The firefly T-2 is intended for stimulation of healthy muscles in order to improve or facilitate muscle performance. The firefly™ T-2 is not intended to be used in conjunction with therapy or treatment of medical conditions of any kind.

Device Description

The firefly™ T-2 Neuromuscular Stimulator (firefly™ T-2) is a disposable, fully integrated unit composed of a constant current pulse generator with embedded software and battery enclosed in an over-molded plastic casing, and a silver electrode with a hydrogel coating that provides a means of attachment of the device and electrical contact with the patient. Two buttons are used to control the On/Off function and increase or decrease the intensity level of the device output, which is achieved through changes in the delivered pulse width. The firefly™ T-2 is applied so that the electrodes lie over the common peroneal nerve behind the knee. Stimulation of the common peroneal nerve causes contraction of the calf muscles through the direct activation of the motor neurons, resulting in increased blood flow.

AI/ML Overview

This document, K201131, is a 510(k) summary for the firefly™ T-2, a powered muscle stimulator. It is not a study proving the device meets acceptance criteria for a new AI/ML-driven medical device, but rather a submission demonstrating substantial equivalence to a predicate device.

Therefore, I cannot provide a table of acceptance criteria and reported device performance related to AI/ML accuracy metrics (e.g., sensitivity, specificity, AUC) or the other points typically associated with the rigorous validation of an AI/ML model (sample sizes for test/training, expert adjudication, MRMC studies, etc.).

The document focuses on comparing the firefly™ T-2 to its predicate device, the firefly™ T-1, based on technical specifications and functional performance, rather than clinical performance metrics, especially those that would require AI-specific validation.

Here's a breakdown of what the document does provide, and why it doesn't fit the requested AI/ML validation criteria:

Device Type and Purpose:

The firefly™ T-2 is a powered muscle stimulator. Its "intended for stimulation of healthy muscles in order to improve or facilitate muscle performance."
It is explicitly stated as not intended to be used in conjunction with therapy or treatment of medical conditions of any kind.
It operates by stimulating the common peroneal nerve to cause calf muscle contraction, increasing blood flow. This is a biophysical mechanism, not an AI/ML-driven diagnostic or prognostic one.

Reason for Submission (Differences from Predicate):

The firefly™ T-2 is a redesigned version of the firefly™ T-1. The redesign aimed for more efficient current delivery, shorter pulse widths, and improved prevention of current leakage between electrodes by using discrete hydrogel pieces.
The user interface was also improved for ease of use.
Crucially, the document states: "The changes resulting in the firefly™ T-2 device do not alter the device intended use, indications for use or fundamental scientific technology, and none of the changes significantly affect the safety or effectiveness of the device." This implies an engineering change, not a change incorporating AI/ML.

"Acceptance Criteria" implicitly addressed by the submission (not AI-specific):
The "acceptance criteria" here are implicitly related to demonstrating that the redesigned firefly™ T-2 is still substantially equivalent to the predicate firefly™ T-1 and continues to meet relevant safety and performance standards for a powered muscle stimulator.

Safety Standards Compliance:
- IEC 60601-1:2005 + A1:2012 (Medical Electrical Equipment - General Requirements for Safety)
- IEC 60601-2-10:2016 (Particular requirements for the safety of nerve and muscle stimulators)
- IEC 60601-1-2: 2014 (Electromagnetic compatibility)
- ISO 10993-1:2009 (Biocompatibility of materials)
Performance Verification (Comparison to Predicate):
- Output waveform characteristics (verified via oscilloscope).
- Output current measurements under various loads (compared to T-1).
- Validation of hardware and firmware functionality.
- Demonstration that the T-2 performs as designed and intended and is substantially equivalent to the T-1.

