ISS: Thermophoresis in quiescent non-Newtonian fluids for bioseparations

There are many natural and industrial processes where nanoscale particles suspended in a fluid move as a result of a temperature gradient. These particles generally move from hot to cold regions. This phenomenon, which is known as thermophoresis, affects a wide variety of processes, such as drug delivery and bioseparations utilized for detecting viruses.

However, the current understanding of thermophoresis is limited. Experimental studies have conflicting evidence, making it difficult to determine the fundamental mechanisms that drive particle motion. Very few studies have considered the motion of these particles in more complex fluids and gels.

The challenge in interpreting experimental data is that it is difficult to separate effects of thermophoresis from effects of fluid flow arising from variations in the fluid density owing to variations in temperature. To overcome this limitation, this NSF-CASIS project will pair terrestrial experiments with those in microgravity onboard the International Space Station (ISS) where buoyancy-driven fluid flow is negligible.

The goals are to determine the fundamental physics and chemistry driving thermophoresis in simple and complex fluids and to use this information for enhancing viral separation platforms by optimizing fluid properties. In an era when disease control affects everyone, this project will focus on developing enhanced and robust microfluidic viral-load detection devices.

The objective of this project is to measure the thermophoretic motion of particles in complex fluids on the ISS to aid in the design of next-generation bioseparations devices for label-free viral load detection. Gravity-driven buoyancy-induced recirculation due to thermal expansion of the fluid is inhibited in microgravity, which will enable unambiguous measurements of thermophoresis.

The project will use multiple particle tracking microrheology (MPT) to simultaneously obtain local thermophoretic and rheological data. Fluids will range from variable ionic strength Newtonian liquids to non-Newtonian fluids with varying degrees of linear viscoelasticity or a temperature dependent sol-gel transition. The size and surface properties of probe particles will be changed and will span properties of biologically relevant nanoparticles, such as viruses.

Terrestrial experiments will focus on fluid property selection through rheological testing, particle synthesis, and downstream redesign of microfluidic platforms utilizing complex fluids to enhance bioseparations. The team will design these experiments with Tec Masters, Inc. to create a module that remotely performs all operations of sample manipulation, precision heating, high-speed/high-magnification imaging, and data transfer on the ISS.

This basic research and first demonstration of the utility of microrheology in space will impact the rheology, colloid and interfacial science, and bioseparation communities and train postdoctoral, graduate and undergraduate researchers. The promise for enhancing life on Earth through these fundamental and applied experiments will be incorporated into outreach activities for K-12 students and underrepresented student populations.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.