Microfluidic Sweat Sensor with Humidity Control Chamber
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Solution Overview
Problem
Current sweat sensing technologies face challenges in continuous and reliable monitoring due to sweat evaporation, especially from small skin areas, leading to variable results and limited application beyond cystic fibrosis diagnostics and drug/alcohol abuse testing.
Innovation Solution
A device with a microfluidic structure that collects sweat from a specific skin area and uses trans-epidermal water from an adjacent area to maintain humidity, reducing evaporation and ensuring consistent biomarker measurement through a collection chamber and sensor system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If sweat is collected from a small skin area for sensing, then the device size and invasiveness are reduced, but sweat evaporation increases leading to variable measurement results
Solution Approach 1:
A humidity control chamber containing a humidity control solution is introduced as an intermediary between the sweat collection chamber and the external environment. This mediator maintains a controlled humidity environment that prevents excessive evaporation of collected sweat, thereby ensuring measurement reliability even when collecting from small skin areas.
2Duration of action of moving object
If sweat is collected continuously for prolonged monitoring, then continuous health data is obtained, but sweat evaporation leads to concentration changes and dried component accumulation
Solution Approach 1:
The humidity control solution acts as a mediator that maintains stable humidity conditions throughout prolonged monitoring periods, preventing sweat evaporation and composition changes.
Solution Approach 2:
The design separates the humidity control function from the sweat collection function by using a dedicated humidity control chamber with its own solution, allowing independent optimization of both functions for prolonged stable operation.
3Quantity of substance
If absorbent pads with large area are used for sweat collection, then sufficient sweat quantity is obtained, but the device becomes less wearable and more obtrusive
Solution Approach 1:
Capillary forces in microfluidic channels are utilized to transport sweat from the collection chamber to the sensing elements, eliminating the need for large absorbent pads. This hydraulic approach enables sufficient sweat collection and transport within a compact, wearable form factor.
Solution Approach 2:
The transition from two-dimensional pad-based collection to three-dimensional microfluidic channel-based transport allows efficient sweat collection and delivery in a compact volume, improving wearability while maintaining sufficient sweat quantity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device enhances sweat availability and reduces biomarker concentration variability, enabling continuous and reliable monitoring of sweat parameters over prolonged periods, suitable for wearable use.
Implementation Method 1
Fluid, i.e. sweat or trans-epidermal water (TEW), is excreted in the second skin area. The device is configured to utilize this sweat or TEW, as a source of humidity to moisten its microfluidic structure
Implementation Method 2
The device is configured to utilize this sweat or TEW, as a source of humidity to moisten its microfluidic structure, increase the vapor pressure within its microfluidic structure and hence reduce evaporation of sweat
Data Source
Figure 1a~1b
Figure 2~3
Figure 4
AI summary
A device (1) for determining sweat parameters of a user is provided, which device comprises a microfluidic structure (10) having a collection chamber (16) configured to collect sweat from a first skin area (i), and a sensor (12) configured to determine a sweat parameter from sweat from the first skin area (i). The device also comprises an evaporation control chamber (14), which is connected to the microfluidic structure (10), configured to utilize fluid collected at a second area (ii) to moisten the microfluidic structure (10). The moistening of the microfluidic structure (10) aims to increase the available sweat for the sensor to determine a sweat parameter, by increasing the humidity inside the microfluidic structure (10) and thus, decreasing the evaporation of sweat. A method for determining sweat parameters of a user is also provided.