Drift ratchets as biomimetic filters

Diatoms are microscopic, phototrophic, unicellular algae encased in a porous, rigid, siliceous, cell wall known as a frustule and they inhabit the euphotic zones in bodies of seawater and freshwater globally. It is not yet fully understood how diatoms compete with swimming microorganisms for nutrients in their environment. It is believed that the frustule does play a role in giving them a competitive advantage, however, the function of the diatoms’ frustule is not yet fully understood. Among other functions it has been proposed that the frustule acts like a filter for the diatom, sorting nutrients from harmful entities such as pathogens, poisons, colloids and pollutants, from their natural environment. As a result of the micro- and nanoscopic nature of the frustule and its features, diffusion is thought to play an important role in the frustules filtering capabilities. It has been proposed that specific centric species of diatom employ the drift ratchet mechanism to sort and control mass transport towards and away from the diatom cell. This research has determined that this is unlikely due to the size and configuration of the diatom girdle band pores. Instead, a new theory is presented herein, termed “Hydrodynamic Immunity”, in which diatoms use diffusiophoresis to separate nutrients from harmful entities. In conjunction with this work the dimensionless numbers critical for dynamic similarity analysis of a drift ratchet are determined to allow for easy comparison between dynamically similar experiments.<br><br> Finally, a novel hydrodynamic drift ratchet microfluidic device was designed and fabricated as a proof-of-concept to prove definitively whether the drift ratchet mechanism can be generated in an experimental environment, following inconclusive findings from past research experiments. This remains unresolved due to experimental complications; however improvements are suggested to ensure future work is successful at recreating a drift ratchet in experiments.