gels

1. Gels and Jellies

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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6. Gels and Jellies...cont’d
 Gelling agents
 Gelling agents are either hydrophilic polymers
or hydrophilic inorganic clays
 Hydrophilic polymers: acacia, tragacanth,
sodium alginate, pectin, xanthan gum, gelatin,
methyl cellulose, carboxymethylcellulose, etc
 Hydrophilic inorganic substances: e.g.,
bentonite , veguum, etc
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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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