HYDROGELS: Introduction and

Applications in Biology and Engineering

Jorge E. Roldan Louisiana Tech University

Dept. of Biological SciencesJune 25, 2003

OVERVIEWWhat are Hydrogels?

IntroductionApplicationsTypesProperties Advantages and Disadvantages

Why Hydrogels?Tissue engineering Cell Culture SystemsDrug deliveryScaffolds

Conclusion

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

Applications of Hydrogels

Soft contact lensesPills/capsulesBioadhesive carriersImplant coatingsTransdermal drug deliveryElectrophoresis gelsWound healingChromatographic packaging material

Types of Hydrogels

Classification Method of preparation

Homo-polymer, Copolymer, Multi-polymer, Interpenetrating polymeric

Ionic chargeNeutral, Catatonic, Anionic, Ampholytic

Physical structureAmorphous, Semi-crystalline, Hydrogen-bonded

Types of HydrogelsPhysical

Polyanion + Multivalent Cation = “Iontropic” Hydrogels

Chemical Polyanion + Polycation = Polyion Complex Hydrogels

Types of Hydrogels Natural Polymers

Dextran, Chitosan, Collagen, Dextran Sulfate

AdvantagesGenerally have high biocompatibilityIntrinsic cellular interactionsBiodegradableCell controlled degradabilityLow toxicity byproducts

DisadvantagesMechanical StrengthBatch variationAnimal derived materials may pass on viruses

Types of Hydrogels Synthetic Polymers

PEG-PLA-PEG, Poly (vinyl alcohol)

AdvantagesPrecise control and mass producedCan 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

DisadvantagesLow biodegradabilityCan include toxic substances

Combination of natural and synthetic Collagen-acrylate, P (PEG-co-peptides)

Properties of HydrogelsSwelling 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

Properties of HydrogelsPore Size

Fabrication techniques

Shape and surface/volume ratio

H2O content

Strength

Swelling activation

Advantages of HydrogelsEnvironment 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

Disadvantages of Hydrogels Low mechanical strength

Hard to handle

Difficult to load

Sterilization

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 DeliveryTime released delivery

Why Hydrogels?: Background PhysiologyCell Phenotype

The expression of a specific trait.Phenotype Regulation

Environmental influencesECM 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 moleculesDue to mechanical forces resulting from the spatial orientation

cells grow in

Why Hydrogels?: Background PhysiologyAn 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)

Why Hydrogels ?: Tissue Engineering/Cell Culture SystemsScaffold provides extracellular matrix:

Cell adhesion sitesControl of tissue form and thus functionDiffusion of growth factors, metabolites, and

nutrients

Build it, Shape it, and Seed it with cells and nutrients

Why Hydrogels ?: Tissue Engineering BiocompatibleH2O content SterilizibiltyEase of useHigh mechanical

Strength Surface to volume ratioGood cell adhesion High nutrient transport

Why Hydrogels?: Cell Culture SystemsBiocompatible substrate

Non-toxic and have no immunological responses

Cytoarchitecture which favors cell growthFlexibility for cells to rearrange in 3-D

orientationSeeded with appropriate growth and adhesion

factorsPorosity (i.e. channels for nutrients to be

delivered)

Why Hydrogels?: Cell Culture SystemsMimic cytomechanical situations

3-D space provides balanced cytoskeleton forces

Dynamic loading to promote cell growthFlexibility

Provide scaffold for various cellsConsistent, reproducible and easy to

construct

Why Hydrogels?: Drug DeliverySafe degradation productsBiocompatible High loading with ensured molecule efficacy High encapsulationVariable release profile Stable Inexpensive High quality

ConclusionHydrogels 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 fieldsApplications in medicine, engineering, and

biology

Questions