Patterned Friction and Cell Attachment on Schizophobic Polyelectrolyte Surfaces

A series of copolyelectrolytes with randomly positioned fluorinated (hydrophobic) and zwitterionic (hydrophilic) repeat units was synthesized and used to assemble multilayers. Regular layer-by-layer growth was observed for polymers with a charge density as low as 6%. The hydrophobicity of these “schizophobic” surfaces increased with increasing fluorine content. Polymer-on-polymer stamping was used to create patterned areas of low and high friction, probed by lateral force microscopy using a modified hydrophobic tip. “Contractile” A7r5 smooth muscle cells adhered to the fluorinated surfaces, but the introduction of zwitterion functionality induced a motile, less firmly attached morphology consistent with the “synthetic” motile phenotype of this cell line. In contrast with cells well adhered (on fluorinated) or completely nonadhering (on zwitterionic) films, incorporation of closely spaced repeat units with strongly contrasting hydrophobicity appears to generate intermediate cell adhesion behavior

Roughness and Salt Annealing in a Polyelectrolyte Multilayer

The surface roughness of polyelectrolyte multilayers made from poly­(diallyldimethylammonium chloride), PDADMAC, and poly­(styrene sulfonate), PSS, was measured as a function of film deposition conditions. For dry multilayers, the significant roughness which builds up for thicker films is much more apparent for multilayers terminated with PSS. Corresponding roughness for PDADMA-capped multilayers may be seen by imaging in situ under electrolyte. Roughness may be substantially reduced, but not eliminated, by annealing in salt. Annealing does not lead to loss of polyelectrolyte from the film, even under conditions where the salt concentration is high enough to place the film properties beyond the glass transition. Roughness does not correlate with the molecular weight of the polyelectrolyte and is thus not caused by solution or film polymer chain conformations. The wavelength of the roughness features is approximately proportional to film thickness, which supports a mechanism whereby roughness is generated by anisotropic swelling due to water and polyelectrolyte addition in a manner similar to water uptake in hydrogels. Roughness is preserved by the glassy PSS layer and probably incorporated within the film as it grows