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*Taken from; The Orthopaedic Surgury Online Information Centre,

Polyphosphazines in Bone Regeneration. Shayne Rybchinski University of Lethbridge February 26, 2009. *. *Taken from; The Orthopaedic Surgury Online Information Centre, http://tsagalis.net/ on February 11, 2009. Polyphosphazine Formation is a Thermal Ring-Opening Process:.

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*Taken from; The Orthopaedic Surgury Online Information Centre,

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  1. Polyphosphazines in Bone Regeneration Shayne Rybchinski University of Lethbridge February 26, 2009 * *Taken from;The OrthopaedicSurgury Online Information Centre, http://tsagalis.net/ on February 11, 2009

  2. Polyphosphazine Formation is a Thermal Ring-Opening Process: • Prepared by a ring opening of hexachlorocyclotriphosphazene at 250°C 250°C Inert atm. 4-5 hours

  3. Macromolecular Substitution of Polyphosphazines: Polyphosphazines have a wide range of applications due to facile addition of varying side chains through simple nucleophilic substitution: Nu: Nu:

  4. Polyphoshpazine / Hydroxyapatite Complexes in Bone Regeneration: Allograft: • Risk of disease transmission • Immunogenic rejection C10(PO4)6(OH)2 (Ca4(PO4)2O + CaHPO4 • 2H2O Autograft: •Morbidity at sight of graph (tissue damage) Xenograft: • Risk of disease transmission • Immunogenic rejection Synthetic Polymer Graft:

  5. Low temperature formation of hydroxyapatite-poly(alkyl oxybenzoate) phosphazene composites for biomedical applications Greisha, Y. E. , Benderb, J. D., Lakshmic, S., Browna, P. W. , Allcock H. R., and Laurencin, C. T. ; Biomaterials 26 (2005) 1–9 Formation of hydroxyapatite - polyphosphazine polymer composites at physiologic temperature Greish, Y. E., Bender, J. D., Lakshmi, S., Brown, P. W., Allcock, H. R., and Laurencin, C. T.; Journal of Biomedical Materials Research, Part A (2006), 77A(2), 416-425

  6. Experimental Objective: → 2(Ca4(PO4)2O + 2CaHPO4 • 2H2O C10(PO4)6(OH)2 + 4H2O Tetracalcium phosphate + Dicalcium phosphate dihydrate Stoichiometric Hydroxyapatite • Poly (ethyl-oxybenzoate) phosphazine-(PN-EOB) • Poly (propyl-oxybenzoate) phosphazine-(PN-POB) R= • •Poly[bis(carboxylatophenoxy] phosphazene (acid- PCPP)

  7. Experimental Method; Polymer formation: • Poly(dichloro)phosphazine was prepared by ring opening polymerization • Each oxybenzoate-substituted polyphosphazine was prepared from a mixture of Poly(dichloro)phosphazine and it’s respective sodium salt in THF • Acid- PCPP was made by treating PN-POB with t-butlyalkoxide in THF followed by acidic workup • Structure verified with 1H NMR (360 MHz) and 31P NMR (145 MHz) • Mw determined through gel-permeation chromotography

  8. Structural Determination Structure verified with 1H NMR (360 MHz) and 31P NMR (145 MHz) 1H NMR PN-EOB 1H NMR acid-PCPP 1H NMR PN-POB

  9. Experimental; Hydroxyapatite formation: • HAp formation was studied as a function of time by measuring changes in [Ca2+], [PO4-] and pH in solution in presence of varying polymer concentration (0, 5, 10 and 15 wt %) • Kinetics of HAp formation was measured by isothermal calorimetry in the presence of 5, 10 and 15 % (by weight) of each polyphosphazine at 37.5°C • Scanning Electron Microscopy photographs of the Polymer-Ceramic complex taken following HAp formation in the presence or absence of polyphosphazine

  10. pH as a function of HAp formation at 37.5°C over 24 Hr: No polymer 5 wt% acid-PCPP 15 wt% acid-PCPP

  11. [Ca2+] and [PO4-] as a function of HAp formation over 24 Hr: Variation in the concentrations of calcium (a) and phosphate (b) ions in solution as a A function of time during Hap formation at 37.4°C with no polymer or 15 wt% PN-EOB and PN-POB

  12. [Ca2+] and [PO4-] as a function of HAp formation over 24 Hr: Variation in [Ca2+] and [PO4-] as a function of time in the presence of 0 and 15 wt. acid-PCPP

  13. X-Ray Diffraction patterns of HAp formation: XRD patterns of HAp formation as a function of time at 37.4°Cin the presence of 15 wt% PN-POB (A) and PN-EOB (B) XRD patterns indicating Hap formation in the presence of 15 wt. % acid-PCPP

  14. Scanning Electron Micrographs ofHAp formation: Scanning electron micrographs of samples containing (a) No polymer (b) 15 wt% PN-EOB, and (c) 15 wt% PN-POB prepared at 37.4°C.

  15. Calorimetry results of hydroxyapitite formation at 37.5°C: Growth peak Nucleation peak Mixing peak Heat evolved by HAp formation at 37.5°C in the presence of varying concentration of alkyl-ester substituted polymer

  16. Calorimetry results of hydroxyapitite formation at 37.5°C: Heat evolved by HAp formation at 37.5°C in the presence of varying concentration of carboxylic acid substituted polymer

  17. Conclusions: • Hydroxyapatite forms efficiently in the presence or absence of polymer. Although its formation may be somewhat hindered by the presence of polymer. • Hap formed in the presence of polymer may not necessarily be nucleated on the polymer • Authors postulated that Oxy Benzoate polyphosphazenes hinder reaction kinetics due to slow alkyl ester hydrolysis as is evidenced by reduced heat evolved. • Subsequent studies in rabbit systems have indicated that polyphosphazenes may have use as a direct bone regeneration scaffolding without hydroxyapitite component

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