Ooids, Gallstones, Otoliths: Study Provides New Insight into Formation of Mysterious Natural Structures

Temperature oscillation produces stunning self-assembled mineral microspheres containing rhythmic ‘growth rings,’ providing new insight into the formation of similar structures found in nature.

Magnesium carbonate microhemisphere synthesized under passively produced temperature oscillation conditions. Image credit: Shihong Li et al.

Self-assembly is a fundamental aspect found in many organisms and throughout a wide range of materials found in nature, producing many fascinating and organized structures.

Periodic concentric microstructures have been extensively observed in natural materials such as ooids, a type of stone or crystal, whose origin has long been argued.

Such microstructures are also found in many biological samples such as gallstones, otoliths (the inner ear structure of some fish), and spherocrystal structures in egg yolks, which are intriguing but generally elusive.

The mechanisms behind formation of these naturally occurring and highly organized structures has yet to be fully understood, but a recent discovery at Van Andel Research Institute (VARI) may provide new insight on the formation of these structures.

“Chemists have been able to synthesize many complex mineral structures by use of a chemical template, additive or gel system, or by artificially changing the chemical components,” said Dr Shihong Li from the Laboratory of Translational Imaging at VARI, who is the lead author of a paper published in the open-access journal PloS ONE.

“However, the possibility of self-assembly of periodic concentric patterns by a pure mineral synthesized in aqueous solution has rarely been noticed.”

Inspired by the non-classic nucleation and crystallization concept, scientists at the VARI postulated that varying temperature in oscillation mode could cause the patterned microstructural self-assembly of mineralization in solution.

They discovered that magnesium carbonate synthesized in bicarbonate solutions does in fact form rhythmic concentric layered microparticles under temperature oscillation conditions, without needing any chemical template or additive.

“Fascinatingly, the waveform parameters of temperature oscillation can precisely control the rhythm of the layered structure, including the number of the rings and width between the rings,” Dr Li said.

Magnesium carbonate microhemispheres synthesized under passively produced temperature oscillation conditions. Image credit: Shihong Li et al.

Therefore, “these mineral ‘growth rings’ potentially act as a kind of thermal marker of their growth environment.”

The synthesis and observation of these layered microparticles of magnesium carbonate can be simply realized with a thermal cycler and a microscope.

Scientists at VARI are very excited with their discovery that such beautiful tiny crystalline structures can be produced with such a simple and programmable approach without extra intervention.

“This finding provides new insight into the mechanisms behind formation of similar structures found in nature that obviously might not have templates or additives at their disposal,” said study senior author Dr Anthony Chang, Head of Laboratory of Translational Imaging at VARI.

“It may also advance our understanding of the formation of gallstones, which could lead to better prevention and treatment, stimulating ideas for new drug discovery.”

The detailed physiochemical growth mechanism of these magnesium carbonate microparticles necessitates further study; also, the effects of temperature oscillation require further exploration into different systems.

“We believe that our finding represents one of the original models of patterned microstructure formation under non-equilibrium thermodynamics,” Dr Chang said.

The temperature oscillation-modulated self-assembly may give a fundamental viewpoint to recognize the patterned aqueous mineralization in nature, in addition to its potential for the construction of ordered microstructure

“NASA found concentric mineral microstructures of mysterious origin on Mars about two years ago. For new discoveries like this, it is crucial to keep an open mind while looking for the answers. Could our new findings be a piece of this puzzle?” Dr Chang said.

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Li S, Wang ZJ, Chang T-T. 2014. Temperature Oscillation Modulated Self-Assembly of Periodic Concentric Layered Magnesium Carbonate Microparticles. PLoS ONE 9 (2): e88648; doi: 10.1371/journal.pone.0088648