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Nanomaterials for Theranostics: Recent Advances and Future Challenges *
Published in Valerio Voliani, Nanomaterials and Neoplasms, 2021
Eun-Kyung Lim, Taekhoon Kim, Soonmyung Paik, Seungjoo Haam, Yong-Min Huh, Kwangyeol Lee
An interesting biodegradable Si/SiO2 nanostructure for both imaging and drug delivery was reported by Sailor et al. [861] Luminescent porous Si nanoparticles (LPSiNPs) were prepared by electrochemical etching of single-crystal silicon wafers in ethanolic HF solution. Native silicon oxide layer grew on the surface of porous silicon, and this generated a significant luminescence, which was attributed to quantum confinement effects and defects localized at the Si-SiO2 interface. Positively charged DOX molecules could be attached to the negatively charged porous SiO2 surface by electrostatic forces (Fig. 16.47A). For in vivo studies, LPSiNPs (20 mg/kg) were injected intravenously into mice. The injected LPSiNPs accumulated mainly in the MPS-related organs such as the liver and the spleen. However, the LPSiNPs accumulated in the organs were noticeably cleared from the body within a period of 1 week and completely cleared in 4 weeks. The mechanism of clearance was attributed to degradation into soluble silicic acid followed by excretion. This result contrasts with the slow clearance generally observed for other types of inorganic nanoparticle with diameters > 5.5 nm.
Brittle Nails
Published in Nilton Di Chiacchio, Antonella Tosti, Therapies for Nail Disorders, 2020
Besides the orthosilicic acid and its stabilized formulations, such as choline chloride-stabilized orthosilicic acid, the most important sources that release orthosilicic acid as a bioavailable form of silicon are colloidal silicic acid (hydrated silica gel), silica gel (amorphous silicon dioxide), and zeolites.
Chemical Factors
Published in Michael J. Kennish, Ecology of Estuaries Physical and Chemical Aspects, 2019
Estuaries receive silicon from riverine systems in dissolved form, via the weathering of silicate minerals in rocks and the leaching of soils, and in particulate form as detrital quartz and clays (alumino silicates). In waters having a pH <9, dissolved silicon is present as silicic acid (H4SiO4).1 Early workers253 proposed that dissolved silicon is removed in estuaries by the formation and flocculation of polymeric silicon during mixing with electrolytes in seawater, because the mean concentration of dissolved silicon in river water (13.1 mg/ℓ)18 exceeds that in seawater (0 to 10 mg/ℓ)21 and because much of the silicon in river water presumably occurs in colloidal form. Some early investigators ascribed nearly 100% removal of dissolved silicon to nonbiological processes during the early stages of estuarine mixing. Liss,17 in a literature review of silicon studies, doubts the occurrence of a colloidal fraction of silicon in river water, which would make direct coagulation of silicon unlikely during estuarine mixing. Additionally, field studies by Burton et al.254 and Burton and Liss255 connote that only about 10 to 20% of dissolved silicon is removed during estuarine mixing. Liss17 places the level of removal of dissolved silicon in the range of 0 to 30% of the riverine flux, with most probably being removed during the early stages of mixing. A recent detailed treatment of silicon behavior in marine systems can be found in Aston.256
Current status and prospect for future advancements of long-acting antibody formulations
Published in Expert Opinion on Drug Delivery, 2023
Puneet Tyagi, Garrett Harper, Patrick McGeehan, Shawn P Davis
Silica has attracted considerable interest in drug delivery in the recent past due to its advantageous properties, including biodegradability and biocompatibility [27,28]. Silica degrades in the body to silicic acid and is subsequently eliminated from the body via renal excretion [29]. Having been approved by the FDA as GRAS (generally regarded as safe), silica is a common ingredient in oral and topical formulations. In comparison to PLGA polymers, silica degradation does not create an acidic environment as silicic acid has the first pKa at 9.84 [30]. In one of our earlier studies, we reported a sustained release of an active mAb from a silica matrix formed by the polymerization of alkoxysilanes, Si(OR)4, using a technique known as the sol-gel process [31]. By changing the manufacturing process parameters, it is possible to vary the number of the OH groups and specific surface area (from a dense gel to highly porous), both influencing the biodegradation rate of silica. The matrix is slowly dissolved when in contact with body fluids. However, use for silica for injectable long-term therapy needs to be thoroughly investigated for potential side effects.