Why the requested AI/ML criteria are not applicable/found:

AI/ML Specific Acceptance Criteria and Performance Table: Not applicable. The device is a muscle stimulator, not an AI/ML diagnostic.
Sample Size for Test Set and Data Provenance: Not applicable for AI/ML validation. The "testing" refers to electrical and functional verification of the physical device, not an AI model trained on data.
Number of Experts and Qualifications for Ground Truth: Not applicable. Ground truth for an AI model (e.g., disease presence in an image) isn't relevant here. The "ground truth" for this device is simply its physical and electrical properties conforming to specifications.
Adjudication Method: Not applicable.
Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study: Not applicable. This type of study assesses how AI assistive tools affect human reader performance in tasks like image interpretation. This device has no imaging component or human reader interaction for AI-driven interpretation.
Standalone (Algorithm Only) Performance: Not applicable. There is no standalone algorithm in the sense of a medical AI.
Type of Ground Truth Used: The "ground truth" for this device would be its engineering specifications and the physical laws governing electrical stimulation, verified through laboratory testing (e.g., oscilloscope measurements, impedance tests). It's not clinical "outcomes data" or "expert consensus" in the context of an AI model's output.
Sample Size for Training Set & How Ground Truth for Training Set was Established: Not applicable. This device is not developed using AI/ML training data. Its "design" is based on electrical engineering principles and the performance of its predicate device, not on patterns learned from a large dataset.

In summary, the provided document is a regulatory submission for a powered muscle stimulator, focusing on demonstrating substantial equivalence to a predicate device through engineering changes and traditional electrical/mechanical testing, rather than the validation of an AI/ML medical device.

Summary

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Image /page/0/Picture/0 description: The image contains the logo of the U.S. Food and Drug Administration (FDA). On the left is the Department of Health & Human Services logo. To the right of that is the FDA logo, which is a blue square with the letters "FDA" in white. To the right of the blue square is the text "U.S. FOOD & DRUG ADMINISTRATION" in blue.

May 29, 2020

Firstkind Limited % Sheila Hemeon-Heyer President Heyer Regulatory Solutions LLC 125 Cherry Lane Amherst, Massachusetts 01002

Re: K201131 Trade/Device Name: firefly T-2 Regulation Number: 21 CFR 890.5850 Regulation Name: Powered muscle stimulator Regulatory Class: Class II Product Code: NGX

Dear Sheila Hemeon-Heyer:

The Food and Drug Administration (FDA) is sending this letter to notify you of an administrative change related to your previous substantial equivalence (SE) determination letter dated May 28, 2020. Specifically, FDA is updating this SE Letter 510(k) summary file error as an administrative correction.

Please note that the 510(k) submission was not re-reviewed. For questions regarding this letter please contact Dr. Heather Dean, OHT5: Office of Neurological and Physical Medicine Devices, 240-402-9874, Heather.Dean@fda.hhs.gov.

Sincerely,

Heather L. Dean -S

Heather Dean, PhD Acting Assistant Director, Acute Injury Devices DHT5B: Division of Neuromodulation and Physical Medicine Devices OHT5: Office of Neurological and Physical Medicine Devices Office of Product Evaluation and Ouality Center for Devices and Radiological Health

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Image /page/1/Picture/0 description: The image contains the logo of the U.S. Food and Drug Administration (FDA). On the left is the Department of Health & Human Services logo. To the right of that is the FDA logo in blue. Underneath the FDA logo is the text "U.S. FOOD & DRUG ADMINISTRATION".

May 28, 2020

Firstkind Limited % Sheila Hemeon-Heyer President Heyer Regulatory Solutions LLC 125 Cherry Lane Amherst, Massachusetts 01002

Re: K201131

Trade/Device Name: fireflyTM T-2 Regulation Number: 21 CFR 890.5850 Regulation Name: Powered muscle stimulator Regulatory Class: Class II Product Code: NGX Dated: April 28, 2020 Received: April 28, 2020

Dear Sheila Hemeon-Heyer:

We have reviewed your Section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database located at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

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Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801); medical device reporting of medical device-related adverse events) (21 CFR 803) for devices or postmarketing safety reporting (21 CFR 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reportingcombination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820) for devices or current good manufacturing practices (21 CFR 4, Subpart A) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR 1000-1050.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR Part 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to https://www.fda.gov/medical-device-safety/medical-device-reportingmdr-how-report-medical-device-problems.

For comprehensive regulatory information about mediation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medicaldevices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-device-advice-comprehensive-regulatoryassistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email (DICE(@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

Sincerely.

