JP2009097064A - Ti-BASE ALLOY - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Ti-base alloy which has superior biocompatibility and can produce excellent spring characteristics and shape memory effect and also can attain manufacturing cost reduction. <P>SOLUTION: The Ti-base alloy consists of, by atom, 0.01 to 20% Y, 1 to 20% X1 (where X1 is one element among V, Cr, Zr, Nb, Mo, Hf and Ta or a combination of several elements among them), 0 to 20% X2 (where X2 is one element among Al, Ag and Sn or a combination of several elements among them), and the balance Ti with inevitable impurities. Owing to the addition of the Y in the above percentage, crystal grains of the Ti-base alloy can be refined and intercrystalline cracking and slip deformation can be suppressed. In addition, owing to the addition of the X1 element in the above percentage, β-phase of the Ti-base alloy excellent in deformability can be stabilized. In this way, the Ti-base alloy having superior spring characteristics and shape memory effect can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a Ti-based alloy used for medical devices such as catheters and guide wires, and accessories such as eyeglass frames and bracelets, for example.

  Conventionally, Ti-Ni type shape memory alloys are generally used as shape memory alloys. This type of Ti-Ni-based shape memory alloy is accompanied by a remarkable shape memory effect (even if it is deformed below a predetermined transformation point, when it is heated above the transformation point. It is known that it exhibits a property of recovering its shape) and superelasticity (a property of returning to its original shape immediately even when it is deformed at a predetermined transformation point or higher). Examples of utilizing the shape memory effect of the Ti-Ni-based shape memory alloy include temperature sensitive actuators such as air conditioners and microwave ovens, while those utilizing superelasticity include catheters, guide wires, Examples thereof include medical devices such as stents, and accessories such as eyeglass frames and bracelets. However, Ti-Ni shape memory alloys contain Ni which is one of the causes of metal allergies, etc., and are inferior in biocompatibility. Therefore, when used in the above-mentioned medical devices and accessories, synthetic resins, etc. In order to prevent direct contact with the living body.

  In recent years, Ti-based alloys made of elements that do not contain Ni and do not cause metal allergy have been studied. For example, the following Patent Document 1 discloses a β-type Ti alloy obtained by adding 1 to 2 wt% of Ag to a β-type Ti alloy, and the following Patent Document 2 discloses 6 wt% ≦ Mo ≦ 18 wt% and A low-strength, high-ductility Ti alloy for cold working containing 0.5 wt% ≦ Sn ≦ 10 wt% is disclosed. Furthermore, Patent Document 3 below discloses a Ti alloy containing 0.5 to 18 wt% Mo, 13 to 19 wt% V, 0.5 to 6 wt% Al, and 0.5 to 6 wt% Sn, Patent Document 4 listed below discloses a shape memory Ti alloy containing 10 to 15 wt% Mo and 5 wt% Al.

Furthermore, the present inventors have proposed those shown in Patent Documents 5 and 6 below as biocompatible alloys having good workability and excellent biocompatibility. That is, in Patent Document 5 below, 1 at% ≦ Sc ≦ 30 at%, 1 at% ≦ X ≦ 15 at% (provided that one or several of X = V, Cr, Zr, Nb, Mo, Hf, Ta) T-Sc shape memory alloys are disclosed, including combinations). Patent Document 6 below discloses a Ti-based alloy shape memory element containing 4 to 10 at% Mo, 3 to 10 at% Sn, or 1 to 10 at% Sc.
JP-A-53-123323 Japanese Patent Laid-Open No. 1-129941 JP-A-4-214830 JP 59-56554 A JP 2004-204245 A JP 2005-281728 A

  By the way, when the shape memory alloy is used for a medical device such as a catheter or a guide wire or an accessory such as a spectacle frame, even if it is deformed by an external force, it is elastically restored to its original shape without plastic deformation. Often, springiness (superelasticity) is required. On the other hand, when used in a temperature sensitive actuator such as an air conditioner or a microwave oven, there is a demand for a shape memory effect that returns to its original shape when heated at a predetermined temperature.

  Patent Document 1 discloses a β-type Ti alloy with improved corrosion resistance, Patent Document 2 discloses a high workability and low-strength Ti alloy, and Patent Document 3 discloses A Ti alloy with improved workability is disclosed, and Patent Document 4 further discloses a Ti alloy in which the α phase is stabilized by suppressing the precipitation of the ω phase by the addition of Al.

