Percolation networks inside 3D model of the mineralized collagen fibril

Bone is a hierarchical biological material, characterized at the nanoscale by a recurring structure mainly composed of apatite mineral and collagen, i.e. the mineralized collagen fibril (MCF). Although the architecture of the MCF was extensively investigated by experimental and computational studies, it still represents a topic of debate. In this work, we developed a 3D continuum model of the mineral phase in the framework of percolation theory, that describes the transition from isolated to spanning cluster of connected platelets. Using Monte Carlo technique, we computed overall 120 × 106 iterations and investigated the formation of spanning networks of apatite minerals. We computed the percolation probability for different mineral volume fractions characteristic of human bone tissue. The findings highlight that the percolation threshold occurs at lower volume fractions for spanning clusters in the width direction with respect to the critical mineral volume fractions that characterize the percolation transition in the thickness and length directions. The formation of spanning clusters of minerals represents a condition of instability for the MCF, as it could be the onset of a high susceptibility to fracture. The 3D computational model developed in this study provides new, complementary insights to the experimental investigations concerning human MCF.

Mechanisms of Enamel Mineralization Guided by Amelogenin Nanoribbons

The nanofibrous nature and its intricate structural organization are the basis for the extraordinary ability of sound enamel to outlive masticatory forces at minimal failure rates. Apatite nanofibers of several hundreds of micrometers to possibly millimeters in length originate during the secretory stage of amelogenesis as 2-nm-thin and 15-nm-wide ribbons that develop and grow in length under the guidance of a dynamic mixture of specialized proteins, the developing enamel matrix (DEM). A critical role in the unidirectional and oriented growth of enamel mineral ribbons has been attributed to amelogenin, the major constituent of the DEM. This review elaborates on recent studies on the ability of ribbon-like assemblies of amelogenin to template the formation of an amorphous calcium phosphate precursor that transforms into apatite mineral ribbons similar to the ones observed in developing enamel. A mechanistic model of the biological processes that drive biomineralization in enamel is presented in the context of a comparative analysis of enamel mouse models and earlier structural data of the DEM emphasizing a regulatory role of the matrix metalloproteinase 20 in mineral deposition and the involvement of a process-directing agent for the templated mineral growth directed by amelogenin nanoribbons.

Synthesis and Investigation into Apatite-forming Ability of Hydroxyapatite/Chitosan-based Scaffold

In this study, porous scaffolds were fabricated using inorganic material-hydroxyapatite and chitosan for bone-tissue engineering. The combination of hydroxyapatite and chitosan may result in increasing biocompatibility of the scaffolds. The scaffolds were prepared by solvent casting and paticulate leaching method. Bioactivity of the scaffolds was evaluated through in vitro experiments by soaking scaffold samples in simulated body fluid (SBF). The scaffolds obtained were highly porous and interconnected with a mean pore size of around 200µm and porosity about 79 %. The apatite-mineral layer was produced on the HAp/chitosan after 10 days of soaking in SBF, however, it was not observed on the chitosan scaffold after 10 days soaking. The results revealed that the HAp/chitosan scaffold showed better bioactivity than the chitosan scaffold. Keywords Scaffold, Chitosan, Apatite, SBF. In this study, porous scaffolds were fabricated using inorganic material-hydroxyapatite and chitosan for bone-tissue engineering. The combination of hydroxyapatite and chitosan may result in increasing biocompatibility of the scaffolds. The scaffolds were prepared by solvent casting and paticulate leaching method. Bioactivity of the scaffolds was evaluated through in vitro experiments by soaking scaffold samples in simulated body fluid (SBF). The scaffolds obtained were highly porous and interconnected with a mean pore size of around 200µm and porosity about 79 %. The apatite-mineral layer was produced on the HAp/chitosan after 10 days of soaking in SBF, however, it was not observed on the chitosan scaffold after 10 days soaking. The results revealed that the HAp/chitosan scaffold showed better bioactivity than the chitosan scaffold. Keywords: Scaffold, Chitosan, Apatite, SBF. In this study, porous scaffolds were fabricated using inorganic material-hydroxyapatite and chitosan for bone-tissue engineering. The combination of hydroxyapatite and chitosan may result in increasing biocompatibility of the scaffolds. The scaffolds were prepared by solvent casting and paticulate leaching method. Bioactivity of the scaffolds was evaluated through in vitro experiments by soaking scaffold samples in simulated body fluid (SBF). The scaffolds obtained were highly porous and interconnected with a mean pore size of around 200µm and porosity about 79 %. The apatite-mineral layer was produced on the HAp/chitosan after 10 days of soaking in SBF, however, it was not observed on the chitosan scaffold after 10 days soaking. The results revealed that the HAp/chitosan scaffold showed better bioactivity than the chitosan scaffold. Keywords: Scaffold, Chitosan, Apatite, SBF. References [1] M.P. Bostrom, D.A. 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A mineralogical study in contrasts: highly mineralized whale rostrum and human enamel

