Colloid An Introduction

Kausar Ahmad

Kulliyyah of Pharmacy

http://staff.iiu.edu.my/akausar

Physical Pharmacy 2 1

Physical Pharmacy 2

Contents

Lecture 1:• Types of colloids• Types of dispersions

Lecture 2:• Types of emulsions• Emulsification factors

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Colloidal System

Particle size below 1 mm

High specific surface area

Discrete particles dispersed in a different medium

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Types of Colloids

TypeDispersed

phaseContinuous

phase

Emulsion: o/w oil water

Emulsion: w/o water oil

Suspension solid water or oil

Aerosol solid or liquid air

Others Multiple emulsion: w/o/w, o/w/o

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Classification Based on Size

Class Size Examples

Molecular dispersion

< 1.0 nm glucose

Colloidal dispersion

1.0 nm - 0.5 mm Natural rubber latex

Coarse dispersion

> 0.5 mm red blood cells

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Classification of dispersed systems

hydrophilic colloidal dispersion (in water)• surfactant micelles and phospholipid vesicles, also

known as association colloids

lyophilic colloids• proteins, gelatin • rubber, gum

lyophobic/hydrophobic colloids • gold, silver and sulfur• emulsion

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Colloidal Phenomena

detergencymilk

coconut milk

ice-cream

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Pharmaceutical suspensions

Coarse dispersions

• Solid-in-liquid

Main function

• Delivery vehicle for suspended drug particles

Surfactant/dispersant reduces interfacial energy

• Stabilisation by electric repulsive force & steric hindrance effect

Examples: Oral suspensions, topical applications, injectables

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Preparing a Dispersion

Particle size reduction

surface of each primary particle is available to liquid.

Wetting of powder

wet external surfaces & displace air

between internal clusters.

Dispersing by using charged

bulky surfactants

Provide strong interfacial layer

Modifying the viscosity

to minimise sedimentation

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Properties of dispersing agents

adsorption of surfactants at the solid/liquid

interface.

highly charged

provide steric hindrance

END OF LECTURE 1 OF 2

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Pharmaceutical Emulsions

Emulsion• liquid-in-liquid vehicle• o/w or w/o

Main function• provide vehicles for drug delivery and parenteral nutrition. • drug is dissolved in the water or oil phase.

Surfactant/emulsifier reduces interfacial energy• emulsion becomes thermodynamically stable

Examples:• parenterals, creams, lotions

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Emulsification

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WATER

OIL

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homogeniser

emulsifier

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Emulsification Factors

Concentration of dispersed/oil phase

Types & concentrations of

surfactants

Emulsifying temperature

especially for non-ionic surfactants

Type of homogeniser

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Types of Emulsions

Macroemulsion Nanoemulsion

Microemulsion Multiple emulsion

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Nanoemulsion and Microemulsion

Nanoemulsions: 50-200 nm

Microemulsions: 5-50 nm

long term physical stability against creaming, flocculation and coalescence

Due to small size they enhance penetration, spreading and will give uniform distribution on the substrate on which they are applied.

Examples: personal care products and cosmetics, agrochemicals, pharmaceuticals, household products etc.

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Physical Pharmacy 2

Methods of Preparation

Nanoemulsions are easily formulated using high-pressure homogenizers with proper choice of surfactants and/or polymers.

The production of microemulsions may employ the Phase Inversion Temperature (PIT) principle.

These emulsions are stabilised through steric stabilization and by the thickness of the adsorbed layer.

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Multiple Emulsion

Dispersed phase contains droplets of another phase.

o/w/o or w/o/w.

Prepared through a double homogenization process or a one step procedure using the PIT.

Both are important for drug delivery.

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Example of w/o/w emulsion for drug delivery by intra-muscular route

Advantage of w/o:

slow-release because drug has to diffuse through oil

disadvantage: viscosity of medium (oil) is high

solution: to disperse the w/o in aqueous medium.

• On injection, the aqueous phase dissipates rapidly leaving behind the w/o.

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Multiple Emulsion for PharmaceuticalsExamples

Sandostatin LARTM Depot

Novartis (hypothalamic hormones analogue)

Control of hypersecretion at the site of the tumour where

hormone overproduction starts

Human NutropinTM Depot

Alkermes/Genentech (human insulin suspension)

somatropin (rDNA origin) for injectable suspension

long-acting dosage form of recombinant human growth

hormone (rhGH).

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Multiple emulsion Pharmaceutical Problems

• typically accounts for 10-80% of the total drug loading. • This ‘initial burst’ poses a toxicity threat & is a major

hurdle for the development of microspheres.

Rapid release during the first day

• This can last for weeks and is referred to as the ’lag-time’. • During this induction period, the patient is not effectively

treated due to lack of drug release.

Very slow release period after the initial burst period.

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References

PC Hiemenz & Raj Rajagopalan, Principles of Colloid and Surface

Chemistry, Marcel Dekker, New York (1997)

HA Lieberman, MM Rieger & GS Banker, Pharmaceutical Dosage

Forms: Disperse Systems Volume 1, Marcel Dekker, New York (1996)

F Nielloud & G Marti-Mestres, Pharmaceutical Emulsions and

Suspensions, Marcel Dekker, New York (2000)

J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel Dekker,

New York (1994)

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