In a novel technique, tissue engineering experts are using "bio-inks" to send stem cells a message about what kinds of specialized cells they should become.

		Graphic: 'Bio-ink' prints bone and muscle cells

The system could provide new insights into the interactions between growth factors and stem cells in healing and other biological processes, and could lead to innovative approaches to the design of replacement tissues, said lead investigator Julie Phillippi, a Carnegie Mellon University postdoctoral research fellow.

In San Diego yesterday at the American Society for Cell Biology's annual meeting, she presented findings from experiments that used the technology to direct stem cells derived from mouse muscle to become either bone or muscle cells.

The system uses ink-jet technology commonly found in printers, but "instead of ink, we load the printer with protein," she explained.

According to investigator Lee Weiss, research professor at Carnegie Mellon University's Robotics Institute, the printer deposited precise patterns of a growth factor protein, dubbed bio-ink, onto a glass slide coated with a matrix of fibrin, which the body makes in response to a cut or fracture.

Then the slide was placed in a culture dish and topped with a single layer of stem cells isolated from mouse muscle, which were provided by Johnny Huard, director of the stem cell research center at Children's Hospital and a professor at the University of Pittsburgh School of Medicine.

In the experiment, stem cells that were exposed to a growth factor called bone morphogenetic protein generated bone cells; those that weren't generated muscle cells.

Dr. Weiss, an engineer, said the ink-jet component itself is no more sophisticated than what can be found in a home printer.

But the scientists souped up the system to allow very precise placement of the drops of bio-ink on the matrix. Each drop is thousandths of an inch in diameter, much narrower than a hair, he said.

Overprinting permits the concentration of the bio-ink to be varied. The scientists can then see what impact such changes have on the stem cells.

"It gives you a better idea how you might expect things to act in the body," Dr. Weiss said. He added that different growth factors and cells have been tried in other experiments.

Some day it might be possible to insert bio-inked matrices into injured or diseased tissue so that the body's own stem cells can be directed toward a repair, he said. Or, growth factors and stem cells could be delivered as a package.

"What you want to do is give the body just enough cues to help it heal itself," Dr. Weiss said.

Typically, researchers use separate culture dishes to generate different kinds of cells. In the body, however, a variety of cells and tissues are formed together, noted senior investigator Phil Campbell, a research professor at Carnegie Mellon's Institute for Complex Engineered Systems.

More research is being done to develop biosensors and other techniques to track the stem cell differentiation.