From artificial limbs to covers to sockets, 3-D printed prosthetic components and accessories are becoming more prominent both within and outside of certified O&P facilities. But prosthetists, technicians and researchers told O&P News some significant challenges must be overcome for a true market to exist for 3-D printed prostheses. Practitioners and researchers working with 3-D printing shared considerations in areas including materials, patient care, safety and liability, as well as their predictions for the logistical changes and training that would need to take place for prosthetists and O&P facilities to fully embrace 3-D printing in the field.
“There are a lot of applications for flexible materials in the prosthetic field,” Jeff Erenstone, CPO, president and head clinician of Mountain Orthotic & Prosthetic Services in Lake Placid, N.Y., and chief executive officer (CEO) of Create Prosthetics, told O&P News. Create Prosthetics mainly focuses its 3-D printing efforts on prosthetic covers.
“That was the low-hanging fruit for our company to make these covers, but we were able to heavily customize them,” Erenstone said. “We are using the benefits of 3-D printing in a manner we feel is medically appropriate, using materials that last long enough for what a prosthetic patient should expect.”
Meanwhile, other companies use 3-D printers for components.
“WillowWood has been involved in 3-D printing of prosthetic components since 2008. We have [selective laser sintering] SLS and [fuel deposition modeling] FDM machines on site and regularly make components which we use for research and production purposes,” Jim Colvin, WillowWood’s director of research and development, said.
At Prosthetic Design Inc., Brad Poziembo, LP, and colleagues use 3-D printing to create definitive prosthetic sockets, covers, liner molds and some postoperative devices. Poziembo is a researcher for Prosthetic Design Inc. and prosthetist for Dayton Artificial Limb in Dayton, Ohio. The quick turnaround is a big advantage to the process, according to Poziembo.
“We can fit patients the same day, usually within 2 hours,” he said.
In addition, any company can use a 3-D printer to create prototypes, which Erenstone said he does regularly.
“If you come up with an idea, you can go to a computer, work up a [computer aided design] CAD design, start printing it and have it in your hand by the afternoon. I do that multiple times a day,” he said. Before 3-D printing, the step from an idea to a physical object in one’s hand would have taken months. “Now, it is a 1-day thing,” he said.
Of course, the 3-D printed O&P devices that have received the most attention so far are 3-D printed hands provided by groups like e-NABLE. Erenstone noted e-NABLE’s leaders do not refer to their devices as prostheses, but a more accurate term does not currently exist.
Jorge M. Zuniga, PhD, a biomechanics researcher at the University of Nebraska Omaha, developed the first e-NABLE hand, “Cyborg Beast.” In 2015, his research team in the 3-D Research & Innovation Laboratory at Creighton University formed a partnership with Innovative Prosthetics and Orthotics in Nebraska to create 3-D printed prostheses. The partners received a $50,000 grant from Nebraska’s Department of Economic Development to develop low-cost, medical-grade 3-D printed prosthetic devices. Zuniga prefers the terms “temporary prosthesis,” “initial prosthesis” or “immediate postoperative prosthesis [IPOP]” for 3-D printed hands.
“The durability and quality of traditional prostheses are second to none,” Zuniga said. “It is possible that low-cost 3-D printed devices could be used as transitional devices in preparation for a standard or more traditional device. [The] ability to print this device on a small and inexpensive 3-D printer with different in-fills or densities may allow medical institutions with a low budget to offer a highly customized, low-cost option to their patients.”
Zuniga has since created additional 3-D printed devices, including a shoulder-arm-hand prosthesis. In an article published in Prosthetics and Orthotics International, Zuniga and colleagues who assisted in the creation of the arm emphasized its purpose as a “transitional device” meant to aid growing children who may not have access to traditional prostheses and to help them grow more familiar with the feel of a prosthesis.
“Although durability, environment and lack of printing standards for manufacturing of 3-D printed prostheses are factors to consider when using these types of devices, the practicality, cost-effectiveness and customization represent a promising new option for clinicians and their patients,” Zuniga said.
Sources agreed the options are nearly limitless with 3-D printing and new devices need to be compared to traditional devices to weigh the pros and cons.
“The primary barrier to widespread use of 3-D printing in O&P is developing the technology to the point of providing the required durability and functionality in a way that is time- and cost-competitive with traditional methods,” Colvin said.
Michael E. Tompkins, vice president of Technology Development for Hanger Inc., added, “The real benefits of additive manufacturing technology will shine when we can fully realize the customization capabilities to the technology to provide new functionality, increased performance or significant reductions in manufacturing costs.”
