Abstract
Screening cells is often the first step in multitude of in vitro assays modernly used in drug testing and in molecular and cell biology. However, the screening algorithm is often based on detecting the fluorescence intensity, limiting the type of assays conducted on cells. Here, we have developed a microfluidic platform integrating droplet-generation and cell-culture systems for screening cells based on long-lasting and transient responses. This fully automatic microfluidic device is capable of 1) trapping small cell populations in an array of predetermined locations, 2) inspecting cells in a microscope for long periods of time, and 3) selectively retrieving samples of supernatant fluids in droplets from different cell colonies in individual traps for measurements of metabolites and autocrine/paracrine signaling molecules. Local altering microtopography of transparent elastomeric substrate at addressable locations were used to trap and release small fluid volumes (droplets) and cells. Immiscible solution was introduced to main channel isolating each cell culture microwell. Droplets of various sizes could be generated by precise control of flow rates in immiscible solution and deflection of elastomeric substrate. Non-adherent HL-CZ and adherent MDA-MB-231 cell lines were cultured in the device. Results suggested that both cell types could be cultured in isolated microwells for seven days without exchanging cell culture medium; however, exchanging cell culture medium every day for longer times reduced the survival rate. What’s more, MDA-MB-231 cells appeared sensitive to thickness of the elastomeric substrates. Survival rate of MDA-MB-231 cells was much higher when cultured on elastomeric substrates with 60 micrometer thickness in contrast to 30 micrometer. In summary, we have developed a microfluidic platform capable of long-term cell culturing and sampling cell culture medium over time, and have a great promise to yield new insights into cell behavior and development.