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Light Propagation and Interaction in Highly Scattering Media for Deep Tissue Imaging
Published in Lingyan Shi, Robert R. Alfano, Deep Imaging in Tissue and Biomedical Materials, 2017
W. B. Wang, Shi Lingyan, Lu Luyao, Laura A. Sordillo, L. Wang, S.K. Gayen, R.R. Alfanoa
Several scientific and technological developments make realization of the above-mentioned opportunity more probable than ever. First, development of broadly tunable ultrafast lasers, based on Ti: sapphire, Cr: Forsterite, doped fibers as active materials, as well as ultrafast supercontinuum, and application-specific semiconductor diode lasers, provides a wide range of wavelengths for spectroscopy and imaging. Concurrent developments in charge coupled device (CCD) cameras, near-infrared cameras, complementary metal oxide semiconductor (CMOS) cameras, as well as fast and compact personal computers make signal detection, data acquisition, processing, and analysis faster and efficient than ever before. Second, recent advent of vortex light beams with higher orbital angular momentum (OAM) may be advantageous for imaging and spectroscopy depending on how such beams scatter and interact with materials systems. Third, identification of 1100–1350 nm and 1600–1870 nm NIR spectral windows for biological tissue imaging, in addition to the 650–950 nm range that has commonly been used may improve penetration depth. Finally, imaging based on nonlinear optical interactions between light and tissue constituents has been proved to have better spatial resolution and ability to provide sectional images because of the higher power law dependence of nonlinear optical signal on light intensity.
Clinical toxicology of asbestos
Published in Dorsett D. Smith, The Health Effects of Asbestos, 2015
Asbestos particles found in natural mineral deposits do not have fixed dimensions but form as parallel aggregations of long crystalline fibrils or fibers. In natural mineral formations, these fibers can be up to several centimeters long. They are quite brittle, and when stressed, break easily into shorter lengths. In preparing it for commercial use, asbestos-containing rock is crushed mechanically and cleaned in a process called milling. This results in an infinite variety of sizes for commercial asbestos fibers; most are less than 50 µm long, and many are shorter than 1 µm. Chrysotile is the only commercial fiber type in the serpentine group. It is also the only asbestos fiber that is curly and is often found in intertwined bundles. The crystalline structure of chrysotile consists of parallel sheets of silica and magnesium hydroxide (i.e., brucite), which give the appearance of overlapping scrolls in cross-section. The basic structural unit of chrysotile is the fibril, which is a curved sheet of this material that forms into a scroll or tube. Chrysotile fibrils have a fixed diameter of 0.02–0.04 µm, which makes them the thinnest fiber found in nature (in comparison, the diameters of a cotton fiber and a human hair are 10 and 40 µm, respectively). In nature, these chrysotile fibrils are usually found bunched together to form a chrysotile fiber with a typical diameter of 0.75–1.5 µm. Serpentine fibers derive their name from the serpentine rocks in which they are found. Asbestos forms when very hot liquid supersaturated with minerals invades fissures in serpentine rock and then slowly cools and crystallizes into veins. In natural formations, chrysotile is often found with quartz micas, fosterite, brucite, and feldspar, so commercial formulations can be contaminated with these materials. (Ross M. The geologic occurrences and health hazards of amphibole and serpentine asbestos. Rev Mineral 1981;9A:279–323; Guthrie GD, Mossman BT. Health effects of mineral dusts. Rev Mineral 1993;28; Bayram M, Bakan ND. Environmental exposure to asbestos: From geology to mesothelioma. Curr Opin Pulm Med 2014.)