Amber T. Ballard -S

For Vivek Pinto, PhD Director DHT5B: Division of Neuromodulation and Physical Medicine Devices OHT5: Office of Neurological and Physical Medicine Devices Office of Product Evaluation and Ouality Center for Devices and Radiological Health

Enclosure

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Indications for Use

510(k) Number (if known) K201131

Device Name firefly™ T-2

Indications for Use (Describe)

Type of Use (Select one or both, as applicable)
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Prescription Use (Part 21 CFR 801 Subpart D)

|X | Over-The-Counter Use (21 CFR 801 Subpart C)

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510(k) Summary

This summary of 510(k) safety and effectiveness information is being submitted in accordance with the requirements of 21 CFR 807.92.

A.	Submitter:	Firstkind LimitedHawk HousePeregrine Business ParkHigh Wycombe, UKHP13 7DL
	Contact:Tel:Email:	Neil Buckley, Head of Quality and Regulatory Affairs+44 (0) 845 2222 921neil.buckley@firstkindmedical.com

Date Prepared: May 28, 2020 B.

C. Device Name and Classification Information:

Trade Name:	firefly™ T-2
Common Name:	Powered Muscle Stimulator for Muscle Conditioning
Classification Name:	Stimulator, Muscle Powered
Regulation:	21 CFR 890.5850
Product Code:	NGX
Review Panel:	89, Physical Medicine

D. Predicate Device: K134001, firefly™ T-1

Device Description: ய்

The stimulus intensity varies with the pulse width, which can be set to one of seven levels for the firefly™ T-2. The asymmetric biphasic waveform results in a net charge of zero to the patient during each pulse cycle. The pulse rate is fixed at a frequency of 1 Hz and is

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used to isometrically stimulate the leg and foot muscles with a cadence and energy similar to that of walking.

Electrical contact is made with the patient through a hydrogel layer applied during manufacture to the integrated electrode. The patient contacting materials have been previously tested per the requirements of ISO 10993-1 and shown to be biocompatible for prolonged (up to 30 days) contact with intact skin. There are no separate electrode leads or electrodes.

F. Indications for Use:

The firefly™ T-2 is intended for stimulation of healthy muscles in order to improve or facilitate muscle performance. The firefly™ T-2 is not intended to be used in conjunction with therapy or treatment of medical diseases or medical conditions of any kind.

