magnetic microspheres

Views:
 
Category: Education
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

MAGNETIC MICROSPHERES :

MAGNETIC MICROSPHERES Prepared By: Sonam M. Gandhi 1

:

DEFINITION: Magnetic micro carriers are supramolecular particles that are small enough to circulate through capillaries without producing embolic occlusion (<4µm) but are sufficiently susceptible (ferromagnetic) to become captured in micro vessel and dragged into the adjacent tissues by magnetic fields of 0.5 to 0.8 tesla (T). 2

PowerPoint Presentation:

Advantages: Therapeutic responses in target organs occurs at only one tenth of free drug dose. Controlled drug release within target tissues for intervals of 30 min to 30 hr . Avoidance of acute drug toxicity directed against endothelium and normal parenchyma cells. Adaptable to any part of the body. 3

PowerPoint Presentation:

Disadvantages: Magnetic targeting is an expensive, technical approach and requires specialized manufacture and quality control system. It needs specialized magnet for targeting, advanced techniques for monitoring and trained personnel to perform procedures. Magnets must have relatively constant gradients, in order to avoid focal over-dosing with toxic drugs. A large fraction of the magnetite which is entrapped in carriers is deposited permanently in target tissues. Due to these limitations magnetic drug targeting is likely to be approved only for severe diseases. 4

:

Concept of targeting magnetic microspheres: Microspheres containing magnetic material (magnetite) are injected into an artery that supplies to a given site. As the microspheres would be selectively and magnetically localized at the capillary level they have free flow access through large arteries. Thus the microspheres would serve as the time release capsules systems sitting in the desired location. A magnet of sufficient field strength is thus placed externally over the target area to localize the microspheres at the capillary bed in this region. 5

PowerPoint Presentation:

To localize microspheres in a fast moving arterial system, greater field strength is required. When the microspheres are first pushed against the endothelial cells by the magnetic field, an endocytic response was triggered with continuous magnetic influence over certain period of time. Microspheres migrated from endothelial cells into the interstitial compartment and formed a depot for sustained release over an extended period of time. 6

PowerPoint Presentation:

Important characteristics: In targeting using magnetic microspheres, the magnetite content of carrier and also magnitude of applied magnetic field is important. Particle size of drug carrier can affect the degree of drug entrapment. If a high magnetic content is incorporated, thus amount of magnetic fields needed is reduced but the space available for drug entrapment decreases. 7

PowerPoint Presentation:

Drug incorporation and magnetite has to be delicately balanced. Optimum magnetite content would be between 20%-50% of drug weight in the drug carrier complex. 8

PowerPoint Presentation:

Magnetite: A ferromagnetic material when incorporated into microspheres makes them magnetically responsive So that they can be concentrated to the desired site by applying some magnetic field. Iron is strong ferromagnetic material but due to its local tissue irritation and other toxic manifestation it cannot be included into microspheres. But such a problem is not seen when magnetite which is chemically ferrous ferric oxide (Fe 3 o 4 ) biologically compatible and also its ultra fine particle size makes it suitable material. 9

PowerPoint Presentation:

Super paramagnetic particles under the influence of an external magnetic field Super paramagnetic particles in absence of an external magnetic field, monodisperse particle distribution 10

PowerPoint Presentation:

Magnetic guidance: Initially drugs were grafted on to the surface of the magnetic particles, but it suffers from the drawbacks like very low loading capacity and irreversible particle aggregation under the exposure of magnetic field. Coating of the ferromagnetic particles with albumin and other charged polymers decreases the aggregation problem by making it reversible. 11

PowerPoint Presentation:

PREPARATION OF MAGNETIC MICROSPHERES Magnetically responsive microspheres can be prepared by using albumin as a carrier of drug and magnetite. Size of microspheres is kept between 1-2 µm, so that they can be injected into blood vessels without problem of thrombo -embolism. Two methods are employed for the preparation they are Phase separation emulsion polymerization Continuous solvent evaporation 12

PowerPoint Presentation:

Solution in volatile organic solvent ( polymer + drug + magnet) Auxillary Solution Stirring Homogenization Stirring temp (22 o -30 o C) Magnetic Microsphere Separated by centrifugation Freeze drying and storage at 4 o C CONTINUOUS SOLVENT EVAPORATION 13

PowerPoint Presentation:

Aqueous solution Vegetable oil (albumin+drug+magnetite) Emulsification Stabilization by Heat Cross linking agent ( 100-150  C) Microsphere suspension Separated from oil Freeze drying & storage at 4  C PHASE SEPARATION EMULSION POLYMERIZATION 14

PowerPoint Presentation:

15 Assembly used for separation of magnetic microsphere from non magnetic materials

PowerPoint Presentation:

Evaluation of drug release rate in vitro Dialysis method Continuous column elution method 16

PowerPoint Presentation:

Dialysis methods : Albumin microspheres were taken in a funnel, 3ml of phosphate buffer of 7.3 pH was added. The mouth of the funnel is covered with cellophane paper and fastened with rubber band . Then funnel is inverted into a beaker containing 50 ml phosphate buffer. 2.5 ml of aliquots are withdrawn every half an hour and replaced with fresh buffer and estimated for drug release. 17

PowerPoint Presentation:

b. Continuous column elution methods : Microspheres are immobilized on a column containing a fixed weight of glass wool (3.5 gm) as a support material and kept at 37 o C. they are subjected to a constant flow of 50 ml phosphate buffer, fractions are collected at equal intervals and amount of drug release is estimated by using UV spectroscopy. 18

Characterization: Carrier localization: gamma camera imaging; high frequency ultrasound; magnetic resonance technique :

Characterization: Carrier localization : gamma camera imaging; high frequency ultrasound; magnetic resonance technique 19

PowerPoint Presentation:

SEM - scanning electron microscopy 20

PowerPoint Presentation:

In vivo drug distribution : magnetic resonance imaging 21

PowerPoint Presentation:

Microspheres localization : Ultrasound techniques 22

PowerPoint Presentation:

Particle size and shape: SEM 23

authorStream Live Help