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Introduction
Plastics are more and more replacing traditional materials like stainless steel and glass in medical applications, not only for disposable products and packaging materials but also in reusable medical devices. The hygienic treatment of these products is an important prerequisite for reprocessing. During the use and the reprocessing, the materials are exposed to physical, chemical and thermal stresses affecting the ageing process (Tröger et al. , 2008; Massey, 2005).
As part of a research project at the Institute of Medical and Polymer Engineering (Technische Universität München, Germany) in cooperation with SKZ (German Plastics Centre, Würzburg, Germany), several autoclavable thermoplastics are loaded with a cycle of use, cleaning, disinfection and sterilization corresponding to the clinical use. Afterwards their properties and modifications are analysed. The experimental use is realized by a static bending load with different outer fibre strains and an affecting medium, the simulated body fluid (SBF).
The quick and flexible way of manufacturing out of electronic data enables, for example, indentations and joints manufactured in only one step. Those advantages of laser sintering are unique compared to conventional manufacturing technologies, such as injection moulding of plastics. These two manufacturing methods are compared in relation to ageing caused by the sterilization processes. In particular, the mechanical properties in a tensile test, the fracture pattern, the surface topography and the liquid absorption before and after the stress cycles are analysed and discussed. To obtain significant results, the injection moulded specimens are made of polyamide 12 (PA12) pellets (VESTAMID® L1670, Evonik Degussa GmbH, Marl, Germany) and the laser sintered specimens are made of a powder (PA2200, EOS GmbH, Krailling, Germany), which is based on the same VESTAMID®.
Among engineering plastics, polyamide is an often used material for laser sintering. In medical engineering, polyamides are used, for example, for catheter tubes, syringes, artificial cardiac valves and components of dialysis equipment (Wintermantel and Ha, 2009; Jayabalan, 1995).
Materials and methods
To compare laser sintered specimens with injection moulded specimens, the geometry as shown in Figure 1 was designed specially adjusted to the dimensions of the experimental equipment. For the production of injection moulded specimens, the PA12 polymer VESTAMID® L1670 is processed with the injection moulding machine KM50 180 EX (Krauss Maffei Technologies GmbH, Munich, Germany). This material is characterized...