Thermal and Swelling Characteristic of Self-Inflating Hydrogel Expander

Objective: Hydrogels are three-dimensional hydrophilic polymers that absorb large amounts of biological fluids. This behaviour, together with their biocompatibility, has resulted in their use as self-inflating tissue expanders.  In understanding this swelling behaviour, the swelling degree of the hydrogel is crucial. There are various factors that can influence the expansion of the hydrogel which includes physical and chemical interactions within the polymer network system as well as the environment where the swelling takes place.  There is a need to use these self-inflating tissue expanders on the oral cavity. This part of the body will be subject to a wide range of temperatures and so an understanding of the expansion behaviour of the hydrogels under these conditions is important. Therefore, the purpose of this study are (i) to investigate thermal characteristics of the hydrogel polymer and (ii) to evaluate the swelling characteristics of self- inflating hydrogel expanders at two different temperatures. Method: MMA-co-NVP copolymer powder was tested using differential scanning calorimeter and thermal gravimetric analyser. Two groups of 20 x 5 mm MMA-co-NVP hydrogel expanders (n=5) were immersed in Hartmann’s solution at 4°C and 37°C until the equilibrium swelling state was achieved.  The degree of swelling was calculated and the rate of swelling was determined. Result: The glass transition temperature and the decomposition temperature of the hydrogel were 151.26°C and 345.00°C respectively. The degree and rate of swelling at maximal state for the hydrogel at 37°C was significantly higher when compared to 4°C. Conclusion: The findings suggest that MMA-co-NVP is very stable at body temperature. However, the temperature has a significant effect on the degree and rate of swelling at equilibrium even though MMA-co-NVP was not generally recognised as a temperature sensitive hydrogel.  Further work is required to ascertain this finding using other types of physical hydrogels.