3D PRINTING OF STEM CELLS IN LIQUID-LIKE SOLIDS FOR HUMAN NEURAL TISSUE FABRICATION

As the human population is getting older, neurodegenerative diseases are becoming an increasing threat to human health and a growing burden in terms of economic cost. For decades, these diseases have been studied using animal models and simple cell culture systems. However, both approaches have limitations: the translation of animal experiments to humans frequently fails and simple monolayer cultures are inherently unable to serve as adequate models for live tissues. Three-dimensional (3D) human in vitromodels are promising candidates to overcome these limitations because they can be engineered to architecturally and functionally mimic live tissue. The main challenges in creating such models are obtaining high resolution and systematically fine-tuning the cellular microenvironment. It is particularly challenging to fabricate nervous tissue because it is one of the softest tissues  (200-1000 Pa). Constructing highly defined structures with such soft materials is extremely demanding, due to post-fabrication deformations from material sag and interfacial tension. We utilized 3D bioprinting in liquid-like solids (LLS), a technology only recently developed, to overcome these challenges. Human neural stem cells (hNSCs) embedded in a hydrogel were printed inside a custom-made LLS support. The results show that we can print highly defined cell-laden structures (resolution below 50 µm) that retain their shape for more than a week. Such long-lasting architectural integrity of soft hydrogels is not achievable with conventional bioprinting methods. Printing two different populations of cells was also accomplished, an important step towards mimicking different parts of the brain in one structure. Furthermore, we are developing poly(ethylene glycol)-based (PEG) hydrogels with tunable physical and chemical properties in order to enhance the differentiation of  hNSCs into desired types of neurons. We aim to combine these advanced PEG-based hydrogels with our approach of bioprinting in LLS support in order to create an advanced 3D model of the brain with physical and chemical resemblance of brain tissue.  Lastly, extending this method to human induced pluripotent stem cells (iPSCs) would allow us to model Parkinson’s disease and even make the approach patient specific.