CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application, filed under 35 U.S.C. § 371, of International Application No. PCT/JP2018/008442, filed Mar. 6, 2018, which claims priority to Japan Application No. 2017-042037, filed Mar. 6, 2017, the contents of both of which as are hereby incorporated by reference in their entirety.

BACKGROUND

Technical Field

The present disclosure relates to a film formation method, and more particularly relates to a film formation method, a film formation apparatus, and a medical material for use to form a diamond-like carbon film on an inner wall surface of a long thin tube.

Description of Related Art

Medical materials that have recently grown in demand include an artificial blood vessel. Artificial blood vessels that have been typically used are made of polytetrafluoroethylene (ePTFE) containing polytetrafluoroethylene (PTFE) expanded to have its porosity increased. The ePTFE is a material having good biocompatibility, but is not sufficient to prevent occlusion. For this reason, the use of ePTFE artificial blood vessels with a diameter less than 6 mm is very risky.

Although a material derived from humans or animals may be used as a thin artificial blood vessel, such a material has problems in terms of safety and stable supply. To address these problems, there is a need for a thin artificial blood vessel not tissue-derived and difficult to occlude.

A diamond-like carbon (DLC) film, which is an amorphous carbon film containing sp2carbon, sp3carbon, and hydrogen, has superior biocompatibility. Thus, it is expected that forming a DLC film on an inner wall surface of an artificial blood vessel can make it difficult to occlude the artificial blood vessel. However, a DLC film is not easily formed on an inner wall surface of a long thin tube, such as an artificial blood vessel.

Examples of methods for forming a DLC film on an inner wall surface of a tube body include a method in which a discharge electrode is inserted into a tube body (see, for example, Patent Document 1). Further, consideration has been given also to a method in which a tube body is sandwiched between two electrode plates to generate plasma inside the tube body to form a film, without inserting the electrode into the tube body (see, for example, Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Publication No. 2015-147974

Patent Document 2: Japanese Unexamined Patent Publication No. 2008-192567

BRIEF SUMMARY

However, the known film formation method has the following problems. If a discharge electrode is inserted into a tube body, the discharge electrode needs to be longer than the tube body on which a film is to be formed and to be thinner than the inside diameter of the tube body. The discharge electrode on which a high pressure is imposed needs to have a certain thickness or larger, thus making it actually impossible to form a film on an inner wall surface of a thin tube having a diameter of 6 mm or smaller. Further, shortening the distance between the discharge electrode and the inner wall surface may cause a metal component desorbed from the discharge electrode to adhere to the inner wall surface. If a carbon electrode is used as the discharge electrode, metal does not adhere to the inner wall surface. However, it is difficult to form a long thin carbon electrode.

If a tube body is sandwiched between two electrodes, large electrode plates are required to form a film over the entire long tube body. The tube body may be moved between the electrodes, or the electrodes may be moved along the tube body. However, in this case, a mechanism for moving the tube body is required. In addition, a hydrocarbon gas needs to be enclosed in the tube body. Thus, a film cannot be successfully formed on a porous artificial blood vessel even if the tube body is disposed directly between the electrodes.

It is expected that it is useful to form a DLC film on an inner wall surface of a catheter or any other similar object, because the formation of the DLC film provides advantages, such as high biocompatibility and a reduction in friction against the inner wall surface. However, a long thin tube for use in a catheter or any other similar object also causes a problem similar to that of an artificial blood vessel.

It is an object of the present disclosure to be able to easily form a DLC film on an inner wall surface of a medical material serving as a long thin tube.

A film formation method according to an aspect of the present disclosure includes: arranging a non-conductive long thin tube in a chamber capable of adjusting an internal pressure, and generating plasma inside the long thin tube while a source gas containing hydrocarbon is supplied into the chamber, and forming a diamond-like carbon film on an inner wall surface of the long thin tube. The long thin tube is disposed in the chamber such that a discharge electrode is disposed at one end of the long thin tube and such that the other end of the long thin tube is opened. An alternating current bias is intermittently applied between the discharge electrode and a counter electrode spaced apart from the long thin tube.

In the film formation method according to the aspect, the long thin tube may be porous, and may be disposed in the chamber while being housed in an outer cylinder having an inside diameter larger than an outside diameter of the long thin tube.

In this case, the long thin tube may be an artificial blood vessel.

In the film formation method according to the aspect, the long thin tube may be a catheter.

In one embodiment of the film deposition method, the counter electrode may be an inner wall surface of the chamber.

A film formation apparatus according to one aspect of the present disclosure includes: a chamber capable of adjusting an internal pressure; a gas feeder configured to feed a hydrocarbon gas into the chamber; a discharge electrode and a counter electrode provided in the chamber; and a power supply configured to intermittently apply an AC voltage between the discharge electrode and the counter electrode. The discharge electrode is attached to one end of a non-conductive long thin tube to discharge electricity with the counter electrode spaced apart from the long thin tube. Plasma is thus generated in the long thin tube to form a diamond-like carbon film on an inner wall surface of the long thin tube.

The film formation apparatus according to the aspect may further include: an outer cylinder housing the long thin tube. The long thin tube may be porous.

A medical material according to one aspect of the present disclosure includes: a non-conductive long thin tube having an inside diameter from 0.1 mm to 6 mm and a length of 2 cm or more and having an inner wall surface on which a diamond-like carbon film is formed.

In the medical material according to the aspect, the long thin tube may be an artificial blood vessel or a catheter.

A film formation method of the present disclosure allows a DLC film to be easily formed on an inner wall surface of a medical material serving as a long thin tube.

