01 Bio Materials

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HYDROGELS


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Overview

1. Introduction to Hydrogels

2. Structure of Hydrogels

3. Classification of Hydrogels

4. Hydrogels Preparation

5. Hydrogels Swelling

6. Application of Hydrogels7. Study focus in later Stages


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Introduction

What are Hydrogels?

Hydrogels are insoluble three dimensional

network of polymer chains that swell inaqueous solutions.


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Structure of Hydrogels

Polymers capable of swelling substantially inaqueous conditions (Hydrophilic)

Cross-linkage of polymer chains are present

By definition, water must constitute at least

10% of the total weight (or volume) for amaterials to be a hydrogel


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The inter-chain connections can be:

a carbon atom chemical bridge

van der Waals

hydrogen bonds

molecular entanglements


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Defects in crosslink structure:

unreacted functionality

chain loops

Neither of the two configurationscontribute to mechanical strength orphysical properties of the network


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Classification

Method of preparation Homo-polymer, Copolymer, Multi-polymer,

Interpenetrating polymeric hydrogels

Ionic charge Neutral, Catatonic, Anionic, Ampholytic

Physical structure

Amorphous, Semi-crystalline, Hydrogen-bondedNatural & Synthetic Hydrogels Dextran, Collagen, Dextran Sulfate & Poly (vinyl

alcohol), Poly (ethylene glycol)


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Hydrogels: Preparation

Prepared by swelling cross-linkedstructures in water or in biological fluids

containing water

Crosslinks can be induced by

1. Radiation reactions

2. Chemical crosslinking


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Radiation reactions include

electron beams, gamma-rays, X-rays, or UV

lightChemical crosslinking

crosslinking agents

copolymerization-crosslinking reactionsbetween the monomers and a multifunctionalmonomer.


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Hydrogels: Swelling

After polymerization, the hydrophilicpolymer is brought in contact withwater

The network expands

The thermodynamically driven swellingforce is counterbalanced by theretractive force of the cross-linked

structure

Two forces become equal at some pointand equilibrium is reached


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Hydrogels: Swelling

Hydrogels undergo swelling in analogyto dilution of free polymer chains in

solution


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Hydrogels: Swelling

Degree of swelling

solute diffusion coefficient through thehydrogel

surface properties and surface mobility

optical properties (particularly for contactlens applications)

mechanical properties


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Hydrogels: Swelling

Degree of swelling can be quantifiedby:

ratio of sample volume in the swollen stateto volume in the dry state

weight degree of swelling: ratio of theweight of swollen sample to that of the dry

sample One may copolymerize a highly hydrophilic monomer

with other less hydrophilic monomers to achievedesired swelling properties


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Properties of Hydrogels

Swelling properties influenced bychanges in the environment

(pH, temperature, ionic strength, solventcomposition, pressure, and electrical potential)

Can be biodegradable, bio-erodible, andbio-absorbable

Can degrade in controlled fashion


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Advantages of Hydrogels

Environment can protect cells and othersubstances (i.e. drugs, proteins, andpeptides)

Timed release of nutrients to ensure propertissue growth

Good transport properties

Biocompatible Can be injected & easy to modify

Good Mechanical Stability


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Disadvantages of Hydrogels

Low mechanical strength

Hard to handle

Difficult to load

Sterilization


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Hydrogels: Applications

Biomedical use due to bio- and blood-compatibility

Pharmaceutical use due to hydrophilicin nature(controlled/sustained drugrelease)

Earliest biomedical application contactlenses

lubricating surface coating


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Pharmaceutical applications

monomer composition and relative

amounts of multi-polymer hydrogelscan be varied to alter the diffusioncharacteristic and permeability of the

gel containing pharmaceutical agents


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Methods for drug delivery

drug gets trapped in the hydrogel

during polymerization drug introduced during swelling in

water

Release occurs by outflow of drug fromthe gel and inflow of water to the gel.


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Whats next..?

Design of functional hydrogel andEvaluation of its material Properties

Importance of material propertyCharacterization of hydrogels

Synthesis and Characterization of

Polyvinyl alcohol hydrogel


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THANK YOU

By

M Karthik Teja2011H141029H

01 Bio Materials

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