Microstructures with Living Cells

The behavior of cells strongly depends on their environment, and now a laser system being developed in Austria could create microstructures for embedding living cells in suitable surroundings for research and manipulation.

The process under development by Aleksandr Ovsianikov at the Vienna University of Technology allows living cells to be incorporated into intricate custom structures, similar to biological tissue, in which cells are surrounded by the extracellular matrix. This technology is particularly important for artificially growing biotissue, for finding new drugs and for stem cell research.

“Growing cells on a flat surface is easy, but such cell cultures often behave differently from the cells in a real three-dimensional tissue,” Ovsianikov said.

In two dimensions, conventional petri dishes are used. No standard system has yet been available for three-dimensional cell cultures. Such a 3-D matrix must be porous so that the cells can be supplied with all the necessary nutrients. Furthermore, it is important that the geometry and the chemical and mechanical parameters of this matrix can be precisely adjusted to study and induce necessary cell responses, the researchers said.

The structure should also be produced quickly and in large quantities because biological experiments usually have to be carried out in many cell cultures at the same time to yield reliable data.

To meet these requirements, the interdisciplinary Additive Manufacturing Technologies research group at Vienna University of Technology is developing technologies to create 3-D structures with submicron precision.

“We want to develop a universal method which can serve as a standard for three-dimensional cell cultures and which can be adapted for different kinds of tissue and different kinds of cells,” Ovsianikov said.

To accomplish this goal, the scientists developed a laser system to turn liquid into a tailor-made scaffold. First, the cells are suspended in a liquid of mostly water. Next, cell-friendly molecules are added, and a focused laser beam breaks up the double bonds at precise places. A chemical chain reaction then causes the molecules to bond and create a polymer.

A laser beam (red) can be used to produce a three-dimensional grid that keeps the cell in place. The laser technique developed at TU Vienna hardens the liquid material exactly at the focal point. Images courtesy of TU Vienna.

This reaction is triggered only when two laser photons are absorbed at the same time. Only within the focal point of the laser beam is the density of photons high enough for that. Material outside the focal point is not affected by the laser.

“That is how we can define, with unprecedented accuracy, at which points the molecules are supposed to bond and create a solid scaffold,” Ovsianikov said.

The focus of the laser beam is guided through the liquid to create a solid structure in which living cells are incorporated. The surplus molecules not polymerized during the process can be washed away.

This procedure makes it possible to create a hydrogel structure that is similar to the extracellular matrix that surrounds our own cells in living tissue. This biomimetic approach plays an increasingly important role, especially in materials science. Ovsianikov is confident that, in many cases, this technology will render animal testing unnecessary and yield much quicker and more significant results.

Stem cell research is an application of particular interest for this new method.

“It is known that stem cells can turn into different kinds of tissue, depending on their environment,” Ovsianikov said. “On top of a hard surface, they tend to develop into bone cells; on soft substrate, they may turn into neurons.” In the laser-generated 3-D structure, the rigidity of the substrate could be tuned so that different types of tissue can be created.

Ovsianikov was awarded a European Research Council Starting Grant for approximately €1.5 million (about $2 million) to fund the research.

For more information, visit: www.tuwien.ac.at/en