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Teardown of FlowBio



Wearables are on the rise currently, when writing this blog, Google recently released its Fitbit Air, rivaling the Whoop. However, most wearables has been until now been measuring essentially the same biomarkers, skin temperature and heart rate. Companies usually compensate for the lack of direct physiological measurements by adding and accelerometer and generating a lot of data, then throwing that to an AI model to predict a all sort of conditions about us. It works, to some extent, but at some point you would need to add a new biomarker to extract more about the human body. Sweat contains loads of information about the human body, the most obvious are electrolytes, but it also contain some metabolites such as lactate and glucose. It also contains traces hormones like cortisol, which is how dogs sense stress signals in humans. It also contains proteins, dead cells, leftover sunscreen, dust, you name it. What makes sweat interesting also make it hard to extract information from. Using ion-specific electrodes or measuring metabolites has been successfully achieved in academia, but it is expensive and prone to fouling, making their lifespan quite short.


Here comes FlowBio, which admittedly I have but haven't used because it requires yet another device to work such as a Garmin to accurately estimate the fluid loss percentage. FlowBio, along with the other competitor hDrop, are the biggest names for reusable sweat monitoring systems in the market. It measure sweat's conductivity, which is proportional to sodium and chloride ions.


Hardware teardown

Figure 1: PCB top

 

Figure 2: PCB back

The "brain" in here is a Nordic ISP1807, quite an efficient module based on nRF52840 (figure 1). However, it seems like most of the heavy lifting is being done by AD5941, which does the current and voltage impedance measurements of sweat. The system is powered by a LIR1245, having a capacity of around 55 mAh, according to Flowbio, it is capable of operating for 100 hours.



Figure 3: Back case

Figure 4: Back case with cover



What differentiates FlowBio from the competition is what they named "advanced microfluidic technology". It is a rather simple system and it seems to be effective, a double-sided tape acts as the hydrophobic boundary with cutouts to channel the fluid (figure 3), it has both an inlet and an outlet. They do recommend flushing the channel every now and then.

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