A micro-tool for mechanical manipulation of in vitro cell arrays

This paper reports on the fabrication and test of a micro-tool for in vitro cell array manipulation. The device consists of a micro-post array with supporting pillars which can be used to apply simultaneous mechanical force to all elements of a cultured cell array. The mechanical pulling force has been shown to initiate neurite outgrowth, thus allowing one to potentially engineer a large living neural network having defined connectivity. In order to realize this goal, the designed micro-tool must have some important features. For example, it must be transparent to allow visual access through a light microscope. It must also have a gap of 3-5 mum between the tips of the posts and the culture dish to avoid post breakage and to allow matching the height of individual cells. We have used silicon bulk micromachining and anodic bonding to fabricate the micro-post array having the required features. The micro-tool reported in this paper has overall dimensions of 5 x 5 mm(2), which includes an array of 2,500 posts (5 x 5 mum(2)) supported by four pillars (600 x 600 mum(2)). The posts are made from a SiO2/Si3N4 sandwich while the pillars have an additional silicon layer for extra support. The micro-tool was tested on randomly seeded embryonic chick forebrain cells. Moving the micro-post array relative to the cell culture substrate at a constant speed of 36 mum/hour resulted in several neurite-like cytoplasmic processes that were initiated and elongated from cells that had adhered to the posts.