Gel Encapsulation Research Articles

Chitosan-silica hybrid nanosorbents for oil removal from water

Water pollution caused by oil spills is an environmental problem that raises concerns all over the world. Sorbent materials are of great importance for the removal of the remained oil after skimming operation. Nevertheless owing to reduced size, most sorbents are difficult to collect from water and therefore there is need to develop effective oil sorbents that could be easily separated from aquatic environments. Herein new magnetic nanosorbents composed of magnetite nanoparticles functionalized with chitosan hybrid siliceous shells were successfully prepared using a one-step sol–gel encapsulation method. As a proof of concept, these nanosorbents were tested in the magnetically assisted removal of non-polar organic solvents from water. The characterization of the materials using FTIR spectroscopy, solid-state 29Si and 13C NMR spectroscopy and elemental microanalysis confirmed the extensive modification of the particles’ shells with chitosan molecules covalently linked to the siliceous domains. These hybrid particles could efficiently adsorb various non-polar organic solvents from water, a behavior that was ascribed to the presence of chitosan macromolecules grafted at the surface of the particles. This is a new type of sorbent with potential application in the removal of oil from water using magnetic separation technologies.

Sol-gel encapsulation of pullulanase in the presence of hybrid magnetic (Fe3O4-chitosan) nanoparticles improves thermal and operational stability.

Pullulanase was sol-gel encapsulated in the presence of magnetic chitosan/Fe3O4 nanoparticles. The resulting immobilized pullulanase was characterized by scanning electron microscopy, vibrating sample magnetometry, Fourier transform infrared spectroscopy and thermogravimetric analysis. The results showed that the addition of pullulanase created a more regular surface on the sol-gel matrix and an enhanced magnetic response to an applied magnetic field. The maximal activity retention (83.9%) and specific activity (291.7U/mg) of the immobilized pullulanase were observed under optimized conditions including an octyltriethoxysilane:tetraethoxysilane (OTES:TEOS) ratio of 1:2 and enzyme concentration of 0.484mg/mL sol. The immobilized enzyme exhibited good thermal stability. When the temperature was above 60 °C, the immobilized pullulanase showed significantly higher activity than the free enzyme (p < 0.01); enzyme immobilized by simple sol-gel encapsulation and co-immobilized by crosslinking-encapsulation retained 52 and 69% of their initial activity after 5h at 62 °C, respectively, compared to 11% for the free enzyme. Moreover, the stability of the pullulanase was improved by crosslinking-encapsulation, as the enzyme retained more than 85 and 81% of its original activity after 5 and 6 consecutive reuses, respectively, compared to 80 and 72% of its original activity for simple sol-gel encapsulated enzymes. This indicated the leakage of enzyme molecules through the pores of the gel was substantially abated by cross-linking. Such immobilized pullulanase provides high stability and ease of enzyme recovery, characteristics that are advantageous for applications in the food industry that involve continuous starch processing.

Optimization of fibrin gelation for enhanced cell seeding and proliferation in regenerative medicine applications

In order to improve the cell seeding efficiency and cell compatibility inside porous tissue scaffolds, a method of fibrin gel‐mediated cell encapsulation inside the scaffold was optimized. Disc‐type poly(d,l‐glycolic‐co‐lactic acid) (PLGA) scaffolds without a dense surface skin layer were fabricated using an established solvent casting and particulate leaching method as a model porous scaffold, which showed high porosity ranging from 90 ± 2% to 96 ± 2%. The thrombin and fibrinogen concentration as precursors of fibrin gel was varied to control the gelation kinetics as measured by rheology analysis, and optimized conditions were developed for a uniform fibrin gel formation with the target cells inside the porous PLGA scaffold. The fibroblast cell seeding accompanied by a uniform fibrin gel formation at an optimized gelation condition inside the PLGA scaffold resulted in an increase in cell seeding efficiency, a better cell proliferation, and an increase in final cell density inside the scaffold. Scanning electron microscopy images revealed that cells were better spread and grown by fibrin gel encapsulation inside scaffold compared with the case of bare PLGA scaffold. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Inhibiting electro-thermal breakdown of acrylic dielectric elastomer actuators by dielectric gel coating

