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Analytical and numerical analysis of magnetic separation of cardiomyocytes
Abstract
High-gradient magnetic separation (HGMS) has attracted considerable attention in recent time, both experimentally and theoretically. It has established itself as a powerful technique for the manipulation of particles with magnetic properties. In the present study, analytical and numerical analysis of magnetic separation of cardiomyocytes (CMs) is presented. These enriched cells can be used for therapeutic or tissue engineering applications where no ?labeling? method is accepted. Calculation of applied magnetic force for these particles that can be rendered as paramagnetic inside column was performed in order to clarify the effect of magnetic field gradient on the accumulation possibility of these particles. Numerical solutions of 2D fluid-structure finite element methods are compared with semi-analytical results for combination of magnetic field strength and average flow.
Heart disease is the leading cause of death in the world and is likely to remain as such in the foreseeable future. There is a great deal of optimism for cardiac regenerative therapies because recent advances in stem cell technology have made it possible to derive millions of cardiomyocytes
from human embryonic stem cells and induced pluripotent stem cells. These stem cell-derived cardiac cells also have an enormous potential in drug discovery, toxicology studies and fundamental cardiac physiology. Cardiomyocytes do not have well-established, specific surface markers to enable
their separation from heterogeneous cultures using transient antibody labelling and traditional methods such as fluorescence activated cell sorting (FACS) or magnetic activated cell sorting (MACS). Therefore, a major obstacle in realizing their potential is the development of separation methods
that are compatible with clinical applications and can isolate cardiomyocytes and specific cardiac cell subpopulations after in vitro culture in sufficient numbers, purity and quality. This review provides an overview of the present state of the art in labelled and label-free cardiomyocyte
isolation, the challenges to the field and a perspective on the future of cardiac cell separation.
Myoglobin (Mb) has been believed to be absent generally from mammalian smooth muscle tissue. Examination of human rectal,
uterine, bladder, colon, small intestine, arterial, and venous smooth muscle by immunohistochemical techniques shows that
each of these tissues is immunopositive for both smooth muscle myosin and human Mb. Mb-specific primers were used for the
polymerase chain reaction to generate cDNA from smooth muscle tissues. Southern hybridization with a Mb-specific probe gave
a very strong signal with the cDNA from rectum, weaker signals from small intestine and uterus, a faint signal from colon,
and no signal from bladder tissue. High performance liquid chromatography analysis coupled with sequence determination has
shown that contaminating heme-binding serum albumin as well as hemoglobin in extracts of smooth muscle seriously compromise
any heme-based or spectrophotometric assay of Mb. Combined affinity and size exclusion chromatography, however, provide the
necessary resolution. The cDNA-derived amino acid sequence of human smooth muscle Mb was found to be identical to that of
Mb from striated muscle.
The in vivo targeting of tumors with magnetic microspheres is currently realized through the application of external non-uniform magnetic fields generated by rare-earth permanent magnets or electromagnets. Our theoretical work suggests a feasible procedure for local delivery of magnetic nano- and microparticles to a target area. In particular, thin magnetizable wires placed throughout or close to the target area and magnetized by a perpendicular external uniform background magnetic field are used to concentrate magnetic microspheres injected into the target organ's natural blood supply. The capture of the magnetic particles and the building of deposits thereof in the blood vessels of the target area were modeled under circumstances similar to the in vivo situation. This technique could be applied to magnetically targeted cancer therapy or magnetic embolization therapy with magnetic particles that contain anticancer agents, such as chemotherapeutic drugs or therapeutic radioisotopes.
The status of the generalised HGMS theory, which describes the capture of ultra-fine particles, is reviewed and new results concerning the effect of hydrodynamic interactions between the particles are presented. Recent experiments leading to the development of a new class of separating devices are also reviewed.
High Gradient Magnetic Separators typically use a random array of wire matrix elements such as stainless steel wool or expanded metal for the magnetic capture of fine particles. Difficult mineral separation tasks may require systematic and controlled matrix construction to allow more selective separation of one material over another. Of interest here is the dependence of the magnetic capture force on the spacing and shielding of wire matrix elements and how such design parameters lead to a more selective matrix array. A laboratory technique developed in our group provides good confirmation of computer modeling studies. We use arrays of nickel or iron wires, spaced from 6 to 30 times the wire radius. Magnetite filled epoxy is added to the volume around the wire matrix. The wires are magnetized to saturation and the dispersed magnetite moves away from the negative gradients above and below the magnetized wires. The computer studies correlate to the magnetite patterns observed.
Basic differential equations for the buildup of magnetic particles are derived for the case that an isolated ferromagnetic wire is placed perpendicular to the magnetic field and the slurry flows parallel to the wire. These equations are easily solved analytically if the magnetic particles flow into the canister from a small surface element around a fixed point. From this solution, the shape of accumulation cross section is calculated. An experimental result shown agrees well with the present theory.
A single-wire theory of an axially ordered filter has been developed and its consequencies discussed. A typical example of the design of ordered filters has been investigated and attention given to filter elements capable of holding magnetic fibres in a desired position in space.
A new type of the HGMS filter is proposed in which the slurry flows parallel to the ferromagnetic fine wires (Parallel stream type magnetic filter). In this configuration, the capturing magnetic force scarcely competes with the drag force or the gravitational force. The recovery of the filter is calculated based on the particle trajectory model. The experimental result for hematite slurry agrees well with the present theory. A preliminary result is presented on the maintenance test of the filter recovery. This filter is expected to be easy to flush.