Feasibility study of red blood cell debulking by magnetic field-flow fractionation with step-programmed flow

Field-flow fractionation - an excellent tool for fractionation, isolation and/or purification of biomacromolecules

Field-flow fractionation (FFF) with its several variants, has developed into a mature methodology. The scope of the FFF investigations has expanded, covering both a wide range of basic studies and especially a wide range of analytical applications. Special attention of this review is given to the achievements of FFF with reference to recent applications in the fractionation, isolation, and purification of biomacromolecules, and from which especially those of (in alphabetical order) bacteria, cells, extracellular vesicles, liposomes, lipoproteins, nucleic acids, and viruses and virus-like particles. In evaluating the major approaches and trends demonstrated since 2012, the most significant biomacromolecule applications are compiled in tables. It is also evident that asymmetrical flow field-flow fractionation is by far the most dominant technique in the studies. The industry has also shown current interest in FFF and adopted it in some sophisticated fields. FFF, in combination with appropriate detectors, handles biomacromolecules in open channel in a gentle way due to the lack of shear forces and unwanted interactions caused by the stationary phase present in chromatography. In addition, in isolation and purification of biomacromolecules quite high yields can be achieved under optimal conditions.

Immunomagnetic microfluidic integrated system for potency-based multiple separation of heterogeneous stem cells with high throughput capabilities

Multipotent adult stem cells (MASCs) derived from Pluripotent stem cells (PSCs) have found widespread use in various applications, including regenerative therapy and drug screening. For these applications, highly pluripotent PSCs need to be selectively separated from those that show low pluripotency for reusage of PSCs, and MASCs need to be collected for further application. Herein, we developed immunomagnetic microfluidic integrated system (IM-MIS) for separation of stem cells depending on potency level. In this system, each stem cell was multiple-separated in microfluidics chip by magnetophoretic mobility of magnetic-activated cells based on the combination of two sizes of magnetic nanoparticles and two different antibodies. Magnetic particles had a difference in the degree of magnetization, and antibodies recognized potency-related surface markers. IM-MIS showed superior cell separation performance than FACS with high throughput (49.5%) in a short time (<15 min) isolate 1 × 10⁷ cells, and higher purity (92.1%) than MACS. IM-MIS had a cell viability of 89.1%, suggesting that IM-MIS had no effect on cell viability during isolation. Furthermore, IM-MIS did not affect the key characteristics of stem cells including its differentiation potency, phenotype, genotype, and karyotype. IM-MIS may offer a new platform for the development of multi-separation systems for diverse stem cell applications.

Continuous, intrinsic magnetic depletion of erythrocytes from whole blood with a quadrupole magnet and annular flow channel; pilot scale study

The ability to separate RBCs from the other components of whole blood has a number of useful clinical and research applications ranging from removing RBCs from typical clinical blood draw, bone marrow transplants to transfusions of these RBCs to patients after significant blood loss. Viewed from a mechanistic/process perspective, there are three routine methodologies to remove RBCs: 1) RBCs lysis, 2) separation of the RBCs from the nucleated cells (i.e., stem cells) based on density differences typically facilitated through centrifugation or sedimentation agents, and 3) antibody based separation in which a targeted RBC is bound with an affinity ligand that facilitates its removal. More recently, several microfluidic based techniques have also been reported. In this report, we describe the performance of continuous RBC separation achieved by the deflection of intrinsically magnetic, deoxygenated RBCs as they flow through a magnetic energy gradient created by quadrupole magnet. This quadrupole magnetic, with aperture of 9.65 mm, has a maximum field of B₀  = 1.36 T at the pole tips and a constant field gradient of B₀ /r₀  = 286 T/m. The annular flow channel, contained within this quadrupole magnet, is 203 mm long, has an inner radius of 3.98 mm, and an inner, outer radius of 4.36 mm, which corresponds to an annulus radius of 380 micrometer. At the entrance and exit to this annular channel, a manifold was designed which allows a cell suspension and sheath fluid to be injected, and a RBC enriched exit flow (containing the magnetically deflected RBCs) and a RBC depleted exit flow to be collected. Guided by theoretical models previously published, a limited number of operating parameters; total flow rate, flow rate ratios of flows in and flow out, and ratios of RBC to polystyrene control beads was tested. The overall performance of this system is consistent with our previously presented, theoretical models and our intuition. As expected, the normalized recovery of RBCs in the RBC exit fraction ranged from approximately 95% down to 60%, as the total flow rate through the system increased from 0.1 to 0.6 ml/min. At the cell concentrations studied, this corresponds to a flow rate of 1.5 × 10⁶ -9 × 10⁶  cells/min. While the throughput of these pilot scale studies are slow for practical applications, the general agreement with theory, and the small cross-sectional area in which the actual separation is achieved, 77 mm² (annulus radius times the length), and corresponding volume of approximately 2 mls, suggests the potential to scale-up a system for practical applications exists and is actively being pursued.

