Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Patent
1991-02-15
1993-06-08
Kight, III, John
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
528354, 528357, 528501, 528502, C08F 600, C08F 610
Patent
active
052180875
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for modifying a medical material of lactic acid polymer.
BACKGROUND ART
Lactic acid polymers such as polylactic acid are absorbed into the living organism on in vivo hydrolysis, and because of this nature are used for various medical materials, for example, for surgical materials to be imbedded in the living body. These polymers are processed into monofilaments, threads, knits, nonwoven fabrics, woven fabrics, shaped bodies or the like to provide surgical sutures, artificial ligaments, artificial tendons, patches, meshes, bone-joining pins, plates, screws, stapler pins or the like. Since lactic acid polymers are gradually decomposed and absorbed in the living organism, they are known as suitable materials for artificial ligaments, bone-joining pins, artificial tendons, etc. which are generally employed for purposes in which healing takes a prolonged period of time.
This type of medical materials of lactic acid polymers are not satisfactory in the ability to retain the strength in the living organism because the medical material is diminished in the strength, particularly tensile strength, in a relatively short time after implantation in the living body, frequently posing medically unfavorable problems. In view of the possible problems, there is a need for medical materials of lactic acid polymers which can retain sufficient strength in the living body over a longer period of time when used for medical applications.
DISCLOSURE OF THE INVENTION
The present invention provides a modified medical material of lactic acid polymer which can retain sufficient strength in the living organism over a prolonged period of time and a process for preparing the same.
More specifically the present invention provides a method for modifying a medical material of lactic acid polymer, the method comprising heat-treating the material at a temperature which is not lower than 100.degree. C. and is lower than the melting point of the polymer for at least 10 minutes while continuously releasing the gas from the system.
The present inventors' research revealed the following. When a medical material of lactic acid polymer is heat-treated at a temperature which is not lower than 100.C but is lower than the melting point of the polymer for at least 10 minutes while releasing the gas from the system, the medical material is thermally favorably modified and made to retain sufficient strength in the living body over a long period of time. The medical material of lactic acid polymer is pronouncedly improved in the ability to retain the strength in vivo, only when heat-treating the material at not lower than 100.degree. C. for at least 10 minutes while continuously releasing the gas from the system. If the heat-treatment is done at a temperature of lower than 100.degree. C., or for a period of shorter than 10 minutes, or in the system which is unable to continuously release the gas, although under otherwise favorable conditions, the obtained medical material is not fully improved in the ability to retain the strength in the living organism and is reduced in the strength in the living body in a relatively short period of time. While it has yet to be completely clarified why the heat treatment in the invention can pronouncedly improve the ability to retain the strength in the living organism, this is presumably because the undesired impurities such as the oligomer of a monomer, dimer or the like are removed from the polymer on vaporization by heating under the above-specified conditions, and also because the structure, particularly the crystalline structure, of the polymer undergoes some change by heating at 100.degree. C. or higher for 10 minutes or more, thereby properly reducing the hydrolyzing rate of the polymer in the living organism.
Examples of lactic acid polymers to be modified according to the present invention are poly-L-lactic acid, poly-D-lactic acid, poly-D,L-lactic acid, a stereocomplex of poly-D-lactic acid and poly-L-lactic acid and like polylactic acids;
REFERENCES:
patent: 3636956 (1972-01-01), Schneider
patent: 3772420 (1968-12-01), Glick et al.
Ikada Yoshikiyo
Saito Yoshikiyo
Shuon Hye H.
Suzuki Masakazu
Dodson Shelley A.
Gunze Limited
Kight III John
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