Feeling the Burn

In recent years, there have been remarkable advances made in the technologies used in prosthetic arms, offering users unprecedented levels of functionality and control. These advancements have significantly improved the quality of life for amputees, enabling them to regain independence and perform a wide range of daily tasks with greater ease and efficiency.

Modern prosthetic arms are equipped with sophisticated technology, including myoelectric sensors and advanced mechanical components, allowing users to control the movement of their prosthetic limbs with remarkable precision. This means users can perform delicate tasks such as picking up small objects or typing on a keyboard with relative ease. Additionally, some prosthetic arms are designed with multiple degrees of freedom, mimicking the natural movement of a human arm and providing a greater range of motion.

One of the key challenges, however, is the lack of sensation in these prosthetic limbs. While they can restore many functions, users often report feeling disconnected from their prosthetic arms due to the absence of sensory feedback. This limitation can impact the user's ability to interact with their environment effectively and diminishes the overall realism of the prosthetic experience.

Efforts have been made to address this issue by developing technologies capable of restoring sensory feedback to prosthetic arms. However, these approaches typically involve highly invasive procedures, or even brain implants, which carry significant risks and are not always feasible for all users. Additionally, the complexity and cost of these procedures can present barriers to widespread adoption.

A clever team at the Swiss Federal Institute of Technology has taken a completely different approach that has the potential to restore temperature sensitivity to users of prosthetic arms. Their system, called MiniTouch, requires no implants or surgery and is inexpensive to implement. These factors could make high-quality prosthetics available to a wider range of individuals, helping many more people to gain a greater degree of independence.

It is a well-documented phenomenon that amputees can experience phantom sensations in their missing limbs. For these individuals, sensations can be perceived as coming directly from their non-existing limb. Up to 80% of amputees experience some type of phantom sensation at times, whether they are feelings of touch, heat, or otherwise.

While phantom sensations are not understood perfectly, it is believed that the feelings arise from nerves that remain after an amputation. These nerves had previously been connected to tissue in the missing limb, so when they are stimulated, the brain will interpret the received signals as coming from that limb.

The researchers leveraged this phenomenon to build a surprisingly simple system for restoring the sensation of temperature to amputees. MiniTouch includes a temperature sensor in a finger of a prosthetic arm, which feeds measurements to a temperature controller near where the prosthetic limb comes into contact with the remnant limb. The controller adjusts the temperature of a thermally conductive material that is in contact with the skin. It will heat or cool to match the readings captured by the temperature sensor on the finger. For many users, this will result in the distinct sensation of temperature that appears to be coming from the prosthetic hand itself. In a series of experiments with a volunteer, this capability was confirmed, demonstrating the utility of the system.

The MiniTouch hardware can be integrated into virtually any prosthetic arm. While it is not available on the market yet, the researchers are working with partners in industry with the hope of commercializing the technology. Looking further ahead, the team hopes to restore other sensations in amputees, like the feeling of moisture.