I don't think we have the technology to self-assemble circuitry in a mobile liquid (like blood that is pumping through the body). My concern is that is the graphine forms crystalline structures, they will work as microscopic razor blades, creating micro-clots.

These micro-clots will flow through the body, and get caught up in small capillaries, such as in the brain (or more seriously) in the lungs. The smallest capillaries found in the human body, are at the interface between the circulatory and respiratory system (in the alveoli are where the lungs and the blood exchange oxygen and carbon dioxide during the process of breathing in and breathing out.).

Our hearts have 4 chambers, the lower right is where the blood goes in, this pumps to the small upper right, that pumps blood into the lungs (if there are clots in the lungs, this is cardio-pulmonary HYPER-Tension), the blood pressure here is expected to be low, the blood comes back into the heart in the upper Left ventricle, and then the strongest chamber is the Lower left Ventricle which pumps the oxygenated blood through our body.

If you have a large number of clots gathered in your lungs - you basically blow out the relatively weak upper right ventricle - and this is the instant death you hear about with athletes that collapse on the field. That is my greatest fear with the graphine - it's a delayed time bomb.