The Role of Lysozyme in the Formation of Bioinspired Silicon Dioxide.

Several organisms are able to polycondensate tetraoxosilicic(IV) acid to form silicon(IV) dioxide using polycationic molecules. According to an earlier mechanistic proposal, these molecules undergo a phase separation and recent experimental evidence appears to confirm this model. At the same time, polycationic proteins like lysozyme can also promote polycondensation of silicon(IV) dioxide, and they do so under conditions that are not compatible with liquid-liquid phase separation. In this manuscript we investigate this conundrum by molecular simulations.

3D printed scaffolds of biosilica and spongin from marine sponges: analysis of genotoxicity and cytotoxicity for bone tissue repair.

Biosilica (BS) and spongin (SPG) from marine sponges are highlighted for their potential to promote bone regeneration. Moreover, 3D printing is introduced as a technology for producing bone grafts with optimized porous structures, allowing for better cell attachment, proliferation, and differentiation. Thus, this study aimed to characterize the BS and BS/SPG 3D printed scaffolds and to evaluate the biological effects in vitro. The scaffolds were printed using an ink containing 4 wt.% of sodium alginate. The physicochemical characteristics of BS and BS/SPG 3D printed scaffolds were analyzed by SEM, EDS, FTIR, porosity, evaluation of mass loss, and pH measurement. For in vitro analysis, the cellular viability of the MC3T3-E1 cell lineage was assessed using the AlamarBlue® assay and confocal microscopy, while genotoxicity and mineralization potential were evaluated through the micronucleus assay and Alizarin Red S, respectively. SEM analysis revealed spicules in BS, the fibrillar structure of SPG, and material degradation over the immersion period. FTIR indicated peaks corresponding to silicon oxide in BS samples and carbon oxide and amine in SPG samples. BS-SPG scaffolds exhibited higher porosity, while BS scaffolds displayed greater mass loss. pH measurements indicated a significant decrease induced by BS, which was mitigated by SPG over the experimental periods. In vitro studies demonstrated the biocompatibility and non-cytotoxicity of scaffold extracts. .Also, the scaffolds promoted cellular differentiation. The micronucleus test further confirmed the absence of genotoxicity. These findings suggest that 3D printed BS and BS/SPG scaffolds may possess desirable morphological and physicochemical properties, indicating in vitro biocompatibility.

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.

Shedding light on silica biomineralization by comparative analysis of the silica-associated proteomes from three diatom species.

Morphogenesis of the intricate patterns of diatom silica cell walls is a protein-guided process, yet to date only very few such silica biomineralization proteins have been identified. Therefore, it is currently unknown whether all diatoms share conserved proteins of a basal silica forming machinery, and whether unique proteins are responsible for the morphogenesis of species-specific silica patterns. To answer these questions, we extracted proteins from the silica of three diatom species (Thalassiosira pseudonana, Thalassiosira oceanica, and Cyclotella cryptica) by complete demineralization of the cell walls. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis of the extracts identified 92 proteins that we name 'soluble silicome proteins' (SSPs). Surprisingly, no SSPs are common to all three species, and most SSPs showed very low similarity to one another in sequence alignments. In-depth bioinformatics analyses revealed that SSPs could be grouped into distinct classes based on short unconventional sequence motifs whose functions are yet unknown. The results from the in vivo localization of selected SSPs indicates that proteins, which lack sequence homology but share unconventional sequence motifs may exert similar functions in the morphogenesis of the diatom silica cell wall.

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 >620 mAh g-1 at 100 mA g-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.

Removal of the Basic and Diazo Dyes from Aqueous Solution by the Frustules of Halamphora cf. salinicola (Bacillariophyta).

Industrial wastes with hazardous dyes serve as a major source of water pollution, which is considered to have an enormous impact on public health. In this study, an eco-friendly adsorbent, the porous siliceous frustules extracted from the diatom species Halamphora cf. salinicola, grown under laboratory conditions, has been identified. The porous architecture and negative surface charge under a pH of 7, provided by the various functional groups via Si-O, N-H, and O-H on these surfaces, revealed by SEM, the N2 adsorption/desorption isotherm, Zeta-potential measurement, and ATR-FTIR, respectively, made the frustules an efficient mean of removal of the diazo and basic dyes from the aqueous solutions, 74.9%, 94.02%, and 99.81% against Congo Red (CR), Crystal Violet (CV), and Malachite Green (MG), respectively. The maximum adsorption capacities were calculated from isotherms, as follows: 13.04 mg g-1, 41.97 mg g-1, and 33.19 mg g-1 against CR, CV, and MG, respectively. Kinetic and isotherm models showed a higher correlation to Pore diffusion and Sips models for CR, and Pseudo-Second Order and Freundlich models for CV and MG. Therefore, the cleaned frustules of the thermal spring-originated diatom strain Halamphora cf. salinicola could be used as a novel adsorbent of a biological origin against anionic and basic dyes.

