JP7479074B1 - Surface treatment method for medical instruments - Google Patents

Abstract

[Problem] To improve the surface slipperiness of silicone rubber constituting a medical device. [Solution] In a balloon catheter 1 equipped with a catheter tube 2 and a balloon 3 made of silicone rubber, the silicone rubber surfaces of the catheter tube and balloon are immersed in a 10-30% aqueous PEGMA solution for a predetermined period of time, and then the silicone rubber surface is irradiated with UV light for a predetermined period of time, thereby performing surface modification to form a Poly-PEGMA layer on the silicone rubber surface. [Selected Figure] Figure 2

Description

The present invention relates to medical devices, and in particular to medical devices such as catheters that are inserted into the bodies of humans and animals in the medical field, and to methods for treating their surfaces.

In the medical field, catheters have traditionally been widely used as one of the medical devices that are inserted from outside the body into biological lumens, such as blood vessels, urinary tracts, digestive tracts, and tracheas, of humans and animals. In general, catheters must be biosafe and biocompatible for use inside the body as medical devices, and must also have a slippery surface suitable for smooth and safe movement within the lumen without damaging the inner surfaces or tissues of blood vessels, etc.

Catheters are made of flexible rubber materials such as various synthetic resin elastomers, synthetic rubbers such as urethane rubber, silicone rubber, and butadiene rubber, and natural rubbers such as latex rubber. Latex rubber has the problem that the proteins contained in it act as allergens and cause an immediate allergic reaction known as latex allergy (see, for example, Patent Document 1). In contrast, silicone rubber has the advantages of being less irritating to biological tissues, being physiologically stable, and having flexibility suitable for insertion and placement in the body.

However, silicone rubber has the problem that it is difficult to obtain slipperiness due to its high surface friction coefficient and water repellency. A method is known in which the friction coefficient is reduced by adding an oil with low compatibility to silicone rubber (see, for example, Patent Document 2). Also, a method has been proposed in which a coating of a water-soluble polymer and a crosslinked polyurethane network is formed on the surface of a catheter tube made of silicone rubber (see, for example, Patent Document 3).

Patent No. 7011354 JP 2018-65889 A JP 2021-183075 A

However, as described in Patent Document 2, the oil component added to the silicone rubber may seep out from the surface of the silicone rubber during use or storage, so its use in medical devices may not be desirable.

The present invention has been made in consideration of the problems of the prior art, and its purpose is to provide a new and improved method for surface treatment of medical devices, such as catheters, that improves the surface slipperiness of silicone rubber that constitutes the medical device, and thereby to provide a medical device made of silicone rubber with improved surface slipperiness.

The surface treatment method for a medical device of the present invention is characterized in that it includes the steps of functionalizing the silicone rubber surface of a medical device having a component made of silicone rubber with ozone (O ₃ ), immersing the silicone rubber surface of the component in a 10 to 30% aqueous PEGMA solution , and irradiating the silicone rubber surface with ultraviolet (UV) rays for a predetermined period of time to perform surface modification by forming a Poly-PEGMA layer on the silicone rubber surface.

In one embodiment, the predetermined time for immersion in the PEGMA aqueous solution and irradiation of the silicone rubber surface with ultraviolet light is 3 hours.

In another embodiment, the method further includes a step of bubbling nitrogen gas through the PEGMA aqueous solution in which the silicone rubber surface is immersed, thereby removing oxygen from the reaction system containing the silicone rubber and the PEGMA aqueous solution.

In one embodiment, the medical device is a catheter equipped with a catheter tube made of silicone rubber, and the surface modification is performed on the silicone rubber surface of the catheter tube.

The surface treatment method of the present invention can significantly improve the surface slipperiness by modifying the silicone rubber surface of a medical device component with a Poly-PEGMA layer of sufficient thickness.
Further, the present invention provides a medical device comprising a silicone rubber component with improved surface slipperiness.

