Method for analysing the sweat produced by the skin of a user and analysis device for implementing such a method

Abstract

The invention relates to a method for analysing sweat produced by the skin of a user, the method comprising a first step of collecting the sweat released by the skin by means of a collecting means of a first face of a housing (2) to form a continuous flow of sweat, a second step of directing the continuous flow of collected sweat to an analysis module (200) for analysing the continuous flow of sweat of a second face (12) of the housing (2), which face is provided with a microfluidic channel (120). The method comprises a third step of measuring a first conductance (C1, C2,... Cn) of the continuous flow of sweat by means of a first pair of electrodes (22a) housed inside the microfluidic channel (120) and a fourth step of measuring a second conductance (C1', C2',... Cn') of the continuous flow of sweat by means of a second pair of electrodes (22b) housed inside the microfluidic channel (120) and located at an electrode distance (D) from the first pair of electrodes (22a). The method comprises a fifth step of determining a period of time (Δt1, Δt2,... Δtn) taken for the second conductance (C1', C2',... Cn') to become equal to the first conductance (C1, C2,... Cn) and a sixth step of calculating a flow rate of the sweat produced by the skin of the user.

Description

[0001] Method for analyzing sweat emitted by a user's skin and analysis device for implementing such a method

[0002] The field of the present invention is that of methods for analyzing sweat emitted by a user's skin. Its subject is such a method for analyzing sweat emitted by a user's skin as well as an analysis device for implementing such a method.

[0003] WO 2018 / 017619 describes a device for analyzing a user's sweat. The device is configured to measure sweat conductivity, skin conductance, and volumetric sweat rate. For this purpose, the device is intended to be placed on the user's skin, and the device comprises a sweat conductivity sensor, a skin conductance sensor, and a volumetric sweat rate sensor.

[0004] The device includes a sweat collection area that is concave and conducts sweat from the skin to an inlet. The inlet is in fluid communication with a microfluidic channel that terminates in an outlet or sweat collection reservoir.

[0005] The sweat conductivity sensor includes a plurality of conductivity electrodes that are placed on a substrate, such as a printed circuit board, and that are disposed in the microfluidic channel, preferably near the inlet.

[0006] The skin conductance sensor includes a plurality of conductance electrodes that are arranged on the device such that the conductance electrodes contact the user's skin outside of the collection area.

[0007] The volumetric sweat rate sensor includes a plurality of volumetric sweat rate electrodes that are also carried on the substrate and disposed within the microfluidic channel. During operation of the device, when the user begins to sweat, a sweat sample enters the device at the inlet and moves within the microfluidic channel. As the sweat flows and contacts the conductivity electrode, the device measures the conductivity of the sweat sample. Similarly, as the sweat moves within the microfluidic channel, the sweat contacts successive volumetric sweat rate electrodes, which the device interprets as sweat present at the contacted electrode.The device uses the presence of sweat at each electrode, along with a filled volume of the microfluidic channel and a contact time to determine the volumetric sweat rate. This results in the microfluidic channel being long enough to successively accommodate the electrodes between the inlet and outlet.

[0008] In some embodiments of the device, each volumetric sweat rate electrode is also configured to measure sweat conductivity when sweat contacts it.

[0009] Some embodiments of the device may include a microthermal mass flow sensor, a pressure sensor, or other suitable means for independently determining sweat rate.

[0010] Other embodiments of the device may include a temperature sensor, or a temperature sensor may be incorporated into one of the conductance electrodes.

[0011] Some embodiments are configured with a disposable microfluidic channel, while other embodiments include a reusable microfluidic channel that is cleaned between uses, e.g., by removing the microfluidic channel from the device and flushing it with air, deionized water, or a cleaning solution.

[0012] It is understood that such a device performs a volumetric measurement which involves storage of sweat in the microfluidic channel. Thus, the flow measurement is done continuously, as the microfluidic channel fills. However, once it is full, it is no longer possible to continue the measurements without emptying the microfluidic channel, which has several disadvantages: either the collection area must be small in order to reduce the filling speed, or the microfluidic channel must be long to prolong the measurement, or a combination of the two must be used.

[0013] A first problem is that the use of a small collection area combined with a long microfluidic measurement channel can lead to problems arising from the friction exerted by walls delimiting the microfluidic channel on the collected sweat, forcing the eccrine glands to force more and more to emit sweat. In addition, reducing the collection area, to a few millimeters in diameter in general, results in a very significant loss of precision. Moreover, by reducing the collection area, an inference error is exponentially increased. Then, inevitable infiltrations of sweat from areas other than the collection area are the cause of errors that heavily influence the final measurement. This infiltration problem appears as soon as the user makes an intense effort.If, in addition, the device is fixed with adhesives, there are problems with detachment, allergy problems, problems with sweat pockets moving under the adhesive, potentially to the collection area.