  Thus, Patent Documents 1 to 4 describe that various performances such as corrosion resistance and workability are improved by adding various elements to Ti. However, Patent Documents 1 to 4 do not describe the effect of improving the spring property required for medical devices such as catheters, and cannot satisfy the spring property. In Literatures 1 to 3, the shape memory effect necessary for a temperature-sensitive actuator or the like cannot be obtained. In other words, in the above-mentioned Cited Literatures 1 to 4, it is difficult to obtain a Ti alloy having both spring properties and a shape memory effect.

  On the other hand, in the case of the above Patent Documents 5 and 6, although the spring property and the shape memory effect can be obtained, since Sc added to them is an extremely expensive metal (tens of thousands of yen per 1 g), the manufacturing cost is reduced. There's a problem.

  Accordingly, it is an object of the present invention to provide a Ti-based alloy that is excellent in biocompatibility, can obtain good spring properties (superelasticity) and a shape memory effect, and can reduce manufacturing costs. .

  In order to achieve the above object, the first aspect of the present invention is that 0.01 to 20 at% Y, 1 to 20 at% X1 (where X1 = V, Cr, Zr, Nb, Mo, Hf, Ta). 1 or a combination of several), X2 of 0 to 20 at% (where X2 = one or several combinations of Al, Ag, and Sn), and the balance is made of Ti and inevitable impurities. A Ti-based alloy is provided.

  According to the above invention, the Ti-based alloy having the above-described composition can obtain a Ti-based alloy having good biocompatibility without containing Ni that easily affects the human body. It can be used for medical devices such as glasses, and accessories such as eyeglass frames and bracelets.

  Moreover, by adding Y in the above proportion, the crystal grains of the Ti-based alloy can be refined, and as a result, grain boundary cracking and slip deformation can be suppressed, and in addition, X1 in the above proportion. By adding an element, it is possible to stabilize the β phase of a Ti-based alloy having good deformability, and as a result, a Ti-based alloy having good spring properties and a shape memory effect can be obtained. Furthermore, when the X2 element is added in the above ratio, the α phase of the Ti-based alloy can be stabilized, the generation of the ω phase can be suppressed, and an appropriate rigidity can be obtained, thereby preventing a decrease in springiness. it can. In addition, since extremely expensive Sc is unnecessary, the manufacturing cost of the Ti-based alloy can be reduced.

  According to a second aspect of the present invention, in the first aspect, the X1 is Mo, the content thereof is 4 to 10 at%, the X2 is Sn, and the content is 3 to 10 at%. A Ti-based alloy is provided.

  According to the above invention, by adding Mo and Sn at the above ratio, the Ti phase and the α phase of the Ti alloy can be stabilized, the spring property is further improved, and the shape memory effect is also good. Can be obtained.

  According to a third aspect of the present invention, there is provided a Ti-based alloy used in the medical device according to the first or second aspect.

  According to the said invention, it can use suitably for the medical device by which biocompatibility is requested | required.

  According to a fourth aspect of the present invention, in the third aspect, the medical device provides a Ti-based alloy which is one selected from a catheter, a guide wire, and a stent.

  According to the said invention, it can insert suitably in a tubular organ and can use it suitably for a catheter, a guide wire, and a stent in which biocompatibility is especially requested | required.

  According to the present invention, the Ti-based alloy having the above composition can provide a Ti-based alloy that does not contain Ni and has good biocompatibility, such as a medical device such as a guide wire, and an accessory such as a spectacle frame. Further, since it is not necessary to use extremely expensive Sc, the manufacturing cost of the Ti-based alloy can be reduced.

  Then, by adding Y in the above proportion, the grain size of the Ti-based alloy can be refined to suppress the intergranular cracking and slip deformation, and in addition to that, by adding the X1 element in the above proportion, the deformability Can stabilize the β phase of a Ti-based alloy, and a Ti-based alloy having good spring properties and shape memory effects can be obtained. Furthermore, when the X2 element is added in the above ratio, the α phase of the Ti-based alloy can be stabilized, the generation of the ω phase is suppressed, and the spring property is further improved.

