Tissue engineering with electric fields: Investigation of the shape of mammalian cell aggregates formed at interdigitated oppositely castellated electrodes

The shape of aggregates of cells formed by positive dielectrophoresis (DEP) at interdigitated oppositely castellated electrodes under different conditions was investigated and compared with calculations of the electric field gradient |[del, Hamilton operator]E²|, and the electric field E, and E². The results confirm that at low field strength the cells predominantly accumulate above the tips of the electrodes, but at higher electric field strengths the cells predominantly accumulate in the middle of the aggregate. For a given electrode size, a higher applied voltage significantly increases the aggregate footprint. Higher flow rates distort this pattern, with more cells accumulating at the electrodes that are upstream. Calculation of the electric field strength E, E² and the electric field strength gradient |[del, Hamilton operator]E²| in the interdigitated oppositely castellated electrode array shows that, at low flow rates, there is a strong correlation between the aggregate shape and the distribution of the electric field E and E², but not so between the aggregate shape and |[del, Hamilton operator]E²|. The results indicate that interparticle forces such as pearlchain formation strongly affect the aggregation process, but that, when positive DEP is used to make the aggregates, the distribution of the electric field E, or better E², can be used as a useful guide to the final aggregate shape.