Biomineralization is a widespread phenomenon in nature leading to the formation of a variety of solid inorganic structures by living organisms, such as intracellular crystals in prokaryotes, exoskeletons in protozoa, algae, and invertebrates, spicules and lenses, bone, teeth, statoliths, and otoliths, eggshells, plant mineral structures, and also pathological biominerals such as gall stones, kidney stones, and oyster pearls. These biologically produced biominerals are inorganic-organic hybrid composites formed by self-assembled bottom up processes under mild conditions, showing interesting properties, controlled hierarchical structures, and remodeling or repair mechanisms which still remain to be developed into a practical engineering process. Therefore, the formation of biominerals provides a unique guide for the design of materials, especially those that need to be fabricated at ambient temperatures. In biominerals, the small amount of organic component not only reinforces the mechanical properties of the resulting composite but also exerts a crucial control on the mineralization process, contributing to the determination of the size, crystal morphology, specific crystallographic orientation, and superb properties of the particles formed. Therefore, biological routes of structuring biominerals are becoming valuable approaches for novel materials synthesis. Although several principles are applicable to the majority of the biominerals, herein we will focus on the role of polysaccharide polymers in calcium carbonate-based biominerals. As a general principle, the assembly of these biominerals consists of a four-stage process. It starts with the fabrication of a hydrophobic solid organic substrate or scaffolding onto which nucleation of the crystalline phase takes place closely associated with some polyanionic macromolecules. Crystal growth is then controlled by the addition of gel-structuring polyanionic macromolecules, and finally mineralization arrest is accompanied by the secretion of a new inert scaffolding of the same type or the deposition of other hydrophobic inhibitory macromolecules. Currently, a large number of proteins have been described which are involved in the control of biomineralization. These proteins are usually highly negatively charged and contain carboxylate, sulfate, or phosphate as functional groups, which may bind Ca ions and could control crystal nucleation and growth by lowering the interfacial energy between the crystal and the macromolecular substrate. However, the precise mechanism involved in controlling crystal nucleation, growth, and morphology is far from being understood. Combinatorial biology techniques have been recently developed for testing the ability of randomly generated peptides to bind different substrates or ions, thus allowing a correlation between peptide structure and ion binding affinity. However, the main focus is on the role of the backbone structure of the polymer due to the primary structure of the protein, because the synthetic technology does not allow the formation of post-translational modifications, such as sulfation and phosphorylation, which do occur in the eukaryotic cell. Even so, the occurrence of negatively charged groups in macromolecules involved in biomineralization, mainly derived from acidic amino acids, has inspired many researchers to produce synthetic polymers having such groups in order to control the size, orientation, phase, and morphology of inorganic crystals. However, since Abolins-Krogis’ work, a slow but increasing interest has been developed to explore the role of polysaccharides in biomineralization, despite the fact that their involvement in biomineralization seems to appear very early in evolution. There is no single type of polysaccharide associated with biominerals, but such polysaccharides are mainly hydroxylated, carboxylated, or sulfated or contain a mixture of these functional moieties.

Polysaccharides and Proteoglycans in Calcium Carbonate-based Biomineralization

Identification and localization of lysozyme as a component of eggshell membranes and eggshell matrix.

Chemical composition of chicken eggshell and shell membranes

Publisher Summary This chapter summarizes cell biology, morphological organization, crystallography, chemical composition, process of mineralization, and biological function of avian eggshells. It also discusses emerging concepts of biomineralization and speculates about the mechanism of eggshell assembly and its implications for fabrication of polymer-ceramic composites. The eggshell is a microenvironmental compartment for housing developing embryos of a number of species. This unique microenvironment provides physical protection to the embryo and regulates gas, water, and ionic exchange. The avian eggshell can be characterized as a multilayered, polymer–ceramic composite. The three main layers include an outer mucous layer, an intermediate calcified zone, and an inner fibrous membrane layer. The shell membranes are the most internal layer of the eggshell and are formed by two nonmineralized fibrillar sublayers, the outer membrana testae externa, and the inner membrana testae interna or putaminis. The most external layer of the eggshell is referred to as the cuticle. This proteinaceous layer covers the entire calcified portion of the shell to a depth of about 10 μ m. The complementary use of biological, chemical, and crystallographic approaches demonstrates that the avian eggshell is a very promising model for the study of biomineralization. Avian eggshell is one of the most rapidly mineralizing biological systems known.

Biomineralization and Eggshells: Cell-Mediated Acellular Compartments of Mineralized Extracellular Matrix

This study was conducted to find out the multiple uses of eggshells in nutrition and medicine. Eggshells can be utilized for various purposes that minimize their effect on environmental pollution. Eggshells present healthy, balanced calcium due to its trace amounts of other minerals and is probably the best natural source of calcium. One whole medium sized eggshell makes about one teaspoon of powder, which yields about 750-800 mgs of elemental calcium plus other micro elements. Eggshell powder has been reported to increase bone mineral density in people and animals with osteoporosis. In laying hens in the late production phase, eggshell powder has been found to increase egg production and improve the quality of shells. Discarded eggshells are often used as a plant fertilizer and are effective liming sources. This is because eggshells contain calcium that raises, or neutralizes, the pH level of overly acidic soil. Chicken eggshells can be used as an alternative soil stabilizer like lime since they have the same chemical composition. Such stabilized soil can be used as subgrade materials in road construction works. Eggshell membrane consists of collagen as a component. Collagen is a type of protein, fibrous in nature that connects and supports other bodily tissues, such as skin, bone, tendons, muscles and cartilage. Collagen has been isolated mainly from bovine and swine skins and bones Collagen used in medicine, biochemical, pharmaceutical, food and cosmetics industries. After the outbreaks of bovine spongioform encephalopathy, foot and mouth disease, autoimmune and allergic reactions, restrictions on collagen uses from these sources were enforced. Eggshell membrane collagen is very low in autoimmune and allergic reactions as well as high in bio-safety and is of similar characteristics to other mammalian collagen. Eggshells/shell membranes have multiple uses in nutrition, medicine, construction and art works.

A Review of the Uses of Poultry Eggshells and Shell Membranes

Partial biochemical and immunochemical characterization of avian eggshell extracellular matrices.

The fabrication and collagenous substructure of the eggshell membrane in the isthmus of the hen oviduct.

Research Note: Absence from Avian Eggshell Membranes of Epitopes Recognized by Anti-Keratin Antibodies

El objetivo de esta investigacion es analizar en que medida los antecedentes familiares facilitan el acceso de los hijos a las categorias ocupacionales mas altas y/o a la Administracion Publica. Para ello se han utilizado la Encuesta de Estructura, Conciencia y Biografia de Clase, realizada en 1991, y la Encuesta de Calidad de Vida en el Trabajo del ano 2004. Los resultados ponen de manifiesto la persistencia de relaciones intergeneracionales en el exito ocupacional y en el acceso al empleo en la Administracion Publica.

María José Suárez Fernández

Papers

Partial biochemical and immunochemical characterization of avian eggshell extracellular matrices.

The fabrication and collagenous substructure of the eggshell membrane in the isthmus of the hen oviduct.

Research Note: Absence from Avian Eggshell Membranes of Epitopes Recognized by Anti-Keratin Antibodies

¿De tal palo tal astilla?: conexiones intergeneracionales en la ocupación y la elección de empleo en el sector público