Interfacial Tension Effect on Cell Partition in Aqueous Two-Phase Systems

Abstract

Aqueous two-phase systems (ATPS) provide a mild environment for the partition and separation of cells. We report a combined experimental and theoretical study on the effect of interfacial tension of polymeric ATPS on the partitioning of cells between two phases and their interface. Two-phase systems are generated using polyethylene glycol and dextran of specific properties as phase-forming polymers and culture media as the solvent component. Ultralow interfacial tensions of the solutions are precisely measured using an axisymmetric drop shape analysis method. Partition experiments show that two-phase systems with an interfacial tension of 30 μJ/m(2) result in distribution of majority of cells to the bottom dextran phase. An increase in the interfacial tension results in a distribution of cells toward the interface. An independent cancer cell spheroid formation assay confirms these observations: a drop of the dextran phase containing cancer cells is dispensed into the immersion polyethylene glycol phase to form a cell-containing drop. Only at very small interfacial tensions do cells remain within the drop to aggregate into a spheroid. We perform a thermodynamic modeling of cell partition to determine variations of free energy associated with displacement of cells in ATPS with respect to the ultralow interfacial tensions. This modeling corroborates with the experimental results and demonstrates that at the smallest interfacial tension of 30 μJ/m(2), the free energy is a minimum with cells in the bottom phase. Increasing the interfacial tension shifts the minimum energy and partition of cells toward the interfacial region of the two aqueous phases. Examining differences in the partition behavior and minimum free energy modeling of A431.H9 cancer cells and mouse embryonic stem cells shows that the surface properties of cells further modulate partition in ATPS. This combined approach provides a fundamental understanding of interfacial tension role on cell partition in ATPS and a framework for future studies.

Self-regulatory factors of embryonic stem cells in co-culture with stromal cells enhance neural differentiation

“…10,17,20 mESCs microprinted onto a confluent layer of PA6 cells remained partitioned within the DEX phase drop due to an ultralow interfacial tension between the aqueous PEG and DEX phases. 19,21 mESCs adhered to the stromal layer within 3 hrs of incubation (Fig 1a–b). 19,21 The layer of mitotically inactive PA6 cells remained intact and viable during the 2-week culture period while mESCs rapidly proliferated and formed individual colonies (Fig 1c).…”

“…19,21 mESCs adhered to the stromal layer within 3 hrs of incubation (Fig 1a–b). 19,21 The layer of mitotically inactive PA6 cells remained intact and viable during the 2-week culture period while mESCs rapidly proliferated and formed individual colonies (Fig 1c). A density of 500 cells per drop resulted in uniformly-sized colonies of 2.0±0.3mm in average diameter on day 8 of culture, irrespective of type of culture vessel.…”

“…19 mESCs were suspended in an equal volume of the SM and the DEX phase solution to yield a cell density of 10 4 cells/μl. This also reduced the polymer concentration to 6.4% (w/v).…”

“…Expression levels of mRNA for different marker genes were calculated relative to GAPDH and β-actin using the ΔΔC t method. Fold change in mRNA expression was determined as 2 -ΔΔCt 19,20. …”

<i>In Situ</i> Microscope Measurements and Analysis of the Passing of Individual Paramagnetic Particles through the Interfaces of Aqueous Two-Phase Systems by Magnetic Force

“…It was sometimes reported that the logarithmic value of  for ATPS has a linear relation to the logarithmic tie line length (l tl in wt%) of the phase diagram [14,15]. The relation depends on the degrees of polymerization of the polymers.…”