1 has a large-diameter portion 13 on the proximal side, a small-diameter portion 11 on the distal side, and a tapered portion 12 between the large-diameter portion 13 and the small-diameter portion 11. However, the core used in the guidewire according to the present disclosure may have a constant outer diameter from the proximal side to the distal side, or may have a structure in which the diameter changes in multiple stages.

[0041] An inner cylindrical body (coil body) having a length shorter than that of the cylindrical body 2 may be disposed inside the cylindrical body 2 and along the outer periphery of the core 1. For example, the inner cylindrical body may be wound around the core 1 so as to cover the outer periphery from the small diameter portion 11 to a part of the tapered portion 12, and may be disposed so that the cylindrical body 2 and the inner cylindrical body 8 overlap outside the core 1 only at the distal end of the guide wire 10.

[0042] The first coating layer 6 only needs to be formed so as to cover at least the tubular body 2 provided on the outside of the core 1, and may or may not be disposed over the entire length of the tubular body 2. The first coating layer 6 does not need to be formed directly on the outer surface of the tubular body 2; for example, another coating layer may be formed between the tubular body 2 and the first coating layer 6. The second coating layer 7 formed on the outer surface of the proximal end of the guidewire 10 may not be present; for example, the entire outer surface of the guidewire 10 may be coated with the first coating layer 6.

[0043] A modification of the first covering layer 6 of the guidewire 10 described in the above embodiment will be described below with reference to FIG.

[0044] In this modification, the first coating layer 6 has a laminated structure including a hydrophilic coating layer 61 disposed on the outer peripheral surface of the cylindrical body 2, a hydrophobic coating layer 62 disposed radially outside the hydrophilic coating layer 61, and an intermediate layer 63 formed between the hydrophilic coating layer 61 and the hydrophobic coating layer 62. The intermediate layer 63 is formed by mixing a hydrophilic coating material (first coating material) that forms the hydrophilic coating layer 61 and a hydrophobic coating material (second coating material) that forms the hydrophobic coating layer 62.

[0045] The hydrophilic coating layer 61 can be formed by a known coating method, such as by applying the aforementioned hydrophilic coating material to the outer peripheral surface from the distal tip 3 to the cylindrical body 2, the fixing portion 4, and the large-diameter portion 13 of the core 1. The hydrophobic coating layer 62 can be formed by a known coating method, such as by applying the aforementioned hydrophobic coating material to the upper layer of the hydrophilic coating layer 61. When the silicone coating material for forming the hydrophobic coating layer 62 is applied to the upper layer of the hydrophilic coating layer 61, the alcohol component (IPA) contained in the silicone coating material dissolves the hydrophilic coating material on the surface side of the hydrophilic coating layer 61, and an intermediate layer 63 in which the silicone coating material and the hydrophilic coating material are mixed is formed.

[0046] Because the hydrophobic coating layer 62 is made of a silicone coating material, the hydrophobic coating layer 62 is configured to be permeable to liquid. Specifically, the hydrophobic coating layer 62 has openings formed therein that communicate with the outer surface of the intermediate layer 63. In the presence of liquid, the liquid is supplied to the intermediate layer 63 through the openings, or is supplied to the hydrophilic coating layer 61 via the intermediate layer 63, causing the intermediate layer 63 and the hydrophilic coating layer 61 to swell. The intermediate layer 63 and the hydrophilic coating layer 61 swell with the supplied liquid and are exposed to the outside of the hydrophobic coating layer 62 through the openings, thereby improving the hydrophilicity of the outer surface of the guidewire 10.

[0047] The state in which the hydrophobic coating layer 62 has openings may be realized, for example, by forming the hydrophobic coating layer 62 in a mesh-like shape, or by local gaps, cracks, perforations, etc. that are naturally formed in the process of forming the hydrophobic coating layer 62, or by forming the hydrophobic coating layer 62 by a known coating formation method and then performing some kind of surface treatment on the hydrophobic coating layer 62.

[0048] In the guidewire 10 having the first coating layer 6 with such a three-layer structure, the hydrophobic coating layer 62 is disposed on the outside of the hydrophilic coating layer 61 and the intermediate layer 63, thereby preventing the outer surface of the guidewire 10 from becoming sticky even when the surrounding moisture content decreases, and reducing the static friction coefficient. On the other hand, because the hydrophobic coating layer 62 is configured to be liquid-permeable, liquid can reach the inside of the hydrophobic coating layer 62 from the outer surface, causing the intermediate layer 63 containing the components of the hydrophilic coating material and the hydrophilic coating layer 61 to swell, improving the hydrophilicity of the outer surface of the guidewire 10. This results in a guidewire 10 that is easy to operate despite its simple structure.

[0049] Even in the case of a guidewire 10 having a first coating layer 6 with a three-layer structure, the presence of the hydrophobic coating layer 62 as the outermost layer has the effect of reducing the static friction coefficient, and the swelling of the intermediate layer 63 and hydrophilic coating layer 61 improves the hydrophilicity of the outer surface of the guidewire 10 (the intermediate layer 63 and hydrophilic coating layer 61 partially leach out from the hydrophobic coating layer 62), which has the effect of reducing the dynamic friction coefficient. Therefore, a guidewire with good operability that combines these two contradictory properties is realized.

[0050] In particular, since the first coating layer 6 has a three-layer structure, the durability of the hydrophobic coating layer 63 is improved, and even if the hydrophobic coating layer 63 is lost as a result of operation, the increase in the static friction coefficient can be suppressed because the intermediate layer 63 also contains components of the hydrophobic coating material.

Claims

1. A medical device comprising: a long core; a cylindrical body provided on the outside of the core; a hydrophilic coating layer formed from a first coating material and disposed on the outer surface of the cylindrical body; and a hydrophobic coating layer formed from a second coating material and disposed radially outside the hydrophilic coating layer, wherein the hydrophilic coating layer is configured to be water absorbent.

2. The medical device according to claim 1, wherein an opening is formed in the hydrophobic coating layer that communicates with the outer surface of the hydrophilic coating layer.

3. The medical device according to claim 1 or 2, wherein the hydrophilic coating layer swells and is exposed on the outer surface of the hydrophobic coating layer in the presence of a liquid.

4. The medical device of claim 1, further comprising an intermediate layer formed of the first coating material and the second coating material between the hydrophilic coating layer and the hydrophobic coating layer.

5. The medical device of claim 1 or 4, wherein the second coating material contains one or more polar solvents selected from the group consisting of lower chain alcohols, lower alkyl ethers, acetone, halogen-containing solvents, and lower alkyl amines.

6. The medical device according to claim 4 or 5, wherein an opening communicating with the outer surface of the intermediate layer is formed in the hydrophobic coating layer.

7. The medical device according to claim 4 or 5, wherein at least one of the intermediate layer and the hydrophilic coating layer swells and becomes exposed on the outer surface of the hydrophobic coating layer in the presence of a liquid.

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