Transcript Applications in Medical and Biology Magnetic Material Engineering

Magnetic Material Engineering
Magnetic Material Engineering
Chapter 6:
Applications in Medical and Biology
Magnetic Material Engineering
Magnetic nanoparticles
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic nanoparticles
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic nanoparticles
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic nanoparticles
Materials: Fe, Co, Ni, Gd
Spins of unfilled d-bands spontaneously
align parallel inside a domain below a
critical temperature TC (Curie) Laws:
B = H +4H
M = H
: Susceptibility
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic nanoparticles
Hard Magnets: HC and Mrs have high values
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism - a size effect
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism - a size effect
Superparamagnetism:
• high saturation magnetisation MS
• no remanence MR = 0
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism
The Néel relaxation in the absence of magnetic field
Normally, any ferromagnetic or ferrimagnetic material undergoes a transition
to a paramagnetic state above its Curie temperature. Superparamagnetism is
different from this standard transition since it occurs below the Curie
temperature of the material.
Superparamagnetism occurs in nanoparticles which are single domain. This is
possible when their diameter is below 3–50 nm, depending on the materials.
In this condition, it is considered that the magnetization of the
nanoparticles is a single giant magnetic moment, sum of all the individual
magnetic moments carried by the atoms of the nanoparticle.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism
Magnetic anisotropy is the direction dependence of a material's magnetic
properties.
In the absence of an applied magnetic field, a magnetically isotropic material
has no preferential direction for its magnetic moment while a magnetically
anisotropic material will align its moment with one of the easy axes.
Magnetic anisotropy is a prerequisite for hysteresis in ferromagnets: without
it, a ferromagnet is superparamagnetic.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic anisotropy
• Are the magnetic properties same in all directions?
 No
• It depends on the crystallographic direction in which the magnetic dipoles
are aligned
– Crystal anisotropy (Spin Orbit Coupling)
– Shape anisotropy
– Stress anisotropy
– Externally induced anisotropy
– Exchange anisotropy
• E = KVsin2θ (simplest form)
– K the effective uniaxial anisotropy energy per unit volume
– V particle volume
– θ angle between moments and easy axis
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic anisotropy
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism
Because of the nanoparticle’s magnetic anisotropy, the magnetic moment has
usually only two stable orientations antiparallel to each other, separated by
an energy barrier.
The stable orientations define the nanoparticle’s so called “easy axis”.
At finite temperature, there is a finite probability for the magnetization to
flip and reverse its direction. The mean time between two flips is called the
Néel relaxation time τN and is given by the following Néel-Arrhenius
equation:
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism
• N is thus the average length of time that it takes for the nanoparticle’s
magnetization to randomly flip as a result of thermal fluctuations.
• 0 is a length of time, characteristic of the material; its typical value is 10−9 –10−10
second.
• K is the nanoparticle’s magnetic anisotropy energy density and V its volume.
• KV is therefore the energy barrier associated with the magnetization moving from
its initial easy axis direction, through a “hard plane”, to the other easy axis direction.
• kB is the Boltzmann constant andT is the temperature.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism - a size effect
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Superparamagnetism - a size effect
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Cancer Treatments
Magnetic Nanoparticles
Manipulation of Cell membranes
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Nanomagnetic Particle
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic Cell Separation / Cell Labeling
Diagram of Immunomagnetically labeled Cell
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic Cell Separation / Cell Labeling
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Capture of bacteria by using Vancomycin-conjugated magnetic nanoparticle
Control experiment
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Magnetic Drug Delivery
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
MRI
The principles of MRI rely on the spinning of specific nuclei present in
biological tissues.
In nuclei that have an even mass number, i.e. # protons = # neutrons, half
spin in one direction and half spin in the other. Nucleus has no net spin.
However, in nucleus with odd mass #, spin directions are not equal and
opposite, so the nucleus has net spin or angular momentum.
These are know as MR active nuclei.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
MRI
MR active nuclei are characterized by their tendency to align their axis of
rotation to an applied magnetic field.
This occurs because they have angular momentum or spin and, as they
contain positively charged protons, they posses electrical charge.
The laws of electromagnetic induction refer to three individual forces –
motion, magnetism and charge – and state that if two of these are
present, then the third is automatically induced.
MR active nuclei that have a net charge and are spinning (motion),
automatically acquire a magnetic moment and can align with external
magnetic field.
The strength of the total magnetic moment is specific to every nucleus
and determines the sensitivity to magnetic resonance.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
MRI - The hydrogen nucleus
The hydrogen nucleus is the MR active nucleus used in clinical MRI. It
contains a single proton (atomic and mass number 1).
It is used because it is most abundant in the human body and its solitary
proton gives it a relatively large magnetic moment.
Both of these characteristics enable utilization of the maximum amount
of available magnetization in the body.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
The hydrogen nucleus as a magnet
The laws of electromagnetism state that a magnetic field is created when
a charged particle moves.
The hydrogen atom contains one positively charged proton that spins.
Therefore it has a magnetic field induced around it, and acts as a small
magnet.
It has a north and south pole.
Each of which is represented by a magnetic moment.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Alignment
Quantum theory describes properties of electromagnetic radiation in
terms of discrete quantities called quanta.
Applying quantum theory to MRI, hydrogen nuclei posses energy in two
discrete quantities term low and high.
Low energy align their magnetic moments parallel to external field (spinup).
High energy align anti-parallel (spin-down).
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
The MR signal
When a patient is placed within and MR scanner, the protons in the
patients tissues (primarily protons contained in water molecules) align
themselves along the direction of the magnetic field.
A radiofrequency electromagnetic pulse is then applied, which deflects
the protons off their axis along the magnetic field.
As the protons realign themselves with the magnetic field, a signal is
produced.
This signal is detected by an antenna, and with the help of computer
analysis, is converted into an image.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
Image formation
The process by which the protons realign themselves with the magnetic
field is referred to as relaxation.
Different tissues undergo different rates of relaxation, and these
differences create the contrast between different structures, and
the contrast between normal and abnormal tissue, seen on MRI scans.
Chapter 6: Applications in Medical and Biology
Magnetic Material Engineering
MRI of a Female Rat
Before
Chapter 6: Applications in Medical and Biology
After