formulations-hydrogels

define a hydrogel

A hydrogel is a three-dimensional (3D) network of hydrophilic polymers that can swell in water and hold a large amount of water while maintaining the structure due to chemical or physical cross-linking of individual polymer chains.

what bonds do type one gels contain

covalent bonds

what is an example of a type one gel

caoutchouc/rubber

what type of bonds do type 2 gels contain

hydrogen bonds and/or VDW

what are type 2 gels

they are much more reversible

a type 2 gel can be easily broken down and become a solid again

what are the shapes that the polymers can be

what are linear strands like

they are like a network through the aqueous phase while also interacting with eachother

what shape are platelets

-sphereal colloid -very small spheres from 5-10nm

where are platelets mainly found(in what gelling agents )

inorganic gelling agents like bentonide

what are the platelets made of

-little spheres made from selcium dioxide and aerosil which is very common in pharmacuetical sciences

what are the 6 ways that hydrogels can be classified

1-preperation

2-ionic charge

3-source

4-cross linking

5-response

6-physical prperties

what are the 3 preperation types

Homopolymeric system

copolymeric system

interpenetrating system

what is homopolymeric system

only one type of polymer

what is a copolymeric system

-2 different polymers starting a molymeric chains

what is an interpenetrating system

at least 2 different types of systems

2 different networks of polymers

what are the ways that a hydrogel can be classified using ionic charge

cationic

anionic

non-ionic

what are the ionic hydrogels sensitive to (what are the ionic hydrogels sensitive to )

very sensitive to other salt introduction and they can also be sensitive to pH changes

are non-ionic hydrogels sensitive to anything

no

which is strigner ionic systems or non-ionic systems

Non-ionic systems usually form weaker gels than you have in an ionic charge

why are ionic systems stronger than non-ionic

when you have ions present the hydrogen bonding is much stronger

how are hydrogels classifed by source

1-natural

2-semi synthetic (hybrid )

3-synthetic

how can hydrogels be classified based on crosslinking

chemical

physical

what are the 3 ways that a hydrogel can be classified based on response

chemical

biochemical

physical

what is the classification by response based on

you can classify a hydrogel based on its response to certain stimilui

how can a hydrogel be classified based on its chemical response

how does it respond to :

-PH

_glucose

-oxidant (oxidative stress)

how might a chemical response be useful in drug delivery

-you can make a hydrogel that responds to ph change(chemical responses ) can be used in drug delivery where you have a drug in the hydrogel where it is bound and not released and then when the hydrogel experinces a change in pH for example the drug can be released

how can a hydrogel be classified based on its biochemical response

how does it respond to :

-certain antigens

-certain enzymes

-certain ligands

how can a hydrogel be classified based on its physical response

how does it respond to :

-temperature

-pressure

-light

how can drug delivery be included based on temperature

if you want to deliver a drug to a site of inflammation this is what you can use

how can a hydrogel be classifed based on physical properties

-Smart

-conventional

what is a conventional hydrogel

ordinary

list the natural organic gelling agents

-gelatin

starch

alginate

pectin

tragacanth

what can gelatin be used for when it is at a low conc

increase the viscocity

what happens if you increase the conc of gelatin

if you keep increasing the viscocity the system will turn from a liquid to a hydrogel (5-10%)

what happens if you increase the gelatin conc to 90%

-only 5-10% of water left

-you have a hard capsule shell

is starch used

Not very often used in pharmaceutics

what are organic gelling agents often

Organic gelling agents are often 'linear' hydrogel forming agents

explain how organic agents work

Organic gelling agents are often 'linear' hydrogel forming agents

They are linear strands of polymers when you have a solution at higher temp or you are mixing the system these individual molecules are dispersed in water and over time they then find a way to get to a lower energy state and form a network

in this network the molecules interact with eachother and contain many hydroxyl groups and can interact with surrounding water molecules via H bonding

what controlls the solution to gel transition

temperature (when it lowers)

time(longer time = gel )

