Seminar on
MAGNETIC MICROSPHERES
Presented
by
Ushasri
Department of Industrial pharmacy
University college of pharmaceutical sciences
KAKATIYA UNIVERSITY
CONTENTS
INTRODUCTION
DEFINITION
RATIONALE OF THE DRUG DELIVERY SYSTEM
ADVANTAGES AND DISADVANTAGES
PRINCIPLE OF MAGNETIC DRUG TARGETING
FORMULATION
PREPARATION OF MAGNETIC MICROSPHERES
CHARACTERIZATION
APPLICATIONS
CONCLUSION
REFERENCES
INTRODUCTION
 Drug targeting:Delivery of drugs to receptors or organ or any other specific part of
the body exclusively.
 Various nonmagnetic micro carriers are utilized for drug targeting but they show
poor site specificity and are rapidly cleared off by RES .
 Magnetic particles composed of magnetite are well tolerated by body.
 Magnetic fields are believed to be harmless to biological systems and adaptable to
any part of the body.
Up to 60% of injected dose deposited and released in a controlled manner .
Magnetic micro carriers were developed to overcome two major problems
encountered in drug targeting
RES clearance
Target site specificity.
DEFINITION:
Magnetic microspheres are spherical particles, composed
of metallic iron and activated carbon which serves as a delivery
vehicle for the site specific targeting, retention and release of
pharmaceuticals.
It utilizes the physical force of magnetic field for the targeted delivery of
pharmaceutical agents to specific areas of the body.
Size range -1-100µm.
ROA:
IV –NLT(5µm)
Intra arterial-NLT(1ooµm).
The physical force created by the magnetic field draw the magnetic
targeted carrier drug compound through the arteriole wall in to the
targeted disease area. This process is known as extra vasation.
Results in localization and retention of the delivered pharmaceutical
agents at the delivered site even when the magnetic field has been
removed.
This technology uses a small externally positioned magnet to
create a localized magnetic field within the body.
Rationale of thE delivery system
Number of problems exists for successful targeting of biodegradable carriers
1. Rapid sequestration of IV administered drug carriers by mono nuclear phagocytes
of the RES.
Approaches to over come
 By blocking RES prior to administering the drug carrier
 Impart specificity to the drug carrier by incorporating the specific ligand on external
surface of the carrier.
2. Vascular system
 The endothelial cell lining the capillary level vasculature have severely
frustrated attempt at invivo targeting
And shield the carrier from recognization
In order to circumvent the RES and provide a method of site specific drug
delivery a magnetically responsive drug carrier was developed.
Retention of magnetic carrier at target site
 will delay RES clearance
 facilitate extravasation
 prolong the systemic action of the drug .
ADVANTAGES
 Reduces circulating concentration of free drug .
 Minimizes damage to the normal tissue cells and allows an effective treatment of
regioned disease.
 Delivers 60% of the dose to target tissues.
 Making the drug available in controlled fashion within the tissue.
 Advantage of crossing microvascular barriers .
 Minimally reactive with blood components.
 Clinically nontoxic from the stand points of chemical and immunological agents.
 Capable of accommodating a wide variety of water soluble agents.
 Magnetite is readily available from the commercial sources, individual particles are
much smaller (10-20mm) occupy a fraction of the drug space.
DISADVANTAGES
 Requires specialized microspheres and magnets .
Treatment of multiple region requires sequential targeting.
 Demands new methods for noninvasive , localized monitoring term deposition
of drug levels in target tissues.
 Expensive.
Tissue localization of microspheres result long term deposition of magnetite at
levels of 3.5mg/kg.
 Once the drug is released it is no longer attractive to the magnetic field .
 Possibility of embolisation of the blood vessels due to accumulation of magnetic
carriers.
PRINCIPLE OF MAGNETIC DRUG TARGETING
Target
tissue
Drug
/Carrier
Circulation
Major
pathway
RES ORGANS
Liver/Spleen
Phagocytosis
Major
pathway
Target tissue
Magnetic
carrier
Circulation
Little
access
RES organs
(liver,spleen,bonemarrow
FORMULATION OF MAGNETIC MICROSPHERES
Components
Matrix:
It comprises cross linkable material that will cross link upon heating .
