The increasing number of amputees worldwide makes it important to design and develop prostheses for these people to help them during their ADLs. Although the current passive prosthesis provides a range of torques and motions for ADLs during gait cycles, the desired provided torque and range of motions in other tasks, such as stair climbing or fast walking, is still challenging. We have designed and developed a novel robotic transfemoral knee prosthesis in the human-centered design laboratory that uses both passive mechanisms and active actuators to maximize mechanical efficiency and minimize the metabolic cost of the users.