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Cyclic silicate active site and stereochemical match for apatite nucleation on pseudowollastonite bioceramic–bone interfaces

Paper ID Volume ID Publish Year Pages File Format Full-Text
12539 799 2005 8 PDF Available
Title
Cyclic silicate active site and stereochemical match for apatite nucleation on pseudowollastonite bioceramic–bone interfaces
Abstract

Hydroxyapatite (Ca5(PO4)3(OH)) forms on pseudowollastonite (psW) (α-CaSiO3) in vitro in simulated body fluid, human parotid saliva and cell-culture medium, and in vivo in implanted rat tibias. We used crystallographic constraints with ab initio molecular orbital calculations to identify the active site and reaction mechanism for heterogeneous nucleation of the earliest calcium phosphate oligomer/phase. The active site is the planar, cyclic, silicate trimer (Si3O9) on the (0 0 1) face of psW. The trimer has three silanol groups (>SiOH) arranged at 60° from each other, providing a stereochemical match for O atoms bonded to Ca2+ on the (0 0 1) face of hydroxyapatite. Calcium phosphate nucleation is modeled in steps as hydrolysis of surface Ca–O bonds with leaching of Ca2+ into solution, protonation of the surface Si–O groups to form silanols, calcium sorption as an inner-sphere surface complex and, attachment of HPO42−. Our model explains the experimental solution and high resolution transmission electron microscopy data for epitaxial hydroxyapatite growth on psW in vitro and in vivo. We propose that the cyclic silicate trimer is the universal active site for heterogeneous, stereochemically promoted nucleation on silicate-based bioactive ceramics. A critical active site-density and a point of zero charge of the bioceramic less than physiological pH are required for bioactivity.

Keywords
Bioceramics; Calcium silicate; Calcium phosphate; Silicate trimer; Titania; Alumina; Silica; Bioactivity; Glass
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Cyclic silicate active site and stereochemical match for apatite nucleation on pseudowollastonite bioceramic–bone interfaces
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Publisher
Database: Elsevier - ScienceDirect
Journal: Biomaterials - Volume 26, Issue 29, October 2005, Pages 5763–5770
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us