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Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in micro... more Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in microbial fossilization. Characterization of both the organic and mineral components in biomineralized samples is, however, usually difficult at the appropriate spatial resolution (i.e. at the submicrometer scale). Scanning transmission Xray microscopy (STXM) was used to measure C K-edge, P L-edge, and Ca L-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of some calcium-containing minerals common in biomineralization processes and to study the experimental biomineralization by the model microorganism, Caulobacter crescentus. We show that the Ca L 2,3 -edges for hydroxyapatite, calcite, vaterite, and aragonite are unique and can be used as probes to detect these different mineral phases. Using these results, we showed that C. crescentus cells, when cultured in the presence of high calcium concentration, precipitated carbonate hydroxyapatite. In parallel, we detected proteins, polysaccharides, and nucleic acids in the mineralizing bacteria at the single-cell scale. Finally, we discussed the utility of STXM for the study of natural fossilized microbial systems.
Geobiology, 2004
Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in micro... more Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in microbial fossilization. Characterization of both the organic and mineral components in biomineralized samples is, however, usually difficult at the appropriate spatial resolution (i.e. at the submicrometer scale). Scanning transmission Xray microscopy (STXM) was used to measure C K-edge, P L-edge, and Ca L-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of some calcium-containing minerals common in biomineralization processes and to study the experimental biomineralization by the model microorganism, Caulobacter crescentus. We show that the Ca L 2,3 -edges for hydroxyapatite, calcite, vaterite, and aragonite are unique and can be used as probes to detect these different mineral phases. Using these results, we showed that C. crescentus cells, when cultured in the presence of high calcium concentration, precipitated carbonate hydroxyapatite. In parallel, we detected proteins, polysaccharides, and nucleic acids in the mineralizing bacteria at the single-cell scale. Finally, we discussed the utility of STXM for the study of natural fossilized microbial systems.
Investigative Radiology, 1991
The healing of large fractural defects is a difficult clinical problem, especially if it occurs i... more The healing of large fractural defects is a difficult clinical problem, especially if it occurs in elderly or otherwise debilitated patients. The objective of this study is to determine if a new formulation of fibrous calcium phosphate crystals would induce fracture healing in vivo. Fibrous calcium phosphate (FCP) can be grown with unique size, shape, and surface area characteristics as a resorbable or nonresorbable, osteoconductive or osteoinductive material. In comparison with other conventional calcium phosphate particulates, FCP particles possess approximately x 100 to x 1000 more surface area. One-and-one-half centimeter sections were removed from the ulnas of 12 rabbits. Three groups had fibrous calcium phosphate spherulites (4-8 microns, 150-300 microns, 400-600 microns) mixed with collagen and a growth factor-bonding agent injected into the ulnar defect. One site per group was not treated. X-rays were obtained during the study and the percentage of the ulna defect filled in by callous was measured. The percentage was recorded as the amount of fracture healing for each site. Histologic examination of the ulnas was performed following sacrifice at 12 weeks. Fracture sites treated with fibrous calcium phosphate showed significantly greater healing (0.79 +/- 0.3) than control animals (0.36 +/- 0.1) (P less than .05, unpaired t-test) radiographically. Histologic examination showed that the spherulites remain in situ and become embedded within the new growth of fibrous tissue, collagen and new bone. Radiographically and histologically, FCP preparations appear to accelerate fracture healing by inducing new bone formation, into which they often become embedded.
Investigative Radiology, 1991
Bioabsorption of synthetic apatite compounds used to promote bone healing and remodeling has been... more Bioabsorption of synthetic apatite compounds used to promote bone healing and remodeling has been difficult to evaluate. In this study, solid-state phosphorus-31 nuclear magnetic resonance (NMR) has been used to characterize and quantitate bone mineral and a synthetic apatite in order to establish a model for bioabsorption studies. Pulverized solid samples of cortical rabbit bone and a synthetic fluoridated apatite were examined in vitro at variable degrees of hydration. A 9.4 T superconducting spectrometer was used to obtain 31P magic angle spinning NMR spectra and T1 relaxation times. Quantitation was attempted in mixed samples using T1 recovery data. Bone mineral and synthetic apatite could be distinguished by chemical shift and T1 relaxation time in variable hydration states, and were readily differentiated in mixtures by their T1 relaxation time. NMR estimates of relative proportions of components in mixed samples were accurate within 2% of evaluations based on weight. Solid-state 31P NMR therefore provides a suitable method for monitoring the bioabsorption of synthetic apatites.
Acta Orthopaedica, 2002
We created three-part unstable intertrochanteric fractures in 6 pairs of aged, osteopenic, human,... more We created three-part unstable intertrochanteric fractures in 6 pairs of aged, osteopenic, human, cadaveric femora. Fractures were reduced and xed with a Dynamic Hip Screw (DHS) (Synthes, Paoli, PA). Two test groups were evaluated: 1. Fixation with a DHS, and 2. Fixation with a DHS and calcium phosphate bone cement (Norian SRS (Skeletal Repair System)) Acta Orthop Downloaded from informahealthcare.com by 92.43.140.122 on 05/20/14 For personal use only.