Drug Delivery through Epidermal Tissue Cells by Functionalized Biosilica from Diatom Microalgae.

Diatom microalgae are a natural source of fossil biosilica shells, namely the diatomaceous earth (DE), abundantly available at low cost. High surface area, mesoporosity and biocompatibility, as well as the availability of a variety of approaches for surface chemical modification, make DE highly profitable as a nanostructured material for drug delivery applications. Despite this, the studies reported so far in the literature are generally limited to the development of biohybrid systems for drug delivery by oral or parenteral administration. Here we demonstrate the suitability of diatomaceous earth properly functionalized on the surface with n-octyl chains as an efficient system for local drug delivery to skin tissues. Naproxen was selected as a non-steroidal anti-inflammatory model drug for experiments performed both in vitro by immersion of the drug-loaded DE in an artificial sweat solution and, for the first time, by trans-epidermal drug permeation through a 3D-organotypic tissue that better mimics the in vivo permeation mechanism of drugs in human skin tissues. Octyl chains were demonstrated to both favour the DE adhesion onto porcine skin tissues and to control the gradual release and the trans-epidermal permeation of Naproxen within 24 h of the beginning of experiments. The evidence of the viability of human epithelial cells after permeation of the drug released from diatomaceous earth, also confirmed the biocompatibility with human skin of both Naproxen and mesoporous biosilica from diatom microalgae, disclosing promising applications of these drug-delivery systems for therapies of skin diseases.

Diatom-Based Nanomedicine for Colorectal Cancer Treatment: New Approaches for Old Challenges.

Colorectal cancer is among the most prevalent and lethal cancers globally. To address this emergency, countries have developed diffuse screening programs and innovative surgical techniques with a consequent decrease in mortality rates in non-metastatic patients. However, five years after diagnosis, metastatic CRC is still characterized by less than 20% survival. Most patients with metastatic CRC cannot be surgically treated. For them, the only option is treatment with conventional chemotherapies, which cause harmful side effects in normal tissues. In this context, nanomedicine can help traditional medicine overcome its limits. Diatomite nanoparticles (DNPs) are innovative nano-based drug delivery systems derived from the powder of diatom shells. Diatomite is a porous biosilica largely found in many areas of the world and approved by the Food and Drug Administration (FDA) for pharmaceutical and animal feed formulations. Diatomite nanoparticles with a size between 300 and 400 nm were shown to be biocompatible nanocarriers capable of delivering chemotherapeutic agents against specific targets while reducing off-target effects. This review discusses the treatment of colorectal cancer with conventional methods, highlighting the drawbacks of standard medicine and exploring innovative options based on the use of diatomite-based drug delivery systems. Three targeted treatments are considered: anti-angiogenetic drugs, antimetastatic drugs, and immune checkpoint inhibitors.

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%.

Co-production of spirosiloxane and biochar adsorbent from wheat straw by a low-cost and environment-friendly method.

To enhance the value of wheat straw derivatives, wheat straw ash (WSA) was used as a reactant for the first time to synthesize spirocyclic alkoxysilane, an important organosilicon raw material, using an energy-saving and environmentally friendly non-carbon thermal reduction method. After spirocyclic alkoxysilane extraction, the biochar in the wheat straw ash prepared an adsorbent for Cu2+. The maximum copper ion adsorption capacity (Qm) of silica-depleted wheat straw ash (SDWSA) was 31.431nullmg/g, far exceeding those of WSA and similar biomass adsorbents. The effects of the pH, adsorbent dose, and contact time on the adsorption behaviour of the SDWSA for Cu2+ adsorption were systematically investigated. The adsorption mechanism of Cu2+ by the SDWSA was investigated using the Langmuir, Freundlich, pseudo-first-order kinetic, pseudo-second-order kinetic, and Weber and Morris models by combining the preliminary experimental data and characterization results. The adsorption isotherm and Langmuir equation matched perfectly. The Weber and Morris model can describe the mass-transfer mechanism of Cu2+ adsorption by SDWSA. Both film and intraparticle diffusion are rapid control steps. Compared to WSA, SDWSA has a larger specific surface area and a higher content of oxygen-containing functional groups. A large specific surface area provides more adsorption sites. Oxygen-containing functional groups react with Cu2+ through electrostatic interactions, surface complexation, and ion exchange, which are the possible adsorption mechanisms for SDWSA. These methods improve the added value of wheat straw derivatives and promote wheat straw ash recovery and centralized treatment. This makes it possible to use the thermal energy of wheat straw and facilitates the treatment of exhaust gases and carbon capture.

