What is 3D Bioprinting? 3D bioprinting begins with a virtual model of a tissue that is then transformed into living, functional tissue through additive manufacturing technology. This involves the use of bioinks which are deposited in successive layers to build the tissue structure. A bioink is composed of a hydrogel biomaterial that functions as a 3D scaffold, which is either blended with cells or forms a base on which cells can be seeded. In addition to their structural composition, bioinks are comprised of necessary extracellular matrix components that facilitate cell adhesion, proliferation and differentiation to create 3D tissues. Improvements in bioprinting technology has led to the creation of thicker and more complex tissues that can integrate vascular channels to maintain tissue viability. More recently, 3D bioprinting is increasingly used for pharmaceutical development and drug testing. In the future, bioprinting could be a significant boon for regenerative medicine with the development of 3D-printed tissues such as skin grafts, bone grafts, and even full 3D-printed organs for transplantation.

Microgravity may be an ideal environment for 3D bioprinting of tissue structures. On Earth, bioinks must retain a 3D structure that defies gravity, which usually requires higher-viscosity materials. The higher-viscosity bioinks, however, have a negative impact on cell biology and survival during the printing process. Microgravity conditions could, therefore, provide an environment in which lower viscosity bioinks can be utilized while maintaining 3D structure.

Researchers from the biotech company Techshot, Inc. are using microgravity to optimize bioprinting conditions to construct living models of cardiac tissue. In addition, researchers postulate that the microgravity environment mimics an early-stage embryo suspended in the womb, thereby providing optimized conditions for cell proliferation and development. To test this, researchers bioprinted human cardiomyocytes in space and closely monitored their development in real-time. At the end of the study, space-flown and equivalent Earth-grown 3D constructs will be evaluated by histology, immunohistochemistry, and other assays to compare tissue architecture and cell traits. Overall, researchers aim to create 3D bioprinted tissues in microgravity to leverage beneficial effects on cell growth, differentiation, and organization thereby improving the quality and accuracy of tissue features.

Researchers are also utilizing 3D-bioprinting in space to create better in vitro models of cardiac tissues in which to identify novel pathways and mechanisms leading to atrophy. Microgravity is a means to induce accelerated aging in animals and humans, leading to atrophy of various tissues including those of the heart. Researchers will construct 3D-printed cardiac tissues on the space station and study alterations in molecular, cellular, and functional properties of the cells. They hypothesize that epigenetic modifications may be at the root of the cellular and tissue changes. These findings could facilitate the development of pharmaceuticals that could prevent cardiac aging and decline in space and on Earth.

Thus, microgravity provides a clear advantage for bioprinting – and ultimately biomanufacturing in large quantities – tissues and organs which can be used as model systems for research, tissue-specific drug screening and testing, and as replacement parts for humans. This is only the beginning.