  The Ti-based alloy of the present invention can be used for medical devices such as guide wires, catheters, and stents, and accessories such as eyeglass frames and bracelets. For example, FIG. An example used is shown, and FIG. 1B shows an example used for the catheter 20.

  A guide wire 10 shown in FIG. 1A includes a core wire 11 having a tapered end and a resin film 12 coated on the outer periphery of the core wire 11. The Ti-based alloy of the present invention includes the core wire 11. Used for.

  On the other hand, the catheter 20 shown in FIG. 1 (b) is entirely composed of a resin tube 21, and is formed into a mesh cylinder by knitting and / or assembling a metal wire therein, and a reinforcing body 22 having a so-called braided shape is formed. It has a buried structure. The Ti-based alloy of the present invention is used as a metal wire constituting the reinforcing body 22. Although not particularly shown when applied to a catheter, the Ti-based alloy of the present invention is used for a tube-shaped metal catheter itself or a cylindrical body embedded in a part of a catheter made of a resin tube. Used as a reinforcing wire embedded along the axial direction of the catheter, used as a wire that can be arranged along the axial direction of the catheter and bendable at the distal end of the catheter, etc. Is possible.

  The Ti-based alloy of the present invention has biocompatibility, good spring properties, and a shape memory effect so that it can be employed in medical devices such as catheters and guide wires as described above (for example, This is effective when the tip of the guide wire is shaped in advance), and is obtained by adding a predetermined amount of a predetermined element as shown below so as to reduce the manufacturing cost without using expensive Sc. It is a thing.

  That is, the Ti-based alloy of the present invention has 0.01-20 at% Y, 1-20 at% X1 (where X1 = one or several of V, Cr, Zr, Nb, Mo, Hf, Ta). ), And 0 to 20 at% of X2 (where X2 = one or several combinations of Al, Ag, and Sn), with the balance being Ti and inevitable impurities.

  In the present invention, one having a crystal structure equivalent to that of a β-type Ti-based alloy and having a shape memory effect or a superelastic property is used. A β-type or nearβ-type Ti-based alloy is used. In the present invention, a β-type or nearβ-type Ti-based alloy is formed by using the above composition.

  By the way, a Ti-based alloy usually has phases such as α phase, β phase, α + β phase, and ω phase. Since the β phase is a body-centered cubic lattice (bcc), it is known that the deformability is better than the α phase which is a dense hexagonal lattice (hcp), that is, the spring property is better, and the ω phase is changed from the β phase to the α phase. It is known that it is markedly cured when this ω phase is present.

  Next, the reason why the composition of the Ti-based alloy according to the present invention is limited as described above will be described.

  Y plays a role of stabilizing the β-phase of the Ti-based alloy and reacts with oxygen in the matrix (parent phase) of the Ti-based alloy to reduce the crystal grains. Cracks and slip deformation can be suppressed. The content of Y with respect to the Ti-based alloy is 0.01 to 20 at%. If it is less than 0.01 at%, the β phase cannot be sufficiently stabilized and the crystal grains cannot be sufficiently refined. If it exceeds 20 at%, the production cost is increased, the workability is further deteriorated, and the Young's modulus is decreased.

  In this Ti-based alloy, in addition to Y, an X1 element that stabilizes the β phase such as V, Cr, and Mo is added. That is, simply adding Y to Ti is not sufficient to stabilize the structure in the β phase. Therefore, by adding the X1 element in addition to Y, the structure has a good deformability and a spring property. A Ti-base alloy that can be firmly stabilized to a good β phase and that satisfies both the spring property and the shape memory effect is obtained.

  The X1 element is one or a combination of several of V, Cr, Zr, Nb, Mo, Hf, and Ta. The content of the X1 element with respect to the Ti-based alloy is 1 to 20 at%, preferably 3 ~ 15 at%. If the X1 element is less than 1 at%, the β phase cannot be sufficiently stabilized, which is not preferable. If it exceeds 20 at%, the characteristics of the Ti-based alloy deteriorate, which is not preferable.

  Of the X1 elements, V, Nb, and Ta are elements belonging to Group 6 (VIA group). V is 1 to 10 at%, Nb is 1 to 15 at%, and Ta is 1 with respect to the Ti-based alloy. It is preferable to contain ~ 15at%. Zr and Hf are elements belonging to the same group 4 (IVA group) as Ti and are completely dissolved in Ti and do not hinder the elastic deformability, but they are contained in amounts of 1 to 15 at% from the viewpoint of economy and strength. preferable. Cr and Mo are elements that improve the strength and workability of the Ti-based alloy, and are preferably contained in an amount of 1 to 10 at% relative to the Ti-based alloy.

