Separation of a breast cancer cell line from human blood using a quadrupole magnetic flow sorter

Recovery of Magnetic Catalysts: Advanced Design for Process Intensification

The design of microdevices in which components with magnetic character must be separated and recovered from reactive media benefits from the advantages of microfluidics and meets the criteria for process intensification; however, there are open questions, such as the design of the most appropriate magnet arrangement, that need further research in order to increase the magnetic gradient exerted on the particles. Herein, we focus on the continuous recovery of magnetic microparticles, that can be used as support to facilitate the recovery of biocatalysts (magnetic microcatalysts, MMCs) from biological fluids. We analyze and compare the performance of two typical magnetophoretic microdevices for addressing bead recovery: (i) annular channels with a quadrupole orientation of the permanent magnets (quadrupole magnetic sorter, QMS) and (ii) the standard design, which consists of rectangular channels with a single permanent magnet to generate the magnetic field. To this end, an experimentally validated computational fluid dynamics (CFD) numerical model has been employed. Our results reveal that for devices with the same width and length, the micro-QMS, in comparison to a rectangular channel, could accomplish the complete particle retrieval while (i) processing more than 4 times higher fluid velocities, treating more than 360 times higher flow rates or (ii) working with smaller particles, thus reducing by 55% the particle mass. Additionally, the parallel performance of ≈300 micro-QMSs fulfills the processing of flow rates as high as 200 L·h^–1 while entirely capturing the magnetic beads. Thereby, this work shows the potential of the QMS advanced design in the intensification of the recovery of catalysts supports of magnetic character.

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.

Magnetophoresis of diamagnetic microparticles in a weak magnetic field

Magnetic manipulation is a promising technique for lab-on-a-chip platforms. The magnetic approach can avoid problems associated with heat, surface charge, ionic concentration and pH level. The present paper investigates the migration of diamagnetic particles in a ferrofluid core stream that is sandwiched between two diamagnetic streams in a uniform magnetic field. The three-layer flow is expanded in a circular chamber for characterisation based on imaging of magnetic nanoparticles and fluorescent microparticles. A custom-made electromagnet generates a uniform magnetic field across the chamber. In a relatively weak uniform magnetic field, the diamagnetic particles in the ferrofluid move and spread across the chamber. Due to the magnetization gradient formed by the ferrofluid, diamagnetic particles undergo negative magnetophoresis and move towards the diamagnetic streams. The effects of magnetic field strength and the concentration of diamagnetic particles are studied in detail.

Implications of thyroglobulin antibody positivity in patients with differentiated thyroid cancer: a clinical position statement

BACKGROUND

Even though the presence of antithyroglobulin antibodies (TgAbs) represents a significant problem in the follow-up of patients with differentiated thyroid cancer (DTC), the current guidelines on the management of DTC that have been published in recent years contain no text concerning the methods to be used for detecting such antibody-related interference in thyroglobulin (Tg) measurement or how to manage TgAb-positive patients in whom Tg cannot be used reliably as a tumor marker.

AIM

An international group of experts from the European Thyroid Association Cancer Research Network who are involved in the care of DTC patients met twice to form a consensus opinion on how to proceed with treatment and follow-up in TgAb-positive DTC patients based on the available evidence in the literature. Here we will report on the consensus opinions that were reached regarding technical and clinical issues.

RESULTS

This clinical opinion article provides an overview of the available evidence and the resulting consensus recommendations. The current literature does not provide sufficient data for giving evidence-based answers to many questions arising in the care of TgAb-positive DTC patients. Where insufficient evidence was available, a thorough discussion by a group of physician-scientists, all of whom have a distinguished track record in thyroid cancer care, was held to arrive at a consensus expert opinion. The questions and answers discussed were then summarized into an algorithm for the management of TgAb-positive patients.

CONCLUSION

We were able to define 26 consensus expert recommendations and a resulting algorithm for the care of TgAb-positive DTC patients.

Emerging technologies for CTC detection based on depletion of normal cells

Properly conducted, an enrichment step can improve selectivity, sensitivity, yield, and most importantly, significantly reduce the time needed to isolate rare circulating tumor cells (CTCs). The enrichment process can be broadly categorized as positive selection versus negative depletion, or in some cases, a combination of both. We have developed a negative depletion CTC enrichment strategy that relies on the removal of normal cells using immunomagnetic separation in the blood of cancer patients. This method is based on the combination of magnetic and fluid forces in an axial, laminar flow in long cylinders placed in quadrupole magnets. Using this technology, we have successfully isolated CTCs from patients with breast carcinoma and squamous cell carcinoma of the head and neck. In contrast to a positive selection methodology, this approach provides an unbiased characterization of these cells, including markers associated with epithelial mesenchymal transition.