[0014] Another problem with devices using an inlet placed on the skin and measuring sweat flow volumetrically, by storing sweat in the longest possible microfluidic channel, is sweat loss escaping from the collection area. Indeed, the sweat filling the long microfluidic flow measurement channel is subjected to increasing pressure. This pressure is directly supported by the eccrine glands that feed the microfluidic channel, i.e., the eccrine glands located in a particular area close to the inlet. This particular area is generally small, a few square millimeters, and therefore includes few eccrine glands. Indeed, too large an inlet is incompatible with this type of measurement by sweat storage, because there would be too many eccrine glands and the microfluidic channel could fill up too quickly depending on the person and their respective sweating rate.Thus, when the pressure increases during the filling of the microfluidic channel, leakage problems result at the inlet. It is observed that the use of a volumetric measurement with sweat storage presupposes the use of small inlets and requires sizing of the microfluidic channel dependent on the sweat flow rate of the user, because the same channel can fill slowly in one person and very quickly in another. For a given dimension, it is therefore impossible to provide a fixed duration of use, this varying very significantly from one user to another. The only solution is to provide different sizing and to propose a range of devices covering small, medium and large flow rates, which greatly complicates industrial exploitation of such a device.

[0015] Another problem is that such an arrangement of the device does not allow for optimized circulation of sweat inside the microfluidic channel.

[0016] Another problem is that such a device is not suitable for performing at least one measurement per minute in the microfluidic channel.

[0017] WO 2021 / 099610 describes devices and methods for measuring a subject's sweat rate using a wearable system. A sweat rate may be automatically determined based on one or more signals produced by a wetting sensor module in response to a presence of sweat in the wearable system. The one or more signals may be produced using a sweat presence monitoring device, e.g., comprising two or more electrodes that are operable to perform conductance measurements. In some embodiments, sweat drops are periodically collected by the wearable system and individually detected by the wetting sensor module such that the sweat rate is determined based on the periodic detection of the drops.

[0018] The wetting sensor module can indicate whether certain modules are wet and provide an estimate of the flow rate while the system is filling. For example, the device may include a series of electrodes installed in some or all of the modules. By making conductance measurements between pairs of electrodes, it is possible to measure whether there is ionic contact between them and therefore whether the path between them is wet. By using various combinations of electrodes, it is thus possible to track the progress of the fluid along the way, and therefore calculate an estimate of the flow rate using the known geometry and fluid capacity of the system.

[0019] A first problem lies in the fact that these measurements are random and imprecise, based on the presence or absence of drops, which is rather indicative of sweating or an absence of sweating but which does not allow for precise measurement of sweat flow.

[0020] A second problem is that the device focuses on identifying sweating by pore, which does not give a global view of the user's sweating.

[0021] The known devices of the prior art result in a number of problems which need to be resolved.

[0022] The present invention falls within this context and proposes a sweat analysis device capable of solving the above-mentioned problems. The analysis device is capable of analyzing the sweat secreted by the skin of a user against which the device is affixed.

[0023] In general, the device comprises a housing comprising a first face provided with a collection means arranged as a large sweat collector which is capable of collecting sweat emanating from several hundred pores to give an overall view of a user's sweating. The collection means is calibrated, shaped and sized to generate a continuous flow of sweat from the collected sweat and is optimized to maintain such continuity of the sweat flow.

[0024] The housing also comprises a second face equipped with a microelectronic chip which is capable of measuring, in real time inside a microfluidic channel, a concentration of NaCl, then deducing a sweat flow rate by analyzing a variation in conductance of the sweat before it is evacuated. This device is disposable and clips onto an armband allowing the reading and sending of data by remote communication means, such as Bluetooth or the like, in relation to the microelectronic chip to a receiving device, such as a mobile phone or the like. The transmitted data is then stored on a storage means to be analyzed and to provide performance statistics.

[0025] The sweat collector has a collection surface of between 5 cm 2 and 8.5 cm 2 , preferably included 6 cm 2 and 7 cm 2 , preferably still of the order of 6.25 cm2 ' to + / - 10%, which allows sampling at least 600 eccrine glands, particularly at the ventral level of the forearm for example. The sweat collector has a concave face bordered by a rim which encloses a collection area allowing a rapid and precise flow of sweat. The rim prevents sweat from escaping from the sweat collector which would make the measurement inaccurate. It is understood that the rim surrounds the collection surface. The concave face allows rapid collection of sweat and the formation of a regular flow of sweat. The rim and the collection surface delimit a determined collection volume, which is of the order of 500 mm 3 , to within + / - 10%.

