Jan 13, 2018 | By David

3D printing has already made a serious impact on the construction of prosthetics and other medical devices over the last few years, and this looks set to continue as the technology progresses. The development of new materials should be a particularly large contributing factor, with bio-materials offering a whole range of advantages due to their organic basis. A team of researchers at TU Delft have recently created new bio-metamaterials that show promise for the future 3D printing of hip implants, due to its unique combination of important properties.

Implant loosening is one of the problems that can affect the long-term effectiveness of medical devices, particularly ones made for the hip region. By the year 2020, the number of hip prostheses around the world is expected to rise to 2.5 million a year, and with the current technology, about 10 percent of these implants will no longer be firmly fixated 10 years after surgery. The TU Delft team, led by Amir Zadpoor, set out solve this problem by 3D printing implants that will be more permanently fixed, with the combination of two types of bio-metamaterial. One is a conventional bio-metamaterial, whereas the other is what is referred to as an auxetic bio-metamaterial.

Meta-biomaterials are the biomedical variant of so-called metamaterials, materials that display characteristics that are not found in nature. What’s special about the auxetic variant is that they have a negative Poisson’s ratio, which means that when stretched, they become thicker perpendicular to the applied force. According to Zapdoor, "Auxetic meta-biomaterial, designed using simple geometry and printed in titanium, displays the unique mechanical property of expanding when put under pressure. This makes it ideal for use alongside materials that do the opposite...When someone with a hip implant walks, the prosthesis is subjected to various forces. If too much pressure develops on one side of the prosthesis, it can become detached from the bone, which is extremely undesirable."

The 3D printed hybrid prosthetic hip implants combine a material that becomes thicker when stretched and one that becomes thinner. This dual Poisson’s ratio combination will improve the chances of bone growth around the implant, which means that they will be fixed more securely in place. Unnatural forces exerted on the implant will also be reduced, making it less likely that the implant will erode.

Clinical trials have not yet been carried out on the implant. The experiments done so far involved a vertical compression on an implant surrounded by a simulated bone-like material (special foam with the mechanical properties of bone). The force is similar to the stress that would be exerted on an implant in the human body. As a result of this pressure, the new implant expanded, resulting in compression in the surrounding bone on both sides. It is exactly this compression that will ensure improved implant fixation, when the implant is eventually used in a human body. The results of the team’s experiments were published in a paper called "Rationally designed meta-implants: a combination of auxetic and conventional meta-biomaterials," in the Royal Society of Chemistry's peer-reviewed journal Materials Horizons.

The next step for the project will be to explore the materials’ properties in more detail, working in close collaboration with researchers from various academic hospitals. Professor Rob Nelissen, a Medical Delta Professor and orthopaedic surgeon at the Leiden University Medical Centre, was enthusiastic about the potential for the TU Delft team’s findings: "Innovation in the field of hip implants is badly needed, and Professor Zadpoor's new method certainly has the potential to prolong the lifespan of implants", he said. "A phased introduction starting with 3-D measurements of this implant in patients will be necessary in order to guarantee the safe improvement of quality for patients."

 

 

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