For the benefit of the younger readers I should say that this is a reference to the classic Blondie song. Video is here, you can click on it and read this post while listening to a real classic. I wrote it while listening to it more-or-less on a loop.
but seriously, do you, and I, have hearts of glass? In common language, glass means the stuff windows are made of, a transparent solid made from silicon, oxygen, sodium and calcium.
But scientists also use glass to mean anything that has a combination of two properties. The first is that should be a solid, in the sense that it does not flow under gravity as a liquid does, because the atoms are frozen into place. The second requirement it that it is not a crystal, i.e., the molecules in it are not arranged in a crystal lattice. Window glass is a glass in this sense because the silicon, oxygen, sodium and calcium atoms in it are not on a regular crystal lattice but they are frozen into place, i.e., they don’t diffuse around.
So, what about our hearts? Our hearts are made of cells, like the rest of us. Conventional wisdom has it that inside cells is a viscous liquid not a glass. But Parry, Surovtsev et al. studied bacterial cells and they show evidence that these cells are kept from being glassy inside only by their metabolism. When they are nasty to the cells to stop their metabolism the larger objects inside them more-or-less grind to a halt — these larger objects behave as if they are in a glass. Interestingly, it is still unclear, even though Parry and coworkers do a very good job, what part of the cell metabolism is preventing the cell freezing into a glass. There is work to do here.
Now bacterial cells are rather different from our cells, so it is very possible that our cells are rather different. But our cells are also rather poorly understood, so it is at least possible that only constantly burning energy in our heart cells is preventing us all from having hearts of glass.