[0026] The cuff exerts an appropriate pressure force on the sweat collector so that, thanks to the rim a few hundred microns high, the collection area is perfectly isolated from the rest of the body. As a result, sweat cannot cross the rim either to enter the collection area or to leave it. This results in suitable precision of sweat collection in relation to the collection surface. In other words, the sweat collected by the device comes solely and entirely from the collection surface of the device. Indeed, less contamination of the collection area can have very significant repercussions on the inference of the collection carried out. Also, the sweat collector has a concavity and reliefs allowing the rapid flow of sweat. The concavity is designed in such a way that a closing force of the cuff is transmitted to the rim of the sweat collector which puts pressure on the user's skin.This pressure results in a skin roll that the sweat collector hugs, without crushing the skin roll in order to allow a capillary phenomenon. The sweat collector includes hydrophobic zones that allow the channeling of the sweat that appears under the sweat collector and improve and channel a capillary movement of sweat towards a central orifice equipping the collection zone.

[0027] These provisions prevent the roll of skin surrounded by the edge forming when the cuff is closed from being crushed, so as not to suffocate the eccrine glands with excessive mechanical pressure.

[0028] These arrangements nevertheless make it possible to also impose additional hydraulic pressure to generate the continuous flow of sweat in order to measure a sweat flow rate by variation in conductance, while avoiding storing sweat.

[0029] For this purpose, a relationship between a sampled collection volume, a number of eccrine glands present in the collection area, a minimum sweat flow rate and a measurement frequency is evaluated, taking into account the dimensions of the microfluidic channel and the dimensions of the measuring electrodes used.

[0030] The use of the rimmed sweat collector advantageously allows a large area of ​​skin to be sampled and sweat to be obtained from more than 600 eccrine glands. First of all, the volume of sweat collected is considerably increased even during small efforts involving low sweating, of the order of 25 cl / hour, an average minimum flow rate of approximately 0.04 ml / hour (i.e. 40 mm 3 / hour). Such a flow rate is sufficient to fill the microfluidic channel with a volume of 7.4 mm 3of sweat in approximately 10 minutes, i.e. for a microfluidic channel with a section of 0.1 mm x 0.9 mm, the entire channel, which thus allows for an initial measurement of concentration and flow rate approximately 10 minutes after the start of sweating, then for a new series of measurements approximately every minute (new measurements independent of the previous ones since a new layer of sweat covers each of the two pairs of electrodes), even for low sweating.It should also be noted that in the case of vapor phase sweating, corresponding to physical activity at rest, this device (in particular thanks to the dimensional ratios between the collection zone and the microfluidic channel) allows the condensation of sweat in the collection zone which then flows in liquid phase in the microfluidic channel, allowing measurements to be obtained on time scales of the order of 30 minutes to one hour (for resting sweat rates of between 10 cl / hour and 25 cl / hour).

[0031] In order to have a good measurement at an affordable cost, the collection of an area covering at least 600 eccrine glands is essential, this allows the use of a microfluidic channel of 0.1 mm x 0.9 mm of passage section and channel length of the order of 60 mm to + / - 10%, and to insert two pairs of curvilinear electrodes 10 to 20 mm long for a height ranging from 30 to 40 microns and a width ranging from 200 to 300 microns. This results in an optimization of the sweat collector, from the size of the microfluidic channel to the dimensioning of the measuring electrodes and the sweat flow rate.

[0032] It is understood that without flow measurement, the cuff could not provide overall information about the user's body. Indeed, it is the statistical inference of the results from the sampled area of ​​the body that is relevant. This inference owes its accuracy to the measurement made on the sample and the flow rate is the most complex measurement to carry out since sweat is not stored.

[0033] For these reasons, it is advantageously proposed by the present invention to make a measurement based on a variation in conductance in the microfluidic channel. Thus, the measurement is made during the time when the sweat flows continuously in the microfluidic channel, before its ejection. It is noted that no storage of the sweat is carried out, the sweat flowing from an inlet orifice to an outlet orifice, thus solving the problems of sizing the microfluidic channel according to the sweat flow rate.

[0034] Such a type of measurement is achievable by the device of the present invention for several reasons taken alone or in combination. The device has a large collection area sized to generate a continuous flow of sweat, the device has a rim which surrounds the collection area ensuring a seal between the collection area and the outside of the collection area, which prevents sweat loss. The collection area constitutes a pump capable of generating the continuous flow of sweat. Thus, it was possible to observe on a user at rest with low sweating the formation of a continuous flow of sweat, in particular by condensation inside the microfluidic channel, due to its dimensions and its arrangement.The device has at least one microfluidic channel of appropriate size and conformation to facilitate a laminar flow of sweat minimizing possible disturbances, such as a diffusion phenomenon, inside the microfluidic channel and the device comprises at least two pairs of electrodes of appropriate dimensions. These characteristics enhance the reliability of the measurements. Thus, the collection volume and the volume of the microfluidic channel have been precisely determined to ensure a continuous flow of sweat successively bathing the two pairs of electrodes. It is all of these points that make it possible to carry out the measurement that will be described below.

