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2007, vol. 61, iss. 5, pp. 229-232
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Supercritical CO2 impregnation of polyethylene components for medical purposes
Impregnacija polietilenskih komponeti za medicinske namene nadkritičnim CO2
aDepartment of Chemical Engineering and Environmental Technology, Graz, Austria bDepartment of Chemistry of Polymeric Materials, Leoben, Austria
email: thomas.gamse@tugraz.at
Abstract
Modem hip and knee endoprosthesis are produced in titanium and to reduce the friction at the contact area polymer parts, mainly ultra-high molecular weight polyethylene (UHMW-PE), are installed. The polyethylene is impregnated with a-tocopherol (vitamin E) before processing for remarkable decrease of oxidative degradation. Cross linked UHMW-PE offers much higher stability, but a-tocopherol cannot be added before processing, because a-tocopherol hinders the cross linking process accompanied by a heavy degradation of the vitamin. The impregnation of UHMW-PE with a-tocopherol has to be performed after the cross linking process and an accurate concentration has to be achieved over the cross section of the whole material. In the first tests UHMW-PE-cubes were stored in pure a-tocopherol under inert atmosphere at temperatures from 100 to 150 °C resulting in a high mass fraction of a-tocopherol in the edge zones and no constant concentration over the cross section. For better distribution and for regulating the mass fraction of a-tocopherol in the cross linked UHMW-PE material supercritical CO2 impregnation tests were investigated. Again UHMW-PE-cubes were impregnated in an autoclave with a-tocopherol dissolved in supercritical CO2 at different pressures and temperatures with variable impregnation times and vitamin E concentrations. Based on the excellent results of supercritical CO2 impregnation standard hip and knee cups were stabilized nearly homogeneously with varying mass fraction of a-tocopherol.
Sažetak
Savremene endoproteze kukova i kolena proizvode se od titana, a da bi se smanjilo trenje kontaktnih površina ugrađuju se polimerni delovi, i to uglavnom od polietilena velike molekulske težine (UHMW-PE). Pre obrade polietilen se impregniše sa a-tokoferolom (vitamin E) koji značajno smanjuje degradaciju oksidacijom. Poprečno vezivanje UHMW-PE omogućava veću stabilnost, ali se a-tokoferol ne može dodavati pre obrade, zato što a-tokoferol sprečava procese poprečnog vezivanja, praćene izraženom degradacijom vitamina. Impregnacija UHMW-PE sa a-tokoferol mora se izvesti posle procesa poprečnog vezivanja i tačna koncentracija mora se postići duž celokupnog poprecnog preseka materijala. U prvim ispitivanjima, UHMW-PE kocke su držane u čistom a-tokoferolu u inertnoj atmosferi na temperati od 100 do 150 °C, što je rezultiralo u velikom masenom udelu a-tokoferola u ivičnim zonama i promenljivoj koncentraciji duž poprečnih preseka. U cilju bolje raspodele kao i regulacije masenog udela a-tokoferola u poprecnim vezivanju UHMW-PE materijala, ispitivana je nadkritična CO2 impregnacija. Ponovo UHMW-PE kocke su impregnisane u autoklavu sa a-tokoferolom rastvorenim u nadkritičnom CO2 na različitim pritiscima i temperaturama sa različitim vremenima impregnacije i koncentracijama vitamina E. Na osnovu odličnih rezultata impregnacijom nadkritičnim CO2, čašice veštačkih kukova i kolena su približno homogeno stabilisane sa različitim masenim udelima a-tokoferola.
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