The outermost enamel of the human tooth and the rostrum of the whale Mesoplodon densirostris are two highly mineralized tissues that contain over 95 wt.% mineral, i.e., bioapatite. However, the same mineral type (carbonated hydroxylapatite) does not yield the same material properties, as revealed by Raman spectroscopy, scanning electron microscopy, electron microprobe analysis and synchrotron X-ray diffraction analysis. Overall, the outermost enamel of a tooth has more homogeneous physical and chemical features than the rostrum. Chemical comparison of rostrum and enamel shows bioapatite in the rostrum to be enriched in Na, Mg, CO3 and S, whereas the outermost enamel shows only a slightly enriched Cl concentration. Morphologically, mineral rods (at tens of μm scale), crystallites and prisms (at μm and sub-μm scale) and platelets (at tens of nm scale) all demonstrate less organized texture in the rostrum than in enamel. Such contrasts between two mineralized tissues suggest distinct pathways of biomineralization, e.g., the nature of the equilibrium between mineral and body fluid. This study illustrates the remarkable flexibility of the apatite mineral structure to match its chemical and physical properties to specific biological needs within the same animal or between species.

Phosphorus removal by the use of apatite in constructed wetlands: Design recommendations

Phosphorus (P) removal in constructed wetlands (CWs) has received particular attention during the last decades by using specific materials which promote P adsorption/precipitation phenomena. Recent studies have shown an interest in using apatite materials to promote P precipitation onto their surface. About ten years of experiments at different scales (laboratory, pilot, full scale) have passed. The process is now open in France. This paper presents the first design recommendations according to the apatite mineral quality and treatment outlet requirements. Kinetics and their evolution with the material saturation degree are presented based on the k-C* model. The process can achieve 1 mgP.l−1 for long term while using surface P removal filter area of 0.5 m2.p.e.−1. With a low land footprint and high P removal efficiency, the interest of the process also result in the orthophosphates accumulation on a phosphate mineral which makes easier to reuse phosphorus from wastewater once saturated

Phosphorus removal by apatite in horizontal flow constructed wetlands for small communities: pilot and full-scale evidence

Phosphorus (P) removals in constructed wetlands (CWs) have received particular attention in recent decades by using specific materials which promote adsorption/precipitation mechanisms. Recent studies have shown interest in using apatite materials to promote P precipitation onto the particle surface. As previous trials were mainly done by lab experiments, this present study aims to evaluate the real potential of apatites to remove P from wastewater in pilot units and a full-scale plant over a 2 year period. P retention kinetics of two qualities of apatites are presented and discussed. In this work apatite appears to have high retention capacity (>80% of P removal) and is still an interesting way for P removal in CWs for limiting the risk of eutrophication downstream of small communities. Nevertheless, the apatite quality appears to be of great importance for a reliable and long term P removal. The use of materials with low content of apatite mineral (40–50%) seems to be not economically relevant.