[0035] It is understood that from a consistent choice of the characteristics of the device including the volume of the collection zone, the geometric conformation of the microfluidic channel, the dimensions of the microfluidic channel and the dimensions of the pairs of electrodes, such as their respective length in particular, it is possible to accurately measure the sweat flow rate.

[0036] Firstly, the large collection area, containing at least 600 eccrine glands, allows for the collection of a high flow rate of at least 0.1 ml / hour. The choice was made to size the collection area so that the collection area has a collection volume of 500 mm 3 , to within + / - 10%.

[0037] Second, the microfluidic channel houses at least two pairs of electrodes capable of measuring sweat conductance, including a first pair of curvilinear electrodes arranged upstream of a second pair of curvilinear electrodes inside the microfluidic channel. The two electrodes are separated by an electrode distance, and each measure the sweat conductance at a time interval At according to a flow rate. Each time the conductance of the liquid changes, a new measurement of the flow rate is made. The choice was made to size the volume of the microfluidic channel so that the microfluidic channel has a channel volume of 5.4 mm, to within + / - 10%.

[0038] When sweat flows, the first pair of electrodes measures a first conductance Ci, C2, ... . Cn, the Ci being spaced by a measurement frequency Fmes, for example 1 min (C2 is therefore measured with a one-minute interval from Ci and note that possibly Ci=C2, etc.)

[0039] The second pair of electrodes is spaced by the non-zero electrode distance of the first pair of electrodes, and the second pair of electrodes is strictly identical to the first pair of electrodes. The second pair of electrodes measures a second conductance C'i, C'2, .... C'n, the C'i being spaced by the same measurement frequency Fmes, for example 1 min (C'2 is therefore measured with a one-minute interval from C'1 and note that possibly C'i=C'2, etc...)

[0040] The second pair of electrodes measures the conductance of the continuous flow of sweat and the instant when the second conductance is equal to the first conductance is recorded. It was decided to observe this measurement concordance for the first pair of electrodes and for the second pair of electrodes to deduce the sweat flow rate accurately, the flow being laminar and continuous inside the microfluidic channel.

[0041] Also, the second pair of electrodes operates continuously, to determine the time interval Ati, At2, .... Atn which separates the conductance measurements Ci, C2, ....Cn of the first pair of electrodes and the conductance measurements Ci', C2', ... ,Cn' of the second pair of electrodes, which are such that Ci'=Ci, C2'— C2 ....Cn'=Cn knowing that the conductance measurement Ci' was made with a time interval Ati compared to the conductance measurement Ci, i=1 ... n. It follows that Ati is the time interval that the continuous flow of sweat of conductance Ci takes to travel the electrode distance D which separates the two electrodes.

[0042] In other words, it is from an equivalence of conductance measured by the second pair of electrodes compared to the first pair of electrodes, that is to say when the continuous flow of sweat of a given concentration of NaCl seen by the second pair of electrodes corresponds to that previously measured by the first pair of electrodes, that it is possible to deduce that it is indeed the same portion of the continuous flow of sweat which has successively crossed the first pair of electrodes, then the second pair of electrodes, and therefore to precisely determine a flow rate of sweat, this precision being obtained from the chosen dimensions of the microfluidic channel and the collection zone as well as the chosen conformation of the microfluidic channel, from a continuous laminar flow with minimized disturbances due to these dimensions and conformations.

[0043] These provisions are such that this flow meter is purely based on the quality of the electrodes and the fact that in a microfluidic situation the diffusion phenomenon is reduced. In other words, if the sweat flow increases in concentration from 30 to 32 mmol / liter, in the microfluidic channel there will be a section of sweat at 30 mmol / liter and another section of sweat with a concentration of 32 mmol / liter, the two sections being separated, in the microfluidic channel, by a thin front. Due to the diffusion phenomenon existing in a microfluidic channel which is reduced thanks to the spiral shape of the channel, it is understood that depending on the proximity of the second pair of electrodes we find the measurement of 32 mmol / liter recorded by the first pair of electrodes.

[0044] To this end, the method of the present invention is a method for analyzing sweat emitted by a user's skin, the method comprising a first step of collecting the sweat emitted by the user's skin by means of a collection means that comprises a first face of a housing to form a continuous flow of sweat.

[0045] The method comprises a second step of supplying the continuous flow of collected sweat to a means for analyzing the continuous flow of sweat which comprises a second face of the housing provided with a microfluidic channel.

