Targeted dissolution: the new generation of implants

Magnesium calcium alloy screws can be dismantled by the body without any problems and they are light and solid. Photo:HZG/ M. Wolff

When autumn arrives it brings wind and rain, leaves fall from the trees and settle on the ground. If someone slips on them, a bone can easily be broken. When a nail or a plate is required for the fixation of such a bone fracture, it is nowadays usually made of titanium, as this material is stable and well-tolerated by the human body. However, this foreign body must often be removed after the bone has healed, as there is otherwise a danger of inflammation or even bone loss.

According to Prof. Dr. Regine Willumeit, the head of the ‘Structural Research on Macromolecules’ department at the Helmholtz-Zentrum Geesthacht: “The aim of modern implant research is to develop a material which can be used in the body like a real replacement material. A biomaterial which at first supports the bone but then disappears of its own accord after the bone has recovered”.

Magnesium is excellently suited to this purpose. This element is naturally present in the human body and has the advantage that it can biodegrade in a pre-determined manner. It must, thereby, be both light and strong but also well-tolerated by the body. Research scientists at the Helmholtz-Zentrum in Geesthacht are therefore focussing their attention on this particular biomaterial.

Prof. Dr. Regine Willumeit, Head of of the ‘Structural Research on Macromolecules’ department. Photo: HZG/ Christian Schmid

The Helmholtz-Zentrum in Geesthacht has shown great expertise for many years in the research and production of prototypes for metallic biodegradable magnesium alloy implants. Material researchers are, for example, engaged in investigations into innovative magnesium-calcium alloys. These reveal material properties similar to those in bone; they are firm and at the same time elastic. Calcium appears to be well suited as an alloy as it would be able to degrade into non-toxic products in the body in the same way as magnesium. The degradation products would even be able to stimulate bone growth.

As Prof. Dr. Regine Willumeit explains: “ We are developing alloys in Geesthacht which have extremely promising properties for use in orthopaedic and traumatological applications. The colleagues at the Magnesium Innovations Center, MagIC, at the HZG, provide us with the starting material, we examine the factors which determine the degradation of the magnesium under physiological conditions”.

Scientists are not only engaged in research into the degradation process of the material itself. Tests are carried out in the Geesthacht laboratories in cell culture on the effects of the degradation on surrounding cells, for example. The scientists involved in this fundamental research into innovative implant materials have comprehensive analysis and test methods at their disposal.

Due to the self-desolving qualities of bioimplants a second surgery is not necessary. Photo: iStock/real444

The development of production processes is still causing researchers headaches. However, they have also made great progress in this area. The scientist Martin Wolff, from the powder technology department, has, for the first time, succeeded in producing magnesium-calcium bone screws by means of the metal powder injection moulding process (MIM).

As he explains: “The challenge in the case of magnesium lies in the high affinity of this material for oxygen. However, even small amounts of oxygen lead to dramatic changes in the mechanical properties of the component. Calcium, as an alloy partner, captures the oxygen in the production process during the so-called sintering procedure, and the material thus becomes firmer. This non-toxic alloying element has proved successful in achieving better results, at least in experiments. However, numerous further investigations now lie ahead, e.g. in cell culture and in the organism, before this material can be utilized as an implant material.

The Helmholtz researchers from Geesthacht will present their results at the Annual Congress of the Deutsche Gesellschaft für Biomaterialien, DGBM (German Society for Biomaterials), which is to be held at the Chamber of Commerce in Hamburg from 1st to 3rd of November 2012. The main focus this year will be on “Degradable Implants and Biomaterials”. The Congress will be led by Prof. Dr. Regine Willumeit.