The reprint ’Aerogel Hybrids and Nanocomposites’ is a collection of the latest publications in the research, development, and use of complex aerogel-based materials. The applications of aerogels in ...hard tissue engineering, new wound-healing materials to challenge bacterial infections, and the making of wearable aerogel fibers reveal their role and potential in the biomedical fields. Catalytic applications of aerogels are well demonstrated by the papers on environmental protection and green hydrogen production. The efficient removal of rare-earth ions, as well as the sensitization of their luminescence in aerogels, makes them environmentally and analytically valuable materials.
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•Drug delivery properties of mesoporous silica-gelatin aerogel.•Rapid drug release measured on-line by 1s time resolution.•Characterization of aerogels by NMR cryoporometry, ...diffusiometry and relaxometry.•Relationship between aerogel structure and drug delivery function.
Specific features of a silica-gelatin aerogel (3 wt.% gelatin content) in relation to drug delivery has been studied. It was confirmed that the release of both ibuprofen (IBU) and ketoprofen (KET) is about tenfold faster from loaded silica-gelatin aerogel than from pure silica aerogel, although the two matrices are structurally very similar. The main goal of the study was to understand the mechanistic background of the striking difference between the delivery properties of these closely related porous materials. Hydrated and dispersed silica-gelatin aerogel has been characterized by NMR cryoporometry, diffusiometry and relaxometry. The pore structure of the silica aerogel remains intact when it disintegrates in water. In contrast, dispersed silica-gelatin aerogel develops a strong hydration sphere, which reshapes the pore walls and deforms the pore structure. The drug release kinetics was studied on a few minutes time scale with 1s time resolution. Simultaneous evaluation of all relevant kinetic and structural information confirmed that strong hydration of the silica-gelatin skeleton facilitates the rapid desorption and dissolution of the drugs from the loaded aerogel. Such a driving force is not operative in pure silica aerogels.
Aerogels are fascinating solid materials known for their highly porous nanostructure and exceptional physical, chemical, and mechanical properties. They show great promise in various technological ...and biomedical applications, including tissue engineering, and bone and cartilage substitution. To evaluate the bioactivity of bone substitutes, researchers typically conduct in vitro tests using simulated body fluids and specific cell lines, while in vivo testing involves the study of materials in different animal species. In this context, our primary focus is to investigate the applications of different types of aerogels, considering their specific materials, microstructure, and porosity in the field of bone and cartilage tissue engineering. From clinically approved materials to experimental aerogels, we present a comprehensive list and summary of various aerogel building blocks and their biological activities. Additionally, we explore how the complexity of aerogel scaffolds influences their in vivo performance, ranging from simple single-component or hybrid aerogels to more intricate and organized structures. We also discuss commonly used formulation and drying methods in aerogel chemistry, including molding, freeze casting, supercritical foaming, freeze drying, subcritical, and supercritical drying techniques. These techniques play a crucial role in shaping aerogels for specific applications. Alongside the progress made, we acknowledge the challenges ahead and assess the near and far future of aerogel-based hard tissue engineering materials, as well as their potential connection with emerging healing techniques.
Production of aerogels starts with solution chemistry and may end with supercritical carbon dioxide drying, which both require a specialized system. Here we present a complete aerogel production ...system that was developed and used in our laboratory over the last nine years. Our aim was to develop a supercritical dryer and a protocol, whereby the CO₂ pump can be left out, and the entire flow system is operated by the pressure of the CO₂ cylinder. Drying pressure and temperature are controlled by the combination of the filling and heating temperatures. A continuous-mode solvent exchange system has also been developed, in which the solvent consumption during the process can be reduced to one-third of the batch method. In the new medium temperature 1.5 L volume supercritical dryer, the temperature is set to a constant 80⁻82 °C, and the pressure can be in the 90⁻200 bar range, depending on the conditions. We have performed approximately 200 dryings thus far, and prepared a wide range of monolithic aerogels, from pristine silica aerogels to polysaccharides and collagen. In this paper, we have summarized not only the technical details, but also the work experiences, as well as advantages and disadvantages of the systems.
