Ring-Sheared Drop (RSD): Microgravity Module for Containerless Flow Studies
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Microgravity is potentially a powerful tool for investigating processes that are sensitive to the presence of solid walls, since fluid containment can be achieved by surface tension. One such process is the transformation of protein in solution into amyloid fibrils; these are protein aggregates associated with neurodegenerative diseases such as Alzheimer’s and Parkinson’s. In addition to solid walls, experiments with gravity are also subject to influences from sedimentation of aggregates and buoyancy-driven convection. The ring-sheared drop (RSD) module is a flow apparatus currently under development to study formation of amyloid fibrils aboard the International Space Station (ISS). A 25 mm diameter drop of protein solution will be contained by surface tension and constrained by a pair of sharp-edged tubes, forming two contact rings. Shear can be imparted by rotating one ring with the other ring kept stationary. Here we report on parabolic flights conducted to test the growth and pinning of 10 mm diameter drops of water in under 10 s of microgravity. Finite element method (FEM) based fluid dynamics computations using a commercial package (COMSOL) assisted in the design of the parabolic flight experiments. Prior to the parabolic flights, the code was validated against experiments in the lab (1 g), on the growth of sessile and pendant droplets. The simulations show good agreement with the experiments. This modeling capability will enable the development of the RSD at the 25 mm scale for the ISS.
KeywordsFluid dynamics Proteins Parabolic flight Drop growth Drop pinning Contact angle
Many individuals have made significant contributions toward the results presented here. We thank Ellen Rabenberg (NASA-MSFC) for her efforts in preparing the parabolic flight hardware as well as performing some of the experiments. We are also grateful to Jeffery Quick (Jacobs Engineering and Science Services and Skill Augmentation, ESSSA group) for developing much of the parabolic flight hardware, including the pump control system. We thank Kevin Depew (NASA-MSFC) who assisted with facilitating the parabolic flight by doing structural and electrical analysis of the flight hardware. We thank Carole Fritsche (Stinger Ghaffarian Technologies, SGT) for her expertise in parabolic flight experiments both as a mentor and a performer herself. We acknowledge Assad A. Oberai (RPI) for his guidance on the computational modeling of droplet dynamics. We thank Sid Gorti (NASA-MSFC) who is the project scientist for his efforts and all the fruitful discussions over the years on many aspects of this project. We are grateful to Donnie Mccaghren (NASA-MSFC) who was the project manager for his tireless efforts and seeing this work to fruition. We thank Robert Roe (NASA-JSC) who was the project manager for the parabolic flight grant for his efforts to ensure a successful flight. Finally, we thank Juan M. Lopez (Arizona State University) for his involvement from the conception of this project to guiding the path toward the experiments aboard the ISS. This work was supported through NASA grants NNX13AQ22G and NNX15AJ83G.
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