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Revolutionizing Prosthetics—Phase 3 Revolutionizing Prosthetics—Phase 3 Alan D. Ravitz, Michael P. McLoughlin, James D. Beaty, Francesco V. Tenore, Matthew S. Johannes, Scott A. Swetz, John B. Helder, Kapil D. Katyal, Matthew P. Para, Kenneth M. Fischer, Timothy C. Gion, and Brock A. Wester n early 2006, APL was awarded a contract to start the first phase of the Revolutionizing Prosthetics 2009 program, a multiyear, multimillion-dollar effort to develop an advanced upper-extremity prosthetic limb, the Modular Prosthetic Limb (MPL). This program’s goal is to develop an advanced limb that would allow a prosthetic wearer to button a shirt, tune a radio, and feel the warmth of a loved one’s hand; such a limb might even provide the warfighter with the opportunity to return to active duty. Currently in the third phase of Revolutionizing Prosthetics, APL is leading the Defense Advanced Research Projects Agency’s effort to provide upper- extremity functionality to people who have no ability to control their native arms, such as amputees and those with high spinal cord injury or neurodegenerative diseases such as amyotrophic lateral sclerosis. Phase 3 of the program involves significant focus on clinical activities including maturing the MPL’s robustness, submitting regulatory filings, designing and executing preclinical and clinical activities, and advancing cortical implant technology. Initial clinical activities during this third year of Phase 3 have involved a sub- ject with tetraplegia using a brain computer interface to control the MPL. Further trials with this subject continue as the program team prepares for four additional subjects during Phase 3. INTRODUCTION Throughout history, the battlefield loss of limbs and/ injuries resulting from recent military operations, in or motor function has been the major driving force for addition to individuals in the general public with simi- technological progress in the field of prosthetics. The lar injuries and conditions, emphasizes the urgent need existence of individuals with amputations or spinal cord to accelerate the progress toward restoring lost function. 366 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 31, NUMBER 4 (2013) The Defense Advanced Research Projects Agency estab- limb in human subjects. Having a closed loop in lished and sponsored the Revolutionizing Prosthetics this context means enabling motion control by (RP) program to restore soldiers with upper-extremity accessing neural signals in the motor cortex while injuries to preinjury levels of function and provide them simultaneously providing tactile and proprioceptive the ability to return to activities of their choice either feedback through electrical stimulation of the within the Armed Services or civilian society. The RP somatosensory cortex. program envisions similar benefits to the general public. The goal of prosthetics is defined as the design, man- 2. Development of wireless electrode arrays: Develop ufacture, and fitting of artificial replacements for lost or a wireless architecture to support implantation of dysfunctional limbs. The human upper extremity is a recording and stimulating electrode arrays suitable highly evolved structure that defines the unique human for long-term use in humans. capability by enabling functional interaction with one’s These two objectives involve a complex set of techni- environment. Because of the sheer complexity of limbs, cal, clinical, programmatic, and regulatory challenges. in terms of tissue composition and mechanical capa- To address these challenges and to accomplish these bilities, the field of prosthetics encompasses one of the objectives, APL formed a world-class team. The Uni- most diverse arrays of disciplines of any field in the medi- versity of Pittsburgh (Pitt) and the California Institute cal sciences. Advances in prosthetics rely not only on of Technology (Caltech) lead efforts to implant Utah traditional fields such as material sciences, power, and Electrode Arrays (UEAs) in human subjects to demon- surgery but also increasingly on emerging areas such as strate the ability to perform closed-loop cortical control. neuroscience, tissue engineering, robotics, sensors, and The University of Utah, with Blackrock Microsystems, nanotechnology. The driving goal of the RP program is is leading the development of wired and wireless elec- to utilize and drive advances in these disparate areas for trode arrays. The University of Chicago, teamed with the benefit of the disabled soldier. Northwestern University, is contributing research and APL has a long history of addressing critical chal- development related to neural stimulation and support lenges for our nation. An experienced systems integrator, of the closed-loop cortical control. Hunter Defense APL is well suited to