Tech

An Egg With a View

Researchers assemble a transparent egg that allows us to sneak a peek at an unborn chick.

The fleshy creature squirms through the orange goo; its enormous, oblong eyes and oversized head are just visible through the mucus-like layer that confines it. No, it’s not an alien or a jinxed science experiment. It’s a developing chick, seen through a transparent synthetic eggshell created by biomedical engineers from Tsinghua University in Beijing.

As described in a paper recently published in SCIENCE CHINA Technological Sciences, the researchers built the see-through shells using polydimethylsiloxane, or PDMS, an organic, silicone-based compound. PDMS is soft and flexible, so when it’s placed on the mold of a regular shell, it conforms to its shape and curvature. That creates a perfect vessel for an embryo, which the researchers extracted from a normal eggshell. After implanting it into the transparent layer, the researchers were able to get a 360-degree view of a developing chick. “This biomimetic shell, resembling a real egg incubation, represents a new platform for studying embryo development, and of course many other biomedical studies,” says Jing Liu, an author on the paper and a professor from Tsinghua University.

Nicola Hemmings, a researcher at Sheffield University in the United Kingdom who studies avian reproductive behavior, says this isn’t the first time a window has been built into an egg. In 1988 Margaret Perry, an embryology researcher (now deceased) from the Roslin Institute in Edinburgh, Scotland, used a more clear-cut technique to view the inside of a live egg. Perry lopped off the top of a chicken egg, cleaned out the shell, and then placed a fertilized embryo inside. By maintaining the right amount of albumen, optimum temperatures, and the correct air-space ratio, she found that the embryo could develop successfully. The entire process was visible through the “skylight” that she cut into the crown of the egg and covered with plastic wrap. “This culture system is still widely and successfully used and provides a direct window into the eggshell, making it completely possible to observe all stages of embryo development,” Hemmings says.

Though this tried-and-trusted technique doesn’t give the same panoramic view as the new PDMS shell, Hemmings notes that Perry’s skylight method led to a hatching success rate of 60 percent. In contrast, the PDMS egg mold supports embryos for up to 17.5 days—five days short of the time chicks need to fully develop and hatch. It’s not clear why this is the case, but it could come down to the PDMS cast, which doesn’t protect an embryo as well as a true shell, Hemmings says.

Despite the lack of hatching success, being able to watch an embryo as it ripens could one day prove useful for the conservation and survival of wild birds. Some species, like the critically endangered kakapo, have trouble reproducing because their eggs just don’t hatch. Another problem is climate change, which can shape an embryo’s development. “Late-stage chick embryos can be highly sensitive to fluctuations in environmental temperature and humidity,” Hemmings says.

The PDMS egg can provide invaluable information to developmental biologists and geneticists. Hemmings says that it will allow them to study fine-scale impacts and genetic manipulations in controlled lab environments.

But the crystal-shell egg, no matter how beautiful or pellucid, is no match for the real thing. “It would be exciting to see an artificial egg produced which truly replicated the conditions provided by a real egg,” Hemmings says. “However, given that bird eggs are the finely tuned product of millions of years of evolution, that would be a very tough thing to pull off.”