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Chapter-1 Introduction
D. Y. Patil University, Kolhapur 1
1.1. Introduction to nanoparticles
In nanotechnology, a nanoparticle (NPs) is defined as a small object that
behaves as a whole unit in terms of its transport and properties. It can be
categorized according to their size and diameters. Mainly they are classified into
compact materials and nanodispersions. A NP is a quasi-zero-dimensional (0D)
nanoobject in which all characteristic linear dimensions are of the same order of
magnitude (not more than 100 nm) [1-3]. Nanodispersions, unlike nanostructured
materials, include a homogeneous dispersion medium (vacuum/gas, liquid, or
solid) and nanosized inclusions dispersed in this medium and isolated from each
other. The distance between the nano-objects in these dispersions can vary over
broad limits from tens of nanometers to fractions of a nanometer. Such
nanostructured systems constitute a bridge between single molecules and infinite
bulk systems. Nanomaterials can be differentiated based on the shapes as zero
dimensional (quantum dots, spherical, elliptical NPs), one dimensional
(nanowires) and two dimensional nanostructures (nanoplates, nanocubes). The
chemical and physical properties of NPs can significantly differ from those of
bulk materials of same chemical composition. The experimental and conceptual
background for the field of nanoscience is constituted by the energetics; the
uniqueness of structural characteristics, response, dynamics and chemistry of
nanostructures. The underlying themes of nanoscience and nanotechnology are
as follows: first, the bottom-up approach of the self assembly of molecular
components where each molecular or nanostructured component plugs itself into
a superstructure [2]; and second, the top-down approach of miniaturization of the
components [3]. Some of the size dependant properties of NPs are: Change in
Thermal properties – melting temperature, Electrical properties – tunneling
current, Magnetic properties – superparamagnetic effect (Ex. Iron oxide is
ferromagnetic in bulk while below 14 nm it shows superparamagnetic
properties), Optical properties – absorption and scattering of light, surface
plasmon resonance effect; Chemical properties–reactivity, catalysis (Ex. Bulk
gold is noble while nanoparticles of gold are catalysts); Mechanical properties –
adhesion, capillary forces.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 2
The use of nanoparticles in biotechnology and medicine merges the fields
of material science, chemistry, physics and biology. Nanostructured materials,
such as NPs, nanowires, nanotubes and thin films, provide a particularly useful
platform for successful development of wide-ranging therapeutic and diagnostic
applications in the biomedical area [4]. Due to the tremendous development of
this field of research worldwide, the term “nanomedicine” was recently coined
[5], long after nanomaterials started to impact biomedical research. (The size
variation is shown in figure 1.1. In nanomedicine, nanoparticles play a vital role
depending upon their characteristics. The types of nanoparticles extensively
explored especially for biomedical applications are shown in Figure 1.2.
Figure 1.1. Sense of Nano Scale
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 3
Figure 1.2.Type of Nanoparticles for biomedical applications
1.2. Magnetic nanoparticles (MNPs)
MNPs are a class of nanoparticles that can be manipulated under the
influence of an external magnetic field. MNPs are composed of magnetic
elements, such as, cobalt, nickel, iron and their oxides. Engineered magnetic NPs
(MNPs) represent a cutting-edge tool in medicine because they can be
simultaneously functionalized and guided by a magnetic field. Magnetic NPs
have become important imaging tools for the prevalent diseases like cancer,
atherosclerosis, diabetes, and others. The unique ability of MNPs to resonantly
response to an external magnetic field has been utilized for magnetic resonance
imaging (MRI), cell tracking, bioseparation, tissue engineering, targeted gene
and drug delivery, and magnetic induction heating hyperthermia [6].
Nanoscale magnetic materials have attracted widespread interest because
of novel effects arising due to the reduction of their spatial extension. This has a
major impact on modern magnetic storage technology [7] as well as on the basic
comprehension of magnetism on the mesoscopic scale [8-9]. As first predicted
by Frenkel and Dorfman [10,11] a particle of a ferromagnetic material is
expected to consist of a single magnetic domain below a critical particle size.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 4
The rough estimates of this critical particle sizes, have first been made by Kittel
[12]. An approximate radius of 15 nm is estimated for a spherical sample of a
common ferromagnetic material. The magnitude of magnetic moment ‘M’ of a
particle is proportional to its volume. These monodomain ferromagnetic particles
can be viewed as large magnetic units, each having a magnetic moment of about
thousands of Bohr magnetons.
