Thematic Articles

Kidney stones are aggregates of microcrystals, most commonly containing calcium oxalate monohydrate (COM) as the primary constituent. The formation of these aggregates in the renal tubules of the kidney and their attachment to epithelial cells lining the renal tubules are thought to involve adhesion events between COM crystal surfaces and urinary species that bind to these surfaces. The pathological behavior of COM is in stark contrast to calcium oxalate dihydrate (COD), a different mineral phase commonly found in voided urine but much less frequently in stones, and whose presence is thought to protect against stone formation. This observation suggests that the structure and composition of calcium oxalate crystal surfaces and the fundamental interactions of these surfaces with urinary species are crucial to unraveling the complex pathology of this debilitating disease.

In this outline of the most prominent factors involved in particle toxicology, we highlight the differences in the toxic potential among airborne particles and describe what is known about the most notorious toxic agents, such as silica and asbestos. The various biological paths and, consequently, the different outcomes in the health risks associated with inhaled, micron-sized particle and fibers, as well as inhaled nanoparticles, are explained on the basis of form, size, and surface reactivity. The most relevant surface properties addressed here are the potential for free radical generation, the adsorption of endogenous molecules, and the degree of hydrophilicity or hydrophobicity of the various materials.

Proteins have long been recognized as important compounds in the biogeochemical cycles of terrestrial ecosystems. They can, for example, provide a source of nitrogen for plants and soil microorganisms following proteolysis and ammonification. Extracellular enzymes liberated in soil are essential catalysts in the mobilization of carbon, nitrogen, phosphorus and sulphur from macromolecular organic matter. Proteins are also implicated in new environmental topics, such as soil carbon storage, horizontal transmission of spongiform encephalopathies and potential negative effects of insecticidal toxins released from transgenic plants.

There is a need for new materials that can stimulate the body’s own regenerative mechanisms and heal tissues. Porous templates (scaffolds) are thought to be required for three-dimensional tissue growth. This article discusses bone regeneration and the specifications of an ideal scaffold and the materials that may be suitable. Bioactive glasses have high potential as scaffold materials as they stimulate bone cells to produce new bone, they are degradable in the body and they bond to bone. The two types of bioactive glasses, their mechanisms for bioactivity and their potential for scaffold production are reviewed. Examples of their current clinical use are highlighted.

Bones and teeth consist of an inorganic calcium phosphate mineral approximated by hydroxylapatite and matrix proteins. The physical and chemical properties of these “bioapatite” crystals are different from those of geologic hydroxylapatite because of the way they are formed, and these unique properties are required for fulfilling the biological functions of bones and teeth. Recent biochemical studies provide insight into the factors controlling the formation and growth of bioapatite crystals and how alteration in the mineralization process can lead to diseases such as osteoporosis. New spectroscopic and microscopic techniques are enabling scientists to characterize changes in crystal properties in these diseases, providing potentially fruitful areas of collaboration among geochemists, mineralogists, and biological researchers and offering hope for the development of novel therapies.

Medical mineralogy and geochemistry is a highly interdisciplinary area of research where the complexity of minerals and mineral surface reactivity in the human body is emphasized. Research in this field will lead to an understanding of the biogeochemical processes responsible for medical conditions, both normal and pathological that involve the interaction of dissolved inorganic species and bioorganic molecules with minerals. In this article, I highlight some fundamental concepts and challenges in this endeavor, and the subsequent articles provide overviews of specific topics.