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Two-Dimensional Nanomaterials for Drug Delivery in Regenerative Medicine
Published in Harishkumar Madhyastha, Durgesh Nandini Chauhan, Nanopharmaceuticals in Regenerative Medicine, 2022
Zahra Mohammadpour, Seyed Morteza Naghib
Layered doubled hydroxides (LDHs) are a class of anionic clays that consist of positively charged metal hydroxide layers and interlayer anionic molecules for charge balance. Their structure is close to brucite. Incorporation of various metal cations into the layers and the interlayer anions’ exchangeability give rise to a flexible composition and a multitude of properties for these laminated structures. The expansive space between the layers of LDHs has made them hosts for various (bio) molecules, drugs, nanoparticles, etc. LDH nanoparticles have shown in vivo biocompatibility (Figueiredo et al. 2018). In regenerative medicine, LDHs have been actively employed for wound healing, immunotherapy, bone regeneration, drug delivery, etc. Isoniazid, an anti-tuberculosis drug, was sustainably released from MgAl LDHs (Saifullah et al. 2014). Saifullah et al. found that the nanodelivery system provided higher biocompatibility than free isoniazid (Saifullah et al. 2014). The possibility to intercalate poorly water-soluble drugs is another feature of LDH nanoparticles. As an example, Gao et al. loaded ibuprofen and ketoprofen into LDHs and mixed them with polycaprolactone (PCL) to fabricate organic–inorganic nanohybrids (Gao et al. 2017). While the drug release from the LDH itself was relatively fast during the first four hours, the release rate from the nanohybrids was much slower. Due to such characteristics, the authors proposed nanofibres as appropriate candidates for implantable drug delivery systems.
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.)
Experimental Asbestosis
Published in Joan Gil, Models of Lung Disease, 2020
The initial intrapleural inoculation (Wagner, 1963) established that it was possible to produce mesotheliomas. The next stage was to see if it were possible to differentiate between the incidence of tumor production according to the type of asbestos fiber, using SPF rats (Wagner and Berry, 1969). The peak tumor incidence occurred at the 700th day after inoculation, with some animals surviving up to 1000 days. The result was a surprise, since the highest incidence of tumors (65%) occurred in the animals treated with the chrysotile samples; the crocidolite produced a 60% incidence of tumors. The experiment was repeated using a healthy strain of conventionally bred Wistar rats. The results were practically identical. The chrysotile used in this experiment was produced from a prototype plant at one of the Canadian mines that was trying to develop a wet weaving process in which the fiber was separated from the crushed ore by a sedimentation process, which left the actual fibers suspended in a detergent solution. The fiber was then sedimented out by the addition of a solution that neutralized the detergent. This resulted in a large number of very fine chrysotile fibers, the majority of which appeared to be straight under the transmission electron microscope. (In general, the chrysotile fibers have a wavy, coiled appearance, unlike the needle straight amphibole fiber [Timbrell et al., 1970a]). As stated previously, the electron microscopic investigation also showed that the chrysotile fibers in solution tended to be shredded into numerous very fine fibrils, whereas the longitudinal shearing characteristic of all asbestos fibers only produced two or three fine amphibole fibers. The possibility that brucite (or nemolite), a fibrous magnesium hydroxide found in the chrysotile deposits, may have been involved was considered. When inoculated the nemolite produced a high incidence of tumors (Wagner et al., 1976), but it was pointed out that by grinding the nemolite we had created a substance did not occur in the milling of the chrysotile ore. Studies of the minerals containing the chrysotile sample did not reveal nemolite. In the 20 years since these results were obtained, there has been considerable speculation as to why the Canadian chrysotile, which in human epidemiological studies produced few mesotheliomas, has been so active in experimental animals. Davis and his colleagues, in a more recent study (1986), obtained very similar results with dust from the final product of this fiber prepared for wet spinning.
The health effects of short fiber chrysotile and amphibole asbestos
Published in Critical Reviews in Toxicology, 2022
Chrysotile was first described as being decomposed by acid by von Kobell (1834). Chrysotile has the approximate composition Mg3Si205(OH)4 and is a sheet silicate composed of silicate and brucite layers (magnesium hydroxide octahedra). The different dimensions of these two components result in a structural mismatch in which the layers curl concentrically or spirally (Pauling 1930). The fiber walls are made up of ∼12–20 of these layers in which there is some mechanical interlocking. However, there is no chemical bonding as such between the layers. Each layer is about 7.3 A° thick, with the magnesium hydroxide part of each layer closest to the fiber surface and the silicon-oxygen tetrahedra “inside” the curl (Whittaker 1957, 1963; Tanji 1984; Titulaer et al. 1993, Table 2). Hargreaves and Taylor (1946) reported that if fibrous chrysotile is treated with dilute acid, the magnesia can be completely removed. The hydrated silica, which remains, though fibrous in form, had completely lost the elasticity characteristic of the original chrysotile and had a structure that was “amorphous” or “glassy” in type.
Layered double hydroxide nanoparticles as an appealing nanoparticle in gene/plasmid and drug delivery system in C2C12 myoblast cells
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Parivar Yazdani, Elham Mansouri, Shirin Eyvazi, Vahid Yousefi, Homan Kahroba, Mohammad Saeid Hejazi, Asghar Mesbahi, Vahideh Tarhriz, Mir Mahdi Abolghasemi
Moreover, the FT-IR spectra of Zn/Al-LDH, VP-Zn/Al-LDH and MD-Zn/Al-LDH nanoparticles in the 400–4000 cm−1 showed the exhibit basic characteristic peaks at ∼451 cm−1 that were attributed to the presence of M–O (metal–oxygen group) bonds stretching vibration. The broad peak centred at ∼3440 cm−1 corresponds to a combination of the stretching vibration of a hydrogen bond between water molecules and metal hydroxyl in the hydroxide groups of the brucite sheets and interlayer water molecules. The absorbance at 1644 cm−1 is related to the bending vibrations of the interlayer water molecules. According to Figure 3, the comparison between the FT-IR spectra of VP-Zn/Al-LDH and LDH various spectra groups such as carboxylic acid COOH, C–H and C–C indicates successful loading of the drug into interlayer of LDH. As indicated, the characteristic peaks of 630 cm−1 (C–C group) and 2924 cm−1 (C–H group) are assigned. The 1373 cm−1 and 1514 cm−1 spectra are related to symmetrical and asymmetric stretching vibrations of a carboxylate group, respectively. The interaction between the carboxylate head and the metal atom was considered in four types: monodentate, bridging, chelating, and ionic interaction [29–31]. According to Zhang et al., the wave-number separation, Δ, between the asymmetric and symmetric IR peaks is applicable to distinguish the type of interaction between the carboxylate head and the metal atom. The largest Δ (200–320 cm−1) corresponded to the monodentate interaction and the smallest Δ (<110 cm−1) to the chelating bidentate. The medium range of Δ (140–190 cm−1) was reported for bridging. In this study, the Δ (1514–1373 = 141 cm−1) was ascribed as bridging bidentate. These results provide further support for VP intercalation into the interlay space of layered double hydroxides.