Prosthetics have a long history, the first prosthetic to be discovered was found in Egypt and it was made approximately in 950-710 B.C.E., for a noblewoman missing a big toe [1]. This gives a clear insight on how patients are physically and psychologically hit by losing a limb. It not only affects their mobility, but it creates a dent in their identity too. For many years, prosthetic technology substantially stayed the same. A prosthetic would be defined as a hard object strapped to the body of a person missing its natural counterpart, a “passive prosthetic”.
A passive prosthetic is a device that does not feature actuation means. Sometimes they are provided with a mechanism to actuate one movement, for example “hand closure”, but this needs to be actuated with the other healthy limb. On the contrary, an active prosthesis is a device that features sensing and motor control. Biosensors are used to measure the electric signals that the brain sends to the muscles, called myosignals. These sensors are placed on the patient’s remaining limb and these sensors can read the electric impulses that the brain sends to the arm. The main difference between these two types of prosthetics is that by being able to move the artificial limb, the patient can move in a more natural way, where the limb is actively providing force and support and not just being dragged around as a weight. This drastically reduces the metabolic cost of wearing a prosthetic [2], therefore empowering people to climb stairs more easily or go out and do sport.
In order to achieve this, patients are required to undergo a surgical procedure called Targeted Muscle Reinnervation (TMR), where the patient’s nerves are redirected towards the skin of the patient at the interface between amputated limb and prosthetics. Having the nerves close to the skin allows for much improved signal reading and therefore better prosthetics control for the patient [3].
In recent years, actively controllable prosthetics have been becoming more popular between amputees, with companies such as Ottobock and Touch Bionics at the forefront of providing these products. However, these systems are still very expensive for patients. There are also many cases of children that during their growth have to change prosthetics a few times, therefore making cost a pressing matter. Luckily many charitable projects are working towards reducing the cost and some healthcare and insurance providers (e.g. Open Bionics or the Open Biomedical Initiative) are able to contribute towards the cost..
Now that actively controllable prosthetics are becoming a reality, the further evolutionary step is to provide the prosthetic and the patient with sensory feedback. In a similar way to how muscular nerves are redirected, sensory nerves can be redirected to the skin, through Targeted Sensory Reinnervation (TSR). This allows researchers such as the Defence Advanced Research Projects Agency (DARPA) to integrate the prosthetics with the patient’s body to a level unseen before. Patients will be able to feel the force they apply with their prosthetic limb, understand the texture of objects they are holding and also the temperature [4].
Furthermore, the mechanical connection between the robotic limb and the body has been improved. In past, prosthetics used to be strapped to the body, causing discomfort, skin rashes and possibly blistering. Nowadays, it is possible to directly connect the prosthetic limb to the patient’s skeleton, for a more secure and natural prosthetic-body connection. Moreover, it is also possible to choose from many types of different prosthetic looks and styles, from natural looking limbs to cyborg looking ones or even inspired from nature [5].