The notion of having automated limbs is no longer something to wait for in the distant future. The research for this field is in the making, with incredible advancements happening rapidly. The mechanical limbs grow more and more complex with each passing innovation, developing into completely operable replacements for our own limbs, joints or organs. These advancements are growing from being simply theorized or tested on small animals, to a more wide-scale consumer: people. Within a TED Talk published in 2013 by Grégoire Courtine, a neuroscientist with a mix background in physics and medicine, called “The paralyzed rat that walked,” the thought of reanimating the spine is looked at. Throughout the video, Courtine explains to have developed a form of awakening the network of communication between the brain and the spinal cord, using chemicals that promote the growth of fiber.

Despite these achievements, it is impossible not to ask if these advancements will ever reach human form. In 2014, Hugh Herr shared the story of how he began to explore technology to create better bionics in a TED conference. After a rock climbing accident where he lost both of his legs, he began to desire for improving the technology for more comfortable and efficient bionics. “Humans can never be broken. Our technology is broken,” said Herr, claiming how we could be at this great point in revolutionary technology, but we are still unable in attaching limbs to our body. With this in mind, he wanted to design bionic legs that were improved mechanically and how the limbs are attached to the body. They must be both dynamic (move like flesh and bone) and electrical (communicate to the nervous system). 

The mechanical technology that Herr applied to the limbs is a technology that would mirror his tissue variations. Where his tissue was dense, the limb were soft, and where his tissue was soft, the limbs were dense. These mirror relationships were first designed with a mathematical model of his biological limb. With an MRI, they looked into his limb to find the complexity of density of the tissues in his limb. The mathematical model allows the bionic limb to provide stiffness where the body is soft, and softness where the body is stiff. The framework finally provides the person with the most comfortable bionic limbs ever worn. 

To improve the dynamics of the limbs and make them move like flesh and bone, the researchers at MIT observed carefully how humans walk and how their muscles work and communicate with the spinal cord. When the heel strikes the floor, the system controls stiffness to soften the shock of the movement, and when the person lifts the foot, the system provides torques and powers to lift the person from the ground, the same way the calf muscles work. This means that now the bionic limbs take the person to their desired destination much faster than with normal bionic limbs. A person can now walk up and down their stairs normally as they should be able to. 

For the purpose of electrical interface, there are electrodes attached to the residual limb of the person that read the signal networks from the nervous system and communicate them to the bionic limbs. These electrodes sense the electrical pulse of the muscles and send those to the bionic limb. So when the person thinks about moving their phantom limb, the robot tracks those movements. Also, the reflexes from the spinal cord to a biological limb are embedded in the chips of this bionic limbs. They’ve accomplished to modulate the sensitivity of the reflex with the neural signal. This means that when the person relaxes the muscles on their limb, they get little torque and power on the bionic limb, and the more he or she fires their biological limb, the more power response comes from the bionic limb. 

Herr and his team want to take this research and close the chapter in which humans can have a bionic limb that fully feels and functions like flesh and bone. They are currently performing experiments to grow transected nerves through microchannels. On one side of the channel, these nerves are attached to muscle and skin cells; in the motor channels, the nerve can sense how the person wishes to move, then be able to send this wirelessly to the bionic limb. Thus, sensors on this limb can be converted into stimulations in adjacent nerve channels and sensory channels. The goal is to provide bionic limbs that move and feel like biological limbs.