Patent Description:
It is estimated that there are over <NUM> million people in the United States with limb loss. Various prosthetic devices have been developed to assist persons with such limb loss. Commercial systems available to date have relied on surface electromyographic (EMG) sensors with limited success, due to the difficulty of obtaining reliable muscle activity data from surface EMG sensors. Recent clinical trials of a system developed by The Alfred E, Mann Foundation For Scientific Research have shown the many advantages of an Implantable Myoelectric Sensor System (IMES™) using implanted myoelectric sensors. See <NPL> and <NPL>.

Surface EMG sensors for prosthetic control are less expensive than implantable EMG sensors and may be more practical for the control of prosthetics as pattern recognition software is developed to interpret the multiple surface EMG signals received in order to properly move the prosthetic limb. EMG sensors can be used in medical systems for various applications, such as for example, measuring parasternal EMG signals in patients with chronic obstructive pulmonary disease (COPD) in order to determine their neural respiratory drive (NRD). See for example, <CIT>. Improved surface EMG sensors and systems would also enable the development and use of powered exoskeletons for therapy and rehabilitation of patients with mobility impairing ailments such as Parkinson's, multiple sclerosis, stroke and other medical conditions. See for example <CIT> and <CIT>. Improved surface EMG sensors could also be useful for the control of strength enhancing exoskeletons for use in military and industrial applications. <CIT> discloses a stimulation system for a patient comprising: at least one implantable device comprising at least one implantable antenna; and an external device comprising at least one external antenna, wherein the at least one external antenna transfers power to the at least one implantable antenna. A patient attachment device or body covering positions the at least one external antenna relative to the patient.

Skin patch sensors for monitoring and/or affecting body parameters, with alignment, positioning and attachment using magnets. The repeated use of releasable adhesive layers to retain skin patch sensors on skin can cause skin irritation, which can be reduced by rotating a skin patch between attachment times around a magnetically coupled pivot point. Skin patch sensors can be configured with internal coils to inductively couple to external power transmitting and communications coils with solenoids in anti-Helmholtz configurations.

<FIG> is a cross sectional side view of a wireless flexible skin patch <NUM> for sensing or affecting a body parameter. In some embodiments, skin patch <NUM> is sensing electromyographic (EMG) signals. Skin patch <NUM> includes electrodes <NUM>, electronic components <NUM> on a flexible circuit board, flexible cover <NUM> and is mounted on flexible adhesive substrate <NUM>. Electronic components <NUM> include one or more coils or antennas for inductively coupling the skin patch to an external power transmitting and communications coil. The electrodes may be made of stainless steel or other metal suitable for use as an electrode to which a disposable electrode may be attached, such as adhesive get type electrodes commonly used for ECG sensing. The disposable electrodes may be part of adhesive substrate <NUM>. The electrodes could also be a micro-array made of metal or silicon that pierces the outer layers of skin in order to reduce the impedance of the interface and to improve the signal strength of the sensed electrical signals. The electrodes may also be a needle electrode, configured for injection into the skin, either subdermally for improved signal strength or deeper into a targeted muscle for selectivity and signal strength. When using needle electrodes, they could be of the bipolar type or monopolar and used in combination with a surface electrode built into adhesive substrate <NUM>. In some embodiments, the skin patch may be configured and positioned on the skin of a person to sense other electrical signals, such as electrocardiographic (ECG) or electroencephalographic EEG signals.

In some embodiments, a skin patch <NUM> may incorporate other sensors such as temperature sensors, accelerometers, gyroscopes, inertial measurement units, or reflectance type blood oximetry sensors to measure blood oxygen and pulse rate. An inertial measurement unit made of a <NUM> axis accelerometer and a <NUM> axis gyroscope, when attached to skin in various chest locations on a person, can sense many parameters such as: respiration rate and strength, cardiac monitoring, patient posture and activity and fall detection.

In some embodiments, the skin patch may be configured and positioned on the skin of a person to generate transcutaneous electrical nerve stimulation (TENS) for therapeutic purposes. More than one coil can be in skin patch <NUM> and may have various configurations such as a planar or spiral coil, as will be discussed with regard to <FIG> or one or more solenoid coils, either discrete coils or part of the flex circuit, positioned for inductive coupling with an external coil providing external RF for wireless power transmission to the skin patch. A coil or coils within skin patch <NUM> and an external coil have to be properly oriented to each other to maximize the coupling coefficient between the coils for maximum efficiency and to maximize the immunity of the link to changes in the coupling coefficient. For example, the solenoid coils in multiple skin patches <NUM> in various positions around a residual limb may couple with a solenoid coil in a prosthetic socket with all of the axes of the solenoid coils substantially parallel to each other for the maximum coupling between the coils. Wireless communications with skin patch <NUM> may be based on a variety of methods, such as, for example, load modulation of the wireless power transmission to the skin patch <NUM>. Such wireless communications may also include near field (NFC), Bluetooth or other communications protocols. The operating parameters of skin patch <NUM> may be controlled by wireless communications from a terminal controller (not shown) operated by a physician or technician or from a patient operated remote control (not shown).

