Microfluidic Chip Pressure Sensing with Color-Switching Hydrogels
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Solution Overview
Problem
Existing microfluidic devices face challenges in reliable pressure sensing due to the need for fully integrable sensors that are sensitive to minute pressure changes without modifying the fluid flow geometry, and existing methods either require external electrical connections or have limited resolution and accessibility to low pressures.
Innovation Solution
A microfluidic or millifluidic chip with a separable pressure sensing unit comprising two transparent, liquid-tight layers and an impermeable membrane, where a photonic hydrogel in a lower cavity changes color in response to fluid pressure, allowing for remote, local, and high-resolution pressure measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a soft sensing element is directly coupled to the flow channel for pressure measurement, then the sensor can detect pressure changes, but the deformation of the sensing element modifies the flow geometry and alters the pressure distribution in the channel
Solution Approach 1:
The sensing system is divided into two separate parts: a flow channel for fluid transport and a sensing cavity for pressure measurement. The membrane acts as a interface between these segments, allowing pressure transmission while maintaining functional separation. This segmentation prevents the sensing element from directly contacting and altering the flow geometry.
Solution Approach 2:
The sensing element (membrane with photonic crystal structure) is extracted from the main flow channel and placed in a separate sensing cavity. This extraction eliminates the direct coupling between the sensing element and the flow path, preventing modification of the flow geometry while still enabling pressure measurement through the membrane.
2Ease of operation
If optical methods are used to detect deformation of sensing elements, then external electrical connections are eliminated, but the resolution remains limited and restricted to pressures above 10 kPa
Solution Approach 1:
The photonic crystal structure within the membrane exhibits color changes in response to mechanical deformation caused by pressure. This colorimetric response provides a visual indication of pressure levels with high resolution, enabling detection of pressures as low as 2 kPa. The color change mechanism enhances the sensitivity and resolution of the optical sensing method.
Solution Approach 2:
The photonic crystal structure's optical parameters (reflective wavelength, color) change in response to pressure-induced deformation of the membrane. This parameter change provides a sensitive and measurable signal that correlates with pressure magnitude, enabling high-resolution pressure measurement down to 2 kPa with the optical method.
3Measurement precision
If a reflection method is used to quantify membrane deformation, then pressure can be measured, but the calibration is very sensitive to smallest changes in the angle of illumination or image capture
Solution Approach 1:
The photonic crystal structure provides inherent color changes that are directly observable and can be captured by standard imaging devices. The colorimetric response is less sensitive to illumination angle and image capture parameters compared to traditional reflection methods, reducing calibration complexity while maintaining measurement precision.
4Adaptability or versatility
If the sensing unit is integrated into the microfluidic chip, then full integration is achieved, but the sensor modifies the fluid flow geometry it is supposed to measure
Solution Approach 1:
The sensing unit is integrated into the chip but functionally segmented from the main flow channel through a membrane barrier. This allows the sensing cavity to be part of the chip structure while preventing interference with the flow geometry in the main channel, maintaining both integrability and measurement accuracy.
Solution Approach 2:
The sensing element is extracted from the flow path and placed in a separate cavity within the chip structure. This extraction allows the chip to maintain full integration while the sensing element does not modify the fluid flow geometry, preserving measurement accuracy.
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 accurate and contact-free pressure measurement down to 2 kPa with a resolution below 50 Pa, decoupling the sensing element from the flow path to avoid geometry modifications and improving accessibility to smaller pressures compared to previous methods.
Implementation Method 1
said lower cavity containing a slab of a photonic hydrogel immersed in an aqueous buffer solution
Implementation Method 2
said membrane is impermeable to the fluid circulating in the channel to be characterized and is able to deform under the pressure exerted by the fluid
Data Source
AI summary
The present invention relates to microfluidic or millifluidic chips (1) comprising at least one pressure sensing unit (4) able to measure a fluid flow pressure. The present invention also relates to a method for a direct and contact-free measuring of a local pressure of a fluid circulating in a microfluidic circuit, using a microfluidic or millifluidic chips (1) according to the invention.