Inspired by the concept of stillsuits I had the idea of making a biokinetic pump or bellows. Placed over the knee or elbow, the flexing of the joint pulls and compresses the bellows. The teeth near the inlet valve are pulled together to create a seal and fluid is forced out of the valve on the top. When the joint deflexes the top valve is pulled closed and the inlet valve opens.

Does it work? Uhh... vaguely. 

I'm uploading this just for fun, and maybe to inspire someone to play with the idea. 

The prototype is pretty roughed up now. I cut it open to see how the inside printed. This also allows you to see the "teeth valve"

Printed on a P1S using 85a TPU. I don't have any printing advice because this really didn't work out well. The end result wasn't elastic enough and very porous. If you want to take a swing at it have fun!