There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

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

How useful is SBF in predicting in vivo bone bioactivity

Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering

There have been a number of major advances made in the field of bioactive ceramics, glasses and glass ceramics during the past 30–40 years. From initial work on the development of materials that are tolerated in the physiological environment, emphasis has now shifted towards the use of ceramic materials that interact with bone tissue by forming a direct bond. It is now possible to choose, by compositional control, whether these materials are biologically stable once incorporated within the skeletal structure or whether they are resorbed over time. This paper reviews the ground-breaking work that was performed during the 1970s and 1980s in the field of bioceramics in the production and characterisation of bioactive and bioresorbable glasses, glass ceramics and calcium phosphates. The review then explores the influence of the original concepts and ideas on the more recent development of ceramic scaffolds, composites and coatings with enhanced bioactivity for bone tissue engineering.

http://eng.sut.ac.th/ceramic/old/course_link/88.pdf

Bioceramics: Past, present and for the future

Bioceramic specimens have been prepared by incorporating a small amount of silicon (0.4 wt %) into the structure of hydroxyapatite [Ca10(PO4)6(OH)2, HA] via an aqueous precipitation reaction to produce a silicon-substituted hydroxyapatite (Si-HA). The results of chemical analysis confirmed the proposed substitution of the silicon (or silicate) ion for the phosphorus (or phosphate) ion in hydroxyapatite. The Si-HA was produced by first preparing a silicon-substituted apatite (Si-Ap) by a precipitation process. A single-phase Si-HA was obtained by heating/calcining the as-prepared Si-Ap to temperatures above 700 degrees C; no secondary phases, such as tricalcium phosphate (TCP), tetracalcium phosphate (TeCP), or calcium oxide (CaO), were observed by X-ray diffraction analysis. Although the X-ray diffraction patterns of Si-HA and stoichiometric HA appeared to be identical, refinement of the diffraction data revealed some small structural differences between the two materials. The silicon substitution in the HA lattice resulted in a small decrease in the a axis and an increase in the c axis of the unit cell. This substitution also caused a decrease in the number of hydroxyl (OH) groups in the unit cell, which was expected from the proposed substitution mechanism. The incorporation of silicon in the HA lattice resulted in an increase in the distortion of the PO4 tetrahedra, indicated by an increase in the distortion index. Analysis of the Si-HA by Fourier transform infrared (FTIR) spectroscopy indicated that although the amount of silicon incorporated into the HA lattice was small, silicon substitution appeared to affect the FTIR spectra of HA, in particular the P-O vibrational bands. The results demonstrate that phase-pure silicon-substituted hydroxyapatite may be prepared using a simple precipitation technique.

Chemical characterization of silicon-substituted hydroxyapatite.

Phase pure hydroxyapatite (HA) and a 0.8 wt % silicon substituted hydroxyapatite (SiHA) were prepared by aqueous precipitation methods. Both HA and SiHA were processed into granules 0.5-1.0 mm in diameter and sintered at 1200 degrees C for 2 h. The sintered granules underwent full structural characterization, prior to implantation into the femoral condyle of New Zealand White rabbits for a period of 23 days. The results show that both the HA and SiHA granules were well accepted by the host tissue, with no presence of any inflammatory cells. New bone formation was observed directly on the surfaces and in the spaces between both HA and SiHA granular implants. The quantitative histomorphometry results indicate that the percentage of bone ingrowth for SiHA (37.5%+/-5.9) was significantly greater than that for phase pure HA (22.0%+/-6.5), in addition the percentage of bone/implant coverage was significantly greater for SiHA (59.8%+/-7.3) compared to HA (47.1%+/-3.6). These findings indicate that the early in vivo bioactivity of hydroxyapatite was significantly improved with the incorporation of silicate ions into the HA structure, making SiHA an attractive alternative to conventional HA materials for use as bone substitute ceramics.

A comparative study on the in vivo behavior of hydroxyapatite and silicon substituted hydroxyapatite granules

Comparison of in vivo dissolution processes in hydroxyapatite and silicon-substituted hydroxyapatite bioceramics

Hydroxyapatite (HA) has been used in clinical bone graft procedures for more than 25 years. However, its poor tensile strength and fracture toughness compared with bone make it unsuitable for major load-bearing devices. Carbon nanotubes (CNTs), with their high aspect ratio and excellent mechanical properties, have the potential to strengthen and toughen HA without offsetting its bioactivity, thus opening up a wider range of possible clinical uses for the material. This review discusses techniques for synthesizing and processing HA-CNT composites, as well as barriers that still remain to their successful development for clinical application.

Serena M. Best

Papers

Bioceramics: Past, present and for the future

Chemical characterization of silicon-substituted hydroxyapatite.

A comparative study on the in vivo behavior of hydroxyapatite and silicon substituted hydroxyapatite granules

Comparison of in vivo dissolution processes in hydroxyapatite and silicon-substituted hydroxyapatite bioceramics

Hydroxyapatite–Carbon Nanotube Composites for Biomedical Applications: A Review