Electrical breakdown of dielectric elastomer actuators (DEA) is very localized; a spark and a pinhole (puncture) in dielectric ends up with short-circuit. This letter shows that prevention of electrothermal breakdown helps defer failure of DEAs even with conductive-grease electrodes. Dielectric gel encapsulation or coating (Dow Corning 3-4170) helps protect acrylic elastomer (VHB 4905), making it thermally more stable and delaying its thermal oxidation (burn) from 218 °C to 300 °C. Dielectric-gel-coated acrylic DEAs can withstand higher local leak-induced heating and thus achieve higher dielectric strengths than non-coated DEAs do.

Improvement of catalytic activity of Candida rugosa lipase in the presence of calix[4]arene bearing iminodicarboxylic/phosphonic acid complexes modified iron oxide nanoparticles

In the present study, iron oxide magnetite nanoparticles, prepared through a co-precipitation method, were coated with phosphonic acid or iminodicarboxylic acid derivatives of calix[4]arene to modulate their surfaces with different acidic groups. Candida rugosa lipase was then directly immobilized onto the modified nanoparticles through sol–gel encapsulation. The catalytic activities and enantioselectivities of the two encapsulated lipases in the hydrolysis reaction of (R/S)-naproxen methyl ester and (R/S)-2-phenoxypropionic acid methyl ester were assessed. The results showed that the activity and enantioselectivity of the lipase were improved when the lipase was encapsulated in the presence of calixarene-based additives; the encapsulated lipase with the phosphonic acid derivative of calix[4]arene had an excellent rate of enantioselectivity against the (R/S)-naproxen methyl and (R/S)-2-phenoxypropionic acid methyl esters, with E=350 and 246, respectively, compared to the free enzyme. The encapsulated lipases (Fe-Calix-N(COOH)) and (Fe-Calix–P) showed good loading ability and little loss of enzyme activity, and the stability of the catalyst was very good; they only lost 6–11% of the enzyme’s activity after five batches.

Engineering of a silica encapsulation platform for hydrocarbon degradation using Pseudomonas sp. NCIB 9816-4.

Industrial application of encapsulated bacteria for biodegradation of hydrocarbons in water requires mechanically stable materials. A silica gel encapsulation method was optimized for Pseudomonas sp. NCIB 9816-4, a bacterium that degrades more than 100 aromatic hydrocarbons. The design process focused on three aspects: (i) mechanical property enhancement; (ii) gel cytocompatibility; and (iii) reduction of the diffusion barrier in the gel. Mechanical testing indicated that the compressive strength at failure (σf ) and elastic modulus (E) changed linearly with the amount of silicon alkoxide used in the gel composition. Measurement of naphthalene biodegradation by encapsulated cells indicated that the gel maintained cytocompatibility at lower levels of alkoxide. However, significant loss in activity was observed due to methanol formation during hydrolysis at high alkoxide concentrations, as measured by FTIR spectroscopy. The silica gel with the highest amount of alkoxide (without toxicity from methanol) had a biodegradation rate of 285 ± 42 nmol/L-s, σf = 652 ± 88 kPa, and E = 15.8 ± 2.0 MPa. Biodegradation was sustained for 1 month before it dropped below 20% of the initial rate. In order to improve the diffusion through the gel, polyvinyl alcohol (PVA) was used as a porogen and resulted in a 48 ± 19% enhancement in biodegradation, but it impacted the mechanical properties negatively. This is the first report studying how the silica composition affects biodegradation of naphthalene by Pseudomonas sp. NCIB 9816-4 and establishes a foundation for future studies of aromatic hydrocarbon biodegradation for industrial application.

Zwitterionic gel encapsulation promotes protein stability, enhances pharmacokinetics, and reduces immunogenicity

Advances in protein therapy are hindered by the poor stability, inadequate pharmacokinetic (PK) profiles, and immunogenicity of many therapeutic proteins. Polyethylene glycol conjugation (PEGylation) is the most successful strategy to date to overcome these shortcomings, and more than 10 PEGylated proteins have been brought to market. However, anti-PEG antibodies induced by treatment raise serious concerns about the future of PEGylated therapeutics. Here, we demonstrate a zwitterionic polymer network encapsulation technology that effectively enhances protein stability and PK while mitigating the immune response. Uricase modified with a comprehensive zwitterionic polycarboxybetaine (PCB) network exhibited exceptional stability and a greatly prolonged circulation half-life. More importantly, the PK behavior was unchanged, and neither anti-uricase nor anti-PCB antibodies were detected after three weekly injections in a rat model. This technology is applicable to a variety of proteins and unlocks the possibility of adopting highly immunogenic proteins for therapeutic or protective applications.

