The placenta may be one of the least understood organs in the human body, but it's important to study considering the health of a developing fetus depends on it. Researchers at Iowa State University have used microfluidic models of the organ – a placenta-on-a-chip – to see if, and how much, caffeine can cross from mother to baby.

Before living humans get involved, studying diseases or testing new drugs usually requires animal models, but the results don't always carry across. A relatively new method designed to be more accurate and avoid using animals relies on what are known as organs on chips –artificial recreations built with microfluidic systems and human cells. In the past, these systems have been made to mimic organs like the lungs, heart, intestines and muscles, as well as the placenta.

In the body, the placenta feeds oxygen and nutrients from the mother into the fetus by way of the umbilical cord, as well as removing waste from the baby's bloodstream. A thin barrier separates the mother's bloodstream from the fetus's, and it's important to study what molecules can cross that barrier and in what concentrations.

In this case, the Iowa State researchers designed a chip that works like the placental barrier, and tested how well compounds could cross it. The chip is made with two tiny channels measuring 100 microns high and 400 microns wide, with a porous biocompatible membrane separating them.

Next they grew human cells on each side of the membrane to mimic the mother and fetus cells. The maternal side was represented with trophoblasts cells (cells that form a key part of the placenta) while human umbilical vein endothelial cells were chosen to line the fetus side.

The final piece of the puzzle was the compound that would be tested. The researchers chose caffeine, since it's so common in our diets and while normally harmless it could pose problems for a developing fetus, since they don't yet have the right enzymes to process it.

To test this out, the researchers added caffeine to the maternal side of the placenta-on-a-chip and watched for changes over seven and a half hours. They started with a safe concentration of 0.25 milligrams per milliliter, and found that after 6.5 hours the concentration on the maternal side was down to 0.1513 mg per ml.

Importantly, a concentration of 0.0033 mg was recorded on the fetal side by the five-hour mark. That indicates that caffeine can indeed cross the placental barrier.

Of course, the model itself still isn't perfect – for one it doesn't take into account the entire body. Other projects have tried to network these organ-mimicking devices together to create entire bodies-on-chips, that may provide wider context and allow closer comparisons to the real thing.

Still, the researchers say the finding suggests that caffeine, and similar substances a pregnant woman could consume, might need to be considered for further study.

The research was published in the journal Global Challenges.