Gel E Flashcards
(30 cards)
What is a gel in pharmaceutical terms?
A semisolid system with a liquid phase constrained in a 3D polymeric matrix.
What are the two types of gels based on phase system?
Single-phase and two-phase gels.
What is a two-phase gel also called?
Magma (e.g., Milk of Magnesia).
What are the three gel microstructures?
Covalently bonded, physically bonded, and well-ordered gel structures.
What are hydrogels and organogels?
Hydrogels use water as the continuous phase, organogels use organic solvents.
What is the critical gelling concentration (cgc)?
The minimum polymer concentration required to form a gel.
What is syneresis?
Spontaneous separation of liquid from a gel due to contraction of polymer network.
What is retrogradation?
Spontaneous reformation of a gel on standing, e.g., polyvinyl alcohol.
What is yield point?
The stress at which flow begins in a gel.
What is rupture strength?
The stress at which a gel breaks rather than flows.
What is a viscoelastic substance?
A material with both fluid and solid-like behavior under stress.
What does thixotropy mean?
Time-dependent shear thinning; gel structure rebuilds after stress is removed.
Name the five types of gelling agents.
Proteins, polysaccharides, semisynthetic polymers, synthetic polymers, inorganic substances.
Give an example of a protein gelling agent.
Gelatin or collagen.
What is sodium alginate used for?
Used in dental impressions and wound dressings; forms rigid hydrogels.
What is hyaluronic acid used for?
Ophthalmic surgery, joint lubrication, tissue hydration.
What polysaccharide is extracted from red seaweed?
Carrageenan.
What is the function of carboxymethylcellulose (NaCMC)?
Used in therapeutic vaginal gels; stable from pH 2–10.
What is HPMC used for?
Lubricating gel and ophthalmic aid; stable from pH 3–11.
What is a key feature of poloxamer gel?
Inverted thermoreversibility: gels at body temperature, liquid when cool.
What synthetic polymer is used in artificial tears?
Polyvinyl alcohol (PVA).
What is a characteristic of carbomer gels?
Plastic flow, pH- and salt-sensitive, excellent clarity (e.g., Carbomer 940).
What is the role of smectite clays like bentonite?
Thickening and suspending agents; exhibit plastic flow.
What are mucilages?
Thick aqueous solutions of gums used to suspend insoluble substances.
