L6: Gels Flashcards
How are drugs incorporated into gels?
They can be SUSPENDED in the matrix, or DISSOLVED in the liquid
A pharmaceutical gel is a semisolid system of at least two constituents, what are they?
A condensed mass, enclosed and interpenetrated by a liquid.
Explain what happens when the particles of drug are added in to the gel.
They link together to form INTERLACED NETWORK, imparting the RIGIDITY to the structure, continuous phase is held between the meshes.
In gels, when the coherent matrix is rich in liquid, what is the product called?
Jelly.
In gels, if the liquid is removed, and only gel framework remains, what is this called and give an example?
Xerogel.
Gelatin sheets, tragacanth flakes
Explain what a single phase gel/system is.
Contain linear/branched polymer MACROMOLECULES, that dissolve in water, have no definite boundaries with the dispensing medium.
What are macromolecules classed as?
Natural polymers –> tragacanth
Semisynthetic cellulose derivatives –> methyl cellulose
Synthetic polymers –> carbomer polymers
Why do macromolecules not form true solutions?
Because of their size.
Form colloidal dispersions instead (sol).
What’s different about a macromolecule (colloidal dispersion) even if it is liquid and appears to be a solution?
Sometimes cloudy.
More viscous than base solvent.
What do two phase gels contain rather than macromolecules?
Floccules of small particles.
The structure of a two phase gel is not always stable, on shaking, what happens to it?
It becomes a liquid.
What is the two phase gel referred to as, if the particles are large?
Magma.
Give examples of two phase systems.
Aluminium hydroxide gel
Magnesia magma
What are gels that contain water called? And how are they formed?
Hydrophilic gels. (Hydrogels).
Formed by lyophilic sols.
Aqueous gels can be divided into 2 groups, depending on what?
On the nature of the bonds between the chains of the network.
Explain what ‘type 1 gels’ are.
Irreversible systems
With 3D network, Formed by COVALENT bonds between the macromolecules.
Type 1 gels are ‘irreversible systems with a 3D network’ formed by what?
By COVALENT bonds between the MACROMOLECULES.
How is the network made in type 1 gels?
May be made by POLYMERISING water soluble polymers with a CROSS-LINKING agent.
If the polymers in type 1 gels contain little water, they are said to be…
Rigid.
What can happen when the polymers in type 1 gels absorb water?
Can swell and become more flexible.
(Type 1 gels) The network polymers can swell in water, but cannot dissolve, why?
Due to the stable cross linking structure.
The network polymers in type1 gels have been used in…..
…the fabrication of expanding implants.
….the prolonged drug release system.
Explain what type 2 gels are.
3D network, held together by weaker bonds. E.g. Hydrogen bonds, dipole dipole attraction.
Heat reversible.
type 2 gels are heat reversible, what does this mean?
They can change from ‘sol’ to gel on either heating, or cooling.