Journal of Materials Science-materials in Medicine, 1997
The synthesis and properties of carbonated apatite materials have received considerable attention... more The synthesis and properties of carbonated apatite materials have received considerable attention due to their importance for medical and dental applications. Such apatites closely resemble the mineral phase of bone, exhibiting superior osteoconductive and osteogenic properties. When formed at physiological temperature they present significant potential for bone repair and fracture fixation. The present study investigates the mechanical properties of a carbonated apatite cancellous bone cement. Flexural strength was measured in three and four point bending, and the fracture toughness and fatigue crack-growth behaviour was measured using chevron and disc-shaped compact tension specimens. The average flexural strength was found to be ∼0.468 MPa, and the fracture toughness was ∼0.14 MPa√m. Fatigue crack-growth rates exhibited a power law dependence on the applied stress intensity range with a crack growth exponent m=17. The fatigue threshold value was found to be ∼0.085 MPa√m. The mechanical properties exhibited by the carbonated apatite were found to be similar to those of other brittle cellular foams. Toughness values and fatigue crack-growth thresholds were compared to other brittle foams, bone and ceramic materials. Implications for structural integrity and longer term reliability are discussed.
Bone, 1997
The mechanical properties of bones are greatly influenced by the ratio of organic constituents to... more The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues. (Bone 20:485-490; 1997) © 1997 by Elsevier Science Inc. All rights reserved.
Journal of Biomedical Materials Research, 1993
To determine the meaning of graylevels in backscattered electron (BSE) images of actual bone tiss... more To determine the meaning of graylevels in backscattered electron (BSE) images of actual bone tissues, the influence of mineral content and mineral composition on BSE image graylevels was studied using chick bone tissue representing a broad age range. These tissues were analyzed for BSE image graylevels, Ca/P molar ratios, mineral composition, mineral content (v/v), ash fraction (w/w), and density (g/cm3). Linear regression analyses showed that the weighted mean graylevels (WMGLs) in BSE images were positively correlated to ash fraction (r2 = 0.711), mineral content (r2 = 0.720), and density (r2 = 0.843). Although the Ca/P ratio increased from 1.65 in embryos to 1.80 in 2-year olds, the compositional changes corresponding to this Ca/P molar ratio were estimated to produce a relatively minor (< 4.0%) change in BSE image graylevel. These results demonstrate that graylevels in BSE images of actual bone tissue can be attributed to mineral content and density, but only as a coincidence of their association with atomic number. © 1993 John Wiley & Sons, Inc.
Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in micro... more Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in microbial fossilization. Characterization of both the organic and mineral components in biomineralized samples is, however, usually difficult at the appropriate spatial resolution (i.e. at the submicrometer scale). Scanning transmission Xray microscopy (STXM) was used to measure C K-edge, P L-edge, and Ca L-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of some calcium-containing minerals common in biomineralization processes and to study the experimental biomineralization by the model microorganism, Caulobacter crescentus. We show that the Ca L 2,3 -edges for hydroxyapatite, calcite, vaterite, and aragonite are unique and can be used as probes to detect these different mineral phases. Using these results, we showed that C. crescentus cells, when cultured in the presence of high calcium concentration, precipitated carbonate hydroxyapatite. In parallel, we detected proteins, polysaccharides, and nucleic acids in the mineralizing bacteria at the single-cell scale. Finally, we discussed the utility of STXM for the study of natural fossilized microbial systems.
Geobiology, 2004
Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in micro... more Calcium phosphates and calcium carbonates are among the most prevalent minerals involved in microbial fossilization. Characterization of both the organic and mineral components in biomineralized samples is, however, usually difficult at the appropriate spatial resolution (i.e. at the submicrometer scale). Scanning transmission Xray microscopy (STXM) was used to measure C K-edge, P L-edge, and Ca L-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of some calcium-containing minerals common in biomineralization processes and to study the experimental biomineralization by the model microorganism, Caulobacter crescentus. We show that the Ca L 2,3 -edges for hydroxyapatite, calcite, vaterite, and aragonite are unique and can be used as probes to detect these different mineral phases. Using these results, we showed that C. crescentus cells, when cultured in the presence of high calcium concentration, precipitated carbonate hydroxyapatite. In parallel, we detected proteins, polysaccharides, and nucleic acids in the mineralizing bacteria at the single-cell scale. Finally, we discussed the utility of STXM for the study of natural fossilized microbial systems.
