Medical Mineralogy:
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Washington University in St. Louis |
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Our research group has been studying evidence of fluid-rock interactions and applying Raman spectroscopy to geological materials for many years. Some of our recent research projects convinced us that the specific ways in which geologists view minerals have applicability in other fields, especially in medicine. The most important solid materials in the body, of course, are the bones and teeth, which are composed of material similar to the mineral apatite. However, humans also suffer from undesired mineralization, such as kidney and gall stones, calcification of joints, and calcification of arteries and heart tissue. These "calcifications" can be comprised of several different minerals, including calcite (calcium carbonate), aragonite (calcium carbonate), apatite (calcium phosphate), weddellite (calcium oxalate dihydrate), and whewellite (calcium oxalate monohydrate). Fortunately, the laser Raman microprobe technique allows for the rapid, non-destructive identification of minerals that are relevant to the human body. Raman spectroscopy can be applied to thin-sections of human tissue as readily as to thin-sections of rock. Currently, we are studying bone material and synthetic phosphate phases that may be precursors to the final bone material in our bodies. We are collaborating with a colleague at Washington University School of Medicine's Department of Orthopaedic Surgery who studies the effects of in vitro fluoride exposure on the mechanical properties of mouse bones. Because the Raman spectrum of a material is sensitive to the details of its structural state (which can be affected by recrystallization and changes in mineral chemistry), we were able to monitor spectral differences between the bones soaked in the fluoride solution and the control samples.
Pasteris et al. (2001) Apatite in bone is not hydroxylapatite:
There must be a reason,
In another interdisciplinary collaboration with John Freeman , Jill Pasteris , and other colleagues from Washington University (a plastic surgeon and a mechanical engineer), we studied capsular breast tissue of women with silicone breast implants. Our mineralogic interest in this medical field was initiated by reports in the pathology literature about the finding of "crystalline silica" in mammary tissue in women who had silicone breast implants and the claim that such crystalline silica had originated from the materials used in the implants. Our feasibility study showed that laser Raman microprobe spectroscopy is ideally suited to clarify whether silicone, amorphous silica, or crystalline silica occurs in micrometer-sized moieties in standard 5-micrometer-thick tissue sections. Neither crystalline silica nor amorphous silica was found in the limited number of tissue sections studied so far. Our review of the pathology literature on such materials-based issues as silicosis and "calcifications" revealed some misapplication and misunderstanding of the optical mineralogy term "birefringence", which resulted in misleading and wrong identifications of minerals in tissue sections by some pathologists. Our conclusion is that useful collaborations can be developed between (1) pathologists who observe foreign materials in tissue sections and understand the medical context of their findings and (2) mineralogists who routinely use optical, chemical and structural analysis to characterize micrometer-sized crystalline materials and who understand materials properties. Mineralogy clearly is not what it used to be, and "getting
out into the field" has taken on a whole new meaning for some geologists! |
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