Naked Science Forum
Non Life Sciences => Technology => Topic started by: scientizscht on 19/07/2019 19:04:54
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Hello!
Continuous glucose monitors are supposed to have a microneedle that goes into your skin and via that it measures your glucose continuously.
How does the microneedle suck the blood to put it in contact with the sensor surface? I.e. why the blood just doesn't go up to half way through the microneedle due to surface tension and just stop there without accessing the sensor?
How does the system work really?
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Not particularly well, it seems. I've reviewed several research projects using CGM sensors and in each case the recommendation from the researchers or the manufacturers has been for frequent recalibration - as often as twice a day - against a standard fingerprick sample.
From diabetes.co,.uk
Continuous glucose monitoring isn't blood glucose monitoring as the sensors with a CGM machine are placed into your body but not into the bloodstream.
The sensors measure the glucose in your interstitial fluid - the fluid in and around your body’s cells.
The relationship between glucose concentrations in interstitial fluid (ISF) and blood has generated great interest due to the possibility of gaining up to 288 glucose level readings a day without having to do finger pricks.
It's a difficult problem. Electrochemical sensors generally require a flowing liquid to remove reaction or electrolysis product from the electrodes, and static body fluids are remarkably corrosive to electronic gubbins.
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For how they are supposed to work:
Go to: https://patents.google.com/
Enter: Continuous Glucose Monitor
Voila!
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Why not just put the sensors at the (pointy) ends of the needles?
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Any sensor requires a fixed wetted surface area (electrochemical) or path length (optical) - not easy to achieve at the pointy end. A "tip and sleeve" electrochemical sensor can work for a while but they are all subject to the problems of erosion, contamination, or simple phase lag (the sample you have in your optical tube is not representative of the present blood glucose level) if sampling is by osmosis or diffusion.
It is a very annoying problem. The physics and chemistry of glucose measurement are well established in vitro, but in vivo engineering is orders of magnitude more complicated. I've been aware of patents and projects appearing over the last 40 years, with no really satisfactory product reaching the market.