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Structural properties of magnetic nanoparticles determine their heating behavior - an estimation of the in vivo heating potential.

Ludwig R, Stapf M, Dutz S, Müller R, Teichgräber U, Hilger I - Nanoscale Res Lett (2014)

Bottom Line: Multicore MNP manufactured via different synthesis routes (fluidMAG-D, fluidMAG/12-D) showed different SAR although they exhibited comparable core and hydrodynamic sizes.Similar processes are supposed to take place in vivo, particularly when MNP are immobilized in cells and tissues.This aspect should be adequately considered when determining the SAR of MNP for magnetic hyperthermia.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Experimental Radiology, Division of Diagnostic and Interventional Radiology, University Hospital Jena - Friedrich Schiller University Jena, Forschungszentrum Lobeda, Erlanger Allee 101, D-07747 Jena, Germany.

ABSTRACT
Magnetically induced heating of magnetic nanoparticles (MNP) in an alternating magnetic field (AMF) is a promising minimally invasive tool for localized tumor treatment by sensitizing or killing tumor cells with the help of thermal stress. Therefore, the selection of MNP exhibiting a sufficient heating capacity (specific absorption rate, SAR) to achieve satisfactory temperatures in vivo is necessary. Up to now, the SAR of MNP is mainly determined using ferrofluidic suspensions and may distinctly differ from the SAR in vivo due to immobilization of MNP in tissues and cells. The aim of our investigations was to study the correlation between the SAR and the degree of MNP immobilization in dependence of their physicochemical features. In this study, the included MNP exhibited varying physicochemical properties and were either made up of single cores or multicores. Whereas the single core MNP exhibited a core size of approximately 15 nm, the multicore MNP consisted of multiple smaller single cores (5 to 15 nm) with 65 to 175 nm diameter in total. Furthermore, different MNP coatings, including dimercaptosuccinic acid (DMSA), polyacrylic acid (PAA), polyethylenglycol (PEG), and starch, wereinvestigated. SAR values were determined after the suspension of MNP in water. MNP immobilization in tissues was simulated with 1% agarose gels and 10% polyvinyl alcohol (PVA) hydrogels. The highest SAR values were observed in ferrofluidic suspensions, whereas a strong reduction of the SAR after the immobilization of MNP with PVA was found. Generally, PVA embedment led to a higher immobilization of MNP compared to immobilization in agarose gels. The investigated single core MNP exhibited higher SAR values than the multicore MNP of the same core size within the used magnetic field parameters. Multicore MNP manufactured via different synthesis routes (fluidMAG-D, fluidMAG/12-D) showed different SAR although they exhibited comparable core and hydrodynamic sizes. Additionally, no correlation between ζ-potential and SAR values after immobilization was observed. Our data show that immobilization of MNP, independent of their physicochemical properties, can distinctly affect their SAR. Similar processes are supposed to take place in vivo, particularly when MNP are immobilized in cells and tissues. This aspect should be adequately considered when determining the SAR of MNP for magnetic hyperthermia.

No MeSH data available.


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Immobilization in polyvinyl alcohol decreases SAR of multicore nanomag-D MNP by a factor of two. SAR values of multicore nanomag-D MNP with differently functionalized PEG300 in water suspension and immobilized in 1% agar and 10% PVA. Additionally, hydrodynamic diameters (Øhydr.) for each MNP type are shown. Values in brackets indicate core size determined by TEM micrographs. Error bars indicate standard deviation of three independent measurements.
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Figure 6: Immobilization in polyvinyl alcohol decreases SAR of multicore nanomag-D MNP by a factor of two. SAR values of multicore nanomag-D MNP with differently functionalized PEG300 in water suspension and immobilized in 1% agar and 10% PVA. Additionally, hydrodynamic diameters (Øhydr.) for each MNP type are shown. Values in brackets indicate core size determined by TEM micrographs. Error bars indicate standard deviation of three independent measurements.

Mentions: Additionally, in order to characterize a possible non-superparamagnetic particle fraction, which might considerably influence the SAR, fluidic MNP were immobilized by their drying at 50°C and measured afterwards. For this kind of measurement, the use of agarose or PVA for MNP immobilization was not necessary. Hysteresis parameters of magnetization loops M(H) with Hmax = 1,110 kA/m reveal small differences in the coercivity HC and remanence ratio Mr/MS (fluidMAG/12-D: HC = 0.32 kA/m, Mr/MS = 0.016; fluidMAG-D: HC = 0.19 kA/m, Mr/MS = 0.009; Figure 5A). In the case of the minor loops with Hmax = 15.4 kA/m, the corresponding data are as follows: fluidMAG/12-D: HC = 0.17 kA/m, Mr/MS = 0.018; fluidMAG-D: HC = 0.08 kA/m, Mr/MS = 0.008 (Figure 5A). A slight difference of the slope of the curves at zero field was obvious. Magnetization values were not considered since the amount of non-magnetic (diamagnetic) material in the dried samples (coating) is not known. Additionally, the switching field distribution S(H) was calculated. FluidMAG/12-D MNP showed, compared to fluidMAG-D MNP, a bigger fraction of MNP switching at ‘higher’ fields (H >0) but below the excitation field of 15.4 kA/m (Figure 5B).Analysis of nanomag-D MNP (core size: 5 to 15 nm) with hydrodynamic diameters between 156 to 165 nm and coated with differently functionalized PEG exhibited SAR values between 335 and 434 W/g Fe (Figure 6). The observed differences in absolute SAR values of fluidic nanomag-D MNP of the same size were related to the nature of the synthesis process of the uncoated MNP and varied among different batches.