Usually an ellipsoidal shape of the particles is assumed, where the
magnetic moments have the tendency to align along the longest axis, which
defines the direction of largest “shape” anisotropy energy [12]. The remarkable
new phenomena observed in nanomaterials arise from the subtle interplay
between the intrinsic properties, size distribution of the NPs, finite-size effects
and the interparticle interactions. Finite-size effects dominate the magnetic
behaviour of individual NPs, increasing their relevance as the particle size
decreases. Superparamagnetism is the most studied finite-size effect in small
particle systems, which is a finite-size effect since the particle anisotropy is
generally proportional to its volume.
The magnetic behaviour of particle at the surface differs from that
corresponding to core, because of the compositional gradients, distinct atomic
coordination, concentration, and nature of defects present in both the regions.
Therefore, whereas the core usually displays a spin arrangement similar to that of
the bulk material; a much higher magnetic disorder is present at the surface
giving rise to magnetic behaviours covering from that of a dead magnetic layer
to that of a spin glass- like. The competition between both magnetic orders—
surface and core—determines the ground state of the particle, which can be very
far from the simple assumption of a single domain with the perfect magnetic
ordering corresponding to the bulk material. And this is another important finite-
size effect that largely influences the magnetic response of the NPs [4, 13].
Challenges arise each day as these NPs find their way to emerging technologies
where a thorough understanding of their chemical stability, dispersion in
different media, particle-particle interactions, surface chemistry, and magnetic
response are fundamental for successful implementation.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 5
1.2.1. Types of magnetic NPs
The random and competing interparticle interactions present in
concentrated nanostructured materials may strongly modify the dynamic
response of these systems. Firstly, by affecting the height of the energy barrier
which determines the relaxation time of each individual particle, and secondly,
by producing a collective state which shares most of the phenomenology
attributed to the magnetic glass behaviour. In some cases, where interparticle
interactions have some degree of coherence, the formation of long-range domain
like structures have been observed well below the percolation threshold, for
example, in textured thin films of Co-based granular alloys. These phenomena
can be controlled by varying the particle size and interparticle distance, whose
values are a consequence of the finite-size effects. Surface disorder and
roughness influence the spin dependent electron scattering at the magnetic/non-
magnetic interfaces in giant magneto resistive granular heterogeneous alloys and
magnetic multilayers. Besides, insulating granular solids, constituted by the
dispersion of ferromagnetic particles in an insulating matrix, display a wide
richness of transport phenomena related to finite-size and proximity effects, in
particular, the so-called Coulomb blockade and spin-polarized tunnelling
conduction. Based on the magnetic response, MNPs are classified as diamagnetic
(No response to external magnetic field, negative susceptibility), paramagnetic
(weak response, low positive susceptibility) and ferromagnetic (high positive
susceptibility). Depending on the size, magnetic nanoparticles even represent
special class of magnetism known as superparamagnetism (zero coercivity, zero
remenance).
