2. Hydrogel
• Hydrogel can be defined as a crosslinked polymeric
network which has the capacity to hold water within its
porous structure.
• Amount of water varies from 10% to as high as 99.5%.
• The water holding capacity of the hydrogels arise mainly
due to the presence of hydrophilic groups, viz. amino,
carboxyl and hydroxyl groups, in the polymer chains.
6. • Structure of gel and surface topography
Transmission
Electron
Microscopy
•Network arrangement
•Pores distribution
•Fibre diameter and
internal structure
Scanning Electron
Microscopy
• Surface topography
• Composition
• Electrical
conductivity
7. • Visco – elastic properties
Measures elasticity and stiffness of hydrogel
An image of the alginate
membrane under ball
indentation using the long
working distance microscope
A schematic of the hydrogel sample
holder and the loading ball
9. • Porosity
▫ Mercury Intrusion
method
Pore size
Pore geometry
Pore size distribution
Interconnectivity
of pores
% of void space
10. Chemical Characterization
• Chemical structure of hydrogel
▫ Infrared Spectroscopy
▫ Fourier Transform Infrared Spectroscopy (FTIR)
• It is based on the principle that the basic components of a substance,
i.e. chemical bonds, usually can be excited and absorb infrared light at
frequencies that are typical of the types of the chemical bonds. The
resulting IR absorption spectrum represents a fingerprint of measured
sample.
• Widely used to investigate the structural arrangement in hydrogel by
comparison with the starting materials
11. Ref. A. Cooper et al. / Carbohydrate Polymers 85 (2011) 149–156
12. • Quantification of the amount of free and bound
water in hydrogels
▫ Nuclear Magnetic Resonance (NMR)
▫ Proton NMR gives information about the interchange of
water molecules between free and bound states
▫ Differential Scanning Calorimetry (DSC)
▫ Thermo-analytical method
▫ Based on difference in the amount of heat required to
increase the temperature of a sample and reference
▫ Can also find out percentage of crystallinity of gel