Protocol efficiently measuring the swelling rate of hydrogels

Hydrogels are polymeric materials which can swell in water and retain a significant fraction of water within their structure without dissolving in water. Swelling rate is one of the most important properties of hydrogels. To measure the swelling rate, the profile of swelling capacity versus time of a hydrogel sample is obtained by performing free-absorbency capacity measurements at consecutive time intervals. Traditionally, either the tea-bag method, the sieve method, or the filtration method is used for the free-absorbency capacity measurements depending on the amount of the available sample and the desired precision. However, each method has its own systematic drawbacks. In this paper, a novel method called sieve filtration method is proposed for the measurement of the swelling rate of hydrogels. A protocol for this method is described in detail. The measurement results obtained from the proposed method and the traditional methods are compared. The proposed method has the following advantages over the traditional methods: • It is more efficient than the traditional methods due to full contact of the hydrogel powders with water or aqueous solution as well as fast and complete removal of excessive fluid from the water-absorbed gel. • It enables repeatable and reproducible measurement of the swelling rate of hydrogels. • It is easy to implement, suitable for various types of hydrogels and aqueous solutions; and it requires small amounts of sample, minimal technical skill, and inexpensive equipment.