1.2.2. Important properties of MNPs
Several forms of magnetism exist in nature, with superparamagnetism
(SPM) seeming to be preferred for MNPs applied to biomedical problems. SPM
occurs when particles are small enough for thermal fluctuations to cause random
flipping of magnetic moments. Randomization of the orientation of these
magnetic moments results in an average magnetization of zero in the absence of
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 6
an applied magnetic field. The characteristic time from one moment flip to the
next is called the Neel relaxation time and is approximated by Neel-Arrhenius
relation [16]:
where τ0 is the time between flip attempts and is typically in the range 10-9
to 10-
12 s depending on the material, K is the magnetic anisotropy energy, V is the
particle volume, kB is the Boltzmann constant, and T is temperature. From
equation, it is observed that the relaxation time decreases or flipping frequency
increases as the particle size decreases. The size limit required to achieve
superparamagnetism can vary with core material composition, but is typically
<30 nm for iron oxide crystals. Considering this threshold, MNPs with a core
larger than 20-30 nm typically consist of clusters of multiple smaller iron oxide
domains rather than a single large crystal. SPMNPs are ideal for in vivo use as
the presence of attractive forces between neighbouring MNPs (from permanent
or remnant magnetization) could lead to the formation large aggregates, which
are more easily cleared from the circulation and pose greater risks for vascular
embolism. Greater magnetic susceptibility and magnetic saturation are the
additional attractive properties of superparamagnetic MNPs compared to
paramagnetic materials when exposed to an external magnetic field [14-15]. This
high magnetic susceptibility is the result of reorientation of individual. High
magnetization iron oxide crystals responding to applied field are illustrated in
figure 1.3.
Because of their, interesting properties magnetic nanoparticles with
especially iron oxide based spinel ferrites became a first choice for biomedical
applications. The spinel structure and hence iron oxide based system is discussed
in detail below.
0 expB
KV
k T
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 7
Figure 1.3. Illustration of superparamagnetic NP response to applied magnetic
field. The dashed circle denotes the randomization of moments in the absence of
external Magnetic field
1.3. Introduction to spinel ferrites
The spinels are class of minerals of general formulation A2+
B23+
O42-
which crystallise in the cubic (isometric) crystal system where the oxide anions
arranged in a cubic close-packed lattice whereas the cations A and B occupying
some or all of the octahedral and tetrahedral sites in the lattice. A and B can be
di-, tri- or quadrivalent cations, including iron, magnesium, manganese, zinc,
chromium, silicon, aluminium, and titanium . Though the anion is normally
oxide, the analogous thiospinel structure includes the rest of chalcogenides. A-
and B- can also be the same metals under different charges, such as the case in
Fe3O4 (as Fe2+
Fe23+
O42-
). Usually Spinel crystallizes in the isometric system and
common crystal forms are octahedral and twinned. It has an imperfect octahedral
cleavage and a conchoidal fracture. Its specific gravity is 3.5-4. 1, its hardness is
8, and it is transparent to opaque with a vitreous to dull cluster. It may be
colourless, but is usually of various shades of colours such as red, blue,
green, yellow, brown or black.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 8
The crystal structure of spinel was determined independently by Bragg
and Grimes [16 and 17]. The majority of spinel compounds belong to space
group Fd3m. Figure 1.4 shows the primitive tetrahedral unit cell of spinel. This
cell consists of two molecular AB2X4 units and is represented by two octants in
Figure, with atomic positions indicated in diagram. Four primitive cells, arranged
as shown in Fig, combine to form cubic unit cell of spinel. There are Z=8
formula units per cubic unit cell, each of which consists of 32 anions and 24
cations, for a total 56 atoms. The Bravais lattice of conventional unit cell is face
centered cubic (fcc); the basis consists of two components. The anionic sublattice
is arranged in a pseudo-cubic close packed (ccp) spatial arrangement, although
some spinels possesses almost ideal ccp anionic sublattice. As a consequence the
spinel lattice parameters are large, in natural MgAl2O4, a= 0.8089 nm. There are
96 interstices between the anions in the unit cell; however, in AB2X4 compounds
only 24 are occupied by cations. Out of 64 interstices that exist between anions;
8 are occupied by cations and remaining 16 cations occupy half of the 32
octahedral interstices. The tetrahedrally co-ordinated cations form a diamond
cubic sublattice with repeat units equal to lattice parameter. Description of
atomic positions in spinel is dependent on the choice of setting of origin in Fd3m
space group. Normal spinel structures are usually cubic closed-packed (ccp)
oxides with one octahedral and two tetrahedral sites per oxide. Tetrahedral points
are smaller than the octahedral points. B3+
ions occupy the octahedral holes due
to the charge factor, but only can occupy half of the octahedral holes. A2+
ions
occupy 1/8 of the tetrahedral holes. If the ions are similar in size; this maximises
the lattice energy. A common example of a normal spinel is MgAl2O4.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 9
Fig 1.4. Primitive tetragonal and conventional cubic unit cells of spinel. The
primitive cell consists of two octants of the cubic unit cell. Atom positions are
shown for the primitive cell only; however the atomic positions denoted in the
primitive cell repeat with the pattern indicated by shading in the other octants.
