Synthesis of Cu(II)-containing TiO2-SiO2 binary xerogels by hydrolysis of a mixture of tetrabutoxytitanium, tetraethoxysilane, and copper(II) chloride in a water-ammonia atmosphere

A Cu(II)-containing binary xerogel TiO₂-SiO₂ was synthesized by joint hydrolysis of tetrabutoxytitanium, teraethoxysilane and copper(II) chloride dissolved in their mixture. The synthesis was performed in a vapor of 10% aqueous ammonia under static conditions. EPR spectroscopy was used to examine the state of Cu(II) in the xerogel matrix. Data on specific features of the behavior of saccharose within xerogel pores under heating were obtained. The catalytic activity of the xerogel was tested by the kinetic method on model reactions of hydrogen peroxide decomposition and oxidative dehydrogenation of trimethylhydroquinone.     

Application of hydrogen peroxide encapsulated in silica xerogels to oxidation reactions

Hydrogen peroxide was encapsulated into a silica xerogel matrix by the sol-gel technique. The composite was tested as an oxidizing agent both under conventional and microwave conditions in a few model reactions: Noyori's method of octanal and 2-octanol oxidation and cycloctene epoxidation in a 1,1,1-trifluoroethanol/Na2WO4 system. The results were compared with yields obtained for reactions with 30% H2O2 and urea-hydrogen peroxide (UHP) as oxidizing agents. It was found that the composite has activity similar to 30% H2O2 and has a several advantages over UHP such as the fact that silica and H2O are the only products of the composite decomposition or no contamination by urea or its derivatives occurs; the xerogel is easier to heated by microwave irradiation than UHP and could be used as both an oxidizing agent and as solid support for microwave assisted solvent-free oxidations.     

Blue-shifted fluorescence spectrum in silica xerogels with incorporation of extract’s leaves

The spectral characteristics of different kind of leaves extracts fluorescence embedded in silica xerogel matrix under structural evolution promoted by heat treatment was studied. We obtain a higher PSII thermostability for extract of leaves, rich in chlorophyll such as spinach, made in darker condition than extract of leaves made in lighter (non-dark) conditions, both embedded in xerogel matrix, which remain bioactive over a very long period of time. In other kind of leaves such geranium, after chlorophyll decomposition the quenching center are formed at temperatures about 800 °C, whereas in buxus sempervirens leaves fluorescing aggregates remain in temperatures as high as 1,000 °C, when their are embedded in silica xerogel matrix. In general blue-shift fluorescence is observed in all cases indicating the PSII denaturizing and formation of fluorescing aggregates in relatively high temperatures.     

Uniform and size-tunable mesoporous silica with fibrous morphology for drug delivery

A family of mesoporous silica microspheres with fibrous morphology and different particle sizes ranging from about 400 to 900 nm has been successfully synthesized through a facile self-assembly process. The structural, morphological, and textural properties of the samples were well characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), N(2) adsorption/desorption, and thermal gravimetry (TG). The results reveal that this silica-based mesoporous material exhibits excellent physical properties, including a fibrous spherical morphology, good thermal stability, large pore volume, high specific surface area and narrow size distribution. Additionally, the size and textural properties can be tuned by altering the silica precursor/template molar ratio. The formation and the self-assembly evolution process have also been proposed. The obtained materials were further used as a drug delivery carrier to investigate the in vitro drug release properties using doxorubicin (DOX) as a representative model drug. It was found that this kind of silica exhibits good biocompatibility and obvious sustained drug release properties, suggesting its potential application in biological fields.     

