Control over magnetite (Fe₃O₄) formation is difficult to achieve in synthetic systems without using non-aqueous media and high temperatures. In contrast, Nature employs often intrinsically disordered proteins to tightly tailor the size, shape, purity, and organization of the nanocrystals to optimize their magnetic properties. Inspired by such “flexible polyelectrolytes,” here random copolypeptides having different amino acid compositions are used as control agents in the bioinspired coprecipitation of magnetite through a ferrihydrite precursor, following a recently developed mineralization protocol. Importantly, the copolypeptide library is designed such that the amino acid composition can be optimized to simultaneously direct the size of the nanoparticles as well as their dispersibility in aqueous media in a one-pot manner. Acidic amino acids are demonstrated to regulate the crystal size by delaying nucleation and reducing growth. Their relative content thus can be balanced to tune between the superparamagnetic and ferrimagnetic regimes, and high contents of negatively charged amino acids result in colloidal stabilization of superparamagnetic nanoparticles at high pH. Conversely, with positively charged lysine-rich copolypeptides ferrimagnetic crystals are obtained which are stabilized at neutral pH and self-organize in chains, as visualized by cryo-transmission electron microscopy. Altogether, the presented findings give important insights for the future development of additive-mediated nanomaterial syntheses.

Hybrid materials are at the forefront of modern research and technology; hence a large number of publications on hybrid materials has already appeared in the scientific literature. This essay focuses on the specifics and peculiarities of hybrid materials based on two-dimensional (2D) building blocks and confinements, for two reasons: (1) 2D materials have a very broad field of application, but they also illustrate many of the scientific challenges the community faces, both on a fundamental and an application level; (2) all authors of this essay are involved in research on 2D materials, but their perspective and vision of how the field will develop in the future and how it is possible to benefit from these new developments are rooted in very different scientific subfields. The current article will thus present a personal, yet quite broad, account of how hybrid materials, specifically 2D hybrid materials, will provide means to aid modern societies in fields as different as healthcare and energy.

The Guest Editors emphasize the rapidly growing research in advanced materials. “Telecommunication, health and environment, energy and transportation, and sustainability are just a few examples where new materials have been key for technological advancement.”

Biological systems show impressive control over the shape, size and organization of mineral structures, which often leads to advanced physical properties that are tuned to the function of these materials. Such control is also found in magnetotactic bacteria, which produce—in aqueous medium and at room temperature—magnetite nanoparticles with precisely controlled morphologies and sizes that are generally only accessible in synthetic systems with the use of organic solvents and/or the use of high-temperature methods. The synthesis of magnetite under biomimetic conditions, that is, in water and at room temperature and using polymeric additives as control agents, is of interest as a green production method for magnetic nanoparticles. Inspired by the process of magnetite biomineralization, a rational approach is taken by the use of a solid precursor for the synthesis of magnetite nanoparticles. The conversion of a ferrous hydroxide precursor, which we demonstrate with cryo-TEM and low-dose electron diffraction, is used to achieve control over the solution supersaturation such that crystal growth can be regulated through the interaction with poly-(α,β)-dl-aspartic acid, a soluble, negatively charged polymer. In this way, stable suspensions of nanocrystals are achieved that show remanence and coercivity at the size limit of superparamagnetism, and which are able to align their magnetic moments forming strings in solution as is demonstrated by cryo-electron tomography.

Living organisms are well known for building a wide range of specially designed organic–inorganic hybrid materials such as bone, teeth, and shells, which are highly sophisticated in terms of their adaptation to function. This has inspired physicists, chemists, and materials scientists to mimic such structures and their properties. In this Review we describe how strategies used by nature to build and tune the properties of biominerals have been applied to the synthesis of materials for biomedical, industrial, and technological purposes. Bio-inspired approaches such as molecular templating, supramolecular templating, organized surfaces, and phage display as well as methods to replicate the structure and function of biominerals are discussed. We also show that the application of in situ techniques to study and visualize the bio-inspired materials is of paramount importance to understand, control, and optimize their preparation. Biominerals are synthesized in aqueous media under ambient conditions, and these approaches can lead to materials with a reduced ecological footprint than can traditional methods.

