Advanced sensory feedback is less critical for bionic feet than it is for hands. As long as the user can track a bionic foot’s position and movement, as well as receive basic information about point(s) of contact, this may be sufficient. This article explores a range of options to obtain this type of sensory feedback.
Sorting Out the Different Types of Feedback
Not all of the feedback available to bionic foot users matches the traditional definition of sensory input. Osseointegration and the Agonist-Antagonist Myoneural Interface (AMI) provide feedback that may be just as important.
However, in this article, we’re going to focus mainly on the traditional forms of feedback so that users who have not undergone osseointegration or AMI may clearly understand their sensory options.
SENSY from SensArs Neuroprosthetics
The following video provides a brief overview of SENSY technology:
As you can see, this technology involves more than just sensory feedback from a bionic foot. In an attempt to convey information on leg position, it also gathers sensory input from a bionic knee.
Ignore the knee component for now. The main points relevant to bionic feet are:
- Sensors on the sole of the bionic foot detect contact and pressure.
- This information is relayed to surgically implanted electrodes that electrically stimulate nerve bundles to trick the brain into feeling what the bionic sole is experiencing. This is known as a “neural interface”.
SENSY is not yet ready for commercial use, as SensArs is still working on a prototype. But commercial versions of this technology are not that far off.
The Massachusetts Institute of Technology (MIT) has been at the forefront of bionic leg research and development for many years. They have developed multiple technologies that have subsequently become successful commercial bionic devices (e.g. Ottobock’s Empower Ankle, and Ossur’s Rheo Knee and Rheo Knee XC).
The following video describes another MIT prototype, this one being used in conjunction with MIT’s new AMI technology. The point of interest in this video begins at the 6:00 minute mark:
Here are a couple of key observations:
- The publication date for this video is December 2019. If a research lab like MIT is only just recently experimenting with sensory feedback from bionic feet, it tells you how little emphasis has been placed on this subject to date.
- The method being used to relay the sensory feedback to the brain is through electrical stimulation of the skin, not through surgically implanted electrodes. The feedback conveyed through skin stimulation is not as detailed as the information that can be communicated through a true neural interface, but it also isn’t as expensive and doesn’t present the same risks of infection or scarring.
We don’t inject our opinion into our articles very often, but we believe that, when combined with AMI technology, this simplified approach may prove to be sufficient for most users.
Integrum’s e-Opra System
There is one exception to our view that most users will opt for simpler but less invasive forms of sensory feedback from bionic feet, and that’s where osseointegration is combined with sensory feedback into one implant solution.
This is the case with Integrum’s e-Opra Implant System:
The advantage here is obvious: since the patient is already undergoing major surgery to perform the implant, the costs/risks of adding a neural interface are much reduced.
Note, the e-Opra Implant System is not yet available commercially. Also, the use of this system for lower limbs is just now undergoing a multi-year clinical evaluation that won’t be formally completed until January 2023, so commercialization is still a few years away.
Sensory feedback is only one aspect of a deeper connection between a bionic limb and its user. To get the whole picture, see Understanding Bionic Touch.
For information on lower-limb bionic control systems in general, see Bionic Leg & Foot Control Systems.
For a comprehensive description of all current lower-limb technologies, devices, and research, see our complete guide.