Diatom Biosilica Research Articles

Diatoms in Focus: Chemically Doped Biosilica for Customized Nanomaterials.

Diatoms are photosynthetic microalgae widely diffused around the globe and well adapted to thrive in diverse environments. Their success is closely related to the nanostructured biosilica shell (frustule) that serves as exoskeleton. Said structures have attracted great attention, thanks to their hierarchically ordered network of micro- and nanopores. Frustules display high specific surface, mechanical resistance and photonic properties, useful for the design of functional and complex materials, with applications including sensing, biomedicine, optoelectronics and energy storage and conversion. Current technology allows to alter the chemical composition of extracted frustules with a diverse array of elements, via chemical and biochemical strategies, without compromising their valuable morphology. We started our research on diatoms from the viewpoint of material scientists, envisaging the possibilities of these nanostructured silica shells as a general platform to obtain functional materials for several applications via chemical functionalization. Our first paper in the field was published in ChemPlusChem ten years ago. Ten years later, in this Perspective, we gather the most recent and relevant functional materials derived from diatom biosilica to show the growth and diversification that this field is currently experiencing, and the key role it will play in the near future.

Diatom biosilica modified with Ce-Tb mixed oxide twinning nanoparticles and with polyphases quasi-crystalline Tb oxide nanoparticles

In this study, we developed a novel composite material by combining natural diatom biosilica with Ce-Tb mixed oxide and polyphase quasi-crystalline Tb oxide nanoparticles. Diatom biosilica, characterised by its highly ordered three-dimensional structure and excellent thermal, mechanical, and optical properties, serves as an ideal matrix for the synthesis of advanced functional materials. The composites were extensively characterised using techniques such as SEM, TEM, TGA, EDS, XRD, FTIR, and PL spectroscopy. The results indicate significant UV absorption (250–400 nm), strong visible photoluminescence (300–500 nm), and notable anti-Stokes emission (∼420 nm) under 800 nm excitation. Additionally, the composites exhibit remarkable thermal stability and hydrophobicity, making them promising candidates for applications in optoelectronic devices, photovoltaic systems, and high-resolution display technologies.

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.

Fabrication of natural mesoporous Diatom biosilica microcapsules with high oil-carrying capacity and tribological property

In this study, fluorosilane-modified hollow mesoporous Diatom biosilica oil-carrying microcapsules (Oil@HMSNs/DE-F) were successfully synthesized using diatomite as hard-template, and dimethylsiloxane oil and hollow mesoporous silica as the core materials. Such microcapsules exhibited high oil-carrying capacity (41 %) and oil-carrying stability, which significantly higher than the Oil@DE-F microcapsules (33 %) (Comparison). Tribological tests showed that the Oil@HMSNs/DE-F composite coatings have excellent tribological properties and mechanical properties. Amazingly, 6 wt% Oil@HMSNs/DE-F epoxy composites coatings reduced the coefficient of friction by 79.9 % and the wear rate by 98.1 % compared to pure epoxy.

Antimicrobial and Hemostatic Diatom Biosilica Composite Sponge.

The 3D nanopatterned silica shells of diatoms have gained attention as drug delivery vehicles because of their high porosity, extensive surface area, and compatibility with living organisms. Tooth extraction may result in various complications, including impaired blood clotting, desiccation of the root canal, and infection. Therapeutic sponges that possess multiple properties, such as the ability to stop bleeding and kill bacteria, provide numerous advantages for the healing of the area where a tooth has been removed. This study involved the fabrication of a composite material with antibacterial and hemostatic properties for dental extraction sponges. We achieved this by utilizing the porous nature and hemostatic capabilities of diatom biosilica. The antibiotic used was doxycycline. The gelatin-based diatom biosilica composite with antibiotics had the ability to prevent bleeding and release the antibiotic over a longer time compared to gelatin sponge. These properties indicate its potential as a highly promising medical device for facilitating rapid healing following tooth extraction.

Diatom Biosilica Functionalised with Metabolically Deposited Cerium Oxide Nanoparticles.

