Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

https://www.researchgate.net/file.PostFileLoader.html?id=526892a1d4c118a61d4360bd&assetKey=AS%3A272155479085058%401441898330516

Porosity of 3D biomaterial scaffolds and osteogenesis.

Surface treatments of titanium dental implants for rapid osseointegration

Macroporous ceramics with pore sizes from 400 nm to 4 mm and porosity within the range 20%–97% have been produced for a number of well-established and emerging applications, such as molten metal filtration, catalysis, refractory insulation, and hot gas filtration. These applications take advantage of the unique properties achieved through the incorporation of macropores into solid ceramics. In this article, we review the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition. Emphasis is given to versatile and simple approaches that allow one to control the microstructural features that ultimately determine the properties of the macroporous material. Replica, sacrificial template, and direct foaming techniques are described and compared in terms of microstructures and mechanical properties that can be achieved. Finally, directions to future investigations on the processing of macroporous ceramics are proposed.

/pdf/processing-routes-to-macroporous-ceramics-a-review-1urld578zq.pdf

Processing Routes to Macroporous Ceramics: A Review

At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2008.0151

Biomaterials in orthopaedics.

A process for the preparation of a single phase magnesium- and carbonate-substituted hydroxyapatite composition, which process comprises the steps of (i) preparing an aqueous solution containing CO32- and PO?4?3- ions in the substantial absence of cations other than H+ ions; (ii) mixing the solution from step (i) with an aqueous calcium- and magnesium-containing solution or suspension; and (iii) collecting and drying the precipitate formed in step (ii); the ratio of (Ca+Mg/P) in the calcium- and magnesium-containing solution or suspension and the phosphorus-containing solution, when mixed together, being maintained at 1.67, or above. The product of the process is novel and comprises up to 0.5 % magnesium and up to 1 % of carbonate substituted into the hydroxyapatite structure and which does not contain Na+ or NH?4?+ ions, the ratio of (Ca+Mg/P) being greater than 1.67.

Process for the preparation of magnesium and carbonate substituted hydroxyapatite

The effect of low levels of zirconia addition on the mechanical properties of hydroxyapatite

Two batches of calcium phosphate implants, termed HA1 and HA2 were prepared with calcium to phosphorus ratios of 1.67 and 1.70 respectively. XRD demonstrated that the HA1 implants were composed of phase pure hydroxyapatite, while the phase composition of the HA2 implants contained approximately 5% calcium oxide with the balance being hydroxyapatite. Sintered cylindrical implants, 3 mm in diameter, were prepared from each of the powders, containing slots I mm wide x 2 mm deep in one circular face. The implants were implanted laterally in the distal femur of 6 month old New Zealand white rabbits for a period of 3 weeks. Subsequent histological evaluation demonstrated that the presence of the CaO impurity phase significantly reduced the osteoconductivity, as demonstrated by minimal penetration of new bone within HA2 implant slots and a significant reduction in direct bone apposition on any of the HA2 implant surfaces as compared with HA1 implants. This study has confirmed the need for precise control of the phase purity of hydroxyapatite based bioceramics for optimal biological performance

