Already used in the automotive and aerospace industries, additive manufacturing, or 3-D printing, has recently emerged as an option for creating inexpensive medical solutions. The technology has been adopted in dentistry to print crowns, and researchers have been experimenting with the fabrication of bone scaffolding, hip and knee implants and even organs. This technology is also gaining popularity in the O&P industry, where it is being used to create prototypes, custom orthoses and prosthetic sockets.

“I see plenty of opportunity for a connect between orthotics and prosthetics and 3-D printing because the uniqueness of the body really requires a unique part to couple with it in order to be effective,” Scott Summit, director of technology for Bespoke Products, which was recently acquired by 3-D Systems, told O&P Business News.

Additive manufacturing involves printing a 3-D shape from a computer-aided design (CAD) model. The process involves using the CAD model to build the object layer by layer. Depending on the type of printer and material being used, the process can take anywhere from a few hours to an entire day, and the precision and accuracy afforded by 3-D printing makes it ideal for fabricating orthotic and prosthetic devices.

“What we hope is that manufacturing will be done in less time and will also be done more inexpensively,” said Constantinos Mavroidis, PhD, distinguished professor of engineering and the director of the Biomedical Mechatronics Laboratory at Northeastern University in Boston.

The most common types of additive manufacturing are selective laser sintering (SLS), which involves using a high-powered laser to sinter particles of metal powder together; stereolithography (SLA), in which a liquid resin is hardened with an ultraviolet laser, and fused deposition modeling (FDM), an inkjet-based process where an extrusion nozzle is used to create each printed layer.

“It is an incredibly versatile tool,” Summit said. “There is no one type of 3-D printing, and there is no one way clinicians might consider using it.”

Digital processes

One of the main benefits of 3-D printing is the digital scanning process used to create the design. With digital scanning, a clinician can create an accurate and detailed 3-D digital file, which can reduce time and waste associated with plaster casting.

“You can make customized orthotic and prosthetic devices, but it has to rely on some form of medical imaging or imaging data,” Arif Sirinterlikci, PhD, professor of engineering and director of engineering Laboratories at Robert Morris University in Moon Twp., Pa., told O&P Business News. “Customization is key.”

Summit agreed. “You can manipulate things subtly digitally in a way that you can’t if it is tempered plaster or a plaster form,” he said.

Digital scans can also be stored in a database for easy reference if a device needs to be refabricated or modified.

“By digitizing the manufacturing process, we have the design of the orthosis in the database, so whenever you need to create a new one, the orthotist just has to go in and reprint whatever he or she developed before,” Mavroidis said.

This idea can also be applied to prosthetic socket fabrication, and it is expected that this will most likely be the next application of this technology.

“There has been lots of research in this area, and it is in the works behind the scenes in many places,” Summit said. “I suspect it is not long before that will become the new standard.”

“I think foot orthoses will be the first commercial application for this technology, but I think prosthetic sockets will probably follow closely behind,” Jari Pallari, PhD, research and development manager at Peacocks Medical Group in the UK, said. “It is a matter of using the design freedom to generate added value into those new kinds of sockets you could make.”

Other applications for 3-D printing include exoskeletons, such as the Wilmington Robotic Exoskeleton, a body-powered exoskeleton designed to assist children with neuromuscular diseases, and cranial helmets.

“They are using ABS plastic in exoskeletons, and it is durable plastic,” Sirinterlikci said.

Three-dimensional printing also affords clinicians more room for creativity and ingenuity. For example, Mavroidis and his colleagues are working on fabricating smart orthoses, which contain sensors printed directly into the device.

“We are trying to create smart orthoses that have sensors that will to be able to record some of the parameters, either of the orthosis itself or of the patient’s gait,” Mavroidis said. “We can see the mechanical state of the orthosis, and we could predict if the orthosis is going to break, so we can plan for a replacement. We can also record a patient’s gait over time throughout the day.”

Clinicians also can create more complex structures that would otherwise be impossible when fabricating devices by hand.

“You can create structures, like complex lattice structures for example, that could not be machined or created out of carbon fiber,” Summit said. “And that means you can invite flexion in a certain part of the socket and have it stiff in another part depending on the type of geometry you use.”

Digital technology also has the potential to enable clinicians to predict device performance before it is fabricated.

“You have all of these engineering tools at your disposal, such as finite element analysis, so you can basically take your patient-specific shape geometry, and then you can apply certain loading conditions based on patient pathology, weight, activity, etc. — and then ask the engineering software, ‘how will this structure behave under this kind of load?’” Pallari said. “And then you can reinforce parts of the structure to make it stiffer, or you can take material off to make it locally more compliant. You can personalize the function of the part in an analytical way that is repeatable.”

Materials used in 3-D printing can also be recycled, reducing the amount of waste created in the fabrication process.

“One of the great things for some additive processes is that you can recycle the material that is left over from the manufacturing process,” Pallari said. “For example, if you mill something from a block of foam, you generate a lot of waste, but if you have an additive process, you are basically just using the material that you need to actually make the part itself. So that is one of the main advantages of additive manufacturing vs. subtractive manufacturing.”

Challenges

Although digital scanning technology is a great benefit, it can also present challenges. The popularity of CAD/CAM software is growing in the O&P industry, but most systems are designed for more traditional fabrication techniques.

“The CAD/CAM systems are tailored most towards milling applications and not additive manufacturing,” Pallari said. “To be able to use those systems to design your parts that would be additive manufactured with 3-D printing, you would need another piece of software, which again would be expensive and would require you to be savvy with the CAD side of things.”