含10mol%氧化硅的钙磷酸盐玻璃陶瓷的合成及其体外生物活性

采用高分子网络凝胶法合成出SiO2-CaO-P2O5生物玻璃陶瓷,该材料具有较低含硅量和高钙磷比(nCa/nP=1.57)的特点,更接近人体硬组织的成分。将材料在SBF溶液浸泡研究材料的体外生物活性,通过TG/DTA,XRD,FTIR和SEM等方法对粉体和浸泡后的样品表面进行表征,ICP-AES对SBF溶液中钙、磷、硅离子的浓度进行检测。结果表明,氧化硅的添加有利于玻璃陶瓷表面磷灰石晶相的形成;随着浸泡时间的延长,沉积在样品表面的碳酸羟基磷灰石层逐渐由球型突起变为叶片状,溶液中钙、磷离子浓度降低,而硅离子浓度增加,说明材料具有良好的生物活性,适宜作为牙齿和骨骼的替代或修复材料。     

Three-dimensional porous HPMA-co-DMAEM hydrogels for biomedical application

The aim of this work is to develop a novel biocompatible drug delivery carrier and tissue engineering scaffold with the ability of controlled drug release and also tissue regeneration. We have synthesized N-(2-hydroxypropyl)methacrylamide and 2-(dimethylamino)ethyl methacrylate copolymer-based hydrogels loaded with doxorubicin and tested in vitro. The manifestation of temperature sensitivity is noted with a sharp decrease or increase in hydrogel optical transparency that happens with the temperature exceeding a critical transition value. The drug release profile exhibited pH-sensitive behavior of the hydrogel. The hydrolytic degradation of gel and in vitro studies of polymer–doxorubicin conjugate and doxorubicin release from hydrogel matrix indicated that hydrogels were stable under acidic conditions (in buffers at pH 4.64 and 6.65). In both drug forms, polymer–doxorubicin conjugate and free doxorubicin could be released from the hydrogel scaffold at a rate depending directly on either the rate of drug diffusion from the hydrogel or rate of hydrogel degradation or at rate controlled by a combination of the both processes. In vitro analysis showed homogenous cell attachment and proliferation on synthesized hydrogel matrix. In vivo implantation demonstrated integration of the gel with the surrounding tissue of mice within 2 weeks and prominent neo-angiogenesis observed in the following weeks. This multifunctional hydrogels can easily overcome biological hurdles in the in vivo conditions where the pH range changes drastically and could attain higher site-specific drug delivery improving the efficacy of the treatment in various therapeutical applications, especially in cancer therapy, and could also be used as tissue engineering scaffold due to its porous interconnected and biocompatible behavior.     

Congo Red Immobilized on a Silica/Aniline Xerogel: Preparation and Application as an Amperometric Sensor for Ascorbic Acid

Congo red (CR) was immobilized on a silica/aniline xerogel through electrostatic interaction. The dye is strongly retained and is not easily leached from the xerogel matrix. The material containing the adsorbed dye was used to prepare a carbon paste electrode and the electrochemical properties of the hybrid material were investigated using cyclic voltammetry and amperometry. The modified electrode was used to study the electrochemical oxidation of ascorbic acid. The adsorbed dye mediates ascorbic acid oxidation at the solid electrode surface‐solution interface at an anodic potential of 0.18 V at pH 7, in a 0.5 mol L^?1 KCl solution. This novel modified carbon paste electrode shows good analytical performance for the determination of ascorbic acid in commercial Vitamin C tablets.     

Synthesis of novel Schiff base doped sol–gel silicas

Sulfonamide Schiff bases were doped uniformly in silica sol–gels prepared from liquid precursors by a fast and easy way at room temperature and processed to form xerogels. Schiff bases are efficient chelating agents, bioactive and catalytically active compounds. The structures of the newly synthesized Schiff base doped xerogels were elucidated by their physical (morphology, surface area, porosity), spectral (FTIR) and analytical (CHNSO/Si) data. The powder X-ray diffraction studies were carried out to confirm the formation of single phase. Characterization confirmed that Schiff base molecules are entrapped inside the pores as well as physically bound onto the silica surface. All Schiff base doped xerogels are stable mesoporous materials showing hydrophilic properties. Loadings of Schiff bases from 0.10 to 0.23 g/g of xerogel were obtained resulting amorphous materials. The doping of Schiff bases with xerogel caused change in surface area, pore volume and pore diameter of xerogel without damaging the main framework of siliceous skeleton. Morphology and colour of xerogel was also changed after doping. The entrapment of Schiff bases in xerogel caused increase in their decomposition temperatures. The final Schiff base doped xerogels show remarkable thermal stability.     