One A-site in the primitive cell is not visible in the drawing; it is on the center of
the base of the cubic unit cell. The lattice parameter range (a=0.8-0.9nm) is
approximately the range corresponding to oxide spinels
Inverse spinel structures however are slightly different where one must
take into account the crystal field stabilization energies (CFSE) of the transition
metals present. Some of the ions may have a distinct preference on the octahedral
site which is dependent on the d-electron count. If the A2+
ions have a strong
preference to the octahedral site then they will force their way into it and
displace half of the B3+
ions from the octahedral sites to the tetrahedral sites. If
the B3+
ions have a low or zero octahedral site stabilization energy (OSSE), then
they have no preference and will adopt the tetrahedral site. The example of an
inverse spinel is Fe3O4, if the Fe2+
(A2+
) ions are d6 high-spin and the Fe
3+ (B
3+)
ions are d5 high-spin.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 10
1.3.1. Ferrite nanoparticles
Ceramic-like ferromagnetic materials, which are mainly composed of
ferric oxide, a-Fe2O3, are called “ferrites”. As the saturation magnetization of
ferrites is less than half that of ferromagnetic alloys, they have several
advantages as applicability at higher corrosion resistance, greater heat resistance,
lower price and higher frequency. Several practical applications of ferrites have
been expanded by completely utilizing these advantages.
Magnetite, (Fe3O4) which is a natural mineral, a genuine ferrite, and it is
said that ancient people had recognized its magnetism and that it was used as a
mariner’s compass in China more than two millennia ago. The first attempt to
prepare various types of ferrites and to industrialize ferrites was not made until
the beginning of this century. Rapidly development of radio, television, carrier
telephony, and computer circuitry and microwave devices arouse attention of
people to the importance of these ferrite materials. Since then the science
evidenced the tremendous advancement in the field of manufacturing and
processing of ferrite materials.
Crystal structure of ferrite
The crystal structure of a ferrite can be regarded as an interlocking
network of positively-charged metal ions (Fe3+
, M2+
) and negatively charged
divalent oxygen ions (O2-
). [8,9]
Like to the mineral spinel, magnetic spinels have the general formula
MOFe2O3 or MFe2O4 where M is the divalent metal ion. The trivalent Al is
usually replaced by Fe3+
or by Fe3+
in combination with other trivalent ions.
Although the majority of ferrites contain iron oxide as the name might imply
there are some "ferrites" based on Cr, Mn, and other elements. Although Mn and
Cr are not ferromagnetic elements, in combination with other elements such as
oxygen and different metal ions, they can behave as magnetic ions. Thus,
chromites and manganites are possible but not important commercially. In the
magnetic spinels, the divalent M2+
can be replaced by Mn2+
, Ni2+
, Cu2+
, Co2+
,
Fe2+
, Li2+
, Zn2+
, Mg2+
or more often, combinations of these. The presence of
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 11
Fe3+
, Fe2+
, Ni2+
, Co2+
and Mn2+
can be used to provide the unpaired electron
spins and therefore part of the magnetic moment of a spinel. Other divalent ions
such as Mg2+
or Zn2+
(or monovalent Li) are not paramagnetic but are used to
disproportionate the Fe3+
ions on the crystal lattice sites to provide or increase
the magnetic moment.
1.3.2. MgFe2O4
Magnesium ferrite, MgO.Fe2O3 or MgFe2O4, can be made partially
normal at high temperatures and this normal structure can also be quenched in a
manner similar to copper ferrite. Slow cooling gives inverse structure and rapid
cooling gives normal structure. When M in the chemical formula of spinel ferrite
is a metal carrying no magnetic moment such as Mg2+
, the magnetic couplings
purely originate from the magnetic moment of Fe cations and may be relatively
weaker. Magnetic anisotropy in MgFe2O4 is lower than that of other spinel
ferrites in which all the metal cations have large magnetic moments.