Lebende Organismen bilden spezielle organisch-anorganische Hybridmaterialien wie Knochen, Zähne und Schalen, die an ihre jeweilige Funktion hervorragend angepasst sind. Das hat Physiker, Chemiker und Materialwissenschaftler dazu angeregt, solche Strukturen mit besonderen Eigenschaften nachzuahmen. In diesem Aufsatz beschreiben wir, welche aus der Natur entlehnten Strategien man verwendet, um Biominerale aufzubauen und ihre Eigenschaften für biomedizinische, industrielle und technische Anwendungen abzustimmen. Biologisch inspirierte Ansätze wie molekulares Templatieren, supramolekulares Templatieren, organisierte Oberflächen und Phagen-Display werden ebenso diskutiert wie Methoden, mit denen Struktur und Funktion von Biomineralen nachgeahmt werden können. Wir zeigen, welche Rolle die In-situ-Untersuchung und In-situ-Visualisierung für das Verständnis der biologisch inspirierten Materialien und die Kontrolle und Optimierung ihrer Herstellung spielen. Biominerale bilden sich in wässrigen Medien unter Normalbedingungen, sodass aus ihnen abgeleitete Herstellungsverfahren ökologisch vorteilhafter sind als die herkömmlichen Methoden.

Porous biomorphic silicon carbide (bioSiC) is a structurally realistic, high-strength, and biocompatible material which is promising for application in load-bearing implants. The deposition of an osteoconductive coating is essential for further improvement of its integration with the surrounding tissue. A new strategy towards biomimetic calcium phosphate coatings on bioSiC is described. X-ray photoelectron spectroscopy (XPS) analysis shows that using 10-undecenoic acid methyl ester a covalently bound monolayer can be synthesized on the surface of the bioSiC. After hydrolysis it exposes carboxylic acid groups that promote the selective nucleation and growth of a very well-defined crystalline layer of calcium phosphate. The resulting calcium phosphate coating is characterized by X-ray diffraction and electron microscopy techniques. Further, ion beam imaging is employed to quantify the mineral deposition meanwhile, three-dimensional dual-beam imaging (FIB/SEM) is used to visualize the bioSiC/mineral interface. The monolayer is show to actively induce the nucleation of a well-defined and highly crystalline mixed octacalcium phosphate/hydroxyapatite (OCP/HAP) coating on implantable bioSiC substrates with complex geometry. The mild biomimetic procedure, in principle, allows for the inclusion of bioactive compounds that aid in tissue regeneration. Moreover, the mixed OCP/HAP phase will have a higher solubility compared to HAP, which, in combination with its porous structure, is expected to render the coating more reabsorbable than standard HAP coatings.

In der Materialchemie werden in Lösung gezüchtete Nanostrukturen oft mithilfe der Transmissionselektronenmikroskopie (TEM) untersucht. Häufig werden die TEM-Proben bei der Probenvorbereitung getrocknet und kontrastiert, und bei der Bildaufnahme selbst kommt es zur Wechselwirkung zwischen der Probe und dem Elektronenstrahl. Beide Prozesse rufen zur Vorsicht bei der Interpretation der erhaltenen elektronenmikroskopischen Aufnahmen auf. Alternativ dazu kann durch kryogene Probenpräparation und anschließende Abbildung mit kryogener Niederdosis-TEM ein beinahe nativer solvatisierter Zustand konserviert werden. In unserem Kurzaufsatz geben wir eine kritische Analyse der Probenvorbereitung und, noch wichtiger, der Datenaufnahme und Interpretation von elektronenmikroskopischen Aufnahmen. Die Übersicht soll auch Leitlinien für die Anwendung von (Kryo-)TEM als leistungsstarkes und zuverlässiges Hilfsmittel für die Analyse kolloidaler und selbstorganisierter Strukturen mit Abmessungen im Nanometerbereich bieten.

The investigation of solution-borne nanostructures by transmission electron microscopy (TEM) is a frequently used analytical method in materials chemistry. In many cases, the preparation of the TEM sample involves drying and staining steps, and the collection of images leads to the interaction of the specimen with the electron beam. Both aspects call for cautious interpretation of the resulting electron micrographs. Alternatively, a near-native solvated state can be preserved by cryogenic vitrification and subsequent imaging by low-dose cryogenic TEM. In this Minireview, we provide a critical analysis of sample preparation, and more importantly, of the acquisition and interpretation of electron micrographs. This overview should provide a framework for the application of (cryo)-TEM as a powerful and reliable tool for the analysis of colloidal and self-assembled structures with nanoscopic dimensions.