Magnetically-Guided Nanoparticles for
Targeted Drug Delivery
Final 2011 RET Report
Prepared by
Seth Baker
Percy Julian Middle School
Laboratory for Product and Process Design
Director: Andreas A. Linninger
____________________
Seth Baker
RET Fellow
____________________
Prof. Andreas Linninger
RET Mentor
University of Illinois at Chicago, Chicago, IL.
Date: 8/4/2011
1.0 Abstract
Due to the complex properties of the brain, which includes tissue anisotropy,
elaborate vasculature, and natural endothelial barriers, targeted drug delivery to the brain
has remained a challenge for scientists. Magnetically-guided nanoparticles offer a
possible therapeutic method for effective targeted drug delivery into brain tissue.
Convection-enhanced delivery and capillary experiments are conducted using 35 and 173
pound pull force magnets to guide magnetite (Fe3O4) nanoparticles toward specific areas
in brain phantom agarose gels using magnetic fields. The results of the convectionenhanced delivery experiments were inconclusive, however capillary experiments
showed promise with guidance of magnetic nanoparticles toward external magnetic
fields. Further investigations are suggested to determine optimal magnetic field strength,
concentrations of magnetic nanoparticle solution, and possible coatings to reduce
agglomeration of nanoparticles.
Preliminary testing on the delivery of magnetic
nanoparticles in rat brain tissue and a brief overview of the brain vasculature,
nanoparticles and magnetism is also given.
2.0 Table of Contents
1.0 Abstract ………………………………………………………………………… 2
2.0 Table of Content ……………………………………………………………….. 3
3.0
Introduction …………………………………………………………………......4
4.0 Background ………………………………………………...………………….. 5
4.1 Vasculature…………………………………………………………………..5
4.2 Nanoparticles …………………………………………..………...……………..6
4.3 Functionalizing………………………..…………………………………….…...7
4.4 Magnetism ……………………………………………………………………8
5.0 Motivations ………………………………………………………………..........10
6.0 Current Study …………………………………………………………………...11
7.0 Materials and Methods ………………………………………...………………..12
7.1 Preparation of Nanoparticle Solutions……..…………………………………………………..12
7.2 Magnetic Guidance during Convection-Enhanced Delivery of Nanoparticles …………..13
7.3 Capillary Experiments in Agarose Gel………………..……………………...…15
7.4 Delivery of Magnetic Nanoparticles in Rat Brain Tissue……………………..………16
8.0 Results ………………………………………………………...……………..… 18
9.0 Conclusion ……………………………………………………………..……......21
9.1 Future Studies………………………………………………………………...22
10.0
Acknowledgements ………………………………………….…………….......23
11.0
References …………………………………………………………………..…25
3.0 Introduction
Treatment options for many neurological conditions are often inadequate due to
the limited approaches to accurately deliver therapeutic drugs to the brain. A major
factor in this limitation is the inability to target therapeutics to a specific area of the brain.
Therapeutics that penetrate or by-pass the blood brain barrier, a natural protective
mechanism located in the brain microvasculature, can lead to systemic toxicity and affect
unintended areas of the brain. A novel approach to target the delivery of therapeutics is
the use of magnetically-guided nanoparticles infused through convection-enhanced
delivery (CED) (Perlstein 2008).
This approach involves using magnets to guide
functionalized nanoparticles to specific areas while bypassing the blood brain barrier and
decreasing the possibility of systemic toxicity. The technique of convection enhanced
delivery involves the continuous injection of an infusate by a syringe pump connected to
a catheter system while under positive pressure. CED has been shown to effectively
bypass the blood-brain barrier and to produce much larger volume distributions of
infusate when compared to pure diffusion alone.
In order to establish a standard protocol for magnetically-guided nanoparticle
delivery into brain tissue, a series of surrogate brain gels and magnets can be used to
determine the variables that affect the movement of nanoparticles. Once variables have
been tested, a standardized protocol for targeting nanoparticles into brain tissue can be
designed.
Protocols must also be determined to allow for accurate measurement of nanoparticle
delivery into brain tissue. These protocols include preparing brain tissue, delivering
magnetic nanoparticles to brain tissue, and staining the samples for accurate visualization
of nanoparticle movement. Rat brain samples can also be used to measure the accuracy
of the brain gel phantoms, as well as to study the unique properties of brain tissue.