MgFe2O4 is used as a catalyst in dehydrogenation of butene, humidity
sensor and recently is more applicable in achieving local hyperthermia when
compared with other ferrites. MgFe2O4 nanoparticles exhibit high resistivity~107
Ohm (low conductivity). Therefore it is the material of choice for microwave
applications, and yolk cables. Recently the use of magnetic nanoparticles in
cancer therapy emerges as a one of the important cancer modality either alone or
in combination with existing modalities. As the heat loss by magnetic
nanoparticle governed by relaxation losses, eddy current losses and hysteresis
losses, it is difficult to differentiate one loss from another. One of the approaches
is to use magnetic nanoparticles with high electrical resistivity. Eddy currents are
negligible in case of high electrical resistivity. Also the heat loss is slow in case
of high resistive material as compared conductive particles. Therefore ferrite
nanoparticles with resistivity over ~107 Ohm are preferred for magnetic
hyperthermia over other metal nanoparticles to avoid excess heating due to eddy
current losses.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 12
Some important properties of MgFe2O4 are given in Table 1.1 [20-22].
Numerous methods have been discussed in literature for the synthesis of
MgFe2O4 magnetic nanoparticles. MgFe2O4 NPs were preferred as a potential
heating agent in magnetic particle hyperthermia. The key challenge is to produce
quantity and quality MgFe2O4 NPs with required properties such as high
chemical stability, high crystallinity, high saturation magnetization and with
good colloidal stability with or without surfactant/polymer in water. Because of
its low anisotropy and high resistivity MgFe2O4 nanoparticles are important
materials in technological applications. The magnetic properties of MgFe2O4 NPs
can be tuned by substitution of divalent metal cations (Mn2+
or Zn2+
).
Chemical formula MgFe2O4 or MgO.Fe2O3
Lattice constant ~ 8.36 Å
Oxygen parameter ~ 0.381±0.001
Density ~ 4.52 g/cm3
Magnetic moment 0 μB (Theor.) and ~1.1 μB (Expt.)
Curie temperature ~ 440 °C
Crystal anisotropy (at 20 °C) ~ ˗ 25 x 103 erg/cm
3
Linear magnetization magneto striction ~ - 6x 106
(20 °C)
Resistivity ~ 107 ohm
Tetrahedral radius 0.58 Å
Octahedral radius 0.78 Å
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 13
1.4. Literature survey
The use of magnetic NPs for magnetic induction heating in magnetic
particle hyperthermia has gained lot of attention since last decade. Though the
use of magnetic NPs for hyperthermia was not new, the appliances to medical
field were forbidden due to improper instrumentation, inexact thermotherapy and
lack of core knowledge. Synthesis of monodispersed, highly water dispersible
single domain (ferri- or superpara-) magnetic NPs is the prime challenge to the
researchers in this field. Similarly, heating due to magnetic losses depend on
sample composition and field parameters. In the present section, the synthesis
and major biomedical applications of MFe2O4 NPs have been reviewed.
Chen et al have shown that the co-precipitated MgFe2O4 nanoparticles
exhibit superparamagnetic properties for particle sizes 6 and 12 nm. They also
anticipated that the nanoparticles of MgFe2O4 may possess superparamagnetic
properties even at relatively large sizes [22]. Though the MgFe2O4 nanoparticles
have proven to be a technological important material, its potentiality in
biomedical applications was not fully explored.
