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| 2. |
- Camire, Christopher
(författare)
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Enhancing material and biological properties of calcium phosphate bone substitute
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calcium phosphate materials (CaPs) have proven biocompatible and useful in clinical situations. One CaP showing promise in the clinic is alpha phase tricalcium phosphate ([alpha]-TCP). [alpha]-TCP in powder form can be hydrated and undergoes a reaction resulting in calcium deficient hydroxyapatite (CDHA). The similarity of CDHA and human bone makes [alpha]-TCP a very viable material for application in bone defect. Studies were carried out investigating methods to enhance material and biological properties of calcium phosphate bone substitutes. Hydration reaction, reaction completion, and strength characteristics were studied, as well as effects of particle size on the reactivity of such compounds. Reactivity with relation to material crystallite size was further studied. X-ray amorphous fraction of powders and crystallite size was then investigated with relation to the speed of strength development. Addition of silicon to the [alpha]-TCP matrix was also examined. A silicon doped [alpha]-TCP was achieved which yielded promising results of increased osteoblastic activity both in vitro and in vivo. It was seen with proper milling procedure that it was possible to prepare an [alpha]-TCP powder by solid state reaction that was potentially similar to one prepared using precipitation technique and that during hydration most of the strength developed during later stages of reaction. Surface area of the [alpha]-TCP has a significant impact on the reactivity however according to calculations, is not an accurate measure of degree of reaction. During high energy milling crystallite size is altered which has significant relation to thermal events during hydration as well as speed of reaction. The time needed to achieve maximum strength of hydrated [alpha]-TCP compounds appeared to relate to final CDHA crystal size and implied existence of a threshold of super-saturation needed to form CDHA at an accelerated rate. The [alpha]-TCP lattice was able to incorporate silicon and the in vitro and in vivo reactivity of the silica doped [alpha]-TCP was significantly increased upon testing in a bone harvest chamber rabbit model. CaPs as materials in the clinic are note only versatile, with the possibility of injectability, but can be adjusted in many ways to fit the desired application.
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| 3. |
- Camire, Christopher, et al.
(författare)
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Material characterization and in vivo behavior of silicon substituted alpha-tricalcium phosphate cement.
- 2006
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Ingår i: Journal of Biomedical Materials Research. Part B - Applied Biomaterials. - : Wiley. - 1552-4981 .- 1552-4973. ; 76B:2, s. 424-431
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Tidskriftsartikel (refereegranskat)abstract
- The possibility and biological effects of substituting silicon in a-tricalcium phosphate (alpha-TCP) by way of solid-state reaction have been evaluated. a-TCP powders with varying substitution amounts (1 and 5 mol % Ca2SiO4) were synthesized by reacting mixtures of CaCO3, Ca(2)P(2)O7, and SiO2, at a rate of 4 degrees C(min)(-1) to 1100 degrees C, left to dwell for 2 h and then heated to 1325 degrees C at 4 degrees C(min)(-1) and left to dwell for a period of 4 h. The powders were then rapidly quenched in air. Si incorporation could be verified by X-ray diffraction analysis, indicating an increase of the lattice volume with increasing Si content from 4284.1(8) to 4334(1) angstrom(3) for pure alpha-TCP and alpha-Si5%TCP, respectively. The hydrolysis of milled alpha-SiTCP powders was monitored by isothermal calorimetry, and the compressive strength of set cements was tested. The results showed changes in speed and amount of heat released during reactivity tests and a decrease in mechanical strength (60, 50, and 5 MPa) with increasing Si content. In vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bonelike apatite layer on the surface of the set cements could be observed and was thickest for 1% Si (20 mu m). These results were in good agreement with the in vivo studies performed, which showed strong evidence that the cement containing 1% silicon doped alpha-TCP enhanced mesenchymal cell differentiation and increased osteoblast activity compared with alpha-TCP. (c) 2005 Wiley Periodicals, Inc.
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| 4. |
- Camire, Christopher, et al.
(författare)
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Production methodology and reactivity of silica substituted a phase tricalcium phosphate
- 2004
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Ingår i: Transactions - 7th World Biomaterials Congress. - 1877040193 ; , s. 1437-1437
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Konferensbidrag (refereegranskat)abstract
- A silica substituted alpha phase tricalcium phosphate was developed by way of solid state reaction. The difference in reactivity of two different production methods using isothermal calorimetry and X- ray diffraction was also recorded. It was suggested that a silica substituted alpha phase tricalcium phosphate can be produced and characterized by way of X-ray measurement. Referencing selected significant peaks for α-TCP, β-TCP and apatite.
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| 5. |
- Camire, Christopher, et al.
(författare)
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Study of particle size dependant reactivity in an alpha-TCP orthophosphate cement
- 2004
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Ingår i: Key Engineering Materials. - 1013-9826. ; 254-256, s. 269-272
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Tidskriftsartikel (refereegranskat)abstract
- Calcium phosphates have been of great interest in the field of medicine for many decades due to their biocompatibility, hardening properties and diverse areas of application. In this study two different alpha phase tricalcium phosphate powders were produced of distinctly different particle size distributions. These two powders were then tested for reactivity and phase evolution. X-ray diffraction was used to characterise the beginning and final products and the exotherm were measured with an isothermal calorimeter. The powders were then viewed relative to their starting properties and differences were drawn. Fine material exhibited a much larger exotherm, which was not directly proportional to the difference in surface area of the particulate. The difference has been attributed to the variant concentrations of nucleation sites assisting the ionic dissolution and precipitation reaction. For proper and ultimately efficient use of this material in the clinic it remains important to fully understand and have control over reactivity. Higher success rates and more reliable fracture fixation will result.
