Principles of biomineralization

Abstract Detailed investigations of interfacial crystallization procedures are important to understand the basic principles of biomineralization processes. These interfacial phenomena can also be used to form new types of biomimetic composite materials. In a series of experiments we studied the influence of Langmuir-monolayers on the formation of ultra-thin calcium carbonate Aims. We systematically compared experiments performed at the water surface wi results obtained at the water/oil interface. 

The main principles of biomineralization can be discerned from several excellent reviews that are available on the subject [56,57,116,117], The first step in many forms seems to be space delineation by cells. Materials frequently used for this purpose are lipid bilayers either in the cell wall or as a part of matrix vesicles located outside the cell. A less frequently used material is composed of polymerized, water—insoluble proteins and/or polysaccharides [116]. Several mechanisms of crystallization within biological cells or vesicles have been described ... 

Our understanding of the mechanisms of biomineralization is superficial435. In the past 20 years, most researchers have concentrated upon the extracellular concepts of epitaxy, matrix composition and solubility products while recently the role of cellular organelles and enzymes have attracted more attention. But there are some accepted principles which necessarily carry theoretical implications445. ... 

Looking at the literature in the field of biomineralization, one notices, that the majority of articles is descriptive in nature. On the basis of electron micrographs or thin section studies, the intricate relationships between mineral phase and organic matrix are investigated. Other papers deal with the chemical composition of the mineralized tissue and the minerals. Only a few authors address themselves to the question of metal ion transport mechanisms in cellular systems and the solid state principles involved in mineral deposition on organic substrates. All three sets of information, however, are essential to understand calcification processes. It appears, therefore, that information on the functionality of metal ions in living systems and their role in mineral deposition are particularly desired in this area of research. 

During the deposition of biophosphates a selective fractionation of chemical elements occurs. Although this process has been known in principle for some time380, 381, detailed studies had to await the development of new analytical tools such as the electron microprobe382. In order to relate the enrichment or depletion of elements in the course of biomineralization with time, precise time markes are needed380, 383 389). So the problem of elemental fractionation becomes a twofold one, i.e. quantitative measurements a few micrometer apart and accurate timing at about hourly intervals. 

The aforementioned DQ technique is well suited to characterize the spatial distributions such as phosphorus nuclei in biomaterials or apatitic systems (vide infra). However, it should be noted that the variation in the parameter A, if any, could be due to a number of factors such as the change in the protonation states and motional dynamics, not necessarily reflecting any change in the second moment. Therefore, 31P DQ NMR is a very useful method in the study of biomineralization but the results should be largely interpreted in a qualitative manner. In principle, the second moment can also be obtained by measuring the attenuation of... 

The chiton tooth radula is perhaps the best documented example of the general principle in biomineralization, namely that the organic matrix is formed first, and only then are the spaces within the framework filled by the mineral. 

Principles of Solid-State Biological Inorganic Chemistry An Overview of the Major Classes of Biominerals... 

As we begin to unravel the mechanisms by which biominerals are produced, more recently efforts have been directed to replicating key fabrication strategies and structural features into materials design. In this introductory section, we present a brief account of the principles involved in the formation of biominerals or if you prefer, the mles of thumb which govern the deposition of solid-state inorganic material. 

Two procedures for the formation of nanosized particles within these films are employed. The first procedure combines the principles of colloid chemistry, selforganization and the growth of monolayers. The formation of nanosize particles is performed in the presence of stabilization agents and components forming LBFs. Chemical and photochemical reduction of metal salts in aqueous solutions can cause particle formation. The resulting layers act as specific templates. This approach is also of interest in studies of biomineralization, including studies using the sol-gel method. 

Pearl luster pigments, which can be natural or synthetic, show outstanding qualities of luster, brilliance and iridescent color effects based upon optically thin layers. This visual impression develops by reflection and scattering of light on thin multiple layers. In nature this is not limited to pearls and mussel shells alone there are a multitude of birds, fish, precious stones and minerals, even insects which demonstrate a pearl luster effect. Experiments to understand the optical principles of natural pearl luster demonstrate that the brilliant colors are based upon structured biopolymers and upon layered structures which are developed by biomineralization. 

Japp, J. (1994). Evolution by Association —A History of Symbiosis. Oxford University Press, Oxford Mann, S. (2001). Biomineralization Principles and Concepts in Bioinorganic Materials Chemistry. Oxford University Press, Oxford... 

Biomineralization. In biomineralization, inorganic elements are extracted from the environment and selectively precipitated by organisms. Usually, templates consisting of suitable macro-molecules serve as a substrate for the heterogeneous nu-cleation of bulk mineralized structures such as bone, teeth and shells. Biological control mechanisms are reflected not only in the type of the mineral phase formed but also in its morphology and crystallographic orientation (Mann et al., 1989 Lowenstamm and Weiner, 1989). Two examples (perhaps oversimplified) may illustrate the principle (Ochial, 1991) ... 

The regulation of supersaturation levels at the mineralization site by active ion transport can, in principle, control the rate of nucleation of the biomineral as indicated in Eq. (3) of Sect. 3.1. Also, the choice between pathways A and B in Fig. 3.9 will be determined to some degree by the structure of the critical nucleus initially formed. 

Materials synthesis in biology is often conducted in compartments that delimit the extent of growth as well as provide a microenvironment in which parameters such as supersaturation of a precipitating phase can be delicately controlled by active transport of ions. This is how many biomineralization processes take place—for example, the formation of exquisitely patterned mineral plates in the soft tissues of coccolithophores. Mimesis of this principle... 

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