The aim of this project is to develop new bioactive bone substitute materials for loaded parts of the human skeleton, for example knee and hip joints, and to elaborate the corresponding manufacturing technology.
Materials used today for medical implants like stainless steel, titanium, alumina, zirconia, polymers and their composites can be considered as bio-inert materials and are in general not directly attached to the bones. Therefore such implants do not provide the complete rehabilitation of the used or destroyed articulation and do not allow for loading as before. To our knowledge, no solutions have yet been found for bigger articulations like joints of finger bones.
The natural bone has a very complicated structure which is optimized at several scales: first there is a cellular structure with nanometric dimensions; second there is a fibrous structure with whiskers and fibres from micrometer to millimetre size, and; third there is the geometry of the bone which is very often a surprisingly perfect solution to the problem of minimizing the internal stresses for a given load. All elements interact mutually and with surrounding tissues. Unfortunately, our knowledge will not allow an exact reproduction of the structure of natural bones, but by the use of nanotechnologies, some of the essential features may by approached.
Some of the key elements in the manufacturing process of nanosized hydroxyapatite (HA) powders have been investigated in the last years. In addition, several nanosized ceramic powders have become available, especially zirconia powders with different stabilizing elements (magnesia, yttria, ceria) are currently manufactured with plasma technology. The considerable reduction in the sintering temperature of these materials makes it now possible to head for ceramic composites with HA, which decompose at about 1550 K, a temperature far too low to sinter ordinary ceramic powders.
Although HA compositions can be made which are partially resorbed by the human body, the mechanical properties of the pure HA are too poor to make parts of artificial articulations from it. Therefore the task of this project will be to develop bioactive materials with:
* A dense, structure-strengthened material, which can withstand applied loads and wear when it is used as an implant for articulations
* A bioactive material exhibiting a controlled degree of porosity, providing good binding through interaction with the surrounding tissue.
This work includes material research and, on the other hand, research on the methods of manufacturing these pieces.
Testing of biological and biochemical safety will be performed in the second part (particularly regarding the tribological behaviour and possible contamination by the formation of particles due to abrasion).
Keywords: bioactive bone implant material, nanostructured hydroxyapatite composite, nanosized plasma processed ceramic powders.