How Biomechatronics Works

By: Craig Freudenrich, Ph.D.

Hugh Herr and MIT Biomechantronics

Hugh Herr's group at MIT is developing a sieve integrated circuit electrode (an integrated circuit is a tiny plastic chip with an entire electrical circuit imprinted on it). In this setup, two stumps of nerve are connected through a guidance channel (a small tube that keeps the nerve endings close to each other). In the channel, there is a sieve with each hole connected to an electrode on an integrated circuit board. As the nerve fibers grow through the holes to connect with each end, they contact the electrodes, thereby creating an interface.

Advanced Orthotics and Prosthetic Devices

Hugh Herr's lab is also making prosthetic devices that better mimic true human movements:


  • A knee prosthesis senses knee force, torque, and position and adjusts the swing and movement of the knee to the individual user. In the knee is a magnetorheologic fluid, which is oil containing a suspension of tiny iron particles (0.1-10 microns in diameter). An electromagnetic field applied across the oil can change the thickness or viscosity of the fluid because the iron particles form chains as they align with the magnetic field. Because the viscosity of the fluid can be adjusted by fine tuning the electromagnetic field, this controls and adjusts the resistance of the knee on a moment-to-moment basis, thereby giving the user a realist gait. (See for a video of this device). Commercially, this knee is a product called Rheo-KneeTM, which is made by Ossur.
  • To treat drop foot gait, an orthotic device was developed that controls and varies the stiffness of the ankle joint on a moment-to-moment basis as the user steps forward. This device gives the user a more normal gait than current orthotic devices.