Self-assembled two-dimensional thermoresponsive microgel arrays for cell growth/detachment control

Monodisperse poly(N-isopropylacrylamide-styrene) (PNIPAAmSt) microgels with different St/NIPAAm ratios have been synthesized via a one-step surfactant-free emulsion polymerization process. The resulting microgel dispersions were used to fabricate 2D arrays on the surface of silicon wafers/glass coverslips through dip coating. The thermal responsiveness of the PNIPAAmSt microgel arrays was examined by spectroscopic ellipsometry and the results unraveled that the thermoresponsive behavior of the arrays was highly consistent with the microgels dispersed in the bulk, showing high dependence on the content of styrene. The structure of the films varied from nonclose-packed 2D arrays to close-packed 2D arrays, depending on both properties of the microgels and array fabrication conditions. When the weight ratio of styrene was below 40%, the microgel arrays demonstrated effective control for cell growth and detachment across their volume phase transition temperatures (around 28 °C). The extent of swelling of the microgels was the key factor to determine whether the cells could detach from the film easily. For the rather close-packed 2D arrays prepared by the same kind of PNIPAAmSt microgels, the gaps between microgel particles showed no obvious effect on the rate of cell detachment.