Liposomes and Gels

Gels

Viscoelastic solid like materials comprised of an elastic cross-linked network and a solvent

Entrapment and adhesion of the liquid on a solid 3d matrix

Gel characteristics - water soluble polymers

Increased viscosity above gels

Rubber like elasticity appearance

retain shape under low stress

deform at high stress

New gels

Derived from low molecular mass compounds

Act as a smart gel - respond to environment

Classification of gels

Source - natural/artificial

Medium- organo/hydro/xero

Constitution - supramolecular/macromolecular

Cross linking - physical/chemical

Hydrogels

Retain significant volume of water

Remain water insoluble

Hydrogel uses

topical drug delivery

Soft contact lenses

Implant coating

Hydrogel diffusion

If gel is hydrated, diffusion occurs through pores

I gel hydration is low, drug dissolves in polymer and transported between chains

Hydrogel cross linking

Increases the hydrophobicity

decreases diffusion rate of drug

Swelling of hydrogels

Swollen state - low temp - drug release on

Shrunken state - high temp - off

Gel formation from macromolecular compounds

Either chemical cross-linking or physical interactions

Strong bond formation

Can not be dissolved

Thermally irreversible

Formation from weak non-covalent interactions

Reversible

Type 1 gels

Irreversible

3d network formed by covalent bonds between macromolecules

Type 2 gels

Heat-reversible

Held by intermolecular bonds

Gel on cooling below gel point

e.g. PVA

Supramolecules

Gels derived from low molecular mass compounds

How are supramolecular gels formed

Self-aggregation of small gelator molecules to form self assembled fibrillar networks - SAFINS

SAFINS

formed through non-covalent interactions

These are weak so readily transferred to a fluid by heating

Thermally reversible

Supramolecular molecules condense

1. Ordered aggregation forming crystallisation
2. Random aggregation forms amorphous precipitate
3. Between process yield a gel

Supramolecular gels application

Organogels - cosmetics

Biomedical application - tissue engineering