Patterning of Embryonic Stem Cells Using the Bio Flip Chip

Summary

We demonstrate a simple method for placing cells at desired locations on a substrate. This method patterns cells by flipping a silicone chip containing microwells filled with cells onto the substrate. This method provides a new way to modulate diffusible and juxtacrine signaling between cells.

Abstract

Cell-cell interactions consisting of diffusible signaling and cell-cell contact (juxtacrine signaling) are important in numerous biological processes such as tumor growth, stem cell differentiation, and stem cell self-renewal. A number of methods currently exist to modulate cell signaling in vitro. One method of modulating the total amount of diffusible signaling is to vary the cell seeding density during culture. Due to the random nature of cell seeding, this results in considerable variation in the actual cell-cell spacing and amount of cell-cell contact, and cannot prescribe the local environment. A more specific approach for modulating cell signaling is to use molecular inhibitors or genetic approaches to knock down specific signaling proteins, but both of these methods are best suited to manipulating small numbers of molecules. Here, we demonstrate a new approach to modulating cell-cell signaling that modulates the local environment of a cluster of cells by placing different numbers of cells at desired locations on a substrate. This method provides a complementary way to control the local diffusible and juxtacrine signaling between cells. Our method makes use of the Bio Flip Chip (BFC), a microfabricated silicone chip containing hundreds-to-thousands of microwells, each sized to hold either a single cell or small numbers of cells. We load the chip with cells simply by pipetting them onto the array of wells and washing unloaded cells off the array. The chip is then flipped onto a substrate, whereby the cells fall out of the wells and onto the substrate, maintaining their patterning. After the cells have attached, the chip can be removed (or left on). This approach to cell patterning is unique in that it: 1) doesn't alter the chemistry of the substrate, thus allowing cells to proliferate and migrate; 2) allows patterning onto any substrate, including tissue-culture polystyrene, glass, matrigel, and even feeder cell layers; and 3) is compatible with traditional microcontact printing, allowing the creation of extracellular matrix islands with cells placed inside those islands. In this video, we demonstrate the patterning of mouse embryonic stem cells onto tissue-culture polystyrene using the BFC.

Protocol

Making a BFC

BFCs are made by molding polydimethylsiloxane (PDMS) over a 4" Si master wafer.

Making a master wafer

1. Start by dehydrating the Si wafers for 30 min at 130°C.
2. Place the wafer on a spin-coater, pour SU8-2050 (Microchem) onto the wafer, ramp from 300 rpm/s to 3000-4000 rpm, and spin for 30 s to yield feature heights of 40-30 mm, respectively.
3. After spinning, place the wafer on a 65°C hotplate, immediately ramp up the temperature to 95°C for 5-6 min, and then ramp it down to 65°C.
4. Expose the wafers to a UV dose of 200 mJ/cm²

Discussion

Although the protocol and video shown here describe using the BFC ¹ to pattern mouse embryonic stem cells (mESCs), BFCs can be used to pattern practically any cell type of interest. The only change one may need to make is to alter the size of the microwells. In our experience, to use the BFC to pattern single cells of another cell type, a microwell diameter and height equal to 10 microns greater than the unattached cell diameter works best.

BFCs can also be used to pattern cells on.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
PDMS	Dow Corning	Sylgard 184
Silicon master mould
Tissue culture dishes	Falcon BD	35-3001	35 mm
3/4" binder clips
PBS
hexamethyldisiloxane	Shin-Etsu MicroSi
New Item	MicroChem Corp.	SU8-2050
PM acetate
Isopropanol
BSA			7.5% Bovine Serum Albumin