Spinel ferrite, MFe2O4 (M = Co, Fe, Cd, Zn, Mn, or Mg) is a particularly
important magnetic material system [23, 24]. These NPs may possess novel
magnetic properties, particularly superparamagnetic behavior. At
superparamagnetic state; the collective behavior of the magnetic NPs is the same
as that of paramagnetic atoms. Each particle behaves like a paramagnetic atom
but with a giant magnetic moment. There is a well-defined magnetic order within
each NP. Furthermore, spinel ferrite NPs provide great experimental systems in
which one can study the correlation between the crystal chemistry and
superparamagnetic properties of magnetic NPs. When M in the chemical formula
of spinel ferrite is a metal carrying no magnetic moment such as Mg2+,
the
magnetic couplings purely originate from the magnetic moment of Fe cations
and may be relatively weaker. Magnetic anisotropy in MgFe2O4 could be lower
than that of other spinel ferrites in which all the metal cations have large
magnetic moments. Therefore, it is logical to anticipate that the NPs of MgFe2O4
may possess superparamagnetic properties even at relatively large sizes [25].
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 14
Heat generation ability of nano-MgFe2O4 based ferrite in AC magnetic
field is studied by Hirazawa et al [26]. They prepared NPs by bead milling. The
highest heat ability (ΔT=34°C) in the AC magnetic field (370 kHz,1.77kA/m)
was obtained for fine MgFe2O4 powder having about 6 nm crystal size (the
samples were milled for 6 to 8 h using 0.1 mm beads).
Giri et al [27] have explored the potentiality of different ferrite NP
(MnFe2O4 system) for hyperthermia therapy applications. The specific
absorption rate (SAR) was measured by calorimetric measurement at a frequency
of 300 kHz and a field of 10–45 kA/m. The variation of SAR and magnetization
of Fe1−xMnxFe2O4 with Mn concentration was studied and suggested that the
biocompatibility and higher SAR may make these materials useful for
hyperthermia applications. Wetzel et al [28] investigated the induction heating
behavior of NiFe2O4 soft ferrites in AC field with 5.85 MHz and 50–500 Oe.
Franco et al [29] prepared MgFe2O4 nanoparticles by combustion method and
studied their magnetic properties with respect to varying temperature. The results
were promising as compared to conventional methods to prepare MgFe2O4NPs
and combustion method was proposed to be quick and efficient method to
synthesized industrial scale MgFe2O4 NPs with enhanced magnetic properties.
Kim et al [30] have investigated various ferrite (Fe-, Li-, Ni/Zn/Cu-, Co-,
Co/Ni, Ba- and Sr-ferrites) NPs for their application in magnetic particle
hyperthermia. Temperature variation under an alternating magnetic field was
observed. Their results shown that Co-ferrite exhibited the most applicable
temperature change ΔT =19.25K (29.62 W/g), in distilled water when the field
was 110 A/m. The synthesis method was coprecipitation and sol gel. The applied
frequency was above 7 MHz.
Bae et al [31] studied cytotoxicity, AC magnetic field induced heating and
bio-related physical properties of two kinds of spinel ferrite NPs. Soft (NiFe2O4)
and hard (CoFe2O4) with variable mean particle sizes were investigated to
confirm their effectiveness as an in vivo magnetic NP hyperthermia agent in
biomedicine. Magnetically induced heating temperature of the NPs measured
both in a solid and an agar state at different applied magnetic fields and
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 15
frequencies clarified that the maximum heating temperature of NiFe2O4 NPs is
much higher than that of CoFe2O4 NPs. In particular, the sufficiently high
heating temperature of the solid-state NiFe2O4 NPs readily controlled in the
range of 21.5°C–45°C at the physiologically tolerable and biological safe range
of the applied magnetic field and frequency below 50 kHz allowed that NiFe2O4
NPs can be considered as a promising candidate for an in vivo hyperthermia
agent.
Lee et al [32] studied the self-heating temperature rising characteristics of
CoFe2O4 hard spinel ferrite NPs and compared to those of soft spinel ferrite in
order to explore the effects of magnetic anisotropy and magnetic susceptibility
on the behavior of self heating temperature rising characteristics for
hyperthermia application. The maximum temperature elevated by using specially
designed RF-MRI modified LC circuit in a solid state, was 4.6 °C. The extremely
low elevated temperature and small specific absorption rate (SAR) relevant to
the gentle slope from the time vs temperature rising curve were found to be
primarily due to a stronger anisotropy (or a smaller magnetic susceptibility) of
CoFe2O4 hard spinel ferrite NPs compared to the soft spinel ferrite NPs. They
conclude that the CoFe2O4 NPs with 165 nm in size are not suitable for
hyperthermia therapy applications.