[0046] The method comprises a third step of measuring a first conductance of the continuous flow of sweat by a first pair of electrodes housed inside the microfluidic channel.

[0047] The method comprises a fourth step of measuring a second conductance of the continuous flow of sweat by a second pair of electrodes housed inside the microfluidic channel and placed at an electrode distance from the first pair of electrodes.

[0048] The method comprises a fifth step of determining a time interval elapsed for the second conductance to be equal to the first conductance.

[0049] The method includes a sixth step of calculating a sweat flow rate produced by the user's skin.

[0050] The device for implementing such a method comprises a housing which has a first face intended to be in contact with the user's skin. The first face is equipped with a sweat collection means comprising a collection area of ​​a collection volume. The housing has a second face which is equipped with a sweat analysis means which comprises at least one microfluidic channel having a channel volume and housing a first pair of electrodes capable of measuring a first conductance of the sweat, and a second pair of electrodes capable of measuring a second conductance.

[0051] The device advantageously comprises at least one of the following technical characteristics, taken alone or in combination:

[0052] - a ratio between a collection volume and the volume of the canal is between 80 and 110, preferably in the order of 90 to + / - 10%,

[0053] - the microfluidic channel successively comprises a first linear portion, then a first semi-circular portion, then a second linear portion, then a second semi-circular portion, then a third linear portion,

[0054] - the second semi-circular portion houses the pairs of electrodes which are curvilinear

[0055] - the second semi-circular portion comprises a first half of the second semi-circular portion which houses the first pair of electrodes and a second half of the second semi-circular portion which houses the second pair of electrodes, - the microfluidic channel has a rectangular section,

[0056] - the rectangular section of the microfluidic channel is of the order of 0.09 mm 2 , to within + / - 10%.

[0057] - the collection area is surrounded by a rim,

[0058] - the collection means comprises at least one hydrophobic zone,

[0059] - the housing is made up of a single-piece assembly.

[0060] - the case is made from molded plastic material,

[0061] - the box is equipped with a microelectronic chip which includes calculation means and which is associated with communication means,

[0062] - the device comprises at least one cuff which is attached to a support housing the housing to hold the first face against the user's skin and to ensure contact on the user's skin of the collection means with a pressure greater than 15 g per cm 2 .

[0063] Other characteristics and advantages of the invention will become apparent from the description which follows on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the appended figures on the other hand, which are briefly described below:

[0064] [Fig. 1] is a schematic side illustration of an analysis device according to the present invention,

[0065] [Fig. 2] is a schematic illustration of a median sectional view of a housing constituting the analysis device illustrated in Fig. 1,

[0066] [Fig. 3] is a schematic illustration of a bottom view of the housing shown in Fig. 2 illustrating a means of collecting said device,

[0067] [Fig. 4] is a schematic illustration of a top view of a preferred alternative embodiment of the housing shown in Figures 2 and 3.

[0068] [Fig. 5] is a schematic illustration of a cross-sectional view of the microfluidic channel.

[0069] [Fig. 6] is a schematic illustration of a measurement block constituting the device illustrated in Figure 1. In [Fig. 1] and [Fig. 2], a device 1 is shown for analyzing sweat present on a user's skin P. It is understood from this that the device 1 is portable and is adapted to analyze the sweat generated by eccrine glands that comprise the user's skin P during physical exertion, the user being for example an athlete competing in a sporting event, or a patient whose sweat analysis may prove medically relevant. For this purpose, the device 1 comprises an armband 70, or a bracelet for holding the device 1 on the user, for example on an arm, a leg or the torso of the latter. It is noted that the cuff 70 is configured so that the skin P of the user forms a bulge under the effect of the pressure exerted by the device 1 on the skin P of the user.In particular, the cuff is capable of ensuring contact with the user's skin with the collection means with a pressure greater than 15 g per cm. 2 More particularly, the device 1 is arranged to be clipped, fitted, or fixed by any other holding means, on a support 60 which is provided with the cuff 70.

[0070] The support 60 comprises an opening 61 which is capable of housing a casing 2 constituting the device 1. The casing 2 comprises a first face 11 intended to be in contact with the skin P of the user and a second face 12, preferably opposite the first face 11 and preferably still parallel to the first face 11. It is understood that the opening 61 opens out through the casing 2 so that the first face 11 is in contact with the skin P of the user.

[0071] The housing 2 is made up of a single-piece assembly in the sense that the housing 2 is formed from an inseparable assembly, except from an alteration or even a destruction of the housing 2. For this purpose, the housing 2 is for example made by molding a plastic material in particular.

