Biological Crystallization

At least since the explosion of diversity that life experienced about 540 million years ago, multicellular organisms have constantly been exploring different pathways to use minerals for building sophisticated structures with different purposes. While that search occurs by trial and error, the efficient hierarchical mineral architectures found by life are made by the strict control of the nucleation and growth steps during their formation, with different patterns depending on the scale. This chapter will cover the current knowledge on the nucleation, growth, and organization of mineral crystals within living organisms, either inorganic or organic crystalline structures. We review the biological control of these processes for a number of functional composite inorganic/organic biominerals such as mollusk shells, echinoderm spines, bones, teeth, otoliths, eggshells, magnetosomes, pearls, and stromatolites. We have also included organic structures such as the mammalian stratum corneum, reptilian molts, fish scales, and butterfly wings. Furthermore, some common techniques to study in vitro the role of biological molecules or templates on crystallization, including batch, vapor diffusion, or gel crystallization, or to induce crystallization in vivo, are described. Finally, current trends and future perspectives of biological crystallization linked to its potential applications in fields such as biomedicine, paleontology, pathological crystallization, and materials science—where it is a source of inspiration for the fabrication of composite materials—are briefly summarized.