In Situ Gelation of P(NIPAM-HEMA) Microgel Dispersion and Its Applications as Injectable 3D Cell Scaffold

In this work we try to develop a new thermal gelling injectable scaffold for three-dimensional cell culture. Instead of using linear, branched, or grafted macromolecules, thermosensitive microgel particles or microspheres are used as building blocks for the construction of the macroscopic hydrogel scaffold. As a proof of concept, thermosensitive poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (P(NIPAM-HEMA)) microgel particles were synthesized, which present a volume phase transition temperature (VPTT) at about 29 degrees C. Rheological test shows that the concentrated P(NIPAM-HEMA) microgel dispersion is colloidally stable when heated above its VPTT, indicating hydrophobic interaction alone can not induce thermal gelation of the dispersion. In the presence of a low concentration of CaCl2, however, with the introduction of additional ionic cross-linking, the microgel dispersion gelates and forms macroscopic hydrogel. Gelation temperature of the microgel dispersion decreases with increasing ionic strength. SEM observation reveals that the resultant bulky gel has an interconnected porous microstructure. 293T cells, a human cell line, were encapsulated inside the hydrogel by simple mixing with the microgel dispersion at room temperature and heating to 37 degrees C. MTT (3-[4,5-dimethylthiazol-2-yl]-3,5-diphenyl tetrazolium bromide) assays reveal that the cells are viable and proliferate inside the 3D scaffold.