Limits...
In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses.

Becerra-Fajardo L, Ivorra A - PLoS ONE (2015)

Bottom Line: This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant.In addition, we numerically show that the high frequency current bursts comply with safety standards both in terms of tissue heating and unwanted electro-stimulation.We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible.

View Article: PubMed Central - PubMed

Affiliation: Department of Information and Communication Technologies, Universitat Pompeu Fabra, Barcelona, Spain.

ABSTRACT
Electrical stimulation is used in order to restore nerve mediated functions in patients with neurological disorders, but its applicability is constrained by the invasiveness of the systems required to perform it. As an alternative to implantable systems consisting of central stimulation units wired to the stimulation electrodes, networks of wireless microstimulators have been devised for fine movement restoration. Miniaturization of these microstimulators is currently hampered by the available methods for powering them. Previously, we have proposed and demonstrated a heterodox electrical stimulation method based on electronic rectification of high frequency current bursts. These bursts can be delivered through textile electrodes on the skin. This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant. We envision microstimulators designs based on application-specific integrated circuits (ASICs) that will be flexible, thread-like (diameters < 0.5 mm) and not only with controlled stimulation capabilities but also with sensing capabilities for artificial proprioception. We in vivo demonstrate that neuroprostheses composed of addressable microstimulators based on this electrical stimulation method are feasible and can perform controlled charge-balanced electrical stimulation of muscles. We developed miniature external circuit prototypes connected to two bipolar probes that were percutaneously implanted in agonist and antagonist muscles of the hindlimb of an anesthetized rabbit. The electronic implant architecture was able to decode commands that were amplitude modulated on the high frequency (1 MHz) auxiliary current bursts. The devices were capable of independently stimulating the target tissues, accomplishing controlled dorsiflexion and plantarflexion joint movements. In addition, we numerically show that the high frequency current bursts comply with safety standards both in terms of tissue heating and unwanted electro-stimulation. We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible.

No MeSH data available.


Related in: MedlinePlus

Representation of the ASK modulated voltage signal employed both for communications and for powering the circuit prototypes.It consists of three active stages: A) Power Up stage; B) Synchronization and Data stage, in which a specific circuit prototype is addressed and thereby activated; and C) Stimulation bursts stage, in which, for each burst, the activated circuit prototype delivers to tissues a biphasic symmetrical pulse of 200 + 200 μs with an interphase dwell of 30 μs.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4493086&req=5

pone.0131666.g003: Representation of the ASK modulated voltage signal employed both for communications and for powering the circuit prototypes.It consists of three active stages: A) Power Up stage; B) Synchronization and Data stage, in which a specific circuit prototype is addressed and thereby activated; and C) Stimulation bursts stage, in which, for each burst, the activated circuit prototype delivers to tissues a biphasic symmetrical pulse of 200 + 200 μs with an interphase dwell of 30 μs.

Mentions: The modulated 1 MHz signals consist of three distinguishable active stages (Fig 3) of specific relative amplitudes in order to minimize tissue heating (this is explained in detail in the Compliance of the Auxiliary Current with Safety Standards section). First, an 85 ms low amplitude unmodulated signal is used for the “Power up” stage. That is, for guaranteeing power up and stabilization of the whole circuitry and, in particular, of the microcontroller. Then, the “Power up” stage is followed by a 600 μs “Synch&Data” stage in which the control unit synchronizes and reads the information sent on the HF current. This stage consists of a sequence of three rising-edge transitions for synchronizing the decoder to the modulated signal and a 9 bit data stream (8 address bits and 1 parity bit). Bits are received at a baud rate of 20 kBd. After the “Synch&Data” stage, an 800 μs zero-amplitude slot is included for processing purposes. Processing tasks comprise decoding the information sent in the “Synch&Data” stage, the parity bit check, and comparing the decoded address with the programmed address in order to activate it for stimulation. At last, an unmodulated signal of maximum amplitude is used for the “Stimulation burst” stage. It is during these “Stimulation bursts” when LF currents (i.e. half-wave rectified alternating current (AC)) flow through the circuit and nerve stimulation is performed. The duration of these bursts (450 μs) is fixed in this study. The first 20 μs are employed for preprocessing purposes (control unit wake-up and power supply unit stabilization). Then, for 200 μs, rectified current flows from muscle electrode 1 to muscle electrode 2 (cathodic current according to our definition of the electrodes) and, after a brief slot of 30 μs in which no rectified current flows through the circuit, rectified current flows from electrode 2 to electrode 1 for 200 μs (anodic current). Therefore, a biphasic symmetric pulse of 200 + 200 μs is applied to tissues with an interphase dwell of 30 μs. This interphase dwell is a short time delay typically used in electrical stimulation between the cathodic and anodic pulse that allows the propagation of the action potential away from the stimulation site before the injected charge is recovered by the electrode [22]. The number of “Stimulation bursts” and their frequency F are variable and are determined by the user interface that sets the modulated signal (later explained).


