The first step to improve the prototype of the double cap was to define the optimal proportion of the double cap connector. To recall, the connector function is to pierce an aluminum seal to allow the flow of the bioreporter into the water sample, after having started to screw the two vials together.
Here is the workflow of the double cap (you can also see it on movies) :
We end up with the following dimensions for this part, with a thickness of 0.5mm :
Industrial draw of the connector (with LibreCAD)
The next step was to model the connector with Blender (open source software). Note that we choose a thickness of 0.5mm for the whole part, but it can be increased to 1mm, depending on the 3D printer accuracy.
Then we export a .stl file, format for the 3D printer software. Here are the files for the connector :
- Connector with a thickness of 0.5mm : connector0_5mm
- Connector with a thickness of 1mm : connector1mm
The final step took place at Hackuarium, where with the help of Sam, the first connector was printed. We used Cura to define the caracteristics of the printing :
- Temperature : 220°C (for PLA)
- Material : PLA filament (1.75mm)
- 4mm nozzle
- 190*190 bed (temperature 70°C)
The 3D printed connector (thickness 1mm)
The printing took 11min, for 0.46 meter of filament (1gram). The price, estimated from the cost of a spool of filament, is about 0.04CHF.
We then have to glue the connector between two preexisting vial caps.
Assemblage of the connector between the two caps
After having glued the two preexisting caps with the connector, we can make some tests.
The obtained double cap
We position the tip of the connector in front of the start of the screw pitch of the cap. As expected, the aluminum seal is pierced after we started to screw.
This proposition presents a disadvantage : we have to find a glue which resists to water, is strong enough and hermetic. For example, with Patex glue, the device was broken after about 20 uses.
This double cap has a license CC BY. 
That is why the new objective is to model the double cap in one single part : the connector with its two caps to screw the water sample and the bioreporter vials.
biodesign for the real world 
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