FIG. 1A is a schematic diagram showing a typical example of a catheter to which the present invention is applied, and FIG. FIG. 2 is a flow diagram showing a manufacturing process for a catheter according to the present invention. FIG. 1(a) is a schematic diagram showing a reaction scheme for forming a Poly-PEGMA layer on the surface of silicone rubber by the surface treatment method of the present invention, and FIG. 1(b) is a structural formula of PEGMA formed on the surface of silicone rubber. 1A and 1B are SEM images at magnifications of 1000 and 10,000, respectively, of the surface and a cross section near the surface of Sample 1 that was surface-treated with a 10% aqueous PEGMA solution. 13A and 13B are SEM images at magnifications of 1000 and 10,000 respectively of the surface and a cross section near the surface of Sample 3 that was surface-treated with a 10% aqueous PEGMA solution. 1A and 1B are SEM images at magnifications of 1000 and 10,000, respectively, of the surface and a cross section near the surface of Sample 4 that was surface-treated with a 30% aqueous solution of PEGMA. 1A and 1B are SEM images at magnifications of 1000 and 10,000 taken of the surface and a cross section near the surface of Sample 5 that was surface-treated with a 30% aqueous PEGMA solution. 1A and 1B are SEM images at magnifications of 1000 and 10,000 taken of the surface and a cross section near the surface of Sample 6 that was surface-treated with a 30% aqueous PEGMA solution. 1A and 1B are SEM images at magnifications of 1000 and 10,000, respectively, of the surface and a cross section near the surface of Comparative Sample 1 that was not subjected to the surface treatment of the present invention. 1A and 1B are SEM images at magnifications of 1000 and 10,000, respectively, of the surface and a cross section near the surface of Comparative Sample 2 that was not subjected to the surface treatment of the present invention. 1A and 1B are SEM images at magnifications of 1000 and 10,000, respectively, of the surface and a cross section near the surface of Comparative Sample 3 that was not subjected to the surface treatment of the present invention. 13( a ) and 13 ( b ) are display screens showing the results of EDS analysis performed on sample 5 . 4A and 4B are display screens showing the results of EDS analysis performed on comparative sample 2. 1A to 1C are graphs showing test results in which the coefficient of friction of the surface of Sample 3, which was surface-treated by the method of the present invention using a 10% PEGMA aqueous solution and setting the treatment time of ultraviolet light irradiation to 3 hours, was measured N=3 times. 1A to 1C are graphs showing test results of measuring the coefficient of friction of the surface of Sample 6, which was surface-treated by the method of the present invention using a 30% PEGMA aqueous solution and a UV irradiation treatment time of 3 hours. 4(a) to 4(c) are graphs showing test results of measuring the friction coefficient of the surface of Comparative Sample 3, which has not been subjected to the surface treatment of the present invention.

The present invention will now be described in detail with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention. In the drawings, the same or similar components are designated by the same reference numerals throughout the specification.

Figure 1 shows a balloon catheter 1 as a typical embodiment of a medical device to which the present invention is applied. The balloon catheter 1 of this embodiment is suitable for treating a stenosed area that has developed in a biological lumen, such as a patient's blood vessel, by expanding the area. Here, the term "patient" includes both humans and animals who are the subjects of medical treatment.

As shown in Figure 1, the balloon catheter 1 is an over-the-wire type, and comprises a flexible, elongated catheter tube 2, a balloon 3 provided near the tip, and a hub 4 on the base end side. In this specification, the tip side of the balloon catheter 1 refers to the side that is inserted into the body lumen, and the base side refers to the side that is placed outside the body and operated by the practitioner.

The catheter tube 2 has a double tube structure in which an inner tube 22 is concentrically arranged inside an outer tube 21. Between the outer tube 21 and the inner tube 22, an expansion lumen 5 is formed for passing a pressurized fluid that expands the balloon 3. The inside of the inner tube 22 defines a guidewire lumen 6 for inserting a guidewire (not shown) over its entire length.

