2. Gels and Jellies
Gels are semi-rigid disperse systems in which the
movement of the dispersing medium is restricted
by an interlacing (cross-linking) three
dimensional network of particles or solvated
macromolecules of the dispersed phase.
When linear, water-soluble polymers are cross-
linked, they swell in water but no longer dissolve.
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3. Gels and Jellies
Jellies
• Are class of gels in which the structural
coherent matrix contains a high proportion of
liquid, usually water.
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4. Gels and Jellies.........cont’d
Generally gels become clear when all particles of
the dispersed phase are completely dissolved in
the dispersion medium (molecular dispersion).
Incomplete dissolution gels become turbid
(translucent).
Consumers prefer clear gels.
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5. Gels and Jellies...cont’d
Formation of gels
• Gels are essentially composed of gelling
agents which is dispersed in a vehicle.
• The dispersion medium is usually water
hydrogel.
• Most pharmaceutical gels are hydrogels.
• Other ingredients are added to improve the
stability and quality of the product.
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7. Gels and Jellies...cont’d
Other additives
Humectants: loss of water can quickly lead
dryness in gels and humectants like glycerol,
propylene glycol, sorbitol solutions may be
added to retain water.
Preservatives: gels have high water content
and therefore are liable to support microbial
growth unless a suitable preservative is
added.
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8. Gels and Jellies........cont’d
Chelating agents: gelling agents and
medicaments sensitive to heavy metals are
sometimes protected by chelating agents
such as EDTA.
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9. Gels and Jellies........cont’d
Sodium Carboxymethyl cellulose jelly
Formula:
Sodium carboxymethyl cellulose……. 5.0 g
Glycerol……………………………………….…15.0 g
Methylhydroxybenzoate…………….…..0.1 g
Patent Blue V……………………….………..0.1 g
Purified water, ad………………………..100.0 g
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10. Preparation of gels
Procedure:
Dissolve water soluble components other than
the gelling agent in the vehicle with gentle
stirring.
Add the gelling agent into the stirred mixture
slowly to prevent aggregation and stirring is
continued until dissolution of the polymer has
occurred.
Excessive stirring of pharmaceutical gels
results in entrapment of air.
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11. Preparation of gels……...cont’d
Considerations:
• If a powder gelling agent is added to the
dispersing medium in a haphazard manner,
there is a tendency for the agent to clump.
• To prepare homogenous dispersion:
sieve the gelling agent on the surface of
dispersion medium a little at a time with
continuous stirring or
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12. Preparation of gels...cont’d
Use water miscible dispersing agents that
will be poorly adsorbed by the gelling
agent, example, absolute alcohol, glycerin,
propylene glycol.
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13. Preparation of gel...cont’d
Some gelling agents are more soluble in cold
water than in hot water. Example,
Methyl Cellulose, poloxamers.
Structure of poloxamer.
a=2-130, b= 15-67
a = oxyethylene ; b= oxypropylene 13
14. Preparation of gel.......cont’d
• Some gelling agents require a neutralizer or a
pH adjusting chemical to create a gel after it is
dispersed in dispersion medium. Eg.,
Carbomers.
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15. Preparation of gels……...cont’d
Most gelling agents require 24-48 hrs for
complete hydration and reach maximum
viscosity and clarity.
Gelling agents are used in concentration of 0.5
-10% depending on the agent.
It is easier to add the active drug before the
gel is formed if it does not interfere with gel
formation.
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16. Gels and Jellies........cont’d
Application of gels and jellies
Gels and jellies are used for delivery of
medication, lubrication and miscellaneous
purposes.
Medicated Jellies
Jellies contain considerable amount of water
which makes them suitable for water soluble
drugs.
Insoluble drugs spoil the feel and appearance of
the product.
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17. Gels and Jellies...cont’d
Lubricating jellies
Catheters, rubber gloves and many other
dignostic agents require lubrication before use.
The smoothness and lubricity makes them very
suitable for this purpose.
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18. Gels and Jellies...cont’d
Packaging
• Lubricating jellies generally have thinner consistency and
usually packed in tubes.
• Stiff gels are packed in ointment jars.
• Containers should be well filled and airtight to prevent
evaporation.
Labeling
• similar to ointments
Storage
• Tem (20-25 oC) to prevent loss of water via evaporation.
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19. Syneresis and swelling of gels
When a gel stands for some time, it often shrinks
naturally, and some of the liquid is pressed out.
This phenomenon is known as syneresis.
It is due to the continued coarsening of the
matrix or fibrous structure of the gel with a
consequent squeezing-out effect.
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20. Syneresis and swelling of Gels…..
The opposite of syneresis is the taking up of
liquid by a gel with an increase in volume. This
phenomenon is known as swelling.
Gels may also take up a certain amount of liquid
without a measurable increase in volume, and
this is called imbibition.
Only those liquids that solvate a gel can bring
about swelling.
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