Diatom biosilica: Source, Physical-chemical characterization, modification, and application

Polyamines of unique structure are integrated in Synura echinulata biosilica

Unicellar, biomineralizing algae like diatoms or Synurales are ubiquitous in various habitats all over the world and have an outstanding role in different biogeochemical cycles. They are well known for their elaborate nanopatterned cell structures consisting of amorphous biosilica, which is intracellularly synthesized. Special biomolecules assist in the silica formation. In particular, species-specific long-chain polyamines (LCPAs) are commonly found in diatom biosilica and seem to play a special role due to their ability to self-assemble and induce silica precipitation. In contrast to diatoms, no species from the order Synurales have been tested yet for the presence of LCPAs. Therefore, the present work deals with the analysis of Synura echinulata biosilica using a novel HPLC-HR-MS/MS method. The presence of unique LCPAs is shown, and their structure is elucidated via MS/MS experiments. LCPAs from S. echinulata are based on amino butyl repeat units-in contrast to all previously described LCPAs from other organisms, which are based on aminopropyl repeat units. The ubiquitous presence of LCPAs in biomineralizing species strongly indicates a general role of LCPAs in silica biomineralization.

The role of biosilica and its potential for sensing technologies: A review

Efficiently managing agricultural waste while innovating to derive value-added products is a significant challenge in the 21st century. In recent decades, these by-products have been increasingly explored as alternative sources for materials such as biosilica. Biosilica is renowned for its high surface area, biocompatibility, chemical stability, and modifiable surface, which makes it suitable for various applications. Additionally, the biomineralization process-biosilicification-in living organisms like diatoms offers an eco-friendly pathway for silica production. Despite the potential applications of biosilica, research on its use in sensor technology remains limited. This review aims to address this gap by covering the primary methodologies for extracting silica from biomass, discussing key techniques for its characterization, and highlighting its potential for functionalization in diverse applications. Special emphasis is given to the utility of diatom-derived biosilicas in developing sensors for detecting gaseous molecules and biomolecules.

Diatom biosilica for liquid chromatography

This work presents, for the first time, the preparation method and subsequent use of biosilica in column liquid chromatography in reverse-phase mode. Diatom biosilica consists of the siliceous exoskeletons (frustules) of unicellular algae. Controlled cultivation of Pseudostaurosira trainorii diatoms resulted in frustules with an average diameter of approximately 4 µm, sidewall thickness of 1 µm, and a bottom thickness of 110-150 nm. These frustules contained pores (holes) with diameters ranging from 150 to 300 nm. XRD measurements revealed an opal A silica structure, with some lamellar features, and the material was characterized by a surface area of 21.1 m²/g. The raw material required careful preparation to remove residual organics by heating it. Following this, the surface was modified with octadecyldimethylchlorosilane to create a reverse-phase chromatographic adsorbent. The resulting columns demonstrated good chromatographic performance, with a theoretical plate number (N) of 22,000 plates for alkylbenzenes on a 160 mm long column, and permeability (KF) of 5.33 × 10⁻¹⁵ m². The prepared material exhibited lower hydrophobicity compared to the commercially available HALO C18 stationary phase, which can be attributed to its lower surface area and high number of silanol groups. As a result, only partial separation of six polyaromatic hydrocarbons was achieved due to excessive tailing. However, five anti-inflammatory drugs and two veterinary antibiotics were successfully separated.

A Descriptive Review on the Potential Use of Diatom Biosilica as a Powerful Functional Biomaterial: A Natural Drug Delivery System

Although various chemically synthesized materials are essential in medicine, food, and agriculture, they can exert unexpected side effects on the environment and human health by releasing certain toxic chemicals. Therefore, eco-friendly and biocompatible biomaterials based on natural resources are being actively explored. Recently, biosilica derived from diatoms has attracted attention in various biomedical fields, including drug delivery systems (DDS), due to its uniform porous nano-pattern, hierarchical structure, and abundant silanol functional groups. Importantly, the structural characteristics of diatom biosilica improve the solubility of poorly soluble substances and enable sustained release of loaded drugs. Additionally, diatom biosilica predominantly comprises SiO2, has high biocompatibility, and can easily hybridize with other DDS platforms, including hydrogels and cationic DDS, owing to its strong negative charge and abundant silanol groups. This review explores the potential applications of various diatom biosilica-based DDS in various biomedical fields, with a particular focus on hybrid DDS utilizing them.

Diatom-guided bone healing via a hybrid natural scaffold

Bone tissue engineering (BTE) involves the design of three-dimensional (3D) scaffolds that aim to address current challenges of bone defect healing, such as limited donor availability, disease transmission risks, and the necessity for multiple invasive surgeries. Scaffolds can mimic natural bone structure to accelerate the mechanisms involved in the healing process. Herein, a crosslinked combination of biopolymers, including gelatin (GEL), chitosan (CS), and hyaluronic acid (HA), loaded with diatom (Di) and β-sitosterol (BS), is used to produce GCH-Di-S scaffold by freeze-drying method. The GCH scaffold possesses a uniform structure, is biodegradable and biocompatible, and exhibits high porosity and interconnected pores, all required for effective bone repair. The incorporation of Di within the scaffold contributes to the adjustment of porosity and degradation, as well as effectively enhancing the mechanical property and biomineralization. In vivo studies have confirmed the safety of the scaffold and its potential to stimulate the creation of new bone tissue. This is achieved by providing an osteoconductive platform for cell attachment, prompting calcification, and augmenting the proliferation of osteoblasts, which further contributes to angiogenesis and anti-inflammatory effects of BS.

Recent Progress in Diatom Biosilica: A Natural Nanoporous Silica Material as Sustained Release Carrier

A drug delivery system (DDS) is a useful technology that efficiently delivers a target drug to a patient's specific diseased tissue with minimal side effects. DDS is a convergence of several areas of study, comprising pharmacy, medicine, biotechnology, and chemistry fields. In the traditional pharmacological concept, developing drugs for disease treatment has been the primary research field of pharmacology. The significance of DDS in delivering drugs with optimal formulation to target areas to increase bioavailability and minimize side effects has been recently highlighted. In addition, since the burst release found in various DDS platforms can reduce drug delivery efficiency due to unpredictable drug loss, many recent DDS studies have focused on developing carriers with a sustained release. Among various drug carriers, mesoporous silica DDS (MS-DDS) is applied to various drug administration routes, based on its sustained releases, nanosized porous structures, and excellent solubility for poorly soluble drugs. However, the synthesized MS-DDS has caused complications such as toxicity in the body, long-term accumulation, and poor excretion ability owing to acid treatment-centered manufacturing methods. Therefore, biosilica obtained from diatoms, as a natural MS-DDS, has recently emerged as an alternative to synthesized MS-DDS. This natural silica carrier is an optimal DDS platform because culturing diatoms is easy, and the silica can be separated from diatoms using a simple treatment. In this review, we discuss the manufacturing methods and applications to various disease models based on the advantages of biosilica.