Silk ink detects bacteria

In hospitals and doctor’s offices, keeping surfaces and clothes free from bacteria is paramount. Yet it is not always easy to detect where microorganisms hide. Researchers at Tufts University have found a way to address the problem with the help of an inkjet printer and a new kind of bioactive ink. The team headed by professor Fiorenzo Omenetto made a bioink from silk and printed it onto hospital gloves. The ink changes color when it comes into contact with certain kinds of bacteria.

Omenetto’s team made a pair of hospital gloves with the word “contaminated” printed onto the finger using silk ink mixed with polydiacetylenes. These inks react when they come into contact with E.coli, turning the text from blue to red. Scientists have suggested before that inkjet printing may be well-suited to apply bioactive molecules to a variety of surfaces but because bioactive components are often heat-sensitive, the printed biosensors often lost their functionality soon after printing.

Omenetto, Professor of Biomedical Engineering at Tufts University, has looked into the unique characteristics of the “old new material” silk for several years, as he explained in a 2011 TED Talk. Purified silk protein, or fibroin, offers intrinsic strength and protective properties that make it ideal for a range of biomedical and optoelectronic applications. “This natural polymer is an ideal “cocoon” that can stabilize compounds such as enzymes, antibodies and growth factors while lending itself to many different mechanically robust formats,” said Omenetto. The properties of silk led to the greatest breakthrough in the project: an ink formulation that is easily printable and washable.

The advantage of this process is that the inks can be printed on commercially available inkjet printers. “We used Dimatix inkjet printer to control the many parameters that regulate the formation of a picoliter-sized drop”, said Omenetto in an email interview. “This has then allowed us to tune the ink’s rheological properties involved in the inkjet printing process to best fit the inkjet technology.” Once the parameters were set, prints were carried out both in commercial printers with piezoelectric nozzles and in custom microfluidic printers.

There are a few details that need to be addressed before the method is ready for widespread use, Omenetto points out, but they are rather minor, including nozzle cleanup after use.

Omenetto and his team plan to explore multiple functional inks on many different formats as next steps in their research process. They want to put transducing printed elements in the form of conductive inks or biological sensors on a variety of objects, including gloves and fabric. One practical application is a smart bandage that delivers antibiotics embedded in the fabric. The scientists are also exploring ways to create different functional inks by leveraging the silk platform. If the research continues to be successful, silk inks could become the new material ushering in an era of smart bio-sensing soft materials.