Diatom biosilica: Source, physical-chemical characterization, modification, and application.

Growing research interest in the use of diatomaceous biosilica results from its unique properties such as chemical inertness, biocompatibility, high mechanical and thermal stability, low thermal conductivity, and homogeneous porous structure with a large specific surface. Unlike the production of synthetic silica materials with a micro- or nanoscale structure in an expensive conventional manufacturing process, diatomaceous biosilica can be produced in huge quantities without significant expenditure of energy and materials. This fact makes it an unlimited, easily accessible, natural, inexpensive, and renewable material. Moreover, the production of biosilica is extremely environmental friendly, as there is essentially no toxic waste and the process does not require more energy compared to the production of synthetic silica-based materials. For all these reasons, diatoms are an intriguing alternative to synthetic materials in developing cheap biomaterials used in a different branches of industry. In this review, the state-of-art of biosilica materials, their characteristics approaches, and possible ways of application have been reported.

3D Biocomposites Comprising Marine Collagen and Silica-Based Materials Inspired on the Composition of Marine Sponge Skeletons Envisaging Bone Tissue Regeneration.

Ocean resources are a priceless repository of unique species and bioactive compounds with denouement properties that can be used in the fabrication of advanced biomaterials as new templates for supporting the cell culture envisaging tissue engineering approaches. The collagen of marine origin can be sustainably isolated from the underrated fish processing industry by-products, while silica and related materials can be found in the spicules of marine sponges and diatoms frustules. Aiming to address the potential of biomaterials composed from marine collagen and silica-based materials in the context of bone regeneration, four different 3D porous structure formulations (COL, COL:BG, COL:D.E, and COL:BS) were fabricated by freeze-drying. The skins of Atlantic cod (Gadus morhua) were used as raw materials for the collagen (COL) isolation, which was successfully characterized by SDS-PAGE, FTIR, CD, and amino acid analyses, and identified as a type I collagen, produced with a 1.5% yield and a preserved characteristic triple helix conformation. Bioactive glass 45S5 bioglass® (BG), diatomaceous earth (D.E.) powder, and biosilica (BS) isolated from the Axinella infundibuliformis sponge were chosen as silica-based materials, which were obtained as microparticles and characterized by distinct morphological features. The biomaterials revealed microporous structures, showing a porosity higher than 85%, a mean pore size range of 138-315 µm depending on their composition, with 70% interconnectivity which can be favorable for cell migration and ensure the needed nutrient supply. In vitro, biological assays were conducted by culturing L929 fibroblast-like cells, which confirmed not only the non-toxic nature of the developed biomaterials but also their capability to support cell adhesion and proliferation, particularly the COL:BS biomaterials, as observed by calcein-AM staining upon seven days of culture. Moreover, phalloidin and DAPI staining revealed well-spread cells, populating the entire construct. This study established marine collagen/silica biocomposites as potential scaffolds for tissue engineering, setting the basis for future studies, particularly envisaging the regeneration of non-load-bearing bone tissues.

Novel Drug and Gene Delivery System and Imaging Agent Based on Marine Diatom Biosilica Nanoparticles.

Mesoporous silica nanoparticles (MSNs) have great potential for applications as a drug delivery system (DDS) due to their unique properties such as large pore size, high surface area, biocompatibility, biodegradability, and stable aqueous dispersion. The MSN-mediated DDS can carry chemotherapeutic agents, optical sensors, photothermal agents, short interfering RNA (siRNA), and gene therapeutic agents. The MSN-assisted imaging techniques are applicable in cancer diagnosis. However, their synthesis via a chemical route requires toxic chemicals and is challenging, time-consuming, and energy-intensive, making the process expensive and non-viable. Fortunately, nature has provided a viable alternative material in the form of biosilica from marine resources. In this review, the applications of biosilica nanoparticles synthesized from marine diatoms in the field of drug delivery, biosensing, imaging agents, and regenerative medicine, are highlighted. Insights into the use of biosilica in the field of DDSs are elaborated, with a focus on different strategies to improve the physico-chemical properties with regards to drug loading and release efficiency, targeted delivery, and site-specific binding capacity by surface functionalization. The limitations, as well as the future scope to develop them as potential drug delivery vehicles and imaging agents, in the overall therapeutic management, are discussed.