[0072] In [Fig. 3], the first face 11 is equipped with a means 100 for collecting sweat which comprises a collection zone 101 having a collection surface S. The collection zone 101 constitutes the first face 11 and is included inside a rim 13 which the first face 11 comprises. The rim 13 is arranged so that, when the cuff 70 presses on the device 1, the user's skin P forms a bead opposite the collection zone 101. In addition, the rim 13 is arranged to prevent the sweat produced by the bead from being evacuated from the collection zone 101 and to prevent sweat produced outside the collection zone 101 from being admitted inside the latter. In other words, the rim 13 is shaped into a barrier to the collection area 101 that cannot be crossed by sweat.It is understood that the collection zone 101 is arranged to recover the sweat produced by the eccrine glands of the skin ridge P and that the collection zone 101 has the collection surface S expressed in mm. 2 . For example, the collection surface S is for example of the order of 6.25 cm 2 , to within + / - 10%, if the collection zone 101 is shaped substantially into a square with sides of 2.5 centimeters. Furthermore, the collection zone 101 has a collection volume V which is of the order of 500 mm 3 , to within + / - 10%. It is understood that the collection volume V is delimited by the first face 11, the rim 13 and a plane P1 in which a free edge 13' of the rim 13 is inscribed, the free edge 13' of the rim 13 being intended to be in contact with the skin P of the user.

[0073] The second face 12 is equipped with a sweat analysis means 200 which comprises at least one microfluidic channel 120, as illustrated in FIGS. 4 and 5.

[0074] The collection means 100 and the analysis means 200 are connected by means of a supply means 300, more particularly visible in [Fig. 2], which is arranged as a connecting means between the collection means 100 and the analysis means 200, by connecting the first face 11 and the second face 12. According to a preferred embodiment, the supply means 300 comprises at least one conduit 3 which extends for example orthogonally to the first face 11 and to the second face 12. The conduit 3 extends between an inlet orifice 31 equipping a first center A1 of the first face 11 and an outlet orifice 32 equipping a second center A2 of the second face 12.

[0075] The collection means 100 comprises at least one relief 113 which constitutes a sweat guide ramp, the sweat tending to flow along the relief 113 towards the first center A1. Preferably, the reliefs 113 are in plurality and are radially extended from the inlet orifice 31 towards the peripheral rim 13. More particularly, each relief 113 extends between a first end 41 placed on a circle C arranged around the first center A1 and a second end 42. Certain reliefs 113 comprise a second end 42 which may constitute the peripheral rim 13, while other reliefs 113 comprise a second end 42 which is arranged at a non-zero end distance X from the rim 13. It is noted that the reliefs 113 are indifferently of a parallelepiped conformation, a sinusoidal conformation or the like.

[0076] The collection means 100 preferably comprises at least one hydrophobic zone 111. The hydrophobic zone 111 is for example obtained by laser nanostructuring of the first surface 11 of the housing 2.

[0077] The collection means 100 is preferably concave, so as to facilitate a flow of sweat from the hydrophobic zone 111 towards the first center A1 which forms the low point of the concavity of the collection zone 101. To further facilitate such a flow, the inlet orifice 31 is arranged in a funnel.

[0078] In [Fig. 4], the analysis means 200 comprises the microfluidic channel 120 fluidically connected to the hydrophobic zone 111 via the supply means 300. The microfluidic channel 120 extends between an inlet 120a equipping the conduit 3 and an outlet 120b equipping a peripheral edge 13' of the second face 12. Between the inlet 120a and the outlet 120b, the microfluidic channel 120 has a channel length L' which is of the order of 60 mm, to within + / - 10%. The microfluidic channel 120 comprises at least two measurement zones 201a, 201b each capable of housing at least one pair of electrodes 22a, 22b.

[0079] Referring also to [Fig. 5], the microfluidic channel 120 is of rectangular cross-section. The microfluidic channel 120 is delimited by an upper wall 121 and a lower wall 122 spaced apart from each other by a first distance D1 which is of the order of 100 pm to within + / - 10%. The microfluidic channel 120 is also delimited by a first side wall 123 and a second side wall 124 spaced apart from each other by a second distance D2 which is of the order of 900 pm to within + / - 10%. Such a conformation of the microfluidic channel 120 is a deliberate choice which notably allows a laminar flow, free from turbulence and disturbance to the sweat which circulates inside the microfluidic channel.The microfluidic channel 120 has a channel volume V' that extends between the inlet 120a and the outlet 120b and is located at the end of the microfluidic channel 120 such that the channel volume V' from the inlet point to the outlet point is between 5 and 6 mm. 3 , preferably equal to 5.4 mm 3 .

