Hydrogels

presentation by:

Aarsha surendren

msc bps cbpst ,eloor

OverviewDefinitionClassificationPreparationUsesExample-PEGImportant PropertiesDrug DeliveryBiological scaffold

What is a Hydrogel?Hydrogels are the 3D network of hydrophilic

polymers held together by assosiation bonds such as

covalent bondsWeaker cohesive forces hydrogen bonding Ionic bond Intermolecular hydrophobic associationThe networks are composed of homo polymers or

copolymers, and are insoluble due to the presence of chemical crosslinks or physical crosslinks, such as entanglements or crystallites.

These crosslinks provide the network structure and physical integrity.

Hydrogels is a network of polymer chains that are hydrophilic, water insoluble ,sometimes found as a colloidal gel in which water is the dispersion medium.

Hydrogel are highly adsorbent natural or synthetic polymers.

Hydrogel can contain over 99.9% water.The high water content of the material contributes to their biocompatibility.

They exhibit a thermodynamic compactability with water which allow them to swell in aqueous media.

Method of Preparationof hydrogels

CrosslinkingIsotactic ultra high pressureNucleophilic substitution reactionUsing gelling agentsUse of irradiationFreeze thawing

How they’re made.

Can cross link polymers via:HeatPressure Chemical reactionCrosslinking using enzymesPhotopolymeriziation

Use light UV, visibleRadiation

Electron beams Gama rays X-rays

pH sensitive hydrogelspH responsive

hydrogels contain acidic or basic pendent groups

In appropriate media these groups ionize forming charges on the gel

Increases swelling forces due to localization of charges on the pendent group

Mesh size can change significantly with little change in pH

Temperature sensitive hydrogelsExhibit lower

critical solution temperatures (LCST), temperature at which at which a polymer is solubleAbove this

temperature the hydrogel is hydrophobic and does not significantly swell in water.

Polyethylene Glycol (PEG)Properties

Clear, viscous, odorless, miscible in water, non-toxic

UsesWound dressing, soft

tissue replacement, drug delivery.

Laxatives, Skin Creams, Lubricants, Food Additive, Twinkies?

Advantages of hydrogelsHydrogels possess a degree of flexibility very similar

to natural tissue,due to their significant water content.Entrapment of microbial cells within hydrogel beads

has the advantage of low toxicity.Environmentally sensitive hydrogels have the ability to

sense changes of pH ,temperature , or the concentration of metabolite and release their load as results of such a change.

Timed release of growth factors and other nutrients to ensure proper tissue growth.

hydrogels have good transport properties .Biocompactability.Can be injected. easy to modify.

Disadvantages of hydrogelsHydrogels are expensive.The surgical risk associated with the device

implantation and retrieval .Hydrogels are non-adherent ;they may need to

be secured by a secondary dressing.They are used as contact lenses .These cause

lens deposition, hypoxia, dehydration and red eye reactions.

They have low mechanical strength.Difficulty in handling.Difficulty in loading.Difficulty in sterilization .

Applications of Hydrogel

Drug DeliveryA dry hydrogel contains a water soluble drugDrug is immobile in the hydrogel matrix and

begins to diffuse out when the hydrogel begins to swell with water.Depends on two processes:

Water migration inward Drug diffusion outward

Drug Delivery

Drug delivery electric discharge method

Drug Delivery

SCAFFOLD MATERIALS: PolymerTwo categories:A) Materials for porous solid-state scaffolds and B) Materials for hydrogel scaffolds The chosen of scaffolding materials depends on the

environment of original ECM due to specific application for scaffold. Ex:CartilageECM=Hydrated,Bone ECM=Dense

Materials for hydrogelScaffolds

Application: Blood vessel, skin, cartilage, ligaments, and tendons

Material properties:• Ability to fill irregularly

shaped tissue defects.• the allowance of

minimally invasive procedures such as arthroscopic surgeries

• the ease of incorporation of cells and bioactive agents

Materials for porous solid-state scaffolds

Application: Bone tissue engineering

Material properties: Solid and stable porous

structures.Not dissolve or melt under

in vitro tissue culture condition or when implanted in-vivo

Degrade through hydrolysis of the ester bonds

POLYGLYCOLIC ACIDMost widely used scaffolding

polymersPGA is hydrophilic nature so that it

degrades rapidly in aqueous solutions or in vivo, and loses mechanical integrity between two and four weeks.

processed into non-woven fibrous fabrics

Polylactic acid (PLA)The extra methyl group in the PLA repeating unit (compared with PGA) makes it more hydrophobic, reduces the molecular affinity to water, and leads to a slower hydrolysis rate.It takes many months or even years

for a PLA scaffold or implant to lose mechanical integrity in vitro or in vivo

Collagena major natural

extracellular matrix component

fabricated scaffolding materials

Biological scaffolds in tissue engineeringscaffold made from 99%

polyglycolic acid and 1% polylactic acid Same material used in

dissolving surgical stitchesFibers woven into a loose

mesh that was 97% air (not water) room for cells to grow into

Scaffold formed into shape of ear Seeded with cartilage cells

from donorUse “Nude Mouse”

ANY QUESTIONS?????

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