Silica Microspheres Research Articles

Surface Chain-Transfer Ring-Opening Metathesis Polymerization.

Ring-opening metathesis polymerization (ROMP) is a powerful method to graft various types of polymer chains to a given surface. While surface-initiated ROMP (SI-ROMP) serves as an efficient tool for surface modification and is therefore widely reported, the method requires grafting (1) the olefin substrate and (2) the metathesis catalyst to the surface prior to the polymerization with multiple synthetic and work up steps. To overcome this difficulty, we proposed the use of the chain-transfer reaction as an alternative method for surface modification. Terminal olefins are grafted to the surface without the need to graft the metathesis catalysts, and polymers with olefin backbones are polymerized and grafted simultaneously via both ROMP and chain transfer (cross-metathesis between olefins from backbones and surfaces). Compared to SI-ROMP, this surface-chain transfer ROMP (SC-ROMP) method avoids grafting the catalyst and growing polymer chains from the surface and could be achieved in a single step. Various types of surfaces like carbon nanotubes, carbon fibers, graphene nanosheets, and silica microspheres are used for demonstration. We envision that this work could bring a convenient and effective solution to surface modification via ROMP.

Preparation of porous silica microspheres using silica nanoparticles with different morphologies and their properties as catalyst carriers

Preparation of porous silica microspheres using silica nanoparticles with different morphologies and their properties as catalyst carriers

AI aided microfluidic auto continuous separation and sorting of microspheres simultaneously based on their morphological and optical properties

We report a novel method of continuous online microsphere/particle separation and sorting that integrated techniques of microsphere-imaging, microfluidic chip, moving micro-object super-resolution analysis, and AI image recognition into a simple system. It is the first method with the ability to determine the size of moving micro-objects with nanoscale resolution and separate/sort them simultaneously according to their size, shape, and refractive index. In the experiment, the separation and sorting of polystyrene, silica, and PMMA microspheres from the mixture solutions of several different microspheres using a microfluidic device demonstrated that the sorting was accurate and highly efficient and could classify micro-objects with a nanoscale size difference of ∼ 10 nm and a refractive index difference of 10−5. The method is suitable for coupling with various micro-object separation/sorting instruments for different micro-object separations. It can also divide micro-objects either with or without coating.

Dual suppression amplification based on resonance energy transfer and enzymatic biocatalytic precipitation for IgG electrochemiluminescence ultrasensitive assay

Due to the necessity of ultrasensitive bioassays in life science, electrochemiluminescence (ECL) methodologies coupled with amplification strategies has drawn great attention recently. Herein, a versatile and robust dual suppression-based signal amplification strategy was proposed for IgG specifically ultrasensitive detection. A sandwich ECL sensor was constructed by employing Ru(bpy)32+ adsorbed on silica microspheres (Ru@SiO2) as luminophor. Fe3O4 nanoparticles (Fe3O4 NPs) were introduced on sensing platform through an antigen-antibody affinity, which played double roles. As an acceptor of resonance energy transfer (RET), Fe3O4 NPs remarkably quenched the ECL signal of Ru@SiO2. Meanwhile, Fe3O4 NPs, as a typical peroxidase-mimicking enzyme, catalyzed H2O2 to produce insoluble product based on enzymatic biocatalytic precipitation (BCP). As such, an efficient dual suppressive ECL platform has been achieved by the integration of ECL-RET and BCP techniques, which has been applied to ultrasensitively detect IgG with a linear range and limit of detection of 10 fg/mL to 1 μg/mL and 4.9 fg/mL, respectively. The new integrated system with RET and BCP may provide a potential promising in the development of highly efficient ECL systems for clinical diagnosis.

Imidazole-octyl mixed-mode stationary phase based on macroporous silica for the purification of ovomucoid and ovotransferrin.

