Cool microcontact printing to fabricate thermosensitive microgel patterns.

A facile method, cool microcontact printing (cool μCP), of fabricating microgel patterns under ambient conditions is developed. By using spontaneously condensed water on the surface of cold items and the phase transition of polymer microgels below the lower critical solution temperature (LCST), a cool poly(dimethylsiloxane) (PDMS) stamp can be easily decorated with a thin layer of water ink and its pattern can substantially transfer to a substrate that is assembled with microgels. As a proof of concept, one kind of thermosensitive microgel (i.e., poly(N-isopropylacrylamide) (pNIPAM)) is selected to demonstrate our method. A series of pNIPAM microgel patterns with various geometries can be easily generated by featured PDMS stamps through a cool μCP method. The results of control experiment using room-temperature PDMS stamps or patterning the pNIPAM microgel-incorporated fluorescent probe reveal that condensed cold water on a cool PDMS stamp plays an important role when microgel particles are lifted off. In addition, it is also observed that both humidity and contact pressure have effects on the shapes of the pattern fabricated by cool μCP, and more precise or sophisticate patterns can be obtained by adjusting the conditions. It is envisioned that this practically available method, as a good extension to μCP, can facilitate the design of complex patterns, affording great convenience for many inherent applications ranging from photonics to chemical sensing to biotechnology.