HONG KONG: Scientists in Japan have created a "womb" for incubating artificially fertilized eggs in their earliest days, helping them grow nearly as fast as they would in the uterus, a researcher said on Friday.

Currently, test-tube human embryos are kept in "microdroplets" - a mixture of mineral oil and culture fluid to keep them from drying out. But that lags the superior conditions provided by the womb and artificially fertilised embryos tend to grow a lot slower in microdroplets compared to naturally conceived embryos.

This is not ideal because larger, faster-growing embryos are believed to stand a better chance of survival after being reinserted back into the mother's womb. In the latest issue of New Scientist Magazine, researchers in Japan said they had devised a "chip" measuring 2 mm across and 0.5 mm high, which they said simulates more closely the conditions of a natural womb.

Fresh IVF embryos are slipped into the chips, which rest on a membrane of cultured uterus cells. Once they are ready to attach themselves to the uterus wall, the eggs are reinserted into the mother's womb. "The idea is to give a more comfortable environment for the embryos...it works like a bed for embryos," said Teruo Fujii of the University of Tokyo's Institute of Industrial Science.

Fujii's team experimented with mouse embryos and found that those grown in chips grew quicker than those in microdroplets. Eighty per cent of embryos held inside the chips were ready for the uterus in 72 hours, while only 20% of embryos held in microdroplets grew to that stage in the same amount of time. "It's a large difference between the conventional method and our device," Fujii said in a telephone interview. "Embryos that develop fast are of higher quality... so the artificial uterus environment can give us a way to make embryos develop faster and simulate a situation closer to the (womb)," he said. The Japanese scientists hope to use the chip for human embryos eventually. But interestingly, the eggs inside female mice still had the best environment, with 90% of them ready for the uterus in 72 hours.