*6.4.1 Dried and reconstituted vesicles (DRVs)*

This method follows freeze drying for empty SUVs to form powder (See **Figure 14**). Then that freeze dried powder is rehydrated with aqueous phase media containing materials that are to be entrapped. This dispersion contains solid lipids which are in subdivided form. Freeze drying organizes membrane structure when rehydrated with water to fuse and reseal vesicles. For preparing uni or olio lamellar vesicles of 1.0 μm or less in diameterthis method is used [28].

#### *6.4.2 Extrusion method by freeze thaw*

This is extension to above DRV method and lipid film formed by film hydration is mixed with solute containing entrapped materials to form vesicles. The obtained dispersion extruded for three times after two freeze thaws, vortexed and again freeze thawed 6 times followed by 8 extrusions. Then liposomes get fused and forms large unilamellar vesicles, and this method mostly used for proteins encapsulation [29].

#### **6.5 Solvent dispersion methods**

In these methods the lipids and non-aqueous soluble drug are added in organic phase and then that lipid phase injected into aqueous phase.

**Figure 14.** *Preparation of dried reconstituted liposomal vesicles.*

#### *6.5.1 Solvent injection method*

In this solvent injection method (See **Figure 15**) lipids are added into organic phase (ethanol or ether or chloroform) and that lipid phase is injected into aqueous phase to obtain liposomes [30]. This method again sub divided two methods depending on solvent used.

#### *6.5.1.1 Ethanol injection method*

A lipid solution of ethanol is rapidly injected to a large quantity of aqueous buffer. This ethanol injection method gives small liposomes without any extrusion or sonication [31, 32]. This method has some disadvantages that the liposomes formed are very dilute, difficulty of ethanol removal from azeotropic mixture and possible inactivation of various biologically active macromolecules in the presence ethanol.

#### *6.5.1.2 Ether injection method*

This ether injection method is different to ethanol injection. Ether is aqueously insoluble and requires hot condition to remove solvent from liposomal dispersion. This method involves single jet injecting lipid phase containing ether into heated aqueous phase. A solution of lipids dissolved in diethyl ether or ether-methanol mixture is gradually injected to an aqueous solution of the material to be encapsulated at 55–65°C or under reduced pressure. The ether vaporizes and the dispersed lipid forms primarily unilamellar liposomes [33]. Ether injection method has advantage over ethanol injection method because the used ether is removed to obtain a concentrated liposomal dispersion and high entrapment efficiency.

#### *6.5.2 Double emulsion vesicles*

The double emulsions are prepared by controlling flow rates at three different phases (i.e. 2 aqueous phases and 1 oil/lipid phase) to form single drop of aqueous *Drug Delivery through Liposomes DOI: http://dx.doi.org/10.5772/intechopen.97727*

**Figure 15.** *Solvent injection method.*

**Figure 16.** *Double emulsion liposomal vesicles.*

solution within a single drop of oil in a continuous aqueous phase (See **Figure 16**). A method by using glass capillary micro fluidic device was fabricated from double emulsion containing phospholipid vesicles [34].

## *6.5.3 Reverse phase evaporation*

The solvent containing lipid is taken in rota flask and evaporated by rotary evaporator kept under low pressure. The formed lipid film was nitrogen purged and then dissolved again in diethyl ether or isopropyl ether containing organic phase to form vesicles. This forms an emulsion and that formed emulsion is again evaporated at low pressure and forms semisolid gel. These obtained liposomal vesicles are called reverse phase evaporation vesicles (REV) [35, 36].
