3D Printing Low-Cost Prosthetic and Orthotic Devices

blank blank Feb 01, 2020


The Victoria Hand Project (VHP) is a Canadian non-profit with a mission to provide low-cost, orthotic and upper-limb prosthetic care to disadvantaged individuals. The International Society for Prosthetics and Orthotics and World Health Organization (WHO) estimates that 80% of amputees live in low-income countries, yet only 5% of amputees have access to prosthetic care [1]. In many developing countries, government healthcare systems are not able to provide prosthetic and orthotic care to those in need. 

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Figure 1: Palpasha using the Victoria Hand to write, Nepal, 2019

VHP helps provide care by creating partnerships in developing countries to manufacture and fit 3D-printed orthotic and prosthetic (O&P) devices. The 3D Print Group, a group of technicians or engineers, will 3D print the components, assemble the devices, and 3D scan the patient to make the custom devices. The Clinical Care Group, a group of doctors or orthotics/prosthetists at a hospital or a clinic, will take the patient’s measurements, create a plaster impression, and fit the device to the user. 

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Figure 2: VHP’s deployment process around the world

The 3D Print Group will be outfitted with the required equipment (i.e. 3D printers, 3D scanning system, computer, tools) and supplies to manufacture the prosthetic and orthotic devices directly within the community. You can learn more about the operations and history of the Victoria Hand Project, and our deployment model, in our prior Expert Corner blog post.

Why Use 3D Printing?

When compared to the traditional manufacturing process for O&P devices (ex. CNC milling), 3D printing has numerous advantages such as:

  • Low-cost: 3D printing helps lower the overall manufacturing costs.
  • Printed on-site, on-demand: The prosthetic and orthotic devices can be printed on-demand (i.e. when someone approaches the clinic) and components do not need to be stocked in the clinic.
  • Create complex objects: Many parts of the Victoria Hand require complex geometry (ex. The ball-and-socket wrist) and would be impossible or very expensive to create using traditional methods.
  • Create custom devices: Each user has a unique anatomy. 3D printing can allow for a more comfortable fit and the device can be made to closely match the user’s anatomy.
  • Low-start-up costs: The equipment costs required to outfit a prosthetics workshop are much lower than traditional equipment, such as a large oven for heating plastic, and grinders for post-processing.

The design and testing of prosthetic and orthotic devices are done in Victoria, Canada by undergraduate engineering students and recent engineering graduates. This includes design conceptualization, design using SolidWorks or Fusion 360, and benchtop testing. Any design updates to the O&P devices can be implemented by the team in Victoria, and easily sent to the partners in developing countries via the internet. 

PLA (Polylactic Acid) is used as the material of choice for the Victoria Hand and the LimbForge arm. Early tests were performed on various 3D-printed material types (i.e. PLA, ABS, Nylon, PETG, etc.) and colors. It was determined that black PLA was a favorable material to use due to the high strength, better biocompatibility when compared to other materials, and ease of printing. ABS (Acrylonitrile Butadiene Styrene), another alternative, also has high strength and is tougher than PLA, but it is more difficult to print with and is more toxic. 

Undergraduate and graduate students who work/volunteer with VHP continue to perform testing on the hand components and various materials. This helps us determine if a part is strong enough for deployment in the field and if we can improve the strength of the materials. An example of this was setting up the fingers in a cantilever position and loading the end with weight.

Features of the Victoria Hand

The Victoria Hand Project offers a number of solutions for amputees in need of upper-limb prosthetic care, depending on their personal preference. The Victoria Hand is highly-functional, while the LimbForge arm does not function but has a better cosmetic appearance. Users can choose if they would like a functional hand for help in their daily life, or if they would prefer a cosmetic hand to feel more comfortable in public.

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Figure 3: The functional Victoria Hand (left) and the cosmetic LimbForge arm (right).