The adhesive substrate <NUM> includes two layers of adhesive, one layer of adhesive on one side to releasably mount the substrate to the skin patch and a second layer of adhesive on the opposite side of the substrate to releasable mount the skin patch <NUM> to skin. Substrate <NUM> may be made of paper or a flexible layer of plastic for improved adhesion to curved surfaces of skin such as on an arm or a leg. In some embodiments, skin patch <NUM> is made with a flexible base and cover to provide the ability to be flexed upon adhesive mounting to better conform to the curvature of the limb to which it is attached, to provide a lower profile and for improved signal capture. In some embodiments, the substrate is a layer of compressible foam to provide a better fit for the skin patch to the curvature of the limb to which it is attached. In some embodiments, adhesive gel electrodes are incorporated into the adhesive substrate. In some embodiments, the skin patch is powered by a rechargeable or primary battery, where the primary battery may be changed by a user or by a technician. If the skin patch is powered by a rechargeable battery, the rechargeable battery can be charged wirelessly or through a wired connection.

<FIG> is a top view of a wireless skin patch <NUM>, shown without a cover, for sensing or affecting a body parameter. Skin patch <NUM> includes base <NUM>, electrodes <NUM>, electronic components <NUM> and planar or spiral coil <NUM>. Skin patch <NUM> may be releasably attached to skin by an adhesive substrate as discussed with regard to <FIG>. Spiral coil <NUM> may be inductively coupled to an external planar coil or to a pair of solenoids in an anti-Helmholtz configuration as will be discussed with regard to <FIG>.

<FIG> is a view of part of a prosthesis control system <NUM> for EMG control of a prosthetic limb. Residual limb <NUM> is coupled to system <NUM> and includes prosthetic socket <NUM> and prosthesis <NUM>. Several skin patch EMG sensors <NUM> monitor multiple EMG signals in residual limb <NUM> and transmit EMG data signals to prosthesis control system <NUM>. Prosthesis control system <NUM> includes solenoid <NUM> for transmitting alternating current to power EMG sensors <NUM> and for bidirectional communications with EMG sensors <NUM>. Prosthetic socket <NUM> includes electronic systems, such as a power supply, a controller, analog and digital signal processing to receive the multiple EMG data signals from skin patches <NUM> to generate motion control commands, which are sent to a prosthesis controller. The prosthesis controller is connected to and actuates the motion of prosthesis <NUM>. The operating parameters of prosthesis control system <NUM> may be controlled by wireless communications from a terminal controller (not shown) operated by a physician or technician or from a patient operated remote control (not shown). The electronic systems of the prosthesis system <NUM> are discussed with respect to <FIG>.

<FIG> is a view of a wireless skin patch <NUM> positioned on a patient's chest <NUM>. As was described with respect to skin patch <NUM>, skin patch <NUM> may be any one of a variety of sensors such as EMG, ECG or a motion sensor using an inertial measuring unit.

<FIG> is a top view of a skin patch <NUM> with magnetic alignment features. Skin patch <NUM> includes base <NUM>, circular magnet <NUM> and optional longitudinal magnets <NUM>. The arrows <NUM> indicate that skin patch <NUM> may be rotated around the pivot point defined by implanted element <NUM> in between repeated attachments of skin patch <NUM> to the same general skin location. Other aspects of skin patch <NUM>, such as the electronic components and coil are not shown to simplify this figure. Circular element <NUM> is a ferromagnetic element for implantation below the skin as an alignment point for repeated positioning of skin patch <NUM> to the same location on skin. After element <NUM> is implanted below the skin, skin patch <NUM> is positioned in proximity to element <NUM> and magnet <NUM> magnetically couples to element <NUM> and skin patch <NUM> can be attached to that section of skin where element <NUM> is located, using an adhesive substrate, such as was described with respect to <FIG>. In some embodiments, element <NUM> is a magnet and is oriented such that after implantation, it magnetically couples to magnet <NUM> at the time of the attachment of skin patch <NUM> to the skin location defined by the implanted element <NUM>. In some embodiments, skin patch <NUM> includes additional magnets <NUM> which can also be used for the alignment of skin patch <NUM> to a skin location using implanted magnets <NUM> as shown in <FIG>.

