One of the neater things that's going on in biology is the genetic modification of species. By changing the instructions in their genes, we can make certain plants and animals produce things that are useful to humans.
People have been using animals and plants to produce things we can use for centuries. We drink cow's milk, for example. And we make clothes out of cotton. We also use silk, which is made by silkworms.
But genetic modification is a whole new ball game. For example, research being done at Hiroshima University has shown that your everyday silkworm can be genetically altered to produce a form of human collagen. They build it right into their silk.
Collagen is just a protein. However, it's very important because it happens to be the structural protein that goes into building your skin, tendons, ligaments, and even your bones.
One thing you could do is use it to make skin grafts. Silkworms already spin about sixty thousand tons of silk every year, so if collagen-laced silk can be reliably produced, it would be a cheap and ready supply of grafting material--say for people who have burn injuries and need new skin.
You might also be able to produce albumen, which is a protein found in human blood. And what about bones, tendons, ligaments? There might be more uses down the road.