(nearly) frictionless joint
If in the days of Newton, bananas had been available and Newton had slipped on one of them, the laws of tribology would have been enunciated by him there and then
Tribology is the scientific study of friction — its origin and the methods to overcome it. Not surprisingly, Nature is adept at reducing solid-solid friction, and the articular joint is perhaps the most remarkable example of a (nearly) frictionless system.
The cartilage surfaces in our joints are able to move past each other effortlessly, even at loading pressures up to 100 atm. This is due to 1) the ability of hydrophilic polymer brushes on the surfaces to swell in the aqueous environment of the joint, preventing direct contact between the sliding surfaces and 2) the inherent ability of water films (even nanofilms) to act as excellent lubricant (hydration lubrication). Incidentally, hydration lubrication also explains why banana peels are slippery!
Inspired by this, I am exploring the possibility of minimizing liquid-solid friction, for a surface covered by synthetic polymer brushes, which similarly swell under water. Such a surface can be highly oil-repellent under water and prevents fouling organisms (such as bacteria) from attaching.
See also here.