  Furthermore, in the Ti-based alloy of the present invention, an X2 element that is a metal element for stabilizing the α phase of the Ti-based alloy may be added. The X2 element is one kind or a combination of several kinds of Al, Ag, and Sn, and is contained in 0 to 20 at%. In this Ti-based alloy, there is no problem even if X2 element is not included. However, when a predetermined amount is added, the α-phase of the Ti-based alloy is stabilized and the formation of the ω-phase is suppressed to obtain an appropriate rigidity. As a result, a decrease in springiness can be prevented. In addition, when X2 element exceeds 20 at% and is contained in the Ti-based alloy, the α phase is extremely increased and the spring property is lowered, which is not preferable.

  In a preferred embodiment, the Ti-based alloy contains 0.01 to 20 at% Y, 4 to 10 at% Mo, and 3 to 10 at% Sn, with the balance being Ti and inevitable impurities. Here, as described above, Mo plays a role of stabilizing the β phase of the structure of the Ti-based alloy, and improves the strength and workability of the Ti-based alloy. It is not preferable because it cannot be sufficiently stabilized, and if it exceeds 10 at%, excessive solid solution strengthening occurs and the ductility becomes insufficient. Similarly, as described above, Sn is a metal element that stabilizes the α phase and suppresses the formation of the ω phase. The content of Sn with respect to the Ti-based alloy is 3 to 10 at%. If it is less than 10%, it is not preferable because stabilization of the α-phase and generation of the ω-phase can be moderately suppressed to obtain an appropriate rigidity, and if it exceeds 10 at%, the α-phase is extremely increased and the spring property is lowered. is there.

  Next, the function and effect of the Ti-based alloy of the present invention will be described.

  That is, the Ti-based alloy of the present invention is made from 0.01 to 20 at% Y, 1 to 20 at% X1 (where X1 = one or several of V, Cr, Zr, Nb, Mo, Hf, Ta). In combination with 0 to 20 at% of X2 (where X2 = one or several combinations of Al, Ag, and Sn), and the balance is composed of Ti and inevitable impurities, affecting the human body. It is possible to obtain a Ti-based alloy having good biocompatibility without containing Ni, which can easily affect the skin, and can be used for medical devices such as guide wires, catheters, and stents, and accessories such as eyeglass frames and bracelets.

  Moreover, by adding Y in the above proportion, the crystal grains of the Ti-based alloy can be refined, and as a result, grain boundary cracking and slip deformation can be suppressed, and in addition, X1 in the above proportion. By adding an element, it is possible to stabilize the β phase of a Ti-based alloy having good deformability, and as a result, a Ti-based alloy having good spring properties and a shape memory effect can be obtained. Furthermore, when the X2 element is added in the above ratio, the α phase of the Ti-based alloy can be stabilized, the generation of the ω phase can be suppressed, and an appropriate rigidity can be obtained, thereby preventing a decrease in springiness. it can. In addition, since extremely expensive Sc is unnecessary, the manufacturing cost of the Ti-based alloy can be reduced.

  Further, according to the Ti-based alloy containing 0.01 to 20 at% Y, 1 to 10 at% Mo, and 3 to 10 at% Sn in the embodiment, with the balance being Ti and inevitable impurities, Mo is added at the above ratio. By adding, the β phase of the Ti alloy can be stabilized, and by adding Sn in the above ratio, the α phase of the Ti alloy is stabilized, and the ω phase that remarkably hardens the Ti-based alloy. Generation of Ti can be suppressed, moderate rigidity can be maintained, deterioration of the spring property can be prevented, and a Ti-based alloy having better spring property and good shape memory effect can be obtained.

(1) Production of Ti-based alloy As shown in Tables 1 to 3 below, a Ti-based alloy having an alloy composition (see Sample Nos. 1 to 17) that can be β-type or near β-type was produced by argon arc melting. Melting was performed in an arc melting furnace using a water-cooled copper hearth and a non-consumable tungsten electrode in an argon atmosphere. In order to reduce segregation of alloy components, melting and solidification were repeated 6 times by reversing the top of the ingot. Each ingot thus produced was held in a vacuum atmosphere at 1000 ° C. for 24 hours for homogenization treatment. After the homogenization treatment, each ingot was cooled in the furnace.