Computational Fluid Dynamics Simulation of a Quadrupole Magnetic Sorter Flow Channel: Effect of Splitter Position on Nonspecific Crossover

In the Quadrupole Magnetic Sorter (QMS) magnetic particles enter a vertical flow annulus and are separated from non-magnetic particles by radial deflection into an outer annulus where the purified magnetic particles are collected via a flow splitter. The purity of magnetically isolated particles in QMS is affected by the migration of nonmagnetic particles across transport lamina in the annular flow channel. Computational Fluid Dynamics (CFD) simulations were used to predict the flow patterns, pressure drop and nonspecific crossover in QMS flow channel for the isolation of pancreatic islets of Langerhans. Simulation results were compared with the experimental results to validate the CFD model. Results of the simulations were used to show that one design gives up to 10% less nonspecific crossover than another and this model can be used to optimise the flow channel design to achieve maximum purity of magnetic particles.

The use of a linear Halbach array combined with a step-SPLITT channel for continuous sorting of magnetic species

The Quadrupole Magnetic Sorter (QMS), employing an annular flow channel concentric with the aperture of a quadrupole magnet, is well established for cell and particle separations. Here we propose a magnetic particle separator comprising a linear array of cylindrical magnets, analogous to the array proposed by Klaus Halbach, mated to a substantially improved form of parallel-plate SPLITT channel, known as the step-SPLITT channel. While the magnetic force and throughput are generally lower than for the QMS, the new separator has advantages in ease of fabrication and the ability to vary the magnetic force to suit the separands. Preliminary experiments yield results consistent with prediction and show promise regarding future separations of cells of biomedical interest.

Characterization of nonspecific crossover in split-flow thin channel fractionation

Split-flow thin channel (SPLITT) fractionation is a technique for continuous separation of particles or macromolecules in a fluid stream into fractions according to the lateral migration induced by application of a field perpendicular to the direction of flow. Typical applications have involved isolation of different fractions from a polydisperse sample. Some specialized applications involve the separation of the fraction influenced by the transverse field from the fraction that is not. For example, immunomagnetically labeled biological cells may be separated from nonlabeled cells with the application of a transverse magnetic field gradient. In such cases, it may be critically important to minimize contamination of the labeled cells with nonlabeled cells while at the same time maximizing the throughput. Such contamination is known as nonspecific crossover (NSC) and refers to the real or apparent migration of nonmobile particles or cells across stream lines with the mobile material. The possible mechanisms for NSC are discussed, and experimental results interpreted in terms of shear-induced diffusion (SID) caused by viscous interactions between particles in a sheared flow. It is concluded that SID may contribute to NSC, but that further experiments and mathematical modeling are necessary to more fully explore the phenomenon.

2D modeling and preliminary in vitro investigation of a prototype high gradient magnetic separator for biomedical applications

High gradient magnetic separation (HGMS) of magnetic materials from fluids or waste products has many established industrial applications. However, there is currently no technology employing HGMS for ex-vivo biomedical applications, such as for the removal of magnetic drug- or toxin-loaded spheres from the human blood stream. Importantly, human HGMS applications require special design modifications as, in contrast to conventional use where magnetic elements are permanently imbedded within the separation chambers, medical separators need to avoid direct contact between the magnetic materials and blood to reduce the risk of blood clotting and to facilitate convenient and safe treatment access for many individuals. We describe and investigate the performance of a magnetic separator prototype designed for biomedical applications. First, the capture efficiency of a prototype HGMS separator unit consisting of a short tubing segment and two opposing magnetizable fine wires along the outside of the tubing was investigated using 2D mathematical modeling. Second, the first-pass effectiveness to remove commercially available, magnetic polystyrene spheres from human blood using a single separator unit was experimentally verified. The theoretical and experimental data correlated well at low flow velocities (<5.0 cm/s) and high external magnetic fields (>0.05 T). This prototype separator unit removed >90% in a single pass of the magnetic spheres from water at mean flow velocity < or =8.0 cm/s and from blood mimic fluids (ethylene glycol-water solutions) at mean flow velocity < or =2.0 cm/s. In summary, we describe and prove the feasibility of a HGMS separator for biomedical applications.

