Lower Limb Assistive Devices

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The loss of mobility and independence is commonly described as one of the most horrific traumas that an individual can endure. To cope with this challenge, amputees rely on prostheses, or better known as artificial limbs. With reference to the American Academy of Orthotists and Prosthetists, by the year 2020, in the United States alone, the total number of individuals who use orthotics and prosthetics is expected to reach 7.3 and 2.4 million, respectively. More alarming, data indicate increasing growth in use of assistive devices particularly among the young age segment 18 to 44 years old who expect to enjoy a healthy and active daily life.* Despite progression in technology and medicine, lower limb amputees still endure many challenges that prohibit them from regaining their original movement abilities and reducing the metabolic energy consumption during locomotion. Current developed lower limb prostheses have drastically improved over the past decade; however, the vast majority still lacks the actuation elements that correspond to the skeletal muscle in a biological limb. From a mechanical perspective, the common available devices offer patients stability and often include a mechanism to absorb and dissipate energy for a comfort gait; however, these devices are incapable of harvesting and generating net power about the joints of the limb. This deficiency may be reasonably acceptable for level ground walking; however, users are unable to ascend and descend stairs or to stand up from a sitting position. * Developing powered lower limb prostheses has been an engineering challenge for the past decades. Many prototypes have been in development in research laboratories and presently a commercial device is available from OSSUR (i.e. Power Knee). However, the success of these devices has been mainly hindered by the efficiency of their actuation system which recurrently relies on heavy and powerful electrical motors and gears. Unlike skeletal muscle, electrical motors do not possess a passive behavior, which prohibits them from harvesting gait energy, and thus, continuous electrical energy must be consumed throughout joint motion and even during steady position. While there are a large number of actuators that can be used for a wide range of commercial applications, very few have been feasible for lower limb assistive technologies. Such self-contained applications require a compact, lightweight, powerful and energy efficient type of actuator. Possessing similar mechanical behaviors, the Pneumatic Artificial Muscle (PAM) has been long-sought as a promising actuator for human assistive devices. Due to its biological muscle-like properties, PAMs have the potential to be used actively and passively, thus allowing for gait energy to be harvested, which can yield to a highly efficient actuation system.* Whereas there have been many claims that the PAM is an ideal actuator for biomedical applications, there is no quantitative study that confirms the feasibility of the PAM for lower limb assistive devices. This research has first achieved a comprehensive study of lower limbs biomechanics to characterize its actuation requirements and subsequently validated a newly designed PAM for lower limb assistive devices. Next, this research proposes the design of PAM powered transfemoral and transtibial prostheses which would permit lower limb amputees to regain their freedom of movement and reduce the metabolic energy consumption during locomotion. Unlike current technologically advanced lower limb prostheses, the proposed devices will be affordable and functional allowing the user's original movement abilities to be restored and a reduction of the metabolic energy consumption during locomotion is achieved.