Hydroxyapatite: Hexagonal or Monoclinic?

Ma, Guobin; Liu, Xiang Yang

doi:10.1021/cg900156w

Cited by 157 publications

(134 citation statements)

References 14 publications

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“…With respect to morphology, because CDAP has been found to possess monoclinic symmetry (47) and forms through recrystallization of either ACP or OCP, there is no reason why the habit of bone apatite platelets should mirror the hexagonal symmetry of HAP. Moreover, a plate-like habit is consistent with monoclinic symmetry.…”

Section: Results and Analysismentioning

confidence: 99%

Energetic basis for the molecular-scale organization of bone

Tao

Battle

Pan

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The remarkable properties of bone derive from a highly organized arrangement of coaligned nanometer-scale apatite platelets within a fibrillar collagen matrix. The origin of this arrangement is poorly understood and the crystal structures of hydroxyapatite (HAP) and the nonmineralized collagen fibrils alone do not provide an explanation. Moreover, little is known about collagen-apatite interaction energies, which should strongly influence both the molecular-scale organization and the resulting mechanical properties of the composite. We investigated collagen-mineral interactions by combining dynamic force spectroscopy (DFS) measurements of binding energies with molecular dynamics (MD) simulations of binding and atomic force microscopy (AFM) observations of collagen adsorption on single crystals of calcium phosphate for four mineral phases of potential importance in bone formation. In all cases, we observe a strong preferential orientation of collagen binding, but comparison between the observed orientations and transmission electron microscopy (TEM) analyses of native tissues shows that only calcium-deficient apatite (CDAP) provides an interface with collagen that is consistent with both. MD simulations predict preferred collagen orientations that agree with observations, and results from both MD and DFS reveal large values for the binding energy due to multiple binding sites. These findings reconcile apparent contradictions inherent in a hydroxyapatite or carbonated apatite (CAP) model of bone mineral and provide an energetic rationale for the molecular-scale organization of bone.biomineralization | bone | protein-mineral interface | dynamic force spectroscopy B one is a natural protein-mineral composite consisting of nonstoichiometric nanometer-scale carbonated apatite crystallites inside a fibrillar protein matrix. The matrix is mainly composed of type I collagen and is organized on multiple length scales (1, 2). At the shortest scale, three polypeptide chains form a triple helix referred to as a tropocollagen molecule that is ∼300 nm in length and 1.5 nm in diameter. These helices are arranged in a quasi-hexagonal bundle in which they overlap and intertwine to form microfibrils containing "hole zones," where there is a gap between the N termini of one helix and the C termini of another (3-5). These microfibrils are further bundled both laterally and longitudinally to form native collagen (3, 4).Within this highly organized scaffold, apatite crystallites form nanometer-scale platelets (6-9) with their [001] axes preferentially aligned parallel to the fibril axis (10-15) and the platelet faces defined by {100} crystal planes (16). Recent in vitro investigations of hydroxyapatite (HAP) formation within collagen fibrils revealed a multistage process in which amorphous calcium phosphate (ACP) first infiltrated through the hole zones and then converted into HAP platelets with initial mineral deposition occurring near the hole zones (11, 13). In vitro transmission electron microscopy (TEM) and atomic force microscop...

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Section: Results and Analysismentioning

confidence: 99%

Energetic basis for the molecular-scale organization of bone

Tao

Battle

Pan

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…A non-exhaustive list of solved and unsolved problems are illustrated in the following: (i) "HAp: hexagonal or monoclinic?" [42] and "Crystallographic structure of human tooth enamel by electron microscopy and X-ray diffraction: hexagonal or monoclinic?" [43] are representative titles of recent works concerning apatites growing in a bio-environment (bio-apatites).…”

Section: Solved and Unsolved Problems About The Relationship Betweenmentioning

confidence: 99%

“…Only a few papers deal with the monoclinic form, relegating its appearance to the biologically precipitated HAp [42] or the cases of high-temperature crystallization of HAp [20,[29][30][31].…”

Section: The Growth Of Nanosized Vs Micrometric Hap Crystals In Thementioning

confidence: 99%

About the Genetic Mechanisms of Apatites: A Survey on the Methodological Approaches

2017

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Apatites are properly considered as a strategic material owing to the broad range of their practical uses, primarily biomedical but chemical, pharmaceutical, environmental and geological as well. The apatite group of minerals has been the subject of a huge number of papers, mainly devoted to the mass crystallization of nanosized hydroxyapatite (or carboapatite) as a scaffold for osteoinduction purposes. Many wet and dry methods of synthesis have been proposed. The products have been characterized using various techniques, from the transmission electron microscopy to many spectroscopic methods like IR and Raman. The experimental approach usually found in literature allows getting tailor made micro-and nano-crystals ready to be used in a wide variety of fields. Despite the wide interest in synthesis and characterization, little attention has been paid to the relationships between bulk structure and corresponding surfaces and to the role plaid by surfaces on the mechanisms involved during the early stages of growth of apatites. In order to improve the understanding of their structure and chemical variability, close attention will be focused on the structural complexity of hydroxyapatite (HAp), on the richness of its surfaces and their role in the interaction with the precursor phases, and in growth kinetics and morphology.

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“…Table 2 shows the results obtained from XRD e ATR-IR techniques concerning the bone specimens here investigated. For the natural bioapatite used to describe the XRD powder patterns, it is customary to make use of the hexagonal structure with space group P63/m, even if in some cases a monoclinic structure P21/c may reveal more flexible in order the model closely follows the experimental data points [39]. Regarding the identified mineral phases we must make a distinction between fossil and modern/burned bones.…”

Section: A) Samplingmentioning

confidence: 99%

A structural approach in the study of bones: fossil and burnt bones at nanosize scale

Piga¹,

Baró²,

Golvano-Escobal³

et al. 2017

inArt 2016

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We review the different factors affecting significantly mineral structure and composition of bones.Particularly, it is assessed that micro-nano-structural and chemical properties of skeleton bones change drastically during burning; the micro-and nano-structural changes attending those phases manifest themselves, amongst others, in observable alterations to the bones colour, morphology, microstructure, mechanical strength and crystallinity.Intense changes involving the structure and chemical composition of bones also occur during the fossilization process. Bioapatite material is contaminated by an heavy fluorination process which, on a long-time scale reduces sensibly the volume of the original unit cell, mainly the a-axis of the 2 hexagonal P63/m space group. Moreover, the bioapatite suffers to a varying degree of extent by phase contamination from the nearby environment, to the point that rarely a fluorapatite single phase may be found in fossil bones here examined.TEM images supply precise and localized information, on apatite crystal shape and dimension, and on different processes that occur during thermal processes or fossilization of ancient bone.complementary to that given by X-ray Diffraction and Attenuated Total Reflection Infrared spectroscopy. We are presenting a synthesis of XRD, ATR-IR and TEM results on the nanostructure of various modern, burned and palaeontological bones.

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Hydroxyapatite: Hexagonal or Monoclinic?

Cited by 157 publications

References 14 publications

Energetic basis for the molecular-scale organization of bone

Energetic basis for the molecular-scale organization of bone

About the Genetic Mechanisms of Apatites: A Survey on the Methodological Approaches

A structural approach in the study of bones: fossil and burnt bones at nanosize scale

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