Mono-dispersed highly-charged poly(styrene/sodium styrene sulfonate) particles were prepared by two-stage shot-growth emulsifier-free polymerization. The solidified colloidal crystal (SCC) hydrogel was fabricated by the photoinitiated polymerization of acrylamide around the particles, and the strengthened solidified colloidal crystal (SSCC) hydrogel was then prepared by replacing some of the aqueous solution inside the SCC with an aqueous solution of monomer acrylamide and polymerizing the monomer within the SCC. Extinction spectra were obtained for both hydrogels, and slight broadening of the extinction peak for SSCC compared with that for SCC was observed. Dynamic viscoelastic measurement on SCC and SSCC hydrogels showed that the complex moduli G* for SSCC was nearly five times higher than that for SCC, indicating that the stiffness of the hydrogel was significantly improved upon formation of SSCC. It was also found that the crystalline lattice of SSCC was much more stable against large oscillatory deformation and it was more durable in urea sensing applications. (C) 2002 Elsevier Science B.V. All rights reserved.