Immobilization of Proteins in Silica Gel: Biochemical and Biophysical Properties

The development of silica-based sol-gel techniques compatible with the retention of protein structure and function started more than 20 years ago, mainly for the design of biotechnological devices or biomedical appli- cations. Silica gels are optically transparent, exhibit good mechanical stability, are manufactured with different geometries, and are easily separated from the reaction media. Biomolecules encapsulated in silica gel normally re- tain their structural and functional properties, are stabilized with respect to chemical and physical insults, and can sometimes exhibit enhanced activity in comparison to the soluble form. This review briefly describes the chemistry of protein encapsula- tion within the pores of a silica gel three-dimensional network, the mechanism of interaction between the protein and the gel matrix, and its effects on protein structure, function, stability and dynamics. The main applications in the field of biosensor design are described. Special emphasis is devoted to silica gel encapsulation as a tool to selectively stabilize subsets of protein conformations for biochemical and biophysical studies, an application where silica-based encapsulation demonstrated superior performance with respect to other immo- bilization techniques.

Innovative low concentration PV systems with bifacial solar panels

Three different Low Concentration PV (LCPV) systems with bifacial PV panels were developed. Design of these systems is described in the article. The daily energy production of pseudo parabolic concentrator systems was enhanced by up to +167% in comparison with standard fixed PV panels. The operating temperature of PV panels in summer was +95°C so the silicone gel encapsulation technology was used to avoid reliability troubles.

Sol–gel microencapsulation of oil phase with Pickering and nonionic surfactant based emulsions

Sol–gel polycondensation was used to encapsulate two different kinds of core with a silica shell, i.e. castor oil which is considered as a model active agent, and bisphenol A bis(diphenyl phosphate), an insoluble liquid fire retardant. The influence of the nature of the emulsifier was also studied, i.e. Pickering emulsion based on the interface stabilization performed by the organization of solid nanoparticles was compared to a classical emulsion process using a non-ionic surfactant. The influence of both cores and emulsifiers on the stability of emulsion was studied by granulometric analysis, optical microscopy and macroscopic morphology (from nacked-eye observations). The sol–gel encapsulation efficiency was assessed by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. Finally, thermal stability of microcapsules was evaluated by thermogravimetric analysis (TGA). Results show that both Pickering and classical emulsions processing allow successful sol–gel encapsulation of castor oil and bisphenol A bis (diphenyl phosphate) with a satisfying thermal stability for textile application. However, the use of Pickering emulsion with nanoparticles provides more highly stable emulsions and promotes silica shell formation.

Sol–gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure–activity correlations in hybrid materials targeting Zn(II) antibacterial use

In the emerging issue of enhanced multi-resistant properties in infectious pathogens, new nanomaterials with optimally efficient antibacterial activity and lower toxicity than other species attract considerable research interest. In an effort to develop such efficient antibacterials, we a) synthesized acid-catalyzed silica-gel matrices, b) evaluated the suitability of these matrices as potential carrier materials for controlled release of ZnSO4 and a new Zn(II) binary complex with a suitably designed well-defined Schiff base, and c) investigated structural and textural properties of the nanomaterials. Physicochemical characterization of the (empty-loaded) silica-nanoparticles led to an optimized material configuration linked to the delivery of the encapsulated antibacterial zinc load. Entrapment and drug release studies showed the competence of hybrid nanoparticles with respect to the a) zinc loading capacity, b) congruence with zinc physicochemical attributes, and c) release profile of their zinc load. The material antimicrobial properties were demonstrated against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus) and negative (Escherichia coli, Pseudomonas aeruginosa, Xanthomonas campestris) bacteria using modified agar diffusion methods. ZnSO4 showed less extensive antimicrobial behavior compared to Zn(II)-Schiff, implying that the Zn(II)-bound ligand enhances zinc antimicrobial properties. All zinc-loaded nanoparticles were less antimicrobially active than zinc compounds alone, as encapsulation controls their release, thereby attenuating their antimicrobial activity. To this end, as the amount of loaded zinc increases, the antimicrobial behavior of the nano-agent improves. Collectively, for the first time, sol–gel zinc-loaded silica-nanoparticles were shown to exhibit well-defined antimicrobial activity, justifying due attention to further development of antibacterial nanotechnology.

