All paste-based pneumatic extrusion 3D printing processes (a type of 3D printing that is rapidly becoming a stand-alone sector for its many different possible applications) share the same challenge: finding the correct viscosity for the paste material to be fluid enough to be extruded, and, yet, thick enough to solidify once extruded in order to support the material’s own weight. This is true of cement extrusion, as well as any food-paste extrusion, silicon, alginate, resins and, yes, cellular hydrogels for bioprinting. A team of scientists at the University of Florida, which includes Thomas E. Angelini from the University’s Soft Matter Research Lab, have found that a particular type of granular gel offers the best solution to this issue.
According to a paper published in Science Advances, the UFL team were trying to find a way to deal with the problems of low surface tension and structure deterioration that occurs when printing soft materials. The gel offers the unique combination of being liquid when it is extruded in space (under pressure), and then behaving as a solid when no pressure is applied to it.
In this way, it behaves just like the gel material in hand sanitizers. It acts as a solid while inside the container and becomes liquid once pressure from the pump is applied to it, to then solidify rapidly when the pressure is released. The same approach was used in a pneumatic extrusion 3D printing device, in order to create several three dimensional and geometrically complex objects.
This approach could enable the extrusion of materials mixed into the gel, thus making it possible to create more complex structures without necessarily recurring to elevated temperatures or UV rays that risk damaging the paste-materials, especially in the case of biomaterials.
“Holding material within the gel negates the effects of surface tension, gravity, and particle diffusion,” the study’s authors explained, “and enables a wide variety of materials to be written by this process, including silicones, hydrogels, colloids, and living cells.” For example, they have used this process to create complex multi-scale structures using PVA hydrogels and fluorescent colloids. Exact compositions of the materials used are accurately described in the published paper.
The authors also suggest this approach could be used to create more accurate pre-surgical models of soft organs and tissues that the surgeons are going to operate on. Other applications include tissue engineering, flexible electronics, particle engineering, smart materials, and encapsulation technologies.
In order to demonstrate the possibilities of this new 3D printing method, the UFL researchers created several objects including even a soft artificial octopus, with eight tilted and tapering helical shells that mimic tentacles with microscopic (100 micron) resolution in the helical path the compose them. The octopus was then removed from the gel and retained its structural integrity while freely fluctuating in water.
In a similar way, a model of a jellyfish was also created that exhibited lifelike motion. More objects will come, including blood vessel like structures. That of 3D printing paste materials to form large complex structures was one of the biggest hurdles to overcome: as is often the case in this industry, it seems that even this achievement will be accomplished very soon.