In vitro osteogenic differentiation of stem cells with different sources on composite scaffold containing natural bioceramic and polycaprolactone
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Fatemeh Sadat Hosseini, Fatemeh Soleimanifar, Abdolreza Ardeshirylajimi, Saeid Vakilian, Majid Mossahebi-Mohammadi, Seyed Ehsan Enderami, Arash Khojasteh, Shohreh Zare Karizi
As another main part of the tissue engineering, scaffolds help stem cells to grow as well as tissue formation because they are pseudo three-dimensional organization. In the area of damaged tissues, the mechanical structure, the ability to transport efficient food and other growth factors has also been destroyed [9,10]. Using these scaffolds, in addition to the platform needed to control the growth of stem cells, the problems mentioned above are also overcome. When the stem cells to form a three-dimensional tissue structure, the scaffold is gradually degraded and only differentiated cells remain. In such a system using growth factors, stem cell differentiation into a variety of different tissues is possible without changing the basic matrix materials [11,12]. Bioactive ceramics such as hydroxyapatite (HAP), tri-calcium phosphate (TCP) and bioactive glasses are known as ceramics that are applied to induce specific biological activity in damaged bone via reaction with physiological fluids and through cellular interactions form tenacious bonds to achieve tight fixation [13,14]. Bio-ceramics usually have higher Young’s modulus than human cortical bone; therefore, they should combine with synthetic biomaterials to modify their mechanical properties. Examples of these composite nanofibrous scaffolds such as bioactive hybrids are polycaprolactone (PCL)/silica hybrids, PCL/bioactive glass hybrid, PCL/HAP composite and PCL/calcium phosphate [15]. Currently, it has been reported that PCL nanocomposite with forsterite (Mg2SiO4) as a new bioceramic shows adequate mechanical properties and good bioactivity [15]. It was also demonstrated that addition of bio-ceramics could modulate PCL degradation [16–18]. Moreover, PCL/bioceramic nanocomposite scaffolds resulted in greater protein adsorption and enhanced mineralization. Improving both mechanical strength and bioactivity could be beneficial in the processing of bone cements [15].
A critical review of the 2020 EPA risk assessment for chrysotile and its many shortcomings
Published in Critical Reviews in Toxicology, 2021
Dennis Paustenbach, David Brew, Sabina Ligas, Jonathan Heywood
However, it should be noted that brake wear debris was at least 99% converted to forsterite due to heating during use (Lynch and Ayer 1968; Hatch 1970; Hickish and Knight 1970; Anderson 1973; Davis and Coniam 1973; Jacko et al. 1973; Rowson 1978; Williams and Muhlbaier 1982; Cha et al. 1983; Sheehy et al. 1989; Spencer 2003; Paustenbach et al. 2004; Boelter et al. 2007; Madl et al. 2009), and forsterite does not have asbestos-like characteristics (Langer 2003).
Assessment of the physicochemical properties of chrysotile-containing brake debris pertaining to toxicity
Published in Inhalation Toxicology, 2019
Matthew S. P. Boyles, Craig A. Poland, Jennifer Raftis, Rodger Duffin
Due to the generation of friction, there is the possibility of heat modification of chrysotile during the grinding of the brake pads. While chrysotile asbestos has been widely used due to its noncombustible and insulating capacity (e.g. in fire-proof suits), it is not actually impervious to change under heat. As described by Zaremba et al. (2010), heating of chrysotile leads to thermal decomposition due to the dehydroxylation of the chrysotile fibrils. With sufficient heat, this can result in the complete breakdown of the mineral structure and the formation of forsterite. The importance of this lies in the fact that forsterite has a very different structure, lower biodurability, and toxicity profile when compared to chrysotile (Gualtieri et al. 2012). Indeed, heat treatment has been suggested as a recycling strategy for chrysotile-containing materials (Gualtieri and Tartaglia 2000). The question of if heat generation during grinding could significantly modify chrysotile including the transformation to forsterite hinges on the heat generated. Dehydroxylation can begin at temperatures as low as 150 °C (Langer 2003), yet destruction of chrysotile and formation of forsterite occurs at much higher temperatures of 600–725 °C (Zaremba et al. 2010). It was described by Langer (2003) braking can result in ‘normal’ service temperatures of up to 650 °C but also ‘hot spots’ with temperatures well reaching as high as 1000 °C. However, the action of grinding is not the same as that of braking. While not an in-depth study, the temperatures on the surface of the middle of the brake shoe collected seconds after a series of many swipes back and forth with an AAMCO arc grinder were approximately 55 °C. Overall, it was found that while grinding can cause the shoes get hot to the touch, it is not hot enough to burn bare skin (RJ Lee Personal communication). Based on the minimal heating and short duration, it is unlikely that grinding alone could cause significant heat modification of chrysotile contained within the brake pad and certainly not the formation of forsterite.