POLYMER GELS WITH ENGINEERED ENVIRONMENTALLY RESPONSIVE SURFACE PATTERNS

The polymer gels called hydrogels may be induced to swell or shrink (t aking up or expelling water between the crosslinked polymer chains) in response to a variety of environmental stimuli, such as changes in pH or temperature, or the presence of a specific chemical substrate(1). These gels are being explored for several technological applications, particularly as biomedical materials(2). When hydrogels swell or shrin k, complex patterns may be generated on their surfaces(3-7). Here we r eport the synthesis and controlled modulation of engineered surface pa tterns on environmentally responsive hydrogels. We modify the characte r of a gel surface by selectively depositing another material using a mask. For example, we use sputter deposition to imprint the surface of an N-isopropylacrylamide (NIPA) gel with a square array of gold thin films. The periodicity of the array can be continuously varied as a fu nction of temperature or electric field (which alter the gel's volume) , and so such an array might serve as an optical grating for sensor ap plications. We also deposit small areas of an NIPA gel on the surface of an acrylamide gel; the patterned area can be rendered invisible rev ersibly by switching the temperature above or below the lower critical solution temperature of the NIPA gel. We anticipate that these surfac e patterning techniques may find applications in display and sensor te chnology.