A novel plasma source for surface chemical patterning and spatial control of cell adhesion.

The aim of this work was to develop and characterise a plasma source, which could be used to modify polymeric surfaces and incorporate well-defined regions of controlled chemistry. A novel plasma treatment system in which the ion energy and flux at the substrate can be independently controlled was developed. Argon plasma was separated into two regions with stainless steel meshes. The ion energy and flux in the substrate processing region was manipulated by applying an electrical bias to these meshes. This 'tailored' plasma was used to investigate the relative contributions of ions and vacuum ultra-violet (VUV) photons in the plasma treatment of polystyrene (PS). The level of surface modification induced by the plasma treatment was ascertained by X-ray photoelectron spectroscopy (XPS). Isolation of the VUV component by use of the biased mesh system revealed that in this system, these photons were the primary species causing oxygen incorporation into the PS surface. The modified PS was successfully employed as a culture substrate for bone marrow stromal cells (BMSC). By use of transmission electron microscopy (TEM) grids placed on the PS surface during exposure to the source, micron scale surface chemical patterns were produced. The pattern of hydrophilic and hydrophobic regions was visualised by condensing water onto the surface. On these substrates, bone marrow stromal cells (BMSC) formed patterns with features as small as 5 μm. The ability to independently control the ion energy and flux at the substrate has enabled the identification of the primary plasma species involved in surface modification of PS in this system. Combined with simple patterning technology, the novel plasma source has been used to produce well-defined micron scale chemical patterns on PS. The biological utility of such patterned substrates has been demonstrated by spatial control over cell attachment and spreading.