Effect of Molecular Weight of Phase Polymers on Partition of Cells in Aqueous Two-Phase Systems

ABSTRACTDue to their aqueous environment and biocompatible polymers, aqueous two-phase systems (ATPS) provide a mild environment for partition of cells. A comprehensive understanding of cell partition in ATPS will facilitate cell separation and fractionation in ATPS for downstream cell-based analytical applications and various cellular and molecular biology studies. We report the effect of molecular weight of phase polymers on partition of cells between two aqueous phases and their interface. We generate three different ATPS by dissolving polyethylene glycol and dextran of different molecular weights in a standard cell culture medium of fixed composition. After suspending cells in each ATPS, we quantify the number of cells partitioned into each segregated phase and the interface between the two phases. Importantly, we use two-phase solutions of an identical interfacial tension from each ATPS to avoid the effect of interfacial tension on cell partition. Our results indicate that decreasing the molecular weight of one of the phase polymers results in distribution of a greater number of cells toward the phase rich in that polymer. Regardless of molecular weight of polymers used, two-phase solutions made with higher concentrations of polymers cause a significant shift toward cell partition to the interface. This study elucidates the role of polymer molecular weight on cell partition in ATPS and offers formulations for rapid and effective cell partition.

A Nonuniform Cell Partition for the Analysis of Nonlinear Stochastic Systems

This paper presents a study of nonuniform cell partition for analyzing the response of nonlinear stochastic systems by using the generalized cell mapping (GCM) method. The necessity of nonuniform cell partition for nonlinear systems is discussed first. An ad hoc scheme is then presented for determining optimal cell sizes based on the statistical analysis of the GCM method. The proposed nonuniform cell partition provides a roughly uniform accuracy for the estimate of the one-step transition probability density function over a large region in the state space where the system varies significantly from being linear to being strongly nonlinear. The nonuniform cell partition is shown to lead to more accurate steady-state solutions and enhance the computational efficiency of the GCM method.