[0080] In [Fig. 4], the microfluidic channel 120 successively comprises a first linear portion 131 of a first length L1 which is of the order of 4.4 mm to within + / - 10%, then a first semi-circular portion 132 whose first side wall 123 is inscribed on a first arc of a circle of a first radius of curvature R1 which is of the order of 4.6 mm to within + / - 10%, then a second linear portion 133 of a second length L2 which is of the order of 5 mm to within + / - 10%, then a second semi-circular portion 134 whose first side wall 123 is inscribed on a second arc of a circle of a second radius of curvature R2 which is of the order of 4.6 mm to within + / - 10%, then a third linear portion 135 of a third length L3 which is of the order of 11 .6 mm to + / - 10%.Such a spiral conformation of the microfluidic channel 120 is again a deliberate choice which offers a guarantee of laminar flow, free from turbulence and disturbance to the sweat circulating inside the microfluidic channel. It follows that the microfluidic channel has a channel length L' which is of the order of 60 mm, to within + / - 10%.

[0081] The two pairs of electrodes 22a, 22b are curvilinear and are distributed inside the second semi-circular portion 134. More particularly, the second semi-circular portion 134 comprises a first half of the second semi-circular portion 134a which houses the first pair of electrodes 22a and a second half of the second semi-circular portion 134b which houses the second pair of electrodes 22b. Thus, and advantageously, a ratio between the collection volume V and the volume of the channel V' is between 80 and 110, preferably of the order of 92.5 to within + / - 10%.

[0082] Such a ratio provides optimized circulation of sweat inside the microfluidic channel 120. Thus, such a device 1 is suitable for carrying out at least one measurement per minute in a microfluidic channel 120 having a passage section of less than 0.1 mm 2 , and in particular a passage section of the order of 0.09 mm 2 to within + / - 10%, the microfluidic channel 120 being of a length of the order of 6 cm to within + / - 10%.

[0083] Preferably, the pairs of electrodes 22a, 22b are in plurality and are arranged in distinct measurement zones 201a, 201b, the pairs of electrodes 22a, 22b are indifferently selective or non-selective to obtain data relating to a water loss; an ion concentration; a Na+ ion concentration; a Cl- ion concentration; a lactate concentration; a temperature and / or a calorie loss.

[0084] The microfluidic channel 120 comprises a first measurement area 201a which houses a first pair of electrodes 22a such as a pair of electrodes intended to measure a conductance of sweat.

[0085] The microfluidic channel 120 comprises a second measurement zone 201 b which houses a second pair of electrodes 22 b identical to the first pair of electrodes 22 a.

[0086] The first pair of electrodes 22a and the second pair of electrodes 22b are spaced apart from each other by a non-zero electrode distance D taken inside the microfluidic channel 120.

[0087] In [Fig. 6], to measure the concentration of NaCl present in the continuous flow of sweat and to determine the sweat flow rate, two measuring blocks 24 were made with a voltage generator 25, a divider bridge 26 and two converters 27 of the Vrms / DC type. The output voltages Ve of the converters 27 are then sent to a single microcontroller 28 constituting an electronic chip 23, visible in [Fig. 2]. The voltage generator 25, equipped with a capacitor, is set to 200 mV and 200 KHz to power the divider bridge 26.

[0088] The input of the divider bridge starts with a 400 Q resistor R and ends with a screen-printed electrode, with validatable conductivity and NaCI dependent, before joining the ground M.

[0089] A first Vrms to DC converter is used to read the voltage across the voltage generator Ve and a second Vrms to DC converter is used to read the voltage across the variable electrode Vs. The output voltages of the converters 27 are sent back to the microcontroller 28.

[0090] Preferably, the second face 12 of the housing 2 houses the microelectronic chip 23 as well as the measuring blocks 24 in relation to the electrodes 22a, 22b housed inside the measuring zones 201a, 201b. The microelectronic chip 23 comprises calculation means capable of carrying out the determination and calculation steps of the method described below.

[0091] These calculation methods are particularly suitable for deducing the conductance Ci of the continuous flow of sweat from the following relationship:

[0092] Then, a concentration X in NaCI is deduced from the following formula:

[0093] X = 0.0868 Ci2 + 5.4606 Ci - 0.097

[0094] It is noted that the microcontroller 28 is connected to a voltage regulator 29, a battery charger 30, an accelerometer 31, a temperature sensor 32 and a humidity sensor 33, the voltage regulator 29 and the battery charger 30 being connected to an accumulator 34.

[0095] The microelectronic chip 23 is for example in relation with at least one NFC / RFID chip or physical connectors (connection pads or sockets), a rechargeable microbattery and a Bluetooth module which equip the support 60. According to one embodiment, the device 1 comprises means for storing said data.

[0096] These provisions are such that the device 1 is capable of implementing an analysis method of the present invention.

