Hong Ooi, Ing, et al. “Swelling Properties of Poly(N-Isopropylacrylamide) Calcium Alginate Interpenetrating Polymer Network Hydrogel Containing Zirconia”. Asian Journal of Chemistry, vol. 27, no. 9, May 2015, pp. 3489-93, doi:10.14233/ajchem.2015.19015.