Although we've seen "bio-inks" that allow sensors to be drawn directly on a person's skin and other surfaces to gauge things like glucose levels, functional inks such as this are usually heat-sensitive, meaning they aren't suitable for use in inkjet printers. Researchers at Tufts University have now developed silk-based inks containing bacteria-sensing agents that can withstand the rigors of inkjet printing, opening the door much wider for printing biomolecules.

The breakthrough comes courtesy of a purified silk protein called fibroin, which is strong enough to stabilize various types of compounds, such as antibodies, enzymes, nanoparticles, antibiotics and growth factors, by acting as a protective "cocoon".

"We thought that if we were able to develop an inkjet-printable silk solution, we would have a universal building block to generate multiple functional printed formats that could lead to a wide variety of applications in which inks remain active over time," said Fiorenzo Omenetto, Ph.D., the Frank C. Doble Professor of Engineering at Tufts School of Engineering.

The researchers doped the silk ink base with different bio-compounds to create a set of functional, inkjet-printable silk inks and tested them. Their creations included:

  • an ink with bacterial-sensing polydiacetylenes (PDAs), which was used to print the word "contaminated" on surgical gloves. When the gloves were exposed to E. coli bacteria, the word changed from blue to red.
  • a plastic dish imprinted with BMP-2 proteins that stimulate bone growth to control the direction of tissue growth.
  • sodium ampicillin printed on a bacterial culture printed to test the effectiveness of a topographical distribution of the antibiotic.
  • gold nanoparticles printed on paper, which has potential applications in a variety of areas, such as color engineering, surface plasmon resonance based sensing and bio-imaging.
  • enzymes printed on paper, to test the ability of the ink to carry small functional biomolecules.

In addition to bio-sensing gloves that could react selectively to different pathological agents, Omenetto says the ability to print antibiotics in topographical patterns would enable "smart" bandages in which therapeutics are custom incorporated into the bandage to match a specific injury.

Additionally, although the researcher's tests only involved the use of one ink cartridge, they believe it would be possible to use a multi-cartridge system to combine complex functions in the one print. They expect the technology will enable more effective tools in the fields of therapeutics, regenerative medicine and biosensing.

A paper describing the research was published in the Journal Advanced Materials.