Scientists at MIT and Tufts University have developed a tough new material that improves upon the strength of natural silk, and which can be made in different forms. As silk is a naturally biocompatible substance that produces no adverse reactions in the human body, the material, a reconstituted silk called regenerated silk fiber, could lead to a range of commercial applications and uses in biomedicine, such as scaffolding for the growth of new skin.

Despite the improvements in the synthesis of artificial materials, research has failed to produce an artificial silk whose fibers are as strong as the natural version, whose microstructures provide its stiff and stretchy qualities. However, in this study, reported in Nature Communications [Ling et al. Nat Commun. (2017) DOI: 10.1038/s41467-017-00613-5], the team took silk from silkworms and broke it down chemically before reassembling it to produce a material with twice the stiffness and which can be shaped into complex shapes and structures such as meshes, meshes, tubes, coils and sheets.

"We're not satisfied with what [the silkworms] make, we want to make our own new materials"Markus Buehler

On dissolving silkworm cocoons, it was crucial that they didn’t break the fibers down completely but only to the stage where the molecular structure breaks up into an intermediate form composed of microfibrils – small, thread-like assemblies that maintain key hierarchical structures that provide natural silk with its strength. This was then extruded through a small aperture to produce a fiber twice as stiff as conventional silk and nearly as stiff as the drag-line silk of a spider.

These forms can be developed using the reconstituted material in a 3D printing system that is tailored for silk solution, and the process could be carried out with conventional manufacturing technologies, allowing for scaling up to commercial quantities, with its properties being managed as required by altering the speed of the extrusion process. In addition, the fibers are extremely sensitive to changing levels of humidity and temperature, and can be made electrically conductive through the addition of a coating of another material, such as a layer of carbon nanotubes. This could help their use in sensing devices, where a surface covered with a layer of the fibers could be responsive to touch or changes in the ambient conditions.

The regenerated silk fiber process could also bring cheaper silk, as natural silk thread and fabric is expensive, primarily because of the labor-intensive process of unraveling the thread from the cocoon and then weaving it. Another application could be in bedsheets produced from the fibers that are used in care facilities to prevent bedsores by monitoring pressure and providing automatic warnings when patients are too long in the same position.