Gels are transparent semisolid preparation meant for external application to the skin or mucous membrane. Gels are semisolid systems consisting of either suspension made up of small inorganic particles or large organic molecules in a liquid vehicle that appear jelly-like by the addition of a gelling agent.
These are organic hydrocolloids or hydrophilic inorganic substances.
They contain Tragacanth, Sodium Alginate, Pectin, Starch, Gelatin, Cellulose Derivatives, Carbomer, and PolyVinyl Alcohol Clays. These are numerous gelling agents varying in gelling ability.
Clear gels are microemulsions in which the diameter of the dispersed phase globules is in the range of 10 to 60 nm. These emulsions are thermodynamically stable. Microemulsions are transparent as the globule diameter of the disperse phase is less than the wavelength of light.
Microemulsions can be distinguished from other types of gels by the vibrations or “ringing” that occurs when the emulsion is subjected to impact.
The procedure of Clear Gel:
Table of Contents
- A gel is prepared by mixing a suitable thickening agent with an aqueous vehicle.
- The drug is dissolved in an aqueous vehicle and the thickening is added by triturating in a mortar.
- The trituration is carried out until a homogenous preparation is formed.
Quantity for 50 gm
Sodium Carboxy methyl cellulose (thickening agent) – 2.5 gm
Glycerol (binding agent) – 1.5 gm
Preservative -0.05 gm
Colour -0.0005 gm Purified water (vehicle)
To make-50 gm
Dissolved methylparaben in water by heating. Add SCMC to glycerine and stir thoroughly. Add this mixture to the aqueous vehicle and stir in a uniform, homogenous preparation is formed. Add the dye color and stir. Transfer to a suitable container.
Evaluation of Gel:
The various evaluation parameters involved in the assessment of the properties of the gels are as follows:
1. Yield Value: It is a measure of the force required to extrude the material from the deformable bottle tube. It can be determined by the use of an instrument called the Penetrometer.Penetrometer consist of a metal needle that pierces through the system and the distance of penetration of the needle is measured, from which the yield value may be calculated.
2. Spreadability: The Spreadability test is performed to determine the extent of the Spreadability of gels based on their rheological properties.
3. Stability: This test is known as the shipping test and is performed to determine the extent of stability of gels at varying temperatures, which the product may experience while exporting to other countries.
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