Blood progenitor cell separation from clinical leukapheresis product by magnetic nanoparticle binding and magnetophoresis

Positive selection of CD34+ blood progenitor cells from circulation has been reported to improve patient recovery in applications of autologous transplantation. Current magnetic separation methods rely on cell capture and release on solid supports rather than sorting from flowing suspensions, which limits the range of therapeutic applications and the process scale up. We tested CD34+ cell immunomagnetic labeling and isolation from fresh leukocyte fraction of peripheral blood (leukapheresis) using the continuous quadrupole magnetic flow sorter (QMS), consisting of a flow channel (SHOT, Greenville, IN) and a quadrupole magnet with a maximum field intensity (B(o)) of 1.42 T and a mean force field strength (S(m)) of 1.45 x 10(8) TA/m(2). Both the sample magnetophoretic mobility (m) and the inlet and outlet flow patterns highly affect the QMS performance. Seven commercial progenitor cell labeling reagent combinations were quantitatively evaluated by measuring magnetophoretic mobility of a high CD34 expression cell line, KG-1a, using the cell tracking velocimeter (CTV). The CD34 Progenitor Cell Isolation Kit (Miltenyi Biotec, Bergisch Gladbach, Germany) showed the strongest labeling of KG-1a cells and was selected for progenitor cell enrichment from 11 fresh and 11 cryopreserved clinical leukapheresis samples derived from different donors. The CD34+ cells were isolated with a purity of 60-96%, a recovery of 18-60%, an enrichment rate of 12-169, and a throughput of (1.7-9.3) x 10(4) cells/s. The results also showed a highly regular dependence of the QMS performance on the flow conditions that agreed with the theoretical predictions based on the CD34+ cell magnetophoretic mobility.

Magnetic counter-gravity flow separation of electrically prepolarised lymphoid cells

A novel principle is proposed for a differential separation of live cells (such as leucocytes) from a main flow. A microfluidic device with planar insulated electrodes as the side walls of the channel was manufactured and tested. An array of insulated vertical conductor wires was inserted along the axis of the channel and used to impose Lorentz forces upon polarisable particles that moved with the flow. Polystyrene microspheres and lymphoid cell lines (DOHH2 and K562) were used to test the ability of the setting to impose a force field that induced consistent vertical motion. The direction of electric current was found to directly influence the number of cells or microspheres that were sampled at the surface of the flow. Lorentz force was considered to be active upon cells due to an overall polarisation of the membrane surface. The consequence of the magnetic force was that the polarised cells were moved vertically upwards (opposing gravity). The setting was effective for increasing the number of extracted cells from a main flow or for increasing the concentration of DOHH2 cells in a mixed population with K562 in culture medium. The limitations of the work parameters (potential-current) were found to be dependent upon the cell type.

Magnetic separation of micro-spheres from viscous biological fluids

A magnetically based detoxification system is being developed as a therapeutic tool for selective and rapid removal of biohazards, i.e. chemicals and radioactive substances, from human blood. One of the key components of this system is a portable magnetic separator capable of separating polymer-based magnetic nano/micro-spheres from arterial blood flow in an ex vivo unit. The magnetic separator consists of an array of alternating and parallel capillary tubing and magnetizable wires, which is exposed to an applied magnetic field created by two parallel permanent magnets such that the magnetic field is perpendicular to both the wires and the fluid flow. In this paper, the performance of this separator was evaluated via preliminary in vitro flow experiments using a separator unit consisting of single capillary glass tubing and two metal wires. Pure water, ethylene glycol-water solution (v:v=39:61 and v:v=49:51) and human whole blood were used as the fluids. The results showed that when the viscosity increased from 1.0 cp to 3.0 cp, the capture efficiency (CE) decreased from 90% to 56%. However, it is still feasible to obtain >90% CE in blood flow if the separator design is optimized to create higher magnetic gradients and magnetic fields in the separation area.

Application of immunomagnetic cell enrichment in combination with RT-PCR for the detection of rare circulating head and neck tumor cells in human peripheral blood

