CONDUCTIVE POLYMERIC COMPOSITION

Abstract

The invention relates to an ionic conductive polymeric composition defined by the following general formula: (PH)x+(SOH)y+z(MCl); in which: —PH represents a polymer containing protic functions; —SOH represents a plasticizing polyol with a molecular mass of not less than 75 g/mol and not greater than 250 g/mol, in the form of discrete molecules; —MCl represents sodium or potassium chloride (M=Na or K); —0.3≤x/y≤3, x representing the amount by weight of the polymer PH, and y the amount by weight of the polyol SOH; —0.5%≤z≤15%, z representing the percentage by weight of MCl relative to the polyol SOH. Said polymeric composition may be used particularly as conductive material in electrodes for measuring electrophysiological signals.

Claims

1. An ionically-conductive polymer composition defined by the following general formula:
(PH)x+(SOH)y+z(MCl); wherein: PH represents a polymer containing protic functions constituted by hydroxyl groups; SOH represents a plasticizing polyol having a molecular mass greater than or equal to 75 g/mol and less than or equal to 250 g/mol, in the form of discrete molecules; MCl represents sodium chloride or potassium chloride (M=Na or K); 0.3≤x/y≤3, x representing the amount by weight of the polymer PH, and y representing the amount by weight of the polyol SOH; 0.5%≤z≤15%, z representing the weight percentage of MCl relative to the polyol SOH.

2. The polymer composition according to claim 1, wherein the polymer PH is a poly(vinyl alcohol) with a degree of saponification of greater than or equal to 60% and less than or equal to 100%, and an average molecular mass M.sub.w of greater than or equal to 5×10.sup.4.

3. The polymer composition according to claim 1, wherein the plasticizing polyol SOH is chosen from glycerol, propylene glycol, dipropylene glycol or mixtures thereof.

4. The polymer composition according to claim 1, wherein the ratio x/y is such that 0.50≤x/y≤1.00.

5. The polymer composition according to claim 1, wherein the percentage z is 1%≤z≤15%.

6. The polymer composition according to claim 1, wherein it further comprises an electrically-conductive particulate carbon-based filler, and in that the weight percentage of said conductive filler relative to the polymer PH is from 20% to 50%.

7. The polymer composition according to claim 6, further comprising a redox couple enabling the transition from ionic conductivity to electronic conductivity.

8. An electrode for measuring an electrophysiological signal comprising a polymer composition according to claim 1.

9. A device for measuring an electrophysiological signal comprising one or more electrodes according to claim 8.

Description

EXAMPLE 1: PREPARATION OF CONDUCTIVE POLYMER COMPOSITIONS

[0037] Mixtures in various proportions of polyvinyl alcohol, glycerol and sodium chloride were produced.

[0038] The polyvinyl alcohol (M.sub.w˜195,000, SIGMA-ALDRICH), the glycerol (reagent grade, ≥99.0% (GC), SIGMA-ALDRICH) and the sodium chloride are weighed in a beaker and dissolved in demineralized water (PVA/water weight ratio=1:10) by heating to around 60° C. for around 1 hour, with stirring using a magnetic stirrer bar.

[0039] In another series of experiments, a polymer composition filled with graphite powder was prepared, according to the protocol described above, except that the graphite powder is added to the other constituents prior to dissolving. Various concentrations of graphite powder (Graphit GNP 12, purity 99.5%, particle size 16-63 μm) were tested.

EXAMPLE 2: MANUFACTURE OF ELECTRODES

[0040] When the solution of polymer composition has reached a viscosity sufficient to stop the rotation of the magnetic stirrer bar, it can be used for the manufacture of the electrodes.

[0041] Flat electrode: This electrode is prepared by immersing a Gold Cup (OpenBCI) passive gold electrode in the solution of polymer composition for a few moments. Once the gold electrode is coated with composition, the assembly is left to dry in the open air and at room temperature for at least 3 days approximately.

[0042] Spiked electrode: An electrode mold with spikes is manufactured by 3D printing (material: polylactic acid). This mold is filled with the solution of polymer composition and a Gold Cup electrode is then immersed therein. The assembly is left to dry in the open air and at room temperature for at least 1 week, before removing from the mold.

EXAMPLE 3: TEST OF THE CONDUCTIVE PROPERTIES OF THE ELECTRODES

1) Measurement of the Signal-to-Noise Ratio

[0043] The signal-to-noise ratio (SNR) is a ratio of signal power to noise power. It is a measure of the fidelity of signal transmission.

[0044] In order to determine it, the electrodes manufactured as described above were tested to measure the α (8-12 Hz) activity by EEG.

EEG Setup:

[0045] 3 electrodes were used for each measurement: a measurement electrode, a reference electrode, and a polarization (bias) electrode.

[0046] In the case of the flat electrodes, all the electrodes were placed on areas of hairless skin, namely on the forehead for the measurement electrode, and on the lobe of each ear for the reference electrode and the bias electrode.

[0047] In the case of using spiked electrodes, the measurement electrode is placed on the top of the cranium (vertex: Cz position according to the International System 10-20) and the reference and bias electrodes on the lobe of each ear.