A process-simplified hard template approach was established to synthesize the monodisperse macroporous silica microspheres with homogeneous structures by twice alkali-thermal treatment and calcination routes. Porous vinyl-functionalized polysesquioxane microspheres (V-PMSQ) were synthesized through a hydrolyzation-polycondensation method and used as templates. The template particles with large aperture and high pore volume were obtained by adjusting the pH value and reaction time of the twice alkali-thermal reaction. After calcination, monodisperse silica microspheres with an average pore size of 30nm, homogeneous pore structures, and narrow particle size distribution were fabricated, which can be directly used as chromatographic matrices without classification. After that, a new reversed-phase/strong anion-exchange (RP/SAX) mixed-mode stationary phase Sil-S-VOIM was prepared by bonding the 1-vinyl-3-octyl-imidazole ligands to the above silica microspheres through a "thiol-ene" click reaction. The performance of the Sil-S-VOIM column was evaluated by one acidic protein (transferrin) and two basic proteins (lysozyme, α-chymotrypsin) and compared to a single imidazole-modified Sil-S-VIM column and an octyl-modified Sil-C8 column, respectively. Due to the synergistic effect of electrostatic repulsion and hydrophobic interactions, baseline separations of the above proteins were observed only on the Sil-S-VOIM column, with resolutions of 2.55 and 2.01 between lysozyme and transferrin, and between transferrin and α-chymotrypsin, respectively, indicating good selectivity and separation ability compared with single-mode stationary phases. It was applied to the isolation of egg white samples with peaks identified by SDS-PAGE and MALDI-TOF-MS. The results showed that the selective retention and isolation of ovomucoid and ovotransferrin were successfully achieved, with yields of 78.8% and 67.2%, respectively. The protocol described in this work is simpler, faster, and has higher protein recovery. Overall, this new mixed-mode stationary phase provided a promising potential for the separation and determination of intact proteins.

Osmosis-induced hydrodynamic centering of W/O/W double emulsion droplets for quasi-concentric microcapsule/microsphere fabrication

Water-in-oil-in-water (W/O/W) double emulsion droplets are a typical colloidal system applied in various practical fields. However, certain high-specification applications necessitate exact geometric homogeneity in terms of both shell diameter and thickness. Despite achieving uniformity in shell diameter, on-chip microfluidic emulsification always leads to an eccentric phenomenon due to innate density differences of the droplet solution. At the same time, the current regulation methods have multiple limitations, including their applicability, regulatory scope, and objective restrictions. Herein, we propose an off-chip osmosis-induced hydrodynamic method to accurately regulate the eccentricity of W/O/W double emulsion droplets. The rational selection of hypertonic osmosis can energize the droplets and induce inward transmembrane water flux. This flow helps to reposition the droplet core to align concentrically with the shell, regardless of the initial dimension and eccentricity of the droplets. As the osmotic induction reduces due to the dilution of the inner solute molar concentration, the optimal droplet configuration can be achieved when osmosis-induced hydrodynamic regulation sufficiently counteracts the adverse effects of droplet solution density difference. The microcapsules can thus be produced by instant UV polymerization of the regulated double emulsion droplets, and the silica microspheres with fine geometric homogeneity can be prepared through further heat treatment, which is expected to meet the stringent morphological requirements in practical applications.

Chitosan/polyacrylic acid/octadecene double-crosslinked network hydrogel functionalized porous silica microspheres for multimode liquid chromatographic separation

In this study, chitosan (CS) and polyacrylic acid (PAA) were used to construct a double-crosslinked network hydrogel, which was employed as the functional material for silica microspheres to prepare a CS/PAA hydrogel modified liquid chromatographic stationary phase. During preparation, octadecene (ODE) was introduced into the CS/PAA hydrogel to improve its hydrophobicity and separation ability. The electrostatic interaction between the amino group of CS and the carboxyl group of PAA effectively prevented the swelling of the CS/PAA hydrogel, which ensured the successful application of the obtained CS/PAA hydrogel@SiO2 in chromatographic analysis. Polar nucleosides/bases and B-vitamins were selectively separated using hydrophilic interaction liquid chromatography. Hydrophobic polycyclic aromatic hydrocarbons and alkylphenols were effectively separated through reversed-phase liquid chromatography. Moreover, the effective separation of aromatic positional isomers and chiral enantiomers was achieved. This study confirms the potential application of the CS/PAA hydrogel in chromatographic separation. What is noteworthy is that the method developed in this study also provides a feasible strategy to solve the swelling issue associated with the hydrogel-based liquid chromatographic stationary phase.

