**7. Future challenges and directions**

Scientists working on upper limb prosthesis define their goal in this field as to develop a 'simultaneous, independent, and proportional control of multiple degrees of freedom with acceptable performance and near "normal" control complexity and response time' [25]. The major challenges faced in prosthetics are: electromechanical implementation, use of EMG control signals and the interface between robotic and clinical communities [26]. Designing a robotic mechanism which is fully capable of integrating with human neuromuscular system is a tough proposition. The requirements can only be fulfilled if the apparatus is of light and flexible material with small but powerful actuators, size effective electronic components, sensors which can easily adapt with the skin and a long lasting battery life. Only then the machine will qualify to be used in everyday practical life [26].

The human hand has 20 degrees of freedom, and the body works in a unique variety of ways to tackle various hindrances placed in front of it. It is therefore, a great challenge to extract all of these motions from the body and utilize them in a resourceful way. Nowadays, two degree of freedom mechanisms are most common. To achieve further DOFs, sensors will be required to be placed at more sophisticated locations, which is a tough task.

The most important challenge of robotic prosthesis in rehabilitation is the feasibility of the mechanism. The apparatus should be comfortable, silent and aesthetically viable for the subject [26]. Our target should be the effective use of the robotic artificial limb on the physically disabled, not to waste our efforts in fruitless objects. Hence, for the reliability of the mechanism's implementation on the amputated population, clinician's approval should be made a part of the procedure.

Due to its practicality and noninvasiveness, SEMG proves to play a significant role in medical applications and rehabilitation prosthesis. However, the human machine interface will decide if the robotic mechanism will be used in everyday life application or not. It is very important to improve the Quality of Life (QOL) of elder and disabled population. It is believed that in the near future, "we will be able to replace entire limbs with prosthetics that can replicate one's own biological functions precisely, casting natural outward appearance and requiring minimum upkeep" [26].

Robotic researchers and biomedical engineers have been trying to combine their techniques to make the perfect biomechatronic mechanism. However, in order to ensure that challenges are met and to create a more smart and intelligent machine, communication between clinicians, users and engineers should be established on a greater scale.
