Pharmaceutics II: Semisolid Dispersion Systems

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Questions and Answers

What is the primary requirement for achieving effective gelation in certain systems?

neither external heat nor body temperature

Both external heat and body temperature

Only the body temperature (correct)

External source of heat

What is the effect of heating above the LCST on LCST systems?

They remain unchanged by heating above the LCST

They expand by heating above the LCST

They dissolve by heating above the LCST

They contract by heating above the LCST (correct)

What is the result of cooling a polymeric solution at body temperature in UCST systems?

It becomes a solid

It evaporates

It remains a liquid

It is transformed into a highly viscous gel (correct)

What is the response of pH-responsive systems to changes in pH?

The polymeric network conformation can be changed Signup and view all the answers

What is the main characteristic of a semisolid dispersion system?

Contains a gelling agent in sufficient quantities to impart a 3D polymeric matrix Signup and view all the answers

What is the mechanism of gelation in photo-responsive systems?

Photo-polymerization Signup and view all the answers

What is the physical property of gels that makes them smooth and elegant in appearance?

Smooth texture Signup and view all the answers

What is the main difference between one-phase/monophasic gel systems and two-phase/biphasic gel systems?

The gelling agent is soluble in the dispersing liquid Signup and view all the answers

What is the phenomenon of swelling of gel when placed in water?

Imbibition Signup and view all the answers

What is an example of a one-phase/monophasic gel system?

Hydrophilic polymer in aqueous phase Signup and view all the answers

What is the purpose of controlled release gels?

To increase the contact time at the site of absorption Signup and view all the answers

What is the process of a gel shrinking and losing the entire liquid present inside it after standing for a long time?

Syneresis Signup and view all the answers

What is a characteristic of a two-phase/biphasic gel system?

The gel is turbid Signup and view all the answers

What is an example of a two-phase/biphasic gel system?

Gelatinous cross-linked precipitate of a substance in the aqueous phase Signup and view all the answers

What is the primary function of sorbitan monostearate in organogels?

To act as a hydrophobic non-ionic surfactant Signup and view all the answers

Why is it important for controlled release gels to have sustained drug release?

To gain benefits from prolonged contact time Signup and view all the answers

What is the main characteristic of hydrogels?

High water content and flexibility Signup and view all the answers

What is the process of achieving gelation in organogels?

Dissolving/dispersing the organogelator in hot solvent Signup and view all the answers

What is the purpose of the gelling agent in a gel?

To impart a 3D polymeric matrix Signup and view all the answers

What is the role of polysorbate (tween) in organogels?

To improve the gel's stability Signup and view all the answers

What is the characteristic of in-situ sol-gel reversible hydrogels?

Reversible solution-to-gel transformation Signup and view all the answers

What is the mechanism of cross-linking in hydrogels?

Temperature change, ionic interaction, and absorption of photons Signup and view all the answers

What is the main advantage of hydrogels?

High degree of flexibility Signup and view all the answers

What is the characteristic of temperature-responsive systems?

Dependence on environmental temperature difference Signup and view all the answers

Study Notes

Definition and Characteristics of Gels

A semisolid dispersion system containing a gelling agent that imparts a three-dimensional polymeric matrix.
Provides a cooling sensation when applied to the skin.
Usually translucent and non-greasy.
Used for medication and lubrication.

Classification of Gels

One-phase/monophasic gel system: Gelling agent is soluble in the dispersing liquid, resulting in a clear appearance.
Two-phase/biphasic gel system: Gelling agent is insoluble in the dispersing liquid, resulting in a turbid appearance.

Controlled Release Gels

Gel formulations with suitable rheological and mucoadhesive properties that increase contact time at the site of absorption.
Classified into two systems: Lower Critical Solution Temperature (LCST) and Upper Critical Solution Temperature (UCST) systems.

pH-Responsive Systems

Polymeric network conformation can be changed by alterations in pH of the medium.
Polymers carry ionizable functional groups in their chemical structures.
Solution exists as a free-flowing liquid at pH below 5 and can be converted into gels by increasing pH value.

Photo-Responsive Systems

Contain photosensitive initiator and light source associated with the polymeric matrix.
Photo-polymerization mechanism is performed when the external stimulus (light) penetrates through the cornea, causing gelation.

Physical Properties of Gels

Smooth texture
Elegant in appearance
Non-dehydrating
Transparent and translucent
Non-greasy
Semi-solid in nature

Imbibition and Syneresis

Imbibition: The phenomenon of swelling of gel when placed in water due to osmosis of water into the gel medium.
Syneresis: The process in which gel shrinks and loses the entire liquid present inside it after standing for a long time, a form of instability.

Physiological Properties of Gels

Non-irritating
Do not alter membrane/skin functioning
Miscible with skin secretion
Have low sensitization index

Types of Gels

Organogels (Oleaginous Gels)

Contain sorbitan monostearate as a hydrophobic non-ionic surfactant and organic solvents.
Gelation is achieved by dissolving/dispersing the organogelator in hot solvent to produce an organic solution/dispersion.

Hydrogels

Gel systems in which water is immobilized by insoluble polymer.
Elements of hydrogels are water and a polymeric substance that is hydrophilic, but not water soluble.
Absorb liquid when exposed to water.
High absorbent, containing over 90% water.
High degree of flexibility, similar to natural tissues.

Cross-Linking Mechanisms of Hydrogels

Temperature change (thermo-responsive cross-linking)
Absorption of photons (photo-responsive cross-linking)
Ionic interaction between anionic polymer and small cations (ion-responsive cross-linking)
Presence of enzymes (enzymatic-responsive cross-linking)

In-Situ Sol-Gel Reversible Hydrogels

Polymeric solutions that undergo reversible solution-to-gel transformation under the influence of environmental conditions like temperature change, pH change, or light.
Classified into four types: Temperature-responsive, pH-responsive, Photo-responsive, and Temperature-responsive systems.

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Description

Learn about semisolid dispersion systems, their characteristics, and applications in pharmaceutics. Topics include gelling agents, polymeric matrices, and uses in medication and lubrication.