After skin patch <NUM> has been attached at a skin location and is later detached from the skin location, a new adhesive substrate can be attached to skin patch <NUM>. Then skin patch <NUM> can be positioned above implanted element <NUM> using the magnetic coupling between magnet <NUM> and implant <NUM> to align skin patch <NUM> with the skin location and skin patch <NUM> can be rotated as indicated by arrows <NUM> about a pivot point defined by implant <NUM>. This can reduce the amount of skin used for such repeated attaching of skin patch <NUM> and thus reduce skin irritation.

<FIG> is a cross sectional side view of skin patch <NUM> retained on skin <NUM> with magnetic alignment features. Skin patch <NUM> includes base <NUM>, circular magnet <NUM> and optional longitudinal magnets <NUM>. Shown implanted below the skin <NUM> are element <NUM> and optional ferromagnetic elements <NUM>, which in some embodiments are magnets. Magnets <NUM> and <NUM> are used for alignment with elements <NUM> and <NUM> and skin patch <NUM> can be held in position on the skin using an adhesive substrate. In some embodiments, elements <NUM> and <NUM> are magnets and the magnetic coupling and the attractive forces between the magnets <NUM> and <NUM> above the skin, and the magnets <NUM> and <NUM> below the skin, can be sufficient to keep skin patch <NUM> in position on the skin, even if no adhesive substrate is used to retain skin patch <NUM> on the skin. The central aperture in magnet <NUM> can be used to provide an opening for one or more electrodes in some embodiments.

<FIG> is a top view of skin patch <NUM> with magnetic positioning features. Skin patch <NUM> includes base <NUM> and longitudinal magnets <NUM> and is similar to skin patch <NUM> in <FIG>, except that there is no central magnet <NUM>, which provides more space for various sensors in the center of skin patch <NUM>. Elements <NUM> are ferromagnetic elements for implantation below the skin as alignment points for repeated positioning of skin patch <NUM> to the same location on skin. In some embodiments, elements <NUM> are magnets.

<FIG> is a cross sectional side view of skin patch <NUM> retained on skin <NUM> with magnetic positioning features. Skin patch <NUM> includes base <NUM> and longitudinal magnets <NUM>. Shown implanted below the skin <NUM> are ferromagnetic elements <NUM>, which in some embodiments can be magnets. Magnets <NUM> are used for alignment with elements <NUM> and skin patch <NUM> can be held in position on the skin using an adhesive substrate. In some embodiments, elements <NUM> are also magnets and the attractive forces between the magnets <NUM> above the skin, and the magnets <NUM> below the skin, can be sufficient to keep skin patch <NUM> in position on the skin, even if no adhesive substrate is used to retain skin patch <NUM> on the skin.

<FIG> is a view of several possible positions for skin patch <NUM> as it is rotated around a pivot point defined by magnet <NUM> offset from the center of the skin patch, and an implanted ferromagnetic element just below the position of magnet <NUM>, which is not shown in <FIG>. For example, skin patch <NUM> can be in position 900A for an adhesive attachment to the skin location underneath and after skin patch <NUM> is detached from the skin, it can be reattached via rotation as indicated by arrows <NUM> at location 900B or 900C or any other position that can be reached by rotation around a pivot point defined by the magnetic coupling of magnet <NUM> to an implanted ferromagnetic element below magnet <NUM>. Such rotation between attachments to the same general skin location will reduce the amount of skin exposed to adhesives and thus reduce the area size of any resultant skin irritation. Magnet <NUM> may have any of a variety of polygon type shapes and be configured with or without a central aperture.

<FIG> illustrate a flow chart of a method <NUM> for releasably attaching a skin patch with first and second substrates to the same general skin location at different times. Exemplary method <NUM> can apply to the skin patches shown in <FIG>. In block <NUM>, a ferromagnetic element is implanted subcutaneously at a skin location. In block <NUM>, a skin patch is provided for sensing and/or affecting a body parameter. The skin patch has a magnet configured to align with and magnetically couple to the implanted element. In block <NUM>, a first substrate is attached to the bottom of the skin patch. The first substrate has a first surface with an adhesive coating for releasable attachment to the bottom surface of the skin patch. The first substrate has a second surface with an adhesive coating on the second layer of the first substrate for releasable attachment to the skin location. In block <NUM>, the skin patch is positioned at the skin location with the implanted ferromagnetic element in alignment with the magnet and with magnetic coupling between the magnet and the implanted ferromagnetic element.