Wet sol–gel silica matrices as delivery devices for phenytoin

Wet sol–gel silica matrices produced under different hydrolysis conditions were used as delivery devices to the active principle of an antiepileptic drug (phenytoin sodium), encapsulated during the condensation stage. Post-incorporation into dry silica powder was an alternative loading procedure. It was proven by infrared spectroscopy that neither the silica network nor the drug loose integrity by encapsulation. The kinetics of in vitro drug release was studied at 37 °C, to water and to artificial cerebrospinal fluid (ACSF). Emphasis has been given to the release to ACSF under dynamic conditions (with fluid renovation, emulating what occurs in the brain). Different delivery regimes were identified and correlated with the loading method and the matrix structure. Matrices with lower total porosity and smaller average pore size proved to be better for a long term release. Renovation of ACSF is relevant to assure a constant concentration of phenytoin in the vicinity of the device.     

New Bioactive Ceramics Obtained by Heat Treatment of Modified Polymeric Precursors

Summary: The aim of this work was to obtain pseudowollastonite-based ceramics and to determine its bioactive features. The materials were obtained by new method, namely thermal treatment of ceramic active fillers-containing polysiloxane polymeric precursor. As active fillers, commercially available Ca(OH)₂ and silica nanopowders (SiO₂) were used. The phase composition of ceramic products were analysed by the means of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD). The microstructure of ceramic products were studied by scanning electron microscopy (SEM) with EDS point analysis. The bioactivity was determined in “in vitro” conditions, by immersing of ceramic samples in simulated body fluid (SBF). The results presented in this work indicate that heat treatment of active fillers-containing polysiloxane precursor is an alternative method for receiving of pseudowollastonite-containing materials. Such obtained samples demonstrate bioactivity in “in vitro” conditions.     

Decomposition processes of nickel hydroxide

The dehydration processes of nickel hydroxide were studied by means of thermogravimetry in a temperature range from 300 to 900 K. The kinetics of the low-temperature dehydroxylation (≈300–600 K) was studied under non-isothermal conditions. A model-free method was used to calculate the activation energy and to analyze the stepwise checking; the non-linear regression method was applied to calculate the kinetic parameters of multi-stage decomposition reactions. The features of the dehydroxylation kinetics for the multi-stage process are explained by the formation and decomposition of hydrogel and xerogel phases.     

A study of carboxylic-modified mesoporous silica in controlled delivery for drug famotidine

A series of pure silica MSU and carboxylic-modified MSU materials were prepared. The formation of mesoporous silica materials with terminal carboxylic groups on pore surface was performed by the acid-catalyzed hydrolysis of cyano to carboxylic. Then their potential applications in controlled drug delivery carriers were investigated. Drug famotidine was selected as a model molecule out of the consideration of the terminal amino groups in its molecule. The adsorption experiments show significant adsorption of famotidine on the carboxylic-modified MSU materials. And, the functionalization level of carboxylic groups has been found to be the key factor affecting the adsorption capacities of the modified MSU materials for famotidine. Subsequently, three kinds of release fluids, including simulated gastric medium, simulated intestinal medium, and simulated body fluid, were used to test the famotidine release rate from the carboxylic-modified MSU material. Obvious delayed effect has been observed for the famotidine release from the carboxylic-modified mesoporous silica material under the in vitro assays.     

Partial crystallization in exotic phase stishovite of amorphous silica xerogels induced by incorporation of chlorophyll species

Using the Rietveld refinement, we analyze the structural evolution under thermal treatment of silica xerogel samples with incorporation of extract from frozen spinach leaves, prepared by sol?Cgel method with low molar ratio (R) of water to TEOS of R?=?1, and R?=?5. Partial crystallization of silica xerogel in the form of stishovite has been obtained at atmospheric pressure conditions and temperatures of 200?°C, they both, very lower than those specified by the phase diagram, in samples containing chlorophyll aggregates dispersed in amorphous silica. The results show that the incorporation of spinach extracts leave together with low water contents induce devitrification of the silica matrix in exotic phase stishovite.     

