Hugh Herr, the master of MIT’s bionic prosthetics, developed a magnetic micro-measuring method that can deliver feedback to the prosthesis in a few milliseconds

  MIT bionic leg expert Hugh Hull was forced to amputate his lower limbs due to frostbite during a rock climbing at the age of 17. But he believes that only technology can be disabled, and the human body will never be “mutilated.”

Hugh Hull’s high or low prosthesis

Hugh Hull who is making a prosthesis

  At first, he used metal materials to make prostheses for himself, but the length of the prostheses made was either too long or too short. Later, the prostheses he made became more mature and finally achieved rock climbing again.
  In this way, relying on metal and wood, he once again realized his rock climbing dream.
  Even if he loses his legs, his studies have not fallen at all. He once joked that he often got a D or F in the exam before the amputation, and his mind seemed to be smarter after the amputation. Later, he graduated with a bachelor’s degree in physics from Millersville University in Pennsylvania, and a master’s degree in mechanical engineering from MIT, and then a doctorate in biophysics from Harvard University.
  He is currently a professor in the MIT Media Lab and the director of the biomechanical integration research group of the school. As of 2014, the video of his speech at TED has more than 12 million views.

Hugh Hull

Hugh Hull

  After becoming a scientist, Hugh Hull was no longer satisfied with making simple prostheses, but determined to use technology to make prostheses more comfortable for the disabled.
  The first beneficiary is of course himself. Compared with the loneliness of lying in bed after being amputated, now he has not only saved himself, but also helped more patients like him.
  He and his team spent two hundred days customizing a prosthesis for a dancer, Adriana Aslet-Davis, who lost her left leg in the 2013 Boston Marathon terrorist attack, and allowed the other party to return to the stage. At the end of Hugh Hull’s TED talk, Adriana put on a bionic leg and danced, and the audience stood up and applauded.

Hugh Hull uses the bionic leg before and after comparison

Adriana puts on bionic legs to dance

Hugh Hull

  In addition, he also allowed an American soldier who lost his legs on the battlefield in Afghanistan to run again with bionic legs.
  A few months ago, Hugh Hull’s assistant stated that the 57-year-old Hugh Hull was going to be a father again. Now, only a few months later, he has published more than 100 papers, and once again announced his latest research results.
  For amputees, the biggest challenge is to control the prosthesis so that it can move like a normal limb. Most prostheses use electromyography for corresponding control, which is a method of recording muscle electrical activity, but this method can only provide limited control capabilities.
  This time, Hugh Hull’s team developed a new method called magnetic micrometering, which said it could provide more precise control of the movement of the prosthesis.
  Specifically, the principle of this magnetic micro-measurement method is to implant small magnetic beads into the muscle tissue of the amputation residual limb, so that the length of the muscle can be accurately measured when the muscle is contracted, and the relevant feedback can be transmitted to the bionic prosthesis within a few milliseconds. . Related papers were published on Science Robotics under the title of “Magnetic Microscopy”.

Related papers

  Hugh Hull hopes that magnetic microscopy can replace traditional electromyography and become the main control method that connects the peripheral nervous system to the bionic limbs. The reason for this analysis is that he believes that magnetic microscopy has millimeter-level high-signal control quality, and the implementation cost is very low, which is of great commercial value.
  Another advantage of the magnetic microscopy method is that once the magnetic beads are implanted in the muscle, they can permanently and stably work in the muscle without replacement.
  Professor Li Qingguo and Hugh Hull from the School of Mechanical and Materials Engineering, Queen’s University, Kingston, Ontario, Canada have known each other for many years. The two often meet at field conferences. He said that the research aims to solve the problem of sensing, exoskeleton and prosthetic control. The focus is on recognizing the user’s movement intention, so a “brain” is also needed to transmit signals, but traditional exoskeleton and prosthetic limbs do not have a high-level “brain” for command and control. They are also separated from the human body, so through new sensing Combining methods with people is the end point of this research that can be considered for development in the future.

  The principle that neurons control muscles is that the brain gives signals to the muscles, and then the muscles will contract and produce general movements. When the legs of a healthy person want to exercise, as long as the brain is conscious, the muscles will start to contract, and the legs will follow the movement.
  Hugh Hull hopes that this signal can be transmitted to the muscles through the brain, but if an externally attached EMG sensor is used to measure it, it will be difficult to measure nerve conduction. Unlike in the past, this time the team wanted to directly measure the movement characteristics of the muscles. By implanting small magnetic balls, it can directly measure the movement characteristics of the muscles, so that there is no need to use external EMG sensors to measure.

Experimented on turkey shanks

  The current prostheses use electrodes to electrically measure human muscles. There are two methods. The first is to connect the electrodes to the surface of the skin, and the second is to surgically implant the muscles. The second method is not only costly, but also has to be implanted in the human body, but it can provide more accurate measurements.
  The common disadvantage of these two methods is that EMG can only provide muscle activity information, but not muscle length or speed data.
  For example, when a prosthetic user performs control based on EMG, he can only see an intermediate signal, that is, he can only see the instructions sent by the brain to the muscles, but cannot see the actual execution of the muscles.
  In response to this, he decided to implant a pair of magnetic balls in the muscles. By measuring the relative movement of the magnetic balls, the degree and speed of muscle contraction can be calculated.