The Victoria Hand has various features that allow for increased functionality, which allows the user to use the hand for more daily tasks. Videos of some of these features can be seen on our website

Body-Powered 

The Victoria Hand is completely body-powered and does not require electronics to operate. This helps lower the costs of supplies, makes the manufacturing process less complex, allows the users to use the hand in wet environments, and makes repairs much easier. To actuate the hand, a user wears a shoulder harness that wraps around their shoulders like a backpack. By flexing the shoulders, the user can actuate the hand. An example of the harnessing can be seen in Figure 3 above.

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Adaptive Grasp

In adaptive grasp, each finger uses a compression spring mechanism so they move semi-independently. This allows the hand to conform around objects to ensure a better grasp and a more natural-looking grip.

Ball-and-Socket Wrist

The hand has a ball-and-socket wrist to change the orientation of the hand. This wrist allows the hand to flex/extend 25 degrees each direction and rotate a full 360 degrees. A functional wrist is important since many users are not able to rotate their forearm and may need to awkwardly bend their entire torso when picking up objects.

Back-lock Mechanism

The hand is spring-loaded so when a user relaxes the tension on the cable the hand will open. This would make it very annoying for an amputee who wants to carry an object but needs to continually flex their shoulders to close the hand. The back-lock is a ratcheting mechanism that will lock the hand is the closed position at varying degrees of closed. When the user wants to open the hand they can push a button to release the ratchet pawls and cause the hand to open again.

Rotatable Thumb

The thumb is able to rotate (adduct/abduct) to achieve different positions and grips. This includes a one-finger pinch, a two-finger pinch, a power grasp (i.e. four fingers and thumb grasping), or a lateral grasp (to carry a bag). It can be rotated with the user’s other hand or by pressing against an object. 

Custom Sockets

Creation of a custom socket for the user is a very important feature of the Victoria Hand and LimbForge systems. The hand can have the best features in the world, but if a user finds the socket uncomfortable they will probably never wear it. 

To make a custom socket, the clinician will take a cast of the patient’s remnant limb using gypsum bandage and will take anatomical measurements of the patient’s limbs. The clinician will then fill the cast with Plaster of Paris to create a positive mold of the patient’s remnant limb. They will rectify the plaster impression by adding and removing the Plaster of Paris to adjust the mold shape. The rectified plaster impression is sent to the technicians for 3D scanning. 

VHP uses two different methods for 3D scanning: laser scanning and photogrammetry. Photogrammetry uses approximately 60-80 photos of the plaster impression to create a computer model. Photogrammetry produces a model with ‘true’ colors that are useful when creating the custom socket and is much less expensive than laser scanning ($1000 vs. $3500).

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Figure 5: Plaster impression model made through photogrammetry process

Photogrammetry also makes fieldwork much easier. Partners from far outside the community can capture photos of a plaster impression and send these photos to the 3D Print Group for processing. They are not required to use an expensive, bulky, 3D scanner that may not have access to power.

The 3D Print Group uses the 3D scan to perform a Boolean operation and remove the shape of the remnant limb from the socket. The socket can then be printed in less than 8 hours and fit to the patient.

Future Work

VHP is continuing to deploy the Victoria Hand in 7 developing countries around the world and will expand operations to Kenya in February 2020. VHP’s primary mission was to provide prosthetic care to developing countries but VHP recently received the TD Ready Challenge award to provide care to North Americans. VHP will also be beginning operations in Canada and the United States with funding support from TD Bank Group. This will allow VHP to set up 7 print centers across North America, deploy 200 upper-limb prostheses, and 160 scoliosis braces.

References:

[1] http://www.ispoint.org/sites/default/files/img/ispo-who_training_guidelines.pdf

About the Author:

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Michael Peirone graduated from the University of Victoria in 2016 with a B.Eng in Biomedical Engineering. During his undergraduate degree, Michael completed two internships with Victoria Hand Project (VHP) and volunteered with VHP during his in-class semesters. Upon graduating, he began working with VHP full-time as a mechanical designer. Now as Chief Operating Officer, Michael runs the day-to-day operations of Victoria Hand Project. This includes working with the teams in the partner countries, overseeing design updates on the scoliosis braces and prosthetic arms, and fundraising.

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3D Scanning and 3D Printing for Creating Affordable Prostheses

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