Web-structured films of an amphiphilic polymer from water in oil emulsion:Fabrication and characterization

Fabrication of micro surface morphology of cell culture substrates is one o f the current topics in biomaterials research. Recently we found that regul ar honeycomb structures with micrometer scale dimensions can be fabricated by simple casting of a dilute solution of amphiphilic polymers on solid sub strates. The honeycomb films were applicable to the cell culture substrates , in which cell adhesive parts are much smaller than the lateral dimension of cells. This article describes the fabrication and characterization of th in polymer films which have micrometer scale weblike structure. The weblike structure is fabricated by a two-dimensional emulsion templating. The web- structured films were prepared by easting a water in oil (W/O) emulsion ont o surfaces of glass, cleaved mica, and metal-coated glass. The films had lo wer regularity of surface morphology which indicated the polydisperse size distribution of water microspheres. The average diameter of the holes in th e web structure was considerably influenced by the extent of coalescence am ong the water microspheres, which were dispersed in the emulsion. A surface topographical study of the cast films using atomic force microscopy (AFM) showed that the cast films have web structure with submicrometer height and width. The bottom of the hole was scratched using an AFM tip loaded with a constant force of 100 nN. This way we could measure the thickness of the p olymer films to be 7 nm, which is thicker than the basal films of regular h oneycomb films. Optical characterization using surface plasmon resonance sp ectroscopy (SPR-S) and surface plasmon resonance microscopy (SPR-M) gave fu rther evidence for the existence of thin basal films on the web-structured films. Using these optical methods the thickness of the basal film could be estimated without any destruction of the cast films. The SPR-S measurement provided an average thickness of 14 nm for the basal films. Furthermore th e SPR-M provided plasmon contrast images of the web-structured films, which revealed that the thickness of the basal films varies for each hole in the web structure. Consequently these surface analyses demonstrate that the ca st films from W/O emulsion have a double-layered structure: web structure o f aggregated polymer as the major surface morphology and thin films of a po lymer as a basal structure which covers solid supports.