Spider silk has enormous potential in regenerative medicine due to its strong, stable and biodegradable natural fiber. Researchers have now produced double-sided spider silk fibers, which could provide damaged nerve or muscle cells with a platform for growth. As the researchers report in the journal Angewandte Chemieone side of the fibers is suitable for cell adhesion, while the other side could be used to attach factors or other substances.
Spider silk is non-toxic, biocompatible and attracts virtually no microbes. These properties make it an ideal candidate as a support for the growth of nerve cells. However, in the original form of spider silk, this process can be time-consuming and requires complicated preparation steps. With this in mind, materials scientist Thomas Scheibel of the University of Bayreuth, Germany, together with his team, optimized the natural product in multiple ways simultaneously, using a biotechnology approach.
Scheibel’s team produced spider silk using a genetically modified microorganism. “This gives us quality advantages,” says Scheibel, “and allows for protein modification.” The team not only modified a spider silk protein, but produced Janus spider silk fibers containing two differently optimized proteins in a single material.
Janus fibers take their name from the famous Roman god thanks to their two “faces” or sides. One side of the fibers was formed from a spider silk protein in which the team substituted a single amino acid. This reversed the net charge (from negative to positive) of the protein: “The surface of the material then becomes more attractive to the cells,” says Scheibel.
The other side of the fibers was formed from a spider silk protein to which the team added the amino acid cysteine. The addition of cysteine enables “click chemistry”, a method of functionalizing materials in which reaction partners react with each other so easily that it is as if they had simply been “clicked” together.
The team produced a two-sided, water-soluble fibrous material using side-by-side electrospinning, which involves extracting a yarn from a protein solution in an electric field. Post-processing produced the Janus spider silk fibers as a crystalline, insoluble material. The fiber was then specifically coated on one side with gold nanoparticles using click chemistry, which made the spider silk electrically conductive, allowing the success of the modification to be directly measured.
Janus spider silk fibers coated with gold nanoparticles could be used to stimulate muscle cell growth. “Muscles are excited by electrical impulses, which could be produced using a ‘golden thread’ made from spider silk fibers,” Scheibel explains. However, other modifications could be even more promising; researchers are also studying the binding of growth factors using click chemistry. These would not only promote adhesion of cells to the surface, but also targeted and faster growth of nerve cells along a splint.
Reference: Lang G, Grill C, Scheibel T. Site-specific functionalization of Janus fibers from recombinant spider silk. Angewandte Chemie International Edition. do I:10.1002/anie.202115232
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