OIA1008 GELS & FOAMS

Pharmaceutical gel

A semi-solid dosage form composed of a 3D matrix of molecules or polymers dispersed in a liquid medium.

Gel vehicle types

May be aqueous, hydroalcoholic, alcohol-based, or non-aqueous.

Gel applications

Used for drug delivery via skin, buccal, ophthalmic, nasal, vaginal, and oral routes.

Natural gelling agents

Alginates, carrageenan, tragacanth, pectin, cellulose derivatives.

Synthetic gelling agents

Carbomer (Carbopol 934), polyvinyl alcohol (PVA).

Ideal gelling agent properties

Inert, non-reactive, provides structural integrity yet breaks under shear stress, non-sticky, sterile (for ophthalmic use).

Gel strength vs crosslinking

Higher crosslink density increases apparent viscosity or gel strength.

Alginates (natural)

Derived from brown seaweed; form gels in the presence of divalent cations or acidic pH.

Carrageenan (natural)

From red seaweed; forms gels depending on ion presence — K⁺ for kappa type, Ca²⁺ for iota type.

Tragacanth

Swells slowly in water at ≥2% concentration to form viscous gels; extracted from Astragalus species.

Xanthan gum

Produced via bacterial fermentation; forms jellylike solutions at ≥1% concentration.

Pectin

From citrus rinds; forms gels in acidic aqueous solutions with calcium; strength depends on pH and concentration.

Cellulose derivatives

Include methylcellulose, sodium CMC, hydroxyethyl cellulose, and HPC — provide sticky, jellylike consistency.

Carbomer (Carbopol 934P)

Synthetic acrylic polymer that forms gels at ≥0.5%; requires neutralization to activate gelling.

Carbomer neutralization

With bases like NaOH, KOH, or sodium carbonate — pH must be adjusted to neutral for optimal gel character.

Carbomer sensitivity

Presence of ions (e.g., NaCl) reduces viscosity drastically — important consideration in formulation.

Gel structure

3D network of particles held by hydrogen bonds, covalent or electrostatic interactions.

Syneresis (gel)

Gel shrinkage and expulsion of liquid due to environmental or mechanical stress — causes cracking/collapse.

Swelling (gel)

Absorption of liquid by gel, leading to volume increase; controlled by composition, solvent, pH, and temperature.

Swelling in drug delivery (gels)

Allows for controlled release of active drugs over time — also useful in sensors and actuators.

Flocculation method

Gelation induced by salt addition and rapid mixing to avoid localized precipitation.

Chemical reaction method

Gel formed via reaction between solute and solvent, e.g., Al(OH)₃ gel from aluminum salt + sodium carbonate.

Manufacturing tip

Avoid high-speed mixing that traps air — vacuum may be applied to prevent foaming during polymer dispersion.

Homogeneity test

Visual inspection for consistency and absence of aggregates.

Grittiness test

Microscopic examination for particulate matter.

pH measurement

Using digital pH meter to ensure compatibility with drug and skin.

Drug content assay

UV-spectrophotometric method after extraction in solvent and suitable dilution.

Viscosity test

Measured using Brookfield or cone-and-plate viscometer at 25°C.

Spreadability

Ease of spreading — affects patient acceptability in topical use.

Extrudability

Measure of how easily gel is expelled from container.

In vitro diffusion study

Assesses release of drug through membrane or gel matrix.

Hydrogels

Hydrophilic polymer networks capable of absorbing large volumes of water or fluids.

Xerogels

Dried gels retaining porosity; used in adsorption and filtration.

Aerogels

Made via supercritical drying; low-density, used in aerospace and insulation.

Colloidal gels

Formed from nanoscale particles in liquid; used in food, inks, paints.

Water absorption (hydrogel)

Can absorb ~100x their weight in water — ideal for wound dressings, contact lenses, diapers.

Mechanical properties (hydrogel)

Varies by crosslink density; ranges from soft to stiff structures.

Swelling behavior (hydrogel)

Reversible swelling based on solvent conditions; used in drug delivery and tissue engineering.

Biocompatibility (hydrogel)

Well tolerated by tissues — used in biosensors, scaffolds, ophthalmic delivery.

Pharmaceutical foams

Systems of gas dispersed in a liquid or solid matrix stabilized by surfactants (foaming agents) or broken down by defoamers.