Revolutionizing Prosthetics
Research
The Revolutionizing Prosthetics program started in 2006 with an aim to provide functional restoration for individuals with amputation and other conditions that limit upper-limb control. Under this multifaceted research and development effort, the greater team has focused on a number of critically enabling capabilities, which include the Modular Prosthetic Limb (MPL), the muscle/neural signal acquisition and processing pipeline, and the Virtual Integration Environment (VIE).
Capable of effectuating almost all of the movements as a human arm and hand and with more than 100 sensors in the hand and upper arm, the Modular Prosthetic Limb (MPL) is the world’s most sophisticated upper-extremity prosthesis. There are currently ten MPLs being used for neurorehabilitation research across the United States.
The MPL features:
- Anthropomorphic (lifelike) form factor and appearance
- Human-like strength and dexterity
- High-resolution tactile and position sensing
- Neural interface for intuitive and natural closed-loop control
Sensorization
The arm and hand pictured below contain more than 100 sensors. Many candidate technologies were prototyped and evaluated by using a custom test bed and standardized processes. In addition to sensor-specific performance criteria, other design constraints included integration, reliability, and manufacturability. At the individual joints, sensors measure angle, velocity, and torque. Additional sensors at the fingertip measure force, vibration, fine point contact, and temperature/heat flux.
Key, Sensor, and Number
- *Additional sensors include: incremental rotor position (x17); drive voltage (x17); and upperarm drive current (x7)
Body Attachment
Development of a comfortable yet robust body attachment to support the range of movement and load capacity of the MPL for varying amputation levels was accomplished through investigation of multiple volume accommodating and dynamic shape-changing socket methods. These included pneumatic or air-filled bladders, hydraulic or fluid-filled bladders, vacuum-attachment methods, electro-active polymers, and shape-changing material structures. Improved surface electromyographic electrodes enhance patient comfort, and static and dynamic load distribution can be accommodated with liners, counterbalances, dynamically adapting elements, and active vacuums. Additional socket design challenges were driven by the need to provide space for controllers, for the tactor or other afferent devices, and for peripheral control (Implantable Myoelectric Sensor [IMES] and Utah Slanted Electrode Array [USEA]) transduction elements.
Recommended Reading
- Revolutionizing Prosthetics 2009 Modular Prosthetic Limb–Body Interface: Overview of the Prosthetic Socket Development (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 240–249, 2011)
Cosmesis
The basic requirements for the Revolutionizing Prosthetics cosmesis are that it appear natural, be durable, be able to be manufactured, have minimal weight, meet mechanical requirements (such as minimizing energy consumption due to drag of the cosmesis to extend the operating time of the battery), support sensor function, and be repairable. Acting as an initial barrier against the environment and allowing sensors to measure force, vibration, and temperature through the cosmesis are additional requirements. Two variations of the MPL cosmesis were developed: the work glove, a functional covering that is less expensive and more durable, and the standard glove, a fully realistic cosmetic cover that includes artistic detailing to resemble a natural limb and spectrally insensitive color formulations (metamerism).
Recommended Reading
- An Overview of the Developmental Process for the Modular Prosthetic Limb (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 207–216, 2011)
- The Cosmesis: A Social and Functional Interface (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 250–255, 2011)
Because of the limited quantities of the Modular Prosthetic Limb (MPL), APL has developed a virtual-reality MPL that runs in the Virtual Integration Environment (VIE). The VIE was developed to make the transition from a virtual training environment to the physical world with the actual MPL as seamless as possible, thus facilitating patient training for optimal control of the prosthetic limb. Importantly, the VIE is a platform-independent communication interface to the MPL. It offers an improved three-dimensional MPL simulation environment.
The VIE was created as a development platform for rapid prototyping, evaluation, and deployment of neural signal processing algorithms.
- Based on MATLAB xPC Target; operates in (hard) real time
- Accepts inputs from Cerebus, Plexon, Vikon, etc.