[0097] More particularly, the analysis method of the present invention comprises:

[0098] - a first step of collecting the sweat emitted by the skin P of the user by means of a collection means 100 which the first face comprises

[0099] 11 of the housing 2 to form a continuous flow of sweat,

[0100] - a second step of supplying the continuous flow of sweat collected to a means 200 for analyzing the continuous flow of sweat that the second face comprises

[0101] 12 of the housing 2 provided with the microfluidic channel 120

[0102] - a third step of measuring the first conductance Ci, C2, .... Cn of the continuous flow of sweat by the first pair of electrodes 22a housed inside the microfluidic channel 120,

[0103] - a fourth step of measuring the second conductance Ci', C2', .... Cn' of the continuous flow of sweat by the second pair of electrodes 22b housed inside the microfluidic channel 120 and placed at the electrode distance D from the first pair of electrodes 22a,

[0104] - a fifth step of determining a time interval Ati, At2, .... Atn elapsed so that the second conductance Ci', C2', .... Cn' is equal to the first conductance Ci, C2, .... Cn, and

[0105] - a sixth step of calculating a sweat flow rate produced by the user's skin P

Claims

Claims

1. Method for analyzing sweat emitted by a user's skin (P), the method comprising a first step of collecting the sweat emitted by the user's skin (P) by means of a collection means (100) that comprises a first face (11) of a housing (2) to form a continuous flow of sweat, a second step of supplying the collected continuous flow of sweat to a means (200) for analyzing the continuous flow of sweat that comprises a second face (12) of the housing (2) provided with a microfluidic channel (120), the method comprising a third step of measuring a first conductance (Ci, C2, .... Cn) of the continuous flow of sweat by a first pair of electrodes (22a) housed inside the microfluidic channel (120) and a fourth step of measuring a second conductance (Ci', C2', ....Cn') of the continuous flow of sweat by a second pair of electrodes (22b) housed inside the microfluidic channel (120) and placed at an electrode distance (D) from the first pair of electrodes (22a), characterized in that the method comprises a fifth step of determining a time interval (Ati, At2, .... Atn) elapsed so that the second conductance (Ci', C2', .... Cn') is equal to the first conductance (Ci, C2, ... . Cn) and a sixth step of calculating a flow rate of sweat produced by the skin (P) of the user.

2. Device (1) for implementing a method according to the preceding claim, characterized in that the device (1) comprises a housing (2) which has a first face (11) intended to be in contact with the skin (P) of the user, the first face (11) being equipped with a means (100) for collecting sweat comprising a collection zone (101) of a collection volume (V), the housing (2) having a second face (12) which is equipped with a means (200) for analyzing sweat which comprises at least one microfluidic channel (120) of a channel volume (V') housing a first pair of electrodes (22a) capable of measuring a first conductance (Ci, C2,.... Cn) of the sweat, and a second pair of electrodes (22b) capable of measuring a second conductance (Ci ', C2', ... . Cn').

3. Device (1) according to claim 2, characterized in that a ratio between the collection volume (V) and the volume of the channel (V') is between 80 and 110.

4. Device according to any one of claims 2 and 3, characterized in that the microfluidic channel (120) successively comprises a first linear portion (131), then a first semi-circular portion (132), then a second linear portion (133), then a second semi-circular portion (134), then a third linear portion (135).

5. Device according to claim 4, characterized in that the second semi-circular portion (134) houses the pairs of electrodes (22a, 22b) which are curvilinear.

6. Device according to claim 5, characterized in that the second semi-circular portion (134) comprises a first half of the second semi-circular portion (134a) which houses the first pair of electrodes (22a) and a second half of the second semi-circular portion (134b) which houses the second pair of electrodes (22b).

7. Device according to any one of claims 2 to 5. 6, characterized in that the microfluidic channel (120) has a rectangular section.

8. Device according to any one of claims 2 to 5. 7, characterized in that the rectangular section of the microfluidic channel (120) is of the order of 0.09 mm 2 , to within + / - 10%.

9. Device (1) according to any one of claims 2 to 8, characterized in that the collection zone (101) is surrounded by a rim (13).

10. Device (1) according to any one of claims 2 to 9, characterized in that the collection means (100) comprises at least one hydrophobic zone (111).

11. Device (1) according to any one of claims 2 to 10, characterized in that the housing (2) consists of a single-piece assembly.

12. Device (1) according to any one of claims 2 to 11, characterized in that the housing (2) is made by molding a plastic material.

13. Device (1) according to any one of claims 2 to 12, characterized in that the housing (2) is equipped with a microelectronic chip (23) which comprises calculation means and which is associated with communication means.

14. Device (1) according to any one of claims 2 to 13, characterized in that the device (1) comprises at least one cuff (70) which is attached to a support (60) housing the housing (2) for holding the first face (11) against the skin (P) of the user and for ensuring contact on the skin (P) of the user of the collection means (100) with a pressure greater than 15 g per cm 2 .

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