A self-referencing biosensor for real-time monitoring of physiological ATP transport in plant systems.

The objective of this study was to develop a self-referencing electrochemical biosensor for the direct measurement of ATP flux into the extracellular matrix by living cells/organisms. The working mechanism of the developed biosensor is based on the activity of glycerol kinase and glycerol-3-phosphate oxidase. A stratified bi-enzyme nanocomposite was created using a protein-templated silica sol gel encapsulation technique on top of graphene-modified platinum electrodes. The biosensor exhibited excellent electrochemical performance with a sensitivity of 2.4±1.8 nA/µM, a response time of 20±13 s and a lower detection limit of 1.3±0.7 nM. The self-referencing biosensor was used to measure exogenous ATP efflux by (i) germinating Ceratopteris spores and (ii) growing Zea mays L. roots. This manuscript demonstrates the first development of a non-invasive ATP micro-biosensor for the direct measurement of eATP transport in living tissues. Before this work, assays of eATP have not been able to record the temporally transient movement of ATP at physiological levels (nM and sub-nM). The method demonstrated here accurately measured [eATP] flux in the immediate vicinity of plant cells. Although these proof of concept experiments focus on plant tissues, the technique developed herein is applicable to any living tissue, where nanomolar concentrations of ATP play a critical role in signaling and development. This tool will be invaluable for conducting hypothesis-driven life science research aimed at understanding the role of ATP in the extracellular environment.

ChemInform Abstract: Silica Sol‐Gel Chemistry: Creating Materials and Architectures for Energy Generation and Storage

AbstractReview: 67 refs.

A high-energy-density quasi-solid-state carbon nanotube electrochemical double-layer capacitor with ionogel electrolyte

This paper reports the fabrication of an electric double-layer supercapacitor that incorporates carbon nanotube electrodes with an ionogel electrolyte based on the sol–gel encapsulation of the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate. The quasi-solid nature of the ionogel electrolyte enables this supercapacitor to become a solid-state device, which overcomes the limitations of many high-performance supercapacitors, whose liquid-based electrolyte prohibits the realization of truly compact energy storage that is practical for various existing and emerging portable electronics. The device reported here combines the intrinsic high power of an electrochemical double-layer capacitor with the increased energy density associated with the wide voltage window of the ionogel. The device was characterized by a suite of electrochemistry techniques and demonstrated both high power and high energy density.

Crystallographic, optical and dielectric properties of gel grown praseodymium malonate single crystals

Single crystals of praseodymium malonate hexahydrate are grown by gel encapsulation technique.

Photosynthetic and extracellular production of glucosylglycerol by genetically engineered and gel-encapsulated cyanobacteria.

Glucosylglycerol (GG) has a range of potential applications in health, pharmacy, and cosmetics due to its physiological, protein-stabilizing, and antioxidative properties. In addition to chemical synthesis and enzymatic catalysis, GG can be produced as a protective osmolyte in salt-stressed bacteria, such as the cyanobacterium Synechocystis sp. PCC 6803. Here, we presented an efficient GG production and secretion by genetically modified and encapsulated Synechocystis cells grown in a semicontinuous manner. We improved the production and secretion of GG in Synechocystis by first disrupting both the ggtC and ggtD genes, which encode the subunits of a GG uptake transporter, as well as the ggpR gene, which encodes a repressor for GG synthesis. Then, we confirmed that the rapid GG release from salt-stressed cells of Synechocystis depended on the ion gradient across the cell membrane. Finally, we proved the feasibility of an agar gel encapsulation method in supporting cell growth and the GG production of Synechocystis under semicontinuous culturing conditions.