  The idea started with an algorithm he developed two years ago, which can greatly reduce the time required for the sensor to determine the position of the small magnetic ball in the body. In this research, the algorithm also helped him overcome the main obstacles in controlling the prosthesis by magnetic microscopy, allowing the measurement results to be received in real time.
  In the experiment, Hugh Hull also implanted magnetic balls into the turkey calf muscles to test the tracking ability of the algorithm. In order to avoid movement after the magnetic ball is implanted in the muscle tissue, they set the diameter of the magnetic ball to 3 mm, and the implantation is at least 3 cm apart.
  When moving the ankle joint of a turkey, they can determine the position of the magnetic ball with an accuracy of about the width of a hair (about 37 microns), and the measurement of related data can be completed within 3 milliseconds.

Implant the magnetic ball into the turkey calf muscle

  These measurement data can be input into the host computer to establish a corresponding model. According to the contraction of the remaining muscles, the user can move the prosthesis in the expected manner. Magnetic microscopy can also directly measure muscle length and muscle speed. Through mathematical modeling of the entire limb, the target position and speed of the prosthetic joint to be controlled can be calculated.
  According to Li Qingguo’s analysis, it is difficult for electric prostheses to recognize user intentions, and they generally use external signals to control them, such as position sensors and electromyographic signals. However, these signals are external signals, and these data can be measured after movement occurs, and a large amount of EMG processing is still required after the measurement. When the motion state changes, the EMG signal will also change. It can be said that there is a coupling between the two, so the reliability of control is very low.
  The Hugh Hull team has always wanted to connect the nerve to the sensor. The advantage of this work is that it uses a surface sensor and installs a magnetic ball to measure muscle length and movement changes. This method not only does not cause the patient Trauma, and only need to place some magnetic balls to measure the corresponding data on the muscles, you can measure the patient’s muscle movement intention, and coupled with machine learning algorithms and biological body modeling, it is expected to achieve better control Strategy.

Histological study of a single magnetic ball
Hugh Hull’s Chinese students returned to China as scheduled and have joined Beihang University

  In the future, Hugh Hull hopes to carry out a study on patients with amputations below the knee. The research content is to put sensors that control prostheses on clothes, or on the surface of the skin, or even on the outer surface of the prosthesis.
  Magnetic microscopy can also improve muscle control through a technique called functional electrical stimulation, which is currently used to help patients with spinal cord injuries recover their mobility. Another potential use of magnetic control is to guide the robot’s exoskeleton so that it can be connected to the ankle or other joints to help stroke patients or people with muscle weakness to perform exercises.
  Hugh Hull said: “In essence, magnetic balls and exoskeleton are like artificial muscles that can amplify the biological muscle output of stroke-damaged limbs.” “It’s like the power steering device used in a car.”

Magnetic field sensor array

Yang Xing Gang

  However, there are still problems to be overcome in the future. Li Qingguo said that since it is difficult to control the coordination between human movement and mechanical movement, it is not easy to fix the magnetic ball on the muscles because the muscles are moving at any time. Because of this, the team first used turkey as the experimental object this time, and more research is needed to apply it to humans.
  Talking about the team’s hope that magnetic microscopy can replace electromyography in the future and become the main way to connect the peripheral nervous system with the bionic limbs. In this regard, Li Qingguo commented that the original intention of this idea was to allow exoskeletons and prostheses to achieve a smooth connection with the human body. The connection between humans and machines is the problem that all human-computer interaction interface research wants to solve. Otherwise, the machine is still a machine, and the human is still a human. There is no common coordination between the two.
  The method of electromyography is based on a large amount of data analysis. In the measurement of advanced information, the method of electromyography has certain advantages, and the electromyography does not require any invasion of the human body. The magnetic microscopy requires surgery, and the position of the magnetic ball may change in the human body. After a long period of time, it may still need to be performed again. This is also one of Hugh Hull’s challenges. But overall, the electromyography method can coexist with the magnetic microscopy method, and it is not necessary to replace each other.
  Li Qingguo said that the coordination between human movement and mechanical movement is difficult to control, so it is not easy to fix the magnet ball on the muscle, because the muscle is moving at any time, which will cause the position of the magnet ball to drift. Because of this, the Hugh Hull team started with turkeys this time, thinking that more research on the human body is still needed. It can be said that handling the connection between the magnet ball and human muscles is the next challenge the team faces.
  In general, the research of Hugh Hull’s team is at the forefront of the world. Yang Xingbang, a doctoral graduate of Beihang, who has been interviewed before, has just finished postdoctoral research from his team and has returned to China to officially join Beihang.
  During the postdoctoral period at MIT, Yang Xingbang and Hugh Hull co-published a paper entitled “Cable-driven portable ankle exoskeleton that can achieve plantar flexion and dorsiflexion two-way motion assistance”.