Investigative Radiology, 1991
The healing of large fractural defects is a difficult clinical problem, especially if it occurs i... more The healing of large fractural defects is a difficult clinical problem, especially if it occurs in elderly or otherwise debilitated patients. The objective of this study is to determine if a new formulation of fibrous calcium phosphate crystals would induce fracture healing in vivo. Fibrous calcium phosphate (FCP) can be grown with unique size, shape, and surface area characteristics as a resorbable or nonresorbable, osteoconductive or osteoinductive material. In comparison with other conventional calcium phosphate particulates, FCP particles possess approximately x 100 to x 1000 more surface area. One-and-one-half centimeter sections were removed from the ulnas of 12 rabbits. Three groups had fibrous calcium phosphate spherulites (4-8 microns, 150-300 microns, 400-600 microns) mixed with collagen and a growth factor-bonding agent injected into the ulnar defect. One site per group was not treated. X-rays were obtained during the study and the percentage of the ulna defect filled in by callous was measured. The percentage was recorded as the amount of fracture healing for each site. Histologic examination of the ulnas was performed following sacrifice at 12 weeks. Fracture sites treated with fibrous calcium phosphate showed significantly greater healing (0.79 +/- 0.3) than control animals (0.36 +/- 0.1) (P less than .05, unpaired t-test) radiographically. Histologic examination showed that the spherulites remain in situ and become embedded within the new growth of fibrous tissue, collagen and new bone. Radiographically and histologically, FCP preparations appear to accelerate fracture healing by inducing new bone formation, into which they often become embedded.
Investigative Radiology, 1991
Bioabsorption of synthetic apatite compounds used to promote bone healing and remodeling has been... more Bioabsorption of synthetic apatite compounds used to promote bone healing and remodeling has been difficult to evaluate. In this study, solid-state phosphorus-31 nuclear magnetic resonance (NMR) has been used to characterize and quantitate bone mineral and a synthetic apatite in order to establish a model for bioabsorption studies. Pulverized solid samples of cortical rabbit bone and a synthetic fluoridated apatite were examined in vitro at variable degrees of hydration. A 9.4 T superconducting spectrometer was used to obtain 31P magic angle spinning NMR spectra and T1 relaxation times. Quantitation was attempted in mixed samples using T1 recovery data. Bone mineral and synthetic apatite could be distinguished by chemical shift and T1 relaxation time in variable hydration states, and were readily differentiated in mixtures by their T1 relaxation time. NMR estimates of relative proportions of components in mixed samples were accurate within 2% of evaluations based on weight. Solid-state 31P NMR therefore provides a suitable method for monitoring the bioabsorption of synthetic apatites.
Acta Orthopaedica, 2002
We created three-part unstable intertrochanteric fractures in 6 pairs of aged, osteopenic, human,... more We created three-part unstable intertrochanteric fractures in 6 pairs of aged, osteopenic, human, cadaveric femora. Fractures were reduced and xed with a Dynamic Hip Screw (DHS) (Synthes, Paoli, PA). Two test groups were evaluated: 1. Fixation with a DHS, and 2. Fixation with a DHS and calcium phosphate bone cement (Norian SRS (Skeletal Repair System)) Acta Orthop Downloaded from informahealthcare.com by 92.43.140.122 on 05/20/14 For personal use only.
Journal of Materials Science-materials in Medicine, 1997
The synthesis and properties of carbonated apatite materials have received considerable attention... more The synthesis and properties of carbonated apatite materials have received considerable attention due to their importance for medical and dental applications. Such apatites closely resemble the mineral phase of bone, exhibiting superior osteoconductive and osteogenic properties. When formed at physiological temperature they present significant potential for bone repair and fracture fixation. The present study investigates the mechanical properties of a carbonated apatite cancellous bone cement. Flexural strength was measured in three and four point bending, and the fracture toughness and fatigue crack-growth behaviour was measured using chevron and disc-shaped compact tension specimens. The average flexural strength was found to be ∼0.468 MPa, and the fracture toughness was ∼0.14 MPa√m. Fatigue crack-growth rates exhibited a power law dependence on the applied stress intensity range with a crack growth exponent m=17. The fatigue threshold value was found to be ∼0.085 MPa√m. The mechanical properties exhibited by the carbonated apatite were found to be similar to those of other brittle cellular foams. Toughness values and fatigue crack-growth thresholds were compared to other brittle foams, bone and ceramic materials. Implications for structural integrity and longer term reliability are discussed.
Bone, 1997
The mechanical properties of bones are greatly influenced by the ratio of organic constituents to... more The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues. (Bone 20:485-490; 1997) © 1997 by Elsevier Science Inc. All rights reserved.
Journal of Biomedical Materials Research, 1993
To determine the meaning of graylevels in backscattered electron (BSE) images of actual bone tiss... more To determine the meaning of graylevels in backscattered electron (BSE) images of actual bone tissues, the influence of mineral content and mineral composition on BSE image graylevels was studied using chick bone tissue representing a broad age range. These tissues were analyzed for BSE image graylevels, Ca/P molar ratios, mineral composition, mineral content (v/v), ash fraction (w/w), and density (g/cm3). Linear regression analyses showed that the weighted mean graylevels (WMGLs) in BSE images were positively correlated to ash fraction (r2 = 0.711), mineral content (r2 = 0.720), and density (r2 = 0.843). Although the Ca/P ratio increased from 1.65 in embryos to 1.80 in 2-year olds, the compositional changes corresponding to this Ca/P molar ratio were estimated to produce a relatively minor (< 4.0%) change in BSE image graylevel. These results demonstrate that graylevels in BSE images of actual bone tissue can be attributed to mineral content and density, but only as a coincidence of their association with atomic number. © 1993 John Wiley & Sons, Inc.