Material tested could guarantee body protheses for more than 150 years

Researcher Nere Garmendia, based in the Basque city of Donostia-San Sebastián, has just published her PhD, a thesis which may well mean the first step to solving this problem. According to Garmendia, using a ceramic material called zirconia (ZrO₂), carbon nanotubes and nanoparticles of zirconia, a prosthesis that will last more than 150 years can be produced.

The PhD thesis is titled "Development of a new nanocompound material made of zirconia with coated carbon nanotubes, for orthopaedic applications." Garmendia wished to show that the aging and cracking of prostheses could be avoided. To begin with, carbon nanotubes were added to the zirconia matrix -- a technique that greatly strengthens its resistance. With this composite material as a base research was initiated.

The researcher reinforced the connection between the zirconia matrix and the nanotubes, with the intention of improving the transfer/distribution of loads. The nanotubes were coated with nanoparticles of zirconia and, in order for this to be effected, the nanoparticles were heated beyond their boiling point (hydrothermal synthesis). This coating functioned as a bridge between the zirconia matrix and the nanotubes.

Garmendia explained in her thesis that working at a nanometric scale is precisely the key to achieving long-lasting prostheses. In a prior experiment with micrometric zirconia it was concluded that this material would end up considerably aged after 12 years. Nevertheless, as has been pointed out, apart from the zirconia matrix, adding carbon nanotubes and the nanoparticles of zirconia coating them, the material will not age -- even after 150 years.

The maximum possible density

With the nanotubes coated, Garmendia investigated the capacity for the displacement and dispersion of the composite obtained from the previous process, and also looked for its suitable point of density. Based on this and aided by plaster, she achieved the first compact pieces.

Subsequently, Garmendia specified the number of coated nanotubes each piece had to have in order to achieve the optimum density at the end of the process. According to the researcher, adding zirconia nanoparticles to the nanotubes facilitates the dispersion of the material and reduces its viscosity, apart from helping to increase its density for the next and last stage: the synterization stage. Synterization is a process, used particularly in ceramics, in order to transform the material from powder to a compact solid. Not just any quantity is useful to achieve this maximum possible density and, thus, before synterization, it has to be decided how many nanotubes are to be introduced and, of course, synterization has to be subsequently carried out correctly.

As Garmendia calculated, if the intention is to obtain the maximum possible density (98%), in order to start the composition, 1% of its volume must be of coated nanotubes. Finally, the material has to be synterized in argon for one hour at 1,300 degrees; not more nor less.