Biomineralization in vertebrates is a ubiquitous and tightly regulated process which creates hierarchical structures for the skeleton. Because of the lack of understanding and applicability of cell‐based or biological systems to achieve intrafibrillar mineralization, scientists adopted various in vitro methods to elucidate the mechanism of intrafibrillar mineralization. In this article, biomimetic intrafibrillar mineralization of collagen in its wide ramifications is reviewed. It is intriguing how prevailing intrafibrillar mineralization mechanisms derived from two potentially discordant crystallization philosophies were equally adept, depending on the experimental context, at theorizing the formation of calcium phosphate within a fibrillar template. This complementarity is not unique to biomineralization and has precedence in other fundamental physical interpretations. A new intrafibrillar mineralization process based on the use of polycationic process‐directing agent added uncertainty to the use of existing mechanisms in accounting for the observations.

The crystallization process from a solution begins with nucleation, which determines the structure and size of the resulting crystals. Further understanding of multi-pathway crystallizations from solution through two-step nucleation mechanisms is needed. This study uses density functional theory to probe the thermodynamic properties of alumina clusters at high temperature and reveals the thermodynamic relationship between these clusters and the saturation levels of dissolved oxygen and aluminum in an Fe–O–Al melt. Based on the thermodynamics of cluster formation and the experimental evidence for both excess oxygen in the Fe-O-Al melt and for alumina with a polycrystalline structure in solidified iron, we demonstrate that the appearance of various types of clusters that depends on the saturation ratio determines the nucleation steps that lead to the various crystallization pathways. Such mechanisms may also be important in nucleation and crystallization from solution.

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