Biomedical Engineering – From Theory to Applications

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392 Biomedical Engineering – From Theory to Applications methods for bioengineering of these particles. Specific focus is given to the creation of functional BacMPs by magnetotactic bacteria and their applications. 2. Production of functional magnetic particles Currently, magnetic particles offer vast potential for ushering in new techniques, especially in biomedical applications, as they can be easily manipulated by magnetic force. The important characteristics of these particles include (1) immobilization of higher numbers of probes onto magnetic particles because particle surfaces are wider than those of a flat surface, (2) reduction of reaction times because of good dispersion properties that increase reaction efficiency, (3) facilitation of the bound/free separation step with a magnet, without centrifugation or filtration, and (4) the use of automated robotic systems for all reaction steps. These characteristics offer great benefits for biomedical applications such as rapid and precise measurements or separations of bio-targets. Here, the methods for production of functional magnetic particles are introduced. 2.1 Commercialized magnetic particles Commercialized magnetic particles are usually composed of superparamagnetic iron oxide nanoparticles (Fe3O4 or Fe2O3), which exhibit magnetic properties only in the presence of external magnetic fields. These particles are embedded in polymers such as polysaccharides, polystyrene, silica, or agarose. Micro-sized magnetic particles can be easily removed from suspension with magnets and easily suspended into homogeneous mixtures in the absence of an external magnetic field (Ugelstad et al., 1988). Furthermore, functional groups or biomolecules for the recognition of targets are conjugated to the polymer surfaces of magnetic particles (Fig. 1), and targets can be collected, separated, or detected by the magnetic particles. mRNA anti-CD Cells oligo streptavidin anti body Recognition molecule Fig. 1. Use of general magnetic particles Recognition moleculeimmobilized magnetic particles NH 2- ATGCCATG biotin amino DNA carboxyl Protein Protein A Protein G Target molecule
The Potential of Genetically Engineered Magnetic Particles in Biomedical Applications Biotin or streptavidin-assembled magnetic particles, on which complementary nucleic acid strands are immobilized, are widely used for the recovery or extraction of specific nucleic acids and are marketed worldwide. Moreover, magnetic particles can be used as supports for separation or detection of proteins or cells. For example, protein A- or protein G-assembled magnetic particles are suitable for antibody purification and are more efficient than columnpurification techniques. Currently, polymer magnetic particles marketed as Dynabeads ® (Invitrogen, co.) are one of the most widely used magnetic particles for biotechnology applications (Sawakami-Kobayashi et al., 2003; Prasad et al., 2003). These particles are prepared from mono-sized macroporous polystyrene particles that are magnetized by an in situ formation of ferromagnetic materials inside the pores. Dynabeads ® with diameters of 2.8 m or 4.5 m are the most widely used magnetic particles by scientists around the world, particularly in the fields of immunology, cellular biology, molecular biology, HLA diagnostics, and microbiology. Antibody-immobilized magnetic particles have been used preferentially in target-cell separation of leukocytes (Stampfli et al., 1994; Schratzberger et al., 1997; Schwalbe et al., 2006; Nakamura et al., 2001) for in vitro diagnosis because of the simpler and more rapid methodology as compared to cell sorting using a flow cytometer. These commercially available magnetic particles are chemically synthesized compounds of micrometer and nanometer sizes. Several cell separation systems using nano-sized magnetic particles, such as 50-nm iron oxide particles with polysaccharide- (Miltenyi Biotech, co.) or dextran- (StemCell Technologies Inc.) coated superparamagnetic nanoparticles, are commercially available (Miltenyi, 1995; Wright, 1952). Because these particles are superparamagnetic and are preferred for high-gradient magnetic separation, specially-designed magnetic columns that produce high magnetic field gradients are required for cell separation (Miltenyi, 1995). Nanosized magnetic particles are advantageous for assay sensitivity, rapidity, and precision. However, it remains difficult to synthesize nano-sized magnetic particles with uniform size and shape that adequately disperse in aqueous solutions. Consequently, advanced techniques and high costs are required for the production of nano-sized magnetic particles. Magnetic particles are widely used not only as carriers for recovery or detections of biomolecules, but also used as probes for magnetic detections, or agent for magnetic-fieldinduced heating. Especially, magnetic particles that have high saturation magnetization are ideal candidates for MRI contrast agents, and various kinds of magnetic particles have been developed and used for diagnoses. Recently, Mulder et. al. developed the paramagnetic quantum dots (pQDs) coated with paramagnetic and pegylated lipids which had a high relaxivity. The high relaxivity makes the pQDs contrast agent an attractive candidate for molecular MRI purposes. This nanoparticulate probe makes it detectable by both MRI and fluorescence microscopy (Mulder et al., 2006). It was successful that the synthesis of quantum dots with a water-soluble and paramagnetic micellular coating were used as a molecular imaging probe for both fluorescence microscopy and MRI. The present study uses magnetic nanoparticles as bimodal tools and combines magnetically induced cell labelling and magnetic heating. The particles are used in hyperthermia agents, where the magnetic particles are heated selectively by application of an high frequency magnetic field (Mulder et al., 2006). These magnetic heating treatments using superparamagnetic iron oxide nanoparticles continue to be an active area of cancer research. The research aimed to assess if a selective and higher magnetic nanoparticles accumulation within tumor cells is due to magnetic labeling and consequently a larger heating effect occurs after exposure to an alternating magnetic field in order to eliminate labeled tumor cells effectively (Kettering et 393
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BIOMEDICAL ENGINEERING - FROM THEOR
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free online editions of InTech Book
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VI Contents Chapter 9 Targeted Magn
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X Preface stand-alone and readers c
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2 Biomedical Engineering - From The
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6 Biomedical search engine Scientif
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12 Bireme http://regional.bv salud.
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108 Method (Detection) CIEF-tITP-CZ
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110 Method (Detection) Analyte Matr
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120 6. Conclusion Biomedical Engine
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150 5. Conclusions Biomedical Engin
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162 1 st phase : half year 4 2 nd p
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166 7. Innovative active training B
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172 12. Maturing projects’ story
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180 16. Acknowledgments Biomedical
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190 R* M M M M MR*M O O O O M O R*
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196 Fig. 9. Chemical structure of 5
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198 Relative Intensity (AU) Biomedi
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204 2. Preparation of IO nanopartic
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256 3. Deposition techniques Biomed
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300 2. Nanoparticles in biomedical
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454 In this case, the eigenvalues a
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456 where Biomedical Engineering -
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472 Nb b b l l1 Biomedical Engineer
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478 Load F (μN) Parallel-oriented
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