4.0 Background
Once effective methods in delivery and guidance of magnetic nanoparticles are
established, medical applications can be developed. However before studying the future
of brain therapeutics, a general understanding of brain vasculature, nanoparticles and
magnetism is necessary.
4.1 Vasculature
Vasculature is the arrangement of blood vessels in a body or organ.
There are five general types of vessels found in the human body, arteries and arterioles,
vessels that send blood away from the heart, veins and venules, vessels that send blood
back to the heart, and capillaries, which form a mesh that connects arterioles to venules.
Both arteries and veins form an intricate branched system throughout the body with
vessels ranging in size from the 2-3 cm diameter of the aorta and vena cava, to the 5 μm
diameter of capillaries. Nowhere in the human body is the vasculature more intricate than
in the brain. Although the brain is only 2% of your total body mass, it receives up to 20%
of the blood flow from your heart (Chudler 2007). The neuron cells in the brain must
receive a constant supply of oxygen, and capillaries are arranged to allow this to occur in
a non-pulsating steady flow (Mchedlishvili 1986).
An important mechanism in the brain vasculature is the blood brain barrier. This
selectively permeable barrier creates an interface between the brain’s vascular blood flow
and peripheral brain tissue. Substances that can successfully cross the blood brain barrier
are lipid soluble compounds and small micromolecules, generally less than 500 Da
molecular weight (Pardridge 1998). Nanoparticles with diameters less than10 nm are
able to penetrate the tight junctions of the blood-brain barrier as well (Anderson 2001).
What allow nanoparticles access to brain tissue are the unique cellular structures of the
blood brain barrier and their miniscule size.
4.2 Nanoparticles
Nanoparticles are generally defined as particles with a diameter of less than 100 nm.
One nanometer is 10-9 m, with the average somatic cell size ranging from 10-100 μm. (1
μm = 10-6 m). Nanoparticles administered intravenously can range from 5.5 nm to 200
nm in diameter depending on the clinical use (Pankhurst 2003). Nanoparticles that have
a diameter greater than 200 nm cannot be effectively used in biomedicine unless targeted
for the spleen. This is due to the spleen’s natural filtration of particles greater than 200
nm in size after intravenous administration. Similarly, nanoparticles with a diameter of
less than 5.5 nm are filtered by the kidneys, and therefore most effective for delivery of
therapeutics only to the kidneys (Sun 2008). Within the range of 5.5-200 nm however,
nanoparticles are sufficiently small enough to have direct interaction with cellular
structures (Arruebo 2007). Cell membranes are generally permeable to nanoparticles
with the smallest particles able to cross both the cellular and nuclear membranes. The
size and shape of nanoparticles will determine the effectiveness of penetrating a
membrane. Researchers have found that spherical 40-50 nm particles have the greatest
intake rates. Other nanoparticles offer better biocompatibility and are often used for
biodegradable medical devices.
These include nanoparticles coated in glycol-based
polymers.
Polyethylene glycol (PEG) coated nanoparticles are often used for drug
sustained release, as they have high stability and can remain in the blood stream for
extended times.
Other nanoparticles coated in gold or silica can be “loaded” into
macrophages or coated for receptor-mediated transport across the blood brain barrier.
Several types of nanoparticles used in biomedicine are liposomes, dendrimers,
biodegradable polymers, and core-shell nanoparticles. Nanoparticles delivered directly to
the brain are often coated with a type of polymer or surfactant which allows the
nanoparticles improved permeability across the blood-brain barrier. (Chakraborty 2009).
Nanoparticles infused into the brain via convection-enhanced delivery often utilize
coatings of polyethylene glycol (PEG) or dextran, a glucose polymer to increases the
infusion efficacy (Perlstein 2008). Many nanoparticles are also small enough to penetrate
tumor tissue due to the enhanced permeability and retention (EPR) quality of tumors (Jin
2007).
This hyperpermeability allows nanoparticles to enter tumors through the
increased blood flow that develops as tumors grow. This passive targeting can be
enhanced through magnetic guidance as well (Arruebo 2007).
