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.

CLASSIFICATION OF POLYMERS

1. BASED ON THE SOURCENATURAL 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. 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

5. BASED ON THE STRUCTURE OF POLYMERLINEAR 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

• .

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.

GENERAL MECHANISM OF DRUG RELEASE FROM POLYMER

Three primary mechanism for drug releas, namely :o Diffusiono Degradation o Water penetration(Swelling)

Any of these mechanism can occur in a given release system.

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).

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

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).

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.

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.