This study introduces a novel approach to synthesising a three-dimensional (3D) micro-nanostructured amorphous biosilica. The biosilica is coated with cerium oxide nanoparticles obtained from laboratory-grown unicellular photosynthetic algae (diatoms) doped metabolically with cerium. This unique method utilises the ability of diatom cells to absorb cerium metabolically and deposit it on their silica exoskeleton as cerium oxide nanoparticles. The resulting composite (Ce-DBioSiO2) combines the unique structural and photonic properties of diatom biosilica (DBioSiO2) with the functionality of immobilised CeO2 nanoparticles. The kinetics of the cerium metabolic insertion by diatom cells and the physicochemical properties of the obtained composites were thoroughly investigated. The resulting Ce-DBioSiO2 composite exhibits intense Stokes fluorescence in the violet-blue region under ultraviolet (UV) irradiation and anti-Stokes intense violet and faint green emissions under the 800 nm near-infrared excitation with a xenon lamp at room temperature in an ambient atmosphere.

Microalgae derived honeycomb structured mesoporous diatom biosilica for adsorption of malachite green: Process optimization and modeling

The present study investigated the removal of malachite green dye from aquifers by means of microalgae-derived mesoporous diatom biosilica. The various process variables (dye concentration, pH, and adsorbent dose) influencing the removal of the dye were optimized and their interactive effects on the removal efficiency were explored by response surface methodology. The pH of the solution (pH = 5.26) was found to be the most dominating among other tested variables. The Langmuir isotherm (R2 = 0.995) best fitted the equilibrium adsorption data with an adsorption capacity of 40.7 mg/g at 323 K and pseudo-second-order model (R2 = 0.983) best elucidated the rate of dye removal (10.6 mg/g). The underlying mechanism of adsorption was investigated by Weber-Morris and Boyd models and results revealed that the film diffusion governed the overall adsorption process. The theoretical investigations on the dye structure using DFT-based chemical reactivity descriptors indicated that malachite green cations are electrophilic, reactive and possess the ability to accept electrons, and are strongly adsorbed on the surface of diatom biosilica. Also, the Fukui function analysis proposed the favorable adsorption sites available on the adsorbent surface.

Biofilm removal effect of diatom complex on 3D printed denture base resin

For patients who have difficulty in mechanical cleaning of dental appliances, a denture cleaner that can remove biofilm with dense extracellular polymeric substances is needed. The purpose of this study is to evaluate the efficacy of diatom complex with active micro-locomotion for removing biofilms from 3D printed dentures. The diatom complex, which is made by doping MnO2 nanosheets on diatom biosilica, is mixed with H2O2 to generate fine air bubbles continuously. Denture base resin specimens were 3D printed in a roof shape, and Pseudomonas aeruginosa (107 CFU/mL) was cultured on those for biofilm formation. Cleaning solutions of phosphate-buffered saline (negative control, NC), 3% H2O2 with peracetic acid (positive control, PC), denture cleanser tablet (DCT), 3% H2O2 with 2 mg/mL diatom complex M (Melosira, DM), 3% H2O2 with 2 mg/mL diatom complex A (Aulacoseira, DA), and DCT with 2 mg/mL DM were prepared and applied. To assess the efficacy of biofilm removal quantitatively, absorbance after cleaning was measured. To evaluate the stability of long-term use, surface roughness, ΔE, surface micro-hardness, and flexural strength of the 3D printed dentures were measured before and after cleaning. Cytotoxicity was evaluated using Cell Counting Kit-8. All statistical analyses were conducted using SPSS for Windows with one-way ANOVA, followed by Scheffe’s test as a post hoc (p < 0.05). The group treated with 3% H2O2 with DA demonstrated the lowest absorbance value, followed by the groups treated with 3% H2O2 with DM, PC, DCT, DCT + DM, and finally NC. As a result of Scheffe’s test to evaluate the significance of difference between the mean values of each group, statistically significant differences were shown in all groups based on the NC group. The DA and DM groups showed the largest mean difference though there was no significant difference between the two groups. Regarding the evaluation of physical and mechanical properties of the denture base resin, no statistically significant differences were observed before and after cleaning. In the cytotoxicity test, the relative cell count was over 70%, reflecting an absence of cytotoxicity. The diatom complex utilizing active micro-locomotion has effective biofilm removal ability and has a minimal effect in physical and mechanical properties of the substrate with no cytotoxicity.

Biomimetic Diatom Biosilica and Its Potential for Biomedical Applications and Prospects: A Review.