Nanoparticles used in biomedicine must have a prolonged circulation time in the
bloodstream to be able to deliver therapeutics to targeted sites (Arruebo 2007). Therefore
knowledge of the immune and lymphatic systems is necessary to understand how
nanoparticles are metabolized in the body. Nanoparticles such as magnetite (Fe3O4) are
biocompatible and biodegradable. The iron ions are absorbed into the body’s iron stores
during metabolism and eventually used in the synthesis of hemoglobin (Sun 2008).
4.3 Functionalizing
A major benefit of using nanoparticles for biomedicine is the ability to
functionalize nanoparticles with various agents through the use of organic linkers such as
amine, carboxyl, and thiol groups. These agents can include surface receptors for binding
targeted cells, florescence markers for visualizing the movement of nanoparticles,
chemicals to monitor drug release, and for attaching a wide range of therapeutics. Figure
1 shows a schematic of a bare nanoparticle that undergoes functionalization to drug
molecules. The nanoparticle coating can provide various functions for clinical purposes
and also help the nanoparticles “hide” from the body’s immune and filtration systems
(Sun 2008). Nanoparticles also need surface protection to reduce degeneration. Over a
period of time, “naked” magnetic nanoparticles will oxidize, resulting in lower
magnetism and dispersion. The smaller the nanoparticle, the more susceptible they are to
oxidation. There are generally two types of coatings used to functionalize nanoparticles,
organic shells made of polymers or liposomes, or inorganic shells made of metals such as
gold and silver. (Lu 2007).
Nanoparticle coatings often regulate the solubility,
hydrophilic or hydrophobic properties, stability, and the targeting ability of the particles.
Figure 1 – Functionalizing nanoparticles
4.4 Magnetism
According to Faraday's law of magnetic induction, when a material is placed in the
presence of a magnetic field, the material's electrons will be affected. How they are
affected depends on the atomic structure of the material, whether the electrons are paired
and balanced. The more balance among the electrons, the lower magnetic response.
There are three basic classifications of magnetism with respect to a material's electron
configuration, diamagnetic, paramagnetic, and ferromagnetic.
Materials with all
electrons in pairs are called diamagnetic and have a weak response to a magnetic field.
Diamagnets are slightly repelled by a magnetic filed, and lose any magnetic properties
when a magnetic field is not present. Diamagnetic elements include copper, gold, and
silver.
Materials with some unpaired electrons are called paramagnetic and possess
slightly greater susceptibility to magnetic fields compared to the two types of magnetism.
These elements have a weak attraction to a magnetic field and like diamagnets, lose
magnetic properties when a magnetic field is removed. Paramagnetic elements include
magnesium, molybdenum, lithium, and tantalum.
Ferromagnets are materials that have a high susceptibility to a magnetic field.
These materials (iron, cobalt, nickel) have unpaired electrons and have a strong attraction
to a magnetic field. Ferromagnets are composed of magnetic domains, areas that develop
as the material naturally forms. These domains contain atoms with electrons that are
aligned in a uniform direction. In the presence of a magnetic field, multiple magnetic
domains become aligned until the material is magnetically saturated. Unlike diamagnets
and paramagnets, ferromagnets will retain magnetic properties in the absence of a
magnetic field.
Another classification of magnetism is called superparamagnetism and occurs
only at the nanoscale. Ferromagnetic particles with diameters less than 14 nm, lose their
ferromagnetic properties and behave as a paramagnet. The magnetic domains remain
isolated and the material is classified as superparamagnetic. Superparamagnetism has
higher magnetic susceptibility than paramagnetism, nearly the level of magnetically
saturated ferromagnets (Neuberger 2005) but in the absence of an external magnetic field,
superparamagnetic particles lose magnetic properties. These are ferromagnetic materials
acting as a paramagnet, but with much higher susceptibility. This allows scientists to
“flip” these seemingly paramagnetic materials into near ferromagnetic susceptibility in
the presence of a magnet (Thorek 2005).