Single crystal growth by gel technique and characterization of lithium hydrogen tartrate

Single crystal growth of lithium hydrogen tartrate by gel encapsulation technique is reported. Dependence of crystal count on gel density, gel pH, reactant concentration and temperature are studied and the optimum conditions for these crystals are worked out. The stoichiometric composition of the grown crystals is determined using EDAX/AES and CH analysis. The grown crystals are characterized by X-ray diffraction, FTIR and Uv-Visible spectroscopy. It is established that crystal falls under orthorhombic system and space group P222 with the cell parameters as: a=10.971Å, b=13.125Å and c=5.101Å; α=90.5o, β=γ=90°. The morphology of the crystals as revealed by SEM is illustrated. Crystallite size, micro strain, dislocation density and distortion parameters are calculated from the powder XRD results of the crystal. UV–vis spectroscopy shows indirect allowed transition with an optical band gap of~4.83eV. The crystals are also shown to have high transmittance in the entire visible region. Dependence of dielectric constant, dielectric loss and conductivity on frequency of the applied ac field is analyzed. The frequency-dependent real part of the complex ac conductivity is found to follow the universal dielectric response: σac (ω)~ωs. The trend in the variation of frequency exponent with frequency corroborates the fact that correlated barrier hopping is the dominant charge-transport mechanism in the present system.

Silica sol–gel anchoring on aluminum pigments surface for corrosion resistance based on aluminum oxidized by hydrogen peroxide

The waterborne aluminum pigments were prepared by sol–gel encapsulation method using tetraethoxysilane and γ-aminopropyl triethoxysilane as precursors with H2O2 as anchoring agent. Fourier transformation infrared and X-ray diffraction results indicated that the boehmite formed by H2O2 oxidizing aluminum can successfully reacted with silanol to make the silica sol–gel film anchored on the aluminum surface in the encapsulation process. The reaction conditions were optimized and the products were characterized by scanning electron microscopy, optical microscopy and stability test. It was found that when controlling the pH value of encapsulation media at about 9.5 and H2O2 concentration of 5.1 × 10−5 mol/m2 of aluminum flake surfaces, the boehmite on aluminum flake surfaces carried a strong positive charge and the silica sol–gel film carried a negative charge, which conduct the most anchorage efficiency. A crack free, smooth and dense coating was formed and exhibited best corrosion resistance on the aluminum flake surfaces.

Silica sol–gel anchoring on aluminum pigments surface for corrosion protection based on aluminum oxidized by copper ammonia complex ion

To reduce the volatile organic compounds emission led to the development of waterborne coatings. Correspondingly, waterborne aluminum pigment is desirable to develop. Here, the waterborne aluminum pigments were prepared by sol–gel encapsulation method using tetraethoxysilane and γ-aminopropyl triethoxysilane as precursors with [Cu(NH3)4]2+ as anchoring agent. Fourier transformation infrared and X-ray diffraction results showed that the boehmite formed by [Cu(NH3)4]2+ oxidizing aluminum can successfully react with silanol to make the silica sol–gel film anchored on the aluminum surface in the encapsulation process. The reaction conditions were optimized and the products were characterized by scanning electron microscopy, optical microscopy and stability test. It was found that control the pH of encapsulated media between 8.77 and 10.10, the boehmite on aluminum flake surfaces carried a strong positive charge and the silica sol–gel film carried a negative charge, which conduct the most anchorage efficiency, and the waterborne aluminum pigment exhibit best stability.

Enantioselective hydrolysis of (R,S)-Naproxen methyl ester using Candida rugosa lipase with calix[4]arene derivatives

Candida rugosa lipase has been immobilized on a variety of calix[4]arene derivatives using the sol–gel encapsulation technique, and the catalytic activities of the resulting encapsulated lipases towards the hydrolysis of p-nitrophenyl palmitate and the hydrolytic kinetic resolution of racemic Naproxen methyl ester were evaluated using standard techniques. The results revealed that the calix[4]arene-based immobilized encapsulated lipases 5-CRL and 6-CRL gave higher levels of enantioselectivity and conversion than the free encapsulated lipase.