In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses.

Becerra-Fajardo L, Ivorra A - PLoS ONE (2015)

Representation of the ASK modulated voltage signal employed both for communications and for powering the circuit prototypes.It consists of three active stages: A) Power Up stage; B) Synchronization and Data stage, in which a specific circuit prototype is addressed and thereby activated; and C) Stimulation bursts stage, in which, for each burst, the activated circuit prototype delivers to tissues a biphasic symmetrical pulse of 200 + 200 μs with an interphase dwell of 30 μs.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493086&req=5

pone.0131666.g003: Representation of the ASK modulated voltage signal employed both for communications and for powering the circuit prototypes.It consists of three active stages: A) Power Up stage; B) Synchronization and Data stage, in which a specific circuit prototype is addressed and thereby activated; and C) Stimulation bursts stage, in which, for each burst, the activated circuit prototype delivers to tissues a biphasic symmetrical pulse of 200 + 200 μs with an interphase dwell of 30 μs.
Mentions: The modulated 1 MHz signals consist of three distinguishable active stages (Fig 3) of specific relative amplitudes in order to minimize tissue heating (this is explained in detail in the Compliance of the Auxiliary Current with Safety Standards section). First, an 85 ms low amplitude unmodulated signal is used for the “Power up” stage. That is, for guaranteeing power up and stabilization of the whole circuitry and, in particular, of the microcontroller. Then, the “Power up” stage is followed by a 600 μs “Synch&Data” stage in which the control unit synchronizes and reads the information sent on the HF current. This stage consists of a sequence of three rising-edge transitions for synchronizing the decoder to the modulated signal and a 9 bit data stream (8 address bits and 1 parity bit). Bits are received at a baud rate of 20 kBd. After the “Synch&Data” stage, an 800 μs zero-amplitude slot is included for processing purposes. Processing tasks comprise decoding the information sent in the “Synch&Data” stage, the parity bit check, and comparing the decoded address with the programmed address in order to activate it for stimulation. At last, an unmodulated signal of maximum amplitude is used for the “Stimulation burst” stage. It is during these “Stimulation bursts” when LF currents (i.e. half-wave rectified alternating current (AC)) flow through the circuit and nerve stimulation is performed. The duration of these bursts (450 μs) is fixed in this study. The first 20 μs are employed for preprocessing purposes (control unit wake-up and power supply unit stabilization). Then, for 200 μs, rectified current flows from muscle electrode 1 to muscle electrode 2 (cathodic current according to our definition of the electrodes) and, after a brief slot of 30 μs in which no rectified current flows through the circuit, rectified current flows from electrode 2 to electrode 1 for 200 μs (anodic current). Therefore, a biphasic symmetric pulse of 200 + 200 μs is applied to tissues with an interphase dwell of 30 μs. This interphase dwell is a short time delay typically used in electrical stimulation between the cathodic and anodic pulse that allows the propagation of the action potential away from the stimulation site before the injected charge is recovered by the electrode [22]. The number of “Stimulation bursts” and their frequency F are variable and are determined by the user interface that sets the modulated signal (later explained).

Bottom Line: This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant.In addition, we numerically show that the high frequency current bursts comply with safety standards both in terms of tissue heating and unwanted electro-stimulation.We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible.

View Article: PubMed Central - PubMed

Affiliation: Department of Information and Communication Technologies, Universitat Pompeu Fabra, Barcelona, Spain.

ABSTRACT
Electrical stimulation is used in order to restore nerve mediated functions in patients with neurological disorders, but its applicability is constrained by the invasiveness of the systems required to perform it. As an alternative to implantable systems consisting of central stimulation units wired to the stimulation electrodes, networks of wireless microstimulators have been devised for fine movement restoration. Miniaturization of these microstimulators is currently hampered by the available methods for powering them. Previously, we have proposed and demonstrated a heterodox electrical stimulation method based on electronic rectification of high frequency current bursts. These bursts can be delivered through textile electrodes on the skin. This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant. We envision microstimulators designs based on application-specific integrated circuits (ASICs) that will be flexible, thread-like (diameters < 0.5 mm) and not only with controlled stimulation capabilities but also with sensing capabilities for artificial proprioception. We in vivo demonstrate that neuroprostheses composed of addressable microstimulators based on this electrical stimulation method are feasible and can perform controlled charge-balanced electrical stimulation of muscles. We developed miniature external circuit prototypes connected to two bipolar probes that were percutaneously implanted in agonist and antagonist muscles of the hindlimb of an anesthetized rabbit. The electronic implant architecture was able to decode commands that were amplitude modulated on the high frequency (1 MHz) auxiliary current bursts. The devices were capable of independently stimulating the target tissues, accomplishing controlled dorsiflexion and plantarflexion joint movements. In addition, we numerically show that the high frequency current bursts comply with safety standards both in terms of tissue heating and unwanted electro-stimulation. We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible.

No MeSH data available.


Related in: MedlinePlus