Materials Design and Characterisation

Profile

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Team members of the department Materials Design and Characterisation

Developing metallic biomaterials includes several aspects, which are processed in parallel:
1. Designing the actual material (alloy development), which fulfils the mechanical, biological and functional requirements for application.
2. Producing the material and processing this material in the form of test specimens for studies, but also for prototype implants.
3. Characterising properties (specified under 1 above), the result of which can lead to further design adjustment.
In the Department of Materials Design and Characterisation, we are concerned with all three work packages and our objective is to develop and optimise biodegradable magnesium as well as titanium alloys for permanent implants.

Materials Design

We concentrate on powder metallurgy methods for material development and processing, particularly on metal injection moulding (MIM). A motivation for utilising powder metallurgy methods is that, compared to other technologies, it is a relatively simple alloy variation. It also possesses high microstructural homogeneity and demonstrates great flexibility in terms of the manufactured geometry. Both titanium and magnesium materials are very sophisticated materials. Without understanding the material behaviour and underlying physical processes, during sintering for example, optimal results cannot be achieved with respect to the component properties and the ability to reproduce such properties during manufacturing. This is why we study the processes that occur in titanium and magnesium alloys during powder metallurgical processing and then derive optimized material compositions and process parameters.

Implantable screws for spine fracture treatment. MIM made of TiAl6Nb7 powder (Design: Tricumed Medizintechnik GmbH) .

A complete MIM manufacturing chain, including feedstock production, is available for our research. This manufacturing chain has been specifically adapted for the demands of oxygen-sensitive materials such as titanium and magnesium. Current research topics include investigating the roles of oxygen and carbon in influencing the mechanical characteristics as well as the sintering and refinement of the microstructure by developing special alloys. We have even been capable of processing magnesium alloys using MIM since 2012, a global pioneering achievement.

Characterisation

In addition to the characterisation of material properties by mechanical and optical methods, we focus on material analysis under physiological conditions. In doing so, we are especially concerned with studying the degradation behaviour of magnesium alloys.

Standard tests such as e.g. salt spray tests have turned out to be non-predictive with respect to the behaviour of implant materials in living organisms (in vivo). For this reason, we adapt and develop novel in vitro test procedures, in order to eventually be able to make more reliable statements about the suitability of different alloys as implant materials and their in vivo behaviour.

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In vitro degradation of Magnesium alloy. Top: PEO coated, bottom: bare alloy © Jorge Gonzales

Each newly developed material passes through several series of tests in which different material properties are measured under various physiological conditions. In these tests, the material is exposed to a variety of physiological fluids such as blood, medium or serum. The influence of cells on the material and its properties is studied. In addition, tissue-specific flow rates can be set in the bioreactor which simulate the in vivo situation even better.

If an alloy is found to be particularly promising, the material is passed to the Biological Characterisation department. There, the reactions of different cell types and their specific adaptation and alteration mechanisms in contact with metallic biomaterials are investigated.