An Implantable Bionic Network of Injectable Neural Prosthetic Devices: The Future Platform for Functional Electrical Stimulation and Sensing to Restore Movement and Sensation

55.1 Introduction Functional electrical stimulation (FES) is a rehabilitation technique for the restoration of lost neuro logical function, resulting from conditions such as stroke, spinal cord injury, cerebral palsy, head inju ries, and multiple sclerosis. FES utilizes low-level electrical current applied in programmed patterns to dierent nerves or reex centers in the central nervous system to produce functional movements. e stimulation may be triggered by a single switch (open-loop) or from sensor(s) or neuronal activity (closed-loop). While FES has been used successfully to pace the heart 1 and to restore hearing 2 in the past, it has not been widely adopted as a means of reanimating paralyzed limbs that result from stroke and spi nal cord injury (SCI). It is estimated by the U.S. National Institutes of Health (NIH) that there are more than 600,000 people who experience a stroke each year in the United States, with an associated comprehensive cost of $43 billion per year. 3 Of the more than 4 million stroke survivors alive today, many experience permanent impairments of their ability to move, think, understand and use language, or speak—losses that compromise their independence and quality of life. Furthermore, stroke risk J. Schulman Alfred Mann Foundation for Scientific Research P. Mobley Alfred Mann Foundation for Scientific Research J. Wolfe Alfred Mann Foundation for Scientific Research Ross Davis Florida Institute of Technology I. Arcos Alfred Mann Foundation for Scientific Research experiencing a stroke is increasing. ere are also estimated to be 250,000 Americans living with spinal cord injuries with 10,000–12,000 new spinal cord injuries reported every year in the United States. e cost of managing the care of SCI patients approaches $4 billion each year. 4 e potential of FES to restore function in these areas has been largely unfullled mostly due to the limitations of the FES devices currently available. FES could also be used in limb loss applications to reduce phantom pain and to restore the functional movement of prosthetic limbs. In 2000/2001, about 130,000 lower-limb amputations were performed each year in the United States. 5,6 An optimal FES system should have the following fundamental characteristics. It should (1) provide both stimulating and sensing capabilities, (2) be fully implantable, (3) be minimally invasive, (4) have real-time communication capability, (5) allow a practically unlimited number of stimulation and sensing channels, and (6) function without external equipment or interconnected leads between components. is chapter describes a network of wireless implantable microstimulators/microsensors, also known as battery-powered BION •* (BIOnic Neuron) devices for functional electrical stimulation and sensing (FES-BPB system). is new platform was designed to overcome the limitations of the current FES tech nology by providing 1. Microdevices that can be programmed to be either stimulators or sensors for use in closed-loop applications 2. Minimally invasive implantation procedures to reduce labor-intensive surgery and associated patient risks and to provide rapid recovery 3. Wireless bidirectional communications and telemetry to all stimulators and sensors, which eliminates the use of both transcutaneous leads (which are susceptible to infection), and surface applied coils and stimulators 4. Real-time communication between the stimulators, sensors, and control unit, to maintain continuous closed-loop control 5. Flexibility and functional expandability since there are no leads and each implant has a full complement of programmable stimulators and sensors 6. A large number of channels, which allows the same system to be used for a variety of applications without interference in the same patient 7. Self-powered operation using rechargeable batteries to power the implantable devices. External equipment (e.g., power antennas) are only needed during battery recharging 8. Wireless sensors capable of measuring biopotentials, angle, position, pressure, temperature, and permanent magnet elds 55.2 Evolution of the Implantable BION Devices In 1988, J. Loeb proposed and W.J. Heetderks showed mathematically that the concept of a wireless net work of injectable microstimulators powered by an external antenna/coil was possible. 7 It was thought that these microstimulators would eliminate many of the problems associated with the use of percutane ous electrodes, since they do not incorporate leads. J.H. Schulman, G.E. Loeb, and P.R. Troyk, under sup port contracts from the U.S. NIH (contract N01-NS-9-2327), the Alfred Mann Foundation (AMF, Santa Clarita, CA), and the Canadian Network for Neural Regeneration and Functional Recovery, developed an injectable, glass-enclosed microstimulator (Figure 55.1) that is powered and controlled by an external alternating magnetic eld generated by a coil connected to a control unit. is rst 255-channel stimulat ing system, later called the radio-frequency (RF) BION device, allowed instantaneous control of stimula tion pulse amplitude, frequency, pulse width, pulse position timing, and pulse charge-recovery current. 8 AMF continued to develop and improve the wireless RF BION device. As a result of these eorts, a second-generation RF BION device, which incorporates a ceramic case, an output capacitor, and Zener * BION is a registered trademark of the Advanced Bionics Corporation, a Boston Scientic company. diodes to protect the device against electrostatic discharges, was developed (Figure 55.1). 