Biomaterials that can degrade on demand have been 3D printed by engineers at Brown University. The materials were fabricated by means of stereolithographic printing, which uses an ultraviolet laser controlled by a computer-aided design system to trace patterns across the surface of a photoactive polymer solution. The polymers link together to form solid 3D structures from solution, and the tracing process is repeated until an object is built from the bottom up.
The capacity of the materials to degrade is imparted by the development of reversible ionic bonds. Precursor solutions were prepared with sodium alginate, a compound derived from seaweed that is known to be capable of ionic crosslinking. Different combinations of ionic salts, including magnesium, barium and calcium, were then added to 3D print objects with varying stiffness levels, a factor which affected how quickly the structures dissolved.
“The idea is that the attachments between polymers should come apart when the ions are removed, which we can do by adding a chelating agent that grabs all the ions,” said assistant professor Ian Wong. “This way we can pattern transient structures that dissolve away when we want them to.”
These materials could find use in designing intricately patterned microfluidic devices or in making cell cultures than can change dynamically during experiments. The researchers demonstrated this by using alginate as a template for making lab-on-a-chip devices with complex microfluidic channels.
“We can print the shape of the channel using alginate, then print a permanent structure around it using a second biomaterial,” said Thomas M. Valentin, lead author. “Then we simply dissolve away the alginate and we have a hollow channel. We don’t have to do any cutting or complex assembly.”
The degradable alginate structures were also applied to the development of dynamic environments for experiments with live cells. During experiments with alginate barriers surrounded by human mammary cells, the researchers observed how the cells migrate when the barrier is dissolved away. These studies can be useful in advancing wound-healing processes or in increasing our understanding of cancer cell migration.
Neither the alginate barrier nor the chelating agent used to dissolve it away exerted appreciable toxicity to the cells, indicating the promise of degradable alginate barriers for such experiments.