A common trope in science fiction is that of biotechnology. Technically things like artificial hearts and prosthetic legs are biotechnology and so what is really being thought of is nanobiotechnology. Of course having millions of tiny robots in your blood stream to repair damage is a couple of centuries off, but any progress can only be happening in the right direction. One of the things that makes making technology cooperate with the body difficult is the concept of chirality and optical isomerism. To put is simply when a carbon is surrounded by four different chemical groups there are two distinct orientations of those groups that can be achieved, known as left and right handed. Despite being made of the exact same atoms the orientation changes the properties, lactic acid is what most people know to be produced in your muscles, but is also the chemical in sour milk just with the reflected version.
Most of the bodies chemicals, and definitely all the amino acids (except one), are left handed. Left handed chemicals struggle to react with right handed ones like a right hand struggles to fit the left glove. This means that this has to be considered when nanotechnology is being designed as to perform the desired effect. Of course the easiest way to make the body work with an inorganic chemical is to make the body create it in the fist place. in order to construct a gold nanocrystal scientists have managed to get a DNA molecule to make it for them. DNA has evolved over the eons to do many different things in the body and this high versatility is what makes it one of the most promising chemicals for this kind of construction. It might even be possible to have the DNA construct a specific shape for the crystal or perhaps dope it during formation as to give it a different property. Now it is required that a use be found for such metallic crystals in the body and we would be having a great start towards those prophesied nanobots we all want.