Symbiosis of Silica Biomorphs and Magnetite Mesocrystals

Abstract

Silica biomorphs are extraordinary inorganic superstructures formed via autocatalytic co‐precipitation and bottom‐up self‐assembly of alkaline‐earth carbonates and silica. However, they show no inherent functionality except for their striking textural motifs and curved morphologies. This work presents strategies to magnetize silica biomorphs, thus creating thermally stable ceramic microswimmers with unique elaborate shapes. This is achieved by growing super paramagnetic magnetite mesocrystals on and around the complex curved surfaces of biomorphs, while keeping their morphology and maintaining mesocrystal integrity. Selective mesocrystal formation on certain parts of the substrates is induced by chemical modification of the biomorph surface, increasing the loading of magnetite on the silica–carbonate structures and, in suitable cases, rendering them able to respond to external magnetic fields and move as microswimmer entities. In this way, the complex ultrastructure of silica biomorphs is successfully used as a template for functional ceramics. Furthermore, selective dissolution of the carbonate core from the biomorphs leads to hollow magnetic structures that could be filled with actives, thus serving as microcarriers with considerable loading capacity.

Nonclassical Recrystallization

“…In ordertog enerate mesocrystals, the nanocrystal dispersions were destabilized by ethanolv ia the gas phase (see Figure S1 for light microscopy image). [17] The most important steps of the crystallization processes are analysed by AUC and electron microscopy measurementsa nd shown in Figure2.T he nanocrystal dispersions, ar hombohedral mesocrystala nd the mesocrystals urfaces of Batch Ia re presented before (d H = 15 AE 0.3 nm) and after (d H = 14.7 AE 0.3 nm) the recrystallization (abbreviated "rc" in the figures) from heptane in Figure 2. Additionally,t he supernatant has been investigated after the assembly process was finished.…”

“…[16] Mesocrystals were crystallized via gas phase diffusiond estabilization in different solvents (cyclohexane Uvasol 99.9 %; THF VWR Chemicals 99.9 %; toluene VWR Chemicals 99.9 %; ethanol VWR Chemicals 99.9 %). [17] An anocrystal dispersion with 3 mLmL À1 oleic acid (Sigma-Aldrich 99.9 %) was destabilized with 1:1r atio (ethanol :s olvent). The recrystallization process involves that the coloured supernatant is removed via syringe subsequent the crystallization process is finished (see Figure S2).…”

Light-switchable anchors on magnetized biomorphic microcarriers

“…The elongated architecture of worm-like and helicoidal shaped biomorphs renders them with the potential to be used as microcarrier hulls. 9 Magnetic nanoparticles like magnetite nanocubes are used as responding units, which are needed for controlled movement through various media. 10,11 The benefit of this system is the ability to attach mesocrystals at specific sides of the biomorph (cf.…”

“…1). 9,12 Mesocrystals form in a non-classical pathway via the oriented assembly of nonspherical nanocrystals into superlattices. 13,14 In order to create further functionality, the structures must be equipped with an additional responding unit that allows addressing of a switchable anchor point for controlled compound load/release.…”

“…Previous studies employed postfunctionalization by the use of silane coupling chemistry. 9,15 The incorporation of light-switchable molecules into various systems and the development of so-called dynamic materials came into the focus of attention during the last decades. Not only the synthesis of materials for data storage, 16 electronic devices 17 or sensors 18 but also the biological applications of photo-responsive compounds, e.g.…”