Parameter	Predicate Devicefirefly™ T-1 (K134001)	Subject Devicefirefly™ T-2	Comparison
Use environment	Over-the-counter (non-prescription) use in athletic training facilities or the home.	Over-the-counter (non-prescription) use in athletic training facilities or the home.	Same
Anatomical Sites	The firefly with the embedded electrodes is applied to the posterior aspect of the knee only for stimulation of the peroneal nerve.	The firefly with the embedded electrodes is applied to the posterior aspect of the knee only for stimulation of the peroneal nerve.	Same
Stimulator Parameters
Power source	One CR2032 primary lithium coin cell. Not replaceable by user	One CR2032 primary lithium coin cell. Not replaceable by user	Same
-Method of Line Current Isolation	N/A	N/A	Same
-Patient Leakage Current-Normal Condition	< 20μΑ	< 20μΑ
-Single FaultCondition	< 20μΑ	< 20μΑ
Parameter	firefly™ T-1	firefly™ T-2	Comparison
Number of outputmodes	Single mode with sevendiscrete stimulation settingscorresponding to the sevenpulse widths.	Single mode with sevendiscrete stimulation settingscorresponding to the sevenpulse widths.	Same
Number of outputchannels /synchronous oralternating?	Single channelN/A	Single channelN/A	Same
-Method of channelisolation	N/A (single channel)	N/A (single channel)	Same
Regulated currentor regulatedvoltage	Current	Current	Same
Microprocessorcontrolled?	Yes	Yes	Same
Automaticoverload trip	Yes	Yes	Same
Automatic no-loadtrip	Yes	Yes	Same
Automatic shut-off	Yes	Yes	Same
User over-ridecontrol	Yes	Yes	Same
Indicator display:- On/Off status	Yes	Yes	Same
- Low battery-Voltage / currentlevel	Yes (device switches off)N/A (device has fixedconstant current). Stimuluslevel is indicated by flashingLED.	Yes (device switches off)N/A (device has fixedconstant current). Stimuluslevel is indicated by flashingLED.	Same
Timer range inminutes	1800 minutes maximum(device is disabled after 30hours battery run time)	1800 minutes maximum(device is disabled after 30hours battery run time)	Same
Compliance withvoluntarystandards	YesIEC 60601-1:1998 A1, A2IEC 60601-2-10:1987, A1EN 60601-1-2:2007ISO 10993-1:2009	YesIEC 60601-1:2005IEC 60601-2-10:2012EN 60601-1-2:2015ISO 10993-1:2009	firefly T-2 complieswith currentrecognized versions ofapplicable standards.
Compliance with21 CFR 898	N/A (electrodes are integralwith the device, there are noseparate leads)	N/A (electrodes are integralwith the device, there are noseparate leads)	Same
Parameter	firefly™ T-1	firefly™ T-2	Comparison
Weight	18 g	10g	firefly T-2 is slightlylighter than T-1.
Dimensions	6" x 1.6" x 0.4"	7.8" x 1.2" x 0.4"	firefly T-2 is slightlylonger and narrowerthan T-1.
Housing materialand construction	Plastic injection molding	Plastic injection molding	Same
Waveform Parameters
Mode or ProgramName	N/A, single modeUsed for Active Recovery	N/A, single modeUsed for Active Recovery	Same
Waveform- Pulsedmonophasic orbiphasic- Shape	Biphasic (asymmetricalbiphasic with zero net DC)Rectangular, with chargebalancing second phase	Biphasic (asymmetricalbiphasic with zero net DC)Rectangular, with chargebalancing second phase	Same
Maximum outputvoltage (± 15%)	13.5 V @ 500 Ω54 V @ 2 kΩ110 V @ 10 k Ω	14.0 V @ 500 Ω53.5 V @ 2 kΩ255 V @ 10 k Ω	Design of firefly T-2 hasbeen improved tomaintain desiredcurrent output even athigh loads.
Maximum outputcurrent (± 15%)	27 mA @ 500 Ω27 mA @ 2 kΩ11 mA @ 10 kΩ	27.9 mA @ 500 Ω26.8 mA @ 2 kΩ25.5 mA @ 10 kΩ	Design of firefly T-2has been improved tomaintain desiredcurrent output even athigh loads.
Pulse widths	70, 100, 140, 200, 280, 400,560 µs	50, 70, 100, 140, 200, 280,400 µs	firefly T-2 pulse widthsdecreased at eachsetting to compensatefor better currentoutput.
Frequency	1 Hz	1 Hz	Same
For interferentialmodes only:-Beat Frequency(Hz)	N/A	N/A	Same
For multiphasicwaveforms only-Symmetrical	No	No	Same
phases-Phaseduration(s)	70-560 µs for positive phase,second (negative) phase is anexponential decay with a 0.1 stime constant.	50-400 µs for positive phase,second (negative) phase isan exponential decay with a0.1 s time constant.	Same except forreduced pulseduration at eachsetting for firefly T-2
Parameter	firefly™ T-1	firefly™ T-2	Comparison
Net charge	0 μC at 500 Ω	0 μC at 500 Ω	Same
-How achieved	Capacitor coupling	Capacitor coupling	Same
Maximum phasecharge (@500Ω)	18.3 μC	18.3 μC	Same
Maximum currentdensity (@500Ω)	0.169 mA/cm² rms	0.169 mA/cm² rms	Same
Maximum avgcurrent (averageabsolute value),mA (@500Ω)	0.037 mA	0.037 mA	Same
Maximum avgpower density(using smallestelectrodes)(@500Ω)	0.000044 W/cm²	0.000044 W/cm²	Same
Burst mode	N/A, single pulse, no burstmode	N/A, single pulse, no burstmode	Same
ON Time (seconds)/ OFF Time(seconds)	N/A Stimulation is continuallyon or off when power is on oroff.	N/A Stimulation is continuallyon or off when power is on oroff.	Same
Electrodes	Two electrodes integratedwithin the device. A singlepiece of hydrogel covers theelectrodes and the underside ofthe electronics housing.Biocompatibility for thehydrogel has been established.	Two electrode integratedwithin the device. Thehydrogel is in 3 discretesections covering each ofthe electrodes and theanterior section of strap.Biocompatibility for thehydrogel has beenestablished.	Design of firefly T-2 hasbeen improved toprevent leakage currentbetween the twoelectrodes through thehydrogel.
Cables/ connectors	Integrated device: noseparate cables	Integrated device: noseparate cables	Same
User Contact	Contact is made throughintegrated self-adhesiveelectrodes. The firefly T-1 is asingle channel device	Contact is made throughintegrated self-adhesiveelectrodes. The firefly T-2 is asingle channel device	Same