All-optical tuning of the frequency of Yb3+/Er3+ co-doped microsphere WGM laser pumped by 1 µm ASE light source

In this paper, the laser generated by Yb3+/Er3+ co-doped silica microspheres excited and tuned by amplified spontaneous emission (ASE) light source was studied. The adoption of ASE light avoids the synchronous adjustment of the coupling condition of the microcavity during broadband tuning process, and facilitates the actual application of the microcavity-based tunable laser. The stable single-mode laser at approximate 1595 nm was generated in the Yb3+/Er3+ co-doped silica microsphere due to the polarization insensitivity of the ASE light source with a center wavelength of 1 µm. For the all-optical modulation of laser mode, a thin layer of copper film was coated on the spherical crown of the microsphere by magnetron sputtering. Controllable heating of the microsphere and linear tuning of laser mode were realized through the absorption of ASE light by the copper film injecting from the stem of the microsphere. The tuning range reached 190 GHz.

Light Enhancement of Green Up-Conversion Emission from Er-Doped Silica Microspheres by Carbon Quantum Dot Coatings.

Combination of high quality cavity such as glass microsphere and emitting nano-particle coating layers can create novel strongly emitting devices. Herein, we demonstrate an erbium-doped silica microsphere coated by dual-emission carbon quantum dots, which have the sizes of 3-5nm, emitting green up-conversion with narrow line-width green light at wavelength of 537nm. The dual-emission carbon quantum dots fabricated by hydrothermal process and have luminescent emission wavelengths in the range of 410-550nm. The carbon quantum dot coated erbium silica microsphere is pumped at wavelength of 976nm through the optical fibre on which microsphere attached on the tip. The dual-emission carbon quantum dot layers attributed to the strong green up-conversion light enhancement similar coated noble metallic thin films, however the light enhancement from dual-emission carbon quantum dot coated erbium silica microsphere depended on the thickness of coating layers. This result is useful for making visible emitting micro-devices and photonic integrated circuits.

A novel target-triggered signal chemiluminescence kit for thrombin detection based on fusiform Au/MIL-53(Fe)

In this work, a fusiform Au/MIL-53(Fe) catalyst was used to construct a chemiluminescence (CL) kit for the sensitive and rapid detection of thrombin (THR). The porous silica microspheres encapsulated with luminol in holes by thrombin aptamer (THR-APT/Luminol/SPSiO2) and the fusiform Au/MIL-53(Fe) modified with thrombin aptamer complementary chains (Au/MIL-53(Fe)-SSDNA) were prepared. Then, a CL kit for THR detection was constructed by using the prepared composites. When thrombin is added to the reaction system, it binds to its aptamer (THR-APT) to open the holes of SPSiO2, which cause luminol and Au/MIL-53(Fe) release. Released luminol enters the detection system and triggers the reaction of luminol–H2O2–NaOH with the catalyst of Au/MIL-53(Fe), and produces a CL signal. The detection limit and the linear range of the kit were 4.7 × 10−15 M and 1.5 × 10−14 – 3.5 × 10−10 M, respectively. The CL kit also showed high stability, selectivity and reproducibility, and was successfully applied to the determination of THR in serum samples. Therefore, the proposed method for detecting THR has great application potential in the diagnosis of blood-related disease markers.

Evaluation of the osteoconductivity and the degradation of novel hydroxyapatite/polyurethane combined with mesoporous silica microspheres in a rabbit osteomyelitis model.

Bone defects caused by osteomyelitis can lead to severe disability. Surgeons still face significant challenges in treating bone defects. Nano-hydroxyapatite (n-HA) plays an important role in bone tissue engineering due to its excellent biocompatibility and osteoconductivity. Levofloxacin (Levo) was encapsulated in mesoporous silica nanoparticles (MSNs) via electrostatic attraction to serve as a drug delivery system. MSNs were incorporated with n-HA and polyurethane (PU). The degradation and osteoconductivity properties of these novel composite scaffolds and their effectiveness in treating chronic osteomyelitis in a rabbit model were assessed. Gross pathology, radiographic imaging, micro-computed tomography, Van Gieson staining, and hematoxylin and eosin staining were conducted at 6 and 12 weeks. The group of composite scaffolds combining n-HA/PU with MSNs containing 5 mg Levo (n-HA/PU + Nano +5 mg Levo) composite scaffolds showed superior antibacterial properties compared to the other groups. At 12 weeks, the n-HA/PU + Nano +5 mg Levo composite scaffolds group exhibited significantly greater volume of new trabecular bone formation compared to the other three groups. The surface of the novel composite scaffolds exhibited degradation after 6 weeks implantation. The internal structure of the scaffolds collapsed noticeably after 12 weeks of implantation. The rate of material degradation corresponded to the rate of new bone ingrowth. This novel composite scaffold, which is biodegradable and osteoconductive, has potential as a drug delivery system for treating chronic osteomyelitis accompanied by bone defects.

