Microfluidic Sweat Monitoring with Passive Capillary Valves
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Solution Overview
Problem
Current microfluidic systems for biofluid monitoring face challenges such as irregular sampling, contamination, and cross-contamination due to the lack of control over fluid dynamics and the need for multiple measurement chambers, which limits their applicability for continuous and accurate monitoring of biofluids like sweat.
Innovation Solution
A microfluidic system with a single measuring chamber, a passive fluid pump, and a retention valve that generates capillary pressure greater than biofluid generation pressure, allowing for continuous monitoring with chronological assurance and reducing cross-contamination by temporarily stopping fluid flow to ensure accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional sweat sampling methods use occlusive bandages to collect sweat, then sweat can be collected, but skin irritation occurs and only small volumes are obtained
Solution Approach 1:
The patent introduces a microfluidic device as an intermediary between the skin and the analysis system. The device includes a collection chamber with a membrane that allows sweat to pass through while preventing direct contact between the occlusive material and the skin, thereby eliminating skin irritation while still collecting sufficient sweat volume for analysis
Solution Approach 2:
The sampling system is segmented into multiple functional components: a collection chamber for sweat accumulation, a membrane for selective passage, a microfluidic channel for transport, and a analysis chamber. This segmentation allows each component to perform its specific function optimally, enabling both comfortable wear and sufficient sample collection
2Object-affected harmful factors
If non-occlusive bandages are used for sweat collection, then skin comfort is maintained, but water evaporates causing false concentration measurements
Solution Approach 1:
The membrane in the collection chamber acts as an intermediary that prevents water evaporation while allowing sweat collection. The membrane creates a sealed environment that maintains sweat composition integrity, ensuring accurate concentration measurements while the external collection interface remains comfortable for the user
Solution Approach 2:
The microfluidic system creates a controlled copy of the sweat collection and analysis process, where sweat is collected in a sealed chamber, transported through controlled channels, and analyzed in a dedicated chamber. This controlled environment replicates ideal sampling conditions that prevent evaporation and maintain measurement accuracy
3Measurement precision
If multiple measuring chambers are used to ensure chronological assurance and avoid cross-contamination, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent employs dynamic passive valves that automatically open and close based on pressure differentials to control fluid flow between chambers. This dynamic control mechanism ensures chronological assurance and prevents cross-contamination between samples without requiring multiple independent chambers, thereby reducing device complexity while maintaining measurement precision
Solution Approach 2:
The passive valves in the system are self-regulating, automatically controlling fluid flow based on pressure conditions without external intervention. This self-service mechanism ensures proper temporal sequencing of measurements and prevents cross-contamination through automatic valve actuation, simplifying the overall system architecture
4Extent of automation
If passive capillary valves and pumps are used for autonomous operation, then external energy sources are eliminated, but control over fluid dynamics becomes limited
Solution Approach 1:
The system uses self-service passive capillary pumps and valves that automatically control fluid flow based on pressure differentials and surface tension forces. These components autonomously regulate sweat collection, transport, and release without external energy sources, achieving both autonomous operation and adequate fluid dynamics control for the application
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
Enables continuous, reliable, and reproducible monitoring of biofluids over extended periods with reduced complexity and dimensions, addressing issues of irregular sampling and cross-contamination, and allowing for multiple independent measurements without the need for external energy sources.
Implementation Method 1
a passive fluid pump, fluidly communicated with the measuring chamber, and adapted to generate a capillary pressure greater than the biofluid generation pressure
Implementation Method 2
The retention passive valve is configured to stop biofluid flow towards the fluid pump for a certain period of time, when the measuring chamber is filled with biofluid
Data Source
AI summary
The present invention refers to a microfluidic system based on passive capillary valves and pumps, that allows a discontinuous and autonomous measurement process for extensive periods of time. The microfluidic system comprises: at least one measuring chamber, at least one inlet for the input of a biofluid, a microfluidic intake channel fluidly communicating the inlet with the measuring chamber, at least one sensor suitable for measuring a parameter of an analyte of a biofluid. A passive fluid pump is fluidly communicated with the measuring chamber, and it is adapted to generate a capillary pressure greater than the biofluid generation pressure. A retention valve is interposed between the measuring chamber and the fluid pump, and the retention passive valve is configured to stop flow of biofluid for a certain period of time, when the measuring chamber if filled with biofluid. The invention provides a robust device, capable of collecting and conveying a biofluid, preferably sweat, for repetitive and electrochemical measurements.