gcsescience.com                                                          70                                                          gcsescience.com

Products from Oil

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

A hydrogel is an example of a smart material. It can change its structure
in response to salt concentration, pH and temperature.

Hydrogels are used in nappies, wound dressings and drug delivery systems.
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
which means that it can be removed easily without damaging the skin. 

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.

We shall look at how the hydrogel on the previous page changes
in response to an increase in salt concentration.
The chains in the cross linked hydrogel which are uncoiled
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.

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.

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.

        Headings        Polymers        Search        Questions        

gcsescience.com     Contents     The Periodic Table     Index     Quizzes    gcsescience.com

Copyright © 2008 Dr. Colin France. All Rights Reserved.