Printable Silk Inks Promote Bio-Sensing Needs

Silk inks containing enzymes, antibiotics, antibodies, nanoparticles, and growth factors could turn inkjet printing into an effective healthcare tool, according to a new study.

Fibroin, developed by researchers at Tufts University (Medford, MA, USA), is a purified, liquid formulation of regenerated silk protein that offers intrinsic strength and protective properties for a range of biomedical and optoelectronic applications. Fibroin can be printed using inkjet technology to form stabilizing “cocoons” for various compounds, such as enzymes, antibodies, and growth factors on numerous surfaces. Potential uses include bio-sensing, therapeutics, and regenerative medicine.

The researchers also created and tested a custom library of inkjet-printable, functional silk inks, each with different active components. For example, bacterial-sensing polydiacetylenes (PDAs) were printed on surgical gloves; the word "contaminated" printed on the glove changed from blue to red after exposure to E. coli. Proteins that stimulate bone growth (BMP-2) were printed on a plastic dish to test topographical control of directed tissue growth.

The researchers also printed the sodium ampicillin on a bacterial culture to test the effectiveness and topographical distribution of the antibiotic; gold nanoparticles were printed on paper, for possible application in photonics and biology; and enzymes were printed on paper to test the ability of the ink to entrain small functional biomolecules. The study describing the fibroin printable silk technology was published early online on June 16, 2015, in Advanced Materials.

“The heat-sensitive nature of these unstable compounds means printed materials rapidly lose functionality, limiting their use,” said senior author Fiorenzo Omenetto, PhD. “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.”

Silk is a natural fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm (Bombyx mori). Silk emitted by the silkworm consists of two main proteins, with fibroin forming the structural center of the silk, and serecin surrounding it. The high proportion (50%) of glycine in serecin allows tight packing, and the resulting fibers are strong and resistant to breakage. The tensile strength is due to the many interceded hydrogen bonds, and when stretched the force is applied to these numerous bonds and they do not break.

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