Another inventive medical-technology breakthrough at TU Delft. Researchers there have developed a material that can greatly extend the lifespan of hip implants. It involves a hybrid meta-bio material made with a 3D printer.
It is a material that cannot be found in nature but can be created with a 3D printer and already existing biomaterials: a hybrid meta-biomaterial that promotes bone ingrowth. Researchers at TU Delft developed a meta-implant that combines conventional meta-biomaterial with auxetic meta-biomaterial. This is important because the latter - unlike natural materials - has a negative Poisson's ratio. This means that the material expands laterally (it becomes thicker) when stretched. With this property, the material can provide better anchoring of hip implants, among other things. On 2 January 2018, the Delft scientists published their findings in the scientific journal Materials Horizons.
Currently, the global number of hip replacements is expected to rise to 2.5 million a year around the year 2020. Some 10 per cent of these implants, with the current techniques used, will no longer be properly anchored in the body within a decade. This prompted Prof Amir Zadpoor of TU Delft to search for a way to prevent this. Which he thinks he has now found with the help of the auxetic meta-biomaterial.
Forces
Meta-biomaterials are the biomedical variant of so-called metamaterials, which exhibit unusual properties not found in nature; they can be invisible, are extremely strong yet extremely light and exhibit negative thermal expansion. The publication by Zadpoor and his colleagues shows that these unusual properties are very interesting for the development of medical implants. 'Because auxetic meta-biomaterial, created with simple geometry and the use of titanium, has the special mechanical property that it expands when pressure is applied to it, it is ideally suited to complement materials that do just the opposite,' explains Zadpoor. 'When someone with a hip implant walks, for example, various forces arise on the prosthesis. In case of too much pressure on one side of the prosthesis, there may be a case of subtracting from the bone, which is very undesirable.'
Loosening
The researchers suspect that a hybrid prosthesis made partly from meta-biomaterial with a positive Poisson's ratio and partly from meta-biomaterial with a negative Poisson's ratio could become much better anchored in the body. 'The hybrid meta-biomaterial can thus have a better chance to fuse with the bone, which will make the implant much more firmly attached.' Zadpoor also thinks this new material will overcome the main cause of prosthesis loosening in the future: 'Because there are fewer unnatural forces acting on the prosthesis, there is less chance that plastic particles will be released when the hip socket wears down, increasing the likelihood of loosening.'
Further research
So far in an experiment, Zadpoor has loaded an implant with vertical forces downward, surrounded by bone-like material (special foam with the mechanical properties of bone). The force simulates the loading of an implant in the human body. This force causes the implant - made of the new hybrid meta-biomaterial - to expand, causing compression in the surrounding bone on both sides of the implant (the turquoise blue discolouration in the image above). Precisely this can ensure better anchoring. Clinical trials have not yet taken place. The research question that the Delft group, in collaboration with researchers from several university hospitals, will focus on in the coming years is how exactly these properties can be used to develop better implants.
Potential
'Innovation of hip implants is badly needed and this new method by Prof Zadpoor certainly has the potential to extend the lifespan of implants. This should then be followed by a phased introduction with 3D measurements of this implant in the patient first to achieve a safe quality improvement for patients,' says Prof Rob Nelissen, orthopaedic surgeon at Leiden University Medical Centre and Medical Delta Professor.
By: Kelly Bakker
Source: TU Delft
