The 2021 theme for SME’s Digital Manufacturing Challenge was “Digital Manufacturing for Rapid Medical Response.” This challenge encouraged proposals of digital manufacturing solutions to strengthen the infrastructure for mitigation and/or prevention of health challenges associated with disruptive and devastating events such as the COVID-19/coronavirus pandemic.
Some functional examples provided by SME included the use of AM to help with supply shortages of medical equipment ranging from basic personal protective equipment, such as face shields, to more sophisticated respirators and ventilators. The Multi-Scale Additive Manufacturing (MSAM) Laboratory at the University of Waterloo in Waterloo, Ontario had been previously involved in such efforts by 3D printing parts for face shields used by health care workers battling COVID-19 [1]. These efforts inspired us to identify applications where our own research areas in metal AM could be useful for rapid medical response. We proposed a digital manufacturing approach for the rapid development of prosthetic transtibial (“below knee”) leg assemblies for use in emergency medicine.
Amputation surgery is often necessary for severe musculoskeletal trauma following large natural disasters, military conflicts and industry/infrastructure-related accidents. The inability to perform rapid triage due to logistical, socioeconomic and safety reasons following a mass casualty event further increases the necessity of limb amputation surgeries as blood loss and infection compromise the remaining tissue. Following amputation, a custom-fitted prosthesis would be an ideal solution for individuals to continue to actively participate in society. However, the time and cost associated with obtaining a fitted prosthesis is often prohibitive in developing nations and difficult to support for private aid organizations due to the individualized nature of care required through the fitting process. Therefore, it is essential to take advantage of recent developments in digital manufacturing to reduce the time and costs associated with providing customized prostheses to affected individuals, enabling functional recovery as soon as possible. Furthermore, a digital workflow and distributed manufacturing can address manufacturing needs rapidly and remotely.
Our proposed approach for rapid deployment combines conventionally scalable manufacturing technologies (adapters, prosthetic foot) with digital manufacturing (custom pylons, sockets) technologies. Patient-specific prostheses can then be assembled and fit by any prosthetist or hobbyist manufacturer to provide rapid point-of-care treatment. In the instance of rapid response to catastrophic global events, it is more common that devices be rapidly provided with disregard for fit, customization, functionality and longevity. By front-ending these design requirements, we hope to deliver an improved final product to the user.
Customization of the socket design using 3D scanning and AM is proposed, as this approach can greatly reduce the costly and time-consuming practitioner visits generally required for custom socket designs. 3D scanning of the residual limb can be obtained through software applications on personal smartphones by placing contrasting markers on the skin followed by a series of video captures. 3D reconstructions of the residual limbs can then be transferred to the manufacturing facilities where the the socket designs can be manufactured from polylactic acid (PLA) filaments on fused-deposition modeling (FDM) printers. A biomedical-grade silicone cushioning insert can be provided to ensure comfort and fit with the socket as a temporary stopgap measure until access to medical care can allow for custom fitting to occur.
The use of stress-field-driven, lightweight lattice structures and a popular aluminum alloy (AlSi10Mg) would help with lightweighting, functionality and customization of the pylons in the prosthesis’ assembly. Laser powder-bed fusion of the pylon components is proposed due to the increasing presence of affordable machines and reduction in overall manufacturing costs for batch production, which is to be expected for pylons as this metal AM technology currently has the highest industrial uptake.
Conventional manufacturing is proposed for the prosthetic foot using spring-molded carbon-fiber infused PLA. The ankle connectors required for the prosthetic leg assembly can also be manufactured using conventional metal forming and machining operations because the proposed pylon design would have the same diameter and only vary in length.
The use of digital manufacturing for the rapid deployment of customized sockets and pylons for transtibial prostheses would have lasting social implications by improving implant customization, alongside the functionality, durability and lightweighting features.
Reference
[1] “University of Waterloo Is 3D Printing Face Shield Components to Help Protect Front-line Medical Workers,” University of Waterloo, 2020.
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