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| 6. |
- Camire, Christopher, et al.
(författare)
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Study of Particle Size Dependant Reactivity in an α-TCP Orthophosphate Cement
- 2004
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Ingår i: Key Engineering Materials. - 1013-9826. ; 254-256, s. 269-272
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Konferensbidrag (refereegranskat)abstract
- Calcium phosphates have been of great interest in the field of medicine for many decades due to their biocompatibility, hardening properties and diverse areas of application. In this study two different alpha phase tricalcium phosphate powders were produced of distinctly different particle size distributions. These two powders were then tested for reactivity and phase evolution. X-ray diffraction was used to characterise the beginning and final products and the exotherm were measured with an isothermal calorimeter. The powders were then viewed relative to their starting properties and differences were drawn. Fine material exhibited a much larger exotherm, which was not directly proportional to the difference in surface area of the particulate. The difference has been attributed to the variant concentrations of nucleation sites assisting the ionic dissolution and precipitation reaction. For proper and ultimately efficient use of this material in the clinic it remains important to fully understand and have control over reactivity. Higher success rates and more reliable fracture fixation will result.
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| 7. |
- Camire, Christopher, et al.
(författare)
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The effect of crystallinity on strength development of alpha-TCP bone substitutes.
- 2006
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Ingår i: Journal of Biomedical Materials Research. Part B - Applied Biomaterials. - : Wiley. - 1552-4981 .- 1552-4973. ; 79B:1, s. 159-165
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Tidskriftsartikel (refereegranskat)abstract
- Alpha phase tricalcium phosphates (alpha-TCP) were produced using a solid-state reaction method and milled for various periods of time. The resulting four materials were alpha-TCPs, ranging in crystalline content. Powders were exposed to X-ray diffraction for material identification as well as for use in crystallinity and purity calculations. Powder particle size was investigated using laser diffraction. Materials were mixed with 2.5% Na2HPO4 solution to initiate the hydration of alpha-TCP to calcium-deficient hydroxyapatite (CDHA). Isothermal calorimetry was performed to observe thermal response of the powders over a period of time. During the reaction process, at various time points up to 216 h, the material was compression tested to observe strength development. Materials proved to be predominantly alpha phase, while amorphous content determined by XRD varied. Reactivity, as measured by isothermal calorimetry, varied with crystallinity of the alpha-TCP powder. Speed of strength development did not change except for the most finely ground powder. In addition, crystal size of the CDHA was changed only in the product formed from the most highly ground material. It is proposed that increasing reactivity of alpha-TCP cements does not result in a corresponding increase in rate of strength development until there is sufficient supersaturation to produce significant crystal nucleation.
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| 9. |
- Jegou Saint-Jean, Simon, et al.
(författare)
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Preparation and study of the reactivity of Sr-substituted alpha tricalcium phosphates
- 2004
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Ingår i: Transactions - 7th World Biomaterials Congress. - 1877040193 ; , s. 1438-1438
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Konferensbidrag (refereegranskat)abstract
- The substitution in varying amounts of strontium (Sr) for calcium in the alpha tricalcium phosphate (α TCP) structure was investigated. The effects on the reactivity towards the formation of hydroxypalatite on hydration were also studied. The prepared α-TCP and the fully hydrated α-TCP powders were characterized by means of X-ray diffraction and the CuKα1 radiation. It was found that the alpha form of Sr-substituted TCP could be prepared by rapid quenching in air and the reactivity of the Sr-substituted TCPs with water was also found to be lowered with increasing Sr amounts.
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| 10. |
- Jegou Saint-Jean, Simon, et al.
(författare)
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Study of the reactivity and in vitro bioactivity of Sr-substituted alpha-TCP cements
- 2005
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Ingår i: Journal of Materials Science: Materials in Medicine. - : Springer Science and Business Media LLC. - 1573-4838 .- 0957-4530. ; 16:11, s. 993-1001
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Tidskriftsartikel (refereegranskat)abstract
- In this study the effect of strontium substitution on the hydrolysis of alpha-tricalcium phosphate (alpha-TCP) toward the formation of calcium deficient hydroxyapatite (CDHA) was investigated. For that purpose substituted alpha-TCP powders with 1, 5 and 10 mol% Sr substitution for Ca were synthesized by reacting at 1500 degrees C stoichiometric amounts of CaCO3, SrCO3, and Ca2P2O7, followed by rapid quenching in air. XRD analysis of the powders revealed the presence of alpha-TCP (traces of beta-TCP) with enlarged unit cell volume at increased Sr contents, indicating the incorporation of Sr in the crystal structure. Strontium was also incorporated in the apatite phase as revealed by XRD analysis of the set cements. The hydrolysis of milled alpha-SrTCP powders and a pure alpha-TCP (control) was monitored by isothermal calorimetry and the compressive strength of set cements was tested. The results showed a decrease in the reactivity with increasing Sr content and similar final mechanical strength within the Sr series, though lower than the control. The in vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bone-like apatite layer on the surface of the set cements indicated a potential in vivo bioactivity. (C) 2005 Springer Science + Business Media, Inc.
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