Coincident with the convergence of a unique layered solid freeform fabrication (SFF) technologies along with microfabrication techniques, a three-dimensional bioprinted micro-organ can serve as an in vitro platform for cell culture, drug screening, or to elicit further biological insights, particularly for NASA's interest of a flight-suitable high-fidelity microscale platform to study drug metabolism in space and planetary environments. This book details the principles, methodology, and engineering science basis that undergird the direct cell writing fabrication process development and adaptation of microfluidic devices for the creation of a in vivo simulating drug screening model. This model involves the combinatorial setup of an automated syringe- based, layered direct cell writing bioprinting process with soft lithographic micro-patterning techniques to fabricate a microscale in vitro device housing a chamber of bioprinted three-dimensional microorgan that biomimics the cell's natural microenvironment for enhanced performance and functionality.