Filtration & fl uid control Leakage measurement
Diagrams of microfl uidic chips, a benefi cial technology in need of protocol and standardisation.
about the diversity of operational conditions and media used. However, surveys we held indicated that most users are operating their devices at temperatures between 4–50°C or slightly above that and at pressures below two bar. Information from other surveys indicated that the community members are generally working with water-based fluids containing biomolecular matter, and flows between 1µl/min and 100 µl/min. It was estimated that far more than 75% of microfluidic devices are operating in this hot spot, making it ideal to develop test protocols. The team decided to develop the most urgently needed test protocols first, namely for fast-changing flow rates, leakage measurement and flow resistivity. Microfluidic devices are characterised by their speed. During the short time the device operates, accurate control of flow is essential. Diverse types of equipment are used to generate and control flows in microfluidic systems; however volumetric flow rate accuracy has not yet reached a satisfactory level. It is necessary to characterise components within a system to correctly model and predict the system level behaviour and to optimise component usability and interchangeability. Currently, there are no industry-wide accepted tests, qualification protocols or generic compliance certificates to objectively compare microfluidic flow control products from different suppliers.
“Deviation from the intended cross section of microfl uidic channels leads to an increase or decrease of the fl ow resistivity and thereby infl uencing the performance of the device.”
In a concerted effort to tackle the increasing demand, several national metrology institutes, have already developed protocols and calibration services for micro and nano flow rates. Traceability to national standards has been available since 2012 down to 0.1μl/ min and in 2022 down to 5nl/min, but there is the need to transpose this information to the microfluidic field with its specific demands.
104
Due to the tiny amounts of medium leaking in or out of microfluidic devices, detection is more challenging than leakage in devices with a larger internal volume. To know if a device leaks or not is not enough. Knowledge of the amount of medium leaking from a microfluidic device over a certain period of time is essential for statistical process control, which is needed to safeguard product quality. After discussion between experts, the first leakage testing protocol was created and published as a whitepaper on the Microfluidics Association website. Due to the diversity of microfluidic devices, there are several protocols applicable. There is a strong preference towards using air or dry nitrogen as a test medium, as it allows the quantitative measurement to be done in a fast and nondestructive way, leaving no contamination inside the microchannels. However, most microfluidic devices use liquids as a work medium, and the relation between leakages of gas and of liquid through small channels is more complex than a difference in viscosity of the media used. Experiments are underway to determine this relation and to develop leakage test protocols that are nondestructive.
Flow resistivity
Deviation from the intended cross section of microfluidic channels leads to an increase or decrease of the flow resistivity and thereby influencing the performance of the device. These deviations can be caused by variations in etching in the case of glass products or deforming during bonding of polymeric products. Surface properties, such as roughness or wettability, will also influence flow resistivity and pressure decay.
The microfluidic industry therefore needs tools and protocols for the measurement of channel dimensions in 3D. The preferred moment for the measurement is for glass-based devices after channel structuring and polymer-based devices after bonding. The ability to measure the entire area of the wafer, or even sample area of it in a short amount of time is desirable and it would give an indication of the process homogeneity and stability over the wafer. It also would predict internal pressure decay and flow resistivity. Particular challenges are the range of sizes to be measured – which can vary from nanometres to hundreds of microns to millimetres – as well the complex cross sections and patterns of devices Despite the weight of this and other challenges, for the first time in the over 25 years of microfluidic development and industrialisation, serious efforts are ongoing towards the development of standards for this field. ●
Medical Device Developments /
www.nsmedicaldevices.com
grinimal/
Shutterstock.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170
