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.

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(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.