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Powder based processing is a common approach in manufacturing of metallic or bioceramic implants. It allows net shape production along with broad variation in material choice, density and surface characteristics. In this paper, powder injection moulding is applied for manufacturing of interference screws for ligament fixation. The suitability of this process is reflected by the successful processing of stainless steel, titanium, hydroxyapatite (HA) and polylactic acid (PLA). With some process modifications, PLA / HA composites with high HA shares up to 70% are obtained by pressing and sintering. By suitable selection of powders and space holders, porosity can be steered for optimum bone compatibility in tissue engineering.
Introduction
In connection with the increasing claim of people for a mobile and active life, the treatment of knee injuries is a growing medical challenge. For instance in case of rupture of the cruciate ligament, commonly a transplant of a patient's fibre is used for reconstruction of the ligament. This transplant is usually fixed with two bone screws, so-called interference screws. These fix the fibre within the bone, and engraftment takes place within 6 to 8 weeks [1].
Materials commonly used for manufacturing of interference screws are titanium alloys or medical grade stainless steel. More recently, biodegradable polymers (PLA) and PLA based composites which can be processed by injection moulding are being chosen as alternatives to metal screws where appropriate. As the material is resorbed by the human body over time, the number of surgeries to extract screws after healing can be significantly reduced. For further enhanced bioactivity, commercial PLA / HA based composites (HA) content up to max. 40%) are also on the market. HA is the main constituent...