Hydrogels are three-dimensional polymer networks that can swell in water and have both solid and liquid properties, making them ideal for controlled drug delivery. They can be classified based on their origin, water content, porosity, cross-linking, and biodegradability. Hydrogels are responsive to environmental stimuli which allows for controlled drug release in response to factors like temperature, pH, and the presence of specific molecules.

2.  Three-dimensional networks of
hydrophilic polymer chains that do not
dissolve but can swell in water
 both solid like and liquid like properties
 high biocompatibility
 environmental stimuli respondent
(temperature, pH, light, specific molecules)
 Ideal for controlled drug delivery

3. - various criteria for the classification of hydrogels
Origin Natural
Synthetic
Water content or Low swelling
degree of swelling Medium swelling
High swelling
Superabsorbent
Porosity Nonporous
Microporous
Macroporous
Superporous
Cross-linking Chemical (covalent
bonding)
Physical (noncovalent
bonding)
Biodegradability Biodegradable

4. Swelling property is influenced by:
•type and composition of monomers
•other environmental factors such as :
temperature, pH, ionic strength
•cross-linking Mechanical
strength and
permeability
Rs = (Ws-Wd) / Wd
Rs = swelling ratio
Ws = weight of swollen hydrogels
Wd = weight of dried hydrogels
Cross-linking and/or copolymerization with hydrophobic comonomers
density↑, mechanical strength↑, swelling property ↓

5. Chemical Physical
hydrogels hydrogels
Covalently Noncovalently
crosslinked crosslinked
▪ Hydrogen bonding
▪ hydrophobic
interaction
▪ crystallinity
▪ stereocomplex
formation
Thermoset Thermoplastic hydrogels
▪ ionic complexation
hydrogels
Volume phase Sol-gel phase transition
transition
Reliable shape stability Limited shape stability
and memory and memory

6. Chemical crosslinking
Polymerization of water soluble monomers in the presence
of bi- or multifunctional cross-linking agent
+ Copolymerizatio
n
MonomerCrosslinker
or
Polymerization Hydrogel
network
Vinyl group-containing water-soluble polymers

7. Physical crosslinking Chemical and Physical
crosslinking
• Cross-linking without
chemical reaction
• ionic interaction, hydrogen
bonding, antigen-antibody
interaction, supramolecular
association
• Ionic hydrogel

8. Monomer abbreviation Monomer
HEMA Hydroxyethyl methacrylate
HEEMA Hydroxyethoxyethyl methacrylate
HDEEMA Hydroxydiethoxyethyl
methacrylate
MEMA Methoxyethyl methacrylate
MEEMA Methoxyethoxyethyl methacrylate
MDEEMA Methoxydiethoxyethyl methacrylate
EGDMA Ethylene glycol dimethacrylate
NVP N-vinyl-2-pyrrolidone
NIPAAm N-isopropyl Aam
AA Acrylic acid
HPMA N-(2-hydroxypropyl) methacrylamide
EG Ethylene glycol
PEGMA PEG methacrylate

9. - Benefits of controlled drug delivery
 more effective therapies with reduced side effects
 the maintenance of effective drug concentration
levels in the blood
 patient’s convenience as medicines hence increased
patient compliance
- Release mechanisms of drug molecules
: diffusion, dissolution, osmosis, ion exchange

10. - Diffusion controlled Drug Delivery
(1) Polymer matrix
Water-insoluble
Polymer matrices
time
(2) Reservoir system
Water-insoluble
Polymer membrane
time

11.  Environment-Sensitive Hydrogels
• respond to environmental change
: temperature, pH, specific molecule
• reversible volume phase transition or sol-gel phase
transition
• “intelligent” or “smart” hydrogel
Drug-loaded gel
Change in pH for
gel swelling
Change in temperature for
gel collapse
Drug release through Drug release by the
the swollen network squeezing action

12. Environmental-Sensitive Hydrogels used for Drug Delivery
Environment Typical polymers Main Mechanism Applications
al Factor
Temperature PNIPAAm, PDEAAm, PEO- Competition between On/off drug release,
PPO block copolymers hydrophobic interaction and squeezing device
hydrogen bonding
pH Polyelectrolytes, PAA, PDEAEM Ionization of polymer chains pH-dependent oral drug
upon pH change delivery
Glucose pH-sensitive hydrogels; pH change caused by glucose Self-regulated insulin
Concanavalin A-grafted oxidase; reversible interaction delivery
polymers; polymers containing between glucose-containing
phenylborate groups polymers and Concanavalin A;
reversible solgel transformation
Electric Polyelectrolytes (pH-sensitive) Reversible swelling or Actuator, artificial muscle,
signal deswelling in the presence of on off drug release
electric field
Light Copolymer of PNIPAAm and Temperature change via the Optical switches,
light sensitive chromophore, incorporated photosensitive ophthalmic drug delivery
such as triphenylmethane and molecules; dissociation into ion
leuco derivatives pairs by UV irradiation
Antigen Semi-IPN with grafted Competition between polymer- Modulated drug release in
antibodies or antigens grafted antigen and free the presence of a specific
antigen antigen; sensor for
immunoassay and antigen

13. Specific applications of Hydrogels in Oral Drug Delivery

14. Specific applications of Hydrogels in Oral Drug Delivery
Fast-disintegrating tablet formulations
 fast swelling and superabsorbent properties
 microparticles of superporous hydrogels
mucoadhesive hydrogels
• buccal drug delivery
Gastric emptying of oral dosage forms
• The physical properties (size and density) of
the oral dosage form
• The presence of food in the stomach
 Intragastric floating system
• low density
• float on top of the gastric juice

15. Specific applications of Hydrogels in Oral Drug Delivery
 Mucoadhesive system
• cross-linked PAA
• highly mucoadhesive at pH (1-3) of the stomach
(∵ hydrogen bonding)
 Superporous hydrogels
• Swell to a very large size
• High swelling ratio ( > a few hundreds)
• Fast swelling property - avoid premature
emptying by the housekeeper waves
• Gastric retention device (ex. Dogs-from several
hours to a day)
• Ac-Di-Sol (cross-linked carboxymethylcellulose
sodium)

16. Specific applications of Hydrogels in Oral Drug Delivery
- Hydrotropic Hydrogels for delivery of poorly soluble drug
-Hydrotropic agent : Diverse class of water soluble compounds
at high
concentration, enhance water solubilities of poorly soluble
solutes
ex) N,N-dimethylnicotinamide (3.5M), N,N-
diethylnicotinamide
- Many drugs : poorly soluble in water
: low absorption and low bioavailability
- Low-molecular-weight hydrotropes : high concentration
- Polymeric forms of hydrotropes (e.g., hydrotropic hydrogels)

17. • Hydrogels have played role in the development
of various controlled-release formulation
• biocompatible and increasing the solubility of
poorly soluble drug
• Hydrogels with novel properties will continue to
play important role in drug delivery
• smart hydrogels and new controlled-release
formulation