Tissue engineering, with the ultimate goal of engineering artificial tissues or organs to replace malfunctioning or diseased ones inside the human body, provides a substitute for organ transplantation. Driven by the growing, tremendous gap between the demand for and the supply of donated organs, tissue engineering has been advancing rapidly. There has been great success in engineering artificial organs such as skin, bone, cartilage and bladders because they have simple geometry, low cell oxygen consumption rates and little requirements for blood vessels. However, difficulties have been experienced with engineering thick, complex tissues or organs, such as hearts, livers or kidneys, primarily due to the lack of an efficient media exchange system for delivering nutrients and oxygen and removing waste. Very few types of cells can tolerate being more than 200 μm away from a blood vessel because of the limited oxygen diffusion rate. Without a vasculature system, three-dimensional (3D) engineered thick tissues or organs cannot get sufficient nutrients, gas exchange or waste removal, so nonhomogeneous cell distribution and limited cell activities result. Systems must be developed to transport nutrients, growth factors and oxygen to cells while extracting metabolic waste products such as lactic acid, carbon dioxide and hydrogen ions so the cells can grow, proliferate and make extracellular matrix (ECM), forming large-scale tissues and organs. However, available biomanufacturing technologies encounter difficulties in manufacturing and integrating vasculature networks into engineered constructs.
This work proposed a novel 3D bioprinting technology that offers great potential for integration into thick tissue engineering. The presented system offered several advantages, including that it was perfusable, it could print conduits with smooth, uniform and well-defined walls and good biocompatibility, it had no post-fabrication procedure, and it enabled direct bioprinting of complex media exchange networks.