For centuries, from wood blocks and the printing press to laser jet printing, 2D printing was the forefront of replication. While those innovations have rapidly advanced in recent decades as the computer age has moved into high gear, they pale in comparison to some of the most cutting-edge work happening today.
In the last 30 years, 3D printing has pushed the envelope, particularly in the last decade as 3D printers have become significantly cheaper and more accessible. This has yielded significant progress, with 3D printing now used to generate everything from trivial knick-knacks to car parts to future biological implants like hearts and other organs.
Now, printing is entering the next stage of development and blasting through boundaries. Welcome to 4D printing. And just what is that fourth dimension? It’s a time element expressed by a change in the shape of the 3D-printed object. In other words, we’re still using a 3D printer but these novel 4D printing inks – aka liquid crystal elastomers – allow for that additional dimension of time through a change in shape.
Researchers at Rice University in Houston, Texas are using 4D printing with new polymers – made from petrochemical building blocks – that allow printed objects to shift, change shape, or reconfigure. The effort works by creating “a liquid crystal polymer ink that incorporates sets of chemical links between molecules that are mutually exclusive.”
By using different temperatures, electric current, pressure, and other factors, the polymers can adjust shape or form on demand. And these novel and complex molecules start with the base petrochemicals, like ethylene and propylene for the PETMP component; propylene and benzene for the mequinol component; ethylene for the EDDET part; and, propylene and toluene for the RM257. These components are combined to create the liquid crystal elastomer for the Rice team.
At the Massachusetts Institute of Technology, researchers started in 2013 with a self-folding cube through 4D printing that folds up when placed into hot water. Since then the team, led by Skylar Tibbits, has constructed quite a few different 4D products that undergo a variety of physical changes in time (the 4th dimension).
Those 4D “inks” are a concoction of different acrylates made possible by the petrochemical propylene. But wait, there’s more…propylene is also used with benzene to create the bisphenol epoxy acrylate; and, propylene is used to create the epichlorohydrin that makes the world of epoxies possible. To really stretch it, propylene is used to make the trimethylolpropane in the TMPTA component.
As you can probably tell, we like our propylene molecule. A lot.
While 4D printing is still very much in a nascent stage, it has significant potential and applicability for designers and products. Engineers are examining the ways 4D printed objects could be used to repair pipe systems or how 3D printed furniture – currently limited in size given restrictions of the printers themselves – could change with 4D printing.
Medical researchers are also developing new approaches for 4D printing that could assist with testing for brain tumors and other cancers. At Rutgers Cancer Institute, researchers are using 4D printed “arrays that self-transform from cell-culture inserts into histological cassettes for rapid programmable drug testing.”
With each new turn and advancement in the printing process, polymers made from petrochemicals and other innovative building blocks are enhancing the range of outcomes. How it will advance human health and wellness remains to be seen, but the future possibilities are immense.