Femtogram Resolution of Iron Content on a Per Cell Basis: Ex Vivo Storage of Human Red Blood Cells Leads to Loss of Hemoglobin

The magnetic characteristics of hemoglobin (Hb) changes with the binding of dioxygen (O2) to the heme prosthetic groups of the globin chains: from paramagnetic ferrous Hb to diamagnetic ferrous oxyhemoglobin (oxyHb) with reversibly bound O2, or paramagnetic ferric methemoglobin (metHb). When multiplied over the number of Hb molecules in a red blood cell (RBC), the effect is detectable through motion analysis of RBCs in a high magnetic field and gradient. This motion is referred to as magnetophoretic mobility, which can be conveniently expressed as a fraction of the cell sedimentation velocity. In this Article, using a previously developed and reported instrument, cell tracking velocimetry (CTV), we are able to detect difference in Hb concentration in two RBC populations to a resolution of 1 × 107 Hb molecules per cell (4 × 107 atoms of Fe per cell or 4-5 femtograms of Fe). Similar resolution achieved with inductively coupled plasma-mass spectrometry requires on the order of 105-106 cells and provides an average, whereas CTV provides a measurement for each cell. CTV analysis revealed that RBCs lose, on average, 17% of their Hb after 42 days of storage, the maximum FDA-approved length of time for the cold storage of RBCs in additive solution. This difference in Hb concentration was the result of routine RBC storage; clinical implications are discussed.

Working principle and application of magnetic separation for biomedical diagnostic at high- and low-field gradients

Magnetic separation is a versatile technique used in sample preparation for diagnostic purpose. For such application, an external magnetic field is applied to drive the separation of target entity (e.g. bacteria, viruses, parasites and cancer cells) from a complex raw sample in order to ease the subsequent task(s) for disease diagnosis. This separation process not only can be achieved via the utilization of high magnetic field gradient, but also, in most cases, low magnetic field gradient with magnitude less than 100 T m^-1 is equally feasible. It is the aim of this review paper to summarize the usage of both high gradient magnetic separation and low gradient magnetic separation (LGMS) techniques in this area of research. It is noteworthy that effectiveness of the magnetic separation process not only determines the outcome of a diagnosis but also directly influences its accuracy as well as sensing time involved. Therefore, understanding the factors that simultaneously influence the efficiency of both magnetic separation process and target detection is necessary. Moreover, for LGMS, there are several important considerations that should be taken into account in order to ensure its successful implementation. Hence, this review paper aims to provide an overview to relate all this crucial information by linking the magnetic separation theory to biomedical diagnostic applications.

The potential for liquid biopsies in the precision medical treatment of breast cancer

Currently the clinical management of breast cancer relies on relatively few prognostic/predictive clinical markers (estrogen receptor, progesterone receptor, HER2), based on primary tumor biology. Circulating biomarkers, such as circulating tumor DNA (ctDNA) or circulating tumor cells (CTCs) may enhance our treatment options by focusing on the very cells that are the direct precursors of distant metastatic disease, and probably inherently different than the primary tumor's biology. To shift the current clinical paradigm, assessing tumor biology in real time by molecularly profiling CTCs or ctDNA may serve to discover therapeutic targets, detect minimal residual disease and predict response to treatment. This review serves to elucidate the detection, characterization, and clinical application of CTCs and ctDNA with the goal of precision treatment of breast cancer.

Serially Ordered Magnetization of Nanoclusters via Control of Various Transition Metal Dopants for the Multifractionation of Cells in Microfluidic Magnetophoresis Devices

A novel method (i.e., continuous magnetic cell separation in a microfluidic channel) is demonstrated to be capable of inducing multifractionation of mixed cell suspensions into multiple outlet fractions. Here, multicomponent cell separation is performed with three different distinguishable magnetic nanoclusters (MnFe2O4, Fe3O4, and CoFe2O4), which are tagged on A431 cells. Because of their mass magnetizations, which can be ideally altered by doping with magnetic atom compositions (Mn, Fe, and Co), the trajectories of cells with each magnetic nanocluster in a flow are shown to be distinct when dragged under the same external magnetic field; the rest of the magnetic characteristics of the nanoclusters are identically fixed. This proof of concept study, which utilizes the magnetization-controlled nanoclusters (NCs), suggests that precise and effective multifractionation is achievable with high-throughput and systematic accuracy for dynamic cell separation.

Fundamentals and application of magnetic particles in cell isolation and enrichment: a review

Magnetic sorting using magnetic beads has become a routine methodology for the separation of key cell populations from biological suspensions. Due to the inherent ability of magnets to provide forces at a distance, magnetic cell manipulation is now a standardized process step in numerous processes in tissue engineering, medicine, and in fundamental biological research. Herein we review the current status of magnetic particles to enable isolation and separation of cells, with a strong focus on the fundamental governing physical phenomena, properties and syntheses of magnetic particles and on current applications of magnet-based cell separation in laboratory and clinical settings. We highlight the contribution of cell separation to biomedical research and medicine and detail modern cell-separation methods (both magnetic and non-magnetic). In addition to a review of the current state-of-the-art in magnet-based cell sorting, we discuss current challenges and available opportunities for further research, development and commercialization of magnetic particle-based cell-separation systems.