Detection of rare, circulating tumor cells (CTC's) in human peripheral blood is a potential indicator of prognosis and diagnosis in oncology. Typical methods to detect these CTC's are either by immunocytochemistry (ICCS) or RT-PCR. However without accurate, rapid, and reproducible enrichment processes, these detection techniques are labor intensive and/or unreliable. In this article, a repeatable enrichment process that included a flow-through immunomagnetic cell separation system, the quadrupole magnetic sorter (QMS) was optimized with the aid of a statistical analysis software package. The QMS was operated in a negative mode of operation by immunomagnetically targeting normal human peripheral blood lymphocytes (PBL) through the CD45 surface marker. Three head and neck squamous carcinoma cell lines (HNSCC), Detroit-562, SCC-4, and CAL-27, were used to determine the sensitivity of RT-PCR for the epidermal growth factor receptor (EGFR) in spiked PBL. The detection purity needed for detection was found to be one cell in 10(4), one cell in 10(3), and one cell in 10(5) for the Detroit-562, SCC-4, and CAL-27, respectively. The actual number of cancer cells needed for RT-PCR detection ranged from 30 to 1 cell. To mimic the potential concentration of rare CTC present in peripheral blood of cancer patients, the spiking concentration was chosen to be one cancer cell per 10(5) total leukocytes from healthy donors. Using a single step immunomagnetic labeling, the final, optimized enrichment process produced a 57.6 +/- 30.3-fold (n = 6) enrichment of the rare cancer cells with a final cancer cell recovery of (77.8 +/- 6.6)%.

Comparison of two immunomagnetic separation technologies to deplete T cells from human blood samples

The objective of this study was to compare the performance of two immunomagnetic separation technologies to deplete T cells from buffy coats of human blood. Specifically, two versions of the commercial MACS(R) Technology: MiniMACS and SuperMACS, and a prototype, flow-through system, the QMS, were evaluated. Peripheral blood mononuclear leukocytes (PBL) were isolated from buffy coats and an immunomagnetic separation of CD3(+) cells was conducted using company and optimized labeling protocols. To mimic peripheral blood containing bone marrow purged hematopoietic stem cells, HSC, CD34 expressing-cells (KG1a) were spiked into PBL prior to T-cell depletion once optimized depletion conditions were determined. Once the labeling protocol was optimized, the MiniMACS system performed well by producing a highly enriched CD3(+) fraction, and a respectable level of depletion of T cells and recovery of KG1a cells in the depleted fraction; an average log(10) depletion of T cells of 2.88 +/- 0.17 and an average recovery of the KG1a cells of 60.8 +/- 5.94% (n = 14). The performance of the SuperMACS system was very similar with an average log(10) depletion of T cells of 2.89 +/- 0.22 and an average recovery of KG1a of 63.1 +/- 8.55% (n = 10). In contrast, the QMS system produced an average log(10) depletion of T cells of 3.98 +/- 0.33 (n = 16) with a corresponding average recovery of 57.9 +/- 16.6% of the spiked CD34+ cells. The aforementioned QMS performance values were obtained using sorting speeds ranging from 2.5 x 10(4) to 1.7 x 10(5) cells per second. It is suggested that the lack of a 100% recovery of the unlabeled KG1a cells is the result of a previously reported "drafting" phenomena which pulls unlabeled cells in the direction of the magnetically labeled cells thereby resulting in loss of the unlabeled cells.

Polymer nano-engineering for biomedical applications

Polymeric materials possess many attractive properties such as high toughness and recyclability. Some possess excellent biocompatibility, are biodegradable, and can provide various bio-functionalities. Proper combination of functional polymers and biomolecules can offer tailored properties for various biomedical applications. This overview article covers three major sections: Applications of Polymeric Structures and Devices, Nanoscale Polymer Fabrication Technologies, and Conclusions and Future Directions.

Enrichment of rare cancer cells through depletion of normal cells using density and flow-through, immunomagnetic cell separation

OBJECTIVE

To develop a reliable technique to enrich for rare cells in blood suspensions using only negative selection steps including a flow-through immunomagnetic cell separations system and by optimizing variables normally encountered during such enrichment processes.

METHODS

A human breast cancer cell line was cultivated and spiked at a ratio of 1 cancer cell to 10(5) total leukocytes in buffy coat or 1 cancer cell to 10(8) total cells in whole blood samples. The final, optimized process consisted of: a red cell lysis step, immunomagnetically staining leukocytes with an anti-CD45 PE, anti- MACS sandwich, immunomagnetic sorting using a flow-through system (QMS), and a final cell analysis step using either an automated cell counter, filtration, and visual counting or a cytospin analysis.

RESULTS

The final, optimized process produced a final enrichment of the rare cancer cells of 5.17 log(10) and an average, final recovery of 46%. It should be noted that a negative depletion protocol was used (i.e., no labeling of the rare cancer cells was used).

CONCLUSIONS

To the authors' knowledge, no examples in the literature exist of a 5.17 log(10) enrichment of cancer cells in human blood using a negative depletion protocol. The closest example is a 4 log(10) enrichment in which two positive magnetic cell separation steps were used (none were used in this study). Ongoing studies are investigating further modifications of the precommercial, prototype flow-through immunmagnetic separation system to increase both the enrichment and recovery rate. However, even at current performance levels, the presented process could significantly improve visual and molecular analysis of rare cells in blood.