G. Technical Comparison with the Predicate Device and Discussion of Differences

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Discussion of differences

The firefly™ T-2 device has been redesigned from the original firefly™ T-1 device for more efficient current delivery, enabling shorter pulse widths at each stimulus level. Because the T-1 device had a sinqle piece of hydrogel covering both electrodes: there was a small amount of leakage current between the electrodes. The leakage current could reduce the effectiveness of stimulation in users with high skin resistance. The T-2 device was redesigned using discrete pieces of hydrogel over each electrodes to prevent any current leakage. To compensate for the result that more current is available to the uiser, the pulse widths have been reduced to ensure that the same charge is delivered for each pulse width setting.

The firefly™ T-2 interface has been designed to improve ease of use. Using + and buttons to increase and decrease intensity is somewhat easier than using different length presses on a single button. The two LED indicators used with the T-2 make it easier to see whether the device is operating. One LED for the T-2 device flashes rapidly when the switch is operated by a button press, providing the operator with visual feedback that the button has been operated. The other LED indicates the stimulation level in the same manner as for the T-1.

The changes resulting in the firefly™ T-2 device do not alter the device intended use, indications for use or fundamental scientific technology, and none of the changes significantly affect the safety or effectiveness of the device.

H. Testing to Validate Changes

The device changes described in this Special 510(k) were implemented under the company's design change procedures. A risk assessment of the changes resulted in the following verification and validation activities:

Electrical Safety and Electromagnetic Compatibility Testing - The firefly™ T-2 has been certified to comply with the applicable clauses of the following standards:

o IEC 60601-1:2005 + A1:2012: Medical Electrical Equipment - Part 1: General Requirements for Safety (FDA recognition #19-40
IEC 60601-2-10:2016 Medical electrical equipment Part 2-10: Particular . requirements for the safety of nerve and muscle stimulators (FDA recognition # 17-16)
. IEC 60601-1-2: 2014 Medical electrical equipment - Part 1-2: General requirements for basic safety and essential performance - Collateral standard: Electromagnetic compatibility - Requirements and tests (FDA recognition #19-8)

Hardware/Firmware Testing

As with the predicate device, the firefly™ T-2 hardware and firmware work together and need to be tested together in order to verify the correct functioning of the device. Testing included the following:

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Verification of output waveform characteristics via oscilloscope output tracings at . 500Ω, 2kΩ and 10kΩ
Measurements to compare the firefly™ T-2 output currents to those of the firefly™ . T-1 under loads ranging from 500Ω to 10kΩ
Validation of all firefly™ T-2 hardware and firmware functionality ●

All test results demonstrated that the firefly™ T-2 meets the predefined device technical and functional requirements specifications.

I. Conclusions

The information and testing presented in this 510(k) demonstrate that the firefly™ T-2 performs as designed and intended and is substantially equivalent to the predicate device, the firefly™ T-1.

Regulation Number and Section

§ 890.5850 Powered muscle stimulator.

(a)
Identification. A powered muscle stimulator is an electrically powered device intended for medical purposes that repeatedly contracts muscles by passing electrical currents through electrodes contacting the affected body area.(b)
Classification. Class II (performance standards).