The matrix material forms the bulk micro particle structure in which the agent is
dispersed orencapsulated.
The matrix material should be biodegradable.
It is either a polymer or a protein .
Ex: Albumin ,Egg albumin , Bovine serum albumin.
Thermo setting polymers include poly urethanes, phenol/formaldehyde and
urea formaldehyde resins.
HYDROPHOBIC LIQUID PHASE
The flash point of the oil should be higher than the denaturation temparature of
the protein.
If solvents are used the boiling point should be higher than the denaturation
temparature.
Ex: cotton seed oil, Corn seed oil, Silicon oil.
SURFACTANTS
•Used to decrease the hydrophobicity of matrix material to mitigate agglomeration
of microdroplets,
• Disperse the carriers more evenly
Eg: Sorbitan esters, polyoxyethylene ethers, Glycerol esters, Sorbitan
sesquiolate
MAGNETS
 Iron oxide such as magnetite (Fe3O4) or magnemite ( ‫ץ‬-Fe2O3) are more stable
against oxidation and are preferentially used as core material instead of iron.
 Estoper M particles are super paramagnetic and used in immuno assays,cell
separation and nucleic acid purification.
Ex: Silica magnet particles
Cellulose magnetic particles
Ferro fluids
LIGANDS
Incorporated in order to prevent the RES clearance.
Ex:Avidin, Biotin, Streptavidin, Lectins.
PREPARATION OF MAGNETIC MICROSPHERES
The magnetic microspheres are prepared by :
1)Heat denaturation
2)Chemical cross linking:
also prepared by stabilising the albumin matrix with aldehyde cross linking agent.
Ex: glutaraldehyde.
 These have been solubilized in organic phase.
Emulsion is homogenized by sonication method for 1min at 100W at 27°c.
Sonifier with a 0.635 cm titanium probe inside a circulating attachment chamber is used.
Preparation involves emulsification fOllowed by heat
denaturation
Aqueous solution of human serum albumin+ drug+ magnetite
Emusified with 30ml of cotton seed oil by the use of surfactant
Emulsion is homogenized by sonication
Results in the formation of non-cross linked microspheres.
matrix stabilization
1)Heat denaturation
2)Chemical crosslinking
In the heat denaturation process stabilization varied with temperature and time.
This procedure generates small non cross linked microspheres.
Matrix stabilization is subsequently achieved by :
Heat denaturation at a temperature between 100-165°c
Treatment with oil soluble reagents such as 0.2M 2,3-butane dione or glutaraldehyde.
In the case of chemical cross linkers denaturation varies with exposure time
Oil and the cross linking agents are removed by multiple diethyl ether washings.
STORAGE
Magnetic micro spheres are stored in the powder form
 These are stored at a temperature of 4°c.
CHARACTERIZATION OF MAGNETIC
MICRO SPHERES
DETERMINATION OF DRUG LOADING AND ENTRAPMENT
EFFICIENCY
Drug loaded microspheres are digested with suitable reagent at room
temperature and kept for 24 hrs to precipitate the protein .The digested
homogenate is centrifuged and supernatant is analyzed for drug content by
measuring its absorbance. The drug loading in microspheres is estimated by
using the formula .
L = QM/WM*100
L = %Drug loading of micro spheres
QM= Quantity of drug present
WM= Weight of microspheres
DETERMENATION OF MAGNETITE CONTENT
The magnetite content in microspheres is estimated quantitatively by
hydrolyzing an aliquot of the microspheres in concentrated HCl and the resultant
hydrolysate for iron is determined by atomic absorption spectroscopy at 248nm .It
has been demonstrated that microspheres containing magnetite of 20-28%w/w
are effectively targeted by at the site by using the magnet of 5000-8000G.
PARTICLE SIZE ANALYSIS:
1) scanning electron microscopy
2) Laser diffraction
3) Zeta sizer
4) Confocal laser scanning microscopy
MAGNETIC RESPONSIVITY MEASUREMENT
Mille pore pumps air in to the flask containing normal saline .
It results in the flow of saline into the tube exposed to an electro magnet.
The pump pressure maintained was 0.5 cm/s resembles the rate blood flow in the
capillaries.
