“Their fingers remember,” comments Dr. Rudolph Venter, the orthopedic surgeon running the three dimensional (3D) printing laboratory at Tygerberg Hospital. Venter is researching how being able to plan surgeries using 3D models of a patient’s anatomy will affect surgeons.
“I’m doing research into the usefulness of having something you can hold in your hand, as opposed to just seeing it on the screen,” he explains. “The planning for orthopedic surgery has always been visual, but the operation is practical and tactical.”
The 3D models are generated using the patient’s CT and MRI scans. Using these models of the patient’s unique anatomy allows surgeons to bridge the gap between merely seeing the problem and actually feeling the deformities. According to Venter, being able to touch the model and practise the procedure before the actual surgery allows the doctors to go into surgery with more confidence.
The laboratory, at the division of orthopedic surgery at Tygerberg hospital, is the result of a collaboration between engineers and doctors from Stellenbosch University (SU) and the Faculty of Medicine and Health science. The launch of the laboratory was announced in January 2019.
“I can’t take credit for the machines or the software,” explains Venter. “A surgeon like me who is not an engineer can learn to use it.”
He learnt how to use the printer from the Biomedical Engineers Research Group at SU.
Dr. Rudolph Venter, the orthopedic surgeon running the 3D printing lab at Tygerberg Hospital’s orthopedic division. PHOTO: Wilma Stassen.
Venter is assisted by Wayne Swart, a senior technician at the Mechanical and Mechatronic Engineering department of Stellenbosch University. According to Swart, the research group has been working together since 2012. The process of printing 3D models of anatomy, also referred to “haptic maps”, started three years ago.
Using these printers is relatively simple, according to Dawie Van den Heever, an associate professor at Mechanical and Electronic Engineering at Stellenbosch University. He is also the Head of the Biomedical Engineering Research Group at the university.
The printers require a 3D model that has been created in or exported to a format that the printer can read. “You basically need to make a 3D model of the thing you want to print, and export that into an STL file,” says Van den Heever.
A 3D model of a deformed spine that was printed at the Tygerberg laboratory. PHOTO: Elri Voigt
Johan Van Der Merwe – a Biomedical engineering researcher and Stellenbosch University lecturer – also works with Dr. Venter. According to him printing a 3D model can take several hours.
“It can take up 9 or more hours, depending on what you print…It’s a very involved process,” Van Der Merwe says.
There are two types of printers at Tygerberg hospital. One is called the FDM (Fused Deposition Modeling), and SHS (Selective Heat Sintering). The FDM model uses pieces of a thin plastic coil, that is melted by the machine and sprayed onto the printing platform in the shape of the 3D model. This process is done in layers until the 3D model is finished.
Van den Heever explains how this works, “You can almost see it like a normal printer, which just prints on 2D. You have the same moving head, (present in printers) all that happens is that the head can move in the Z directions (the depth of the object).”
The SHS model makes use of layers of a special powder, made of nylon polymer, instead of plastic. The printing process consists of an object being built through layers (or slices).
Swart explains the process, “A thin layer of powder is spread over the building area. A heating element then selectively sinters (harden by melting) the powder regions together that constitute part of the object being built at that specific slice. When the slice is completed, the building platform moves down and the process is repeated.”
Eventually, the powder emerges as a single block known as a cake, with the 3D model inside, which is taken to a cleaning machine and the loose powder is sprayed off to reveal the 3D shape.
The main difference between these two types of printers is the complexity of the models they can print. “With the powder based one, you can make very complex shapes. You have the powder bed that is supporting the shape,” Van den Heever explains.
Dr. Rudolph Venter holds a printed 3D model of part of a shoulder next to a skeleton to illustrate where the bone is located. PHOTO: Elri Voigt
Venter has high hopes for the 3D laboratory, “I’m hoping the lab will become a bigger medical 3D printing facility that all of the different health departments can access. As well as access someone who maintains the machines and knows the material and what these materials can and can’t do.”