Efficient Adsorption of Chromium Ions from Aqueous Solutions by Plant-Derived Silica.

Nowadays, there is great interest in the use of plant waste to obtain materials for environmental protection. In this study, silica powders were prepared with a simple and low-cost procedure from biomass materials such as horsetail and common reed, as well as wheat and rye straws. The starting biomass materials were leached in a boiling HCl solution. After washing and drying, the samples were incinerated at 700 °C for 1 h in air. The organic components of the samples were burned leaving final white powders. These powders were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and low-temperature nitrogen sorption. The amorphous powders (biosilica) contained mainly SiO2, as indicated by FTIR analysis. Horsetail-derived silica was chosen for testing the removal of dichromate ions from water solutions. This biosilica had a good ability to adsorb Cr(VI) ions, which increased after modification of the powder with the dodecylamine surfactant. It can be concluded that the applied procedure allowed obtaining high purity biosilica from plant waste with good efficiency. The produced biosilica was helpful in removing chromium ions and showed low cytotoxicity to human endothelial cells, suggesting that it can be safely used in environmental remediation.

Fabrication of silica on chitin in ambient conditions using silicatein fused with a chitin-binding domain.

High temperatures, harsh pH conditions, and toxic chemicals involved in the conventional synthesis and coating of silica limit the fabrication of new-generation hybrid materials immobilizing live cells and biomolecules such as enzymes and drugs. This hinders the application of inorganic-organic biohybrid materials in various fields, including bioelectronics, energy generation, and biomedicine. Silicatein, an enzyme found in siliceous sponges, catalyzes the polymerization of silica under mild conditions, that is, at room temperature and neutral pH. Silicatein was fused with a chitin-binding domain (ChBD) to selectively bind the fusion silicatein on the chitin material and with a small soluble tag called InakC, a hydrophilic protein from Pseudomonas syringae, to control the unfavorable aggregation of silicatein. The fusion silicatein was soluble in aqueous media and was successfully found to be adsorbed on the chitin material. The immobilized fusion silicatein acted as an interfacial catalyst to fabricate silica on chitin under ambient conditions. This technique can be used to fabricate inorganic-organic hybrid materials to immobilize biomolecules and can be applied to develop novel biocatalytic systems, biosensors, and tissue culture scaffolds.

Diatom Biosilica Doped with Palladium(II) Chloride Nanoparticles as New Efficient Photocatalysts for Methyl Orange Degradation.

A new catalyst based on biosilica doped with palladium(II) chloride nanoparticles was prepared and tested for efficient degradation of methyl orange (MO) in water solution under UV light excitation. The obtained photocatalyst was characterized by X-ray diffraction, TEM and N2 adsorption/desorption isotherms. The photocatalytic degradation process was studied as a function of pH of the solution, temperature, UV irradiation time, and MO initial concentration. The possibilities of recycling and durability of the prepared photocatalysts were also tested. Products of photocatalytic degradation were identified by liquid chromatography-mass spectrometry analyses. The photocatalyst exhibited excellent photodegradation activity toward MO degradation under UV light irradiation. Rapid photocatalytic degradation was found to take place within one minute with an efficiency of 85% reaching over 98% after 75 min. The proposed mechanism of photodegradation is based on the assumption that both HO• and O2•- radicals, as strongly oxidizing species that can participate in the dye degradation reaction, are generated by the attacks of photons emitted from diatom biosilica (photonic scattering effect) under the influence of UV light excitation. The degradation efficiency significantly increases as the intensity of photons emitted from biosilica is enhanced by palladium(II) chloride nanoparticles immobilized on biosilica (synergetic photonic scattering effect).

A hybrid biomaterial of biosilica and C-phycocyanin for enhanced photodynamic effect towards tumor cells.

