Lower price for 3D-printed prosthetics

Materials World magazine
,
1 Jul 2018

3D printing is being used to lower the cost of pricey robotic prosthetics. Kathryn Allen reports. 

Advanced robotic prosthetic limbs can cost upwards of £25,000, while basic robotic hands start at £3,000. As these prosthetic limbs will likely not last an amputee’s lifetime, the considerable costs are often not one-off payments. But, students at the University of Manchester, UK, have developed an affordable alternative for amputees – a 3D-printed robotic prosthetic hand, costing £307. 

Produced by final year mechanical engineering student Alexander Agboola-Dobson and his team, the prosthetic was created using stereolithography (SLA), a form of 3D printing, and a resin plastic. Agboola-Dobson told Materials World, ‘We used Form 2 SLA printers from Formlabs, so we decided to go with their standard clear resin as we felt it would be most suitable for our prototype. It offered high print resolution, of up to 25μm, a reasonably good stiffness and toughness, and we didn’t feel it necessary to use their more specialised resins.’ 

Printing cheaper prosthetics 

Using 3D printing allowed costs to be saved. According to Agboola-Dobson, ‘specialised dies, tools, and moulds required for injection moulding are not needed in 3D printing, massively reducing unit costs of custom manufactured components’. 

Savings were also made using low-cost electronics. Instead of opting for small and powerful linear actuators to operate the prosthetic’s fingers, which are commonly used in 3D-printed prosthetics, the team used low-cost rotary servos. The method of printing produces a more life-like appearance than the none-robotic, purely functional prosthetics available on the NHS. 

The Manchester team hopes to eventually reduce the cost of the prosthetic further, using fused deposition modelling (FDM) 3D printing. Agboola-Dobson said, ‘SLA is amazing for getting a near injection moulded result from a 3D-printing process, which was the reason we chose to use it. A downside of SLA is the cost of resin and the printers themselves – the resin we used amounted to almost a quarter of the cost of the prototype hand. FDM, on the other hand, can be much cheaper in terms of both the material cost and machine (printer) cost, but comes with the downside of producing a lower standard of surface finish.’ 

The hand is controlled using three small surface electromyography sensors placed on separate arm muscles of the user. When the user moves a particular muscle, the sensor detects it and activates a pre-programmed gesture. The prosthetic is able to undertake tasks including picking up objects, opening doors, typing, and using a knife and fork. 

Bluetooth connectivity and a paired app improve customisation. Agboola-Dobson explains, ‘The purpose of the app is to allow users, on-the-go, to customise the gestures uploaded to the device and create their own. Say, for example, the user was in a situation in which they didn’t have the correct gesture available on the device (only three may be uploaded at once as there are three muscle sensors), then they could simply open the app and upload the correct one.’ 

Cost savings

FDM is already being used across the pond to progress the development of prosthetics, reducing costs and improving accessibility. In May 2018, the USA’s first clinical trial of 3D-printed bionic arms for children was launched as part of a collaboration between Oregon Health and Science University and non-profit organisation Limbitless Solutions, USA. 

The high cost of advanced prosthetics for children, who quickly outgrow them, can make them inaccessible. However, Limbitless’ myoelectric – relating to electrical impulses produced by the body’s muscles – arms are produced at the University of Central Florida, USA, at a hardware cost of less than US$1,000. These prosthetics are controlled using leads attached to the skin, activated by muscle movement. 

John Sparkman, Limbitless’ Vice President and R&D Director, told Materials World, ‘All of the devices that will be distributed during the clinical trials will be made with a 3D printer, which builds the devices using an FDM process. The material that is used is acrylonitrile butadiene styrene, which is the same material Legos are currently made from. After printing, we post process the parts and give them their final finish.’ 

The trial will see 20 children, aged between six and 17, fitted with the prosthetics and taught to use them, monitoring functionality. The team hopes the trial will help determine whether the US Food and Drug Administration will approve the prosthetic. 

The company is working to reduce the cost of the prosthetic arm. Albert Manero, President of Limbitless, said, ‘The use of 3D printing allows for a cost savings for a small run (less than thousands) of parts, particularly as opposed to injection moulding. It also allows us to rapidly iterate the design, while saving manufacturing and design costs along the way.’