5.0 Motivations
According to recent reports from the World Health Organization, nearly 1 billion
people suffer from neurological disorders such as Alzheimer’s, Parkinson’s, depression,
stroke, and epilepsy (World Health Organization 2009). Many of the individuals who are
afflicted with these disorders remain untreated due to limited options for therapeutic drug
delivery (Pardridge 1997). The World Health Organization also projects that 25% of the
world’s current population will develop one or more neurological disorders (World
Health Organization 2001).
With the prevalence rising for neurological disorders,
research is necessary to develop new treatments. Delivering therapeutics to the brain
creates unique challenges because of the complexity of the brain’s vasculature, and
natural endothelial barriers such as the blood brain barrier.
According to William
Pardridge from the University of California, Los Angeles, School of Medicine, “The
blood-brain barrier is the bottleneck in brain drug development and is the single most
important factor limiting the future growth of neurotherapeutics” (Pardridge 2005).
There are also problems when medicinal chemistry creates drugs with increased lipid
solubility. While it increases the permeability across the blood brain barrier, it also
increases permeability across all other body membranes which minimizes the uptake in
the brain, and can lead to toxicity in the body. Nanoparticles loaded with therapeutics
can move across the blood brain barrier by passive diffusion, however without guidance
therapeutics entering the brain will disperse systemically. Controlling the distribution and
targeting specific sites in the brain therefore becomes critical as cytotoxic drugs need to
be limited in their delivery with systemic toxicity greatly reducing the effectiveness of
therapeutics (Dobson 2006). A possible strategy for delivering medication to targeted
areas of the brain is the use magnetically guided nanoparticles. This method has greater
control over fluid distribution than diffusion and reduces systemic toxicity that bloodbrain barrier disruption and implantations can create.
Use of magnetically guided
nanoparticle delivery can also allow for lower therapeutic dosage, which in turn also
reduces systemic toxicity.
6.0 Current Study
There are two related topics in the current study. First, convection-enhanced
delivery and capillary infusion is used to investigate magnetically guided nanoparticles in
agarose gel brain phantoms. For this study, a standard protocol to inject nanoparticles is
investigated by varying the nanoparticle diameter, catheter design, and magnetic field. A
second study is conducted to investigate magnetic nanoparticle delivery into brain tissue,
along with staining techniques for visualizing nanoparticles and brain slicing techniques.
In the first section, the methods and materials for both infusion methods in
agarose gel and magnetic nanoparticle delivery into brain tissue are discussed. Next, the
results of the infusions are presented followed by a conclusion section. In this section,
the results are analyzed and future studies including infusion into cerebral spinal fluid
and the use of spinal phantoms as well as future techniques in reducing agglomeration of
nanoparticles are discussed.
7.0 Materials and Methods
Convection-enhanced delivery and capillary infusion were both conducted in
agarose gel brain phantoms.
The experimental design and nanoparticle distribution
profiles are observed to investigate a standard protocol for infusion and guidance of
magnetic nanoparticles into porous material.
Nanoparticle solutions used in these
experiments were obtained from Dr. Gayle Woloschak’s lab at Northwestern University
and came with different sizes ranging from 5-30 nm. The particles were either bare
magnetite or were composed of a magnetite core with either a sucrose or ficoll coating.
7.1 Preparation of Nanoparticle Solutions
Nanoparticles solutions were prepared by taking 0.5 ml of an acidic solution of
suspended magnetite particles and adding 2M sodium hydroxide dropwise until the
solution reached a neutral pH. This solution was then vortex to mix the solution and
centrifuged to remove the supernatant from the nanoparticles. The nanoparticles were
then washed with1 ml of distilled water and sonicated until the nanoparticles were evenly
dispersed. The pH was tested and the solution was centrifuged again; removal of the
supernatant followed by an additional washing with dH2O was repeated once more in
order to remove free ions from the solution and to maintain a neutral pH.
The
nanoparticles were then resuspended in dH2O and tested for magnetic susceptibility. This
was done by placing the nanoparticle solution near a magnet to observe magnetic
attraction. Figure 2 shows 30 nm magnetite movement toward a 173 pound pull force
magnet over an 8 minute trial. Once magnetic susceptibility was determined, the
nanoparticles could be used in the agarose gel experiments.
