Dr. Hassel, an implant that is supposed to dissolve in the body after a while. What criteria do you use to choose the basic material?
Thomas Hassel: We needed a bioabsorbable metal that is not toxic to the body. And magnesium has this unique property to where we are able to apply and use it as a scaffold. Iron would have been another option, but it does not have the corrosion rate required for our implant. The degradation rate of magnesium works far better for our purposes. What’s more, the metal’s mechanical properties are very well suited.
Why is it supposed to biodegrade? Patches on the left side of the heart in the low-pressure area don’t do this.
Hassel: Only the scaffold that supports the decellularized patch matrix in the beginning is meant to biodegrade. The patch that replaces the biological function is sufficiently protected by its own mechanical properties on the left side in the low-pressure system. On the high-pressure side, it is too mechanically unstable for the surrounding environment conditions, which is why we apply an additional scaffold, which in turn dissolves and loses its function during the time the actual patch is being revitalized.
How long does it take the magnesium to dissolve?
Hassel: We expect between three and five months.
The magnesium receives an additional coating. What coatings have you tested so far?
Hassel: At first, you try the natural oxide coating. You can make it thin or thick, there are various manufacturing methods with which you can influence the coating thickness. This type of natural coating would be ideal. However, it is not possible with magnesium, which is why we chose a magnesium fluoride coating. It is similar to the oxide coating. The fluoride layer results in the metal surface being tightly enclosed at first. This layer is then gradually removed due to the biological setting in the heart; the material starts to corrode and is reabsorbed by the body. Another option would be to apply biopolymers to the surface or work with magnesium hydroxide coatings, but right now, we prefer magnesium fluoride coating.
How do you prevent the body’s rejection response?
Hassel: So far, we have achieved excellent results in animal testing, so we assume that the selected coating is the ideal one. In addition, magnesium itself has been known for quite some time as an implant material. Tests have already been conducted during the 1920s with it. Then as now, there were never any known rejection responses.
How did the shape of the magnesium scaffold originate?
Hassel: What’s important is for the patches to follow the movement of the cardiac muscle. At first, we shaped the patches from metal and applied them flat onto the heart. The fact that we didn’t consider the shape of the heart caught our attention, because the surgeon had trouble properly applying the sample onto the heart. This is why we started to mold the three dimensional shape of the heart, so there won’t be any plastic deformation during surgery. We conducted project simulations with our partners for this to be able to detect stress peaks. These findings led us to new geometries that now allow for respective homogeneous stress states, even when they are homogeneously distorted.
When do you anticipate using the patch on human beings?
Hassel: This is difficult for us mechanical engineers to determine and depends on the cardiologists. We are collaborating with Professor Axel Haverich at the Hannover Medical School and his team, which is responsible for the implant evaluation in animals and the subsequent transfer of these findings to human beings. But that’s all likely to take a little while longer.
The interview was conducted by Simone Ernst and translated by Elena O'Meara.