# Silicon Compounds in Sponges
## 1 Introduction  
The important role of silicon in nature has now been reliably proven [1; 2; 3; 4; 5]. In terms of abundance in Earth's crust, silicon ranks second after oxygen. In it, about 12% is occupied by the mineral-silica compounds based on silicon dioxide (quartz, quartzite, flint, feldspar), as well as silicates and aluminosilicates. In tissues of plants and animals, silicon is in the form of water-soluble compounds such as orthosilicate acid (\(H_{2}SiO_{4}\)), orthosilicate esters (\(R_{4}SiO_{4}\), where R is an organic radical), as well as in the form of insoluble mineral polymers formed by polysilicic acids (\(nSiO_{2}\). \(mH_{2}O\)) and amorphous silica (\(SiO_{2}\)), and crystalline impurities [5]. The viability of all terrestrial organisms at ambient temperature is determined by the stability of cell membranes and the spatial structure of proteins-amino acids linked by peptide bonds (_C_ (_O_) _NH-)_ in a certain order. Silicon can bind through the nitrogen atom with proteins, amino acids and amino sugars, and carbohydrates through the formation of the _Si_-O_-C (_N_) bond; however, the biochemical aspects of silicon metabolism are still poorly understood [5]. Earlier, in the study of silica plants as a source of renewable raw materials for the production of amorphous silicon dioxide, which has a wide area of use depending onthe physicochemical characteristics ([PERSON], 2007; [PERSON], 2008; [PERSON], 2010; [PERSON], 2011), we have identified some structural features of silica in samples isolated from different plants: rice, oats, horsetails, needles of larch, spruce, pine, and cedar, which in some parameters turned out to be comparable with the data obtained for the _Asconema setubalense_ sea siliceous sponge ([PERSON], 2011). It was interesting to compare the characteristics of plant silica samples with other types of marine and freshwater siliceous sponges. In modern materials science, studies of natural composite organosilicon biominerals are in demand to create new structural functional biomimetic materials. The remarkable body structure of sea sponges serves as a model for biomimetic structure for tissue engineering applications ([PERSON], 2011; [PERSON], 2012; [PERSON], 2013; [PERSON], 2014; [PERSON], 2015; [PERSON], 2016; [PERSON], 2017; Ken, 2018; [PERSON], 2019; Ken, 2020; Ken, 2021; Ken, 2022; Ken, 2023; Ken, 2024; Ken, 2025). The most common biomimetic approach, in which the object is previously disassembled into its constituent components. In addition to silicon, chitin and collagen were found in the spicules of the sponges. Then, some of them can be used in a new synthesis, supplemented with other components. Macro and microstructural characteristics of deep-sea sponges serve as bioinspired models for tissue engineering. The first nanostructured 3D composite spongin-atacamite model was created ([PERSON], 2011; [PERSON], 2012; [PERSON], 2013; [PERSON], 2014; [PERSON], 2015; [PERSON], 2016; [PERSON], 2017; [PERSON], 2018; [PERSON], 2019; [PERSON], 2020; [PERSON], 2021; [PERSON], 20  
Earlier, based on spicules of glass sponges, we managed to create both flat and three-dimensional three-dimensional silicon-organic composite material in laboratory conditions without their preliminary destruction [39]. Since the silicon-organic skeletons of six-rayed sponges (Hexactinellida) are very diverse (Figure 1), and in the spicules of ordinary sponges (Demospongia), the silicon-organic rods are surrounded by an extensive clutch of organic material, it was interesting to study the chemical composition of spicules of different organization. The results obtained allow us to conclude that there are no fundamental differences in the chemical composition of spicules, and all of them can be used as a starting material for the creation of new composite silicon-organic functional materials. The same silicon-organic material was found in fossil sponges [40]. Spicules of some species of silicon sponges can be a source for obtaining silicon, chitin and collagen-like material [18; 20; 21; 22; 23; 24; 29; 30].