Synthesis and luminescent properties of Eu(III)/Tb(III) rare earth complex-coated the core-shell structured silica microspheres: Unleashing the potential for white light emission

A rare earth organic complex, SiO2@ATPA-Si-RE (RE = Eu, Tb), exhibiting a core-shell structure, was synthesized using the ligand (HOOC)2C6H3NHCONH(CH2)3Si(OCH2CH3)3(ATPA-Si) to connect the silica microspheres core and coordinate with rare earth ions. The pH value of the reaction was adjusted to produce organic complex shells with thicknesses of 2.0 nm and 5.0 nm, while the SiO2 core measured a diameter of 125 nm. Luminescence spectra indicated that the emission intensity of the SiO2@ATPA-Si-RE (RE = Eu, Tb) core-shell structure was stronger than that of the ATPA-Si-RE organic complex due to a perfect match between the triplet energy level of SiO2@ATPA-Si and the excited energy level of rare earth ions (Eu3+, Tb3+). Remarkably, the core-shell structure with a 2.0 nm shell thickness possessed a greater emission intensity compared to the 5.0 nm shell thickness. Moreover, these findings unveiled the tunability of luminescence color, ranging from green or red to white, by adjusting the doping ratio of Eu3+ and Tb3+ ions and the coating thickness of complexes. Particularly, a warm white light emission, characterized by CIE coordinates (0.389, 0.347), a color rendering index value of 86.7, and a low correlated color temperature value of 3550 K, was achieved using the organic complex with a 2.0 nm thickness coated on SiO2 microspheres with a doping ratio of Eu3+ at 0.7 mmol and Tb3+ at 0.3 mmol. Conversely, the complexes with a 5.0 nm coating thickness and Tb3+ doping ratio of 0.3 mmol yielded a cold white light emission. These findings demonstrate the potential applications in next-generation lighting industry and display systems.

Preparation of a new PVDF membrane with inverse opal structure for high-precision separation

Inspired by natural isoporous materials and the highly arranged structure of photonic crystals (PCs), an inverse opal (IO)-structured membrane with a highly interconnected through-hole structure, a high porosity, and a nearly uniform pore size was prepared by multiosmosis method. Silica (SiO2) microspheres were assembled as building blocks into opal crystals, and poly (vinylidene fluoride) (PVDF) acted as the frame material of the membrane. The influencing factors in the fabrication of high-quality opal PCs were studied. Binary PVDF/SiO2 composite PCs were obtained by multiosmosis of a PVDF solution, and the infiltration mechanism was investigated, which indicated that the PVDF polymers were uniformly cured throughout the crystal area to form SiO2/air/PVDF composite PCs until completely infiltrated. Then, the IO-structured membrane was achieved after etching SiO2 microspheres. Different particle sizes of SiO2 microspheres were used to prepare PVDF membranes with various pore sizes. The pure water flux and porosity could reach as high as 5208.71 L m−2h−1 and 83.59%, respectively. The membranes displayed excellent rejection of SiO2 microspheres, almost 100%, and great antifouling performance. This work provided a simple and efficient method for constructing a filtration membrane with IO structure, which hopefully would solve the problems encountered in realizing efficient, high-precision separation.

Clinically Translatable Phosphonated Silica Microspheres for Selective Internal Radiation Therapy of Hepatocellular Carcinoma

Selective internal radiation therapy (SIRT) is used as a locoregional therapy for hepatocellular carcinoma (HCC) to delay the progression of HCC. Thus far, various kinds of radioactive microspheres with different materials and radionuclides have been developed to be utilized in SIRT, but they remain unsatisfactory in some ways. Herein, using a facile method, phosphonated silica microspheres (PSMs) are prepared and further radiolabeled with 177Lu in a rapid and effective manner. The results suggest that the radiolabeling efficiency is higher than 99%, and the specific activity of the product is 10 kBq per microsphere. 177Lu‐PSM exhibits outstanding in vivo radiolabeling stability, excellent antitumor activity, and single‐photon‐emission computed tomography–computed tomography (SPECT/CT) imaging capability. In addition, it is shown that PSM can be produced in large quantities at a relatively low cost. The results indicate that 177Lu‐PSM might hold considerable potential for translation to clinical applications.

