Transcript Introduction to Colloids

Colloid
An Introduction
Kausar Ahmad
Kulliyyah of Pharmacy
http://staff.iium.edu.my/akausar
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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
Dispersed
phase
Continuous
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
Type
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Classification Based on Size
Class
Molecular
dispersion
Colloidal
dispersion
Coarse
dispersion
Size
< 1.0 nm
Examples
glucose
1.0 nm - 0.5 mm Natural rubber latex
> 0.5 mm
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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
detergency
milk
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
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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
emulsifier
homogeniser
OIL
WATER
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Emulsification Factors
Concentration of
dispersed/oil phase
Types &
concentrations of
surfactants
Emulsifying
temperature
especially for nonionic 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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Methods of Preparation
Nanoemulsions are easily formulated using highpressure 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 Pharmaceuticals
Examples
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
Rapid release during the first day
• 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.
Very slow release period after the initial
burst period.
• 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.
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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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