Flow Homogenization Enables a Massively Parallel Fluidic Design for High-throughput and Multiplexed Cell Isolation.

Microfluidic devices are widely used for applications such as cell isolation. Currently, the most common method to improve throughput for microfluidic devices involves fabrication of multiple, identical channels in parallel. However, this 'numbering up' only occurs in one dimension, thereby limiting gains in volumetric throughput. In contrast, macro-fluidic devices permit high volumetric flow-rates but lack the finer control of microfluidics. Here, we demonstrate how a micro-pore array design enables flow homogenization across a magnetic cell capture device, thus creating a massively parallel series of micro-scale flow channels with consistent fluidic and magnetic properties, regardless of spatial location. This design enables scaling in 2-dimensions, allowing flow-rates exceeding 100 mL/hr while maintaining >90% capture efficiencies of spiked lung cancer cells from blood in a simulated circulating tumor cell system. Additionally, this design facilitates modularity in operation, which we demonstrate by combining two different devices in tandem for multiplexed cell separation in a single pass with no additional cell losses from processing.

Effect of Magnetic Field Gradient on Effectiveness of the Magnetic Sifter for Cell Purification.

In our experiments with NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen, we demonstrate capture efficiencies above 90% even at sample flow rates of 5 ml/h through our microfabricated magnetic sifter. We also improve the elution efficiencies from between 50% and 60% to close to 90% via optimization of the permanent magnet size and position used to magnetize the sifter. We then explain our observations via the use of finite element software for magnetic field and field gradient distributions, and a particle tracing algorithm, illustrating the impact of magnetic field gradients on the performance of the magnetic sifter. The high capture and elution efficiencies observed here is especially significant for magnetic separation of biologically interesting but rare moieties such as cancer stem cells for downstream analysis.

Rapid Characterization of Magnetic Moment of Cells for Magnetic Separation.

NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen were previously shown to be captured at high efficiencies by a microfabricated magnetic sifter. If fine control and optimization of the magnetic separation process is to be achieved, it is vital to be able to characterize the labeled cells' magnetic moment rapidly. We have thus adapted a rapid prototyping method to obtain the saturation magnetic moment of these cells. This method utilizes a cross-correlation algorithm to analyze the cells' motion in a simple fluidic channel to obtain their magnetophoretic velocity, and is effective even when the magnetic moments of cells are small. This rapid characterization is proven useful in optimizing our microfabricated magnetic sifter procedures for magnetic cell capture.

Field gradients can control the alignment of nanorods.

This work is motivated by the unexpected experimental observation that field gradients can control the alignment of nonmagnetic nanorods immersed inside magnetic fluids. In the presence of local field gradients, nanorods were observed to align perpendicular to the external field at low field strengths, but parallel to the external field at high field strengths. The switching behavior results from the competition between a preference to align with the external field (orientational potential energy) and preference to move into regions of minimum magnetic field (positional potential energy). A theoretical model is developed to explain this experimental behavior by investigating the statistics of nanorod alignment as a function of both the external uniform magnetic field strength and the local magnetic field variation above a periodic array of micromagnets. Computational phase diagrams are developed which indicate that the relative population of nanorods in parallel and perpendicular states can be adjusted through several control parameters. However, an energy barrier to rotation was discovered to influence the rate kinetics and restrict the utility of this assembly technique to nanorods which are slightly shorter than the micromagnet length. Experimental results concerning the orientation of nanorods inside magnetic fluid are also presented and shown to be in strong agreement with the theoretical work.