The balloon 3 has its base end 3a integrally and airtightly and liquidtightly joined to the tip end 21a of the outer tube 21, and its tip end 3b integrally and airtightly and liquidtightly joined to the outer peripheral surface near the tip of the inner tube that extends further toward the tip side than the tip of the outer tube 21. As a result, the internal space 3c of the balloon 3 is connected to the expansion lumen 5 so that the pressurized fluid can be introduced.

At the tip of the catheter tube 2, a tip member 7 is provided integrally with the tip of the inner tube 22 in an airtight and liquid-tight manner so as to cover the tip of the inner tube 22. The tip member 7 preferably has a tapered curved outer shape so as not to damage biological tissue when the catheter tube 2 is inserted and moved. A through hole (not shown) is opened at the center of the tip of the tip member 7, which is concentric with the guide wire lumen and through which the guide wire can be inserted. Furthermore, a marker member 8 for imaging is fixed to the inner tube at an axial position corresponding to the balloon 3 on the outer circumferential surface of the tube.

The hub 4 is branched into a central branch tube 41 extending concentrically with the catheter tube 2, a main side tube 42 extending obliquely to one side, and an auxiliary side tube 43 extending obliquely to the opposite side across the branch tube 41. The branch tube 41 has a through passage that is concentrically connected to the guidewire lumen of the inner tube, and the through passage is provided with a conventionally known self-sealing valve, which can be configured to allow the guidewire to pass through while self-sealing when the guidewire is pulled out.

The main side tube 42 has an internal perfusion passage that communicates with the expansion lumen, and in use, the pressurized fluid is supplied from an external perfusion line (not shown) connected to its base end opening 42a. The auxiliary side tube 43 also has an internal auxiliary passage that communicates with the expansion lumen, but its base end opening 43a is usually airtight and liquid-tightly closed by tightening the cap member 43b. When monitoring the perfusion pressure of the pressurized fluid that is supplied to the expansion lumen and expands the balloon 3, the cap member 43b is removed and a fluid pressure measurement line is connected to the base end opening of the auxiliary passage.

The balloon catheter 1 is made almost entirely of silicone rubber, except for the marker member 8. Specifically, the outer tube 21 and inner tube 22, balloon 3, hub 4, and tip member 7 that make up the catheter tube 2 are made of silicone rubber. The connections between these silicone rubber parts are fixed airtight and liquidtight, for example, by fusion or adhesion. The marker member 8 is made of a plate material that has excellent visibility under X-ray fluoroscopy during use, such as a metal such as platinum, gold, silver, iridium, titanium, or tungsten, or an alloy of these metals.

The surface exposed to the outside of the balloon catheter 1 is subjected to a surface treatment to improve the surface slipperiness by the method of the present invention described below. Preferably, the surface treatment is applied to the parts that are inserted into the biological lumen during use, i.e., the outer surfaces 21s, 3s, and 7s of the outer tube 21, balloon 3, and tip member 7. The balloon catheter 1, whose outer surfaces have improved surface slipperiness, can be smoothly inserted and moved into the biological lumen without damaging the inner surface or tissue.

In another embodiment, the surface treatment of the present invention is also applied to the outer surface 22s of the inner tube 22 of the catheter tube 2. Generally, silicone rubber is characterized by self-adhesiveness. Therefore, when assembling the catheter tube 2, the inner tube 22 that has not been surface-treated is likely to be attracted to or caught on the inner surface 21i of the outer tube 21 when its outer surface comes into contact with the inner surface 21i of the outer tube 21, which may result in the smooth insertion and positioning of the inner tube 21 being hindered. By increasing the surface slipperiness of the outer surface 22s of the inner tube in advance in this way, it is possible to ensure smooth and easy assembly of the inner tube 2 to the outer tube 21.

