While in my undergrad at Cal Poly, I met with biomedical engineering students about a problem I was previously unaware of: children who desperately need knee replacements due to severe conditions, but cannot get one because they’re still growing. I invented the concept for a prosthesis comprised of many layers of titanium and water. The intuition is simple: titanium oxidizes and forms titanium dioxide in an expansion of the shape of the layer, while maintaining a high compressive strength. Using chemical and mechanical engineering, this expansion rate can be set to the approximate growth vectors of the adolescent based on water prevalenc, which can be added post-op and aided by body generated heat. I wrote up the concept with some basic chemistry and mechanical analysis and some rudimentary designs. This went on to research projects at Cal Poly but did not make it to publication.

Though interesting, there does not appear to be a configuration of layers such that the both the Pilling–Bedworth ratio driven expansion rate and mechanical integrity under knee loads requirements are met, and so little further exploration is warranted into this solution. Still, this issue remains unsolved and more novel ideas need to be brought to the table.