Cell biology has very particular characteristics. During the last decade, researchers and scientists have astounded us with their discoveries in bioprinting and regenerative medicine, proving that a great deal of what happens at the lab is basically knowing and understanding cells. These microscopic structures are the foundation of most projects where cells are patterned to grow into mature tissues, interacting with other cells and non-cellular components of their local environment, such as the extracellular matrix and nutrient sources.
But there have been a few challenges along the way, basically: how to keep the cells alive, what materials to use for cells to live in, and keeping up with the requirements of micro parts in the production sector as well as in academic and industrial research. And that is a big part of bioprinting. Tissue growth and the behavior of cells can be controlled and investigated particularly well by embedding the cells in a delicate 3D framework, yet some methods are very imprecise or only allow a very short time window in which the cells can be processed without being damaged. Moreover, the materials used must be cell-friendly during and after the process, restricting the variety of possible materials, which includes biocompatible synthetic and natural polymers. Now a new high-resolution bioprinting process developed at Vienna University of Technology (TU Wien), in Austria, ensures living cells can be integrated into fine structures created in a 3D printer extremely fast.
Thanks to a special bioink and 3D printing system, cells can be embedded in a 3D matrix printed with micrometer precision, at a printing speed of one meter per second. This high-resolution bioprinting process with completely new materials allows the fabrication of structures and surface textures mimicking the microenvironment of cells.
“The behavior of a cell depends crucially on the mechanical, chemical and geometric properties of its environment,” said Aleksandr Ovsianikov, head of the 3D Printing and Biofabrication research group at the Institute of Materials Science and Technology at TU Wien. “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 and whether they are stable or degrade over time”.
The high-resolution 3D printing technology and the materials are being commercialized by UpNano GmbH, a spin-off company of TU Wien. The ultrafast high-resolution 3D printing system called NanoOne is based on multiphoton lithography and combines the precision of two-photon polymerization. UpNano claims that their patented process enables the batch production of microparts with the highest resolution and complexity in the market, enabling the economic production of polymer parts from micro to mesoscale. The biocompatible process in combination with optimized materials facilitates cell, tissue, and biofabrication. Meaning that the living cells of choice can be mixed into the material and printed directly or seeded on sterile, pre-fabricated scaffold structures.
In order to achieve an extremely high resolution, two-photon polymerization methods have been used at TU Wien for years. This method uses a chemical reaction that is only initiated when a molecule of the material simultaneously absorbs two photons of the laser beam. According to the institute, this is only possible where the laser beam has a particularly high intensity. At these points, the substance hardens, while it remains liquid everywhere else. Therefore, this two-photon method is best suited to produce extremely fine structures with high precision.
However, these high-resolution techniques usually have the disadvantage of being very slow–often in the range of micrometers or a few millimeters per second. At TU Wien, however, cell-friendly materials can be processed at a speed of more than one meter per second, and they claim that only if the entire process can be completed within a few hours there is a good chance of the cells surviving and developing further.
According to Ovsianikov, “printing microscopically fine 3D objects is no longer a problem today, however, the use of living cells presents science with completely new challenges: until now, there has simply been a lack of suitable chemical substances. 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.”
UpNano’s high-performance two-photon materials are engineered and optimized to utilize the full potential of the NanoOne printing system. In addition to UpBio, the hydrogel material for biological applications and bioprinting, UpNano offers photopolymers (UpPhoto) and sol-gel hybrid materials (UpSol). Living cells of choice can be mixed into the material and printed directly, and cells embedded in an UpBio matrix can be used for 3D in vitro cell tests, which gain increasing importance in cell culture, tissue regeneration and pharmaceutical research.
“Our method provides many possibilities to adapt to the environment of the cells. Depending on how the structure is built, it can be made stiffer or softer. Even fine, continuous gradients are possible. In this way, we can 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.”
Ovsianikov is convinced that this is an important step forward for cell research: “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”.
The research project is an international and interdisciplinary cooperation in which three different institutes of the TU Vienna were involved: Ovsianikov’s research group was responsible for the printing technology itself, the Institute of Applied Synthetic Chemistry at TU Wien developed fast and cell-friendly photoinitiators (the substances that initiate the hardening process when illuminated) and TU Wien’s Institute of Lightweight Structures and Structural Biomechanics analyzed the mechanical properties of the printed structures.
The advantages of the NanoOne high-resolution printing system enable the additive manufacturing of polymeric microparts in research, science, and industry, with achievable part sizes, ranging from micro to mesoscale, with structure details in a submicrometer range and throughput of the system that opens up a universe of application possibilities. Considering that UpNano is a very new company, founded in 2018, we can expect researchers to come up with some very interesting solutions in a universe of applications.
[Image credit: UpNano and TU Wien]
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