X-ray or gamma ray systems or devices – Specific application – Absorption
Patent
1988-07-01
1991-04-30
Church, Craig E.
X-ray or gamma ray systems or devices
Specific application
Absorption
G21K 500
Patent
active
050125036
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method for sterilization of polyvinyl alcohol gel and more particularly it relates to a method for .gamma.-ray sterilization of hydrogel obtained by freezing and thawing of aqueous polyvinyl alcohol solution or by partial dehydration under vacuum of aqueous polyvinyl alcohol solution in frozen state wherein sterility harmless for living tissues can be obtained by avoiding by-production of soluble .gamma.-ray decomposition products.
BACKGROUND ART
Sterilization, pasteurization and disinfection are essential for medical materials which contact directly or indirectly with living tissues. Various methods of sterilization, pasteurization and disinfection have been proposed and it is well known that either one of them is employed depending on properties of medical materials and purposes of use thereof and efforts have been made to ensure and accomplish safety and innocuousness of materials.
Among these methods, advantages of .gamma.-ray sterilization method are noticed in that the method can sterilize the materials through container in which the materials are completely enclosed and besides the method is effective for bacterial spores high in heat resistance and further Pseudomonas aeruginosa, spores of tubercle bacillus and Gram-negative bacteria which often show resistance against medicines (disinfectants) and the .gamma.-ray sterilization method is considered to have high reliability in sterilization of rubber articles and plastic articles (general polymer materials poor in heat resistance) to which is difficult to apply high pressure steam sterilization method and dry sterilization method.
As the method which comprises enclosing a non-heat resistant material in a container made of plastic film and then sterilizing the material through the container, gas sterilization method with ethylene oxide is famous and is widely used in hospitals and medical device makers. In this case, it is necessary to perform desorption of residual gas adsorbed to materials carefully and over a long period of time and further to keep watch to ensure that amount of still remaining ethylene oxide (and ethylene glycol, ethylene chlorohydrin, etc. as modification components thereof) is less than permissible limits. Especially, when this gas sterilization method is applied to sterilization of hydrogels (water-containing gels) represented by polyacrylamide, much care must be taken for discharge of a large amount of gas dissolved in water as well as adsorbed gas. Although it can be said that regulation value can be met (degassing to 2000 ppm), there is some fear of remaining toxicity which may cause hemolysis and thrombus.
.gamma.-ray sterilization method does not require operation for removal of residual toxin as required in the above gas sterilization method and disinfection with chemicals (ethyl alcohol, formalin, glutaraldehyde, chlorohexidine, benzalkonium chloride, etc.) and hence, merits as sterilization method for non-heat resistant medical materials have been widely recognized. However, it has been warned that irradiation of a large quantity of .gamma.-ray results in denaturation (radical decomposition and oxidation decomposition of materials) of most of rubbers and plastics to produce soluble (water-soluble) low molecular weight deterioration products and furthermore, mechanical strength of the materials per se often decreases. (Takuma Ohba; "Kobunshi", 22, 607 (1973)).
The phenomena of formation of radicals due to irradiation with .gamma.-ray, which cause deterioration by oxidation in which coexisting oxygen participates have been confirmed in natural polymers (protein) and synthetic polymers and aqueous solutions of these polymers. [See, P. S. Elias et al (translators, Rikimaru Hayashi et al); "Shokuhin Shosya no Kagaku" ("Chemistry of Irradiation of Food", p. 11 (1981) published from Gakkai Shuppan Center; Mineo Sado, "Ikishi" (J. Medical Instruments) 55, 480 (1985); and Kenji Sato, "Rinshoishi" (J. Clinics), 11, 422 (1985)]. Further, it was attempted to conduct irradiation witho
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Nambu Masao
Onishi Tadayuki
Onohara Masayuki
Church Craig E.
Nippon Oil Company Ltd.
Sumitomo Bakelite Company Ltd.
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