Curving fibrous crystals are frequently found in several kinds of biominerals. Here, detailed structures of the curving morphologies are characterized using hydroxyapatite in the enamel layers and calcium carbonate crystals in gastropod shells. The orientation adjustment of the fibrous units occurs through stepwise bending at the grain boundaries with a gradual change of the crystallographic direction. Artificial curving crystals are successfully produced in viscous solution systems. Various kinds of curving crystals are formed through stepwise bending similar to biominerals. The change in the ion flow is deduced to be essential to control the growth direction of the rod like crystals
Foraminifers are unicellular eukaryotes that primarily inhabit the ocean. Calcareous foraminifers have been forming calcium carbonate shells. The calcareous shells are used as environmental indicators as a geologic record because they are stored in sediments for an extended period. However, the necessary process of shell formation of foraminifera was not well studied. Therefore, we have investigated how calcium and carbonate ions uptake by the biological process at the site of calcification. We also show how the microscopic structure of the calcification site where the shell formation process proceeds. In our study, after optically observing the shell formation process, fluorescence imaging was performed to record the environment inside and outside the calcification site. Besides, the electron microscopy clarified that organic structures define the detailed calcareous structures. These relationships had been almost ignored in this couple of decades. By obtaining samples of various stages during shell formation through laboratory culture experiments, we were able to study the mechanism of chamber formation.
Biominerals, which are “hard tissues” mineralized by organisms, indicate distinctive microstructures formed by organic substances, which may regulate the crystal growth of minerals. Since biominerals have various excellent features including mechanical strength as a nano-composite material, many researchers have attempted to reveal their formation mechanism for industrial applications. In our studies, we have focused on the Japanese pearl oyster Pinctada fucata. P. fucata is used for pearl aquaculture in Japan and has fine shell microstructures consisting of calcium carbonates and some organic matrices. The shell is composed of three mineralized structures (two shell layers and the ligament) of different microstructures and an unmineralized outer organic membrane. Although all those mineralized structures contain calcium carbonate crystals, the crystal morphology, size, orientation and polymorphism are completely different among those structures. P. fucata may use a specific set of organic molecules to control the crystal growth in each structure. However, the information about the important organic molecules for the formation of calcium carbonates in the shell of P. fucata is still limited. In this article, we review several organic molecules associated with shell formation that we identified from those shell structures.
With some exceptions, most land plants are static. Being static always involves the risk of being preyed. To counter that, plants have evolved various defence mechanisms against herbivores. These defence mechanisms can be divided into two main strategies. The first is called chemical defence, which involves synthesizing and storing organic compounds such as alkaloids, terpenes, polyphenols, and proteolytic enzymes. These organic compounds act as chemical weapons that are toxic to herbivores, or causes digestion and nutrient blockages. The second mechanism is physical defence, where the cellulose in the cell walls is often reinforced with deposits of inorganic minerals, forming an organic-inorganic hybrid armour. In this paper, we review several reports on plant biomineralization, which is an example of physical defence in plants, and discuss the molecular mechanism and significance of the mineral formation process from a biological point of view.
Octacalcium bis (hydrogenphosphate) tetrakis (phosphate), having a chemical composition Ca8(HPO4)2(PO4)4·5H2O, frequently expressed as Ca8H2(PO4)6·5H2O and abbreviated to octacalcium phosphate (OCP), have become recognized to show a highly osteoconductive performance in comparison with other calcium phosphate materials. Such a bioactive property has been found to be induced while OCP is mineralized to a poorly crystallized calcium-deficient hydroxyapatite (Ca-deficient HA) involving inorganic ion incorporation or release and serum protein adsorption under physiological condition. OCP displays non-stoichiometric composition and distinct morphological feature in the crystals. These physicochemical characteristics are acquired depending on the synthesis condition. OCP is capable of stimulating osteoblastic differentiation and osteoclast formation from their precursor cells in vitro therefore may activate these cells directly or indirectly under an environment induced by its mineralizing process to Ca-deficient HA if implanted in bone defects. These osteoconductive properties can be modified by the crystals stoichiometry through distinct biological responses.
Corals are surviving and adapting to drastic change in Earth’s history and create nanometer to planetary scale complex structures throughout geological time. Once coral larvae settle on the rocky substrate, coral biomineralization occurs to produce their skeletons and coral growth and accumulation of their skeletons with other organisms and sediments eventually form coral reefs where maintain the highest diversity in marine ecosystem. Coral-algal symbiosis is sensitive to global and regional scale environmental changes and coral skeletons are useful to reconstruct the century scale climatic and environmental changes with high temporal resolution such as global warming, ocean acidification, and ocean pollution. Coral calcification plays important role to long to short term carbon cycles via their cellular level of organic and inorganic carbon production in coral-algal symbiosis. Therefore, understanding coral biomineralization is crucial to figure out the better evaluation of global climate changes and carbon cycle in the past and future.