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A microfluidic chip measures embryo metabolism Each year, ⬎130,000 U.S. women undergo in vitro fertilization (IVF) to help them conceive, at an average cost of ⬃$12,000 per attempt. Only ⬃30% of IVF cycles result in a successful pregnancy, and often, several embryos are implanted at a time to increase the success rate of the procedure. This can lead to a multiple pregnancy (two or more fetuses carried simultaneously), which can cause problems such as low birth weight or cerebral palsy for the resulting infants. Traditionally, doctors assessed the viability of embryos by examining them under an optical microscope, but recently interest has grown in using metabolic screening to predict embryo success. Now, in work published in AC (DOI 10.1021/ac8010473), Todd Thorsen of the Massachusetts Institute of Technology, Mark Johnson of the University of Michigan, David Gardner at the University of Melbourne (Australia), and colleagues have created a microfluidic system to make analyzing the metabolic profile of embryos faster and easier. Researchers can obtain the metabolic profile of an embryo noninvasively by analyzing how the embryo alters the composition of the culture medium that surrounds it. By focusing on energetic substrates such as glucose, lactate, and pyruvate, they can indirectly assess energy metabolism and thereby infer information about the viability and possibly even the developmental potential of the embryo. The tricky part is that embryos are cultured individually in small volumes of several microliters or less of media. “It gets beyond the realm of volumes that can reliably be handled with standard pipettes found in regular laboratories,” says Johnson. Instead, scientists typically use “constriction pipettes” to sample media and perform microfluorometric assays. These glass pipettes have been heated and pulled to make a narrow constriction near the tip that can be
used as a marker to measure the volume. “The issue is that the constriction pipettes, first of all, have to be custommade. Secondly, these constrictions tend to clog and require a lot of cleaning,”
Before analysis, samples of embryo medium are stored in a petri dish under oil (to prevent evaporation).
says Johnson. “When I started in this field, I thought, ‘There has to be a better way to do this.’” Enter Thorsen and his experience in microfluidics. Johnson heard him speak at a nanotechnology meeting, and a collaboration was born. After several years of work, the project has now produced a microfluidic platform that can analyze several key energetic substrates in nanoliter volumes of culture medium with NADPH-based enzymatic assays. The goal was to take most of the manual labor out of the process, says Thorsen. “[We wanted] to really make well-defined, controlled assays that can be done reproducibly without user intervention.” In the new system, the medium surrounding an embryo (the researchers used mouse embryos for this study) is manually sampled and fed into the chip. From there, the movement and mixing of the sample, enzyme cocktails, and rinse buffer are completely automated. The result is a major increase in productivity. “On a good day, when I was doing these assays with the constriction pipettes, I’d be happy if I’d do 50 samplesOthat was over the course of a
10.1021/AC801488V 2008 AMERICAN CHEMICAL SOCIETY
Published on Web 08/08/2008
full 8-hour day,” says Johnson. Now, he adds, the researchers can set the microfluidic chip to run overnight, and when they return in the morning, 300⫺400 data points are ready for analysis. Thorsen and Johnson say that the next step is to further automate the sampling process. “What we are really going for is something that is all in one, so we can do the culture and the assaying onchip without disturbing the embryo,” says Thorsen. The problem is that chemicals, including those commonly used to fabricate microfluidic chips, can affect the viability of the developing embryo. “It’s definitely daunting because embryos are exquisitely sensitive to environmental toxins, particularly a host of organic compounds,” says Johnson. “So the jury is still out as to whether PDMS is going to be the polymer of choice for culturing embryos.” The researchers are still working on this and other problems with the hope of eventually improving the IVF process. IVF “is a very competitive field,” says Johnson. “All of the IVF clinics are looking for the next step to enhance their pregnancy rates. If this or another method allows us to select embryos more effectively than just by morphology, I think that IVF clinics will seriously consider adopting it.” —Jennifer Griffiths
SEPTEMBER 1, 2008 / ANALYTICAL CHEMISTRY
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