(2) Sample preparation and workability evaluation After cutting out a plate material having a thickness of 2 to 3 mm from each ingot homogenized with each composition as described above, each plate material was rolled so as to be 0.4 mm or less. And Example and the comparative example were produced (sample No. 1-17). In addition, this rolling was performed at normal temperature (that is, below the recrystallization temperature), and each plate was cold worked.

  The superiority and inferiority of workability at this time are also shown in Tables 1-3. In Tables 1 to 3, ◯ indicates that processing was possible without any problem, △ indicates that the processing speed had to be somewhat slow, but there was no problem with processing itself, and × indicates cracking or breakage during processing. This shows the case where cold working is difficult.

  As shown in Tables 1 to 3 above, in the case of sample 14 as a comparative example, Mo is 3 at% and the β phase cannot be sufficiently stabilized, and the amount of Sn is small and the generation of the ω phase is not sufficiently suppressed. However, it is speculated that this led to deterioration of workability. Moreover, the samples 1-6 and 8-13 which are an Example were all producible without a problem.

  After each sample was prepared as described above, a heat treatment was performed in which a part of each sample was held at 1000 ° C. for 1 hour, and then immersed in ice-salt water and quenched to perform a β-phase single-phase treatment. .

(3) Shape memory characteristic evaluation The shape memory characteristic evaluation was evaluated by a simple bending test using the samples 1 to 17 described above. This will be described with reference to FIG. First, a flat plate-like sample having a thickness of approximately 0.4 mm and extending in a straight line was wound while being bent along a cylinder having a radius of 4 mm. At this time, the strain applied to each sample is about 4-5%. Thereafter, the winding of each sample on the cylinder was released to make it free, and then each sample was heated with a lighter. In this way, each sample tries to elastically return to its original flat plate shape by its own spring property (called a springback) after the winding is released (see FIG. 2). . In FIG. 2, the symbol a indicates an initial flat sample, the symbol b indicates a sample that has been elastically restored by the springback after the winding is released, and the symbol c attempts to recover the shape to the initial shape by heating. The sample in the state to be shown is shown.

  The shape memory characteristics are determined by the total amount of the springback amount (%) (superelasticity) after releasing the winding restraint of each sample and the amount of residual strain elimination (%) due to heating of each sample (shape memory effect). evaluated. The shape memory effect is obtained when the springback amount of 3% or more is ○, 2% or more is △, and less than 2% is ×, and the total of these springback amounts and residual strain elimination during heating is 3% or more. ○ Less than 3% was marked as x. These results are also shown in Tables 1-3. As a result, in the case of the example, it was confirmed that both the superelasticity and the shape memory effect were satisfied.

(4) Shape memory effect and superelasticity FIGS. 3 and 4 show 1000 of the Ti-5Mo-4.6Sn-0 to 2Y alloy (samples 1 to 4 and 6, 7) shown in Table 1 above. A tissue photograph after the ° C treatment is shown. FIG. 3A shows a structure photograph of 0Y (sample 7), FIG. 3B shows a structure photograph of 0.1Y (sample 1), and FIG. 3C shows 0.25Y. Fig. 4 (a) shows a 0.5Y tissue photograph (sample 3), and Fig. 4 (b) shows a 1Y tissue photograph (sample 4). ), And FIG. 4C shows a 2Y tissue photograph (sample 6). Referring to each structure photograph, it can be understood that the crystal grains of the structure of the Ti-based alloy are sufficiently refined by adding 0.1 at% of Y to Ti.

  FIG. 5 is a chart showing the relationship between the Vickers hardness (HV) and the Y addition amount (at%) for each of the samples 1 to 7. According to this, it can be seen that Y has a remarkable hardness change effect by addition of 0.25 at%, and the effect is less than that. In general, it is known that there is a correlation between hardness and Young's modulus. That is, it is known that if the hardness is low, the Young's modulus also decreases. From this, it can be seen that, in this Ti-based alloy, as the amount of Y increases, the Young's modulus also decreases, and in that case, application to implant products used for dental treatment and the like is expected. be able to.