Intricate mesoporous biosilica has many biomedical applications as a nanocarrier. However, its potential use in photodynamic therapy (PDT) has received little attention. This work reports the first fabrication of bio-engineered materials by covalently conjugating C-phycocyanin (C-PC), a natural photosensitizer, to biosilica for the PDT of tumor-associated macrophages. The resulting hybrid material showed outstanding photodynamic activity under 620 nm laser irradiation. Furthermore, it enhanced the relatively weak photodynamic effect of C-PC. This study also explored methods of biofunctionalizing biosilica for cancer phototherapy, a new pharmacological application of non-toxic C-PC.

Dynamic subcellular translocation of V-type H+ -ATPase is essential for biomineralization of the diatom silica cell wall.

Diatom cell walls, called frustules, are main sources of biogenic silica in the ocean and their intricate morphology is an inspiration for nanoengineering. Here we show dynamic aspects of frustule biosynthesis involving acidification of the silica deposition vesicle (SDV) by V-type H+  ATPase (VHA). Transgenic Thalassiosira pseudonana expressing the VHA B subunit tagged with enhanced green fluorescent protein (VHAB -eGFP) enabled subcellular protein localization in live cells. In exponentially growing cultures, VHAB -eGFP was present in various subcellular localizations including the cytoplasm, SDVs and vacuoles. We studied the role of VHA during frustule biosynthesis in synchronized cell cultures of T. pseudonana. During the making of new biosilica components, VHAB -eGFP first localized in the girdle band SDVs, and subsequently in valve SDVs. In single cell time-lapse imaging experiments, VHAB -eGFP localization in SDVs precluded accumulation of the acidotropic silica biomineralization marker PDMPO. Furthermore, pharmacological VHA inhibition prevented PDMPO accumulation in the SDV, frustule biosynthesis and cell division, as well as insertion of the silicalemma-associated protein SAP1 into the SDVs. Finally, partial inhibition of VHA activity affected the nanoscale morphology of the valve. Altogether, these results indicate that VHA is essential for frustule biosynthesis by acidifying the SDVs and regulating the insertion of other structural proteins into the SDV.

Anticancer Compounds Derived from Marine Diatoms.

Cancer is the main cause of death worldwide, so the discovery of new and effective therapeutic agents must be urgently addressed. Diatoms are rich in minerals and secondary metabolites such as saturated and unsaturated fatty acids, esters, acyl lipids, sterols, proteins, and flavonoids. These bioactive compounds have been reported as potent anti-cancer, anti-oxidant and anti-bacterial agents. Diatoms are unicellular photosynthetic organisms, which are important in the biogeochemical circulation of silica, nitrogen, and carbon, attributable to their short growth-cycle and high yield. The biosilica of diatoms is potentially effective as a carrier for targeted drug delivery in cancer therapy due to its high surface area, nano-porosity, bio-compatibility, and bio-degradability. In vivo studies have shown no significant symptoms of tissue damage in animal models, suggesting the suitability of a diatoms-based system as a safe nanocarrier in nano-medicine applications. This review presents an overview of diatoms' microalgae possessing anti-cancer activities and the potential role of the diatoms and biosilica in the delivery of anticancer drugs. Diatoms-based antibodies and vitamin B12 as drug carriers are also elaborated.

Dry Two-Step Self-Assembly of Stable Supported Lipid Bilayers on Silicon Substrates.

Artificial membranes are models for biological systems and are important for applications. We introduce a dry two-step self-assembly method consisting of the high-vacuum evaporation of phospholipid molecules over silicon, followed by a subsequent annealing step in air. We evaporate dipalmitoylphosphatidylcholine (DPPC) molecules over bare silicon without the use of polymer cushions or solvents. High-resolution ellipsometry and AFM temperature-dependent measurements are performed in air to detect the characteristic phase transitions of DPPC bilayers. Complementary AFM force-spectroscopy breakthrough events are induced to detect single- and multi-bilayer formation. These combined experimental methods confirm the formation of stable non-hydrated supported lipid bilayers with phase transitions gel to ripple at 311.5 ± 0.9 K, ripple to liquid crystalline at 323.8 ± 2.5 K and liquid crystalline to fluid disordered at 330.4 ± 0.9 K, consistent with such structures reported in wet environments. We find that the AFM tip induces a restructuring or intercalation of the bilayer that is strongly related to the applied tip-force. These dry supported lipid bilayers show long-term stability. These findings are relevant for the development of functional biointerfaces, specifically for fabrication of biosensors and membrane protein platforms. The observed stability is relevant in the context of lifetimes of systems protected by bilayers in dry environments.