Multiple Emulsions

Presented to Prof. Dr. Nazar Mohammad

Ranjha

Presented By Mahvash Ansari, M-Phil Pharmaceutics, 2008-2010, Roll # 02

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Multiple EmulsionMultiple emulsion systems are novel developments in the field of emulsion technology and are more complex type of dispersed system. Multiple emulsions are the emulsion system in which the dispersed phase contain smaller droplets that have the same composition as the external phase. This is made possible by double emulsification hence the systems are also called as “double emulsion”.

Like simple emulsions, the multiple emulsions are also considered to be of two types:

• Oil-in-Water-in-Oil (O/W/O) emulsion system

• Water-in-Oil-in-Water (W/O/W) emulsion system

In O/W/O systems an aqueous phase (hydrophilic) separates internal and external oil phase. In other words, O/W/O is a system in which water droplets may be surrounded in oil phase, which in true encloses one or more oil droplets.

In W/O/W systems, an organic phase (hydrophobic) separates internal and external aqueous phases. In other words, W/O/W is a system in which oil droplets may be surrounded by an aqueous phase, which in turn encloses one or several water droplets. These systems are the most studied among the multiple emulsions. The immiscible oil phase, which separates two miscible aqueous phases is known as “liquid membrane” and acts as a different barrier and semi-permeable membrane for the drugs or moieties entrapped in the internal aqueous phase.

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Schematic Diagram of W/O/W & O/W/O

Emulsions

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Pre-Formulation of Double

Emulsion

The formulate a double emulsion, it is necessary to choose, at least, an oil

and two surfactants, one low in HLB and one high in HLB. In the example

mentioned here, we have been working with span surfactants (HLB<5) and

Tween surfactants (HLB>10) and with a vegetable oil (caprylic/ capric

triglyceride).

The first stage involves making “state diagrams” that provide the means for

pre-selecting formulas. Those selected for in-depth study are the very white

emulsions that cream slowly and/or moderately.

HBL (blend)=f +HBL (A) + (1-f) *HBL (B)

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Methods of Preparation

Multiple emulsions are best prepared by re-emulsification of primary

emulsion. The following are the method of multiple emulsions:

Two Steps Emulsification (Double Emulsification)

Phase Inversion Technique (One Step Technique)

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Two Steps Emulsification

(Double Emulsification)

Two steps emulsification methods involve re-emulsification of primary W/O or O/W emulsion using a suitable emulsifier agent. The first step involves, obtaining an ordinary W/O or O/W primary emulsion wherein an appropriate emulsifier system is utilized. In the second step, the freshly prepared W/O or O/W primary emulsion is re-emulsified with an excess of aqueous phase or oil phase. The finally prepared emulsion could be W/O /W or O/W/O respectively.

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Two Steps Emulsification

(Double Emulsification)

Two steps emulsification methods involve re-emulsification of primary W/O or O/W emulsion using a suitable emulsifier agent. The first step involves, obtaining an ordinary W/O or O/W primary emulsion wherein an appropriate emulsifier system is utilized. In the second step, the freshly prepared W/O or O/W primary emulsion is re-emulsified with an excess of aqueous phase or oil phase. The finally prepared emulsion could be W/O /W or O/W/O respectively.

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Two Steps Emulsification

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Modified Two Steps Emulsification

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Phase Inversion Technique

(One Step Technique)

An increase in volume concentration of dispersed phase may cause an

increase in the phase volume ratio, which subsequently leads the formation of multiple emulsions. The method typically involves the addition of an aqueous phase contains the hydrophilic emulsifier [ Tween 80/sodium dodecylsulphate (SDS) or Cetyl trimethyl ammonium salt CTAB)] to an oil phase consisted of liquid paraffin and containg lipophilic emulsifier (Span 80). A well-defined volume of oil phase is placed in a vessei of pin mixer. An aqueous solution of emulsifier is then introduced successively to the oil phase in the vessel at a rate of 5 ml/min, while the pin mixer rotates steadily at 88 rpm at room temperature. When volume fraction of the aqueous solution of hydrophilic emulsifier exceeds 0.7, the continuous oil phase is substituted by the aqueous phase containing a number of the vesicular globules among the simple oil droplets, leading to phase inversion and formation of W/O/W multiple emulsion.

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One Step Technique

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Membrane Emulsification

TechniqueIn this method, a W/O emulsion (a dispersed phase) is extruded into an external aqueous phase (a continuous phase) with a constant pressure through a Porous Glass Membrane, which should have controlled and homogenous pores. The particle size of the resulting emulsion can be controlled with proper selection of Porous Glass Membrane as the droplet size depends upon the pore size of the droplet size depends upon the pore size of the membrane. The relation between membrane pore size and particle size of W/O/W emulsion exhibits good correlation as described by the following equation :

Y= 5.03 X + 0.19

Where X is the pore size and Y is the mean particle size of the multiple prepared using membrane emulsifier technique.

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INVITRO

CHARACTERIZATION

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Average Globule Size and Size

Distribution

The optical microscopy method using calibrated ocular and stage micrometer can be utilized for globule size determinations of both multiple emulsion droplets as well as droplets of internal dispersed phase.

