On Hydrated silica many studies agree on toxicity if inhaled and on the safety of the skin if smeared. This component, tested diluted 50% in occlusive mode for 24 hours showed no irritation on laboratory animals and no sensitization reaction to the patch test (1).

From laboratory tests, Hydrated silica improves the resistance and thermal stability of vaccines (2).

Gouda N, Miyata K, Christie RJ, Suma T, Kishimura A, Fukushima S, Nomoto T, Liu X, Nishiyama N, Kataoka K. Silica nanogelling of environment-responsive PEGylated polyplexes for enhanced stability and intracellular delivery of siRNA. Biomaterials. 2013 Jan;34(2):562-70. doi: 10.1016/j.biomaterials.2012.09.077. 

Abstract. In this study, poly(ethylene glycol) (PEG)-block-polycation/siRNA complexes (PEGylated polyplexes) were wrapped with a hydrated silica, termed "silica nanogelling", in order to enhance their stability and functionality. 

Kumar S, Soukup M, Elbaum R. Silicification in Grasses: Variation between Different Cell Types. Front Plant Sci. 2017 Mar 28;8:438. doi: 10.3389/fpls.2017.00438. 

Abstract. Plants take up silicon as mono-silicic acid, which is released to soil by the weathering of silicate minerals. Silicic acid can be taken up by plant roots passively or actively, and later it is deposited in its polymerized form as amorphous hydrated silica. Major silica depositions in grasses occur in root endodermis, leaf epidermal cells, and outer epidermal cells of inflorescence bracts. Debates are rife about the mechanism of silica deposition, and two contrasting scenarios are often proposed to explain it. According to the passive mode of silicification, silica deposition is a result of silicic acid condensation due to dehydration, such as during transpirational loss of water from the aboveground organs. In general, silicification and transpiration are positively correlated, and continued silicification is sometimes observed after cell and tissue maturity. The other mode of silicification proposes the involvement of some biological factors, and is based on observations that silicification is not necessarily coupled with transpiration. Here, we review evidence for both mechanisms of silicification, and propose that the deposition mechanism is specific to the cell type. Considering all the cell types together, our conclusion is that grass silica deposition can be divided into three modes: spontaneous cell wall silicification, directed cell wall silicification, and directed paramural silicification in silica cells

Li P, Ohtsuki C, Kokubo T, Nakanishi K, Soga N, de Groot K. The role of hydrated silica, titania, and alumina in inducing apatite on implants. J Biomed Mater Res. 1994 Jan;28(1):7-15. doi: 10.1002/jbm.820280103. 

Abstract. Pure soluble silica prepared by a sol-gel method induced bone-like hydroxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not. This finding directly supports the hypothesis that hydrated silica plays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass-ceramics, which leads to bone-bonding. Gel-derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further insight into the unique osseointegration of titanium and its alloys. It is suspected that gel-derived titania develops an apatite layer by taking calcium and phosphate from the body fluid, thus producing bone-bonding. Although sufficient AlOH groups may remain in the alumina gel, they do not serve to initiate apatite generation when immersed in SBF. This phenomenon explains the fact that an intermediate fibrous tissue is usually found to separate the alumina implant from bone. One may infer that both abundant OH groups and negatively charged surfaces of gel-derived silica and titania are important for hydroxyapatite induction. material which possesses and/or develops both a negatively charged surface and abundant OH groups in a physiologically-related fluid is most likely to be an efficient apatite inducer. Such materials are suitable candidates to serve as bone-bonding biomaterials.

References________________________________________________________________________

(1) Sccs, Hoet PH. Opinion of the Scientific Committee on Consumer Safety (SCCS) - Revision of the opinion on the safety of the use of Silica, Hydrated Silica, and Silica Surface Modified with Alkyl Silylates (nano form) in cosmetic products. Regul Toxicol Pharmacol. 2016 Feb;74:79-80. doi: 10.1016/j.yrtph.2015.11.005. 

(2) Wang G, Wang HJ, Zhou H, Nian QG, Song Z, Deng YQ, Wang X, Zhu SY, Li XF, Qin CF, Tang R. Hydrated silica exterior produced by biomimetic silicification confers viral vaccine heat-resistance. ACS Nano. 2015 Jan 27;9(1):799-808. doi: 10.1021/nn5063276.

