FUTURE ARM PROSTHETICS

Exploring opportunities to make upper limb prostheses more affordable, functional and appealing.

Modern electric prosthetic hands and arms are fascinating pieces of engineering, yet still there are many problems prevailing. These devices are typically very expensive, heavy, difficult to control and not very robust. Most of them have a rather robotic or puppet-like appearance. All this leads to low accessibility and low acceptance rates among users. Simpler, body-powered prostheses have been around for over 100 years, but despite their high functionality, they are only getting limited attention in today’s industry developments due to the focus on high tech.

With this project, I aim to look at how recent developments in technology (e.g. new 3D printing methods) could help creating prostheses that offer higher user benefits while making them more accessible. I believe that this could be achieved by creating simpler, more versatile devices that focus on practicability, comfort and individualisation.

MFA Degree Project
Umeå Institute of Design
Duration: 20 weeks
2024 - ongoing

In collaboration with:

01

PROCESS

Background

People with physical disabilities are often excluded and isolated. This is both due to certain bodily limitations, but also due to societal stigma. Assistive devices like prostheses or ortheses can help them to regain their mobility. This allows them to live independent, healthy and active lives and lets them partake in the society with lesser limitations. This also reduces the need for certain healthcare services (World Health Organization, 2017).

The big issues

Limited accessability

Why?

• High cost 

• Limited availability

• Lack of healthcare personnel

Low rate of acceptance

Why?

• Too little functional benefits

• Lack in comfort

• Unsatisfactory appearance & stigma

Why is it so difficult to solve this?

High individuality

functional & aesthetic requirements

High R&D costs

for a small market

Limited human resources

e.g. prosthetists

Industry

The prosthetics industry focuses on high-tech bionic prosthetics to maintain profitability. The resulting products are highly expensive, while they only add limited benefits for the users. 

Low-cost mechanical prostheses only get little attention from the industry and has seen only little advancements over the last decades.

Efforts to counter this often don‘t have the funding and the development depth to actually create beneficial solutions.

Existing products

Multi-Grip Myoelectric Prostheses

Multi-articulating electric hands controlled by myoelectric sensors are today's state of the art. They can move the fingers independently. These hands can perform a variety of grips, although users tend to use only few of them.

Pro

• Multiple grips

• No muscle strain

• contained product

• kind of human-like

Contra

• High cost

• Difficult and slow motor control.

• Low robustness.

• No sensory feedback

• High weight

• Limited battery life

• Noise

• Lack of warmth and humanness

Standard Myoelectric Prostheses

The "old" myoelectric standard prosthesis features only one opening/closing movement that can be utilized for a limited range of tasks. 

Pro

• Moderate cost

• No muscle strain

• Contained product

• kind of human-like

Contra

• Limited functionality

• High weight

• Slow control

• No sensory feedback

• Limited battery life

• Noise

• "Puppet-appearance"

Body-Powered / Mechanical Prostheses

Body-powered prostheses work by pulling a cable with your shoulder movements. These prosthesis have been around for more than 100 years, but little has changed. The are still considered to be very functional.

Pro

• Moderate costs

• Fast control

• High durability

• Natural force feedback

• Lightweight

Contra

• Limited movements

• Complex fitting of harness

• Physically demanding

• Complicated donning & doffing

• Brutal appearance

Design Opportunity

As a conclusion of my desktop, user and stakeholder research it has become clear that there are multiple opportunities to contribute to a better future of prosthetics. I see the main potential in bringing back simpler, more robust solutions that are not only more affordable, but also offer certain functional and aesthetic benefits. This could be achievable using new accessible technologies like 3D-printing.

Design of a practical, comfortable, appealing and affordable prosthesis for transradial amputees, filling the gaps the industry leaves behind.

Increase accessability.

by focussing on the necessary and by leveraging new technologies.

Increase acceptance.

by offering higher individual benefits in
functionality, comfort and appearance.

Exploration

I explored different concepts via sketching and prototyping and validated ideas with users and experts.

