Lecture 4 - Disperse Forms (Part 3 - Colloidal dispensions, Gels, & Use of Dispense systems) Flashcards
What are Colloidal dispersions?
Dispersions may be classified by particle size; forms a continuum from true solutions to coarse suspensions and emulsions ex: milk in water
Colloidal dispersions where particle size from 1 nm to 1 μm:
- May consist of single large molecules of high molecular weight
- May appear as true solutions but scatter light (Tyndall effect)
- Dispersion maintained by Brownian movement (random movement of particles in that system)
- Can be a method of ‘solubilizing’ insoluble drugs
What are Colloids?
May be lyophobic or lyophilic (hydrophobic or hydrophilic when continuous phase aqueous)
Hydrophilic:
- Hydrophilic have affinity for water, hydrate and swell to increase viscosity
- Higher viscosity improves system stability by reducing interaction between particles
What might Colloids carry?
May carry a surface charge depending on pH of system and chemical functional groups of colloid
- Acacia, cellulose derivatives negative charge due to –COOH and SO4 groups
- Gelatin and protein contain amino acid so charge dependent on system pH
Charge keeps particles separated
Hydrophilic systems quite stable with affinity between particles and the continuous phase
Why are Colloids hydrophobic?
- Because no interaction between colloid and continuous phase, less stable than hydrophilic
- Attraction then association between colloidal particle cause settling
- Can stabilize by developing some attraction between particles and continuous phase with surfactants or protective colloids like gelatin which can coat the particle
What might some hydrophobic colloids carry?
Some hydrophobic colloids may carry a charge or adsorb ions from the solution
- Mutual repulsive forces and Brownian movement then keep colloid dispersed
- Addition of electrolyte may neutralize charge and cause settling (Like flocculation…)
What are nanocarriers?
used for targeted drug delivery to specific cells (ex: cancer cells) therefore get specifically
- deliver drugs in system in an effective way
What are Gels?
Usually hydrophilic colloidal systems with high degree of cross-linking or association
High viscosity and continuous phase movement restricted by three dimensional network of solvated macromolecules
- Concentration of gelling agent 0.5-2%
Gel is a semi-solid preparation of small inorganic or large organic molecules interpenetrated by liquid
- If particle size large called a magma eg Bentonite magma NF
If gel made of discrete particles referred to as…
two-phase
What if a gel is single phase?
Single phase if large organic macromolecules uniformly distributed with no apparent boundaries between dispersed and continuous phase (dissolved completely)
Single phase systems using natural gums (tragacanth, acacia, xanthan, carrageenan……)
What are gels useful for?
Gels useful for preparing oral, topical, nasal, ophthalmic and vaginal dose forms
What are the # of classification systems of gels?
Inorganic or organic Hydrogels or organogels
What are jellies?
Jellies are structurally coherent and contain water and a thickening agent
- Drug usually dissolved in the water prior to adding the thickening agent (little bit more watery)
- Subject to microbial growth so should be preserved
- Often need protection to prevent drying out (make sure tightly covered)
What are the problems with gel prep?
Problem during preparation is wetting of the gelling agent
- If LUMPS form very difficult to disperse and hydrate May add powder in portions with vigorous mixing
- May disperse powder in a medium in which it is insoluble, disperse powder then add to solvent with mixing
- In some situations process of levigation may be helpful
Many gelling agents including:
Alginic acid
Bentonite or Vee Gum (magnesium aluminum silicate)
Carbomer (Carbopol) – alcohol compatible
Poloxamer (15-50% concentration)