Furthermore, silicone rubber has the characteristic that its strength decreases significantly when its surface is damaged. Therefore, when the inner surface of the balloon 3 comes into contact with the outer surface 22s of the adjacent inner tube 22, which has not been subjected to the above-mentioned surface treatment, there is a risk that they will adhere to each other and prevent the normal expansion of the balloon 3. In addition, the inner surface 3i of the balloon 3 that is adhered to the outer surface 22s of the inner tube 22 may be damaged when peeled off, causing variations in strength and causing one-sided bulging. By increasing the surface slipperiness of the inner tube outer surface 22s in advance by the above-mentioned surface treatment, it is possible to prevent the balloon inner surface 3i from adhering to the inner tube outer surface 22s, and ensure normal expansion of the balloon 3.

Next, a detailed description will be given of a method for improving surface slipperiness by applying the surface treatment of the present invention to the outer surface of the balloon catheter 1 shown in Figure 1 as the treated material. Figure 2 is a flow diagram showing the steps of a preferred embodiment of the surface treatment method of the present invention. As described above, in this embodiment, the hub 4 of the balloon catheter 1 is held outside the patient's body during use, so the outer surface of the rest of the hub 4, i.e., the part further to the tip, is treated as the treated surface.

First, the outer surface of the material to be treated (balloon catheter 1) is cleaned by wet ultrasonic cleaning (step St1). In this embodiment, this ultrasonic cleaning is performed in two stages: a degreasing process in which the material to be treated is immersed in methanol and ultrasonically treated for a predetermined time (e.g., about 10 minutes), and then a finishing cleaning process in which the material to be treated is immersed in distilled water and ultrasonically treated for a predetermined time (e.g., about 10 minutes). In this step St1, the entire balloon catheter 1 is ultrasonically cleaned, and the hub 4 does not need to be excluded.

Furthermore, the material to be treated is dry-cleaned using ozone (O ₃ ) (step St2). In this embodiment, a commercially available suitable ultraviolet (UV) ozone cleaning device is used. After placing the material to be treated in the UV ozone cleaning device, an appropriate concentration of oxygen (O ₂ ) gas is introduced, and an O ₃ atmosphere is generated in the device by irradiating UV rays of a predetermined wavelength. The material to be treated is left as it is in the device, and the surface to be treated is exposed to the O ₃ atmosphere for a predetermined time. This completely removes contaminants that could not be removed by the ultrasonic cleaning in step St1 from the surface to be treated, and also applies a pretreatment suitable for the surface modification treatment to be performed later to the surface to be treated.

The concentration of the _O2 gas introduced into the UV ozone cleaning device is determined according to the _O3 concentration of the _O3 atmosphere generated by irradiation with UV rays. The predetermined time for exposing the surface to the _O3 atmosphere is set to a time sufficient for completely removing contaminants from the surface to be treated and for performing the pretreatment required for the surface modification treatment, according to the desired _O3 concentration of the _O3 atmosphere. According to the test results of the inventors of the present application, the concentration of the _O2 gas can be set to, for example, 0.02 MPa. In this case, it was found that the predetermined time for exposure to the _O3 atmosphere is preferably 30 to 60 minutes, and more preferably 60 minutes.

Next, the material to be treated that has been cleaned and pretreated in this manner is transferred to a polymerization reaction device, where the photopolymerization reaction process is carried out. The polymerization reaction device is composed of a reaction vessel that stores an aqueous solution of polyethylene glycol monomethacrylate (PEGMA), and a UV irradiator that irradiates UV rays generated by a UV light source such as a commercially available high-pressure mercury lamp.

This photopolymerization reaction treatment applies the surface modification of the present invention to the treated surface, imparting good surface slipperiness. At this stage, it is preferable to exclude the hub 4 from the surface treatment of the present invention by, for example, appropriately masking it. This allows the outer surface of the hub 4 to maintain the high friction coefficient and water repellency inherent to silicone rubber, which is advantageous for manipulating the balloon catheter 1 during use.

In the photopolymerization reaction process, first, the material to be treated is completely immersed in the aqueous PEGMA solution of a predetermined concentration stored in the reaction vessel (step St3). The reaction vessel is selected to have sufficient dimensions, volume, and shape to accommodate the material to be treated (balloon catheter 1). In another embodiment, the material to be treated can be partially immersed in the aqueous PEGMA solution, i.e., only the portion to be treated with the surface treatment according to the present invention.

