As a start, biology evolves in an environment that is mostly water. While the percentage of water in human bodies is about 65%, it is generally higher in plants (about 90%), and even more so in week-old human embryos (up to 97%)! Where is the water? In human beings, 1/3 of it can be found in the extracellular medium, while 2/3 of it lies within the intracellular medium, a confined environment that is typically a few microns in diameter. From the words of Alberts et al., "Water accounts for about 70% of a cell's weight, and most intracellular reactions occur in an aqueous environment. Life on Earth began in the ocean, and the conditions in that primeval environment put a permanent stamp on the chemistry of living things. Life therefore hinges on the properties of water."
As scientists and engineers develop nanoscale sensor and actuator devices for the study of biomolecular systems, NFM will play an increasingly important role. The study of fundamental nanoscale flow processes is a key aspect of our effort to understand and interact with biological systems. Many biomolecular processes such as the transport of DNA and proteins are carried out in aqueous environments, and aerobic organisms depend on gas exchange for survival. The development of envisioned nanoscale biomedical devices such as nanoexplorers and cell manipulators will require understanding of natural and forced transport processes of flows in the nanoscale. In addition, it will be important to understand transport processes around biomolecular sensing devices to increase the probability of finding target molecules and identifying important biological processes in the cellular and subcellular level in isolated or high background noise environments.
While there can be a large variety of nanoscale systems (from the individual molecules themselves to the assembly of those molecules into complex structures such as cellular membranes), it would be a formidable task to try to understand the essential physics of these systems by peering at every known device. For more than a century, engineering fluid mechanics has taught us that simple, canonical experiments, such as the flow around a circular cylinder, can provide us with all of the fundamental physics needed to understand the flow dynamics of much more complex systems, such as the aerodynamics of airplanes or the hydrodynamics of ships. Following this conjecture, one may consider that the study of fundamental nanoscale flow physics of prototypical configurations will enable further advances in the development of complex scientific and engineering devices. At the same time, we are reminded that thousands of airplanes had been flying without the engineers having understood every minute detail about turbulent flow.
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