Discovering Intrinsic Magnetism of Silk Fibroins

Abstract

Silk fibroin (SF) is an interesting biomaterials with intriguing mechanical, optical, piezoelectric, and biocompatible properties. The present study reports the first magnetic experiments to show that organic radicals in the building blocks of SF induce permanent magnetization in these materials. A saturation magnetization of 2.8 × 10−3 emu g−1 and non‐zero remnant magnetization of 2.2 × 10−4 emu g−1 with a coercive field of 65 Oe is observed in multiple SFs. Tightly bound β‐sheets of polyglycine‐alanine motifs provides sufficient steric hinderance to organic radicals and protects them from attack of reactive species. Moreover, it also shows that silk's ferromagnetic character can be enhanced by simple mechanical stretching and heating. This work demonstrates a new paradigm of magnetic proteins and opens a route toward the biomimetic discovery of iron‐free magnetic proteins.