We are investigating whether physiologically relevant multi-cellular structures can be artificially engineered by dielectrophoresis - a technique for moving cells using radio-frequency electrical fields. We are using insulin-secreting cell lines (beta-TC-6 and INS-1), commonly employed by cell physiologists to investigate how pancreatic structures, known as islets of Langerhans, regulate insulin levels in the blood. Islets constitute approximately 1-2% of the mass of the pancreas, each islet being ~50-500 µm in diameter, containing ~1000 cells. 

Our long-term aim is to use artificial assemblies of insulin secreting cells, that mimic islets, in assays for monitoring cell-cell signaling through gap junctions, and to understand how these control the synchronous functioning of islets.  This work could also lead to the engineering of islet implants to alleviate diabetes.

As shown in the graph below, analysis of the electrorotation spectrum for a cell enables the dielectrophoretic behavior to be predicted.  The applied radio frequency fields induce electric charge relaxations on the cell surface and in the surrounding fluid.  The electrorotation and dielectrophoretic responses are determined by the phase relationships between these charge relaxation times, and can be modeled to a fair degree of accuracy.

We have characterized a statistically relevant number of beta-TC-6 and INS-1 cells for their electrorotation (and hence dielectrophoretic) properties for a range of suspension medium conductivities and glucose content.  The data indicate that for a signal frequency of 10kHz, using isotonic suspending media conductivities of 25~75 mS/m, the cells will be repelled from the electrodes by negative dielectrophoresis.  At frequencies around 100kHz the cells experience no force, whilst for frequencies between 1-10MHz they are attracted to the electrodes by positive dielectrophoresis (Pethig et al., 2005).

Results:  Based on the electrorotation data, we have established the conditions where the cells can be corralled together by negative dielectrophoresis, as shown below.

The microelectrodes used to create the cell assemblies are formed of gold evaporated onto a seed layer of chromium on glass.  The gold is patterned by photolithography into a ‘polynomial’ geometry to maximize the field gradients required for dielectrophoresis.  Due to the planar nature of these electrodes, the cell assemblies produced are 2-dimensional in form.  In order to produce 3-dimensional cell structures, we are investigating a new design of dielectrophoresis chamber incorporating transparent ITO electrodes.  This new arrangement enables us to produce an array of 100 column-shaped cell structures (diam. ~150µm, height ~120 µm) with each column containing ~1,000 cells .  These engineered cell structures are thus of the same size and cell density as an average islet of Langerhans.