Hydrogels Study Guide

Question 1

hydrogels are polymeric structures held together as water swollen gels by_____ and ____

Answer 1

–Primary covalent links
 –Ionic forces 
–Hydrogen bonds
 –Hydrophobic interactions
 –Polymer crystallites
 –Physical entanglements 
–Combination of two or more interaction

Question 2

name 3 examples of biological hydrogels

Answer 2

• jello
• extracellular matrix components
• polysaccharides
• blood clot
• mucin-lining in the stomach
• glycocalyx-lining epithelial cells of blood vessels
• sinus secretions

Question 3

state two applications of hydrogels

Answer 3

Biomedical use due to bio- and blood-compatibility •

Pharmaceutical – controlled/sustained drug release •

Earliest biomedical application contact lenses –
favorable refractive index –
high oxygen permeability •

lubricating surface coating – used with catheters, drainage tubes and gloves – non-toxic

Question 4

define hydrogels

Answer 4

they are water insoluble and they are polymers capable of swelling substantailly in aqueous conditions. it has a polymeric network in which water is dispersed throughout the strucutre. Overall it is a three dimmensional network of polymeric chains that are crosslinked by chemical or physical bonding…

Question 5

classify hydrogels based on ionic charges

Answer 5

-neutral hydrogels- no charge
anionic hydrogels- neg charge
cationic hyrdogels-possitive charge
ampholytic hydrogels-multidude of charges however net =0

Question 6

describe classification of hydrogels based on structures

Answer 6

• amorphous hydrogels (chains randomly arranged)
• semicrystalline hyrdogels (dense regions of ordered macromolecules)
• hydrogen-bonded hydrogels

Question 7

State the different ways of crosslink formation in hydrogels

Answer 7

Cross link formation can form in ideal network t. multifuctional junctions. unreacted functionality. or chain loops.

Question 8

elaborate on how the degree of swelling of hydrogels could be quantified by?

Answer 8

• Degree of swelling can be quantified by:
–ratio of sample volume in the swollen state to volume in the dry state
–weight degree of swelling: ratio of the weight of swollen sample to that of the dry sample

V= V swollen gell/(volume polymer)

Question 9

give 3 examples of biological hydrogels

Answer 9

• jello
• extracelluar matrix components
• DNA/RNA
• Blood clot
• Mucin
• Glcocalyx
• sinus secretions

Question 10

name three reactions that could induce cross links to form hydrogels

Answer 10

radiation-such as electron beams, gamma rays, xrays, or uv light

chemical reactions

• introducing cross linking agents that link two chains together
• copolymerization-crosslinking reactions

Question 11

Why is the degree of swelling in hydrogels important

Answer 11

–solute diffusion coefficient through the hydrogel
–surface properties and surface mobility
–optical properties (particularly for contact lens applications)
–mechanical properties

Question 12

which one of the following is a natural hydrogel forming polymer; 
polyehelene glycol, 
polylactic acid,
 polysodium alginate,
 or polyn-isopropyl acrylamide

Answer 12

polysodium alginate

Question 13

what percent of water must be in a hydrogel for it to be considered as a super absorbent hydrogel

Answer 13

95% of total weight/volume must = water

Question 14

define superabsorbent hydrogels

Answer 14

the hydrogel is superabsorbent if the content of water exceeds 95% of the total weight or volume

Question 15

how would a drug be delivered using a hydrogel?

Answer 15

–drug gets trapped in the hydrogel during polymerization –drug introduced during swelling in water

Question 16

state two defects in crosslinked structures of hydrogels?

Answer 16

unreacted functionality

chain loops

Question 17

state hydrogel classification based on polymer preparation methods

Answer 17

• homopolymer hydrogel (one type of hydrophillic mer)
• copolymer hydrogels (two types of mers, at least one hydrophillic)
• multipolymer hydrogels- (more than three types of mer
• interpenetrating polymer hydrogels (swelling a network of polymer in mer making intermeshing network of polymer 1 and polymer 2

Question 18

state hydrogel classification based on structure

Answer 18

• amorphous hydrogels (chains randomly arranged)
• semicrystalline hydrogels (dense regions of ordered macromolecules, i.e crystallites)
• hydrogen-bonded hydrogels

Question 19

Properties of hydrogels depend on

Answer 19

–polymer volume fraction –degree of crosslinking –temperature –swelling agent

Question 20

Name two distinguising features of hydrogels.

Answer 20

it is a polymer capable of swelling substantially in aqueous conditions…. it also has a network in which water is dispersed throughout the entire structure.