9 ese RF BION devices are currently being used or have been used in several clinical studies being conducted by AMF and its aliated organizations, the Alfred Mann Institute (University of Southern California, Los Angeles, CA) and Advanced Bionics Corporation (Santa Clarita, CA). As of September 2004, 33 patients have been implanted with RF BION devices for the treatment of urinary incontinence, obstructive sleep apnea, pain associated with shoulder subluxation, knee osteoarthritis, forearm contracture, and foot drop applications. 10–13 While the wireless RF BION device eliminates the need for the leads associated with the percutane ous electrodes, it requires the patient to wear an external coil during use, to transmit power and data to the implanted device. To both improve the patient acceptance of this technology and increase the reliability of the system, it was necessary to eliminate the need to constantly use an external coil to power and control the device. us, the idea for a battery-powered BION device (hereinaer BPB) was conceived at the AMF. AMF developed, with guidance from Jet Propulsion Lab (JPL), a small cylindrical lithium ion rechargeable battery. A new company (Quallion, Inc.) was formed and nanced by Alfred Mann to manufacture and improve these unique highly reliable batteries. Today, these batteries can be safely recharged if discharged to 0 V and are expected to operate for over 10 years. ese batteries were designed specically for the BPB (Figure 55.2). AMF licensed the BPB technology to Advanced Bionics Corp., which designed and implemented the rst BPB (stimulator only) for urinary incontinence (referred to as the UI–BPB). is was the rst BION RF Powered Length (mm) Diameter (mm) BION Family Glass RF BION 15 2 16.7 2.4 28 3.1 25 3.15 Ceramic RF BION UI-BPB BPB for FE S Battery Powered FIGURE 55.1 Evolution of the BION devices. It shows four BIONS to the same scale. FIGURE 55.2 Quallion battery for the BPB. to have two-way telemetry (Figure 55.1). e telemetry receiver in this UI-BPB turns on for a very short time interval every 1.5 s, to conserve battery power. us, rapid synchronization for limb control is not feasible with the UI-BPB. As of September 2004, the UI-BPB has been implanted in 35 patients for the treatment of urinary incontinence and migraine headaches. 14 Owing to its lack of sensing capabilities and slow communication response time, the UI-BPB is not well suited for FES applications. AMF is currently developing the next generation of the BPB. is BPB (Figure 55.1) allows the cre ation of a wireless FES network, including both stimulation and sensing in each BPB for fully implant able closed-loop applications; data processing for sensed signals; high-speed bidirectional telemetry; wireless oscilloscope monitoring for tting purposes, via back telemetry of voltage-sensed signals; a rechargeable battery (enabling prolonged operation without external power); and capability of commu nications with over 850 BPBs simultaneously (eectively 100 communications/s). 15 e ceramic BION devices (Figure 55.1) use an extremely strong zirconia with 3% yttrium ceramic case. e FDA pointed out that long-term immersion in water signicantly weakens this ceramic (Joe Schulman, personal communication). Over a 3-year period, AMF came up with a process to improve the longevity of this ceramic. Today, accelerated life testing has shown that this ceramic will retain 80% of its strength aer 80 years of soaking in saline solution. 16–18 55.3 Battery-Powered BION System for Functional Electrical Stimulation and Sensing e system is a network of implantable battery-powered BION devices that can be used for both stimulation and e system is of a control a a recharging and and and only during the implantation are also of the e system can be up for use in tting and A of the system is shown in e is the communication and control for the e to and data from all the BPBs and the recharging ere are for the (1) an external which will be the and have a to the and (2) an implantable which will be implanted in a in the e implantable will have a small patient control e of on a that allows the to and the system for each e recharging and is used the rechargeable battery of the BPB to be e process requires the of the coil to the on the the BPB is is the battery of the BPB is on the of use and stimulation by the the battery could in stimulation conditions stimulation of pulse amplitude, pulse width, and per for about per is to the battery. e BPB stimulation capability pulse at 14 V with pulse and per can the battery in a very short time and would result in the need to the battery for of time and more e external coil only power to the implanted devices. and battery are by each BPB to the BPB can a eld the eld to without of the the a to the e BPB has a to the eld from a permanent e function of the magnet is to the stimulation is is a in the BPB is stimulating in an and the patient not have to control unit. the magnet is on the over the the BPB is a magnetic the BPB the external magnetic eld and the stimulation the magnet is the stimulation turns back is is the of the magnetic can be programmed during e BPB implantation is performed in a minimally invasive and is using a of designed and e functional of the system is 1. control e is the communication and control for the e to and data from each of up to a of 850 BPBs in the system of a the patient the system the the activity of the