Attaching protein-adsorbing silica particles to the surface of cotton substrates for bioaerosol capture including SARS-CoV-2

The novel coronavirus pandemic (COVID-19) has necessitated a global increase in the use of face masks to limit the airborne spread of the virus. The global demand for personal protective equipment has at times led to shortages of face masks for the public, therefore makeshift masks have become commonplace. The severe acute respiratory syndrome caused by coronavirus-2 (SARS-CoV-2) has a spherical particle size of ~97 nm. However, the airborne transmission of this virus requires the expulsion of droplets, typically ~0.6–500 µm in diameter (by coughing, sneezing, breathing, and talking). In this paper, we propose a face covering that has been designed to effectively capture SARS-CoV-2 whilst providing uncompromised comfort and breathability for the wearer. Herein, we describe a material approach that uses amorphous silica microspheres attached to cotton fibres to capture bioaerosols, including SARS CoV-2. This has been demonstrated for the capture of aerosolised proteins (cytochrome c, myoglobin, ubiquitin, bovine serum albumin) and aerosolised inactivated SARS CoV-2, showing average filtration efficiencies of ~93% with minimal impact on breathability.

Porous silica supported Ag core-Pd shell composite: Seed-mediated stepwise reduction and tunable dispersion for boosting catalytic hydrogen evolution

For developing efficient and practical catalysts to achieve controllable hydrogen evolution from chemical hydrogen storage material, we herein demonstrate a seed-mediated stepwise reduction and tunable dispersion protocol to fabricate porous silica supported Ag core - Pd shell composites (Pd@Ag/SiO2) with serial metal molar ratios. By reasonable regulation for reduction sequence and growing conditions, the Pd@Ag bimetal layered nanostructure could be piloted to take orderly shape; via adjusting addition time and dosage for the reactants and additives, the resultant Pd@Ag nanoagents can be firmly attached on porous silica. The little by little assembled nanoagents with mean size of 10 nm on the silica microspheres construct a loose and porous secondary microstructure, leading to increment of specific surface area to some degrees. The generation of electron synergistic effect among the metals and carrier, verified by the XPS analysis, contributes to boosting the catalytic ability. The catalytic activity of the bimetal composites all exceed that of mono-metal composites, of which the bimetal composite Pd0.75@Ag0.25/SiO2 holds the top catalytic ability, even beyond that of Pd/SiO2 or Pd-NPs, followed by Pd0.5@Ag0.5/SiO2 and Pd0.25@Ag0.75/SiO2. The AB hydrolysis catalyzed by Pd0.75@Ag0.25/SiO2 at the given temperatures (293 to 313 K) is validated to be a first-order reaction, with apparent activation energy of 42.46 kJ·mol−1 and TOF value of 109.99 min−1. The catalyst Pd0.75@Ag0.25/SiO2 presents satisfactory stability, still retaining 83.2 % initial catalytic activity after five repeated use.

Sol-Gel-Controlled Size and Morphology of Mesoporous Silica Microspheres Using Hard Templates.

Mesoporous silica microspheres (MPSMs) represent a promising material as a stationary phase for HPLC separations. The use of hard templates provides a preparation strategy for producing such monodisperse silica microspheres. Here, 15 MPSMs were systematically synthesized by varying the sol-gel reaction parameters of water-to-precursor ratio and ammonia concentration in the presence of a porous p(GMA-co-EDMA) polymeric hard template. Changing the sol-gel process factors resulted in a wide range of MPSMs with varying particle sizes from smaller than one to several micrometers. The application of response surface methodology allowed to derive quantitative predictive models based on the process factor effects on particle size, pore size, pore volume, and specific surface area of the MPSMs. A narrow size distribution of the silica particles was maintained over the entire experimental space. Two larger-scale batches of MPSMs were prepared, and the particles were functionalized with trimethoxy(octadecyl) silane for the application as stationary phase in reversed-phases liquid chromatography. The separation of proteins and amino acids was successfully accomplished, and the effect of the pore properties of the silica particles on separation was demonstrated.

