01 bio materials
TRANSCRIPT
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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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Structure of Hydrogels
The inter-chain connections can be:
a carbon atom chemical bridge
van der Waals
hydrogen bonds
molecular entanglements
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Structure of Hydrogels
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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Hydrogels: Preparation
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: Preparation
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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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Hydrogels: Applications
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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Hydrogels: Applications
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