Abstract
Diatoms are unicellular eukaryotic microalgae widely distributed in aquatic environments, possessing a porous silica cell wall known as frustule. Diatom frustules are considered as a sustainable source for several industrial applications because of their high biocompatibility and the easiness of surface functionalisation, which make frustules suitable for regenerative medicine and as drug carriers. Frustules are made of hydrated silica, and can be extracted and purified both from living and fossil diatoms using acid treatments or high temperatures. Biosilica frustules have proved to be suitable for biomedical applications, but, unfortunately, they are not officially recognised as safe by governmental food and medical agencies yet. In the present review, we highlight the frustule formation process, the most common purification techniques, as well as advantages and bottlenecks related to the employment of diatom-derived silica for medical purposes, suggesting possible solutions for a large-scale biosilica production.
Highlights
Frustule formation occurs through the polymerization of silicic acid in specific compartments, namely, the silica deposition vesicles (SDV), associated to the membrane silicalemma [39,40]
The following three main levels of cell wall structure organization have been found: (1) microscale, the largest one that determines the outline shape of the valve or girdle band; (2) the mesoscale, at which organized substructures are formed within the SDV; and (3) the nanoscale, which comprises the first products of polymerization and generates different frustule structures/textures of nanometric dimensions ([38] and references therein)
This allows the recycling of the sulphuric acid used for cleaning, decreasing the amount of both the reagent needed for purification and the liquid wastes
Summary
The effectiveness of living or fossil diatom-derived silica for biomedical applications (drug loadings, bone tissue regeneration) has been largely investigated by various research groups, and at least four recent reviews clearly summarize the most relevant studies [18,24,25,26]. We pinpoint the major advantages and bottlenecks related to the employment of diatom silica sources To this aim, we list examples of diatom-based systems that revealed satisfactory results in the laboratory and might be suitable for scale-up in industrial applications, and the few drawbacks that hinder the use of diatom-derived biosilica as a medical device.
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