Researchers have developed a microfluidic device that automatically orients hundreds of fruit fly and other embryos to prepare them for research. The device could facilitate the study of such issues as how organisms develop their complex structures from single cells -- one of the most fascinating aspects of biology.
Lu designed and fabricated the device with the help of Kwanghun Chung and Emily Gong, who worked on the project as Georgia Tech graduate and undergraduate students, respectively. Fabricated from polydimethylsiloxane (PDMS), the compact device is the size of a microscope slide and contains approximately 700 traps for embryos, which are shaped like grains of rice but smaller in size.
In operation, fluid flows through an "S"-shaped channel wide enough for embryos of any orientation to move easily through it. The fluid efficiently directs the embryos toward the traps, while sweeping out extra and improperly trapped embryos.
"The flow pattern significantly increased the frequency at which embryos contacted the traps and were loaded into them," explained Lu. "Experimentally, we found on average 90 percent of the embryos became trapped in the device, which will be valuable for studies that only have a small number of embryos available."
When an embryo approaches an empty trap, it experiences non‐uniform pressure and shear from the surrounding fluid. The resulting force flips the embryo vertically and inserts it into the cylindrical trap in an upright position, with its dorsoventral axis parallel to the ground. The embryo is then secured inside the trap, without any need for user intervention or control. The lock‐in feature allows the device to be disconnected from the rest of the hardware and transported for imaging or storage with the embryos enclosed.
"At one point, we mailed a microfluidic embryo trap array device full of trapped fruit fly embryos to our collaborators at Princeton University, and upon arrival, the embryos were still upright in their locked traps," said Lu.
To demonstrate the device's capabilities, Lu collaborated with Stanislav Shvartsman, an associate professor in the Department of Chemical and Biological Engineering at Princeton University, and his graduate student Yoosik Kim. The Princeton researchers used the device to quantify gradients of signaling molecules called morphogens in fixed embryos and also used it to monitor nuclear divisions in live embryos.
In one experiment, the Princeton researchers determined the spatial extent of the distribution of Dorsal, a transcription factor that initiates the dorsal‐to‐ventral patterning of the Drosophila embryo. They also demonstrated that this gradient could be quantitatively compared between wild-type and mutant embryos.
"The trap array device provided a significant increase in the number of fixed and live embryos we could image simultaneously and allowed us to accurately resolve issues of interest to developmental biologists today," explained Lu.
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