溶胶-凝胶法制备Ni-SiO2催化剂的表征与性能

以正硅酸乙酯和硝酸镍为原料,采用溶胶-凝胶法,将硝酸镍分别溶于水和乙醇制得凝胶,分别经超临界干燥和常规干燥制备了一系列Ni-SiO2气凝胶和干凝胶催化剂,运用BET、XRD、TPR、IR、H2-TPD和活性评价等方法对催化剂的物理化学性质和催化间二硝基苯加氢性能进行研究.结果表明,Ni-SiO2气凝胶催化剂均具有较高的比表面积,但由于金属镍烧结导致活性比表面积较小,加氢性能较差;以乙醇为溶剂制备的干凝胶催化剂的镍物种分散度较高,但镍与载体之间的相互作用过强,致使催化剂的还原度降低,活性组分利用率下降;以水为溶剂制备的干凝胶催化剂具有较高的活性比表面积,表现出很高的催化活性和选择性.     

非表面活性剂溶胶凝胶法制备介孔干胶包埋活酵母

通过非表面活性剂溶胶凝胶法,采用海藻糖和甘油既作为保护剂又作为造孔剂,并使用羟乙基纤维素(HEC)作为添加剂以减轻凝胶过程中的收缩,成功地将酵母原位包埋在具有介孔结构的干胶中,维持了酵母的存活并探索了包埋酵母的代谢动力学与材料孔径参数改良的相关性.选择四乙氧基硅烷(TEOS)和甲基三乙氧基硅烷(MTES)共同作为前驱体,并将湿胶(含水量60%)转变为干胶(含水量10%)以增强材料,部分实现了游离酵母的抑制.通过单轴抗压强度测试说明干胶的单轴压缩强度整体上是湿胶的13倍,最低可达7.13 MPa.由平板计数法算得溶胶中的酵母浓度为1.5×108mL-1,折算成干胶粉末则为6.4×108g-1.通过对材料进行比表面积及孔隙分析和代谢动力学表征,发现了包埋酵母的代谢动力学与材料孔径参数的相关性.通过非表面活性剂法制得的干胶的比表面积可达800 m2g-1,孔体积可达0.44 cm3g-1,孔径可达2.7 nm.在此条件下,采用独立取样的统计方法,对无游离酵母的样品点进行代谢动力学表征,包埋酵母60 h内可以代谢掉发酵液中89%的葡萄糖.     

Bis‐clickable Mesoporous Silica Nanoparticles: Straightforward Preparation of Light‐Actuated Nanomachines for Controlled Drug Delivery with Active Targeting

Bis(clickable) mesoporous silica nanospheres (ca. 100 nm) were obtained by the co‐condensation of TEOS with variable amounts (2–5 % each) of two clickable organosilanes in the presence of CTAB. Such nanoparticles could be easily functionalized with two independent functions using the copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction to transform them into nanomachines bearing cancer cell targeting ligands with the ability to deliver drugs on‐demand. The active targeting was made possible after anchoring folic acid by CuAAC click reaction, whereas the controlled delivery was performed by clicked azobenzene fragments. Indeed, the azobenzene groups are able to obstruct the pores of the nanoparticles in the dark whereas upon irradiation in the UV or in the blue range, their trans‐to‐cis photoisomerization provokes disorder in the pores, enabling the delivery of the cargo molecules. The on‐command delivery was proven in solution by dye release experiments, and in vitro by doxorubicin delivery. The added value of the folic acid ligand was clearly evidenced by the difference of cell killing induced by doxorubicin‐loaded nanoparticles under blue irradiation, depending on whether the particles featured the clicked folic acid ligand or not.     

