EBP 412 Specialty Polymer by

METHOD OF LIPOSOME
Methods of liposome preparation

General methods of preparation

All the methods of preparing the liposomes involve four basic stages:

1.Drying down lipids from organic solvent.
2.Dispersing the lipid in aqueous media.
3.Purifying the resultant liposome.
4.Analyzing the final product.

Method of liposome preparation and drug loading

The following methods are used for the preparation of liposome:

1.Passive loading techniques
2.Active loading technique.

Passive loading techniques include three different methods:

1.Mechanical dispersion method.
2.Solvent dispersion method.
3.Detergent removal method (removal of non-encapsulated material).

Mechanical dispersion method

The following are types of mechanical dispersion methods:

1.1. Sonication.

1.2. French pressure cell: extrusion.

1.3. Freeze-thawed liposomes.

1.4. Lipid film hydration by hand shaking, non-hand. shaking or freeze drying.

1.5. Micro-emulsification.

1.6. Membrane extrusion.

1.7. Dried reconstituted vesicles.

Sonication

Sonication is perhaps the most extensively used method for the preparation of SUV. Here, MLVs are sonicated either with a bath type sonicator or a probe sonicator under a passive atmosphere. The main disadvantages of this method are very low internal volume/encapsulation efficacy, possible degradation of phospholipids and compounds to be encapsulated, elimination of large molecules, metal pollution from probe tip, and presence of MLV along with SUV.

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There are two sonication techniques:

a)Probe sonication. The tip of a sonicator is directly engrossed into the liposome dispersion. The energy input into lipid dispersion is very high in this method. The coupling of energy at the tip results in local hotness; therefore, the vessel must be engrossed into a water/ice bath. Throughout the sonication up to 1 h, more than 5% of the lipids can be de-esterified. Also, with the probe sonicator, titanium will slough off and pollute the solution.

b)Bath sonication. The liposome dispersion in a cylinder is placed into a bath sonicator. Controlling the temperature of the lipid dispersion is usually easier in this method, in contrast to sonication by dispersal directly using the tip. The material being sonicated can be protected in a sterile vessel, dissimilar the probe units, or under an inert atmosphere .

French pressure cell: extrusion

French pressure cell involves the extrusion of MLV through a small orifice. An important feature of the French press vesicle method is that the proteins do not seem to be significantly pretentious during the procedure as they are in sonication. An interesting comment is that French press vesicle appears to recall entrapped solutes significantly longer than SUVs do, produced by sonication or detergent removal.

The method involves gentle handling of unstable materials. The method has several advantages over sonication method. The resulting liposomes are rather larger than sonicated SUVs. The drawbacks of the method are that the high temperature is difficult to attain, and the working volumes are comparatively small (about 50 mL as the maximum).

Freeze-thawed liposomes

SUVs are rapidly frozen and thawed slowly. The short-lived sonication disperses aggregated materials to LUV. The creation of unilamellar vesicles is as a result of the fusion of SUV throughout the processes of freezing and thawing. This type of synthesis is strongly inhibited by increasing the phospholipid concentration and by increasing the ionic strength of the medium. The encapsulation efficacies from 20% to 30% were obtained.

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