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Polymers - Smart Materials - Hydrogels.
Wound Dressings and Drug Delivery.

What are the Uses of Hydrogels?

Hydrogels are used to make soft contact lenses, nappies,
wound dressings and drug delivery systems.

How is a Hydrogel used for a Wound Dressing?

A wound dressing is put over a cut in the skin to help the skin heal.
The hydrogel is applied as a thin layer which is moist and soothing.
It stops the wound drying out and protects it from infection.
The hydrogel can control bleeding and does not stick to the surface
so it can be removed easily without damaging the skin.

How is a Hydrogel used for Drug Delivery?

In drug delivery the hydrogel can release an antibiotic (or other drug)
at a controlled rate to the body tissue beneath. This is better than
taking an antibiotic as a pill by mouth which has an effect on the
whole body and increases the chance of a bad reaction to the drug.

The hydrogel is called a carrier when it is loaded with a drug.
As the swelling of the hydrogel increases, the chains of the
cross linked network move further apart and the drug
can diffuse more quickly through the hydrogel to the skin.

What is the Structure of a Hydrogel with Salty Water?

We shall look at how the hydrogel on the previous page
changes in response to an increase in salt concentration.
The chains in the uncoiled cross linked hydrogel
attract water molecules by hydrogen bonding.
As more salt (for example sodium chloride) is added
to the hydrogel, the positive sodium ions take up places
next to the negative oxide ions and there is less space
for the water molecules as shown in the picture below.

This makes the hydrogel lose some water. The
negative charges along the chain repel each other less in the
presence of the sodium ions and so the chains become more
coiled up. This also squeezes out water from the hydrogel.
The result is that a small change in salt concentration can have
a significant effect on the amount of water leaving the hydrogel.

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