A Japanese research team said Thursday that it has become the world's first to create miniaturized organs closely resembling the human placenta in structure and functions.

The team, including researchers of Tokyo Medical and Dental University, expects that the human placenta organoids, the miniature version, can be applied to research to understand how viruses infect the placenta and to develop safe new drugs.

The team's research results were published in the online edition of the British journal Nature Communications.

The placenta, formed after pregnancy, serves as a barrier to protect the fetus from foreign substances such as viruses.

There are many mysteries that have remained unsolved about the human placenta.

But the structure of the human placenta is different from those of other creatures. There is therefore a limit to what can be learned about the human placenta through animal experiments.

To produce human placenta organoids, the team chose to use placental stem cells because there is an established method to create such cells from human placenta tissue.

The team gave the cells protein that promotes the growth of the placenta and cultured them for about eight days. It then succeeded in producing spherical miniorgans about 0.45 millimeters in size.

A detailed examination of the placenta organoids showed that their villi, or threadlike projections on the surface of membrane, have the same structure as that of placental villi. Villi are covered with cells that act as barriers to foreign substances.

In addition, the organoids' performance of stopping harmful substances from passing was similar to that of the human placenta, according to the team.

Regarding how to use the organoids, a team member said, "We expect we can develop new drugs for fetuses whose negative side effects are suppressed."