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Nanocrystalline Hydroxyapatite (nanocrystalline + hydroxyapatite)

Distribution by Scientific Domains

Polymers and Materials Science	33%

Selected Abstracts

A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2006
Christian Jäger
Abstract Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30,50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Two-year clinical results following treatment of peri-implantitis lesions using a nanocrystalline hydroxyapatite or a natural bone mineral in combination with a collagen membrane

JOURNAL OF CLINICAL PERIODONTOLOGY, Issue 1 2008
Frank Schwarz
Abstract Objectives: The aim of the present case series was to evaluate the 2-year results obtained following treatment of peri-implantitis lesions using either a nanocrystalline hydroxyapatite (NHA) or a natural bone mineral in combination with a collagen membrane (NBM+CM). Material and Methods: Twenty-two patients suffering from moderate peri-implantitis (n=22 intra-bony defects) were randomly treated with (i) access flap surgery (AFS) and the application of NHA, or with AFS and the application of NBM+CM. Clinical parameters were recorded at baseline and after 12, 18, and 24 months of non-submerged healing. Results: Two patients from the NHA group were excluded from the study due to severe pus formation at 12 months. At 24 months, both groups revealed clinically important probing depth (PD) reductions (NHA: 1.5±0.6 mm; NBM+CM: 2.4±0.8 mm) and clinical attachment level (CAL) gains (NHA: 1.0±0.4 mm; NBM+CM: 2.0±0.8 mm). However, these clinical improvements seemed to be better in the NBM+CM group (difference between groups: PD reduction: 0.9±0.2 mm; CAL gain: 1.0±0.3 mm). Conclusion: Both treatment procedures have shown efficacy over a period of 24 months, however, the application of NBM+CM may result in an improved outcome of healing. [source]

Mechanical Activation of Tetracalcium Phosphate

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2004
Uwe Gbureck
It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)2 could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction. [source]

A Solvent-Assisted Compression Molded of Poly(L -lactide)/Hydroxyapatite Electrospun Fibers for Robust Engineered Scaffold Systems

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2009
Nguyen Dang Luong
Abstract In an attempt to enhance the biocompatibility and mechanical strength of fibrous polymeric scaffold systems, nanocrystalline hydroxyapatite (HAp) particles were incorporated into the electrospun poly(L -lactide) (PLLA) fibers and then mechanically interlocked using a vapor-phase solvent adsorption method. The solvent-assisted compression molding substantially increased the tensile strength (from 4.61 to 12.63 MPa) and mechanical modulus (from 50.6 to 627.7 MPa) of the fibrous scaffold, which maintained the interstitial space between the fibers to allow the facile transport of nutrients and waste during cell growth and polymer biodegradation. Macrometer-sized pores (ca. 100,400,µm) were introduced into the scaffolds in a controlled fashion using the salt leaching/gas forming technique to give desired space for a facile cell implantation and growth. Overall, the developed methodology allows the polymer-based scaffold systems to be tailored for various applications in light of surface characteristics, mechanical strength, and pore size of engineered scaffolds. [source]