BPBs by data from implanted devices programmed as sensors, stimulation and monitoring the system It also as the for the providing system control and as well as and the as a between the and the of the system, the of each BPB and the needed BPBs to the functional e also the recharging e with the system in the same that the BPBs and it can be or for operation via the control e a a a only battery only S e e a a e a a S a a a e e S e a a Devices as stimulators S S S A S 3 S 2 S 1 Devices as sensors only at all only implantation only only Wireless FIGURE 55.3 Functional electrical stimulation and system e the following An on the external which a to all if BPB or and protect it would this to the which would a to the and the an external is being it would produce a to the In the an implantable is being the would a to the BPBs to produce a stimulation to the patient and would also with the external if it is the communication e would an e also patient data for the is data can be used to and to the stimulation and sensing of each e of each BPB in the is also in this 2. and e for the system is components. is the which on a e is the on the e with the with the via a communication the tting of the system to a the work in to and of the stimulation and these have been in a tting the can be in the that the can operate in a to the functional the will the stimulation output in response to the it from the BPBs programmed as e a that to the following personal for the including about the in the of BPBs the stimulation for each implanted BPB and allow of the stimulation the of the activity that will be in the FES the that will be used to between activity in response to the the that will a and the to the for either or later use 3. BION device e BPB is a battery-powered that is capable of both electrical stimulation and as a for pressure, or between BPBs and e following the functional of the and e of the BPB are in 6. shows the of the BPB and shows a of an BPB. e BPB has the following 3.1 Stimulation e BPB is a e stimulation output is which also between the battery or and the Stimulation pulse amplitude, width, and can be In can the stimulation to be or in a pulse which can be up with a variety of 55.1 Battery-Powered BION 1. with and 25 stimulation 2. Stimulation to in in or Stimulation control response time current to 14 V Stimulation output 4 to from a in 2 s, 1 10 time 1 2 3 4 2 4 2 1 3. with eld to of 8 than for sensing 1 3 10 or 4. of per patient to 850 at 10 to BPB data 15 data BPB to data 8 data 3 5. of eld magnetic eld continued e bidirectional RF communication between the and the BPBs is a (Figure is at a in the using with a e BPB communication a and processing that with and the e processing in the BPB also small of in the the and the to the including the of of communication that be mathematically In this the would the e communication between the and BPBs is shown in e of the is controlled by the and every BPB will to its e and elds are used for synchronization and for control data for all BPBs for an the with the number the time of all the BPBs it is Battery coil Stimulation Stimulation and communication and sensors and communication FIGURE BION device 55.1 Battery-Powered BION 6. ion Battery and Battery Battery 10 V V Battery life 10 years Battery Battery on 4 1 1 Ceramic FIGURE BION components. to communication the the time for the and data to each of the BPBs in the each BPB turns on its or for only a at the in each to battery. e data stimulation sensing control data and to up to or that number are reported to the which will the are the would be or the would be back to the for the to and the data are by each of the BPBs and are used to to the (e.g., sensed e in the data only or and e power for the BPB is a 10 rechargeable lithium ion battery that allows the implanted device to operate as a lithium ion life and the to to and be safely without to the battery. e process is via a magnetic with an external coil or continuous stimulation at with 100 pulse and 2 pulse a 2 the battery of a BPB as a will provide 100 of continuous a BPB as a the battery will also provide 100 of continuous e lithium ion battery is to have a life of for a which is a of the battery e in many applications are such that the battery would not be discharged to the recharged us, the a of over 10 years if the battery is recharged e BPB the following A magnetic that the magnetic eld from an external magnet and the stimulation for it to be A that with the via the to if and the battery the a Battery that the battery from and BPBs can protect from magnetic elds in of the eld necessary for for a short time, for elds in of the eld for is short time is more than for the BPB to a to the to the and to the patient of the data and data e function is implemented to or electrical sensing is using a and by a e is from a of 10 to a of e of the is from 1 to e is from to 10 is than 0 1 1 2 3 4 7 8 A A 1 2 3 4 7 8 FIGURE BPB communication the from the can be and from the BPB to the to the at a of per is (Figure can be used the of the BPB and during it is not for use due to its power e output of the also to a programmable that can be by the to (1) that or the (Figure or (2) and the sensed (Figure (1) e neuronal that are every 10 and to the (2) and 10 if the can the of the output and up the An output between 0 and will be the every 10 sensing BPBs will be with a at e of this is about 3 in and is to the of the BPB. will be to pressure, and may be from the BPB. e is is can be out either or it the with this can be for by a of the same in the this sensing