[0048] The measurements are carried out over 2 sessions, of 2 minutes each, 1 minute with eyes open, and 1 minute with eyes closed (the power in the α band increasing when the eyes are closed).

Calculation of the Signal-to-Noise Ratio:

[0049] The relative power of alpha activity is calculated using the following formula: Relative power=alpha (8-12 Hz) power/Total power of the signal (1-60 Hz) The signal-to-noise ratio (SNR) is then calculated as described by Tautan et al. (Proc. 7th International Conference on Biomedical Electronics and Devices; Biodevices 2014).

[0050] The higher the SNR, the more sensitive the electrode.

Influence of the PVA:Glycerol Ratio on the Signal-to-Noise Ratio

[0051] The SNR is calculated as described above, for various PVA:glycerol proportions, with a constant concentration of NaCl of 5% by weight relative to the glycerol. The amount of PVA is used as reference. The theoretical proportion of glycerol increases from 0.66 to 1.75.

[0052] The results are illustrated by table 1 below:

TABLE-US-00001 TABLE 1 PVA:Glycerol SNR Average SNR 1:0.66 / / 1:1.03 4.1083 5.1026 1:1.01 5.3627 1:1.01 6.0968 1:1.55 5.3691 5.4716 1:1.52 4.9488 1:1.53 6.0968 1:1.75 5.2216 /

[0053] For the lowest amounts of glycerol (PVA:glycerol ratio<1), no EEG signal was able to be detected. By increasing the proportion of glycerol, the SNR increases, but decreases again for the highest amount of glycerol. Furthermore, in the case of the PVA:glycerol ratio of 1:1.75 glycerol, exudation of glycerol after drying is observed, making the electrode unsuitable for use.

Influence of the Concentration of NaCl on the Signal-to-Noise Ratio

[0054] The influence of the concentration of NaCl was then tested. The results are illustrated in table 2 below. The % of NaCl indicated are weight percentages relative to the glycerol (the saturation concentration of NaCl in the glycerol is 7.5%).

TABLE-US-00002 TABLE 2 PVA:Glycerol NaCl (g) [NaCl] (% w/w) SNR Average SNR 1:1.52 0.04 3.15 / / 1:1.55 0.05 4.90 5.3691 5.4716 1:1.52 0.10 5.00 4.9488 1:1.53 0.08 4.95 6.0968 1:1.46 0.08 6.84 4.0919 3.6745 1:1.51 0.08 6.96 3.4859 1:1.46 0.07 6.86 3.4457 1:1.52 0.12 9.76 6.4631 6.1944 1:1.48 0.10 9.80 5.8284 1:1.47 0.11 11.00 6.2917

[0055] For the lowest concentrations of NaCl, no EEG signal was able to be detected. When the concentration increases, the signal becomes detectable and the SNR increases to reach an optimum at around 5% NaCl. However, when the saturation concentration is approached, the SNR decreases. It is assumed that this decrease could be due to the fact that the presence of too large an amount of ions hinders the mobility thereof. The SNR increases again for supersaturated concentrations. This could be explained by the deposition of salts on the surface of the electrodes after drying, which would increase the conductivity. However, at these high concentrations of NaCl, a deterioration of the surface of the electrodes, which take on an oily appearance and are unsuitable for use, is also observed.

[0056] Tests were also carried out with polymer compounds filled with graphite powder, to evaluate the influence of the graphite filler.

[0057] The results are illustrated in table 3 below. As above, the % of NaCl indicated are weight percentages relative to the glycerol.

TABLE-US-00003 TABLE 3 Graphite (g) PVA:Glycerol:Graphite [NaCl] (% w/w) SNR 0.12 1:1.52:0.18 5.83 / 1.01 1:1.50:0.51 5.67 8.5763

[0058] For the lowest amount of graphite (18% by weight of PVA) no signal is detected. However, for a larger amount, a significant increase in the SNR is observed.

2) Measurement of the Ionic Conductivity

[0059] The ionic conductivity properties of an electrode of the invention (PVA:glycerol ratio=1:1.52; % by weight of NaCl relative to the glycerol=5%) were compared with those of dry electrodes from the prior art: FOCUS Dry Active EEG Electrodes (TRANSCRANIAL); Flex Sensor (COGNIONICS); DREEM electrode (DREEM).

[0060] The impedance of each of the electrodes was measured using an Analog Discovery 2 (DIGILENT) multimeter, and the results represented in the form of a Nyquist diagram.

[0061] The results are illustrated by FIG. 1.

[0062] Key to FIG. 1: x-axis: real part of impedance Z′ (in ohms); y-axis: imaginary part of impedance Z″ (in ohms); : electrode of the invention; Δ: COGNIONICS electrode; X: DREEM electrode; □: FOCUS electrode.

[0063] In the case of the electrode of the invention, the plot of the diagram is formed by a semicircle and a straight line. The semicircle represents a relaxation due to the movement of the ions at high frequencies and the straight line at low frequency represents the polarization at the electrodes. This plot confirms that this electrode is an ionic conductor.

[0064] In the case of the electrodes from the prior art, the plot of the diagram mainly shows clusters of points grouped on the x-axis, and no semicircle representing the movement of the ions is observed. This indicates that the materials of these electrodes are electronic conductors but are not ionic conductors.