Phenosafranine encapsulated mesoporous silica as efficient electrocatalyst for Cr(VI) reduction and its subsequent sensitive determination

This work presents an easy, highly specific, and sensitive route for the electrochemical reduction of Cr(VI) by phenosafranine (PSF+) integrated sulfonic acid functionalized mesoporous silica microspheres (MS-SO3−), denoted as PSF+-MS-SO3−. The synthesized material is characterized using various spectroscopic and microscopic methods. The glassy carbon electrode (GCE) is modified with this material (represented as GCE/PSF+-MS-SO3−) and employed for electroanalytical applications. The electrochemical characteristics of PSF+-MS-SO3− are established by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Further, it is exploited for the electrocatalytic reduction of, Cr(VI). Superior electron transfer kinetics and stable electrochemical response for Cr(VI) are observed at the GCE/PSF+-MS-SO3− electrode. Moreover, the quantitative estimation of Cr(VI) at the GCE/PSF+-MS-SO3− done using linear sweep voltammetry (LSV). Dual linear calibration ranges (1 to 20 µM and 20 to 100 µM) is obtained from the LSV response. A low limit of detection (0.5 µM) and superior sensitivity (1.1 µA µM−1 cm−2) are recognized at this electrode. In addition, significant selectivity in the existence of other interfering ions is also shown by fabricated sensing scaffold. The precise measurement of Cr(VI) in spiked water samples with simple matrix is also demonstrated successfully with sufficient durability and reproducibility.

Magnetic relaxation switching biosensor for one-step detection of Vibrio parahaemolyticus based on click chemistry-mediated sol-gel system

In this study, a magnetic relaxation switching (MRS) biosensor was developed for one-step detection of pathogenic bacteria Vibrio parahaemolyticus (VP). The biosensor is based on a click chemistry-mediated sol-gel system and utilizes low-field nuclear magnetic resonance (LF NMR) detection. VP aptamer (Apt)-coated hollow mesoporous silica microspheres (HMSMs) with saturated sodium ascorbate (SAA) solution sealed inside, HMSMs@SAA&Apt, are designed as the signal unit. When the target VP is present, the Apt binds to VP and releases SAA from the signal unit. The released SAA reduces Cu2+ in the test solution to Cu+, which catalyzes the click chemistry reaction between azide-modified polyethylene glycol (PEG-Azide) and acetylene-modified polyacrylic acid (PAA-Alkyne). The sol-gel transition is triggered, a large amount of "free" water is converted into "bound" water, resulting in the decrease of transverse relaxation time (T2). Under the optimal experimental conditions, the variation of T2 (ΔT2) was linearly related to the logarithm of VP concentration in the range of 10 ∼ 1.0 × 108 CFU/mL, with a limit of detection of 5 CFU/mL. The assay demonstrated good selectivity, stability, and reproducibility. It is completed in one step, holding promising applications in the rapid field detection of pathogenic bacteria.

Synergistic Effects between Multiphase Thermal Insulation Functional Phases on the Mechanical and Heat Insulation Properties of Silicone Rubber Composites.

This work utilizes the synergistic effect between three different functional phases of thermal insulation, i.e., hollow ceramic microspheres (HCMs), hollow silica microspheres (HSMs), and hydroxy silicone oil blowing agent, to prepare a flexible and efficient thermal insulation composite with low thermal conductivity and high structural strength. First, the effects of the three phases on the mechanical and thermomechanical properties of silicon rubber (SR) were analyzed using a scanning electron microscope (SEM), a thermogravimetric (TG) analyzer, a thermal conductivity meter, and a universal testing machine, respectively. Then, the thermal insulation mechanism of multiphase thermal insulation composite materials was analyzed. The results show that the thermal stability and mechanical performance of composites were significantly enhanced, particularly for sample 18H, whose Tmax and char yield reached 621.3 °C and 77.5%, respectively, representing a respective increase of 12.1 and 35.3% compared to those of pure SR. After heat treatment at 1000 °C, the linear shrinkage of the sample diameter was about 9.4%, while the thermal conductivity was as low as 0.064 W/(m·K), which was 53.2% lower than that of the pure matrix SR. We believe that this work can serve as a reference for the preparation of heat insulation and protection materials with low thermal conductivity and high structural strength.