Bone is pretty amazing stuff. It is light, strong, alternatively hard or flexible when or where it needs to be, self-healing and it does all of this having been made using only room temperature processing. With all of our technology today, we can’t come even close in terms of making anything this amazing.
Most of bone is not alive but the cells that manufacture it live within its structure and therefore need to stay connected to their source of nutrients, the blood vessels of the body. Unlike a piece of concrete, the structure of bone is quite complex with two different types of bone.
There is hard, dense bone called cortical bone which is on the outside providing most of the strength and impact resistance we usually think of when we consider our skeletons. Inside of this is a type of spongy (or cancellous) bone which has a lower density (and strength) but which is incredibly tough. The detailed structure consists of rings on the outside (like a tree) with internals structures inside (like the re-bars in a concrete building) allowing for great strength with low weight.
If our bones were solid and dense throughout their volume, they would be strong enough for us to stand up but too heavy to let us walk very fast or run. We would have been sitting ducks for things like Sabre tooth tigers with big teeth and bigger claws. If they were too light, we might have been fast enough to run but a minor spill would have broken them and we would have also ended up as something’s dinner. So our bones are a finely tuned compromise between strength and weight giving us our best shot at surviving in a perilous world.
Interestingly, the balance between strength and weight is a dynamic one that gets constantly adjusted depending on where we are and what we are doing. If for example, you are in a space station for a year, your body realizes that there is not much weight on your bones and they get reduced in strength and weight to be optimized for where you are. This reduction in bone mass can be as high as 1.5% per month in orbit, ten times more rapid than osteoporosis in the elderly. When they return to Earth (and full gravity) astronauts have to be careful to not break their bones by simple walking.
Given that upright walking is pretty much what allowed Human Beings to grow large brains and become Human (because our hands were free to develop and use tools), understanding the mechanics of bone is an important and interesting problem. At Boston University we have a research team led by Elise Morgan that studies the mechanics of bone and its growth and formation. The mechanics of bone allows Human Beings to stand up, walk around, play football and basically do all of the things we think of as human activities. Individuals with diseases such as osteoporosis reducing the strength of their bones suffer a loss in mobility that significantly impairs the quality of their lives. The work being done at BU aims to understand the underlying mechanics of bone strength (and its loss). We hope this research will someday allow those with such debilitating diseases to have a quality of life similar to what they did before becoming ill. We should be proud of our colleagues’ work and its potential impact on the Human condition.