Fluid flow is central to a wide variety of medical engineering applications. Whether it’s the flow of fluids through MEMS devices, or around implanted cardiovascular devices being able to accurately model fluid flow is a critical piece of analyzing the technical challenge. Lagrangian coherent structures may be a theory to keep in mind. Although currently being used to model macro events such as air flow around mountains, sea flow, etc. there appears to be no scale limitations. Engineers at the leading edge of R&D attempting to unknot a challenging flow related design at the macro or micro level may want to look into how this theory is applied.