Sports wearables startup FLOWBIO are developing a real-time sweat sensor – the FLOWPATCH. The FLOWPATCH measures electrolytes and fluid lost in sweat during heavy athletic activity by capturing and analysing the wearer’s sweat and feeding the data to the user’s smartphone via Bluetooth.

For the first time ever, high-level athletes are able to quantify their sweat loss. This means they can optimise hydration levels for better recovery post-training, and better mental clarity and physical performance during training.

Now in the trial stage, FLOWBIO needed to print a limited run of the FLOWPATCH to send to beta testers, including Olympians and a Tour de France team.

The Challenge:

Since the FLOWPATCH was to be worn on the inner forearm and exposed to a high sweat environment, adverse weather, and strong sunlight, it would need to be resistant to corrosion and degradation from UV light. Each unit in its entirety would also need to be strong, durable, highly impact-resistant and skin-safe. 

Furthermore, the product needed to be light and small, but with the inner room and mechanics to house the necessary electronics including a circuit board, Bluetooth module, and battery. The unit also required an LED to indicate status, including connection and activity.

The FLOWPATCH is a real time sweat sensor developed using additive manufacturing technologies.

The Solution:

Three separate, interconnectable components were designed for printing. The first part would be the shell base – which would sit close to the user’s skin. The second – a shell-like part or “dome” sitting on top of and attached to the shell base, with unique inner features to accommodate the required electronics in a compact space. And the third part would be a small, custom, light pipe to transmit the light from the LED from the electronics to the surface, making it visible to the user.

The shell floor was printed in PA2200 – a biocompatible SLS material certified for prolonged skin contact. The material has high strength and durability and is very corrosion resistant (making it well equipped for a barrage of wind, rain, and sweat).

A white material, the PA2200 was dyed black with biocompatible, perspiration-resistant dye using DyeMansion technology. DyeMansion is a novel technology which enables for the first time, production-grade finishing including permanent coloring to be achieved on SLS parts. This means customers can get the strength and durability benefits of SLS along with the aesthetic of their choosing.

The shell casing was vacuum cast in PX225 L4 – an ABS-like thermoplastic with high impact resistance and flexural strength. Easily pigmented, FLOWBIO were able to match the colour of this part to the jet-black dye of the SLS-printed shell base. Having printed a mould using the stereolithography process, vacuum casting was a quick, reliable, and cost-effective method of producing the end-use parts, even given their fine inner features and tight geometries.

A similar approach was followed for the light pipe. It was first prototyped in Watershed: a clear, transparent SLA material. Then a mould was made and a low volume run of the parts was vacuum cast in SG95; a material which simulates clear ABS and has excellent optical properties, including a high refractive index.

The Result:

Using AM and Vacuum Casting technologies at LPE, FLOWBIO produced a skin-safe, strong, and durable product. It’s also lightweight, helped in part by the material efficiency that can be achieved given the design freedom these techniques allow.

And of course, it looks good; small, slick, and jet-black.

Here is professional triathlete Harry Palmer trying it out:

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