Nitrogen ( _N2 ) gas is bubbled into the PEGMA aqueous solution in the reaction vessel in which the material to be treated is immersed in this manner. This removes oxygen from the reaction system in the reaction vessel, which contains the silicone rubber of the material to be treated and the PEGMA aqueous solution, and finally creates an airtight system filled with _N2 gas. As a result, the material to be treated is immersed in the PEGMA aqueous solution of the specified concentration in a state in which oxygen has been completely removed.

Next, the UV irradiator is turned on to light the UV light source, and UV rays are irradiated onto the outer surface of the material to be treated in the reaction vessel at room temperature for a predetermined time (step St4). In the other embodiment described above, when it is desired to partially treat the surface of the material to be treated, it is possible to irradiate UV rays only onto the part of the material to be treated that has been immersed in the PEGMA aqueous solution.

As a result, the outer surface, i.e., the treated surface, is surface-modified by forming a Poly-PEGMA layer that is chemically bonded to the silicone rubber surface. The specified time for irradiating UV rays in step St4 is set according to the PEGMA concentration of the PEGMA aqueous solution so that the surface modification imparts the desired surface slipperiness to the treated surface.

According to the inventor's test results, the predetermined time in step St4 is set to 3 hours, for example, when the PEGMA concentration is 10-30%. This allows a Poly-PEGMA layer to be formed to a sufficient thickness on the surface of the treated material, modifying it and thereby imparting the desired surface slipperiness.

Figure 3(a) shows a schematic diagram of a reaction scheme in which a Poly-PEGMA film 101 is formed in the form of a polymer brush on the surface of a substrate 100 made of raw silicone rubber by the surface treatment method of this embodiment described above in relation to Figure 2. The PEGMA formed on the surface of the silicone rubber substrate 100 is shown by the structural formula in Figure 3(b).

As shown in the left half of Fig. 3(a), the surface of the silicone rubber substrate 100 is provided with a hydroxy group 102 singly bonded to an oxygen atom singly bonded to silicone in the substrate by hydrolysis of _O3 in step St2, and an oxygen group 103 in which two oxygen atoms singly bonded to each other exist in a conformational form. The surface of the silicone rubber substrate 100 is functionalized by the thus introduced hydroxy group 102 and oxygen group 103. The degree of this functionalization is determined by setting the _O3 concentration of the _O3 atmosphere exposed to the surface of the silicone rubber substrate 100 in step St2 and the exposure time.

The right half of Fig. 3(a) shows the result of immersing the silicone rubber substrate 100 with its surface functionalized in this way in an aqueous PEGMA solution of a given concentration in accordance with step St3, and then irradiating it with UV rays for a given time in accordance with step St4. The PEGMA monomer contained in the aqueous PEGMA solution has reactive groups as shown in Fig. 3(b), and therefore reacts with the hydroxyl groups 102 ( ^-OH- ) and oxygen groups 103 ( ^-O2- ) on the surface of the silicone rubber substrate 100 to form covalent bonds.

By appropriately setting the _O3 treatment conditions ( _O3 concentration, exposure time, environmental temperature, etc.) in step St2, the density of reactive groups available for chemical modification with PEGMA as described above can be increased. As the density of reactive groups increases, the PEGMA chains covalently bonded to the reactive groups extend farther away from the surface of the silicone rubber substrate 100 to form polymer brush structures (P(PEGMA) brushes 101). By appropriately setting the PEGMA and UV treatment conditions (PEGMA concentration, immersion time, UV intensity, UV exposure time, environmental temperature, etc.) in steps St3 and St4, a PEGMA film can be grown to a desired thickness on the surface of the silicone rubber substrate 100.

