A very interesting technology to generate motion from the humidity by a research team in Colombia University. Depending on the properties of the bacterial spores, the team was able to generate a motion that can be used for many application.
The bacterial spores germinate into a living bacteria when the right conditions are met. The spores are good in absorbing the water even in the atmosphere as water vapour and when doing so the spores swell and shrink when they loose water and get dry. The research team was able to find a way to capture this tiny movement by adding billions of these spores on a plastic tape and converting it to something useful.
A rotary motion was generated from this straight motion as seen in the following figure.
The increase curvature on the dry side shifts the centre of the mass of the structure and create a torque.
The applications of this motion can be in automobiles and energy creation, however, many thinks it might be too weak at this point for powerful applications.
I think this is classified as an application for biological technology, however in textiles the shape memory polymers can perform and behave in the same way. It can change shape, shrink or expand based on different stimuli including humidity. The application for the humidity shape memory is still in the field of clothing and temperature and humidity regulation. Example below.
When sweating, the increase of humidity between the body and the garment will open the vents allowing the moisture to escape and when it is low, when sitting still, they close to keep the wearer warm.
1 – http://qz.com/429309/these-machines-can-capture-a-new-source-of-clean-energy-evaporating-water/
2 – http://www.nature.com/ncomms/2015/150616/ncomms8346/full/ncomms8346.html
3 – http://iopscience.iop.org/0964-1726/21/5/053001/article