By Caleb Sooknanan ‘20

Three-dimensional (3D) printing — a form of additive manufacturing — involves the joining and solidification of material to create objects from computer files. Glasses made of sugars or carbohydrates have become practical materials for printing more complex structures, such as organs, because of their stiffness and durability. These sugar glass materials can be positioned in layers or freeform paths that utilize freestanding networks for further stability. Nevertheless, more research is needed to understand how carbohydrate glasses could be applied towards 3D printing, as the sugars may burn or crystallize during printing processes. Doctor Rohit Bhargava and researchers from the University of Illinois at Urbana-Champaign constructed a 3D printer with the ability to print intricate biological structures from sugar glass. The researchers built this 3D printer to address the burning and crystallization issues commonly associated with sugar glass printing.

The researchers first compared the glass transition temperatures — temperatures at which solidification occurred — and the crystalline melting points of seven sugars to determine the material that would provide the best printing performance. Isomalt, a sugar alcohol used to manufacture lozenges or tablets that could dissolved orally — was the least vulnerable to burning and crystallization. The researchers designed an isomalt processing guide, followed by an extruder that could control material flow rates through pressure variation and piston movement. The researchers then analyzed the isomalt material’s heat transfer capabilities and possibilities for forming different shapes; they recognized that the radial flow of the heated glass — as it exited the extruder’s nozzle — would have the most significant impact on the resulting filament’s shape. The researchers ensured that the 3D printer possessed the proper mechanical details to print firm isomalt structures. Such details included the proper temperature and pressure conditions for extrusion, the diameter of the nozzle, and a printer speed that would allow the isomalt to harden and accurately represent biological objects.

The researchers suggested that the isomalt printing process could allow other scientists to manufacture complex shapes without unnecessary support material. However, issues may arise with the increased viscosity of isomalt upon heating; these conditions could yield residual stresses from rapid cooling and damage 3D printers. More work is needed to determine how sugar glass 3D printers could avoid these residual stresses, but the process may provide new insights in tissue engineering, microfluidics, and other areas of bioengineering.

References

1. R. Bhargava, et. al., Model-guided design and characterization of a high-precision 3D printing process for carbohydrate glass. Additive Manufacturing 22, 38-50 (2018). doi: 10.1016/j.addma.2018.04.026  
2. Image retrieved from: https://upload.wikimedia.org/wikipedia/commons/5/53/3d_printed_brain_n1.jpg