Colloids Flashcards
Aluminum hydroxide gel
Inorganic gel
Gelatinous precipitates composed of insoluble Al(OH)3 and hydrated aluminum oxide
Usually prepared by chemical reaction (dispersed part of gel)
May interfere with bioavailability of tetracycline by chelating (gel may absorb other drugs inside its structure therefore drugs are not available to be absorbed - cannot take with other drugs at the same time)
Milk of magnesia
7-8.5% Mg(OH)2
Antacid with anti-constipating effects
Inorganic gel
Where should gels be stored? What are signs of instability?
Store in: Tight containers to avoid loss of water, avoid freezing
Observe for: Shrinkage, separation of liquid, discolouration, microbial growth
What is a magma?
A colloidal dosage form in which the particle size of a two-phase system is large
E.g., bentonite magma - insoluble in water, swells to 12x its volume in water; thixotropic gel above 4% concentration, used as suspending agent with alkaline pH
What are microemulsions?
Type of micro delivery system
Swollen micelles, 8-80nm
Have a high surface area, so interfacial tension has to become very low
Thermodynamically stable, optically transparent mixtures of biphasic O/W or W/O systems stabilized with surfactants (usually with an HLB between 15-18)
What are microemulsions used for?
Enhance oral absorption
Enhance transdermal delivery
Target anticancer agents
Develop artificial RBCs
What are liposomes?
Nano-delivery systems
Glycerin backbone of phospholipids, part of glycerin is attached to polar head group, plus a non-polar tail group
Phospholipids come together to form vesicle in certain conditions, similar to structure of cell
Hydrophobic drugs between layers; hyrdophilic drugs in centre
What are liposomes used for?
Drug solubilization and protection
Sustained and controlled drug release
Targeted delivery
Drug internalization (e.g., incorporate negatively charged drugs into liposome can help internalize them)
What are nanoparticles?
Nanospheres = Drug is dispersed in nanoparticle
Nanocapsules = Drug is clumped together
Polymeric micelles with hydrophilic and hydrophobic blocks
What are the important physical properties of colloids that help determine their molecular weights?
Light scattering Diffusion Osmotic pressure Viscosity Sedimentation/creaming
What is light scattering?
Described in terms of turbidity, which is fraction decrease in light intensity due to scattering in all directions
Dependent on size and number of colloidal particles present
Can be used to determine MW, shape, and size of particles
As size increases, concentration increases, turbidity increases, and more light is scattered
What is diffusion a direct effect of? What type of diffusion do colloids have?
Brownian motion
Colloids have slow diffusion - nanoparticle/microemulsion/liposome that is exposed to skin/GI tract but must pass through many layers to be absorbed (must slower diffusion that solubilized particles)
Diffusion coefficient has an inverse relationship with the size of diffusing material
Osmotic pressure and colloids
Colloids induce osmotic pressure
This can be used to determine the MW of the colloid
Viscosity and colloids
Colloids can affect viscosity of media and the magnitude of this effect depends on the shape and MW of the colloid
Can measure viscosity to determine MW
At defined concentration, the viscosity of colloidal dispersions is affected by the MW and the shape of the dispersed phase in the dispersion medium
Sedimentation/creaming and colloids
Very slow because particles are so small
Brownian motion is very significant and opposes sedimentation
Can use centrifuge to speed up particle settling
Replace gravity with angular velocity
