Three-dimensional printing — sometimes called additive manufacturing — uses millions of coordinates to deposit small amounts of material in specific areas based on a computer-aided design (CAD). While the technology dates back to the mid-1980s, it’s only been in the past several years that its potential has come to the forefront, especially in the health care environment. Indeed, 3D printing has successfully replicated everything from personalized prosthetics to complex blood vessels and even a “designer” pill that combines several medications with timed releases.
But one of its most significant impacts in health care is in the area of “traditional prototyping,” (meaning, the process leading to designing medical devices). According to Mohit Prajapati, director of Research & Development and Strategic Initiatives at the Penn Center for Health Care Innovation, this process can be long and expensive. Surgeons work directly with manufacturing companies on multiple iterations of a potential design, incorporating small changes to bring it closer to the desired final design. “Each prototype would be made from stainless steel or other bio-compatible material, which could take several weeks to make – and cost thousands of dollars,” Prajapati said. “And nobody even knows if it’s going to work.”
As part of the Center’s Acceleration Lab, Prajapati has worked with several physicians in this capacity, translating their qualitative descriptions into CAD specifications which, in turn, lead to a computer-generated model in plastic. “It’s a physical representation of the real instrument – the exact size and shape,” he said. “A surgeon can see how it works or even if it works. We make 3D models until they’re sure they have it right.” At that point, the final model is made in titanium steel or another material.
Orthopedic surgeon James Carey, MD, knows firsthand the difference 3D printing can make. Tears in the meniscus — the knee’s shock absorber — typically occur in the back of the knee. But one of the best approaches to repairing such a tear, Carey said, is to go in from the front of the knee and around the curvature of the end of the femur (thigh bone). The challenge is that the instrument used in the repair — a meniscal biter — is rigid, which can make it harder to reach the injury without causing additional damage. “We needed an instrument that could flex at the end — like a finger — so we could angle up to easily move around the femur.”
Usually, designing an instrument requires multiple iterations before reaching the final, approved version. A working prototype in stainless steel costs between $5,000 and $10,000, and it could take weeks to produce, depending on the manufacturer’s availability. With 3D printing, the prototypes would be around $100 each and completed within days.
Carey received a medical device accelerator grant from the Center for Health Care Innovation and started to work with Prajapati to create and print a CAD of the new instrument. Holding the working prototype in his hand “felt right,” Carey said. “A big part of having an instrument adopted by orthpaedic surgeons is how it feels in their hands.” After getting the thumbs up from many colleagues — with varying sizes of hands! — Cary ordered a stainless steel prototype. But this was only the first iteration. After additional changes, a 3D print showed that “it was too thick, but I couldn’t tell from CAD drawings on the screen,” he said.
More changes and another 3D version showed that they were on the right track. The ability to hold the prototypes served a “tremendous value,” Carey said. “It gave me insight that I didn’t have from the drawing” … and at a fraction of the cost of manufacturing a steel prototype.
Beyond instruments, Prajapati has partnered with physicians to create prototypes of surgical devices such as a new implant for spinal fusion. As the technology and quality of 3D printed material improves, he envisions producing parts that are more or less custom fit to each patient. “If we can make an implant to specifications in biocompatible material, we don’t need to have a tray of different sized implants,” he said. “The surgeon can actually measure and say ‘This is what I need,’ have it printed on the spot and ready for use in a patient,” Prajapati said, adding that “if you can fabricate a device quickly, you don’t need to maintain a costly inventory,”
3D printers are also allowing glimpses into the future through devices such as a surgical “basket” for reconstructive breast surgery, for example. According to Suhail Kanchwala, MD, an assistant professor of Plastic Surgery, one of the goals of breast reconstructive surgery is to not only make the shape of the breast natural, but also retain that shape during the healing process, which can be a challenge. “We make the shape of the breast as ideal as possible, but an implant is round and a tissue flap from the abdomen is elliptical,” he said. Even though using a patient’s own tissue usually results in a more natural appearance when compared to implant-based reconstructions, “it’s still an issue.”
Kanchwala theorized a possible solution. What if there was a type of support — a scaffold of sorts — to hold the newly formed breast in place during the healing process? The temporary structure would need the right stretch and strength to keep the new breast in place while allowing it to move naturally. And it would have to be made from a material that’s both biocompatible and bioabsorbable, ultimately degrading when the new breast becomes part of the body.
Although the idea is still in the concept stage, Kanchwala’s work with Shu Yang, PhD, a professor of Materials Science and Engineering, and Randall D. Kamien, PhD, a professor of Physics and Astronomy, both at the University of Pennsylvania — and 3D printing — have given him glimpses of the possibilities. Yang is using principles of kirigami — a cousin to origami that has both folds and cuts — to translate Kanchwala’s idea into a CAD. With MRI slices of a breast image as a guide, Yang created a template of precision cuts, incorporating different kinds of weaving to provide the strength on the bottom of the scaffold to hold the breast in place and the stretchability on top to allow movement.
The first iteration was a 3D paper template that used a patient’s anatomy to show where the cuts should be made. The surgeon would make these cuts in an acellular dermal matrix (a bioabsorbable material) with a scalpel in the OR. But Kanchwala envisions eventually taking this even further — using 3D printing to create a pre-fabricated scaffold design with the cuts already in place. In theory, “before mastectomy, you’d scan the patient’s breast and then, after mastectomy, use that design to ‘print’ a 3D cage construct that’s individualized for the patient,” he explained. The idea, he says, has the potential to transform breast reconstruction surgery.
As 3D printer prices decrease and the capabilities and ability to use biologic material increase, Prajapati foresees that “everything will be made patient specific, as required. Like every department has a computer today, I can see every one having 3D printers.
“We’re helping to turn science fiction into science reality.”
Source: University of Pennsylvania