Figure 2 – 30 nm magnetite at a) 0 minutes b) 4 minutes c) 8 minutes above a 173 lb pull force magnet
7.2
Magnetic
Guidance during
Convection–Enhanced Delivery
of
Nanoparticles
0.6% agarose gel was chosen as a brain phantom as it has similar mechanical
properties and porosity to that of gray brain matter (Chen 1999). To prepare the gel, 0.6
g of dry agarose type 1 (Sigma) and 0.9 g of sodium chloride (Sigma) was added to 100
ml of distilled water. Next, the mass of the mixture was measured, then heated to a low
boil under constant stirring.
Additional distilled water was added to account for
evaporation which occurs during boiling. The gel was then placed in an Isotemp water
bath maintained at 50 oC until it was time to set the gel in experimental chambers.
Next, 10 ml B-D plastic syringes were filled with 8 ml of olive oil using an 18gauge needle, connected to polyethylene tubing (Scientific Commodities Inc). Olive oil
was used to fill the syringes, therefore limiting the amount of nanoparticles necessary for
the infusion.
The nanoparticles were inserted only into the polyethylene tubing
connected to the syringe needle, this was the nanoparticle line. This tubing was then
connected to 1 mm diameter tubing using threaded joint fittings. This tubing was used as
the largest diameter tubing for the construction of the step catheter. Step design catheters
for this experiment used polyethylene, polyetheretherketone (PEEK), and fuzed silica
tubing with internal diameters of 1 mm, 0.3 mm, and 0.16 mm. The longest tubing used
was 1 mm polyethylene, with a shorter 0.3 mm PEEK catheter extending out. Finally the
0.16 mm fuzed silica tubing was inserted into the PEEK catheter. Figure 3 shows a
completed step catheter and penny for scale.
Figure 3 – 0.16 mm step catheter tip inserted into 0.3 mm tubing
Each smaller diameter tube was inserted into the end of a larger diameter and
super glue was applied to seal the connection.
This design reduces reflux of
nanoparticles along the catheter (Krauze 2005). The step catheters were then connected
to the polyethylene tubing used for the nanoparticle solution line. Syringes were placed in
a New Era syringe pump to ensure precise infusion rates. Each catheter was positioned in
a plastic cell (3.8cm x 6.7cm x 2.2cm) and surrounded by liquid agarose gel. The
catheter tips were positioned ¼ inch above the bottom of the cell to insure that the
magnets were placed ¼ inch from the infused particles. Two cells were placed directly
above 173 pound pull force magnets and two cells were use as controls. Figure 4 shows
the convection enhanced delivery set up. The gel was allowed to set for an hour before
the start of infusion. Infusion rates were set at 0.5 μl/min. Once the infusion was
complete, digital photos were taken of the nanoparticle distributions. Then the agarose
was removed from the plastic cells and placed in petri dishes filled with Prussian blue
stain to visualize the magnetite.
The gel was stained for four hours, washed quickly
three times with distilled water and then washed overnight in distilled water for 12 hours
on a rotating platform (RotoMix) before visualization of nanoparticle distribution as seen
in figure 5.
Figure 4 – Experimental set up for agarose gel infusion
Figure 5 – Staining and washing of agarose gel infused with nanoparticles
7.3 Capillary Experiments in Agarose Gel Brain Phantoms
Agarose gel was prepared with the same methods as discussed for convectionenhanced delivery. Next, five 16-gauge needles were attached to 1 ml BD syringes
primed with distilled water and inserted into a hole drilled in the side of a 2 ¼ inch
diameter petri dish. The hole was located ¼ inch above the base of the petri dish. Once
the syringe needles were inserted, they were surrounded by 0.6% liquid agarose gel.
Figure 6 shows the syringe set up for capillary experiments.
