Gel theory

What are the classification of gels

Dispersed solids

Hydrophilic polymers: type 1(hydrogels) and 2 (shear-thinning)

Explain gels based on dispersed solids what they are how they become that interactions, examples etc

these gels are formed when tiny solid is dispersed throughout a liquid

Particles undergo flocculation where the dispersed solids come together and form clumps

Liquid fills the void spaces between the particles

Interaction between particles may be Van Der Waals forces

Aluminium hydroxide Gel USP

Explain gels based on hydrophilic polymers what they are, how do they behave and examples

They are manufactured by dispersing hydrophilic polymers within an aqueous vehicle

Hydrophilic polymers bhave as lyophilic colloids

Their unique properties result from the self-association of the dissolved polymers and its interaction with the aqueous vehicle

There are two types of self-association (reversible and irreversible)

Explain what type 1 gels (hydrogels) are and its properties alnd examples and uses

The interaction between polymer chains is covalent and irreversible

They absorb considerable amount of fluid

Examples of type 1 gel: Poly(HEMA) cross linked with (EGDMA)

Uses: Wound dressing, soft contact lenses, implants for prolonged release of drugs

Explain what type 2 gels are its examples and uses

The interaction between the polymer chains are non-covalent

Examples: Cellulose-based gels, polysaccharides gels from natural sources

Uses of type 2 gels: Topical drug delivery, lubricants

What are the common properties of gelling agents

Tendency for clumping

Some agents are more soluble in cold water Thant in hot water

Some agents require a “neutralizer” or a ph adjusting chemical

Can be adhesive in nature

Time required for hydration

What are the factors affecting gelation of type 2 gels

Concentration and nature of hydrophilic polymers

Molecular weight of the polymer

Nature and ph of the solvent

Ionic strength of the solvent

Temperature

ionic gelation

What are the simplified steps to manufacturing pharmaceutical gels

Step 1: Water soluble components are initially dissolved in the vehicle in a mixing vessel with mechanical stirring.

Step2: Hydrophilic polymer must be added to the stirred mixture slowly to prevent aggregation and stirring until dissolution of the polymer occurred.

(Excessive stirring results in entrapment of air)

What are alginate wound f=dressings

form a soft gel in contact with wound exudate

What are the advantages and disadvantages of a good delivery system

Advantages

Easy to apply

stable over a long period of time

non-greasy

Disadvantages

Perspiration easily removes gels

non occlusive

syneresis