Mrs Bulletin最新文献

Abstract

Spider dragline silk is one of the most versatile natural materials ever known, with several incredible mechanical, optical, thermal, piezoelectric, and biological properties. However, its fundamental magnetic nature remains unknown. In the present study, we report the observation of room-temperature ferromagnetism in metal-free pristine spider dragline silks upon induction of defects in its β-sheet nanocrystals. The magnetism originates in spider silks due to ferromagnetic coupling among carbon radicals (dangling bonds) generated in β-sheet nanocrystals. Direct control over silk’s magnetic properties can be achieved by controlling its microstructure. This was achieved by changing the spinning speed of dragline silks from the spider and observing a direct effect on its magnetism. Owing to the high-temperature stability of silk, their ferromagnetism survives up to 400 K and remains unaffected by high humidity or contact with water. This makes silk-based magnets suitable for medical and technological applications. Spider silk can thus act as a multifunctional nontoxic biomagnet with incredible mechanical properties. Our work demonstrates a new paradigm of magnetic proteins and opens a route toward the bioinspired discovery of iron-free magnetic proteins. Biomimicking its structure is of great importance for designing future medical sensors and actuators, including advancements in tissue engineering and artificial muscles.

Impact statement

It is well known that densely bound β-sheet nanocrystals within silk biopolymers are responsible for their incredible mechanical strength and stiffness. In the present study, we show that these β-sheet nanocrystals also create an ideal environment for stable carbon radicals within the silk structures. A magnetic exchange interaction among these radicals results in a stable and robust carbon-based ferromagnetism at room temperature in these polymers. These are the first ever reports of observation of room-temperature ferromagnetism in pristine spider silks. Inducing defects in these nanocrystals by applying strain on dragline silk samples leads to an enhanced saturation magnetization. A direct effect of nanocrystallite size on the ferromagnetic properties of silk was also observed. Blending magnetism in a bioinspired and metal-free protein-based biomaterial can tremendously impact biomedical applications such as nanoscale drug delivery systems, magnetic resonance imaging contrast agents, magnetic scaffolds, and artificial muscles. Our work will stimulate a new theoretical understanding of the origin of magnetism in peptide-based biomaterials with consequences in quantum biology and spintronics. Our work establishes a novel method to control the magnetic responsivity of proteins by engineering atomic defects.

Graphical abstract

Atomic force microscopy is one of the most important tools in nanoscience. It employs an atomic probe that can resolve surfaces with atomic and subatomic spatial resolution and manipulate atoms. The qPlus sensor is a quartz-based self-sensing cantilever with a high stiffness that, in contrast to Si cantilevers, allows to oscillate at atomic radius amplitudes in the proximity of reactive surfaces and thus provides a high spatial resolution. This article reports on the development of this sensor and discusses applications in materials research.

Graphical abstract

Abstract

The powerful functions of materials in the living world utilize supramolecular systems in which molecules self-assemble through noncovalent connections programmed by their structures. This process is of course also programmed by the nature of the chemical environment in which the structures form introducing the potential to autonomously use external energy inputs partly derived from fuel molecules. Our laboratory has focused over the past three decades on integrating this notion of bioinspired supramolecular engineering into the design of novel materials. We present here three projects on functional supramolecular materials that address important societal needs for our future. The first is inspired by the photosynthetic machinery of green plants, creating materials that harvest light to produce fuels for sustainable energy systems. The second example is that of life-like robotic materials that imitate living creatures and effectively transduce different types of energy into mechanical actuation and locomotion of objects for future technologies. The third topic is supramolecular biomaterials that mimic extracellular matrices and provide unprecedented bioactivity to regenerate tissues to achieve longer “healthspans” for humans. In this example, we discuss a recent breakthrough in the structural design of supramolecular motion, which surprisingly led to biomaterials with the potential to reverse paralysis by repairing the brain and the spinal cord.