While we often talk about bioinks and hydrogel materials for 3D bioprinting applications, a group of engineers from the University of Illinois have developed a new (and sweet!) material and 3D printer system which could have important applications in biomedical engineering, cancer research and device manufacturing.
Using an isomalt-based material (the same sugar alcohol ingredient used in cough drops) and an amazingly precise 3D printer, the research team has demonstrated the ability to produce complex free-form structures which are water-soluble and biodegradable. That is, rather than rely on a layer-by-layer printing technique, the 3D printer draws thin strands of the isomalt material which harden into shape as they are extruded—not unlike a mechanized (and highly accurate) 3D pen.
Because of the material’s water-solubility and biodegradability, the researchers say their free-form isomalt printing technique could be used for a range of biomedical applications, including making biodegradable scaffolds for growing cells.
“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,” explained Rohit Bhargava, a bioengineering professor and the director of the Cancer Center at Illinois. “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.”
Though this isn’t the first time that sugar has been explored as a bioprinting material, the isomalt material used in this project has overcome a number of problems characteristic of working with sugars, including burning and crystallization. Still, it took some effort to engineer a 3D printer that could print stable isomalt structures by maintaining the correct temperature and pressure. As the researchers explain, they also needed to find the optimal nozzle diameter and print speed to ensure that the isomalt material could be extruded smoothly and harden into a stable form.
“After the materials and the mechanics, the third component was computer science,” said Mattew Gelber, first author of the study and recent PhD graduate. “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?”
To answer these questions, the research team worked with Greg Hurst from computational technology company Wolfram Research, who helped them to develop an algorithm for designing scaffold structures and mapping out printing pathways. As you can see in the demo video, the printing pathways and mechanical precision must be exact in order to build sturdy scaffold structures.
For bioengineering applications, the free-form isomalt structures can offer a number of benefits. For one, because the thin cylindrical strands eventually dissolve, complex structures can be printed which can function as blood vessel tubes or tiny channels in microfluidic devices once the material is gone. Secondly—and unlike in layer-by-layer printing—users can precisely control the mechanical properties of each part of a structure.
Bhargava explains: “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. 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.”
Presently, the 3D printing technique is being used to produce scaffolds for a range of microfluidic devices and cell cultures, and Bhargava’s team is developing a special coating for the isomalt material which could help users control how quickly the sugar structures 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 innovative research study, “Model-guided design and characterization of a high-precision 3D printing process for carbohydrate glass,” was recently published in the journal Additive Manufacturing. The paper details how to build the technology and the University of Illinois team hopes this will inspire other researchers to develop other applications for isomalt structures.