Poly(N-vinylcaprolactam) microgels and its related composites

Spherical hydrogels were prepared by precipitation copolymerization of N-vinylcaprolactam and sodium acrylate [P(VCL-co-NaA)] at 60°C. As a thermally sensitive polymer, the increase of temperature in the range 25–40°C can lead to a continuous shrinking of PVCL homopolymer chains. The copolymerization of a few molar percent of NaA into a PVCL chain increases its swelling extent and shifts its shrinking temperature slightly higher. Our results revealed that in the shrinking process, calcium ions (Ca2+) induced a profound complexation of the P(VCL-co-NaA) microgels at a critical temperature (Tc) which was nearly independent of the NaA content. However, both the rate and degree of the complexation increase as the NaA content increases at Tc. One the basis of this study, we further studied the complexation of P(VCL-co-NaA) microgels with gelatin in the presence of calcium ions and prepared chemically crosslinked of the gelatin gels with embedded P(VCL-co-NaA) microgels. Our results showed that the shrinking of the embedded P(VCL-co-NaA) microgels could lead to the shrinking of gelatin gels. The biomedical application of this gelatin/microgel composite have been exploited.