Proto 1 (December 2006)
Prototype 1 (Proto 1) has eight degrees of freedom—a level of control far beyond the current state of the art for prosthetic limbs. As a rapid-development prototype, Proto 1 utilized many commercial off-the-shelf components with the purpose of supporting neural integration research and serving as a test bed for evaluation of haptic feedback and indirect sensory perception approaches. Additionally, Proto 1 was used to demonstrate advanced prosthetic function with classification algorithms for noninvasive and low-invasive control devices. Proto 1 was fitted for the beginning of Revolutionizing Prosthetics clinical evaluations using surface electromyographic control with targeted muscle reinnervation (TMR) patients at the Rehabilitation Institute of Chicago in January 2007.
Proto 2 (August 2007)
During development of Proto 1, the Revolutionizing Prosthetics team engaged in concurrent research, analysis of alternatives, design, and development efforts for design of a limb including: biomimetic operation including all degrees of freedom, speed, dexterity, and force; electromechanical actuation mechanisms; communications, signal analysis, and control strategies; and comfort and appearance (socket and cosmesis). The mechatronic culmination of these efforts was completed in August 2007. Two versions of Proto 2 were designed—one with an intrinsic hand using off-the-shelf brushless direct current motors, and one with an extrinsic hand using a cobotic device in the forearm with a single motor to control the wrist and hand. There are about 25 microprocessors (computer chips) and 80 tactile sensors built into the fingers, fingertips, hand, wrist, and elbow. The Proto 2 limbs incorporated significant advances in many technologies, leading to the ultimate design of the MPL.
Modular Prosthetic Limb (December 2009–present)
The first version of the Modular Prosthetic Limb (MPL v1.0) was completed in December 2009. It featured anthropomorphic form factor and appearance, human-like strength and dexterity, high-resolution tactile and position sensing, and a cortical neural interface for intuitive and natural closed-loop control. Made of lightweight carbon fiber and high-strength alloys, the arm has 25 degrees of freedom, or joint motions (the human arm has about 30). This limb is modular and configurable to the level of a patient's injury. MPL v2.0 was completed in December 2010, and our current efforts focus on refinement of the MPL system technologies by incremental design improvements in order to improve reliability, increase simplicity, leverage commonality among subsystems, maximize performance, and evolve software and controls algorithms. MPL systems are being distributed to clinical partners for use in neural-based research and development of cortical encoding and decoding strategies.
Neural Research (January 2006–present)
Since the beginning of the Revolutionizing Prosthetics program, researchers have advanced the state of the science in neuroprosthetic control.
We are currently focused on technology demonstrations of cortical control of the MPL by spinal cord injury patients. (Note: The National Institutes of Health [NIH] is also supporting other brain–computer interface (BCI) investigators in demonstrating that their approaches might be effective in controlling the MPL.) The neuroscientific goals are to evaluate the efficacy of cortical microstimulation for tactile and proprioceptive feedback in humans; to develop active and wireless implantable microelectrodes for stimulating, recording, and demonstrating the viability of chronic implantation; and to evaluate the feasibility of bilateral closed-loop cortical control. Experiments for the first-ever neuroprosthetic system controlled with signals from the posterior parietal cortex and the first-ever demonstration of closed-loop cortical control of a dexterous neuroprosthesis using recordings from the motor cortex and parietal reach region and stimulation in the primary somatosensory cortex are planned. Additionally, we will identify commercial transition partners for neuroprosthetic technologies and collect data enabling FDA approval of the neuroprosthetic system and components.
The research breakthroughs resulting from these activities will provide prosthetic limb control options not only to amputees but also to patients with an inability to control their native limbs as a result of stroke or degenerative conditions such as amyotrophic lateral sclerosis (ALS).
Virtual Integration Environment (January 2006–present)
Underlying the research, design, and development during all phases of the Revolutionizing Prosthetics program is the Virtual Integration Environment (VIE). The VIE is modular and configurable to support various limb models and algorithms in order to facilitate highly dexterous control of an upper-limb prosthesis. It serves as a complete limb system simulation environment to support neural integration. The VIE is used to visualize and monitor performance of various design approaches, pilot neural signal analysis algorithms, and simulate emerging mechatronic elements. It provides a framework for synchronizing research and efforts across many geographically distributed contributors in order to turn neural research into engineering reality. From the clinical and patient perspective, the VIE is used to train end users to control real or virtual neuroprosthetic devices, and configure and customize clinical and take-home devices.
VIE development is continuing with enhancements for a simplified, platform-independent communication interface to the MPL and an improved three-dimensional MPL simulation environment with scriptable scenarios.