Brightfield micrographs equipped with differential interference contrast optics have been used to characterize the internal droplet of multiple emulsions. Various other techniques used to characterize colloidal carriers like Coulter counter, freeze-fracture electron microscopy and scanning electron microscopy are also used to determine average globule size and size distribution of multiple emulsions. Recently, NMR self-diffusion methods are adapted to multiple emulsion characterization.

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Area of Interfaces

The average globule diameter determined can be used in the calculation of

the total area of interface using the formula

S = 6/d

S = Total area of interface (sa, cm)

d = Diameter of globules (cm)

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Number of Globules

Number of globules per cubic meter can be measured using the haemecytometer cell. The globules in five groups of 16 small squares (total 80 small squares) are counted and the total number of globules in per cubic mm are calculated using the formula (Chatterjee, 1985) :

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Rheological Evaluation

The rheological of multiple emulsions is an important parameter as it relates to emulsion stability and clinical performance. The viscosity and interfacial elasticity are two major parameters, which relate to product rheology. The viscosity of the multiple emulsions can be measured by Brookfield rotational Viscometer.

Interfacial rheology (i.e., interfacial elasticity at the oil-aqueous interface) can be investigated at the mineral oil/water interface using an Oscillatory Surface rheometer.

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Zeta PotentialThe zeta potential measurements are pivotal in the designing of surface modified or ligand anchored multiple emulsion systems. The zeta potential and surface charge can be calculated using Smoluchowski’s equation from the mobility and electrophoretic velocity of dispersed globules using the Zeta-potentiometer. Zeta potential was calculated using following formula:

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Percent Drug Entrapment

Percent equipment of drug or active moiety in the multiple emulsion is generally

determined using dialysis, centrifugation, filtration and conductivity measurements. The

% Entrapment can be calculated using the following equation :

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In Vitro Drug Release

The drug released from the aqueous inner phase of a W/O/W emulsion can

be estimated using the conventional dialysis technique. Aliquots were

withdrawn at different time intervals and estimated using standard

procedure and the data were used to calculate cumulative drug release

profile.

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In Vitro Stability StudiesEmulsion stability is determined by phase separation on storage of W/O/W emulsions.

Freshly prepared multiple emulsion allowed to stand for one week at room

temperature and the volume of aqueous phase separated (Vsep) is measured at

suitable time intervais and percent phase separation is calculated using following

formula:

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Stability of Multiple Emulsions

Emulsion stability is a phenomenon, which depends upon the equilibrium

between water, oil and surfactant. Unfortunately multiple emulsions are

thermodynamically unstable. The possible indications of instability includes:

Leakage of the contents from the inner aqueous phase.

Expulsion of internal droplets in external phase.

Constriction or distension of the internal droplets due to osmotic

gradient across the oil membrane.

Flocculation of internal aqueous phase and multiple emulsion

droplets.

Disruption of oil layer on the surface of internal droplets.

Phase separation.

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Methods to Stabilize Multiple

EmulsionsThe followings are some of the attempt or studies made to restore or

strengthen the stability of multiple emulsions :

Liquid crystal stabilized multiple emulsion

Stabilization in presence of electrolytes

Stabilization by forming polymeric gel

Stabilization by interfacial complexation between non-ionic

surfactant and macromolecules

Steric stabilization

Phase-inversion stabilization of W/O/W emulsion

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Drug Release Mechanisms &

ModelsSome of the mechanisms includes :

• Diffusion of unionized drug (hydrophobic species) through the oil layer

• Carrier medicated transport

• Micellar transport

• Rupture of oil membrane

• Thinning of oil membrane

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Applications in Therapeutics &

Cosmetics

Multiple emulsion systems are finding unlimited uses because of their

vesicular structure with innermost phase closely similar to that of liposomal

vesicles and the selective permeability characteristic of liquid membrane.

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Biomedical & Pharmaceutical

Applications of Multiple Emulsions

Food and cosmetics Other applications

5-Fluorouracil, Bleomycin In cancer therapy and drug targeting

Diclofenac sodium in the fabrication of micro capsulated

dosage form

Different hydrocarbons Separation and extraction technique

Influenza virus Vaccine adjuvant

Salicylates, Barbiturates, Quinine

Sulphate

Drug over dosage treatment

Chloroquin Masking action

Insulin Enhanced oral bioavailability

Drug entrappedApplications

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Triple and Multiple Emulsions

One of the potential applications of double emulsions is to use to encapsulate substances. By the evaporation of the intermediate phase it is possible to prepare capsules made by polymers (or polymerossomes), solid particles (or colloidossomes) and vesicles.

Using the same procedure to prepare double emulsions we prepare micro fluidics devices made by glass capillaries to prepare triple emulsions of w/o/w/o. The device consists in two concentric similar capillaries carefully aligned facing another capillary. Four fluids are pumped through the channels and forced to pass in a small orifice forming the triple emulsion, as shown below.

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Triple and Multiple Emulsions

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Examples Of W/O/W/O Emulsions

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Other Examples

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Examples

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Examples

This kind of emulsion can be used as templates to prepare capsules with two

layers made by different chemical species