Dr. Stephan Weiß is the co-founder of Hypecask. In cooperation, his company developed the “Delta Tower“ 3D printer. COMPAMED.de spoke with him about the development of 3D printing and the potential that this print process offers medical technology.
Dr. Weiß, can you briefly explain how the Delta Tower works.
Dr Stephan Weiß: The printer works based on the well-known fused deposition modeling technology or FDM in short. This means, a plastic filament is transported by a conveyor unit to a nozzle. There, it is heated, melted and then applied layer by layer. This is how the object is being produced.
What advantages do you see compared to the standard casting process for prosthetic legs?
Weiß: First, the 3D model is captured via a scan of the stump. This is much faster than a plaster cast and also much more precise. This way, it is also more comfortable for the patient, because he/she only needs to tense muscles for a short time. Another advantage is the quick and automated production. Mistakes can be fixed relatively quickly on the 3D model if the first printout doesn’t fit. The geometry of course is also an advantage. It also facilitates control over the object’s interior. When you choose the right materials, you can produce a very lightweight shaft that is nevertheless robust. Added to this is the fact that plastic material is comparatively affordable when you obtain it properly.
You have already collaborated with the Fraunhofer Institute. What was the object of your research?
Weiß: The project with the Fraunhofer IPA is aimed at optimizing the prosthetic design and the materials used for FDM printing. The long-term vision is the use of this technology in developing countries. The idea among others is to ultimately use recyclable materials that are so robust to where high functioning prosthetic limbs can be made from plastic waste with little expenditure of time and money.
Is plastic, particularly from recycled materials really so robust and resilient to where certain longevity of the prosthetic limb can be ensured?
Weiß: I think the recycled material is not ready for this yet. In this case, materials research still needs to do some work, either as it relates to clean separation of recycling materials or the development of compatibilizers for mixed materials. Having said that, we were already able to manufacture foot prosthetics with regular PETG plastic. PETG is already quite robust and has great printing properties. These prosthetics have already been worn by people and have successfully run through the test cycles. On its own, the form that has been so cleverly designed by the Fraunhofer IPA already introduces great stability and flexibility into the prosthetic to where the 3D print becomes easy to map, because there is complete geometric freedom during construction. We tested this process with different materials. The next step would then be to test it all with nylon, an even more efficient plastic material.
The problem with commonly used plastics is that they have a very low glass transition temperature. This means that at 60-80 degrees Celsius it could deform under load. Materials research needs to continue in this area to find materials that don’t deform in warmer temperatures, can be printed well and are cost-effective. Especially in the area of recycled material, this is a goal that is being pursued and that can definitely be implemented. Filaments for instance that are fiber-reinforced similar to carbon are already being used. By specifically aligning the fibers along the traveling distance during the printing process, intelligent design could certainly introduce more fortification compared to the conventional way.
The Delta Tower is not suited to manufacture dental implants. You use the ASIGA printer for this, which you market in Germany. How is this printer different?
Weiß: Unlike the Delta Tower, the ASIGA printer works by using stereolithography. This means, liquid resin is solidified via light exposure with a UV projector. The plastic is polymerized locally. The advantage of this is that you achieve a significantly higher resolution. We are talking 10-20 micrometers that can be resolved.
To what extent does the used resin resemble the enamel structure?
Weiß: Unfortunately, what comes out is not as robust as tooth enamel in terms of mechanical properties. You can rather compare it to regular acrylic resin that later turns into acrylic, like plexiglass for instance. Even though it‘s hard, it does not resemble ceramic; so it is better suited for models, but not directly for the crown. At this point, you would take a detour. There are wax-like plastics you can print. They are embedded, cauterized and the form that is left behind is filled with ceramic or metal. The ASIGA printer has long been used in the jewelry industry in this way – in goldsmithing – and can therefore also be utilized to print crowns etc.
How do you rate the future prospects for 3D printing for medical technology, particularly as it pertain to organs and tissues?
Weiß: 3D print technology is particularly well suited, because you can also manufacture complex items. Organs are of course quite complex, but I don’t dare to make a prediction on that just yet. However, we are soon going to publicize a project with which we can also precisely print all kinds of liquid viscosities in 3D from a dosing unit. This would make it possible for instance to dose stem cells or cell mass embedded in hydrogel and place it in the shape of an organ. However, we are only going to provide the technology for this. I believe there are even more research concerns by many parties in this respect. This is why things are definitely going to get very interesting, especially since material development keeps moving at a rapid pace and the more materials are available, the more applications there will be in the future.