POD 1- gels

What are gels?

Semi solid systems

What type of interaction is seen between the particles and vehicle?

covalent or non-covalent

What kind of particles are in gels?

molecular/ coarse/ colloidal

Colloidal

How do you determine the concentration needed of the colloidal particles to form a gel?

Based on their ability to form a 3D network

What may the colloidal particles be?

* dispresed solids
* dispersed polymers

What type of colloidal particles make up gels in terms of their affinity for the solvent?

Lyophillic

Lyophobic

Name 2 examples of lyophobic colloids?

* clay particles ( Mg/Al silicate)
* Mg/ Al hydroxide

= card house flocculation occurs

How do lyophobic particles form a network?

Electrostatic attraction

Mg+ ----------- O-

What concentrations of lyophobic particles are needed to form a gel?

Quite high

\-→ 10w/v

What kind of gels do clays form?

Opalescent

→ powdery

Is thixotrophy exhibited by lyophobic colloids gels?

Yes!

How strong and how to break the interactions of the lyophobic colloids?

weak

shaking will destroy

leave standing and will come back

What’s bentonite?

Al silicate

What happens to bentonite@ ph 5?

gel destroyed and particles precipitate

(Mg+ O- electrostatic forces influenced by ph)

What kind of molecules form lyophilic gels?

macromolecules!

Name 2 types fo lyophillic gels?

1. type 1= hydrogels


1. type 2= common!= celluose derivatives, polysacc, poly acrylic acids

What kind of bonds are found in type 1 gels

hydrogels have IRREVERSIBLE COVALENT BONDS BETWEEN MACROMOLECULES

What type of bonds are created by type 2 gels?

reversible

what are the applications of type 1 gels

contact lenses

fake tits

Why are type 1 lyophillic gels called hydrogels?

More water= they get hydrated and swell

how do hydrogels work

crosslinks very stable (irreversible)

water soluble polymers

Why are hydrogels good fake tits

resist fracture

non-biogradable (aka the cellusoe (bio in plants) are type 2)

\

What special drug delivery system can hydrogels be used for?

Prolonged delivery

What are the forces that hold type 2 gels?

ionic

van der waals

hydrogen bonds

What will happen to type 2 gels if stress is applied?

bonds break→ will flow

\

What kind of plastic flow does type 2 gel echibit?

Pseudoplastic

shear thinning (apply stress and it will flow)

Does temperature effect visvosity in type 2 gels?

yes

those interactions depend on temp

How is the film strenght of type 2?

good when dried

think of a japanese knife cutting thin films of celluose (potato) when cooking rattatoi

What are the conc used in type 2 gels?

1-10

not as much becaus they are superior to clays and fake boobie gels

Can synthetic polymers replace cellouse?

Duh

* polyacrylic acids
* eg CARBOMER GELS

Why is adding a base vital to making polyaacrylic acids viscous?

ionisation of oendant carboxyl group= repulsion

\
gel expands

What conc of synthetic polyacrylic acidfs are used in type 2 gels?

0\.5-2%

we syntrhesize them cuz more potent than natural stuff

What’s the third option in type 2 gels?

polysacc derived from

1. seaweed→ CARRAGEEN (iothar men picking seaweed irish poem in carrageen village)

2. algae- sodium alginate

What sodium alginate be used with?

acidic drugs (basic ones wont work!!!!!!!!!)

list a few wetting agents

opposite of surfactant

ethanol , glycerol, propylene glycol

Whats a consideration to think of when dding preservatives to polymers?

higher conc may be needed

list a few humectnts

propylene glycol

sorbitol

glycerol

what’s imbibition

the gels imbues water

but does not change in volume

whats syneresis?

squeezing out the water as droplets

shrinkage of gel

what are hxerogels?

polymer films

vehicle removed

a film forms

what must haappen first to the drug before it is absorbed?

dissolved

give an example of 2 monomers crosslinking?

poly(HEMA) and EGDMA

what type of flow will type 2 exhibit?>

type2

How many phases are ointments

single phase

what are ointment bases made up of?

waxes, oils, fats

→ % composition of these determines the softness of ointment

list 4 types of bases used for ointments

hydrocarbon

absorbtion

water-miscible (emulsifying)

water soluble (hydrophilic)

what does emolient mean

prevent water loss

what are hydrocrbon ointments based on?

paraffins

can you add water to hydrocarbon ointments?

only a lil

5%

are hydrocarbon ointments inert

yes baby girl

what are hydrocarbon ointments made up of?

hard paraffin

soft paraffin

liquid paraffin

microcrystaline wax

Do absorption bases contain water?

anhydrous vehicle

water can be added tho 15%

What’s the structure of absorbtion bases?

polar + non polar bits