Diatom Silica for Biomedical Applications: Recent Progress and Advances

Abstract

Diatoms are unicellular photosynthetic algae enclosed in porous 3D nanopatterned silica enclosures called "frustules." The diatom frustules are made from biosilica self-assembled into intricate porous shells that feature unique properties including high specific surface area, biocompatibility, tailorable surface chemistry, thermal stability, and high mechanical and chemical resistance. The ability to cultivate diatoms in artificial environments and their abundant availability of diatom frustules as mineable fossilized mineral deposits (diatomite or diatomaceous earth; DE) make diatom silica a promising natural alternative to synthetic porous silica for a broad range of biomedical, environmental, agricultural, and energy applications. This review article provides a comprehensive and current account of the use of natural DE silica materials in biomedical applications focused mainly on drug delivery with some highlights on biosensing, tissue engineering, and clotting agents. The article also covers some basic physical and chemical aspects of DE material such as purification, surface chemical functionalization, biocompatibility, and cellular uptake that are critical for the development of an efficient drug carrier.

Natural Diatom Biosilica as Microshuttles in Drug Delivery Systems

“…Fine grinding and ball milling techniques allow for the reaching of the specific nanometric scale required for injectable nanosuspension. A possible drawback to the use of raw diatoms in therapeutic formulations is the poor degradability of silica in biological fluids [11,51,52]. Synthetic porous silicon (pSi), sponge-like structures made of monocrystalline silicon, have been demonstrated as being fully biodegradable.…”

“…Among the materials eligible as microshuttles (i.e., materials composed of micrometer size particles capable of drug delivery), both natural or synthetic mesoporous silica-based materials have gained rapid interest in the field over the last decades [2,3,4,5,6,7,8]. Indeed silica micro/nano-particles present several benefits compared to other materials due to the ease of particle size control during their synthesis, their chemical inertness, high surface porosity, flexible surface modification, thermal stability, and biocompatibility [2,9,10,11,12,13]. However, the fabrication of synthetic mesoporous silica requires advanced skills, often involves the use of toxic chemicals, and results in the formation of non-reusable polluting byproducts, leading to a poor cost-effective process.…”

Photoactivatable Surface-Functionalized Diatom Microalgae for Colorectal Cancer Targeted Delivery and Enhanced Cytotoxicity of Anticancer Complexes

“…DEMs, as the fossil frustules of diatoms, recently gained attention for their use in drug delivery due to their biocompatibility and ability to shuttle and slowly release different drugs [26][27][28][29]. Diatoms are enclosed in a three-dimensional highly ordered silica shell (called frustule) and represent an inexpensive and well-engineered source of microporous silica [30][31][32][33]. Our original proof of concept relied on the chemical functionalization of the diatom microalgae's surface with vitamin B12, which allowed specific binding of the material to CRC cells and, therefore, discrimination between healthy and diseased tissues.…”

Diatoms Green Nanotechnology for Biosilica-Based Drug Delivery Systems

“…Since their production route is laborious and expensive and involves toxic materials, there is a massive demand to replace these synthetic materials with valid natural surrogates. Surprisingly, nature has provided exciting porous material with three-dimensional (3-D) porous structures: the single-celled photosynthetic diatom algae [5,6,7,8]. Diatom microshells, characterized by unique pill-box micro structures having porosity in the micro/nanoscale range, high surface area, and great biocompatibility, have been shown to be a promising and low-cost biomaterial for drug delivery applications [9,10].…”

“…Diatomite is the most abundant source of biosilica and it is largely used as an inexpensive biosilica mineral in several industrial applications (e.g., food industry, agriculture, pharmaceutics, etc.) [5,11]. Despite the great developments in the field of nanotechnology, the diatoms’ architecture can actually compete with man-made fabricated devices [12,13,14].…”