Printed Prostheses: Not Yet Ready for Developing Countries

Three-dimensional printers are gaining popularity in low- and middle-income countries. They churn out products such as agricultural tools, automotive parts, and anatomical models for medical students. The method is great not only for lowering costs, but also for modeling a concept, adding detail, simplifying repair and maintenance, and allowing for personalization.

It has also become popular in the manufacture of prostheses, in particular prosthetic hands.

Some 2.4 million upper-limb amputees live in developing countries. Groups focused on 3-D printed prostheses—such as Nonspec, OpenBionics, and e-NABLE—often intend to provide an alternative to expensive imported devices for people in low- and middle-income countries.

At the Humanitarian Engineering and Social Entrepreneurship (HESE) Program at Penn State University, we worked with the e-NABLE network to assess the appropriateness of these 3-D printed devices for large-scale dissemination in low- and middle-income countries. We asked, is this method of production appropriate for these assistive devices? What are the device’s abilities and does it address an actual need? How would such a device reach the people who need it?

We performed extensive research in our lab and on the ground in Zambia to evaluate the viability of 3-D printed prosthetic hands and discovered the advantages and challenges to this new technology.

Is 3D Printing Viable?

To determine whether 3D printing in its current state is a viable option for prosthetic devices, HESE manufactured and tested the Raptor Reloaded, a design created by e-NABLE. The Raptor Reloaded is designed for users with wrist disarticulations—as were 10 of the 18 prosthetic hands designed for low- and middle-income countries that we discovered in our research. The CAD model for the Raptor Reloaded can be modified and scaled prior to printing.

Printing takes 32-54 hours, however, which may be an unrealistic wait time for an amputee traveling long distances to receive the prosthesis. In balancing time, cost, and customizability, we determined that a hybrid approach of 3D printing and injection molding would be a better option to decrease manufacturing time while keeping costs low and enabling some customization.

We then followed a protocol similar to that of the Southampton Hand Assessment Procedure, a standardized test of the effectiveness of upper-limb prostheses through manipulation of objects that are common in everyday activities. The results indicated that the current design of the Raptor Reloaded has limited capabilities. For example, users were unable to pick up or maneuver small objects, such as coins and keys, though they could perform simple tasks that did not require fine manipulations of the fingers, such as picking up an empty cup or a small ball. Designed for areas where the main source of income is typically manual labor, these limitations could reduce the appropriateness of the product.

A significant issue facing the distribution chain is the lack of availability of prosthetists and rehabilitative services. According to the World Health Organization, less than 5 percent of the population in low- and middle-income countries has access to these services. With a limited number of training facilities in Africa, a majority of countries must send their students to another country for training.

Additionally, rural workshops and hospitals serve as bottlenecks in the pathway. Even if materials and devices are available, it is still difficult to distribute the prostheses to those in need, given the length of travel often needed to visit a hospital or workshop. Access to rural amputees becomes a particular concern since successful, long-term use of a prosthesis requires maintenance and rehabilitation—at additional time and cost to the amputee. Thus, maybe we should focus not only on providing alternative devices, but also on building an alternative system.

Shifting Design Focus

So, should we even work on 3-D printed devices? Absolutely! Pioneers like e-NABLE are critical for pushing the boundaries of what is possible. Although there are several limitations of current 3-D printed hands, this manufacturing process has potential. One route would be to work with a stronger material than the plastic that is used in current designs. Metal 3D printing, although more expensive, could eventually become a viable option to strengthen the design. Moreover, a design that allows for increased and finer control over movement to allow for a broader range of capabilities would be helpful.

Also, while most of these 3-D printed prostheses are designed for wrist disarticulations, only 4 percent of the upper limb amputees in low- and middle-income countries have wrist amputations. It is likely that the number of wrist disarticulations is even lower. Furthermore, those with wrist disarticulations would be the most likely to adapt post-amputation without the need for a prosthesis.

Shifting the focus of design efforts, then, to a prosthetic leg would be more applicable, as a person is more dependent on the lower body for mobilization and the ability to work, especially in low- and middle-income countries.

Brienna Phillips is a student of biomedical engineering, Sarah Ritter is an assistant professor of engineering design, and Khanjan Mehta is the founding director of the Humanitarian Engineering and Social Entrepreneurship Program and an assistant professor of engineering design. All are at Pennsylvania State University in State College.