Enabling Long-Term Dielectrophoretic Actuation for Cell Manipulation and Analysis in Microfluidic Biochips

After several decades of revolutionary advancements in microelectronics technology and remarkable market growth, the semiconductor industry is now confronted with the rising trend of “More than Moore” (MtM). MtM brings new value to microelectronic devices by increasing the functionalities available for integration. Reliable devices with new functionalities will translate into applications that will expose new or non-existing markets, such as biomedical devices that could transformed the way healthcare is delivered (1). A number of companies have already started research efforts in developing biochips or platforms that can be integrated with cell-based sensors or “living sensors” (2, 3). These devices represent enormous opportunities for the microelectronics market, but at the same time the challenges are equally immense. The integration of electronic tools for manipulation and analyses of cells in microfluidic biochips has been growing in the last decade due to the characteristic attributes microscale technologies offer, as for example, fine control over cellular microenvironments, precise cell positioning and precise flow conditions. Among the existing tools to precisely position cells in a microfluidic device is dielectrophoresis (DEP). This electrokinetic technique can trap cells based on differences in the polarizability between the cells and the media they are suspended in, when both are exposed to a non-uniform electric field. However, certain conditions should be met when using DEP for cell-based analyses. One of the most important requirements when manipulating cells for later culture and analysis is to demonstrate that cell viability and function (e.g., proliferation, differentiation, motility) remain after the DEP manipulation (4). Microfluidic devices work in a fluid flow field environment where cells require some sort of actuation system to hold them in place. Under this fluid flow field condition cells that would be trapped by the DEP forces will easily be dislodged by the flow when the trapping forces are turned off. In order to easily position cells without their removal by the flow (long-term DEP actuation concept) we have engineered a hybrid cell adhesive material (hCAM) that allows for instantaneous cell trapping while at the same time cell growth and function is supported. This concept provides a simple and reliable mechanism for cell anchorage, while keeping the device from the need of more complex elements (e.g., valves and pumps). Long-term DEP actuation can also be used as a cell enrichment process before other steps of the cell-based assay are carried out. This will facilitate a number of studies where a higher number of cells is not only desired, but also needed due to the nature of the study. The use of the long-term DEP actuation concept has already been tested in microfluidic cell-based approaches (4, 5). Cell growth and differentiation (Figure 1), as well as cell entrapment in a multilayer device that allows for intercellular studies by means of cell co-culture on opposite sites of a polyester (PET) membrane (Figure 2) have both been demonstrated. The long-term DEP actuation approach represents a simple and fast method to load cells to a microfluidic device, while at the same time provides cell enrichment in a specific area within the system. Also, the engineered hCAM provides a cell microenvironment from where cells can produce physiologically relevant results Figure 1. Diagram showing the steps for the long-term DEP actuation system (A-F). (G) P19 cells differentiated within a microchannel 8 d after DEP trapping and anchoring. The vertical gray lines are the ITO electrodes used to trap the P19 cells prior to differentiation. Arrowheads point to the projections of differentiated P19 cells [Ref. 4].