Hydrogels - Smart Polymers

Materials which adjust their properties in response to environmental factors such as temperature, pH and ionic strength are rapidly evolving and known as smart materials.

Hydrogels are hydrophilic polymers that can retain many times their own weight in water. They are often polymers of carboxylic acids. The acid groups ionise in water, leaving the polymer with several negative charges along its length. This has two effects. Firstly, the negative charges repel each other and the polymer is forced to expand. Secondly, polar water molecules are attracted to the negative charges. This increases the viscosity of the resulting mixture because the polymer chain now takes up more space and resists the flow of solvent molecules around it.

There are a large number of hydrogels and they expand and contract at different pH values, temperatures and ionic concentrations (Fig.4). A review by Laftah et al .., presented adetailed description of definitions, classification, main properties including swelling, and application of polymer hydrogels . They were termed as “super absorbent polymer hydrogles”. This property is now a days has been extensively used in baby-diapers. Kopecek and chaterji classified smart polymers in her review on the basis of structural properties, types of stimuli they respond and then described their microfluidic applications including the applications in supramolecular chemistry and molecular imprinting .

So many other research work has been recently reviewed on hydrogels like their use in “Smart valve: Polymer actuato, the fine tuning of poly(N isopropylacrylamide) PNIPAM with temperature response to human body and its versatility as interpenetrating polymer network (IPN), double network nanocomposites etc.. Photolithographic patterns using smart hydrogels  as actuators were studied , their use as ultrasonic quantification sensors , controlled drug release , cell culture . pressure/ Microwave sensors . cost effective conductors as a catalysis medium with metal composites.

The criteria of being “ so smart ‘ came from their history of being a simple network , to most versatile in their functioning like electroconductivity , pharmacy and therapeutics .