Devices for integrated, repeated, prolonged, and/or reliable sweat stimulation and biosensing
A sweat sensing device includes a plurality of sweat collection pads communicating with a sensor. Each of the pads is activated by a timing circuit which allows one or more of the pads to be activated at a selected time and subsequent deactivated after a defined period of time. This allows for selective collection of sweat from a plurality of pads over a prolonged period of time. An impedance measuring circuit can be employed to determine if one or more of the pads becomes disconnected, in order to avoid irritation. Further, the devices can use a common microfluidic device which both transports sweat activating substance, such as pilocarpine, to the surface of the skin and directs sweat away from the skin to a sensing device.
1. An apparatus to measure or collect sweat over an extended period of time, comprising:
a plurality of sweat stimulation pads, wherein each sweat stimulation pad includes: a sweat stimulant, an electrode, and a sweat stimulant carrying medium, and wherein the pad is adapted to deliver the sweat stimulant to skin to generate sweat;
one or more sweat collectors;
one or more sensors for measuring a characteristic of an analyte in sweat, wherein the sensor is in fluidic communication with the sweat collector; and
a timing circuit adapted to selectively activate and deactivate said plurality of sweat stimulation pad for one or more limited periods of time, wherein each sweat stimulation pad is selectively operable by said timing circuit.
2. The apparatus of claim 1 wherein at least two pads have different sweat stimulation rates.
3. The apparatus of claim 1 wherein each of said pads includes a sweat flow path leading to a sensor.
4. The apparatus of claim 3 wherein each sweat flow path leads to the same sensor.
5. The apparatus of claim 3 wherein each flow path leads to a separate sensor.
6. The apparatus of claim 3 wherein at least one flow path includes a gate selectively operable to allow sweat flow only during a selected time.
7. The apparatus of claim 1 , further comprising an electrical sensor associated with each sweat stimulation pad, said sensor adapted to detect direct or indirect contact between said pad and skin, which permits deactivation of said pad.
8. The apparatus of claim 7 wherein said electrical sensor detects impedance.
9. The apparatus of claim 1 , further comprising at least one sensor which receives sweat resulting from stimulation by said stimulation pad wherein said sensor and said stimulation pad are not fluidically coupled.
10. The apparatus of claim 1 wherein at least one sweat stimulation pad of the plurality of sweat stimulations pads is configured to stimulate an area of less than 50 mm 2 to reduce irritation perceived by the user of the apparatus.
11. The apparatus of claim 1 wherein at least one sweat stimulation pad of the plurality of sweat stimulations pads is configured to stimulate an area of less than 10 mm 2 to reduce irritation perceived by the user of the apparatus.
12. The apparatus of claim 1 wherein at least one sweat stimulation pad of the plurality of sweat stimulations pads is configured to stimulate an area of less than 2 mm 2 to reduce irritation perceived by the user of the apparatus.
13. The apparatus of claim 1 wherein each of said collection pads includes a gate operable to prevent flow of sweat to a sensor.