Figure 6 – Capillary experiment set up
Once the gel was allowed to set for an hour, the syringe was removed, leaving the
16-gauge needle embedded in the agarose. Next, a 27-gauge needle attached to a 1 ml
BD syringe primed with water was used to remove the remaining water housed inside the
16-gauge lumen embedded in the gel. Then a 1 ml BD syringe primed with nanoparticle
solution and attached to a different 27-gauge needle was used to fill the empty 16-gauge
needle lumen with nanoparticle solution. Next, the 16-gauge needle was very carefully
removed from the gel while the nanoparticle solution exited the lumen and filled the void
space created by the embedded 16-gauge needle. Adhesive putty was then used to seal
the hole in the petri dish. Finally two petri dishes were placed directly above 173 pound
pull force magnets and two were used as controls. The gels were then allowed to set for
24 hours, after which they were stained with Prussian blue and washed in distilled water
to visualize the distribution of magnetite nanoparticles throughout the gel.
7.4 Delivery of Magnetite in Rat Brain Tissue
Before investigating the movement of magnetic nanoparticles in brain tissue, the
sensitivity of Prussian blue stain on brain tissue was first determined. Figure 7 shows
unfixed or fresh rat brain samples were first sliced into ¼ inch coronal slices using a glass
microscope cover slip. These samples were then place in a solution of Prussian blue stain
for 24 hours as seen in figure 8. All tools used for brain preparation were non-metallic to
limit rat brain tissue exposure to metal. This exposure could affect the results when
Prussian blue stain was used to visualize the nanoparticles
Figure 8 – Unfixed brain tissue in Prussian blue stain
Figure 7 – Unfixed brain slicing with glass slide
Next, to determine the susceptibility of brain tissue to magnetite nanoparticles, 10
μl of 30 nm magnetite nanoparticle solution was delivered to the surface of ¼ inch
coronal slices of unfixed rat brain tissue as seen in figure 9. The nanoparticle solution
was prepared the same way as discussed earlier. The brain tissue was then placed in a
plastic petri dish and covered with Prussian blue stain for 24 hours. The tissues were
washed in distilled water and digital photos were taken.
Figure 9 – Delivery of nanoparticles to unfixed brain tissue
8.0 Results
A consistent result of many convection enhanced infusions was agglomeration of
nanoparticles.
As the nanoparticles were placed in the tubing and the agarose gel
solidified, the particles began to become attracted to each other and cluster. As the
infusion began and pressure increased in the tubing, the agglomerated particles blocked
the nanoparticle solution from infusing into the gel. If the fluid could overcome the
initial pressure from the blockage, the agarose gel would sheer from the sudden force of
the nanoparticle solution or the solution would reflux up the catheter. Step catheters
connected to larger gauge tubing resulted in fewer occurrences of reflux, however
inconclusive results of magnetic attraction of nanoparticles were produced Figures 10-11
show reflux free infusion using a step design catheter and reflux with a single gauge
catheter. There was with no noticeable difference in nanoparticle movement between the
35 and 173 pound pull force magnets.
Figure10 – Polymer step catheter
Figure 11 – non-step catheter with reflux
Capillary experiments with nanoparticles did indicate some attraction of
nanoparticles toward a magnetic force as seen in figures 12-14. Both 35 and 173 pound
full force magnets were positioned directly below each petri dish for 24 hours. Compared
to the control, magnetite nanoparticles above the 35 pound pull force magnet were
attracted 1/16th inch toward the magnet and nanoparticles above the 173 pound pull force
moved 1/8th inch toward the magnet.
Figure 12 – Control for 0.6% agarose gel capillary experiment. Red line indicates syringe line
Figure 13 – 35 pound pull force magnet trials. Magnetic force from below.
Figure 14 – 173 pound pull force magnet trials. Magnetic force from below.
One of the most consistent results of the convection enhanced delivery
experiments was the agglomeration of nanoparticles in the infusion tubes [Fig 15].
Agglomerated particles resulted in clogging the infusion lines and prevented infusion into
the gels. The larger the nanoparticle diameter from the superparamagnetic size region,
the more frequently agglomeration occurred.
Figure 15 – Magnetite nanoparticles agglomerated in 18 gauge polyethylene tubing
Results for experimentation on rat brain tissue indicated that unfixed brain tissue
does not naturally contain properties that would result in staining from Prussian blue as
seen in figure 16 and 30 nm magnetite nanoparticles were able to penetrate unfixed rat
brain tissue. Figure 17 shows the location of the particles visible from Prussian blue
stain.