1ml microspheres dispersed in saline containing tween-80 was injected in to the
injection site.
8000G of magnetic field was applied for 15min a,samples collected every minute.
 samples analysed by UV-Visible specrophotometer
at the ‫ג‬max of the drug.
Higher the absorbance –greater the amount of drug
lower the magnetic retention in the tube –
lower the magnetic responsivity .
MEASUREMENT OF ELECTROPHORETIC MOBILITY BY USING
OPTICAL MICROSCOPY
Measurement of electrophoretic mobility
helps in the prediction of magnetic
microspheres behaviour in the
patients blood circulation.
ϰ = magnetic susceptibility.
Vm =volume of the magnetic component
The movement of magnetic microspheres
is determined by the Magnetic propertites of
the particle, magnetic component volume,
magnetic susceptibility ,viscosity,diameter.
A piece of acrylic was placed on the micro scope table.
Glass capillary was filled with microsphere suspension using 1ml syringe.
During filling the magnet was placed18mm away from the capillary
The microscope was manually focused ,the colour video camera connected to
computer ,displays a clear picture.
The magnet was now closely moved to capillary image acquisition was started.
The images were saved per sample at an interval of 10 frame per second.
The difference in two successive images results in differential picture of only the
moving particles.
From the pictures individual parameters for each moving microsphere were
automatically determined.
Limitation
Particle diameter lessthan1.3µm can’t be detected.
DENSITY DETERMENATION
 Measured by using multi volume Pycnometer.
Accurately weighed sample was placed In multivolume pycnometer.
 Helium was introduced at a constant pressure into the chamber.
 Allowed to expand this expansion results in decrease in pressure within the chamber
 Two consecutive readings of reduction in pressure were noted from this the volume
and density of the carrier was determined.
SURFACE HYDROPHOBICITY:
Determined by measuring angle of contact.
The surface hydrophobicity of microspheres has an important influence on the
interaction of colloidal particles with the biological environment .
It regulates the extent and type of hydrophobic interactions of microparticles with
blood components.
INVITRO RELEASE STUDIES
Same as the normal dissolution procedure. Done by using USP paddle apparatus .
Initial release is due to the release of surface drug and small microspheres with
increased surface area & the presence of water soluble drugs.
The drug partition coefficient effects the release rate .
Higher the partition coefficient –faster the release because it results in the
migration of drug to the outer organic phase, during preparation
IN VIVO RELEASE STUDIES :
Micro spheres are tested in vivo to assess the validity of drug targeting concept
.The subcutaneous tissue in the tail of rats is chosen as the initial target site for
microsphere localization.
The ventral caudal artery is selected for microsphere infusion as it supplies the
majority of the blood to tail.
APPLICATIONS
1).Hyperthermic treatment of cancer
Hyperthermia involves heating and destroying the target tissue between temperature 4246°C.
20-30µm of ferromagnetic microspheres are used to induce hyperthermia in cancers, for
tumors located deep inside the body.
2.DETECTION OF GLYCATED HAEMOGLOBIN
The determination of glycated haemoglobin using PVA magnetic microspheres
It is an alternative to currently used methods
Used in blood sugar diagnosis.
Preparation of magnetic microspheres
encapsulated with diclofenac sodiuM
Diclofenac has short half life ,it should be given frequently to maintain
therapeutic activity and is often associated with GIT bleeding ,gastric ulcers
,blood dyscrasias and anaphylaxis.
To over come this toxicity and prolong the therapeutic effect at the target site
magnetic albumin microspheres of diclofenac were prepared.
Using magnetic field to repair damaged retinas:
Conventional way to repair damaged retinas.
Inject silicone fluid or a special gas directly in to the eye to push the retina back
into place.
This makes the repair easier and more precise by allowing the fluid to be
removed to the areas of the eye that are hard to reach.
Magnetic immuno assay of acute myocardial infARction:
Magnetic immunoassay was developed to test the 2 markers of AMI
Myoglobin
Fatty acid binding protein
These markers shows elevated serum levels soon after infarction .
Immuno assay follows a standard solid phase ELISA consisting of the formation of
a complex /sandwich by attaching two different Ab to different epitopes.
Albumin magnetic micro spheres are prepared and coupled with avidin.