In block <NUM>, the skin patch is attached to the skin location with the first substrate. In block <NUM>, the skin patch is used to sense or affect a body parameter. In block <NUM>, the skin patch is detached from the skin location. In block <NUM>, the first substrate is detached from the skin patch. In block <NUM>, a second substrate is attached to the skin patch. The second substrate has a first surface with an adhesive coating for releasable attachment to the bottom surface of the skin patch. The second substrate has a second surface with an adhesive coating on the second layer of the second substrate for releasable attachment to the skin location.

In block <NUM>, the skin patch is positioned at the skin location with the implanted ferromagnetic element in alignment with the magnet and with magnetic coupling between the magnet and the implanted ferromagnetic element. In block <NUM>, the skin patch is rotated using the implanted ferromagnetic element as a pivot point. This reduces the amount of skin being reattached to each time and results in a smaller area of irritated skin. In block <NUM>, the skin patch is attached to the skin location using the second substrate. In block <NUM>, the skin patch is used to sense or affect a body parameter. This process <NUM> can be repeated as needed by repeating steps <NUM> to <NUM> with subsequent adhesive substrates and rotating the skin patch as needed each time before reattaching the skin patch to the same general skin location to reduce the area of irritated skin.

<FIG> is a diagram showing the outline of skin patch <NUM> mounted on limb <NUM> and wirelessly powered by a pair of solenoids <NUM> and <NUM> in an anti-Helmholtz configuration. In an anti-Helmholtz configuration, two solenoids are positioned along the same axis with the current flow in each solenoid being opposite to the current flow in the other solenoid. The distance between the solenoids is equal to the radius of the solenoids. In the center of the space between the solenoids, the magnetic field is zero, but the magnetic field is not zero away from the center and varies as is shown by the approximate field lines <NUM>. Skin patch <NUM> has an internal planar or spiral coil, similar to coil <NUM> in <FIG>, and this internal spiral coil is inductively coupled to the non-zero magnetic field generated by the solenoid coils <NUM> and <NUM> near to the surface of limb <NUM>. An anti-Helmholz solenoid configuration can wirelessly power a number of skin patches <NUM> positioned on the surface of a limb <NUM>. In some embodiments, skin patch <NUM> has an internal solenoid oriented for inductive coupling for power transfer from external solenoids in an anti-Helmholtz configuration.

<FIG> is a block diagram of systems in an exemplary skin patch <NUM> for EMG sensing. Skin patch <NUM> can be similar to the skin patches described with respect to <FIG> and <FIG>. Skin patch <NUM> is positioned on a skin location and senses EMG signals from muscle <NUM> through skin <NUM> using electrodes <NUM>. The electrodes <NUM> are connected to an analog signal processing system <NUM>, which is connected to an analog to digital converter (ADC) <NUM>. The output of ADC <NUM> is modulated by modulator <NUM>, the output of which is connected to skin patch coil <NUM>. Coil <NUM> operates as an antenna to transmit the processed EMG signals to a prosthesis control system, such as described with regard to <FIG> and <FIG>, or in some embodiments, to an exoskeleton control system. In some embodiments, coil <NUM> receives RF power signals which are coupled to power supply <NUM> for powering skin patch <NUM> and for recharging a rechargeable battery. Controller <NUM> generates command signals to the various systems in skin patch <NUM>. Controller <NUM> may be a microcontroller, a microprocessor, or a state machine. Power supply <NUM> may include a primary or rechargeable battery.

Claim 1:
A skin patch for releasable attachment to a skin location comprising:
a sensor (<NUM>) for sensing a body parameter;
a communications system (<NUM>) coupled to the sensor (<NUM>);
an antenna coupled to the communications system (<NUM>) for receiving wireless power transmissions for powering the skin patch (<NUM>), the skin patch being couplable to at least one implantable ferromagnetic element (<NUM>, <NUM>) configured for subcutaneous implantation below the skin location;
at least one magnet (<NUM>, <NUM>) in the skin patch (<NUM>) for supercutaneous positioning in proximity to and for magnetic coupling with the at least one implantable ferromagnetic element (<NUM>, <NUM>), the at least one magnet comprising a central aperture providing an opening for one or more electrodes of the sensor; and
longitudinal magnets adjacent to the at least one magnet in the skin patch for use in aligning the skin patch to the skin location by magnetic coupling the longitudinal magnets with further implantable ferromagnetic elements adjacent to the at least one implantable ferromagnetic element,
wherein the antenna comprises a coil configured to inductively couple with an external plurality of solenoids in an anti-Helmholtz configuration, the antenna providing at least one of the following:
transmitting a wireless data signal corresponding to the sensed body parameter; or
receiving wireless commands to affect the body parameter from an external controller (<NUM>).