A stereolithography-based bioprinting platform for building therapeutic biomaterials from multiple materials could help advance on-demand printing of artificial tissues for regenerative medicine. The platform uses a specially adapted 3D printer that has a custom-built microfluidic chip with multiple inlets. Each inlet prints a different material. The printer also has a digital micromirror device that directs light onto the printing surface, illuminating the outline of the object that is being printed. The 3D bioprinter designed by Ali Khademhosseini and his team at UCLA has two key components: a custom-built microfluidic chip (pictured) and a digital micromirror. Courtesy of Amir Miri. During the 3D printing process, the micromirror adjusts the light pattern to direct the shape of each new layer of the object. The patterning by the digital micromirror device is synchronized by a moving stage and the microfluidic device, which contains four on/off pneumatic valves. The microfluidic device is capable of fast switching between different (cell-loaded) hydrogel bioinks to achieve layer-by-layer multimaterial bioprinting. A UCLA research team used different types of hydrogels to form scaffolds into which tissue can grow. Light directed by the micromirrors triggers the formation of molecular bonds, which cause the gels to firm into solid material. Researchers generated a variety of hydrogel constructs to demonstrate the multimaterial capacity of the system. To validate the biocompatibility of their system, researchers introduced a cell-laden hydrogel (GelMA) into the microfluidic device and fabricated cellularized constructs. A pattern of a hydrogel (PEGDA) frame and three different concentrations of GelMA, loaded with vascular endothelial growth factor, were further assessed in a rat model. According to the team, this process for stereolithographic bioprinting is the first to provide multimaterial fabrication capability at high spatial resolution. The demonstration device used four types of bioinks, but researchers say that the process could accommodate as many inks as needed. The proposed system could provide a robust platform for bioprinting of high-fidelity multimaterial microstructures on demand for applications in tissue engineering, regenerative medicine, and biosensing. Such applications are not easy to achieve efficiently with conventional stereolithographic biofabrication platforms, which use only one type of material. “Tissues are wonderfully complex structures, so to engineer artificial versions of them that function properly, we have to recreate their complexity,” said professor Ali Khademhosseini. “Our new approach offers a way to build complex biocompatible structures made from different materials.” The research was published in Advanced Materials (doi:10.1002/adma.201800242).