In this embodiment, as described above, the silicone rubber substrate 100 is exposed for 30 to 60 minutes to an _O3 atmosphere generated by UV irradiation of _O2 gas with a concentration of 0.02 MPa (step St2), and then immersed in a PEGMA aqueous solution with a concentration of 10 to 30% for 3 hours and irradiated with UV (steps St3 and St4). This results in a silicone rubber substrate 110 (Silicon-g-P(PEGMA)) in which the chemically grafted PEGMA film 101 (Poly-PEGMA brush) has grown to a thickness that can exhibit the desired surface slipperiness.

In order to evaluate the surface treatment of silicone rubber by the method of the present invention, the following samples 1 to 6 and comparative samples 1 to 3 were prepared for comparison. Samples 1 and 4 were cut to a length of about 1 cm from the balloon 3 of the balloon catheter 1 in FIG. 1, and samples 2 and 5 were cut to a length of about 8 mm from the catheter tube 2. Samples 3 and 6 were cut to a 300 mm square from a 1 mm thick silicone rubber plate (manufactured by AS ONE Corporation, Nishi-ku, Osaka City, Osaka Prefecture). Samples 1 to 3 were prepared by using a 10% PEGMA aqueous solution in step 3 (St3) of the surface treatment method of the present invention described in relation to FIG. 2, and samples 3 to 6 were prepared by using a 30% PEGMA aqueous solution. Comparative samples 1 to 3 were prepared by cutting to the same dimensions as samples 1 to 6 from the balloon 3 of the balloon catheter 1, the catheter tube 2, and the silicone rubber plate, which were not subjected to the surface treatment of the present invention.

The samples and the comparative samples were evaluated by the following four methods.
Evaluation method 1: Visual observation Evaluation method 2: Scanning electron microscope (SEM) images (magnifications x1000, x10000)
Evaluation method 3: Finger tactile sensation Evaluation method 4: Energy dispersive X-ray spectroscopy (EDS) analysis Evaluation method 5: Friction test The evaluation results of the above samples by these evaluation methods are explained below.

[Evaluation method 1]
The surface appearances of the surface-treated Samples 1 to 6 were visually observed and evaluated in comparison with the surface appearances of the Comparative Samples 1 to 3, with the following results being obtained.

(Sample 1)
In comparison with Comparative Sample 1, the formation of a Poly-PEGMA film could not be detected.
(Sample 2)
In comparison with Comparative Sample 2, the formation of a Poly-PEGMA film could not be detected.
(Sample 3)
In comparison with Comparative Sample 3, a decrease in transparency was observed, but the formation of a Poly-PEGMA film could not be detected.
(Sample 4)
A whitish surface was observed in comparison with Comparative Sample 1. This suggests the deposition of a Poly-PEGMA film.
(Sample 5)
A whitish surface was observed in comparison with Comparative Sample 2. This suggests the deposition of a Poly-PEGMA film.
(Sample 6)
A significant decrease in transparency was observed in comparison with Comparative Sample 3. This suggests the deposition of a Poly-PEGMA film.

[Evaluation method 2]
The surfaces of the surface-treated samples were photographed with a scanning electron microscope at magnifications of ×1000 and ×10000, and the SEM images were compared with the SEM images of the comparative samples for evaluation. In Figures 4 to 8, (a) and (b) are SEM images of the surfaces of each sample at magnifications of ×1000 and ×10000, respectively. In Figures 9 to 11, (a) and (b) are SEM images of the surfaces of each comparative sample at magnifications of ×1000 and ×10000, respectively.

(Sample 1)
Even when FIG. 4 is compared with FIG. 9, the formation of a film layer having a thickness in the order of μm that can be clearly identified could not be confirmed.
(Sample 3)
Even when FIG. 5 is compared with FIG. 11, the formation of a film layer having a thickness in the order of μm that can be clearly identified could not be confirmed.
(Sample 4)
Even when FIG. 6 is compared with FIG. 9, the formation of a film layer having a thickness in the order of μm that can be clearly distinguished could not be confirmed.
(Sample 5)
Even when FIG. 7 is compared with FIG. 10, the formation of a film layer having a thickness in the order of μm that can be clearly discerned could not be confirmed.
(Sample 6)
Comparing FIG. 8 with FIG. 11, the formation of a Poly-PEGMA film having a thickness of about 15 μm was clearly confirmed.