Materials and process
One area in need of further development to maximize 3-D printing for the field of O&P is materials. Erenstone said current materials are most appropriate for prosthetic covers, and Poziembo’s company created a proprietary copolymer plastic that he said is ideal for creating weight-bearing sockets. However, few options exist for the creation of 3-D printed artificial limbs.
Erenstone said most 3-D printed prostheses are made from polylactic acid, or PLA plastic. The Cyborg Beast hand, for example, is created with a mix of PLA and acrylonitrile butadiene styrene (ABS) plastics.
“If you were to take something made out of PLA and put it in a hot car in Texas, it is going to melt and turn into a blob,” Erenstone said. “It is a great material that will build a structure well and easily, but not something appropriate for long-term use.”
Colvin said, “Most 3-D printed devices have a rough surface because they are fabricated in layers. The rough surface can be susceptible to cracking after multiple loading cycles, which can lead to catastrophic failure.”
However, continued developments in the field of 3-D printing show promise for more durable materials.
“There are now filament extruders that transform raw plastic pellet material, typically used for injection molding, into reels of filament ready for [fused filament fabrication] FFF processing,” Tompkins said. “This will open up many new applications.”
He added, “There are also metal additive manufacturing options available, such as aluminum, stainless steel and titanium. [However,] the costs associated with the metal raw material, process, machinery and secondary clean-up operations may not provide a viable option for most of our applications.”
Erenstone said, “One thing multiple groups are working on is a more complex tool path.”
This would improve durability by allowing the printer to change the grain of material. Currently, 3-D printing creates strong individual layers, but the bond between layers is less strong. Engineers are working on a computer program to allow for a tool path that weaves layers, according to Erenstone. “Whoever figures that one out will greatly increase the strength of 3-D printing,” he said.
Another complication with 3-D printed prostheses is finding a way to fit patient care into the equation.
“Patient care is a critical element of providing a prosthesis or an orthosis,” Colvin said. “Prostheses and orthoses are considered medical devices and are often highly customized. As with any medical device, there are liability and legal issues to be considered, so having a qualified practitioner involved in providing the device and care is important.”
Having worked with e-NABLE for several months and handled their designs, Erenstone said, “I have yet to see anything that has been able to replace the knowledge base of a prosthetist. The need to build a custom-made socket that is custom-contoured for the patient is just as important in 3-D printing as it is in conventional prosthetics.”
Most prosthetists interviewed for this piece told O&P News they would not work on an artificial limb without knowing who created it and what quality standards it meets. In the potential situation of a patient walking into an appointment wearing a 3-D printed hand, Tompkins said, “If the additive manufacturing-produced hand was supplied by a qualified company that is responsible for its products and has provided our clinicians with training in the use and maintenance of the device, we should have no problem assisting the patient. If the hand was printed by an individual, amateur or non-qualified entity, then we would likely not have adequate information regarding the performance and safety characteristics of the hand to allow us to safely service it.”
In addition, prostheses created by people without prosthetic certification carry potential legal problems, particularly in states that require licensure to practice O&P. A practitioner who chooses to service a non-commercial 3-D printed device would have to take on any liability related to subsequent safety or reliability problems, sources said.
Erenstone said, “A practitioner should look at the device and make sure they want to put their seal of approval on it. The FDA allows for this process and it is no different from any other custom-made device. It is important that practitioners understand how to evaluate quality so they can stand behind it. That is why it is important to get a device from a reputable source or have the practitioner make it themselves.”
Safety, quality issues
Potential safety issues with 3-D printed devices vary depending on the device and its placement on the body.
“The dangers of a partial hand device for a congenital amputee seem to be relatively low,” Erenstone said. “When you work your way up the body to a complete arm, [that] is certainly more concerning.”
Erenstone said a 3-D printed hand can go a long way toward helping a child with congenital amputation feel happier and more confident.
“We have to be careful not to discredit the value of making a kid with a partial hand feel like a million bucks,” he said. “But increasing the level of function, that is a whole other can of worms. I have not seen a lot of [3-D printed] devices that increase the level of function.”
Erenstone said he would like to see designers work with prosthetists to ensure safety and quality. Zuniga said this type of collaboration is the purpose of his team’s partnership with Innovative Prosthetics and Orthotics.
“We are concerned about the quality and safety of the patient and our prosthetist, Zuniga [president and CEO of Innovative Prosthetics and Orthotics] is involved in all our operations. 3-D printing technology for the development of prostheses is at an early stage in development, and the supervision of a certified prosthetist is crucial for the proper development and use of our devices,” Zuniga said. “We strongly encourage [others] to include certified prosthetists and other health care professionals in the development, fitting and testing of 3-D printed prostheses.”