Effect of flow development region and fringing magnetic force field on annular split-flow thin fractionation

Split-flow thin (SPLITT) fractionation devices have been widely used to separate macromolecules, colloids, cells and particles. Recently, the quadrupole magnetic flow sorter (QMS) has been reported in the literature as another family of SPLITT fractionation device. However, the separation performance observed in the experimental measurements is generally found to deviate from the ideal behaviour. Possible causes such as hydrodynamic lift force, high particle concentration and imperfect geometries have been extensively examined. However, the effects of flow development regions and fringing magnetic force field at the separation channel inlet and outlet, which are ignored by the theory, have not been investigated. The error introduced by ignoring these effects need to be rigorously studied so that the theory can be used to optimise operation flow rates with confidence. Indeed, we find in this paper that these ignored effects are responsible to the discrepancy between the experimental data and the theoretical predictions. A new theory has been proposed for optimisation of device operation.

Dielectrophoresis-Based Sample Handling in General-Purpose Programmable Diagnostic Instruments

As the molecular origins of disease are better understood, the need for affordable, rapid, and automated technologies that enable microscale molecular diagnostics has become apparent. Widespread use of microsystems that perform sample preparation and molecular analysis could ensure that the benefits of new biomedical discoveries are realized by a maximum number of people, even those in environments lacking any infrastructure. While progress has been made in developing miniaturized diagnostic systems, samples are generally processed off-device using labor-intensive and time-consuming traditional sample preparation methods. We present the concept of an integrated programmable general-purpose sample analysis processor (GSAP) architecture where raw samples are routed to separation and analysis functional blocks contained within a single device. Several dielectrophoresis-based methods that could serve as the foundation for building GSAP functional blocks are reviewed including methods for cell and particle sorting, cell focusing, cell ac impedance analysis, cell lysis, and the manipulation of molecules and reagent droplets.

Magnetic Cell Separation: Characterization of Magnetophoretic Mobility

Magnetic cell separation has become a popular technique to enrich or deplete cells of interest from a heterogeneous cell population. One important aspect of magnetic cell separation is the degree to which a cell binds paramagnetic material. It is this paramagnetic material that imparts a positive magnetophoretic mobility to the target cell, thus allowing effective cell separation. A mathematical relationship has been developed to correlate magnetic labeling to the magnetophoretic mobility of an immunomagnetically labeled cell. Four parameters have been identified that significantly affect magnetophoretic mobility of an immunomagnetically labeled cell: the antibody binding capacity (ABC) of a cell population, the secondary antibody amplification (psi), the particle-magnetic field interaction parameter (DeltachiV(m)), and the cell diameter (D(c)). The ranges of these parameters are calculated and presented along with how the parameters affect the minimum and maximum range of magnetophoretic mobility. A detailed understanding of these parameters allows predictions of cellular magnetophoretic mobilities and provides control of cell mobility through selection of antibodies and magnetic particle conjugates.

Characterization of antibody binding to three cancer-related antigens using flow cytometry and cell tracking velocimetry

Proper antibody labeling is a fundamental step in the positive selection/isolation of rare cancer cells using immunomagnetic cell separation technology. Using either a two-step or single-step labeling protocol, we examined a combination of six different antibodies specific for three different antigens (epithelial specific antigen, epithelial membrane antigen, and HER-2/Neu) on two different breast cancer cell lines (HCC1954 and MCF-7). When a two-step labeling protocol was used (i.e., anti-surface marker-fluoroscein-isothiocyanate [FITC] [primary Ab], anti-FITC magnetic colloid [secondary Ab]) saturation of the primary antibody was determined using fluorescence intensity measurements from flow cytometry (FCM). The saturation of the secondary antibody (or saturation of a single-step labeling) was determined using magnetophoretic mobility measurements from cell tracking velocimetry (CTV). When the maximum magnetophoretic mobility was the primary objective, our results demonstrate that the quantities necessary for antibody saturation with respect to fluorescence intensity were generally higher than those recommended by the manufacturer. The results demonstrate that magnetophoretic mobility varies depending on the types of cell lines, primary antibodies, and concentration of secondary magnetic colloid-conjugated antibody. It is concluded that saturation studies are a vital preparatory step in any separation method involving antibody labeling, especially those that require the specificity of rare cell detection.