Hydrogels are water-swollen, crosslinked polymers that can absorb large amounts of water. They have a variety of applications including in soft contact lenses, drug delivery, wound healing, and tissue engineering. Hydrogels are advantageous for tissue engineering and cell culture as they can mimic extracellular matrix, provide structural support, and allow for nutrient transport. They are also useful for drug delivery as they allow controlled release of molecules. The document discusses the properties, types, advantages and uses of hydrogels.

1. HYDROGELS:
Introduction and Applications in
Biology and Engineering
Jorge E. Roldan
Louisiana Tech University
Dept. of Biological Sciences
June 25, 2003

2. OVERVIEW
What are Hydrogels?
 Introduction
 Applications
 Types
 Properties
 Advantages and Disadvantages
Why Hydrogels?
 Tissue engineering
 Cell Culture Systems
 Drug delivery
 Scaffolds
Conclusion

3. What are Hydrogels?
Water-swollen, crosslinked polymeric structure
produced by reactions of monomers or by
hydrogen bonding
Hydrophilic polymers that can absorb up to
thousands of times their dry weight in H2O
Three-dimensional insoluble polymer networks

4. Applications of Hydrogels
Soft contact lenses
Pills/capsules
Bioadhesive carriers
Implant coatings
Transdermal drug delivery
Electrophoresis gels
Wound healing
Chromatographic packaging material

5. Types of Hydrogels
Classification
Method of preparation
Homo-polymer, Copolymer, Multi-polymer,
Interpenetrating polymeric
Ionic charge
Neutral, Catatonic, Anionic, Ampholytic
Physical structure
Amorphous, Semi-crystalline, Hydrogen-bonded

6. Types of Hydrogels
 Physical
 Polyanion + Multivalent Cation = “Iontropic” Hydrogels
 Chemical
 Polyanion + Polycation = Polyion Complex Hydrogels

7. Types of Hydrogels
Natural Polymers
 Dextran, Chitosan, Collagen, Dextran Sulfate
 Advantages
Generally have high biocompatibility
Intrinsic cellular interactions
Biodegradable
Cell controlled degradability
Low toxicity byproducts
 Disadvantages
Mechanical Strength
Batch variation
Animal derived materials may pass on viruses

8. Types of Hydrogels
Synthetic Polymers
 PEG-PLA-PEG, Poly (vinyl alcohol)
 Advantages
Precise control and mass produced
Can be tailored to give a wide range of properties (can be
designed to meet specific needs)
Low immunogenecity
Minimize risk of biological pathogens or contaminants
 Disadvantages
Low biodegradability
Can include toxic substances
Combination of natural and synthetic
 Collagen-acrylate, P (PEG-co-peptides)

9. Properties of Hydrogels
Swelling properties influenced by
changes in the environment
 pH, temperature, ionic strength, solvent
composition, pressure, and electrical potential
Can be biodegradable, bioerodible, and
bioabsorbable
Can degrade in controlled fashion

10. Properties of Hydrogels
Pore Size
Fabrication techniques
Shape and surface/volume ratio
H2O content
Strength
Swelling activation

11. Advantages of Hydrogels
 Environment can protect cells and other substances (i.e.
drugs, proteins, and peptides)
 Timed release of growth factors and other nutrients to
ensure proper tissue growth
 Good transport properties
 Biocompatible
 Can be injected
 Easy to modify

12. Disadvantages of Hydrogels
Low mechanical strength
Hard to handle
Difficult to load
Sterilization

13. Why Hydrogels?
Tissue Engineering
Scaffolds for tissue engineering
Cell Culture Systems
“In vivo conditions are not accurately mimicked
in the majority of cell culture systems”
Drug Delivery
Time released delivery

14. Why Hydrogels?: Background
Physiology
 Cell Phenotype
 The expression of a specific trait.
 Phenotype Regulation
 Environmental influences
ECM determines adhesion factors, mechanical signals, and
growth factors (i.e. CTGF, TGFβ, and Activin)
 Internal genetic programs
Different combinations of receptors may cause differences in
gene expression
 Cell Differentiation
 To become specialized
Dependent on biochemical signals & ECM molecules
Due to mechanical forces resulting from the spatial orientation
cells grow in

15. Why Hydrogels?: Background
Physiology
An accurate understanding of the mechanisms
by which cells interact with scaffold, is critical
if one wishes to design and control cell
phenotype and ultimate tissue structure (i.e.
surface chemistry, 3-D space and tensional
forces)

16. Why Hydrogels ?: Tissue
Engineering/Cell Culture Systems
Scaffold provides extracellular matrix:
Cell adhesion sites
Control of tissue form and thus function
Diffusion of growth factors, metabolites, and
nutrients
Build it, Shape it, and Seed it with
cells and nutrients

17. Why Hydrogels ?: Tissue
Engineering
 Biocompatible
 H2O content
 Sterilizibilty
 Ease of use
 High mechanical
Strength
 Surface to volume ratio
 Good cell adhesion
 High nutrient transport

18. Why Hydrogels?: Cell Culture
Systems
Biocompatible substrate
Non-toxic and have no immunological
responses
Cytoarchitecture which favors cell growth
Flexibility for cells to rearrange in 3-D
orientation
Seeded with appropriate growth and adhesion
factors
Porosity (i.e. channels for nutrients to be
delivered)

19. Why Hydrogels?: Cell Culture
Systems
Mimic cytomechanical situations
3-D space provides balanced cytoskeleton
forces
Dynamic loading to promote cell growth
Flexibility
Provide scaffold for various cells
Consistent, reproducible and easy to
construct

20. Why Hydrogels?: Drug Delivery
Safe degradation products
Biocompatible
High loading with ensured molecule efficacy
High encapsulation
Variable release profile
Stable
Inexpensive
High quality

21. Conclusion
Hydrogels are network polymers that
swell through a variety of mechanisms in
an aqueous environment
Environment controls mechanisms of
swelling:
pH, ionic strength, solvent composition,
pressure and even electric fields
Applications in medicine, engineering, and
biology

22. Questions