PEEK - a polymer for implants subjected to mechanical loads

Polyetheretherketone (or PEEK) is another plastic that is enjoying a growing success story in medical technology - especially for implants that are subjected to mechanical loads. The material has been tested and approved for permanent use in human implants thanks to its good biocompatibility. "Our PEEK-OPTIMA offers an excellent and balanced combination of mechanical, physical and chemical properties", explains Roland Gröger, Medical Market Development Manager at Invibio Europe, who is responsible for dental, pharmaceutical and cardiovascular applications, in particular. Invibio Ltd. (Thornton Cleveleys, UK) is the market leader for this material for use in medical applications. Due to its semi-crystalline structure it has ideal X-ray properties and excellent radiolucency for computer and magnetic resonance tomography, without showing losses due to scattering or artefacts. In addition, this polymer also has another advantage, improving bonding between the bone and the implant as its elastic modulus is very similar to that of the outer cortical layer of the bone. In order to ensure purity and prevent infection, modern sterilization methods use aggressive chemicals, elevated vapor pressures in autoclaves or high doses of radiation. Products made of PEEK-OPTIMA give the user great freedom in this respect, since they are suitable for use with any of the common methods of sterilization, which is another reason why PEEK has taken over some 80 - 90% of the market from titanium in some areas.


Many new materials that actually have good properties fail because they cannot be processed or machined in order to be used for the intended purpose. For this reason, The Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM, Bremen) has developed a powder injection molding process for biocompatible materials. "The process is available for serial production and allows highly complex parts to be made even without the need for machining to finish them", explains Dr. Philipp Imgrund, Head of the Department of Biomaterials Technology at the IFAM. In the process also referred to as "metal injection molding" (MIM), metal powder is mixed with an organic binder system at a ratio of 65 to 35 percent, although the binder is then removed again when it is melted and formed. It is then sintered to consolidate it to its final density. In addition to using various metals, this method can also be performed using ceramics such as alumina, zirconia or hydroxyapatite (HA). HA is a component of natural bone and is biodegradable. "Mixtures of HA and polylactic acid are especially interesting, as the mechanical properties of dense composite materials of this kind are extremely similar to human bone material", says Imgrund. The first potential uses are interference screws for fixation of cruciate ligaments in the knee. Microstructuring of parts made using the MIM process improves their bioactivity and governs tissue-specific cell behavior.

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