Ca2+-induced complexation between thermally sensitive spherical poly(N-vinyl-caprolactam-co-sodium acrylate) microgels and linear gelatin chains in water

The temperature dependence of the complexation between thermally sensitive spherical poly(N-vinylcaprolactam-co-sodium acrylate) microgels and linear gelatin chains without and with the addition of Ca2+ was studied by a combination of static and dynamic laser light scattering over a wide range of the gelatin/microgel ratios ([G]/[M]) in terms of the complexʹs average hydrodynamic radius (〈Rh〉), weight average molar mass (Mw), average aggregation number (Nagg), and average chain density (〈ρ〉). Without Ca2+, the complexation is weak and each complex, on an average, contains not more than two microgels. In the presence of Ca2+, the complexation occurred at ∼32°C is much stronger and the onset of complexation is independent of [G]/[M], but both Nagg and 〈ρ〉 decrease as [G]/[M] increases because the adsorption of too many hydrophilic gelatin chains on the microgels hinders the complexation and reduces the shrinking of the complexes. The complexation is essentially reversible but there exists a slight hysteresis on cooling. On the basis of this study, a gel composite made of microgel and gelatin was prepared and its biomedical applications have been considered.