Associate Professor Massachusetts General Hospital, United States
Introduction:: One of the most promising techniques to engineer tissues currently being investigated is three-dimensional bioprinting. Different polymers, cells, or some combination thereof can be printed in this manner and additively built to engineer large tissues or whole organs. Despite these advancements, the field is still in its infancy. Specific challengesmust be addressed to realize the full potential of fabricating complex functional tissues and organs. One such challenge is the inability to bioprint soft hydrogels over extended periods of time. With the current gold standard bioprinting process, FRESH bioprinting, the printed tissue is released from the thermoresponsive gelatin support material after printing. This means that it would not be possible to add new tissues or components to what has already been printed. It would be advantageous, however, to do so. Different cells/tissues require different temporal culture demands for proper maturity to be achieved. Therefore, for complex tissues to achieve proper maturity and ultimately function, different components may need to be added at different times according to these different demands. We have begun to approach this problem with a new process termed Sequential Additive Biofabrication Extended over Real-time or SABER bioprinting. SABER allows for tissues to slowly be engineered piecewise over long periods of time while keeping with the major advantage of the high spatial control of bioprinting. This is the first bioprinting process that allows for long-term temporal control of bioprinted tissues.
Materials and Methods:: SABER bioprinting was accomplished through identification of a novel support material to suspend printed objects in specialized bioreactor designs that allow for direct perfusion into the printed tissues. The slurry is thermally sensitive and allows for bioprinting at cold temperatures (4°C) and holds the printed tissues in place in culture temperatures (37°C). A variety of different printing geometries and perfusion cultures were used to test the feasibility of the SABER bioprinting platform. Furthermore, a bioreactor was designed that allows for a tissue to be printed within it, while also acting as a perfusion system. By combining the bioreactor design with the established SABER support, we are able to perfuse the printed tissues during times in between printing sessions, allowing for tissue viability.
Results, Conclusions, and Discussions:: The SABER bioprinting process was verified through a variety of multiday and complex architectural prints of collagen structures. Printed structures were able to be fabricated over multiple days in complex geometries, including a miniaturized heart model printed over four separate days with internal structures present. Tissues were also able to be printed, perfusion cultured, and printed again to create large thickness tissues. These described results highlight the capabilities of SABER bioprinting to dynamically create soft tissues over long periods of time while allowing for perfusion culture. SABER bioprinting has major implications for the field which should allow for improvements in engineering functionally complex tissues and to act as a disease modeling platform.
