What if 3-D printers could use a wide assortment of different materials, from living cells to semiconductors, mixing and matching the “inks” with precision?
Jennifer Lewis, a materials scientist at Harvard University, is developing the chemistry and machines to make that possible. She prints intricately shaped objects from “the ground up,” precisely adding materials that are useful for their mechanical properties, electrical conductivity, or optical traits. This means 3-D printing technology could make objects that sense and respond to their environment. “Integrating form and function,” she says, “is the next big thing that needs to happen in 3-D printing.”
Last year, Lewis and her students showed they could print the microscopic electrodes and other components needed for tiny lithium-ion batteries. Other projects include printed sensors fabricated on plastic patches that athletes could one day wear to detect concussions and measure violent impacts. Most recently, her group printed biological tissue interwoven with a complex network of blood vessels. To do this, the researchers had to make inks out of various types of cells and the materials that form the matrix supporting them. The work addresses one of the lingering challenges in creating artificial organs for drug testing or, someday, for use as replacement parts: how to create a vascular system to keep the cells alive.
Top: Inks made of silver nanoparticles are used to print electrodes as small as a few micrometers.
Bottom: As in the other 3-D printing processes, the operation is controlled and monitored by computers.
Researchers have jury-rigged a 3-D printer, equipped with a microscope, that can precisely print structures with features as small as one micrometer (a human red blood cell is around 10 micrometers in diameter). Another, larger 3-D printer, using printing nozzles with multiple outlets to print multiple inks simultaneously, can fabricate a meter-sized sample with a desired microstructure in minutes.
A glove with strain sensors is made by printing electronics into a stretchable elastomer
The secret to Lewis’s creations lies in inks with properties that allow them to be printed during the same fabrication process. Each ink is a different material, but they all can be printed at room temperature. The various types of materials present different challenges; cells, for example, are delicate and easily destroyed as they are forced through the printing nozzle. In all cases, though, the inks must be formulated to flow out of the nozzle under pressure but retain their form once in place—think of toothpaste, Lewis says.