Ab are monoclonal mouse anti-human cardiac myoglobin.
Enzyme is alkaline phosphate coupled with streptavidin.
Biotin serves as abridging link between microspheres -antibody – alkaline phosphate.
Results in the formation of complex.
These complexes are separated by using external magnetic field.
To this add chemical reagent Nitro-phenol phosphate –produces an yellow substrate.
Intensity of the colour was measured by UV visible spectro photometer at 450nm.
Higher the intensity – greater the myoglobin concentration.
detox regime :
magnetic microspheres also helps to treat after a poison gas attack.
The poison process involves injection of magnetic particles that had been
functionalized to bind with the foreign toxin.
An external magnetic field would then be used to draw the toxin tagged particles
out of the body.
Efficient detoxification will require particles with a reasonably high magnetic
moment that can be pulled together with any attached toxin molecules across a
magnetic field gradient.
Cell separatiOn:
Polymeric microspheres conjugated to antibodies and lectins have been used
previously as cell surface markers for the detection and localization of antigens and
lectin receptors using scanning electron microscopy (SEM) .
 A new, more versatile cell surface probe consisting of iron-containing polymeric
microspheres tagged with fluorescent dyes and chemically coupled to antibodies or
lectins.
 Magnetic and fluorescent properties of microspheres have been utilised in the
magnetic separation of red blood cells (RBC) and lymphoid cells.
Magnetic control of pharmaco kinetic parameters and
drug release
The magnetite was embedded in to the drug filled polymer matrix and showed that
they activate or increase the release of drug from polymer by moving a magnet
over it or by applying oscillating magnet The micro movement within the crack
produce a micro crack and thus made the influx of liquid , dissolution and efflux of
the drug is possible.
USE OF MECHANICAL PROPERTIES OF MAGNETITE IN THERAPY:
This is possible by filling an magnetic component in to the capsule or tablet, speed
of travel can be slow down at specific position by an external magnet ,thus
changing the drug absorption and increases the drug levels in blood.
OTHER APPLICATIONS
Determination of trace hydrazine by differential pulse voltametry
using magnetic microspheres.
Pulsed delivery of insulin in diabetic patients.
Used to deliver therapeutic radio isotopes.
Delivery of fibrinolytic agents in the treatment of deep venous
thromobosis and pulmonary embolism.
 Magnetism has application in numerous fields like
Diagnostics,
Tumour targeting
Molecular biology
Cell isolation
Cell purification
 Radioimmunoassay
Detection of immunoglobulin (Ig) receptors
wheat germ agglutinin (WGA) receptors on lymphocytes
by SEM and fluorescent microscopy..
CONCLUSION:
Magnetic micro carriers have been investigated for targeted drug delivery
especially magnetic targeted chemotherapy due to their better tumor targeting,
therapeutic efficacy, lower toxicity and flexibility .
In spite of certain drawbacks, such as strong magnetic field requires for the
ferro fluid and deposition of magnetite the magnetic microcarriers still play an
important role in the selective targeting, and the controlled delivery of various
drugs.
 It is a challenging area for future research in the drug targeting so more
researches, long term toxicity study, and characterization will ensure the
improvement of magnetic drug delivery system.
The future holds lot of promises in magnetic micro carriers and by further study
this will be developed as novel and efficient approach for targeted drug delivery
system.
References
Methods of dug delivery ,International encyclopedia of pharmacology and
therapeutics section 120 by G.M. Ihler PG.NO-39-56.
Characterization of magnetic particles and their magneto phoretic mobility using
a digital microscopy by u.o. hafell,european cells and materials, vol-3 suplliment 2
,2004,pg.n-24-27.
,”magnetically modulated drug delivery “, targeted and controlled drug delivery
by S.p.vyas and khar,1st edition ,2002,pg.no-417-458.
Microspheres technology and applications “, Encyclopedia of pharmaceutical
technology, 10th edition ,pg.no – 1-29.
,” magnetically modulated therapeutic systems”, international journal of
pharmaceutics, U.O. Hafel , 277(2004) pg.n :19-24.
www.Magnetic magzine.com
www.magnetic microspheres.com
www.pharmainfo net.com
www.materials today.com
www.wikipedia.com
THANK U