Monocytes are less endocytotic than macrophage and a permanent magnet placed on top of the chamber deflects and sort the cells based on their iron loading. on their intrinsic (e.g., electrical, magnetic, and compressibility) and extrinsic properties (e.g., size, shape, morphology and surface markers). The review concludes by highlighting the advantages and limitations of the reviewed techniques which then suggests future research directions. Addressing these challenges will lead to improved purity, throughput, viability and recovery of cells and be an enabler for novel downstream analysis of cells. and achieved throughput of 2000 cells/s. Target cells were encapsulated in a 12 pL emulsion droplet. Using a similar mechanism but with larger droplet size to improve cell viability, Mazutis et al. [31] demonstrated separation of antibody-secreting cells from non-secreting cells at a lower throughput of 200C400 cells/s. Mechanically actuated microfluidic FACS systems have low throughput whereas systems actuated by other forces such as acoustic force, bubble expansion and dielectrophoretic force have 10C100 more throughput. 2.2. Magnetic Activated Cell Sorting (MACS) Magnetic-activated cell sorting (MACS) is another antibody labelled approach similar to FACS. Cells of interest are tagged with marker-specific antibodies conjugated to magnetic labels. The fluid mixture containing tagged and untagged cells is flowed through a strong magnetic field. The magnetically tagged cells are directed into the collection channel by magnetic force. Many commercial extraction kits such as AutoMACS Pro separator (Miltenyibiotec, Bergisch Gladbach, Germany), CELLSEARCH (Janssen Diagnostics, LLC, Raritan, NJ, USA) are available on the market. These kits provide various antibody-labelled magnetic tags for isolation of leukocytes, circulating tumor cells, stem cells, viable cytokine secreting cells, to name a few. These commercial systems can isolate tagged cells with high throughput (109C1010 cells/h), high purity and high recovery rate but require large samples and labels (magnetic particles), which is costly. Processing is VTP-27999 done in batch mode and prolonged duration of operation increases the chance of VTP-27999 cross contamination by non-specific binding with the magnetic particles. The review by Hejazian et al. [34] provides more insight into the fundamental physics and important design considerations for MACS systems. Microfluidics-based magnetic activated cell sorting (MACS) overcomes these limitations and provides a high purity and recovery rate while requiring fewer magnetic particles with continuous flow. To reduce the volume of magnetic particles needed for cell labeling, microfluidic devices create configurations that elicit stronger magnetic force by increasing the magnetic field gradients crossing the cells, either by increasing magnetic field strength or increasing proximity between magnetic source and tagged cells. However, there are limitations to the maximum allowable magnetic field gradients imposed by joule heating which reduces cell viability. Various configurations have been implemented using permanent magnets [35,36,37,38], electromagnets [39,40], and self-assembled magnets [41]. Osman et al. [42] designed a micromagnet array of Neodymium (NdFeB) films which act as permanent magnet with high magnetic field strength (106 T/m). Many MACS methods used the H channel structure to separate target cells from a mixture with two inlets and two outlets [43,44,45,46,47], shown VTP-27999 in Figure 2A. The mixture of magnetically labeled and non-labeled cells are introduced into one of the inlets and sheath flow is introduced into RAB7B the other inlet at the same flow rate. Laminar flow in the micro channel keeps the streams distinct and permanent magnets placed beside the streams attract magnetically tagged cells to cross the stream into the collection channel. By optimizing the placement and distribution of magnetic force, Del Giudice et al. [48] achieved up to 96% separation efficiency at flow rate of up to 4 L/min, using the concept illustrated in Figure 2B. Cells from multiple target groups can be tagged with differently sized magnetic particles and experience different magnetic force and deviations into different outlets [35]. Open in a separate window Figure 2 (A) A schematic of H filter for magnetic based separation (B) Viscoelastic focusing of magnetic particles Reproduced from Reference [48] with permission of The Royal Society of Chemistry; (C) Angled permanent magnet configuration Reproduced from Reference [49] with permission of The Royal Society of Chemistry; (D) Cascade magnetic separation stages, Adapted with permission.