where does tragacanth come from

south west of the USA and mexico

comes from the astragalus gummifer plant

also known as lococweed

why is it called locoweed

When the cattle eat this plants they go crazy and they die

what is tragacanth a polymer of

Galacturonic Acid + Galactose + Galactose + Arabinose + Xylose

what are thecomponents of

70% Bassorin - swelling

30% Tragacanthin - cold water soluble

is tragacanth acid stable

yes

why is the stability of tragacanth in acid important

you can use it if the drug requires an acidic environment

how much tragacanth is used when it is a gelling agent

2-5%

_ONLY FOR PURE TRAGACANTH

what is pectin mainly derived from

food waste such as citrus peel

what are the molecular sizes of pectin

It has a molecular weight to 20,000/40,000

Higher the mr the more effective gelling agent

what pH range is pectin stable at

3-4.5

what groups are present in pectin

methylated carboxyl group

Acetylated hydroxyl group

it is NON_IONIC

where is alginate derived from

algine

what is alginated composed of

D-mannuronic acid and L guluronic acids

-a polymer with many alginic acid groups

molecular weight of algiate acids

240,000da

what is alginate easily soluble in

cold water

at what pH do alginates form a viscous gel

6-7

what % of alginate do you need of alginate to make a gel

2-10

is alginate ionic

-if so what does this mean

yes

at different pH values it will be either protonated or deprotonated

what happen if you have one monovalent element like sodium in the presence of alginates

it will interact with one carbonyl group

what is interesting about systems with alginates

you can have systems which contains up to 40% alcohol

-if you have alcohol in there for hand sanitiser

what happens if you have a polyvalent ion such as calcium in the presence of alginates

-calcium will interact with 2 different carboxyl group forimng a tighter bond and a more stable gel

what happens in the alginate calcium bath when there was rapid sphere formation

-in a solution when calcium is present the calcium can interact with many carboxyl groups and form a highly ordered structure which is called an egg box structure

-

-

-

-

name the semi-synthetic gelling agents

cellulose ethers

starch derivitves

pectin derivites

how are the cellulose ethers different

free OH groups are chemically modifed

whar are the 4 types of cellulose ethers

1-methyl cellulose (MC)

2-D-mannuronic acid and L guluronic acids

3-Hydrocyethyl cellulose

4-sodium carboxymethyl cellulose

what is subbed for H in methyl cellulose

ch3

a methyl group

Molecular weight of MC

20,000-150,000 Da

solubility of MC

Soluble in cold water but NOT organic solvents

what happens to MC in temperature above 50

reverse flocculation

when you increase the temperature the MC will come out of the solution

is MC pH dependent

-why/why not

no

There are no acidic groups/salts the gel ability is indepnedent of the pH value

what would you use as a gelling agent if you had a very acidic/basic solution

Methyl cellulose

what is Methylcellulose incompatible with

phenolic OH groups

what do you sub in for H for Hydroxypropyl cellulose (HPC)

CH3CHOHCH3

solubility of HPC

soluble in cold+hot water Ethanol and propyleneglycol

sparingly soluble in organic solvents

at what temperature does reverse flocculation occur for HPC

40 degrees

is HPC pH dependent

no

-doesnt carry any charges

what is subbed for H to make Hydroxyethyl cellulose (HEC)

CH3CH2OH

solubility of HEC

soluble in hot and cold water

insolube in organic solvents

is the viscocity of HEC pH dependent

NO

in sodium carboxymethyl cellulose (Na-CMC) what is the R group

CH2COO-Na+

solubility of Na-CMC

soluble in cold water insoluble in orgainic solvents

is Na-CMC polar

yes

is Na-CMC viscocity pH dependent

yes

when does flocculation occur for Na-CMC

Ph below 3

what is NA-CMC incompatible wiht

Al3+

Zn2+

name the 2 fully synthetic gelling agents

polyacrylates

polyvinylpyrrolidone (PVP)

what is the brand name of polyacrylates

carbomer

carbopol

explain the structure of polyacrylates

-long chain and it has on every other network a carboxyl group

how much polyacrylate do you need in water and alcohol

0.5-2.5^ in water or up to 30% ethanol

is polyacrylates pH sensitive

yes

what are polyacrylates incompatible with

polyvalent cations

what properties do polyacrylates show

nuco-adhesive properties

-it is a little bit sticky and may be used to isolate microparticles in the nose

what sort of enhancer is a polyacrylates

penetration enhancer

are chemical compounds that can facilitate the penetration of active pharmaceutical ingredients (API) into or through the poorly permeable biological membranes.

what is the brand name of PVP

Povidon

what is the molecular weight range of PVP

10000-350,000 Da

what is PVP soluble in

water

alcohols

glycol

glycerol

what is PVP insoluble in

ether and hydrocarbons

does PVP form complexes

yes

importance of PVP forming complexes

-iodine complexes such as iodine gel can be used to treat the wound to prevent infection

what are the ionorganic gelling agents

fumed silica

bentonite

Al/MG-silicate

fumed silica trade name

aerosil