Biomineralisation process

Powell AK (1997) Polyiron Oxides, Oxyhydroxides and Hydroxides as Models for Biomineralisation Processes. 88 1-38... 

While the initial stage of iron incorporation in mammalian ferritins requires the ferroxidase sites of the H-chains, thereafter the inner surface of the protein shell of the L chains provides nucleation sites which supply ligands that can partially coordinate iron but which leave some coordination spheres available for mineral phase anions. This enables the biomineralisation process to proceed, with formation of one or more small polynuclear ferrihydrite crystallites, which can then act as nucleation centres for mineral growth. Most probably, one of these clusters will become the dominant nucleation centre and growth of the mineral would then occur from this centre. 

The final approach is to use a combination of microarray techniques, antisense ohgonucleotides, functional tests, and the use of monoclonal antibodies to identify matrix proteins and families of matrix proteins involved in the biomineralisation process, and ultimately to establish their function. The recent pubhcation of the genome of the sea urchin Strongylocentrotus purpuratus represents a promising start to the bioinformatic approach to the identification, characterisation, and functional analysis of particular molecules of the matrix involved in biomineralis ation. 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Caio(P04)6(OH)2], usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralisation process leading to the hardest mineralised tissue known, the enamel of mammalian teeth. 

For analyte removal, the sensor surface is flushed with an SDS solution, which is an anionic surfactant. Additionally, imprinted layers proved catalytic for protein crystallisation. One could also regard MIP materials as model system of biomineralisation processes D Souza et al. [76] showed an application where crystal-imprinted materials indeed fundamentally increase calcite growth on the surface and therefore work as seeds. 

Phospholipids often play a key role in biomineralisation processes. Examples are in the formation of coccolith conglomerations of CaCOg crystals and magnetosome arrangements of Fe304 crystals, found in nature [68]. It may be possible to utilise liposomes for the in situ formation of artificial biomaterials. 

The most important materials developed are nanocomposites and nanotubes. Fabrication of the first nanocomposites was inspired by nature (biomineralisation). Nanocomposites based on nanoclays and plastics are seen as ideal materials for improved barrier properties against oxygen, water, carbon dioxide and volatiles [37]. This makes them in particular suitable for retaining flavours in foods. The technology is rather straightforward using commercially available nanoclays and extrusion processing. 

Biological calcification processes are widely distributed in nature. They can be found in microorganisms, in plants, in the animal kingdom and in humans. Under physiological conditions, the results of mineral deposition in biological systems can be represented by the formation of bones, teeth and shell material as well as coccoliths, corals, pearls etc. The variety of biomineralisates can best be expressed by the fact that approximately 128,000 species of molluscs636 are known. The majority of them (Conchifera) form shells of different kinds of size and shape as well as of color. 

While CaC03 crystals (calcite and aragonite) predominantly appear in egg shells and in biomineralisates from invertebrates, calcium phosphates are predominantly involved in processes which play an inportant role in medicine. They will be described here in detail the knowledge of their structures are most relevant for the understanding of the cellular and molecular processes in bones and teeth. 

Biomineralisation is the study of processes that lead to the formation of hierarchically structured organic—inorganic materials generated by living organisms, such as shells, bone, and teeth. Over the last few decades, our ability to identify the often large number of macromolecules involved in the process of biomineralisation and the interactions between them has grown and expanded. 

The processes of biomineralisation are grounded on the complex interaction of inorganic solids and organic templates. Following Mann (1996), biomineralisation, that is formation of hydroxyapatite-based bones and teeth of vertebrates, calcitic egg shells of birds and calcitic and aragonitic shells of mussels can be viewed as a sequence of four consecutive steps. 

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