Maehara et al [33] and Nomura et al [34] have studied selective ferrite
nanoparticles for thermal coagulation therapy. They found that magnesium
ferrite (MgFe2O4) showed the largest increase in temperature (ΔT) under an
alternating magnetic field in all the ferrites examined. For all the samples they
found, ΔT value under alternating magnetic field was increased with an increase
in frequency (200 to 500 kHz). The heating ability for the Magnesium ferrite was
1.4 W/g under AC magnetic field of 4.0 kA/m (200 W, 370 kHz). The heating
ability in alternating magnetic field was clearly depended on the magnitude of
the hysteresis loss for the ferrite powder. They showed that Mg-ferrite can
replace the usual powder “magnetite” although it should be carefully investigated
to establish the safety for putting and keeping them in a human body.
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 16
Jeun et al [35] have studied the effect of particle-particle interaction on
self heating temperature rise properties of the selective ferrites viz. NiFe2O4,
MgFe2O4 and CoFe2O4. The study depicts that the interparticle interactions play
vital role in determining the magnetic properties of MNPs when the distribution
of MNPs is broad. The superior properties of induction heating were obtained in
case of MgFe2O4 NPs compared to other spinel ferrites. The increase in
“magnetic hysteresis loss” that resulted from the particle dipole interaction was
the main physical reason for the significant improvement of ac heating
characteristics. The heating due to magnetic NPs is also strongly affected by
particle size distribution. The study of effect of particle size distribution on
heating characteristics of selective ferrite NPs is systematically presented. All the
experimental results in their work clearly demonstrate that the particle dipole
interaction formed among the NPs should be considered as one of the most
crucial physical parameters in optimizing the magnetic and ac magnetically
induced heating characteristics of NPs for a hyperthermia agent application. The
study further shows that the heat generation and SAR value for MgFe2O4 NPs is
high as compared to other ferrites CoFe2O4 and NiFe2O4.
1.5. Statement of problem
The merging of biotechnology with materials science will allow us to
apply today’s advanced materials and physiochemical techniques to solve
biological problems. Though there is tremendous advancement in the field of
medicine in recent years cancer still remains as a leading cause of death in the
world. Improper diagnosis and detection at early stages are the some of the
reasons behind it. Also the treatment now followed for treating cancer including
radiation therapy, immunotherapy, chemotherapy are comprised of side effects
such as hair loss, eye irritation etc. Thus to diagnose the cancer at the early stage
and to cure it without much side effects remains a challenge to scientific
community. The new tool, magnetic NPs are playing vital role in diagnosis and
therapy of cancer. The magnetic hyperthermia therapy in which the magnetic
NPs used to heat specific organ or whole body (depending upon the tumor) has
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 17
emerged as one the promising cancer modality either alone or in combination
with other existing cancer modalities.
The main emphasis of the present work is to develop tailored magnetic
material at the nanoscale for advanced bio-application such as magnetic particle
hyperthermia (MPH) for treatment of cancer. With this aim an attempt has been
made to prepare the magnesium ferrite NPs with suitable heating characteristics
in AC magnetic field for their use as potential heating mediators in MPH
therapy. The promising combustion method was used to synthesize the
nanoferrites with desirable characteristics. The present work is subjected to five
objectives as follows:
1. To study the effect of preparative parameters on to the microstructural and
magnetic properties of MgFe2O4 NPs synthesized by combustion method
2. To study the effect of divalent magnetic manganese substitution on the
structural and magnetic properties of MgFe2O4 NPs
3. To study the effect of dextran coating on magnetic and suspension
stability properties of MgFe2O4 NPs
4. To study the magnetic induction heating properties of MgFe2O4,
manganese substituted MgFe2O4 and dextran coated MgFe2O4 NPs
synthesized by combustion method
5. To study the biocompatible properties and to study the effectiveness of
NPs for hyperthermia therapy applications
Chapter-1 Introduction
D. Y. Patil University, Kolhapur 18
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