The networks of blood vessels in the body, i.e. the vascular systems, serve as highways for delivering nutrients and removing waste. Without these systems, cells die quickly. Bioengineering new vasculature is a crucial step toward being able to use a patient's own cells to create new replacement organs such as livers or kidneys.
Bioengineers are already working towards this goal with "bioprinting," the process of creating and assembling single layers of cells with direct access to nutrients and oxygen. Creating a full set of new vessels, however, is no easy task. Fluidic pressure pushing through these frail vascular systems can trump their structural seams, and many cell types cannot support the sheer force of 3-D bioprinting.
Researchers at the University of Pennsylvania have come up with a different approach. Until now, the technique was to print and layer tissue leaving hollow channels to act as the tissue's vasculature. Instead of this approach, researchers tried to reverse engineer the process and designed 3-D filament networks inside a mold shaped like a vasculature system. Once the cells formed a solid tissue around the mold and template, all they had to do was remove them.
"Sometimes the simplest solutions come from going back to basics," postdoctoral Jordan Miller said in a school news release. "I got the first hint at this solution when I visited a Body Worlds exhibit, where you can see plastic casts of free-standing, whole organ vasculature."
Miller and his team explained that sugar proved to be the ideal building material for the networks because it is rigid, compatible with a 3-D printer, and it dissolves in water without having any toxic effects on cells. The researchers used a mix of sucrose, glucose, and dextran for structural reinforcement, and opted for the open-source RepRap 3-D printer.
Researchers coated the templates in a degradable corn-based polymer, allowing the sugar template to dissolve and flow out of the gel through the channels they created. This way, the researchers can start flowing nutrients through the vascular architecture when the sugar has fully dissolved.
According to the bioengineers, this method should offer a scalable solution for many types of cells and tissues, because organ vasculature has a consistent architecture. Not only would this mean we could have organ transplants built from one's own cells, but the templates have another great benefit: they are highly stable.
"Cell biologists like the idea of 3D printing to make vascularized tissues in principle, but they would need to have an expert in house and highly specialized equipment to even attempt it," explained Miller. "That's no longer the case; we've made these sugar-based vascular templates stable enough to ship to labs around the world."
Miller is currently teaching a summer class on building and using such printers, but he plans to keep working on the design. "We want to redesign the printer from scratch and focus it entirely on cell biology, tissue engineering and regenerative medicine applications."