Diatom biosilica is an important natural source of porous silica, with three-dimensional ordered and nanopatterned structures referred to as frustules. The unique features of diatom frustules, such as their high specific surface area, thermal stability, biocompatibility, and adaptable surface chemistry, render diatoms valuable materials for high value-added applications. These attributes make diatoms an exceptional cost-effective raw material for industrial use. The functionalization of diatom biosilica surface improves its biophysical properties and increases the potential applications. This review focuses on the potential uses of diatom biosilica including traditional approaches and recent progress in biomedical applications. Not only well-studied drug delivery systems but also promising uses on bone regeneration and wound healing are covered. Furthermore, considerable aspects and possible future directions for the use of diatom biosilica materials are proposed to develop biomedical applications and merit further exploration.

Synthesis and Antimicrobial Activity of 3D Micro-Nanostructured Diatom Biosilica Coated by Epitaxially Growing Ag-AgCl Hybrid Nanoparticles.

The 3D (three-dimensional) micro-nanostructured diatom biosilica obtained from cultivated diatoms was used as a support to immobilize epitaxially growing AgCl-Ag hybrid nanoparticles ((Ag-AgCl)NPs) for the synthesis of nanocomposites with antimicrobial properties. The prepared composites that contained epitaxially grown (Ag-AgCl)NPs were investigated in terms of their morphological and structural characteristics, elemental and mineral composition, crystalline forms, zeta potential, and photoluminescence properties using a variety of instrumental methods including SEM (scanning electron microscopy), TEM (transmission electron microscopy), EDX (energy-dispersive X-ray spectroscopy), XRD (X-ray powder diffraction), zeta-potential measurement, and photoluminescence spectroscopy. The content of (AgCl-Ag)NPs in the hybrid composites amounted to 4.6 mg/g and 8.4 mg/g with AgClNPs/AgNPs ratios as a percentage of 86/14 and 51/49, respectively. Hybrid nanoparticles were evenly dispersed with a dominant size of 5 to 25 nm in composite with an amount of 8.4 mg/g of silver. The average size of the nanoparticles was 7.5 nm; also, there were nanoparticles with a size of 1-2 nm and particles that were 20-40 nm. The synthesis of (Ag-AgCl)NPs and their potential mechanism were studied. The MIC (the minimum inhibitory concentration method) approach was used to investigate the antimicrobial activity against microorganisms Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus. The nanocomposites containing (Ag-AgCl)NPs and natural diatom biosilica showed resistance to bacterial strains from the American Type Cultures Collection and clinical isolates (diabetic foot infection and wound isolates).

The Art of Exploring Diatom Biosilica Biomaterials: From Biofabrication Perspective.

Diatom is a common single-cell microalgae with large species and huge biomass. Diatom biosilica (DB), the shell of diatom, is a natural inorganic material with a micro-nanoporous structure. Its unique hierarchical porous structure gives it great application potential in drug delivery, hemostat materials, and biosensors, etc. However, the structural diversity of DB determines its different biological functions. Screening hundreds of thousands of diatom species for structural features of DB that meet application requirements is like looking for a needle in a seaway. And the chemical modification methods lack effective means to control the micro-nanoporous structure of DB. The formation of DB is a typical biomineralization process, and its structural characteristics are affected by external environmental conditions, genes, and other factors. This allows to manipulate the micro-nanostructure of DB through biological regulation method, thereby transforming the screening mode of the structure function of DB from a needle in a seaway to biofabrication mode. This review focuses on the formation, biological modification, functional activity of DB structure, and its application in biomaterials field, providing regulatory strategies and research idea of DB from the perspective of biofabrication. It will also maximize the possibility of using DB as biological materials.

Efficient Ag+ adsorption of in-vivo thiol-functionalized diatoms and its application for sensitive surface-enhanced Raman scattering

Diatom silica frustules are recognized as a valuable biomaterial with hierarchically porous silica structures and can be used for many applications. To obtain targeted functional diatom-based materials, many strategies have been explored, mainly focusing on diatomite (fossilized diatoms) but rarely on living diatom silica frustules. In this work, the frustules of living diatoms (T. weissflogii) were in-vivo functionalized with thiol (-SH) groups by using (3-mercaptopropyl) trimethoxysilane (MPTMS) as silicon source, through living biomineralization process. The -SH groups were homogeneously distributed in diatom biosilica structures, as revealed by FIB-TEM-EDS result. Two applications of thiol-functionalized frustules were demonstrated. The first was for Ag+ adsorption, showing significantly enhanced adsorption capacity (87.59 mg·g−1) compared with unmodified frustules (33.21 mg·g−1). The adsorption data and the spectroscopic and microscopic analyses revealed that the inner-sphere complexation of -SH with Ag+ was the primary mechanism. The second application showed that Ag+-loaded diatom frustules exhibited a significant surface-enhanced Raman scattering (SERS), which can be used for detecting methylene blue and rhodamine 6G. The charge transfer resonance between Ag2S and probe molecules makes the primary contribution to the distinct enhancement of Raman signals. These findings demonstrate that these in-vivo functionalized -SH groups on diatom silica frustules can still maintain their excellent chemical reactivities, suggesting that this modification strategy could be extended to modify living diatom silica frustules with other functional groups. This study is of great significance for developing functional materials from living diatoms and their applications in the fields of environmental remediation, biosensing, and drug delivery, etc.

