Plasma Treatment Issues

 The fibronectin-coated surfaces change their hydrophilicity by adsorbing a layer

of protein on the surface, but the plasma treated samples modify the surface chemistry of

the base polymer. The literature implies that two factors seem to be at play here. One is

the modification of the surface by creating free radicals that when exposed to air form

peroxides on the surface.[92] This is the method used to add adhesion molecules and other

chemistry to the surface through graft copolymerization. However, as the plasma

treatment increases, an oxidized silica-like layer forms on the surface, especially if the

plasma contains oxygen. This is typically a problem when using silicone coatings as

high-voltage outdoor insulators. Studies have shown this silica-like layer to be up to 150

nm thick on the surface. This layer eventually cracks and then allows the low MW

oligomers to migrate to the surface.[116] This was not considered to be a problem with the

plasma treatment of the samples, but in analysis of the surfaces it was noticed that many

of the plasma treated elastomers had cracks. These were not seen after removing the

samples from the plasma chamber. As the samples were peeled off the dish to be placed

in the wells, cracks were formed that were not there before or immediately after

treatment.

 The main concerns with this phenomenon is the influence the cracks would have

on the cells compared to the intended topography and the effect that a harder silica-like

surface layer would have on the modulus. To examine this affect, a textured sample of

15% vinyl tris silicone was plasma treated under the same conditions as the samples and

examined using optical profilometry and atomic force microscopy (AFM), as seen in

Figure 3.5, Figure 3.6, and Figure 3.7. The sample was bent to simulate removal and