02

FINAL DESIGN

PAL

The final design concept is a hybrid, personalised prosthesis that combines advantages of both modern electronic systems and traditional body-powered prostheses into a lightweight and robust solution, that can be used with a range of inexpensive terminal device modules to provide users with individual benefits.

Configuration

By using readily available technology like 3D-scanning, procedural configurator software and a new way of 3D-printing, the prosthesis can be tailored to the individual user while reducing costs and manual work effort. Professionals can configure the prosthesis together with the patients to fit their needs and desires. Before the prosthetist puts in any effort into manufacturing, the software allows for visualising the prosthesis configuration for the user, which helps to avoid misalignments with the patient’s expectations. Once the prosthesis is fully configured, the software provides the prosthetist – or orthopedic technician – with a detailed build plan and a list of needed parts. This, for example, includes auto-generating ready-to-print 3D-models, creating fabric cutting templates and providing links for ordering standard parts.

The Harness Shirt

The prosthesis’ gripping function is controlled by the user’s shoulder and arm movements using a breathable undershirt, that replaces conventional harnesses. It is locally reinforced to evenly distribute the pulling forces with the goal of reducing strain. The shirt can be comfortably worn underneath regular clothing, and the prosthesis can be conveniently connected and disconnected from it depending on the user’s needs. The shirt is breathable and washable to ensure comfort and hygiene. It is intended that users would have multiple shirts, so they can wear a clean one while washing the used ones.
Using body power eliminates the need for heavy batteries and motors and lets the users control the prosthesis in an intuitive and fast way. The direct connection to the body also creates natural feedback for the gripping force.

Adapter System

The different terminal devices are attached by a low-cost bayonet fitting, that is made by a combination of 3D-printed parts and standard countersunk screws and lock nuts. This helps to keep the cost for the attachment mechanism low, which therefore also reduces the cost for the terminal devices.

The Hand

The hand is simplified, yet still very functional. Users can perform the most used grips, which are the key grip and the tripod grip. The tripod grip configuration also works as a power grip. Users can passively switch between the grips by manually moving the thumb to the right position. The key grip – which is the default grip – represents a natural resting position of the hand. The overall appearance of the hand is friendly and human-like without falling into the uncanny valley. The fabric covering the moving thumb adds a warm feeling and nice sense of touch while protecting the inner mechanism from dirt. It also opens up an opportunity for a certain level of personalisation through the choice of fabric and its colour. The whole hand contains no special components and can therefore be cleaned using a washing machine or even a dishwasher.

Technical Package

The main structure consists of an inner rigid part that connects to the wrist with a tube, and a flexible outer socket. A small electronic lock-switch can be triggered using an EMG signal from the residual limb. It locks the hand’s grip, which makes it easy to move around with a grasped object. It can then be unlocked using the same signal again. The small amount of needed energy for the switch can be harvested from the user’s natural movements, and only little weight is added to the prosthesis. The prosthesis can also be switched to an idle mode, where the user can move around freely without making unwanted movements.

The Socket

The socket’s shape is based on 3D-scans of the user’s
sane arm, and it is manufactured using the proposed rotary
3D-printing approach. Its perforated structure makes it lightweight
and gives it flexible properties. When passively turning
the wrist, the socket deforms with the movement, which creates
a natural form-transition between the arm and the terminal
devices. Its flexibility combined with the soft layer of fabric
on top improves the haptic properties which makes the whole
prosthesis more approachable and friendly.

Physical Model

Finally, I built a physical design model to validate and showcase the visual appearance of the prosthesis. This included the use of fabrics to get close to what the final product could look and feel like.

Key Project Values

For the users: 
A cost-effective, tailor-made prosthesis.
Accessible modularity for individual use cases.
A natural, friendly materiality with personalisable elements.

For the orthopedic technicians: 
An intuitive, supporting way of using 3D-data for the
patients – without having to learn difficult softwares.
A new rotary 3D-printing approach that allows for
creating better sockets.

For the industry:
An inspiration for putting the human more in the center of
development, and not new technologies.

To be refined. Stay tuned!