Abstract This paper presents a novel retinal vessel segmentation method. Opposed to the general approach in similar directional methods, where only the maximal or summed responses of a pixel are ...used, here, the directional responses of a pixel are considered as a vector. The segmentation method is a unique region growing procedure which combines a hysteresis thresholding scheme with the response vector similarity of adjacent pixels. A vessel score map is constructed as the combination of the statistical measures of the response vectors and its local maxima to provide the seeds for the region growing procedure. A nearest neighbor classifier based on a rotation invariant response vector similarity measure is used to filter the seed points. Many techniques in the literature that capture the Gaussian-like cross-section of vessels suffer from the drawback of giving false high responses to the steep intensity transitions at the boundary of the optic disc and bright lesions. To overcome this issue, we also propose a symmetry constrained multiscale matched filtering technique. The proposed vessel segmentation method has been tested on three publicly available image sets, where its performance proved to be competitive with the state-of-the-art and comparable to the accuracy of a human observer, as well.
The physicochemical properties of rare-earth zirconates can be tuned by the rational modification of their structures and phase compositions. In the present work, La3+-, Nd3+-, Gd3+-, and ...Dy3+-zirconate nanostructured materials were prepared by different synthetic protocols, leading to powders, xerogels, and, for the first time, monolithic aerogels. Powders were synthesized by the co-precipitation method, while xerogels and aerogels were synthesized by the sol–gel technique, followed by ambient and supercritical drying, respectively. Their microstructures, thermogravimetric profiles, textural properties, and crystallographic structures are reported. The co-precipitation method led to dense powders (S BET < 1 m2 g–1), while the sol–gel technique resulted in large surface area xerogels (S BET = 144 m2 g–1) and aerogels (S BET = 168 m2 g–1). In addition, the incorporation of lanthanide ions into the zirconia lattice altered the crystal structures of the powders, xerogels, and aerogels. Single-phase pyrochlores were obtained for La2Zr2O7 and Nd2Zr2O7 powders and xerogels, while defect fluorite structures formed in the case of Gd2Zr2O7 and Dy2Zr2O7. All aerogels contain a mixture of cubic and tetragonal ZrO2 phases. Thus, a direct effect is shown between the drying conditions and the resulting crystalline phases of the nanostructured rare-earth zirconates.
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•Static SFE combined with aerogel adsorption is used to protect aroma materials.•Hydrophilic and hydrophobic silica aerogels showed different selectivities.•Trace compounds were ...enriched to an analytically significant level.•Extracted components competed with each other for the active sites on the surface.•Static SFE gives higher number of components and cleaner extracts.
Static supercritical fluid extraction has been used to concentrate the aroma materials of common herbs and spices. The technique has provided a higher number of components and cleaner extract than the one-step ethanol maceration. The one-step supercritical fluid extraction of the aroma compounds has been combined with their in situ adsorption in hydrophilic and hydrophobic silica aerogels. The extracts have been analyzed by a GC–MS technique and 55 aroma compounds have been identified. Most of the compounds have been adsorbed in both polar and apolar silica aerogels with no direct connection with the surface polarity. However, previously undetected compounds enriched to an analytically significant level, while others competed with each other for the active sites on the surface. Functionalized silica aerogels can be used as a new type of aroma storage materials and as selective and tuneable adsorbents for the extraction and enrichment of potentially active components from a complex matrix.
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Methotrexate functionalized silica-gelatin hybrid aerogel (SGM) was synthesized by the sol–gel method and co-gelation. The drug methotrexate (MTX) is covalently linked to the collagen ...molecules of the hybrid aerogel backbone by amide-bond. The characteristic MTX content of the functionalized hybrid aerogel is ca. 6 wt% by the dry weight. The micronization of SGM aerogel in water yields cell sized (d = 10–20 µm) particles. The cytotoxicity of these microparticles against tumor cell lines (SCC VII and HL-60) is unprecedentedly high, it is approximately equivalent to that of an equal dose of free (dissolved) MTX, as proved by in vitro experiments. Thus, the activity of MTX is intact after aerogel functionalization, and the mass specific cytotoxicity of SGM is high enough for medical applications. Drug release studies verified that MTX cannot be liberated from this drug delivery system solely by chemical hydrolysis, however, collagenase enzymatic activity releases MTX from the functionalized hybrid aerogel. The cytotoxicity of SGM towards various cancerous and non-cancerous cell lines correlates with the collagenase activities of cells. Therefore, conjugation with the hybrid aerogel provides a controlled release system for the antineoplastic agent MTX. The morphology of the delivery vehicle was chosen to adapt the size of cancer cells; thus the metastatic pathways of the tumor cells can get flooded.
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