bridge the gaps between academia Technologies is responsible for manufacturing enhance- and industry and help ensure that basic scientific discov- ments to the MPL to meet Phase 3 objectives. APL is eries are rapidly transitioned into the product develop- responsible for overall program management, integra- ment cycle. As in early phases of the RP program, APL tion of the technical and clinical activities, and overall continues to provide the systems integration and pro- systems integration. gram management leadership to define the engineering The objectives of Phase 3 necessitate regulatory approach and focus the efforts of the development activ- approval to ensure the safety and efficacy associated ities and team member interactions. In this role, APL with the planned technology. Accordingly, identifying is responsible for translating the Defense Advanced a regulatory pathway from today’s state of the practice Research Projects Agency’s RP vision into a realizable to the state of the art envisioned by this program is an design and for engaging the team members to address extremely important element of the Phase 3 program the critical technical barriers of chronic neural integra- plan. The extremely advanced technology associated tion and direct neural sensory feedback. with RP3 places achievement of program objectives at risk because of the regulatory challenges the program faces under traditional regulatory processes. Accord- PROGRAM OBJECTIVES ingly, the U.S. Food and Drug Administration (FDA) established a new program called the Innovation Path- The RP Phase 3 (RP3 or Phase 3) program builds way and selected RP3 as the pilot project. The Inno- on the successes of the RP2009 program.1 Specifically, vation Pathway, established for high-risk, advanced RP3’s goal is to use the Modular Prosthetic Limb (MPL) technology initiatives such as RP3, is intended to enable system2 in conjunction with cortical implants for neural “in-stride” dialog between the technical stakeholders recording and stimulation to assist patients with high (the RP3 team in this case) and the FDA regarding spinal cord injury, or tetraplegics, in performing activi- safety and efficacy issues associated with advanced tech- ties of daily living. In addition, RP3 is evaluating wireless nology. The Innovation Pathway experience for RP3 has cortical implants and advanced neural signal-processing proven successful in terms of helping to shape the pro- algorithms with an eye toward long-term use of these gram’s execution in a manner that addressed identified technologies in human subjects. challenges earlier than would otherwise have been pos- The primary objectives for Phase 3 are as follows: sible without the Innovation Pathway. 1. Closed-loop cortical control of the MPL: The major program and technical activities associ- Demonstrate closed-loop cortical control of a ated with RP3 are detailed in the following sections of dexterous, multiple-degree-of-freedom prosthetic this article. JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 31, NUMBER 4 (2013) 367 A. D. RAVITZ ET AL. Primary motor cortex CLINICAL ACTIVITIES—TOWARD RESTORING Somatosensory cortex Frontal lobe MOTOR CONTROL AND SENSORY FEEDBACK Parietal lobe Decades of neuroscience research has provided the foundation for today’s understanding of cortical pro- Occipital lobe cessing of information. Researchers have demonstrated the ability to decode signals from certain regions of the brain (Fig. 1), although much is still unknown. These decoded signals enable brain–computer interfaces, the likes of which include those that can control simple cursor movement on a computer screen to those that can Cerebellum control neuroprosthetic devices through thoughts alone. Temporal lobe RP3’s program goals include developing an end-to- end system to capitalize on today’s neuroscience under- Spinal cord standing and enable tetraplegics to perform functions Medulla oblongata they would normally perform with functional natural limbs. Developing such a system requires several system components and subsystems, as shown in Fig. 2. To achieve motor control of a neuroprosthetic, Figure 1. Regions of the brain. The brain exerts centralized electrode arrays are implanted in the brain’s cortex control over the body by receiving and processing signals from where they can access signals that would normally throughout the body. control a native limb. These motion intent signals are passed from the implanted arrays to a computer that their brains still produce these intent signals. The decodes the intent (e.g., reach to this point in 3-D MPL receives the decoded signals and translates these space, grasp an object such as a doorknob, and other into commands to the motors built into the MPL. The similar actions people naturally perform). Despite
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