Flexible, Bending Stable, and Biocompatible Silk Fibroin/NiFe Films for Bio-Integrated Microwave Applications

Integration of magnetic materials into bio-integrated flexible electronics will bring multi-functionality, such as magnetoception and wireless communication. In practical application, the performance of magnetic materials and devices should remain stable during cyclic bending–unbending and they can be degradable within a designated lifetime. However, direct integration of magnetic materials with flexible and biocompatible materials and maintaining mechanically stable microwave performance have not been achieved yet. Here, ultrathin (5–50 nm) permalloy (NiFe) films deposited on biocompatible silk fibroin (SF) films are shown to be bending stable, and dissolvable. The ferromagnetic properties of NiFe films deposited on SF, Kapton, and silicon are studied and compared by ferromagnetic resonance. Benefiting from the low surface roughness of fibroin, which is only ≈0.8 nm, SF/NiFe films exhibit comparable ferromagnetic properties to Si/NiFe, better than that of Kapton/NiFe films. Moreover, the ferromagnetic resonance field of SF/NiFe films remains highly stable during cyclic bending that is exposed to both compressive and tensile strain/stress, and its temperature stability is very close to that of Si/NiFe. Finally, the whole SF/NiFe films are demonstrated to be dissolvable and biocompatible. Therefore, SF/NiFe films can be a useful and stable platform for flexible and biocompatible microwave applications.