Using Living Cells in a 3D Printer to Bioprint Tissue Structures

A high-resolution 3D printing technique that uses a novel bioink to embed cells in a 3D matrix is currently being developed at TU Wien in Vienna, Austria. This technique is extremely precise and prints at the speed of one meter per second, achieving unprecedented efficiency. This work was published in the journal Advanced Healthcare Materials.

Embedding cells into uniquely designed 3D frameworks allows for the controlled investigation of tissue growth and cell behavior. Bioprinting these models can be challenging due to a lack of precision and short time frames in which the cells can be manipulated without being damaged. The materials used in this process must be compatible with the living cells as well, limiting the number of bioprinting materials that can be used.

“The behavior of a cell behaves depends crucially on the mechanical, chemical and geometric properties of its environment,” explained Aleksandr Ovsianikov, head of the 3D Printing and Biofabrication research group at TU Wien’s Institute of Materials Science and Technology. “The structures in which the cells are embedded must be permeable to nutrients so that the cells can survive and multiply. But it is also important whether the structures are stiff or flexible, whether they are stable or degrade over time”.

Researchers can create intricate microenvironments, or scaffolds, and introduce living cells to them to create unique models, however, it can be difficult to put cells deep within this structure. This technique also leads to poor cell distribution throughout the scaffold, with homogenous distribution being nearly impossible to achieve. Bioprinting presents a much more efficient approach, integrating the living cells into the microstructure while it is being created.

“Until now, there has simply been a lack of suitable chemical substances,” said Ovsianikov. “You need liquids or gels that solidify precisely where you illuminate them with a focused laser beam. However, these materials must not be harmful to the cells, and the whole process has to happen extremely quickly.”

An Improved Approach

TU Wien has been using two-photon polymerization, a technique in which a chemical reaction is only initiated when a molecule of material absorbs two photons of a laser beam at once, for years to yield high resolution. This is only effective when a very intense laser beam is directed at the substrate, which induces the compound to harden. The selectivity of this technique makes it well-suited to create intricate, precise structures.

This extreme accuracy usually comes at the cost of efficiency, but this TU Wien technique processes substrates at a rapid pace of one meter per second. This is crucial for bioprinting structures that contain living cells, being that the process must be completed within a few hours for the cells to have a high likelihood of survival and continued development.

“Our method provides many possibilities to adapt the environment of the cells,” explained Ovsianikov. Depending on how the structure is built, it can be made stiffer or softer. Even fine, continuous gradients are possible. In this way, it is possible to define exactly how the structure should look in order to allow the desired kind of cell growth and cell migration. The laser intensity can also be used to determine how easily the structure will be degraded over time.

“Using these 3D scaffolds, it is possible to investigate the behavior of cells with previously unattainable accuracy. It is possible to study the spread of diseases, and if stem cells are used, it is even possible to produce tailor-made tissue in this way,” Ovsianikov concluded.