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Bio-Friendly Film Material Devised from Silk, Carbon Nanotubes

Carbon nanotubes

Carbon nanotubes spun into fiber (CSIRO, Wikimedia Commons)

31 Oct. 2018. Materials scientists and engineers developed a new material with the natural mechanical and degradable properties of silk, but configured as a film better suited for flexible biomedical devices. The team from University of Pittsburgh and Inha University in Incheon, Korea describe their material in the 26 October issue of the journal Applied Nano Materials (paid subscription required).

Researchers from the lab of Pittsburgh engineering professor Mostafa Bedewy are seeking to harness the superior strength, flexibility, and biodegradability of silk — characteristics of the fiber known for centuries — for today’s advanced biomedical devices, including miniaturized electronic systems implanted in the body. His lab studies interactions of materials at atomic and nanoscale levels, where 1 nanometer equals 1 billionth of a meter, applied to biomedical applications, and transferable to manufacturing.

The team discovered that to make the best use of silk’s unique properties requires a formulation of the material in something other than a fiber. Bedewy notes in a university statement that “we as engineers have recently started to appreciate silk’s potential for many emerging applications such as flexible bioelectronics due to its unique biocompatibility, biodegradability and mechanical flexibility.” He adds, however, “The issue is that if we want to use silk for such applications, we don’t want it to be in the form of fibers. Rather, we want to regenerate silk proteins, called fibroins, in the form of films that exhibit desired optical, mechanical, and chemical properties.”

The researchers found as well that working with fibroins derived from natural silk can be challenging, due to their instability in water and lack of mechanical properties found in silk fibers. To provide the needed stability, the team looked into a method for creating a composite materials combining fibroin proteins with carbon nanotubes, a material studied extensively in their lab.

The researchers knew, for example, that carbon nanotubes, formed from cylindrical carbon molecules and exhibiting high strength and electrical properties, heat up when exposed to microwaves. The team irradiated combined fibroins and carbon nanotubes with microwaves, with the carbon nanotubes absorbing the heat as predicted. They found the composite fibroin protein/carbon nanotube molecules took on a helix-type structure similar to amino acids and proteins, while transforming into a flexible and transparent film.

Further treatment with methanol vapors, say the authors, enabling better control of the silk/carbon nanotube composite film’s mechanical and degradation properties. This control feature makes it possible to custom-design silk/carbon nanotube composite films to meet specific needs for biomedical devices using flexible electronics, as well as sensors for temporary monitoring of conditions that degrade naturally and dissolve in the body.

The researchers point out that their work is still in an early stage, with much to learn about these new materials. “From a scientific perspective,” says Bedewy, “there is still a lot more to understand about the molecular interactions between the functionalization on nanotube surfaces and protein molecules. From an engineering perspective, we want to develop scalable manufacturing processes for taking cocoons of natural silk and transforming them into functional thin films for next generation wearable and implantable electronic devices.”

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