The CAD scanning systems used for 3-D printing also require engineering knowledge in order to customize the printed device.

“The technology is 20 years old, but it is new in a sense because the digital tools are still catching up to the technology,” Summit said. “The challenge is that we need to make tools so they [practitioners] don’t feel they are taking a huge leap from the world of plaster, which they are familiar with and very skilled at, into this world of digital, which might be confusing or awkward and difficult.”

Material choice also can be prohibitive when using 3-D printing. Depending on the chosen process, available materials will differ. For SLS printing, the most popular materials are nylons, but for FDM printers, ABS plastic and polylactic acid are used.

“The materials are an issue; I think there is a good selection, and there are good materials there, but it is a different selection than what the industry is used to and the material performance is not documented as well as it could be,” Pallari said. “For example, fatigue performance and long-term usage performance and those kinds of concerns, are better established with polypropylene and similar materials. If you want to provide 3-D printed products, you have to do your homework and ensure your products are safe and durable.”

Therefore, device fabrication is limited to the type of printer and subsequent materials available.

“Additive manufacturing is definitely making its way to the industry, and it will change the O&P industry in time, but it will not happen overnight,” Pallari said. “It will be like when milling was introduced originally. It is going to happen little by little, and it’s not going to be the solution to every single problem.”

But according to Summit, materials can be manipulated to enhance strength and durability.

“Part of strength comes from the material, but part of it comes from design,” Summit said. “I think strength is limited more by creative engineering and design than by its material attributes.”

Devices can also be post-machined to improve strength and quality.

“You can do all sorts of things to improve the durability and the strength or the rigidity, but obviously it means that you have to do more work,” Pallari said. “You can’t just print something with your desktop machine and give it straight to the patient. You have to process it further.

“Nylon materials can also be purchased impregnated with other materials, such as tiny glass particles, to give it more hardness,” Pallari added.

Costs

Another consideration of additive manufacturing technology is the cost of printers. Some desktop printers cost only a few thousand dollars, but more intricate printers, such as SLS machines that have the ability to print 3-D metal objects, can cost more than $200,000.

“You have cheap desktop systems, but they are not the solution for every problem,” Pallari said. “They can be used in some cases, but if you look at the higher end systems, they are expensive. And even if you want to order parts from a service provider, those parts can still be prohibitively expensive.”

Sirinterlikci added, “A lot of the time the cost of the process, the machine time, is the costliest factor.”

Although the cost of 3-D printers continues to drop, it is more likely that central fabrication facilities will begin to invest in the technology.

“I believe that we are going to see the development of manufacturing companies,” Mavroidis said. “So you don’t need an orthotist to have a printer in his or her own shop. You just need Internet connectivity, since everything is digital. You will just have to transfer the files to a manufacturing facility, and the orthosis will be manufactured there and then shipped.”

For example, 3-Spark, LLC is a startup business associated with Northeastern that offers 3-D printing solutions.

“Our goal is to bring this technology to the market as soon as possible,” Mavroidis, who helped found the company, said.

Similarly, a team from the University of Delaware spun out a start-up venture called Intelligent Digital Manufacturing to develop central fabrication techniques for the creation of 3-D printed devices.

“Every device would have a unique thickness, shape and functional characteristics that are ideally suited for each individual,” said Steven J. Stanhope, PhD, professor of kinesiology and applied physiology at the university. “We envision a paradigm by which individuals would be able to select different levels of bending stiffness that they would be most comfortable with. We could use different forms of free-form printing technologies to rapidly make the devices for individuals, hopefully reduce the cost of health care, and at the same time, dramatically improve functional outcomes.”

Use in developing countries

Some researchers believe that 3-D printing offers a solution for delivering O&P devices to people in developing countries, because of the quick and efficient properties associated with this technology.

“One scenario is that you could issue a large number of people in developing countries with scanners and give them training and off they go around the country to scan people and send that information back to a central location where you have orthotists or prosthetists that have the expertise to know what that person needs,” Pallari said. “Then they do the design and manufacture the device, and then sent it on to be issued. This approach has a problem, however. Can an appropriate device be designed or specified if the clinical specialist has not seen the patient themselves?”

Some organizations, such as The Low Cost Prosthesis Project and Tri County Orthotic and Prosthetic Institute, are investigating how to use bamboo and other natural materials to 3-D fabricate low-cost prostheses.

“They are trying to incorporate cheaper, inexpensive materials. They are trying to use bamboo fibers and natural materials,” Sirinterlikci said. “At my school, we print from wood-based materials. It is harder to print from low cost materials when you are talking about metals, but with polymers and the alternatives, like natural fibers or wood, you could actually reduce the cost and customize.”

The establishment of programs that can fabricate and deliver 3-D fabricated devices in developing countries is still a distant idea, but practitioners in the United States could see the effects of this technology within the next few years.

“I think a lot of these developments are encouraging, and we need to look into new materials, new process developments and things like that,” Sirinterlikci said. “The cost vs. custom-made struggle will be eased with the development of new processes and materials.”

Stanhope expressed similar sentiments.

“I think the way of the future is the personalization of rehabilitative devices,” he said. “If we can obtain the highest possible levels of function and engagement in activities of daily living, we’ll have the capacity for individuals to fight back obesity, chronic health conditions and co-morbid conditions that result from inactivity, and dramatically reduce the cost of health care.” — by Megan Gilbride

A note from the editors:

This story is an overview of the potential of 3-D printing technology in O&P practice. It is not intended to be a comprehensive list of practices or facilities that employ 3-D printing.