Stabilisation of crosslinked ultra-high molecular weight polyethylene (UHMW-PE)-acetabular components with alpha-tocopherol.
A stabilisation of crosslinked ultra-high molecular weight polyethylene (UHMW-PE) with alpha-tocopherol (vitamin E) used for endoprostheses can increase its resistance against oxidative degradation remarkably. However, the method used for conventional UHMW-PE of adding alpha-tocopherol to the UHMW-PE powder before processing can not be applied for crosslinked UHMW-PE, since the alpha-tocopherol hinders the crosslinking process, which would be accompanied by a heavy degradation of this vitamin. The alpha-tocopherol has therefore to be added after the crosslinking process. This paper presents two methods for a stabilisation of finished products with alpha-tocopherol. In method 1, UHMW-PE-cubes (20 x 20 x 20 mm3) were stored in pure alpha-tocopherol under inert atmosphere at temperatures from 100 degrees C to 150 degrees C resulting in a high mass fraction of alpha-tocopherol in the edge zones. For further homogenisation, the cubes were stored in inert atmosphere at temperatures from 160 degrees C to 200 degrees C. In method 2, supercritical CO2 was used to incorporate the vitamin into the UHMW-PE. In an autoclave vessel, the cubes were treated with alpha-tocopherol dissolved in supercritical CO2 for several hours at temperatures from 100 degrees C to 170 degrees C. In both cases, the mass fraction of alpha-tocopherol was detected with the help of a FTIR-microscope. Both methods are well suited to stabilise crosslinked UHMW-PE with alpha-tocopherol. A stabilisation of the sensitive edge layer as well as a nearly homogenous distribution with varying alpha-tocopherol content may be realised by varying the process parameters. Using method 2, standard hip cups were stabilized nearly homogeneously with varying mass fraction of alpha-tocopherol. No oxidation of the UHMW-PE could be detected by infrared spectroscopy (FTIR) and HPLC studies showed a very low degradation of the alpha-tocopherol for both processes.
Wolf
C
C
Department of Chemistry of Polymeric Materials, University of Leoben, 8700 Leoben, Austria. christian.wolf@unileoben.ac.at
Maninger
J
J
Lederer
K
K
Frühwirth-Smounig
H
H
Gamse
T
T
Marr
R
R
D000077:Acetabulum; D001672:Biocompatible Materials / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D006622:Hip Prosthesis; D006801:Humans; D066298:In Vitro Techniques; D011095:Polyethylenes / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D024502:alpha-Tocopherol / Q000737:chemistry / Q000494:pharmacology*
D001672:Biocompatible Materials; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D024502:alpha-Tocopherol