Structural properties of magnetic nanoparticles determine their heating behavior - an estimation of the in vivo heating potential.

Ludwig R, Stapf M, Dutz S, Müller R, Teichgräber U, Hilger I - Nanoscale Res Lett (2014)

Immobilization in polyvinyl alcohol decreases SAR of multicore nanomag-D MNP by a factor of two. SAR values of multicore nanomag-D MNP with differently functionalized PEG300 in water suspension and immobilized in 1% agar and 10% PVA. Additionally, hydrodynamic diameters (Øhydr.) for each MNP type are shown. Values in brackets indicate core size determined by TEM micrographs. Error bars indicate standard deviation of three independent measurements.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230907&req=5

Figure 6: Immobilization in polyvinyl alcohol decreases SAR of multicore nanomag-D MNP by a factor of two. SAR values of multicore nanomag-D MNP with differently functionalized PEG300 in water suspension and immobilized in 1% agar and 10% PVA. Additionally, hydrodynamic diameters (Øhydr.) for each MNP type are shown. Values in brackets indicate core size determined by TEM micrographs. Error bars indicate standard deviation of three independent measurements.
Mentions: Additionally, in order to characterize a possible non-superparamagnetic particle fraction, which might considerably influence the SAR, fluidic MNP were immobilized by their drying at 50°C and measured afterwards. For this kind of measurement, the use of agarose or PVA for MNP immobilization was not necessary. Hysteresis parameters of magnetization loops M(H) with Hmax = 1,110 kA/m reveal small differences in the coercivity HC and remanence ratio Mr/MS (fluidMAG/12-D: HC = 0.32 kA/m, Mr/MS = 0.016; fluidMAG-D: HC = 0.19 kA/m, Mr/MS = 0.009; Figure 5A). In the case of the minor loops with Hmax = 15.4 kA/m, the corresponding data are as follows: fluidMAG/12-D: HC = 0.17 kA/m, Mr/MS = 0.018; fluidMAG-D: HC = 0.08 kA/m, Mr/MS = 0.008 (Figure 5A). A slight difference of the slope of the curves at zero field was obvious. Magnetization values were not considered since the amount of non-magnetic (diamagnetic) material in the dried samples (coating) is not known. Additionally, the switching field distribution S(H) was calculated. FluidMAG/12-D MNP showed, compared to fluidMAG-D MNP, a bigger fraction of MNP switching at ‘higher’ fields (H >0) but below the excitation field of 15.4 kA/m (Figure 5B).Analysis of nanomag-D MNP (core size: 5 to 15 nm) with hydrodynamic diameters between 156 to 165 nm and coated with differently functionalized PEG exhibited SAR values between 335 and 434 W/g Fe (Figure 6). The observed differences in absolute SAR values of fluidic nanomag-D MNP of the same size were related to the nature of the synthesis process of the uncoated MNP and varied among different batches.

Bottom Line: Multicore MNP manufactured via different synthesis routes (fluidMAG-D, fluidMAG/12-D) showed different SAR although they exhibited comparable core and hydrodynamic sizes.Similar processes are supposed to take place in vivo, particularly when MNP are immobilized in cells and tissues.This aspect should be adequately considered when determining the SAR of MNP for magnetic hyperthermia.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Experimental Radiology, Division of Diagnostic and Interventional Radiology, University Hospital Jena - Friedrich Schiller University Jena, Forschungszentrum Lobeda, Erlanger Allee 101, D-07747 Jena, Germany.

ABSTRACT
Magnetically induced heating of magnetic nanoparticles (MNP) in an alternating magnetic field (AMF) is a promising minimally invasive tool for localized tumor treatment by sensitizing or killing tumor cells with the help of thermal stress. Therefore, the selection of MNP exhibiting a sufficient heating capacity (specific absorption rate, SAR) to achieve satisfactory temperatures in vivo is necessary. Up to now, the SAR of MNP is mainly determined using ferrofluidic suspensions and may distinctly differ from the SAR in vivo due to immobilization of MNP in tissues and cells. The aim of our investigations was to study the correlation between the SAR and the degree of MNP immobilization in dependence of their physicochemical features. In this study, the included MNP exhibited varying physicochemical properties and were either made up of single cores or multicores. Whereas the single core MNP exhibited a core size of approximately 15 nm, the multicore MNP consisted of multiple smaller single cores (5 to 15 nm) with 65 to 175 nm diameter in total. Furthermore, different MNP coatings, including dimercaptosuccinic acid (DMSA), polyacrylic acid (PAA), polyethylenglycol (PEG), and starch, wereinvestigated. SAR values were determined after the suspension of MNP in water. MNP immobilization in tissues was simulated with 1% agarose gels and 10% polyvinyl alcohol (PVA) hydrogels. The highest SAR values were observed in ferrofluidic suspensions, whereas a strong reduction of the SAR after the immobilization of MNP with PVA was found. Generally, PVA embedment led to a higher immobilization of MNP compared to immobilization in agarose gels. The investigated single core MNP exhibited higher SAR values than the multicore MNP of the same core size within the used magnetic field parameters. Multicore MNP manufactured via different synthesis routes (fluidMAG-D, fluidMAG/12-D) showed different SAR although they exhibited comparable core and hydrodynamic sizes. Additionally, no correlation between ζ-potential and SAR values after immobilization was observed. Our data show that immobilization of MNP, independent of their physicochemical properties, can distinctly affect their SAR. Similar processes are supposed to take place in vivo, particularly when MNP are immobilized in cells and tissues. This aspect should be adequately considered when determining the SAR of MNP for magnetic hyperthermia.

No MeSH data available.


Related in: MedlinePlus