[Evaluation method 3]
The surfaces of the surface-treated samples and the comparative sample were moistened with a small amount of water and touched by running the fingers of a hand over them to obtain a feel for the surface.

(Sample 3)
The surface slipperiness was slightly improved compared to Comparative Sample 3. Furthermore, when the surface of Sample 3 was wetted with water, a decrease in surface tension was observed.
(Sample 4)
A clearly different feel and surface slipperiness were felt in comparison with Comparative Sample 1. This suggests the formation of at least a thin Poly-PEGMA film.
(Sample 5)
A clearly different feel and surface slipperiness were felt in comparison with Comparative Sample 2. This also suggests the formation of at least a thin Poly-PEGMA film.
(Sample 6)
A clear improvement in surface slipperiness was felt in comparison with Comparative Sample 3. Furthermore, when the surface of Sample 6 was wetted with water, absorption of water by the surface was observed.

[Evaluation method 4]
Using the SEM images obtained by the above-mentioned evaluation method 2, analysis by energy dispersive X-ray spectroscopy (EDS) was performed on Sample 5 and the corresponding Comparative Sample 2. As the regions for EDS analysis, surface regions Rs7 and Rs10 surrounded by squares on the surface and cross-sectional regions Rx7 and Rx10 surrounded by squares slightly below the surface in Fig. 7(b) and Fig. 10(b) were selected.

Figures 12(a) and (b) show the results of EDS analysis performed on sample 5, where spectrum 1 corresponds to surface region Rs7 and spectrum 2 corresponds to cross-sectional region Rx7. Figures 13(a) and (b) show the results of EDS analysis performed on comparative sample 2, which corresponds to sample 5, where spectrum 1 corresponds to surface region Rs10 and spectrum 2 corresponds to cross-sectional region Rx10.

Figures 12(b) and 13(b) show that there is no significant difference in the mass percentages of element C and element Si in both Sample 5 and Comparative Sample 2, and that their abundance ratios are approximately the same. In contrast, in Figure 12(a), the mass percentage of element C is clearly significantly greater than that of element Si. On the other hand, in Figure 13(a), the mass percentages of element C and element Si are approximately the same as in Figure 13(b). The results of the EDS analysis suggest that the surface of Sample 5 contains an increased number of C atoms derived from the Poly-PEGMA film formed by the surface treatment of the present invention.

[Evaluation method 5]
For samples 3 and 6 cut out from the silicone rubber plate, tests were conducted to measure the static and dynamic friction coefficients of the treated surface that had been subjected to the surface treatment of the present invention. The test equipment used was a static and dynamic friction tester TL201Tt manufactured by Trinity Lab Co., Ltd. (Setagaya-ku, Tokyo) along with a surface contact with a clamp for fixing the flat test pieces, samples 3 and 6. For comparison with samples 3 and 6, a static and dynamic friction coefficient measurement test was also conducted on the untreated surface of comparative sample 3, which had not been subjected to the surface treatment of the present invention.

The test method and test conditions are as follows.
(Test method)
A flat test specimen (samples 3 and 6, comparative sample 3) is fixed to the contact surface at the lower end of the surface contactor with the test surface to be measured for its static and dynamic friction coefficient facing downward. The static and dynamic friction measuring device includes a movable table having an upper surface that is movable in the horizontal direction and forms a smooth horizontal friction surface, and a measuring unit, and the surface contactor is placed above the movable table and attached to and held by the measuring unit. The measuring unit applies a constant test load vertically downward to the surface contactor so that the test surface of the test specimen is in contact with and evenly pressed against the horizontal friction surface over the entire contact surface of the surface contactor. In this state, the movable table is driven in the horizontal plane direction to slide a predetermined distance against the friction force generated between the horizontal friction surface and the test surface of the test specimen. The measuring unit measures the friction force acting through the surface contactor, and calculates the static and dynamic friction coefficients of the test surface according to a predetermined formula.

