Joe Harris

Nonclassical crystallization in vivo et in vitro (II): Nanogranular features in biomimetic minerals disclose a general colloid-mediated crystal growth mechanism.

Recent research has shown that biominerals and their biomimetics (i) typically form via an amorphous precursor phase, and (ii) commonly display a nanogranular texture. Apparently, these two key features are closely related, underlining the fact that the formation of biominerals and their biomimetics does not necessarily follow classical crystallization routes, and leaves a characteristic nanotextural imprint which may help to disclose their origins and formation mechanisms. Here we present a general overview of the current theories and models of nonclassical crystallization and their applicability for the advance of our current understanding of biomineralization and biomimetic mineralization. We pay particular attention to the link between nonclassical crystallization routes and the resulting nanogranular textures of biomimetic CaCO3 mineral structures. After a general introductory section, we present an overview of classical nucleation and crystal growth theories and their limitations. Then, we introduce the Ostwalds step rule as a general framework to explain nonclassical crystallization. Subsequently, we describe nonclassical crystallization routes involving stable prenucleation clusters, dense liquid and solid amorphous precursor phases, as well as current nonclassical crystal growth models. The latter include oriented attachment, mesocrystallization and the new model based on the colloidal growth of crystals via attachment of amorphous nanoparticles. Biomimetic examples of nanostructured CaCO3 minerals formed via these nonclassical routes are presented which help us to show that colloid-mediated crystal growth can be regarded as a wide-spread growth mechanism. Implications of these observations for the advance in the current understanding on the formation of biomimetic materials and biominerals are finally outlined.

Nonclassical crystallization in vivo et in vitro (I): Process-structure-property relationships of nanogranular biominerals

A distinct nanogranular fine structure is shared by a wealth of biominerals from several species, classes and taxa. This nanoscopic organization affects the properties and behavior of the biogenic ceramic material and confers on them attributes that are essential to their function. We present a set of structure-relationship properties that are rooted in the nanogranular organization and we propose that they rest on a common pathway of formation, a colloid-driven and hence nonclassical mode of crystallization. With this common modus operandi, we reveal the most fundamental and wide spread process-structure-property relationship in biominerals. With the recent increase in our understanding of nonclassical crystallization in vitro and in vivo, this significant process-structure-property relationship will serve as a source for new design approaches of bio-inspired materials.

Pseudomorphic transformation of amorphous calcium carbonate films follows spherulitic growth mechanisms and can give rise to crystal lattice tilting

Amorphous calcium carbonate films synthesized by the polymer-induced liquid-precursor (PILP) process convert into crystallographically complex calcite spherulites. Tuning the experimental parameters allows for the generation of crystal lattice tilting similar to that found in calcareous biominerals. This contribution evidences the role of spherulitic growth mechanisms in pseudomorphic transformations of calcium carbonate.

Single Nanogranules Preserve Intracrystalline Amorphicity in Biominerals

We revisit the ultrastructural features of different calcareous biominerals and identify remarkable similarities: taxonomically very distant species show a common nanogranular structure, even if different extracellular secretion patterns are employed or calcium carbonate polymorphs formed. By these analyses, we elucidate the locus of the small fraction of intracrystalline organic matrix revealing its intergranular character and localize the intracrystalline amorphous calcium carbonate moiety commonly found in mesocrystalline biominerals and provide a first explanation for the pathway by which it is preserved.

Universal structure motifs in biominerals: a lesson from nature for the efficient design of bioinspired functional materials

Biominerals are typically indispensable structures for their host organism in which they serve varying functions, such as mechanical support and protection, mineral storage, detoxification site, or as a sensor or optical guide. In this perspective article, we highlight the occurrence of both structural diversity and uniformity within these biogenic ceramics. For the first time, we demonstrate that the universality–diversity paradigm, which was initially introduced for proteins by Buehler et al. (Cranford & Buehler 2012 Biomateriomics; Cranford et al. 2013 Adv. Mater. 25, 802–824 (doi:10.1002/adma.201202553); Ackbarow & Buehler 2008 J. Comput. Theor. Nanosci. 5, 1193–1204 (doi:10.1166/jctn.2008.001); Buehler & Yung 2009 Nat. Mater. 8, 175–188 (doi:10.1038/nmat2387)), is also valid in the realm of biomineralization. A nanogranular composite structure is shared by most biominerals which rests on a common, non-classical crystal growth mechanism. The nanogranular composite structure affects various properties of the macroscale biogenic ceramic, a phenomenon we attribute to emergence. Emergence, in turn, is typical for hierarchically organized materials. This is a clear call to renew comparative studies of even distantly related biomineralizing organisms to identify further universal design motifs and their associated emergent properties. Such universal motifs with emergent macro-scale properties may represent an unparalleled toolbox for the efficient design of bioinspired functional materials.