Hydrated Silica is a micro-nano superfine chemical compound with a hydrophobic or hydrophilic surface treatment. The particle size is between 5nm and 40nm. The industrial production process goes through evaporation, hydrolysis by purified hydrogen and purified air, separation, decalcification and finally boiling.

The name describes the structure of the molecule:

• Silica refers to silicon dioxide (SiO2). It is found naturally as quartz and is used in many industrial and consumer products due to its mechanical, chemical, and optical properties.
• Hydrated indicates the presence of water. In the context of hydrated silica, this means that the silicon dioxide particles are incorporated with water molecules.

Description and function of the raw materials used in production:

• Quartz or sand: The primary source of silicon dioxide.
• Water: Used to hydrate the silicon dioxide and form hydrated silica.

Summary of its industrial synthesis process step by step:

1- Quartz or sand undergoes heat treatment to remove impurities.

2- The purified material is then put into solution with water.

3- The solution is acidified, typically using sulfuric acid, to solubilize the silicon.

4- The resulting sodium silicate is then neutralized with acid to form a silica solution.

5- The silica solution is then precipitated as hydrated silica particles.

6- These particles are then filtered, washed, and dried to yield hydrated silica in powder form.

It appears as a white powder insoluble in water and inorganic acid with the exception of hydrofluoric acid, which is soluble in caustic alkaline solution.

What it is used for and where

It has a reinforcing, thickening, anti-foaming thixotropy function

Cosmetics

Included in facial and personal care formulations with minimal doses it produces a mild abrasive effect.

Abrasive agent. It contains abrasive particles to remove stains or biofilm that accumulate on the stratum corneum or teeth. Baking soda, kieselguhr, silica and many others have abrasive properties. Peeling or exfoliating products used in dermatology or cosmetic applications contain abrasive agents in the form of synthetic microspheres, however these microspheres or abrasive particles are not biodegradable and create pollution in aquatic ecosystems.

Absorbent. Absorbs substances dispersed or dissolved in aqueous solutions, water/oil, oil/water.

Anticaking agent. This compound facilitates free flow and prevents aggregation or clumping of substances in a formulation by reducing the tendency of certain particles to stick together.

Bulking agent. It regulates the water content, dilutes other solids, can increase the volume of a product for better flow, acts as a buffer against organic acids, helps to keep the pH of the mixture within a certain level.

Opacifying agent. It is useful into formulations that may be translucent or transparent to make them opaque and less permeable to light.

Viscosity control agent. It controls and adapts, Increasing or decreasing, viscosity to the required level for optimal chemical and physical stability of the product and dosage in gels, suspensions, emulsions, solutions. 

In toothpastes with an abrasive purpose to remove stains or residues and also to prevent possible gum irritation. In commercial toothpastes with a whitening purpose to also remove possible stains, containing pyrophosphate, the addition of hydrated silica improved erosive wear of the enamel (1).

Other applications

Rubber industries as a reinforcing filler for natural and synthetic rubber. Synthetic resin filler, matting agent, soft polishing agent for metals, carrier for pesticides, thickener for inks. 

For more information:     Hydrated silica studies

• Molecular Formula    O₂Si  SiO₂
• Molecular Weight    60.083 g/mol
• Exact Mass   60.084
• CAS    7631-86-9  
• UNII    ETJ7Z6XBU4
• EC Number   215-684-8    231-545-4
• DSSTox Substance ID  DTXSID1029677
• IUPAC  dioxosilane
• InChI=1S/O2Si/c1-3-2
• InChl Key      VYPSYNLAJGMNEJ-UHFFFAOYSA-N
• SMILES   O=[Si]=O
• MDL number    MFCD00011232
• PubChem Substance ID    24882839
• ChEBI  30563
• ICSC    0248    0807    0808    0809
• RXCUI   9771    314826   
• RTECS   VV7325000    VV7330000    VV7335000
• NACRES   NA.23  
• NCI   C29853

Synonyms

• Cristobalite
• Fumed silica
• Silicon dioxide
• Dioxosilane
• Ludox

References________________________________________________________________________

(1) Mosquim V, Martines Souza B, Foratori Junior GA, Wang L, Magalhães AC. The abrasive effect of commercial whitening toothpastes on eroded enamel. Am J Dent. 2017 Jun;30(3):142-146. 

Wang C, Lucas R, Smith AJ, Cooper PR. An in vitro screening assay for dental stain cleaning. BMC Oral Health. 2017 Jan 9;17(1):37. doi: 10.1186/s12903-016-0328-3.