Influence of phase purity on the in vivo response to hydroxyapatite

Phase pure hydroxyapatite (HA), 0.8 wt.% silicon-substituted hydroxyapati te (0.8SiHA) and 1.5 wt.% silicon substituted hydroxyapatite (1.5SiHA) were isostatical ly pressed into discs and sintered between 900-1300 °C for 2 hours in order to assess the effect of silicon/carbonate cont nt on the density, microstructure, hardness and Young’s modulus of HA with sintering temperature. C-H-N chemical analysis of the as-prepared SiHA samples showed increa sed c rbonate absorption with silicon content compared to HA samples, but carbonate levels were not d tec ed when the samples were heat-treated. At low sintering temperatures (900-1000 °C) the densification of SiHA samples was inhibited, with this effect being more significant for the hig h level of silicon substitution (1.5SiHA) ceramics which was reflected in the hardness and Young’s modulus values of the ceramics. However, for high sintering temperatures (1200 and 1300 °C), the sintered densities, hardness and Young’s modulus of HA and SiHA were comparable. Furthermore, examina tion of the microstructures by scanning electron microscopy showed that silicon s ubstitution inhibited grain growth at high sintering temperatures. Introduction The similarities in the chemical composition of synthetic hydroxya patite (HA) and bone mineral has led to extensive use of HA ceramics as bone replacement materials. Alt hough bone bonds directly to the surface of HA, the number of medical applications of HA are li mited, primarily due to its relatively poor mechanical properties and slow rate of osseointegra tion compared to some other bioceramics [1]. A possible approach to improve the bioactivity of HA c eramics is to incorporate small levels of physiologically relevant ions into the HA lattic e. It has been shown that carbonate or silicon-substituted hydroxyapatite ceramics, exhibit enhanced in vitro [2,3] and in vivo [4,5] bioactivity compared to phase pure HA. Although these ionic substitutions e nhance the bioactivity of HA, studies have highlighted that the physical properties, such as t he degree of densification and sintered microstructure are affected with both the type and level of ionic substitution into HA. In particular carbonate substitution significantly reduces the sinteri ng temperature, required to achieve near-full density and equivalent grain size of the ceramic compare d to phase pure HA. However carbonate substituted hydroxyapatites are normally sintered in a moi st carbon dioxide environment which promotes densification [6]. Based on previous studies [6] on carbonate substituted HA, it is reasonable to assume that the substitution of silicon or silicate i ons into HA may also influence the densification and grain growth characteristics of the ceramic. T he aims of this study were, therefore, to determine the effect of silicon substitution and sintering temperature on t h mechanical properties of HA. Materials and Methods Phase pure hydroxyapatite (HA), 0.8 wt.% silicon-substituted hydroxyapati te (0.8SiHA) and 1.5 wt.% silicon-substituted hydroxyapatite (1.5SiHA) were prepared by aqueous precipitation reactions according to the methods described elsewhere [7]. The resulting preci pitate was filtered, dried at Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 919-922 doi:10.4028/www.scientific.net/KEM.240-242.919 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,21:21:03)

Comparison of Sintering and Mechanical Properties of Hydroxyapatite and Silicon-Substituted Hydroxyapatite

In-office products containing oxalates have been claimed to be clinically effective in reducing dentine sensitivity, although there has been limited supporting clinical data. The rationale for their use appears to be based on their potential to act as occluding and/or nerve desensitizing agents. Four commercially available oxalate-containing products were applied to etched dentine discs and the extent of tubule occlusion was observed by scanning electron microscopy. Tenure Quick (aluminium oxalate), Sensodyne Sealant (ferric oxalate) and MS Coat (oxalic acid) covered the dentine surface and occluded the tubules. However, Butler Protect (potassium oxalate) did not cover the surface to any great extent but provided some occlusion. The presence of oxalates after application to glass slides and dentine discs was examined using thin film X-ray diffraction. From samples on glass, only potassium oxalate could be clearly identified (JCPDS 14-0845). No oxalate was detected on dentine discs in either thin film geometry or standard theta two theta mode. We have demonstrated that professionally applied in-office products containing oxalate are capable of covering the dentine surface and/or occluding the tubules to varying degrees. However, X-ray diffraction analysis was unable to confirm the oxalate profile for all products as described in the available commercial literature.

Iain R. Gibson

Papers

Process for the preparation of magnesium and carbonate substituted hydroxyapatite

The effect of low levels of zirconia addition on the mechanical properties of hydroxyapatite

Influence of phase purity on the in vivo response to hydroxyapatite

Comparison of Sintering and Mechanical Properties of Hydroxyapatite and Silicon-Substituted Hydroxyapatite

The effects of oxalate-containing products on the exposed dentine surface: an SEM investigation: EFFECTS OF OXALATES ON DENTINE