Zinc-mineralized diatom biosilica/hydroxybutyl chitosan composite hydrogel for diabetic chronic wound healing

For sustained and stable improvement of the diabetic wound microenvironment, a temperature-sensitive composite hydrogel (ZnDBs/HBC) composed of inorganic zinc mineralized diatom biosilica (ZnDBs) and hydroxybutyl chitosan (HBC) was developed. The interfacial anchoring effect between ZnDBs and HBC enhanced the mechanical strength of the hydrogel. The mechanical strength of the composite hydrogel containing 3 wt% ZnDBs was increased by nearly 2.3times. The hydrogel can be used as a carrier for sustained release of Zn2+ for at least 72 h. In diabetic rats models, ZnDBs/HBC composite hydrogel could accelerate the inflammatory process by regulating the expression of pro-inflammatory factor IL-6 and anti-inflammatory factor IL-10, and also promote tissue cell proliferation and collagen deposition, thereby restoring the normal healing process and accelerating wound healing. The wound contraction rate of the composite hydrogel group was more than 2 times that of the control group. Therefore, ZnDBs/HBC composite hydrogel has the potential to be used as a therapeutic dressing for diabetic chronic wounds.

Improving the performance of recycled concrete by biodeposition of biogenic silica as a surface coating

This study addresses the challenges of sustainability and the implementation of a circular economy in the construction and maintenance of concrete structures used in clean-water applications. Specifically, it examines the use of an innovative surface treatment based on a biofilm comprising diatom biosilica deposition as a waterproofing agent and surface pore sealant to improve the longevity of recycled concrete. To this end biofilm-treated and untreated (control) samples of a concrete mix containing 50% recycled aggregates were subject to four performance tests directed at assessing the durability of concrete structures under environmental conditions: resistance to carbonation, freeze–thaw durability, resistance to water penetration, and electrical resistivity as an indicator of the corrosion resistance of concrete. In addition, the protective biofilm was characterised using SEM. Results suggest that the biogenic silica surface treatment significantly improves the durability of recycled concrete, in particular, for treated compared to untreated samples there was a 56 % reduction of the carbonation front, 26% lower mass loss in freeze–thaw cycles, 57% reduction in the water penetration front under pressure, and 44% higher electrical resistivity. Together these findings confirm that the biofilm used in this study constitutes an effective treatment to improve the properties of recycled concrete and ensure its durability, particularly when used in the construction of structures in contact with constant water fluctuations.

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.

Diatom-Inspired Bionic Hydrophilic Polysaccharide Adhesive for Rapid Sealing Hemostasis.

Diatoms are typical marine biofouling organisms that secrete extracellular polymers (EPS) to achieve strong underwater adhesion. Here, we report a diatom-inspired bionic hydrophilic polysaccharide adhesive composed of diatom biosilica (DB) and bletilla striata polysaccharide (BSP) for rapid sealing hemostasis. The hierarchical porous structure of DB with rich surface silanol groups provides a strong anchored interface effect for BSP, which can significantly enhance cross-linking density and interaction strength of the hydrophilic macromolecular network. BSP/DB adhesive offers 6 times greater mechanical strength and viscosity over BSP under different temperature conditions. The aggregation effect of DBs interface for BSP avoided the washout of BSP/DB adhesive during application in a wet environment before cross-linking occurs. This strengthened the adhesion ability of BSP/DB adhesive to biological tissue that brought out complete sealing hemostasis without blood loss in a rat liver injury model. The dry BSP/DB prepared by lyophilization inherited excellent clotting ability of BSP/DB adhesive, which could realize rapidly the cruor of anticoagulant whole blood within 1 min. The results of animal studies confirmed that dry BSP/DB exhibited superior hemostatic performance over silicate-based inorganic Quikclot, in terms of hemostatic rate, blood loss, dosage, and multiscroll wound closure.

