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What is Polymer?What is Polymer?• “Polymer” word is derived from Greek roots

“Poly” meaning many and “Meros” meaning parts.

• Definition : Polymers are long chain organic

molecules assembled from many smaller molecules called as monomers.

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• Copolymer : Polymers formed from two or

more different monomers are called as copolymers.

- [A – B – A – B – A – B] –• Homopolymer : Polymers formed from bonding of

identical monomers are called as homopolymers.

- [A – A – A – A – A] -

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A. Based on origin : a) Natural Polymers :

e.g. Proteins – Collagen, Keratin, Albumin Carbohydrates – starch, cellulose,

glycogen. DNA, RNA

b) Synthetic Polymers : e.g. polyesters, polyanhydrides, polyamides.

B. Based on Bio-stability : a) Bio-degradable Polymers :

e.g. polyesters, proteins, carbohydrates, etc b) Non – biodegradable Polymers :

e.g. ethyl cellulose, HPMC, acrylic polymers, silicones.

CLASSIFICATIONCLASSIFICATION

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C. Based on Reaction mode of Polymerization :

a) Addition Polymers : Here, the monomer molecules bond to each other without the loss of any other atoms.

e.g. Alkene monomers

b) Condensation Polymers : Usually two different monomers combine with the loss of small molecule, usually water. e.g. polyesters, polyamides.

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D. Based on Interaction with Water : a) Non – biodegradable Hydrophobic Polymers :

These are inert compounds and are eliminated intact from the site of application.

e.g. polyethylene – vinyl acetate, polyvinyl chloride. b) Hydrogels :

They swell but do not dissolve when brought in contact with water.

e.g. polyvinyl pyrrolidone c) Soluble Polymers :

These are moderate mol. wt uncross-linked polymers that dissolve in water.

e.g. HPMC, PEG d) Biodegradable Polymers :

These slowly disappear from the site of administration in response to a chemical reaction such as hydrolysis.

e.g. Polyacrylic acid. Polyglycolic acid.

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Applications in Conventional Applications in Conventional Dosage FormsDosage Forms

• Tablets : - As binders

- To mask unpleasant taste - For enteric coated tablets

• Liquids : - Viscosity enhancers

- For controlling the flow• Semisolids :

- In the gel preparation - In ointments

• In transdermal Patches

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Applications In Controlled Applications In Controlled Drug DeliveryDrug Delivery

• Reservoir Systems - Ocusert System

- Progestasert System- Reservoir Designed Transdermal Patches

• Matrix Systems• Swelling Controlled Release Systems• Biodegradable Systems• Osmotically controlled Drug Delivery

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A. Reservoir System : Ocusert System :

- Novel means of controlled ocular drug delivery - Used for max 7 days treatment of Glaucoma - Consists of core reservoir of pilocarpine &

alginic acid sandwiched between two sheets of transparent, lipophillic, rate controlling membrane of ethylene-vinyl acetate copolymer.

- Inserted in cul-de-sac, lachrymal fluid enters the system and the dissolved drug slowly gets released through polymeric membrane.

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Progestasert system : - Used for once-a-year contraception - Consists of drug saturated liquid medium

encapsulated in a polymeric membrane.

- Progesterone is released at a constant rate of 65 µg/day.

- Polymers used are :Silicone elastomers, polyethylene,

ethylene-vinyl acetate.

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Transdermal Patches : - Drug is sandwiched between drug impermeable backing and drug permeable rate controlling polymer. e.g. Ethylene-vinyl acetate copolymer - In the reservoir, drug is dispersed in solid

polymer matrix.e.g. Polyisobutylene

- On the external surface, there should be adhesive polymer.e.g. Silicone Polymer, Polyacrylates.

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Transdermal Controlled Drug DeliveryTransdermal Controlled Drug Delivery

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B. Osmotically Controlled Drug B. Osmotically Controlled Drug Delivery SystemDelivery System

• Drug is coated with semi-permeable polymer

e.g. Cellulose acetate.• Water generates osmotic

pressure gradient by permeating through semi-permeable membrane.

• Due to that drug pumps out of delivery orifice over a prolonged time at a defined rate.

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C. Biodegradable SystemC. Biodegradable System

• Mainly used for parenteral controlled drug delivery.

• Drug is encapsulated in biodegradable microcapsules which are suspended in aqueous / oleaginous medium and injected subcutaneously or intra-muscularly.

• Polymers used for microcapsules are : Gelatin, dextran, polylactate, lactide –glycolide copolymer.

• The release of drug is controlled by the rate of bio-degradation of polymer.

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D. Matrix SystemsD. Matrix Systems

• Drug particles are enclosed in a matrix environment formed by cross-linking of polymer chains.

• For the drug to get released, it has to be first dissolved in surrounding polymer and then diffuse through the polymer structure.

• Polymers used are :polyalkyls, polyvinyls, etc.

• Example – Nitroglycerine releasing system for prophylaxis or treatment of angina pectoris.

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E. Swelling Controlled Release E. Swelling Controlled Release SystemsSystems

• Drug is enclosed in a collapsible drug compartment inside a rigid, shape-retaining housing.

• The shape between external housing and drug compartment contains laminate of swellable, hydrophillic cross-linked polymer.e.g. polyhydroxyalkyl methacrylate.

• This polymer absorbs GI fluid through annular openings in the bottom of housing.

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Because of this, laminate swells and generates Because of this, laminate swells and generates hydrodynamic pressure and induces the hydrodynamic pressure and induces the

delivery of drug formulation through the orifice.delivery of drug formulation through the orifice.

Drug delivery orifice

Shape retaining housing

Collapsible drug container

Swellable polymer

Liquid drug formulation

Annular openings