- Defines standard input/output interfaces for neural signal analysis algorithms (neural signals in/limb commands out)
- Can simulate an electromechanical system with or without hardware
- Provides three-dimensional visualization and a configurable interactive world via Unity/PhysX
Recommended Reading
- Development of Virtual Integration Environment Sensing Capabilities for the Modular Prosthetic Limb (Society for Neuroscience, Washington, DC, 2014)
- Use of a Virtual Integrated Environment in Prosthetic Limb Development and Phantom Limb Pain (Studies in Health Technology and Informatics, Volume 181, pp. 305–309, 2012)
- A Real-Time Virtual Integration Environment for Neuroprosthetics and Rehabilitation (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 198–206, 2011)
- Using a Virtual Integration Environment in Treating Phantom Limb Pain (Studies in Health Technology and Informatics, Volume 163, pp. 730–736, 2011)
- A Real-Time Virtual Integration Environment for the Design and Development of Neural Prosthetic Systems (Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Vancouver, BC, Canada, 20–25 August 2008, pp. 615–619)
Revolutionizing Prosthetics is developing a robust hybrid neural interface approach that capitalizes on the strengths of individual signal sources and provides a flexible solution set suitable for a breadth of injuries. Sensory feedback is crucial for effective performance of daily activities, so the fully sensorized limb system supports biofidelic feedback options consistent with the hybrid strategy for closed-loop control.
Several types of recording devices are used to record various biological signals from muscles, peripheral nerves, and the cortex for the purpose of motor decoding. Implanted intramuscular electrodes and surface electromyogram electrodes are used to record muscle activity; implantable peripheral nerve electrode intercept signals, propagating along peripheral nerves; and implantable cortical electrode capture spike and local field potentials, near their origins in the primary motor, premotor, and posterior parietal cortices. Collecting all of these signal modalities provides complementary information as well as a certain level of redundancy that maintains long-term high levels of fidelity and provides modularity. This is especially important because we are addressing tetraplegic patients and the full range of upper-extremity amputees—to include shoulder, transhumeral, transradial, and wrist disarticulations in addition to normal interpatient variations. We have a robust neural interface strategy with a strong cortical focus, and support for noninvasive or minimally invasive integration methods as well.
The Revolutionizing Prosthetics program continues to develop neural decoding algorithms that translate electrical signals received from the body into commands for the limb systems or other devices. These algorithms are all supervisory, requiring a representative data set of the desired commands to “train” the algorithms. The signals used for decoding (e.g., electromyographic action potentials, etc.) have a significant impact on the training data and therefore influence the choice for the best type of algorithm. In addition, the complexity of the desired movement can drive the complexity and size of the training data and thus the complexity of the algorithm. Finally, the algorithms are designed with computational and memory constraints in mind, making linear algorithms the most frequently used.
Recommended Reading
- Control System Architecture for the Modular Prosthetic Limb (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 217–222, 2011)
- Revolutionizing Prosthetics: Neuroscience Framework (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 223–229, 2011)
- Revolutionizing Prosthetics: Devices for Neural Integration (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 230–239, 2011)
Johns Hopkins Medicine and APL are collaborating on the use of the Modular Prosthetic Limb (MPL) and targeted muscle reinnervation (TMR) surgery.
TMR is a new surgical procedure that reassigns nerves that once controlled the arm and the hand. By reassigning existing nerves, doctors can make it possible for people who have had upper-arm amputations to control their prosthetic devices by merely thinking about the action they want to perform. Once experimental, this innovative procedure is now available at The Johns Hopkins Hospital. People who undergo the targeted reinnvervation surgery will be fitted with and trained to use a myoelectric prosthetic arm.
Watch the 60 Minutes report, “Breakthrough: Robotic limbs moved by the mind”
APL is collaborating with the Department of Surgery at Johns Hopkins Medicine on clinical trials using the MPL for patients who have received TMR surgery.
Who Might Benefit from TMR Surgery?
Those interested in the procedure to better control their prosthetic arm must undergo a medical review to determine their eligibility. In general, patients must meet the following criteria:
- Amputation above the elbow or at the shoulder within the last 10 years
- Stable soft tissues
- Willingness to participate in rehabilitation
Those who were born without part or all of their arm and those who have nerve damage, degeneration, or paralysis are not candidates for this procedure.
TMR is a specialized surgical procedure developed by the expert staff at Johns Hopkins Medicine, including Albert Chi, M.D., the Medical Director for the Targeted Muscle Reinnervation Program. Dr. Chi also serves Assistant Professor of Surgery at Johns Hopkins Medicine. He is a trauma surgeon whose practice includes critical care, trauma, and acute care surgery. He has a background in biomedical engineering, and his clinical research is focused on improving the lives of individuals with traumatic injuries, with an emphasis on motor control. Dr. Chi is also commissioned as a lieutenant commander in the U.S. Navy Reserve and is dedicated to serving our country and helping care for the wounded warriors returning home and those injured in the field.
For more information regarding TMR surgery or to schedule an appointment, please call Johns Hopkins Medicine at 443-287-0618 or visit the Johns Hopkins Medicine Department of Surgery website.