A new method for producing embryonic stem cells can raise the cell output by hundred times and lower the costs in the meantime, a US research group reported Tuesday.

The new method is important because traditional laboratory methods adopted to grow stem cells are costly and do not produce cells fast enough to meet increasing demands for human embryonic cells, said Shang-Tian Yang, a professor at Ohio State University who led this study.

Presenting their findings in San Diego at the national meeting of the American Chemical Society, Yang and his colleagues said they grew mouse embryonic stem cells in a bioreactor and cell growth increased 193-fold in 15 days.

At the end of that period, cells that had grown in the bioreactor were 10 to 100 folds more than those produced by conventional laboratory methods, they said.

Mass-producing cells in this way could reduce costs by at least 80 percent as it requires less equipment and monitoring, Yang said.

Embryonic stem cells are undifferentiated cells that can develop into any adult cell, including neural, bone, muscle or blood cells, a fact which gives them big potential clinic value.

"We have to find a way to mass-produce them because traditional cell culturing methods can't meet the projected high market demand for stem cells," Yang said.

Yang's team grew some mouse embryonic stem cells in a flask, a conventional way to grow stem cells, while other stem cells grew upon strands of polymer threads inside a bioreactor.

While the bioreactor, a tissue-growing device, could be used to produce adult stem cells, the researchers chose to use it for growing embryonic stem cells in this experiment.

The bioreactor has a chamber that holds the polymer threads on which the stem cells grow and another chamber that holds fluid, or medium. This medium delivers chemical messengers, called cytokines, to the stem cells. The cytokines essentially tell the cells to stay in their undifferentiated state.

The researchers tested both sets of cells, those grown in a flask and the ones grown in the bioreactor, for two key proteins, which could indicate not differentiated stem cells. In the bioreactor experiment, 94 percent of the stem cells tested positive for these proteins, compared to about 85 percent of the cells grown in the flask.

Cells in the bioreactor could grow in three dimensions but those on the bottom of the flask could not, Yang said.

"Cells grown on a flat surface don't act like they would in the body," he said. "The growing surface affects how a cell forms, what it looks like and even how it expresses genes."

Moreover, cells grown in the bioreactor could grow for a much longer period of time than they could in the flask, as cells had more room to grow.

"In the same amount of time we could grow up to a billion stem cells per milliliter in the bioreactor, compared to tens of millions of cells per milliliter with conventional systems," Yang said.

"There's more of a demand for an unlimited supply of embryonic stem cells," Yang said.