(Test condition)
The static and dynamic friction coefficient measurement test was carried out under the following test conditions.
Test load: 50gf
Driving speed of movable table: 10 mm/sec
- Sliding distance of movable table: 10 mm
Number of tests: 3 The static friction coefficient and dynamic friction coefficient derived from this test are defined as follows:
Static friction coefficient: Maximum friction coefficient at the beginning of the sliding of the movable table Dynamic friction coefficient: Average friction coefficient between 3mm and 7mm of the sliding distance of the movable table

(Test results)
14(a) to 14(c) show the coefficient of friction calculated from the frictional force measured in each of the three static and dynamic friction coefficient measurement tests performed on Sample 3, plotted on the vertical axis and the measurement time on the horizontal axis. The static and dynamic friction coefficients derived from the results of the three measurements in accordance with the above definitions, as well as the average values of the three measurements, are shown in Table 1 below.

Figures 15(a) to (c) show the time-dependent changes in the friction coefficient of sample 6, which were measured and calculated in three static and dynamic friction coefficient measurement tests. The static and dynamic friction coefficients derived from the three measurement results according to the above definitions, as well as the average values of the three measurements, are shown in Table 2 below.

Furthermore, for comparative sample 3, the change over time in the friction coefficient measured and calculated in the static and dynamic friction coefficient measurement test three times is shown in Figures 16(a) to (c). The static and dynamic friction coefficients derived from the results of these three measurements according to the above definitions, as well as the average value of these three measurements, are shown in Table 3 below.

Comparing Table 1 with Table 3, it can be seen that the static and kinetic friction coefficients of Sample 3 are significantly lower than those of Comparative Sample 3 in all of the numerical values and average values for each run. Furthermore, comparing Table 2 with Table 3, it can be seen that the static and kinetic friction coefficients of Sample 6 are even more significantly lower than those of Sample 3, and significantly lower than those of Comparative Sample 3, in all of the numerical values and average values for each run. Taking these results together, it has been confirmed that both the static and kinetic friction coefficients of silicone rubber can be significantly reduced by applying the surface treatment of the present invention to the surface.

Although the present invention has been described above in relation to preferred embodiments, it goes without saying that the present invention is not limited to the above embodiments and can be practiced with various modifications or variations within its technical scope. For example, the surface treatment method of the present invention is not limited to the balloon catheter of the above embodiment, but can be similarly applied to catheters such as catheter tubes made of silicone rubber, and various other medical devices having components with silicone rubber surfaces.

Reference Signs List 1 Balloon catheter 2 Catheter tube 3 Balloon 4 Hub 7 Tip member 21 Outer tube 22 Inner tube 100 Substrate 101 Poly-PEGMA film 110 Silicone rubber substrate

Claims (4)

A surface treatment method for a medical device comprising a component formed of silicone rubber, the method comprising the steps of: functionalizing the silicone rubber surface of the component with ozone (O ₃ ); immersing the silicone rubber surface of the component in a 10-30% aqueous PEGMA solution; and irradiating the silicone rubber surface with ultraviolet (UV) rays for a predetermined period of time to perform surface modification by forming a Poly-PEGMA layer on the silicone rubber surface. The method for treating the surface of a medical instrument according to claim 1, wherein the predetermined time for immersing the silicone rubber surface in the PEGMA aqueous solution and irradiating the surface with ultraviolet light is 3 hours. The surface treatment method for a medical device according to claim 1, further comprising the step of bubbling the PEGMA aqueous solution in which the silicone rubber surface is immersed with nitrogen gas to remove oxygen from the reaction system containing the silicone rubber and the PEGMA aqueous solution. The method for treating the surface of a medical device according to any one of claims 1 to 3, wherein the medical device is a catheter having a catheter tube made of silicone rubber, and the surface modification is performed on the silicone rubber surface of the catheter tube.

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