  3 and 4 and the results of the hardness test shown in FIG. 5, it is expected that Y can reduce the crystal grains and reduce the hardness even in a trace amount of less than 0.1 at%. it can.

  FIG. 6 is a chart showing the relationship between the martensitic transformation temperature (Ms) and the Y addition amount (at%) of each sample. That is, samples 3, 5, and 7 were set in a tensile tester and a predetermined load was applied, and the temperature at which the martensitic transformation start temperature (Ms) started was measured. As a result, it was found that the effect of increasing the Ms temperature by increasing Y was about 40 ° C. per at%.

  7 and 8 show a stress σ (MPa) -strain ε (%) diagram when a tensile cycle test of each sample is performed. That is, a cycle in which each of the samples 1 to 4 and 6 and 7 is set in a tensile tester, a tensile load is applied to each sample to cause elongation strain, and then the tensile load is removed is repeated at room temperature. Thus, it was confirmed how much each sample returned to its original shape. 7A shows the result of 0Y (sample 7), FIG. 7B shows the result of 0.1Y (sample 1), and FIG. 7C shows 0.25Y (sample). 2), the result of 0.5Y (sample 3) is shown in FIG. 8 (a), the result of 1Y (sample 4) is shown in FIG. 8 (b), FIG. 8C shows the result of 2Y (sample 6). As shown in FIGS. 8 and 9, the Ti-based alloy to which Y is added at 0.25 at% has a spring property of more than 3%, and the shape of the other sample in the total amount of 3% or more by heating is also obtained. A memory effect was obtained.

(5) Summary From the above test results, it was confirmed that the Ti-based alloy of the present invention has both spring properties and a shape memory effect.

  In addition, from the results of Table 2 above, the low Sn content alloy tends to show a shape memory effect, exhibits good spring property when Sn is contained in 4 to 5 at%, and at 6 at% content, the spring property is slightly. It turns out that it falls.

  Further, in the case of Mo, low Mo cannot sufficiently stabilize the β-base alloy, causing ω-phase formation during solution treatment or aging, leaving a difficulty in workability. On the other hand, high Mo can sufficiently stabilize β, but it becomes difficult to maintain shape memory characteristics of 2 at% or more.

The application example of the Ti base alloy of this invention is shown, (a) is explanatory drawing at the time of applying to a guide wire, (b) is explanatory drawing at the time of applying to a catheter. It is a conceptual diagram which shows the evaluation method of the shape memory characteristic of the Ti base alloy. The structure photograph of Ti base alloy is shown, (a) is a structure photograph of 0Y, (b) is a structure photograph of 0.1Y, (c) is a structure photograph of 0.25Y. The structure photograph of Ti base alloy is shown, (a) is the structure photograph of 0.5Y, (b) is the structure photograph of 1Y, (c) is the structure photograph of 2Y. It is a graph which shows the relationship between Vickers hardness (HV) and Y addition amount (at%) of Ti base alloy. It is a graph which shows the relationship between the martensitic transformation temperature (Ms) and Y addition amount (at%) of Ti base alloy. A stress σ (MPa) -strain ε (%) diagram of a Ti-based alloy when a tensile cycle test is performed is shown, (a) is a result of 0Y, (b) is a result of 0.1Y, (C) is the result of 0.25Y. A stress σ (MPa) -strain ε (%) diagram of a Ti-based alloy when a tensile cycle test is performed is shown. (A) is a result of 0.5Y, (b) is a result of 1Y, (C) is the result of 2Y.

Explanation of symbols

10 Guide wire 20 Catheter

Claims (4)

  0.01-20 at% Y, 1-20 at% X1 (where X1 = one or a combination of several of V, Cr, Zr, Nb, Mo, Hf, Ta), 0-20 at% X2 (However, X2 = Al, Ag, Sn, or a combination of several), and the balance is Ti and inevitable impurities.   2. The Ti-based alloy according to claim 1, wherein X <b> 1 is Mo and the content thereof is 4 to 10 at%, and X <b> 2 is Sn and the content thereof is 3 to 10 at%.   The Ti-based alloy according to claim 1 or 2, which is used for a medical device.   The Ti-based alloy according to claim 3, wherein the medical device is one selected from a catheter, a guide wire, and a stent.