Figure 16 – Coronal slices of rat brain tissue after 24 hours of Prussian blue staining
Figure 17 – Coronal slice of rat brain tissue with 30 nm magnetite particles delivered and stained with
Prussian blue on surface.
9.0 Conclusion
The infusion of nanoparticles into agarose gel presents many challenges.
Although a standard protocol has been determined to achieve reflux free convection
enhanced delivery using metal catheters, and the step design construction of polymer
catheters allows for reflux free infusions, the unique properties of the nanoparticles
prevent consistent infusion to occur. While preparing and setting up the agarose gel
infusion experiments, the nanoparticles in the tubing would begin to agglomerate. This
agglomeration lead to blockage of the tubing prior to the start of infusion.
Using
different surfactants including sodium dodecyl sulfate and polysorbate 20 as a method to
reduce surface tension and disperse the nanoparticles also had limited success. The
surfactants would cause the nanoparticle solution to gel and clog the infusion lines, or the
surfactant would be infused, leaving the nanoparticles in the tubing. Typically surfacants
are coated on nanoparticles during synthesis which reduces agglomeration. However the
nanoparticles used in this study were not synthesized with surfactants but added to
surfactants during preparation. With limited success infusing nanoparticles into the gel,
studying the influence a magnetic force has on magnetic nanoparticles in the brain
phantoms was restricted.
Based on the results from the capillary experiments, when nanoparticles were able
to be injected into the agarose directly after being prepared, they were more likely to have
limited agglomeration. This allowed the magnetic field to influence the movement of the
nanoparticles and the particles were guided toward both the 35 and 173 pound pull force
magnets. There was greater movement toward the stronger magnetic field.
According to the results of the staining and delivery of magnetite nanoparticles on
rat brain tissue, there are no natural artifacts in unfixed brain tissue that would limit the
use of Prussian blue as a visualizing stain. Magnetite nanoparticles also penetrated into
the brain tissue and stain remained in the brain tissue after washing with distilled water.
The nanoparticles and staining technique described could be used as part of future
research on nanoparticle delivery to brain tissue.
9.1 Future Research
Future research is needed to determine an effective method for infusing magnetic
nanoparticles. The challenge of infusing involves preventing nanoparticle agglomeration.
This could be approached in a variety of ways. One method includes setting up the
experiment in separate stages. Letting the agarose gel set before inserting the catheter
would allow for the nanoparticles to be infused directly after preparation. Minimal
agglomeration was observed in the capillary experiments during which nanoparticles
could be prepared directly before injecting into the agarose gel. Similarly, allowing the
infusion to occur prior to placing the magnets could allow the nanoparticles to infuse
without the potential of agglomeration due to the magnetic field. Once infusion was
completed, the magnets could be placed according to protocol, allowing the nanoparticles
to then move toward the magnetic field. Without the magnet placement during infusion,
metal catheter could be used, also reducing the possibility of reflux. Synthesizing
nanoparticles with a surfactant coating may also reduce agglomeration.
Magnetic targeting of nanoparticles can also be applied to research in drug delivery
to the central nervous system through infusion into the cerebral spinal fluid. The use of
spinal phantoms could allow researchers the chance to model the movement of
nanoparticles along the spinal cord with possible delivery into brain tissue. The potential
for therapeutic application of magnetically-guided nanoparticles is considerable.
Nanotechnology can play a critical role in the development of “smart” drugs, with further
research needed to determine the protocol for proper infusion of and reduction in the
agglomeration of magnetic nanoparticles.
10.0 Acknowledgements
I would like to thank the National Science Foundation CBET EEC-0743068 grant
for providing funding for the Research Experience for Teachers (RET) and Research
Experience for Undergraduates (REU) summer 2011 projects at The University of Illinois
Chicago.
In addition I would like to thank the many individuals who assisted me during my
RET experience. The members of the Laboratory for Product and Process Design at UIC
including Dr. Linninger, Eric Lueshen and Sukhi Basati for their constant guidance and
support, Joe Kanikunnel, Indu Venugopal and Bhargav Desai for their generosity in
providing their expertise. Finally, thanks to Dr. Victoria Sharts, and Timothy Walsh for
their encouragement to become involved and pursuit to always improve science
instruction and Caroline for her continued support.
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