[Image from the University of Illinois]
“This is a great way to create shapes around which we can pattern soft materials or grow cells and tissue, then the scaffold dissolves away,” said Rohit Bhargava, a professor of bioengineering and director of the Cancer Center at Illinois, in a press release. “For example, one possible application is to grow tissue or study tumors in the lab. Cell cultures are usually done on flat dishes. That gives us some characteristics of the cells, but it’s not a very dynamic way to look at how a system actually functions in the body. In the body, there are well-defined shapes, and shape and function are very closely related.”
The nozzle for the printer is free-form, meaning that it moves through space. As the isomalt is printed, the melted material begins to harden and leave a sturdy structure behind.
There have been other examples of sugar printing in the past, according to the researchers. The problem with those methods is that the sugar starts to burn or crystallize. The University of Illinois researchers found that the sugar alcohol isomalt is less prone to burning or crystallization.
The team built a printer that had the right combination of mechanical details to print stable isomalt structures, which means the right temperature, pressure to extrude it from the nozzle, diameter of the nozzle and speed to move it so it prints smoothly but can still harden.
“After the materials and the mechanics, the third component was computer science,” Matthew Gelber, the first author on the study, said. “You have a design of a thing you want to make; how do you tell the printer to make it? How do you figure out the sequence to print all these intersecting filaments so it doesn’t collapse?”
The researchers then created an algorithm to help design scaffolds and map printing pathways.
When creating free-form structures with the isomalt material, the researchers say that thin tubes with circular cross-sections can be formed, which is not possible with polymer 3D printing. As the sugar dissolves, series of connected cylindrical tubes and tunnels are left and can be used like blood vessels to transport nutrients in tissue or create channels for microfluidic devices.
One other advantage of printing isomalt structures is the mechanical properties of each part of the structure can be precisely controlled by making slight changes in the printer parameters.
“For example, we printed a bunny. We could, in principle, change the mechanical properties of the tail of the bunny to be different from the back of the bunny, and yet be different from the ears,” Bhargava said. “This is very important biologically. In layer-by-layer printing, you have the same material and you’re depositing the same amount, so it’s very difficult to adjust the mechanical properties.”
The researchers have already begun using the scaffolds in a variety of microfluidic devices and cell cultures. They are currently working on developing a coating to control how quickly the scaffolds can dissolve.
“This printer is an example of engineering that has long-term implications for biological research,” Bhargava said. “This is fundamental engineering coming together with materials science and computer science to make a useful device for biomedical applications.”
The research was published in the journal Additive Manufacturing and was supported by the Backman Institute for Advanced Science and Technology.