Preparation, thermal decomposition and lifetime of Eu(III)-phenanthroline complex doped xerogel

The main purpose of this work is proposing a new method of using non-isothermal formal kinetics analysis to predict the lifetime of luminescent complex materials. The Eu(III)-phenanthroline complex doped xerogel has been in situ synthesized by a catalyst-free sol-gel method. The photoluminescence spectra and TG curves of the xerogel verify the formation and decomposition of Eu(III)-phenanthroline complex in xerogel. The decomposition of the xerogel formally occurs in three steps. The Friedman and FWO isoconversional methods and multivariate non-linear regression method are used for formal kinetic analysis. The overall decomposition process below 800 °C is fitted by three-step consecutive reaction. The best fitted model for each step is F_n (n order reaction, the corresponding function f(α) is (1 − α)ⁿ). Correlation coefficient is 0.99956. The lifetime values of xerogel at different temperatures are predicted based on non-isothermal kinetic models by the 5% decomposition of europium organic complex.     

Thermoresponsive Copolymer/SiO2 Nanoparticles with Dual Functions of Thermally Controlled Drug Release and Simultaneous Carrier Decomposition

The preparation of thermoresponsive drug carriers with a self‐destruction property is presented. These drug carriers were fabricated by incorporation of drug molecules and thermoresponsive copolymer, poly(N‐isopropylacrylamide‐co‐acrylamide), into silica nanoparticles in a one‐pot preparation process. The enhanced drug release was primarily attributed to faster molecule diffusion resulting from the particle decomposition triggered by phase transformation of the copolymer upon the temperature change. The decomposition of the drug carriers into small fragments should benefit their fast excretion from the body. In addition, the resulting drug‐loaded nanoparticles showed faster drug release in an acidic environment (pH 5) than in a neutral one. The controlled drug release of methylene blue and doxorubicin hydrochloride and the self‐decomposition of the drug carriers were successfully characterized by using TEM, UV/Vis spectroscopy, and confocal microscopy. Together with the nontoxicity and excellent biocompatibility of the copolymer/SiO₂ composite, the features of controlled drug release and simultaneous carrier self‐destruction provided a promising opportunity for designing various novel drug‐delivery systems.     

Preparation of low-density 90Y microspheres consisting of mesoporous silica core/yttria shell: a potential therapeutic agent for hepatic tumors

A new low-density silica core/yttria shell microspheres was developed for medical purposes. For preparing the core of this material, sol-emulsion-gel method was used. It was then calcined at 1,000 °C to increase the strength of the mesoporous beads. After cooling, it was added into a solution containing the mixture of yttrium chloride and urea. Under these circumstances, yttrium chloride can decompose to yttrium basic carbonate particles by the gradual hydrolysis of urea. These particles are able to deposit on the surface of mesoporous silica beads. Different coated samples were prepared under various pH, temperature and stirring conditions. Samples were heated to convert yttrium basic carbonate to yttria. The resulting silica core/yttria shell microspheres was characterized by laser diffractometer, scanning electron and optical microscopy techniques. It was found the pH of silica sols, aging time and Span-80 play important role in the stage of mesoporous bead preparation. Furthermore, the findings showed the heating of core/shell microspheres was essential for the ultimate strength of the shell. The in vitro chemical durability tests showed the release of yttrium ion in two simulated body fluids at pH 6 and 7 was negligible after 4 weeks.     

Silica xerogels as a delivery system for the controlled release of different molecular weight heparins

In this work, we investigated a sol–gel derived silica matrix as a delivery system for the prolonged release of different molecular weight heparins, which allows the glycosaminoglicons to retain their whole biological activity. Several xerogels were obtained by embedding different molecular weight heparins into matrices prepared by using different amount of NH₄OH as a catalyst during gel formation. Gel synthesis parameters, drug release properties, and xerogels surface area were evaluated. Unfractionated, low and oligo-molecular weight heparins were embedded into xerogels and the effect of the molecular weight on the release kinetics and the retained biological activity has been investigated. The results show that the surface area of the matrix is a determinant parameter affecting drug release kinetics. This structural feature can be modified by varying the catalyst tetraethoxysilane molar ratio used during the matrix synthesis. In most cases release kinetics fitted the Higuchi diffusive model and a lower diffusion rate was observed from silica matrices characterized by a smaller surface area. In the case of matrices with lower surface area, loaded with unfractionated heparin, zero order kinetics was observed. In this paper, we have defined a heparin release silica xerogel system and we have pointed out how modulation of its synthesis parameters allows adjusting the release of heparin according to therapeutic needs.