Intravitreal safety profiles of sol-gel mesoporous silica microparticles and the degradation product (Si(OH)4)
Published in Drug Delivery, 2020
Yaoyao Sun, Kristyn Huffman, William R. Freeman, Michael J. Sailor, Lingyun Cheng
The pore size of an intravitreal particulate drug delivery system is an important parameter in terms of release rate of the payload and the elimination rate of the vehicle material. Characterizing the dissolution rate and vitreous elimination profile of silicic acid is an important part of optimizing the intravitreal delivery system using mesoporous silica particles. In order to investigate the rate at which sol-gel silica degrades into silicic acid, an in vitro release experiment was carried out. We tested 3 different sized particles for in vitro silicic acid release, 15 µm/10 nm, 25–45 µm/50 nm and 15 µm/100 nm (particle diameter/pore diameter). Briefly, 2 mg of sol-gel silica particles was weighed into a 1.5 mL microcentrifuge tube with 1200 µL of PBS. The vials were incubated at 37 °C. The vials were centrifuged at 5,000 rpm for 5 minutes, and 1000 uL of the supernatant was collected and stored at –80 °C. Then, 1000 uL of PBS was added back to each of the tubes to restore the volume of the dissolution medium. The experiment was carried out daily and all samples were analyzed by the end of week 3. The concentration of silicic acid was determined by ICP-OES.
Silicon dioxide and titanium dioxide particles found in human tissues
Published in Nanotoxicology, 2020
Ruud J. B. Peters, Agnes G. Oomen, Greet van Bemmel, Loes van Vliet, Anna K. Undas, Sandra Munniks, Ronald L. A. W. Bleys, Peter C. Tromp, Walter Brand, Martijn van der Lee
Although SiO2 and TiO2 are authorized ingredients in food, and used in consumer and medical products, knowledge about their tissue concentrations in humans is very limited, and virtually absent with regard to particle content. Therefore, the data from this study are unique and highly useful for risk assessment. The presented concentrations represent the total organ burden of SiO2 and TiO2 particles. While it is assumed that most human subjects followed a western European diet, no historical data on specific exposure conditions of the human subjects are available and therefore we cannot establish a definite relation with the source of the SiO2 and TiO2 particles found in the human tissues. Consumer intake of SiO2 from food has been estimated at 9.4 mg Si/kg bw/day (Dekkers et al. 2011). Based on these and other data, Van Kesteren et al. developed a kinetic model and estimated steady state Si liver concentration in human tissues at 21–23 mg Si/kg (van Kesteren et al. 2015). Apart from that little is known about the total-Si concentrations in human tissues (Table 3) and quantitative information on the presence of particles is absent. While uptake of Si or SiO2 in humans is unknown, recent studies with rodents imply limited oral uptake of silica at realistic consumer exposure levels, while also accumulation in time may occur (van der Zande et al. 2014; van Kesteren et al. 2015). Silica and silicic acid and its calcium, magnesium and aluminum salts occur ubiquitously in the environment and some have been used for many years medically, for example, against osteoporosis. As a consequence, small amounts of silica are normally present in our bodies and according to the WHO the silica concentration in human tissues varies from 10 to 200 mg/100 g on a dry weight basis which translates to 2 to 50 mg Si/kg tissue (Yukawa et al. 1980). The total-Si liver concentrations found in this study are in the range of 8 ± 8 mg Si/kg tissue and are about 50% of the estimated steady state Si liver concentration by Van Kesteren et al. and in the range of the literature data in Table 3. Human exposure by inhalation of silica dust is very common in both working and living environments with SiO2 air concentrations in the range of <0.1–0.5 mg/m3, resulting in an estimated maximum exposure of 5 mg/day (Morfeld et al. 2014; Chen et al. 2012), or 0.08 mg/kg bw/day for a person of 60 kg. While transport from the lungs into the circulatory system is possible and silica particles may also be cleared and transported from the lungs into the digestive tract, the contribution is limited. Dermal exposure to silica nanoparticles did not lead to any effects (Ryu et al. 2014) and, therefore, we conclude that penetration of SiO2 through the skin does not contribute. As for TiO2, oral exposure seems to be the most important source of SiO2 for humans in non-occupational settings, but in contrast to TiO2, other routes may also contribute substantially.