Tompkins has safety concerns associated with 3-D printed devices for lower limbs due to the stress placed on these devices from the wearer’s body weight.
“This stress on an additive manufacturing-printed device could cause a separation of the printed layers, or delamination,” he said. “This delamination could allow a catastrophic failure to occur.”
The varying safety concerns show a need for standardized quality control measures, sources said.
“Before providing an O&P device to a patient, the device should be thoroughly tested for all appropriate safety issues, including structural, usability and biocompatibility requirements,” Colvin said.
Zuniga said his research team is currently working on a review paper that examines those standards.
“I would recommend all medical and education institutions providing these types of devices to follow the appropriate procedures and obtain [approval from an] institutional review board,” he said. “The process is long and technical, but we can help any institution interested in doing research with all the logistics.”
Zuniga said according to the FDA’s product classification listings, prosthetic components and accessories are generally considered to be class I devices.
“Class I devices are considered low risk. They have minimal potential for harm and are specifically defined by the FDA as not intended to be for use in supporting or sustaining life, of importance in preventing impairment to human life and may not present a potential unreasonable risk of illness or injury,” he said.
Sources pointed to a variety of additional challenges to developing a market for more complex 3-D printed O&P devices. One is the need for practitioners to learn a new technology. Erenstone said practitioners need more access to education on the process. He and colleagues from Create Prosthetics will offer an instructional course at the American Orthotic and Prosthetic Association (AOPA) National Assembly in September.
“There is need [for education], because 3-D printing is not straightforward,” he said. “The big barrier is that you have to think of things in a digital manner. If someone is used to working with plaster and creating things with their hands, they are either going to have to learn a new method or they are going to struggle with 3-D printing. [Having] worked with this for a while, you can build up that visual understanding of things to kind of replace that tactile understanding of things that you get with plaster. But, it takes time.”
“Since the procedure to go from patient scan to definitive device requires additional capabilities, there could be some clinicians who may not want to learn the process, nor pay someone else to provide it,” Tompkins said.
He added there are also logistical concerns.
“Some foresee that clinicians would have an additive manufacturing printer in their office to print arms and legs locally. But more likely, due to the additive manufacturing print time, and the specific expertise needed for the CAD/CAM modifications, there will an additive manufacturing facility with process controls and quality testing tools to ensure product consistency, reliability and patient safety,” he said.
Even if all these barriers are overcome, Tompkins said, it is too soon to tell whether insurance companies would offer reimbursement for 3-D printed devices. Lack of reimbursement could prevent development of more complex devices that need more expensive machinery or materials.
Zuniga’s research into the capabilities of 3-D printing for O&P is ongoing, but he said additional research from other groups and institutions is needed.
“There is so much to learn,” he said.
Many companies and institutions are trying to learn more about the possibilities of 3-D printing, including Hanger.
“Hanger has instituted an internal research program to evaluate the various materials, manufacturing processes and software programs required to make safe and viable additive manufacturing-printed devices,” Tompkins said. “This comprehensive program includes a comparison of additive manufacturing vs. traditional fabrication techniques and explores products designed and fabricated without the restrictions of subtractive or other traditional manufacturing technologies.”
Poziembo sees more O&P firms using customized printers in the future. Printers customized for O&P devices would allow users to control parameters, such as heat, wall thickness and material quality. He described the difference as having “a printer that can do one thing great as opposed to a generic printer that can do everything mediocre.”
Poziembo said Prosthetic Design Inc. uses a custom printer that is “perfect for making cylindrical objects,” such as sockets and custom liner molds.
Cost of materials from the printer to the plastic, as well as the cost of training, could make it difficult for practitioners to begin using this technology. As machines with more reliability also come at a higher cost, Tompkins said these could create a barrier to entry for many. He added while additive manufacturing has great potential, it is still unclear how likely it is to replace traditional manufacturing.
“The additive manufacturing process may possibly find its place as a member of our digital fabrication program alongside traditional production technologies, rather than replace them,” he said.
While that may be the case, Erenstone said it is still important for prosthetists to learn more about the process and technology.
“We are already masters of 10 different types of technology,” he said, citing metal bending, plaster work and vacuum forming as examples. “This is one more that we need to master. It is just an evolution of what we are already doing.” – by Amanda Alexander
- Zuniga JM, et al. J Prosthet Orthot Int. 2016;doi:10.1177/0309364616640947
- Cyborg Beast: About Us. Available at www.cyborgbeast.org/#/about. Accessed May 24, 2016.
Disclosure: Colvin, Erenstone, Poziembo, Tompkins and Zuniga report no relevant financial disclosures.