Multi-material 3D printing with silicones in Facial Prosthetics

Ear prothesis (before post-processing) made of different silicones with ACEO®‘s multi-material 3D-printing technology (Photo: ACEO®; Wacker Chemie AG)

Dr. Alexey Unkovskiy focuses on maxillofacial prosthetics at the Eberhard-Karls-Universität in Tübingen, Germany. In a recent project, he used ACEO®’s multi-material 3D printing technology to create a highly customized ear and nose protheses – with great results for his research.

ACEO®: Dr. Unkovskiy, thank you for sharing your story with us. Can you tell us about your professional background?

Dr. Alexey Unkovskiy: I studied dentistry in Moscow, specializing in prosthodontics. In 2013, I started my research at the Center of Dentistry, Oral Medicine and Maxillofacial Surgery at Eberhard-Karls-Universität Tübingen. The main emphasis of my current project is on the digital workflow in prosthodontics and maxillofacial rehabilitation.

Do you also work with other experts in facial prosthetics?

As a dentist, I work in an interdisciplinary team of ENT (ear, nose and throat), maxillofacial surgeons, as well as dental technicians. Within this team, we treat patients who suffer from facial disfigurements and mutilations.

What is the background of your patients?

Around 90% of our patients suffer from oncological diseases and undergo ablative surgery. That means that parts of their faces have to be removed in order to eliminate the cancer.

This may result in facial defects of various extension, ranging from ear, eye or nose absence to huge defects, where even half of the face can be missing.
Apart from this majority, there are patients with congenital defects and patients with trauma, which means they lost parts of their faces due to an accident.

What are facial prostheses made of?

The first thing to know is that some prostheses are generally placed on a very sensitive area: the mucous membranes. For this reason they are made of a soft silicone material. The main aim of the rehabilitation is to restore the former facial geometry and aesthetics, and – whenever possible – the function. Furthermore, a facial prosthesis must match the color of adjacent tissue to make the mutilation mostly inconspicuous. This is a real challenge for material science.
In the past, such facial prostheses were made of hard plastic materials.

What steps does it take to create a prosthesis?

It all starts with a contactless scan of the patient’s face and defect area. This results in an extended image of the whole facial anatomy, so that we can construct virtually all the missing parts, using computer aided design (CAD) software. If possible, we try to scan the patients prior to the surgery, so we can adopt their own anatomy of the resected facial part afterwards.

In case of an ear absence, the intact ear anatomy from the other side can be used as a reference and can be mirrored virtually on the defect side. With these data we construct the prostheses prototypes with CAM (computer-aided manufacturing), using various additive manufacturing methods.

Before we found ACEO®, we printed the prototype with plastics and afterwards tried it on the patient, transferred it into silicone in an analog way using the casting technique – this way the whole production chain can be characterized as semi-digital process.

How did you learn about ACEO®?

My colleague, a medical engineer, introduced me the to ACEO® and their innovative technology to 3D-print real silicone. Since that time the University of Tuebingen and ACEO® have been cooperating a lot. Our first directly printed prostheses were impressive, but still required certain postprocessing, such as coloration and polishing. Since August 2019 we have been working on the prostheses’ individualization. That means we also used ACEO®’s new multi-material 3D-printing technology.

Our latest clinical trials demonstrated an outstanding clinical result, so that the printed silicone prostheses could be applied on the patients and used as a permanent treatment option.

CAD visualization of ear prothesis showing the different shore hardness of silicones used with ACEO’s multi-material 3D-printing technology for earlobe, ear concha and the prosthesis bulk (Photo: ACEO®; Wacker Chemie AG)

How did multi-material 3D-printing with silicone make the difference?

Generally, silicones have many beneficial properties such as high flexibility, UV resistance, they can be colored and used for skin contact applications. The utilization of different silicones for a printing of one prosthesis may help to achieve stunningly realistic results, especially in terms of haptics. In our latest clinical case we used 3 different shore hardnesses for the softer earlobe, the ear concha and the prosthesis bulk.

How do you see the future of ACEO®’s technology in your field?

There are several technical aspects that can be improved on the direct silicone printing. Generally a greater printing resolution may be required to neglect the post-processing. And also the multi-color 3D printing may aid a higher aesthetics and a greater manufacturing efficiency.

Today, there are only a few practices and university medical centers that are dealing with facial prosthetics in Germany. I can imagine that in the next decade, the direct silicone printing with ACEO® may become the state-of-the-art technique and will be integrated into their daily clinical routine.