Researchers based in Dresden, Germany are contemplating not only the future of healthcare materials but also their potential applications beyond Earth. Michael Gelinsky, professor and head of the Center for Translational Bone, Joint, and Soft Tissue Research, along with his team, are developing living inks that could potentially be used by astronauts to treat injuries sustained on lengthy space missions, where aid from Earth isn’t an option –– like Mars.
Analogous to the ink cartridge in your office printer, bioinks contain living cells suspended in a solution of a biopolymer or blend of biopolymers, such as alginate or gelatin. But instead of printing a document, extrusion-based bioprinters use bioinks to produce layered 3D hydrogel constructs embedded with the cells contained in the ink.
These constructs, whose shapes are preprogrammed into a computer, have been used to produce patient-specific implants and generate life-like models that mimic organ tissue, which can be used for basic research purposes.
The challenges with bioinks in space
Currently, cell-laden bioinks have only been printed on Earth, where the necessary facilities, equipment, and staff are available, and the effects of gravity are known. Bioprinting under microgravity, such as on the International Space Station (ISS), where resources and crew are limited, is a more complicated matter.
In order for the cells in bioinks to survive the rocket launch and journey to the ISS, they would have to be stored at low temperatures, potentially up to a month. Ideally, they would be stored in the form of a ready-to-use cartridge that could be loaded by astronauts into an extrusion-based bioprinter installed at the ISS.
“The European Space Agency ESA has commissioned an industry consortium to build such a device, combined with a unit for further cultivation of the bioprinted constructs,” Johannes Windisch, a Ph.D. student in Gelinsky’s research group, informed us. “If pre-mixed (i.e., cell-laden) bioinks could be launched and directly used for the bioprinting process, this would facilitate the whole procedure significantly.”
Preparing and assessing the bioinks
To investigate the feasibility of this scenario, the researchers incorporated green microalgae and different mammalian cell types into alginate–methylcellulose (Alg–MC) scaffolds. These included a human mesenchymal stem cell line (hTERT-MSC), liver (HepG2) and bone (SAOS-2) cell lines, and primary human dental pulp stem cells.
To prepare the bioinks, they first dissolved a mixture of alginate and methylcellulose in water, phosphate-buffered saline, or human plasma. Then, they added the live cells and loaded the different bioink formulations into cartridges, which they stored for one to four weeks at 4°C, a temperature that can be easily maintained throughout the process of delivering cargo to the ISS.
After warming the cartridges to room temperature, they used the bioinks to print 3D scaffolds, which they ionically crosslinked and incubated under optimal conditions for up to 28 days.
The authors found that regardless of the cold-storage period, all the bioinks maintained their printability, despite a decrease in viscosity. Notably, storing the microalgae-laden bioink at 4°C barely affected the viability and functionality of the microalgae, which is known to tolerate a variety of environmental conditions.
Even after four weeks of storage, the microalgae could still undergo photosynthesis, using available light to produce oxygen with an efficiency similar to that of the reference group of fresh microalgae. On space missions, microalgae-laden bioinks could potentially be used for life support, sewage purification, and as a food or nutrient source.
In contrast to microalgae, whose viability was essentially unaffected by low-temperature storage, the viabilities of the human cells declined to varying extents. However, when the cells were restored to optimal conditions after storage, their viabilities recovered. The data suggest that metabolically active cells are more affected by cold storage than quiescent cells, and the storage temperature was more influential than the storage duration.
“For every cell type of interest, first the optimal bioink composition and also the storage conditions need to be evaluated. Our study is just is the starting point for more detailed investigations,” Johannes pointed out.
Earth-based applications
Although the authors envision that these bioinks may one day be used to generate patient-specific tissues to treat injured astronauts, in the meantime, they could be used to produce 3D tissue models for investigating the effects of microgravity, radiation, and other conditions that astronauts are subjected to in space.
“In addition, the effects of microgravity on the bioprinting process need to be investigated further to be able to set up a workflow and define the design of bioprinted constructs that would finally work at the ISS,” said Anja Lode, another of the study’s authors. “For this, our lab will perform first bioprinting experiments on a parabolic flight campaign in September 2023, supported by the German Space Agency at DLR.”
When asked how storable bioinks might improve the current bioprinting processes on Earth and what new applications might arise, Johannes had several ideas.
“Storable bioinks would allow performing bioprinting experiments in labs that are not equipped for the production and harvesting of large cell numbers. They could also facilitate bioprinting applications outside of research labs, for example, in hospitals or even for the treatment of people injured in natural disasters or military conflicts. Finally, the production and trading of storable bioinks could be an interesting business model.”
Reference: Johannes Windisch, Olena Reinhardt, Michael Gelinsky, et al.,Bioinks for Space Missions: The Influence of Long-Term Storage of Alginate-Methylcellulose-Based Bioinks on Printability as well as Cell Viability and Function, Advanced Healthcare Materials (2023). DOI: 10.1002/adhm.202300436
Feature image credit: The New York Public Library on Unsplash
