User:Gowerms/sandbox

Flow of media over a digital microfluidic chip demonstrating ability to manipulate media droplets.

Cell Culture Applications

Connecting the DMF chip to use in the field or world-to-chip interfaces have been accomplished by means of manual pumps and reservoirs to deliver microbes cells, and media to the device. The lack of extensive pumps and valves allow for the elaborate multistep applications involving cells performed with simple and compact use. Microbial cultures have been transferred onto the the chip and allowed to grow with the use of proper sterile procedures and temperature required for microbial incubation. To validate that this was a viable space for microbial growth, a transformation assay was carried out on the device. This involves exposing E.coli to a vector and heat shocking the bacteria until the DNA is taken up by them. This is then followed by running a DNA gel to assure that the wanted vector was taken up by the bacteria.

Human cells have also been manipulated in digital Microfluidic Immunocytochemistry in Single Cells (DISC) where DMF platforms were used to culture and use antibodies to label phosphorylated proteins in the cell.^[75] Cultured cells are then removed and taken off chip for screening. Another technique synthesizes hydrogels within DMF platforms. The process uses electrodes to deliver reagents to produce the hydrogel, and delivery of cell culture reagents for absorption into the gel.^[71][76] The hydrogels are an improvement over 2D cell culture because 3D cell culture have increased cell-cell interactions.^[76] Spherical cell cultures are another method developed around the ability of DMF to deliver droplets to cells. Application of an electric potential allows for automation of droplet transfer directly to the hanging cell culture.^[71][77] This is beneficial as 3 dimensional cell culture and spheroids better mimic in vivo tissue.^[77] Another use of DMF platforms in cell culture is its ability to conduct in vitro cell-free cloning using single molecule PCR inside droplets.^[78] PCR amplified products are then cultured within the cell by using a temperature gradient across the surface of the DMF platform.^[78]

Problems arising from cell culture applications of DMF are protein adsorption to the device floor, and cytotoxicity to cells.

To prevent adsorption of protein to the platform's floor, a surfactant stabilized Silicon oil or hexane was used to coat the surface of the device and droplets were manipulated atop of the oil or hexane. Hexane was later rapidly evaporated from cultures to prevent a toxic affect on cell cultures. Another approach to solve protein adhesion is the addition of pluronics to droplets in the device. Pluronics are general not cytotoxic but some have been shown to be harmful to cell cultures.

Bio-compatibility of device set up is important for bio analyses. Along with finding pluronics that are not cytotoxic, creating a device whose voltage and disruptive movement would not affect cell viability was accomplished. Through the readout of live/dead assays it was shown that both voltage required to move droplets, and the motion of moving cultures did not affect cell viability.