title: Tracing the pathway of compositional changes in bone mineral with age: preliminary study of bioapatite aging in hypermineralized dolphin's bulla.
abstract: BACKGROUND
  Studies of mineral compositional effects during bone aging are complicated by the presence of collagen.
  
  
  METHODS
  Hypermineralized bullae of Atlantic bottlenose dolphins of <3months, 2.5years, and 20years underwent micrometer-scale point analysis by Raman spectroscopy and electron microprobe in addition to bulk analysis for carbon.
  
  
  RESULTS
  Bulla central areas have a mineral content of ~96wt.% and 9-10wt.% carbonate in their bioapatite, which is ~2wt.% more than edge areas. Ca/P atomic ratios (~1.8) and concentrations of Mg, S, and other minor/trace elements are almost constant in central areas over time. Maturity brings greater over-all homogeneity in mineral content, stoichiometry, and morphology throughout the central and edge areas of the bullae. During aging, edge areas become less porous, whereas the concentration of organics in the edge is reduced. Enhancement of coupled substitutions of CO3(2-) for PO4(3-) and Na for Ca during aging increases carbonate content up to ~10wt.% in the adult bulla.
  
  
  CONCLUSIONS
  1) Changes in physical properties during aging did not occur simultaneously with changes in chemical properties of the bone mineral. 2) Compositional changes in bone mineral were minor during the neonatal to sub-adult stage, but significant during later maturity. 3) Na and CO3 concentrations co-vary in a 1:1 molar proportion during aging. 4) The mineral's crystallinity did not decrease as CO3 concentration increased during aging.
  
  
  CONCLUSIONS
  Hypermineralized dolphin's bulla, due to extreme depletion in collagen, is an ideal material for investigating mineralogical changes in bioapatite during bone aging.
authors.affiliation: Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA. Electronic address: pasteris@levee.wustl.edu.
authors.forename: Jill D
authors.initials: JD
authors.lastname: Pasteris
mesh_terms: D000375:Aging / Q000473:pathology / Q000502:physiology*; D000818:Animals; D001031:Apatites / Q000378:metabolism; D001768:Blister / Q000378:metabolism; D015519:Bone Density / Q000502:physiology*; D002254:Carbonates / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D004289:Dolphins / Q000502:physiology*; D013059:Spectrum Analysis, Raman
chemical_list: D001031:Apatites; D002254:Carbonates; D003094:Collagen
keywords: Aging; Bone mineral; Bulla; Carbonated hydroxylapatite; Hypermineralization