backbone is an interesting phenomenon, and is especially important in PDMS systems

due to its low Tg (-123C). Most of the surface rearrangement in plasma treated high

surface energy PDMS samples is due to the migration of low surface energy, low MW

PDMS oligomers from the bulk to the surface.1116' 117]

 Ostuni and Whitesides used the low surface energy of silicones to selectively

pattern the surfaces of textured elastomer substrates with protein solutions. Since the

contact angles of a fibronectin/physiological buffered saline (PBS) solution and a bovine

serum albumin (BSA)/PBS solution on their silicones were over 1000, they could trap air

inside of wells by carefully placing drops of the solutions on the surfaces. This allowed

for the flat surfaces above the well to have one of the proteins adsorbed, and by rapidly

changing the solution and adding a vacuum to pull out the air bubbles, the bottom of the

wells were patterned with another.[64]

 Schmidt and von Recum characterized Dow Corning's Medical Grade Silastic

(MDX4-4210) silicone after texturing the surface with various pillars and wells. They

determined the surface energy of their materials by using the stationary drop method I18]

using diagnostic liquids that were not identified. They calculated Zisman plots that graph

the cosine of the contact angle versus the surface tension of the diagnostic liquid. All of

their samples, both textured and untextured had critical surface tensions of 20.5-21.5

dynes/cm.[119] They showed that the surface energy per unit of surface area decreased for

higher densities of features, and concluded that the surface energy either was not greatly

affected by their topography, or that contact angle methods are not sensitive enough to

detect the difference.