classification of polymers/ mechanism of drug release from polymers/

1. PHARMACEUTICAL POLYMERS
INTRODUCTION
Polymers are used extensively in our daily routine life.In
pharmaceutical preparations also they have several
applications e.g. In manufacturing of bottles, syringes,
vials and also in drug formulations.
DEFINITION
“Polymer” word is derived from Greek roots “Poly” meaning
many and “Meros” meaning parts. Polymers are long chain
organic molecules assembled from many smaller molecules
called as monomers.

2. CLASSIFICATION OF POLYMERS
1. BASED ON THE SOURCE
NATURAL Occurs in nature and known as biopolymers.
EXAMPLE- natural rubber, natural silk and cellulose.
SEMI-SYNTHETIC Chemically modified natural polymers.
EXAMPLE- methyl cellulose, cellulose nitrate and cellulosic.
SYNTHETIC Synthesized in the laboratory known as manmade polymer.
EXAMPLE- polyvinyl alcohol, polyethylene and polysulfone.
2. BASED ON THE TYPES OF POLYMERISATION
ADDITION
POLYMER
They formed from simple addition of monomer molecules to
each other in a quick succession by a chain mechanism.
EXAMPLE- polyethylene, polystyrene and polypropylene.
CONDENSATION
POLYMER
They are formed from intermolecular reactions between
bifunctional or polyfunctional monomer molecule having reactive
functional groups, such as –OH, -COOH, -NH2.
EXAMPLE- polyesters and polyurethane.

3. 3. BASED ON THE DEGRADABILITY
BIODEGRADABLE They degrade naturally in the body.
EXAMPLE- PLA, PGA, polycaprolactone (PCL).
NONBIODEGRADABLE They are not degraded naturally in the body.
EXAMPLE- polyethylene vinyl acetate (PVA), ethyl cellulose
(EC), cellulose acetate (CA).
HYDROPHOBIC
POLYMER
They contain non-polar functional groups, making them
water insoluble.
EXAMPLE- ethyl cellulose, polydimethyl siloxane.
HYDROPHILLIC
POLYMER
They contain polar or charged functiional groups, making
them water soluble.
EXAMPLE- sodium alginate, chitosan and HPMC.
HYDROGEL POLYMER They swell but do not dissolve when brought in contact with
water.
EXAMPLE- polyhydroxy ethyl methyl acrylate, polyvinyl
alchol (PVA), PVP.
4. BASED ON THE POLYMER WATER INTERACTION

4. 5. BASED ON THE STRUCTURE OF POLYMER
LINEAR POLYMER In this polymer monomers are linked with each other
and form a long straight chain, these chains do not have
any side chains.
EXAMPLE- polyethene, PVc and polyesters.
BRANCHED CHAIN
POLYMER
They have a straight long chain with different side chains.
EXAMPLE- polypropylene, amylopectin and glycogen.
CROSS-LINKED POLYMER In this polymer two liner chains are joined together by
covalent bonds and it have three dimensional.
Example - BAKELITE, VULCANISED RUBBER AND
FORMALDEHYDE RESINS.
6. BASED ON THE TYPES OF MONOMER
HOMOPOLYMER A polymer containing a single type of repeat unit.
EXAMPLE- Polystyrene.
HETEROPOLYMER
(COPOLYMER)
If a polymer is made up two different monomers then it
is called copolymer.
EXAMPLE- Butadiene – styrene rubber

5. • .
7. BASED ON THE MOLECULAR FORCES
ELASTOMERS These are rubber-like solids with elastic properties.
The polymer chain chains are held together by the
weakest intermolecular forces, which permits the
polymer to be stretched.
EXAMPLE- buna-S and neoprene.
FIBERS Fibres are the thread forming solids which posses
high tensile strength and modulus, which can be
attributed to the strong intermolecular forces like
hydrogen bonding.
EXAMPLE- polyamides (nylon 6, 6), polyesters, etc.
THERMOPLASTIC POLYMERS These polymers having intermolecular forces
between elastomers and fibres, they can be softened
on heating and hardened on cooling and can be
recycled many times.
Example- polythene, polystyrene, PVC.
THERMOSETTING POLYMERS These polymers are hard and infusible on heating
they are not remoulded also they are non-recyclable.
EXAMPLE- bakeelite, urea-formaldehyde resins, etc.

6. GENERAL MECHANISM OF DRUG RELEASE FROM
POLYMER
Three primary mechanism for drug releas, namely :
o Diffusion
o Degradation
o Water penetration(Swelling)
Any of these mechanism can occur in a given release system.

7. Drug release from polymer by diffusion
Rate limiting step is diffusion of drug through inert water
insoluble membrane barrier.
There are two types
• a) Reservoir
• b) Matrix
Reservoir diffusion system
In membrane-controlled reservoir devices, the drug is contained
in a core, which is surrounded by a polymer membrane, and it
is released by diffusion through this rate- controlling
membrane.
e.g. Poly(N-vinyl pyrrolidone), Poly(ethylene-co-vinyl acetate).

8. Matrix diffusion system
In these devices, the drug is released either by passing through the
pores or between polymer chains, and these are the processes
that control the release rate.
Example- Such as polyehylene, polyvinylacetate.
polymer
• Drug time = 0 time = t

9. Degradation
The drug molecules, which are initially
dispersed in the polymer, are released as
the polymer starts eroding or degrading.
The four most commonly used
biodegradable polymers in drug delivery
systems are poly(lactic acid), poly(lactic-
co-glycolic acid), polyanhydrides,
poly(ortho esters), and
poly(phosphoesters).

10. Water penetration (swelling)
This type of systems are initially dry and when placed in body,
absorb water or other fluid and it swells.
Swelling increases aq. solvent content within the formulation as
well as the polymer mesh size, enabling the drug to diffuse
through the swollen network into external environment.
E.g(N-isopro-pylacrylamide), Ethylene-vinyl alcohol.

11. Various uses of Polymers in pharmaceutical sciences
1. Formulation of Matrix tablets.
2. Formulation of Nanoparticles.
3. Formulation of solid dispersion.
4. In targeted drug delivery systems.
5. In the preparation of Polypeptide vesicles for drug delivery.
6. In formulation of cross linked Polymers.
7. Micelles for cancer therapeutics.