Cell attachment on microscopically textured silicon surfaces

Center, New York State Department of Health andSchool ofPublic Health, University at Albany, Albany NY 12201, andRensselaer Polytechnic Institute, Troy NY 12180ABSTRACTTo assess the effect of surface topography on cell attachment, central nervous system (astroglial cells) cells were grown onsurfaces patterned with two different types of texture. Reactive ion etching (RIB) was used to induce nanometer-scaleroughness in silicon wafers. In a subsequent wet etch, photo-patterned resist protected selected areas of the surface,resulting in a pattern of modified and unmodified texture. Scanning electron microscopy (SEM) showed that theRIE-roughened "primary" surface consists of randomly positioned columnar structures (diameter 50 nm, height 250 nm).The wet-etched "secondary" surfaces had shorter and more sparsely distributed projections, controlled to a degree by wetetch duration. Confocal microscopy and SEM demonstrated that transformed astroglial (LRM55) cells preferred secondarysurfaces. The morphology of cells on secondary surfaces depended on wet etch duration. With brief wet etch, cells hadstellate or mounded morphology and were not closely adherent to the surface. With long wet etch, cells had anepithelial-like morphology and were closely adherent to substrates. Under all conditions, cells discriminated betweenprimary and secondary surfaces. In contrast to LRM55 cells, astrocytes in primary cell culture preferred primary surfaces.Thus changes in surface topography produce cell-specific selectivity and change cell attachment characteristics.Keywords: reactive ion etching, surface topography, cell attachment, astrocytes, silicon1. INTRODUCTIONMicrofabrication methods have been used for the production of patterned silicon surfaces for studying cell adhesionand migration. These surfaces contain patterns typically of micrometer scale"2 but rarely contain features smaller than 100nanometers3. These studies demonstrated that cells align along transitions orattach selectively to chemically modifiedregions68.We have used reactive ion etching (RIE) to produce surfaces with large numbers of randomly arrayed nanometer-scale structures9". RIB can precipitate solids from the plasma depositing them on the surface ofa silicon wafer. Underetching conditions, this produces a "mask" protecting portions of the surface from bombardment by reactive ions resultingin a non-uniform etch. In this study, we have used this affect to produce silicon surfaces containing random arrays ofnanometer-scale structures. This procedure was followed with conventional photolithography and wet chemical etching tosuperimpose micro-scale patterns on these surfaces. The resulting wafers contain complex patterns with two differentsurfaces—a primary surface produced by RIE and a secondary surface resulting from the wet etch.Topographically patterned surfaces were used to study the effects of nano-scale structures on cell attachment. Thesize and shape of the nano-scale structures was modified by varying the duration of chemical etching. The attachmentbehavior of cells was dependent on surface characteristics and correlated with the size and shape of the nano-scalestructures. Side-by-side presentation of different surfaces demonstrated the ability of cells to discriminate one surface fromanother.