There is great interest in the application of nanotechnology to medicine, but concerns for safety are paramount. We present a modelling technique based on CSP and B as a starting point for simulation of networks of nanorobots. The model and the simulations are central features of our proposed approach to the construction of safety cases for nanomedicine applications, and complex networks of cooperating components in general. Our work is based on a case study: the clotting behaviour of (artificial) platelets. We present a model, and discuss its analysis and uses.