Tech fusion enhances prosthetic innovation

Siobhan Doyle

In the realm of prosthetics, form and function converge to create seamless design integration. 

A young man named Zak from Michigan was born without his left hand. A huge fan of film franchises such as Star Wars and the Marvel Comic Universe, Zak was fitted with a ‘Hero Arm’ from medical device company Open Bionics in April 2019 at his local Hanger Clinic in Livonia. The cover of the arm in question resembled that of Marvel’s Iron Man suit.

Zak was able to master the prosthetic within hours: he was riding a bike, reading books, and holding binoculars. His mother also spoke out about the Hero Arm to the press: “Zak’s previous experience with prosthetics – the more traditional ones that were available to us – was not positive they were heavy and not as user-friendly to him, and so he was not overly excited to use them at the time. The newer technology is lighter, he had more input into the colour and design, so he felt more part of the process.”

Similar to that of numerous individuals with limb differences, Zak’s story highlights the importance of crafting prosthetics tailored to each person’s unique requirements, prioritising individual style, as well as comfort and functionality.

The bionic arm

Open Bionics’ Hero Arms work by interpreting signals from the user’s muscles. When the user wears the bionic arm and flexes the muscles in their residual limb just below the elbow, specialised sensors detect small electric signals naturally produced by the muscles. These signals are then converted into intuitive and proportional movements of the bionic hand.

Control of the bionic hand is achieved by tensing the same muscles used to open and close a biological hand. To close the hand of Open Bionics’ Hero Arm and execute a specific grip, a user can visualise flexing the wrist inward while pulling the fingers toward the palm. Conversely, to open the hand, they must envision extending the wrist with the palm facing outward.

The technology integrated into the bionic arm is scientifically termed electromyography, with the special sensors referred to as electromyographical (EMG) electrodes. Myoelectric bionic arms are designed to be plug and play, allowing users to easily attach and detach them. The Hero Arm also features an adaptable dynamic socket for optimal comfort. There is no need for surgery; instead, the team at Open Bionics identify the user’s strongest muscle sites and conduct a 3D scan or cast of their residual limb to custom-build the product.

Open Bionics customises the liner, internal frames, and personalised covers to fit snugly around the user’s limb, accommodating various presentations, from partial wrists to noticeably short residuals. The outcome is an adaptable liner – 3D-printed from a soft, flexible elastomer – that seamlessly integrates with the user, mirroring the curves and contours of the limb precisely.

3D-printing for prostheses

As alluded to by the technologies integrated into Open Bionics’ Hero Arms, additive manufacturing (AM) plays a significant role in the development of prosthetics, opening up new opportunities for customisation and enabling patients with amputations and limb differences to access devices tailored to their needs.

“Despite the benefits prosthetics can offer, the technology still faces problems. Poor fit is a widespread issue reported by users since it can lead to discomfort and skin irritation and may cause some patients to abandon their prosthetic altogether,” says Dave Walsha at DC motor supplier EMS.

“The highly individualised nature of humans, whether it is their body proportions, or the nature of the amputation means that no two users are the same – and therefore, neither should their prosthetics be. This makes component manufacturing hard to standardise, while also increasing the cost per prosthetic.”

Walsha highlights the use of 3D-printing technologies to tackle fit and customisation issues within the sector. “With no minimum order or the need to create specific moulds, prosthetics can be prototyped and developed on an individual basis for an improved fit. This also allows for aesthetic personalisation and a less obtrusive prosthetic.”

The design freedom associated with 3D-printing technology offers countless opportunities for improved design and functionality – such devices can provide superior comfort, customisation, and cost-efficiency compared with traditionally manufactured devices.

Additionally, 3D-printing allows manufacturers to create lighter designs, enabling users to wear them more comfortably for extended periods. This is possible because AM enables the creation of complex structures with minimal material consumption. Considering that materials make up more than 40% of manufacturing costs, the potential for lightweighting can also lead to cost savings for companies in the field.

Motors and drives

In addition, to enhance functionality for users, prosthetic devices often incorporate compact, high-performance motion control solutions such as stepper, brush, and brushless DC motors, gearmotors, and drives, ensuring improved dexterity and sensitivity.

“To address functionality concerns, miniaturisation of the electronics within the prosthetic is essential,” Walsha says. “The DC motors that facilitate the movement of artificial joints must be small enough to fit within a housing built to replicate human limbs. However, these size restrictions should not come as a detriment to the rest of the specification. It is important that these motors still offer a high torque, with the ability to quickly change direction to account for quick or sudden movements.”

Motors and motion products offer prosthetic manufacturers a blend of compact size, minimal noise and weight, high-power density, efficiency, reliability, and cost-effectiveness, enabling prosthetic manufacturers to develop innovative microprocessor-enabled knees and ankles.

Walsha says opting for a coreless or ironless DC motor is preferable for many medical applications, with the prosthetics industry being no exception. “Eliminating the iron contained in traditional DC motors significantly reduces the minimum moment of inertia, allowing for rapid acceleration and deceleration rates and cogging-free running.”

By harnessing the advantages of coreless brushed DC motor technology in motion devices, along with the simplicity and safety of active prosthetics’ induction charging and durable construction, these advancements address numerous challenges faced by amputees with traditional prosthetics, contributing to an enhanced quality of life.

Seamless integration

EMS (Electro Mechanical Systems) works extensively in the MedTech field, contributing to projects like the bebionic3, recognised as one of today’s most advanced bionic hands. Developed by prosthetic manufacturer Steeper, the bebionic3 offers full motion compliance, with each digit individually powered. To maintain this functionality in a smaller hand without compromising performance, Steeper’s Technical Director Ted Varley emphasised the need for a high-power Ø 10mm motor gearbox and encoder. “Our design ethos prioritises placing the motors in the palm to facilitate a more efficient gearbox design and reduce perceived mass, enabling full finger flexion and lifelike movement.”

Transitioning from 15mm Ø Faulhaber motors to a new 10mm Ø motor, Steeper collaborated with EMS and Faulhaber to develop the motor 1024M006SR, tailored for the bebionic3. This motor features enhanced components for improved performance, including a redesigned end cap for easier assembly, more accurate brush positioning, and integrated commutator and brushes with precise geometry. These enhancements yielded superior performance, particularly in grip patterns and stall conditions, with a highly dynamic, flat speed/torque curve ideal for the application.

Moreover, Faulhaber addressed the challenging requirement for a thumb actuator, leveraging their expertise to develop an in-line linear actuator capable of delivering high force in a compact form. Integrating a high precision 4-point contact bearing from their group company Micro Precision Systems (MPS), Faulhaber produced the most powerful and smallest linear actuator capable of sustaining axial forces up to 300N.

The unique characteristics of the bearing enabled a significantly shorter overall length compared with conventional bearings, highlighting Faulhaber’s commitment to innovation in meeting complex MedTech requirements.

Through collaborative efforts and innovative solutions, companies such as Open Bionics, EMS, Faulhaber, and Steeper – all in which specialise in developing different technologies – continue to drive advancements in bionic technology, enhancing the lives of prosthetic users worldwide.