Selective Laser Melting: "This process allows you to effectively combine material properties and desired design"

Today, many companies and even some private households already have 3D printers but not many of them use metal powder for printing. We asked two experts from the Fraunhofer IFAM how selective laser melting (SLM) is used to manufacture components for implantable medical devices.

Mr. Aumund-Kopp, what is selective laser beam melting and how does it work?

Claus Aumund-Kopp: Laser beam melting is a powder bed-based additive manufacturing process. We use fine metal powder, which we apply in thin layers, and then melt with a laser. Once one layer is finished, we distribute another layer of powder on top and melt it. We repeat this process to create the finished product. The last step is to remove the product from the power bed. There are actually many names for this process. Some also call it LPBF or laser powder bed fusion. But don't be confused by that.

What are the size limits for the unit?

Aumund-Kopp: The largest commercially available machine has a build volume of 800 x 600 x 500 mm. This allows the use of 240 liters. Some research facilities also have larger systems but they are not available on the market and are only needed for very specific purposes of research.

Which implants are best suited for this process?

Michael Norda: It is difficult to name specific types of implants. Titanium, cobalt-chrome, or surgical implant steels are used for different types of implant applications but the SLM technique is frequently used to manufacture dental implants.

Aumund-Kopp: This procedure is also used for prosthetic hips to make both the acetabular component (socket) and femoral stem.

Is this technique suited to manufacture custom implants for patients?

Aumund-Kopp: That is actually one of the main advantages of 3D printing. We don’t need tools and are able to print the parts simply by entering the relevant data. This allows us to manufacture a custom prosthesis for each patient. As mentioned earlier, this technology is common in dentistry. In this case, the print job involves up to 500 components, all of which are customized and consecutively numbered of course.

Do manufacturers make special requests to give implants special characteristics and properties?

Aumund-Kopp: It happens occasionally. This usually pertains to material development. There is a wide range of common, reliable materials that are approved for medical implants. Metal 3D printing became popular in the late 1990s, which is when people started working with the materials that were already mentioned. Back then, parameters were established to manufacture safe implants. The next step was to include the special features of this process into the structure and design. If we take the example of hip implants again: The cup, also called the acetabular component, is implanted into the pelvis. Bone tissue needs a rough surface in which the surrounding bone can grow. That’s when manufacturers started to make very rough surfaces, encouraging the natural ingrowth of bone structure. As you can see, this process allows you to effectively combine material properties and the desired design. That’s what many manufacturers dream of and want.

Why is this technique not suited for certain implants?

Norda: There are still some limitations and challenges in terms of the removal of unfused powder. Once the process has been completed, the component sits in a powder bed, which must be fully removed. I would not suggest using this process if you plan to make parts with a delicate or fine structure that allows you to run a cord or a pipe system to measure the temperature or to direct medication into the tissue, for example. That’s because we cannot guarantee that these structures would be entirely powder-free. And people would rightly refuse to accept metal powder in human tissues.