Sorting cells by their dynamical properties.

Recent advances in cell sorting aim at the development of novel methods that are sensitive to various mechanical properties of cells. Microfluidic technologies have a great potential for cell sorting; however, the design of many micro-devices is based on theories developed for rigid spherical particles with size as a separation parameter. Clearly, most bioparticles are non-spherical and deformable and therefore exhibit a much more intricate behavior in fluid flow than rigid spheres. Here, we demonstrate the use of cells' mechanical and dynamical properties as biomarkers for separation by employing a combination of mesoscale hydrodynamic simulations and microfluidic experiments. The dynamic behavior of red blood cells (RBCs) within deterministic lateral displacement (DLD) devices is investigated for different device geometries and viscosity contrasts between the intra-cellular fluid and suspending medium. We find that the viscosity contrast and associated cell dynamics clearly determine the RBC trajectory through a DLD device. Simulation results compare well to experiments and provide new insights into the physical mechanisms which govern the sorting of non-spherical and deformable cells in DLD devices. Finally, we discuss the implications of cell dynamics for sorting schemes based on properties other than cell size, such as mechanics and morphology.

Behavior of rigid and deformable particles in deterministic lateral displacement devices with different post shapes.

Deterministic lateral displacement (DLD) devices have great potential for the separation and sorting of various suspended particles based on their size, shape, deformability, and other intrinsic properties. Currently, the basic idea for the separation mechanism is that the structure and geometry of DLDs uniquely determine the flow field, which in turn defines a critical particle size and the particle lateral displacement within a device. We employ numerical simulations using coarse-grained mesoscopic methods and two-dimensional models to elucidate the dynamics of both rigid spherical particles and deformable red blood cells (RBCs) in different DLD geometries. Several shapes of pillars, including circular, diamond, square, and triangular structures, and a few particle sizes are considered. The simulation results show that a critical particle size can be well defined for rigid spherical particles and depends on the details of the DLD structure and the corresponding flow field within the device. However, non-isotropic and deformable particles such as RBCs exhibit much more complex dynamics within a DLD device, which cannot properly be described by a single parameter such as the critical size. The dynamics and deformation of soft particles within a DLD device become also important, indicating that not only size sorting, but additional sorting targets (e.g., shape, deformability, internal viscosity) are possible.