Prosthetic hands from VINCENT Systems: A lightweight featuring high-tech quality and a sense of touch

The human hand is more complex than it looks. 33 muscles control every movement and ensure a strong grip or handshake. What’s more, our fingertips have different receptors that play an important part in how we perceive surfaces, temperature or pain. The Karlsruhe-based VINCENT Systems Company develops prosthetic hands that raise the bar for prosthetics. This prosthetic device is light-weight, based on the anatomical features of a natural hand and offers a wide variety of functions as well as an artificial sense of touch.

The company’s founder D.Eng. Stefan Schulz has worked in research for many years and is very familiar with the drawbacks of prosthetic hands. In this REHACARE.com interview, he describes how the VINCENT Systems prosthetic devices work and explains what makes them so unique.

Dr. Schulz, your company VINCENT Systems makes the world’s most lightweight and moveable prosthetic hand. What makes your prosthetic devices so innovative?

Dr.-Ing. Stefan Schulz: For the first time, our VINCENT hand systems combine the functionality of a multi-articulating hand with the weight and anatomy of a natural hand. The prosthetic hands can also be used without a cosmetic glove since the high-strength aluminum design is fully covered with soft plastic. In addition to the movement of the individual fingers, which supports an adaptive grasp, bow springs also set up tension towards the clasped object and facilitate a more secure grasp. To choose from the different grip patterns, the control mechanism also eliminates the need for many different switch signals. Just one pulse combined with the open and close signal gives wearers intuitive control over up to 14 different grip patterns. The learning phase is only about one hour.

You try to balance high-tech quality and the advantage of every available technical sophistication to accommodate both weight and function, yet you simultaneously also emphasize a natural, aesthetic look, as well as an intuitive control mechanism for the wearer without an additional assistance system – that’s a big risk to take for a startup company. What made you pursue this ambitious goal, especially as it pertains to lightweight construction and esthetics?

Schulz: Needless to say, as a new company you always have a higher risk in terms of development items and market development. I got motivated to start this company after many years of research in the field of hand prosthetics. That’s why I was aware of the shortfalls of existing hand prosthetics and had ideas on how they could be improved for prosthesis wearers. But that’s also why I didn’t just want to develop a new hand prosthetic, I also wanted to raise the bar and bush the boundaries in prosthetics, most notably by combining technical advances, quality, and design.

What are the challenges in making your prosthetic device?

Schulz: The prosthetic devices have a very complex structure. The challenge is to also guarantee the quality and precision of the components when you go into series production and simultaneously keep manufacturing costs low to where the product continues to be affordable and can be used by a wide audience.

How does the assistance-free control concept that assists in choosing all available grips via muscle signals work?

Schulz: The advantage of our patented STC concept ("single trigger control" concept) is that we can achieve any grip without the help of additional equipment – meaning no additional devices or buttons, or even special gestures etc. To do this, we have arranged the grips in a specific order. Even when it comes to normal open and close signals, as well as a hold open signal for a set period of time, each wearer can select four different types of grips. If the wearer masters one of our trigger signals – this may be a single open impulse, a double open impulse or a co-contraction (a simultaneous contraction of all muscles attached to a joint to stabilize it; Editor’s note) – the wearer can select all 14 available grip patterns. The arrangement of grips can be envisioned like a tree structure with a base and immediately adjacent are the most important grips, whereas other grips can be additionally selected on a second level with the trigger signal.

How does the force feedback system of your prosthetic device work?

Schulz: Our prosthetic devices give the prosthesis wearer feedback through small vibrations on the skin, called vibrotactile feedback. The feedback indicates the force measured on the index finger if something is grasped or pressed and thus equates a very simplified sense of touch. This sense of touch gives wearers feedback on changes in force or touch and has been specifically developed to distinguish smaller forces when grasping or pressing with the index finger. When the force increases and exceeds one of the predetermined thresholds, the prosthesis wearer gets feedback via vibration alert. There is no feedback if the force remains unchanged or decreases.

How can sense of touch help prosthesis wearers to alleviate phantom limb pain?

Schulz: The prosthesis wearer gets grip force feedback via vibration signals in the hand. It stimulates the sensorimotor cortex, which can help reduce any existing phantom limb pain. This works in a similar way to visual stimulation in mirror therapy, where the missing arm is simulated by the healthy arm with the help of a mirror.

VINCENT Systems also offers hand prosthetics for children. Why are prosthetics for children the pinnacle of prosthetics?

Schulz: Prosthetics for children present a special challenge because unlike prosthetic devices for adults, the prosthetic components for children must be considerably reduced in size. Meanwhile, grip force, speed, and robustness must be at the same level as hand prosthetics for adults. Needless to say, due to the miniaturization, the weight must also be significantly reduced. All of these aspects present a major technological challenge.

Your company is also known for its modular design. What is it exactly and what are some of the issues with partial hand systems?

Schulz: Modular design is used for partial hand systems. Every prosthesis wearer has a very individual stump situation. You need to replace individual fingers or a thumb or entire sections of a hand. This only works if a prosthetic device can be customized based on the patient’s anatomical circumstances. The solution is to adapt the motor-powered single fingers to the patient by using individual frame structures. Electronic controls, sensor systems, and batteries can be placed individually. Thanks to an innovation, the batteries can now be adapted to match the anatomical shape. As a result of an innovative USB charging system, our batteries can also be recharged at any time without mains power, giving the prosthesis wearer a longer, independent life expectancy for his/her prosthetic device.

You have an innovative product that was nominated for the German Future Prize as one of three final projects. Plus, you are also active in the U.S. market. What does the future have in store for VINCENT Systems and functional prosthetic hands in general?

Schulz: We still have lots of plans when it comes to the field of prosthetics and as an innovative company, we want to contribute to continuous technological advancements in prosthetics. It’s fun to develop new technologies, while it is also incredibly motivating to improve the quality of life of so many people. That’s also why we won’t run out of new ideas.