An improved blood hemorrhaging treatment using diatoms frustules, by alternating Ca and light levels in cultures

Hemorrhage control requires hemostatic materials that are both effective and biocompatible. Among these, diatom biosilica (DBs) could significantly improve hemorrhage control, but it induces hemolysis (the hemolysis rate > 5%). Thus, the purpose of this study was to explore the influence of Ca2+ biomineralization on DBs for developing fast hemostatic materials with a low hemolysis rate. Here, CaCl2 was added to the diatom medium under high light (cool white, fluorescent lamps, 67.5 µmol m−2 s−1), producing Ca-DBs-3 with a particle size of 40–50 μm and a Ca2+ content of Ca-DBs-3 obtained from the higher concentration CaCl2 group (6.7 mmol L−1) of 0.16%. The liquid absorption capacity of Ca-DBs-3 was 30.43 ± 0.57 times its dry weight; the in vitro clotting time was comparable to QuikClot® zeolite; the hemostatic time and blood loss using the rat tail amputation model were 36.40 ± 2.52 s and 0.39 ± 0.12 g, which were 40.72% and 19.50% of QuikClot® zeolite, respectively. Ca-DBs-3 showed no apparent toxicity to L929 cells (cell viability > 80%) and was non-hemolysis (the hemolysis rate < 2%). This study prepared Ca-DBs-3 with a rapid hemostatic effect and good biocompatibility, providing a path to develop diatom biosilica hemostatic materials.

Tailoring the Surface of Aluminum‐Enriched Diatom Biosilica

AbstractAluminosilicates are widely used as sorbent materials, ion exchangers, and catalysts. While they are often synthesized by hydrothermal methods, microorganisms may open “green” synthesis ways. Diatoms can incorporate aluminum into their micro‐ and nanostructured silica‐based cell walls. Thus, diatoms create intricately structured aluminosilicate materials. The present study investigates not only possible morphological changes during the in vivo Al‐enrichment of the diatom species Thalassiosira pseudonana, but also the increase of the specific surface area of Al‐enriched biosilica in vitro by etching with alkaline solutions.

Diatom Frustules Decorated with Co Nanoparticles for the Advanced Anode of Li-Ion Batteries.

Silica is regarded as a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, large volume variation and poor electrical conductivity are limiting factors for the development of SiO2 anode materials. To solve this problem, combining SiO2 with a conductive phase and designing hollow porous structures are effective ways. In this work, The Co(II)-EDTA chelate on the surface of diatom biosilica (DBS) frustules and obtained DBS@C-Co composites decorated with Co nanoparticles by calcination without a reducing atmosphere is first precipitated. The unique three-dimensional structure of diatom frustules provides enough space for the volume change of silica during lithiation/delithiation. Co nanoparticles effectively improve the electrical conductivity and electrochemical activity of silica. Through the synergistic effect of the hollow porous structure, carbon layer and Co nanoparticles, the DBS@C-Co-60 composite delivers a high reversible capacity of >620mAhg-1 at 100mAg-1 after 270 cycles. This study provides a new method for the synthesis of metal/silica composites and an opportunity for the development of natural resources as advanced active materials for LIBs.

Photoremoval of Bisphenol A Using Hierarchical Zeolites and Diatom Biosilica.

Bisphenol A (4,4-isopropylidenediphenol, BPA) is an organic compound widely used, e.g., in the production of epoxy resins, plastics, and thermal receipt papers. Unfortunately, bisphenol A has negative effects on human health, which has prompted the search for an effective method of its removal. One of the most promising methods of its elimination is photocatalytic removal. The aim of this study was to design an effective method for the photocatalytic removal of bisphenol A using, for the first time, hierarchical zeolites and ruthenium ion-modified diatom biosilica, and silver as photocatalysts and optimization of the reaction conditions: temperature, pH, and composition of the reaction mixture as well as the electromagnetic wavelength. Additionally, for the first time, the electromagnetic wavelength that would be most suitable for the study was selected. All materials used were initially characterized by XRD and low-temperature nitrogen adsorption/desorption isotherms. Ruthenium ion-modified biosilica proved to be the most effective catalyst for bisphenol A removal, which occurred at a rate higher than 99%.