e same coil that is used to the magnetic eld to the BPB may also be programmed as a in BPB or as a receiver in BPB. e function is implemented using BPB as a and the BPB as a e BPB programmed as a and the 1 2 3 FIGURE with the BPB sensing and FIGURE sensing oscilloscope strength of the (Figure e between BPBs is from the of the magnetic which with the of the between the devices. ere are dierent programmable for e are is of and number of ere is no on the number of BPB that can process the strength to each of the BPB receiver is able to back a 100 per A can be used to between 1 and sensing An is as an to against of the BPB and to provide data to such as who do not e is to and is over the from to In the a is the BPB can be communication with the can be to external as the if are per and can be by the 4. and external e a that a magnetic eld in the e with the to to on a e each BPB to which BPB is to be and the BPB is fully e which BPBs are not being and to the patient the coil has to be to the is to several coils can only power coil at a time, the can the to switch coils the BPBs can be e can also the of the in each BPB and can the discharged devices to be FIGURE of BPBs for e recharging a that the recharging process if the external coil to the patient over 5. e patient can stimulation by an external magnet the of the implanted A magnet is being used it is small and and it a very strong magnetic e of this magnet is to the stimulation the magnet is on the over the the BPB is the magnet is the stimulation turns back magnet control are available. 6. system 7. Minimally invasive to implant BPBs To implant a a minimally invasive is e implantation can be in a the implant can be and with and with e implant and is and and a and e implantation are shown in a is A at the connected to an external is the to and the to the the optimal is A is over the Stimulation with the is to a optimal response and e and are the in e BPB has a to the e stimulation is the and by the to the that only the BPB stimulation the saline is the to allow the of the BPB to have electrical to the small in the e BPB is to and its optimal position to the the over the the BPB is the (Figure e and the are e BPB is to that the optimal response is this position is not in to the to stimulation or the BPB can be by on the to the BPB (Figure and e are at the and the is e implanted BPB is 1 aer implantation to that the are an response is the could be and the BPB by on the A new BPB could be to with 3 with saline FIGURE BPB implantation e dierent of the BPB a or and the of multiple BPBs in patient to 850 the many to restore function, in spinal cord injury, cerebral palsy, multiple injury, and for limb sensing in to control for the a paralyzed is implanted with multiple BPBs or nerves of in the and It will be to functional to the and and the to an e of each functional can be controlled from implanted BPBs as sensors, measuring the of the and and implanted BPBs as sensors, measuring the at the (Figure e of this can be using this stimulating and sensing system to the for to the closed-loop of stimulation could be used in FIGURE BPB implantation FIGURE of BPB. FIGURE BPBs measuring in the for and paralyzed sensing of the using BPBs would as to BPBs to the of these the sensors would the closed-loop to reduce or the is could be used to and need to be for at the a for ing on stroke or or the of an BPB devices in these can the and either functional stimulation to or a functional stimulation 8. system in limbs patients (Figure BPBs as sensors, are in the to up which can be used to control the movement of the limb components. A and using the BPB system technology with spinal cord injury or that control over or sensing may be able to of the ability of by monitoring the and back sensed response to the is as activity in the e on and sensors to control the limb back to the the use of the limb would be back to the e can also be used to control and devices. e developed for the BPB are used to a device with multiple stimulation and sensing a single implantable (Figure e has the capability of monitoring up to several that can be implanted or in the or a of e system of a implanted in the the and or several on the or e is to a of BPBs in its communication It also an that allows to either or from e and are shown in e is with the same technology developed for the BPB. It the same as used in the BPB as as the power and stimulation are A FIGURE of BPBs in sensing to or more e battery used in the at e could be for sensing or stimulating e sensing processing capabilities by using the same as in the sensing in the BPB. e stimulating the same stimulation as in the BPB stimulation e a to the from the and to reduce the data to that the can use to control up to 1. and 2. 3. the on and on to the on and on FIGURE device. coil and Ceramic Battery and FIGURE device. 4. and at a National Research 5. of in the United States. National 6. from National 7. W.J. RF of and prosthetic 8. Loeb, Schulman, Troyk, P.R. microstimulator for functional electrical Schulman, J. electrical stimulation with Loeb, G.E. electrical stimulation with to shoulder and knee RF An injectable microstimulator for the treatment of in of e use of the RF BION device to pain due to shoulder in stroke Advanced Bionics Corporation, a Boston Scientic Schulman, J. J. Battery powered BION FES Schulman, J. and of of Southern California, Los Angeles, Research Schulman, J. life and of for Devices Schulman, J. Ceramic to for implantable device. Los Angeles, Research

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