Hydrogels are three-dimensional networks of hydrophilic polymers that can swell in water, first reported in 1960, and are increasingly used in biomedical applications. They can retain large amounts of water due to their chemical or physical cross-linking and are classified based on preparation and cross-linking methods. While hydrogels have advantages such as biocompatibility and flexibility, they also face disadvantages like high cost, low mechanical strength, and challenges in handling and sterilization.

1. HYDROGELS
A hydrogel is a three-dimensional(3D) network of hydrophilic
polymers that can swell in water and hold a large amount of water
while maintaining the structure due to chemical or physical cross-
linking of individual polymer chains.
First reported by Wichterle and Lim
in 1960.
They are first biomaterials designed
for use in human body and are finding
widespread biomedical applications.

2. SOME IMPORTANT POINTS:
• By definition, water must constitute at least 10% of the total
weight (or volume) for a material to be a hydrogel.
• Hydrogels on exposed in a thermodynamically compatible solvent
(water or any biological fluid), can entrap a large fraction of
solvent within the pores or interstitial spaces and can achieve a
fully swollen state.
• The hydrophilicity of the network is due to the presence of
hydrophilic groups such as –NH2, -COOH, -OH, -CONH2, -CONH-
and SO3H.
• The presence of cross-links makes it resistant to dissolution in the
aqueous medium.

3. Classification
 On the basis of Preparation :
- Homo-polymer
- Copolymer
- Semi-interpenetrating network
- Interpenetrating network
 On the basis of cross linking :
- Chemical hydrogels
- Physical hydrogels

4. Application of Hydrogels :
• Flexibility of hydrogels, which is because of their water
content, makes it possible to use them in different
condition ranging from industrial to biological fields.
• Hydrogels are biocompatible
• In drug delivery
• In contact lenses
• In agricultural process
• In wound dressing etc…

5. Disadvantages of Hydrogels :
• Hydrogels are expensive
• Hydrogels have low mechanical strength
• Difficulty in handling
• They are non-adherent and may need to be
secured by a secondary dressing
• Difficulty in loading
• Difficult to be sterilized