Storage In Aqueous Media Research Articles

Study of CO2 absorption by low salinity aqueous solutions of specific salts in the absence and presence of carbonate rocks

Fossil-fuels combustion is currently the main driving force of industrialization; however, it has resulted in CO2 emission that challenges sustained socioeconomic growth. One way to reduce CO2 emissions is to sequester it into saline aquifers or depleted hydrocarbon reservoirs. In this study, CO2 absorption in different aqueous salt solutions is elucidated. CO2 absorption in different salines is also simulated using PHREEQC software to predict the concentration of different species formed by saline-CO2 interactions at equilibrium. Investigated parameters include concentration of different salts at low salinity condition, type of cations and anions, temperature, and carbonate rock on the CO2 absorption and storage in aqueous media at high pressures. Results revealed that both initial absorption rate and final absorbed amount of CO2 in aqueous salt solution decay in the order of MgSO4 > Na2SO4 > CaCl2 > MgCl2 > NaCl. For a given anion in the dissolved salt, the presence of divalent cations promotes CO2 absorption more than that of monovalent cations. Also, for equivalence cations the one with a higher charge density promotes CO2 absorption. It is also evident that for a given cation in the dissolved salt the associated anion which has a higher charge density hinders CO2 absorption more than that with a lower charge density. Similar pattern is maintained for CO2 absorption in saturated carbonate rock. PHREEQC simulations revealed that concentrations of precipitated carbonate salts in CO2-saturated Na2SO4 and NaCl brines are higher than those of the other brines. Moreover, increasing temperature increases concentration of precipitated carbonate salts in CO2-saturated MgSO4, CaCl2, and MgCl2 brines while it has an opposite effect on precipitated carbonate salts formed due to CO2 absorption in Na2SO4 and NaCl brines.

Cyclodextrin-Calcium Carbonate Micro- to Nano-Particles: Targeting Vaterite Form and Hydrophobic Drug Loading/Release

Tailor-made and designed micro- and nanocarriers can bring significant benefits over their traditional macroscopic counterparts in drug delivery applications. For the successful loading and subsequent release of bioactive compounds, carriers should present a high loading capacity, trigger release mechanisms, biodegradability and biocompatibility. Hydrophobic drug molecules can accumulate in fat tissues, resulting in drawbacks for the patient's recovery. To address these issues, we propose to combine the advantageous features of both host molecules (cyclodextrin) and calcium carbonate (CaCO3) particles in order to load hydrophobic chemicals. Herein, hybrid cyclodextrin-CaCO3 micro- to nano-particles have been fabricated by combining Na2CO3 solution and CaCl2 solution in the presence of an additive, namely poly (vinylsulfonic acid) (PVSA) or glycerol (gly). By investigating experimental parameters and keeping the Na2CO3 and CaCl2 concentrations constant (0.33 M), we have evidenced that the PVSA or gly concentration and mixing time have a direct impact on the final cyclodextrine-CaCO3 particle size. Indeed, by increasing the concentration of PVSA (5 mM to 30 mM) or gly (0.7 mM to 4 mM) or the reaction time (from 10 min to 4 h), particles with a size of 200 nm could be reached. Interestingly, the vaterite or calcite form could also be selected, according to the experimental conditions. We hypothesised that the incorporation of PVSA or gly into the precipitation reaction might reduce the nucleation rate by sequestering Ca2+. The obtained particles have been found to keep their crystal structure and surface charge after storage in aqueous media for at least 6 months. In the context of improving the therapeutic benefit of hydrophobic drugs, the developed particles were used to load the hydrophobic drug tocopherol acetate. The resulting particles are biocompatible and highly stable in a physiological environment (pH 7.4, 0.15 M NaCl). A selective release of the cargo is observed in acidic media (pH lower than 5).

Quantitative Regulation of Interlayer Space of NH4 V4 O10 for Fast and Durable Zn2+ and NH4 + Storage.

Layered vanadium-based oxides are the promising cathode materials for aqueous zinc-ion batteries (AZIBs). Herein, an in situ electrochemical strategy that can effectively regulate the interlayer distance of layered NH4 V4 O10 quantitatively is proposed and a close relationship between the optimal performances with interlayer space is revealed. Specifically, via increasing the cutoff voltage from 1.4, 1.6 to 1.8V, the interlayer space of NH4 V4 O10 can be well-controlled and enlarged to 10.21, 11.86, and 12.08 Å, respectively, much larger than the pristine one (9.5 Å). Among them, the cathode being charging to 1.6V (NH4 V4 O10 -C1.6), demonstrates the best Zn2+ storage performances including high capacity of 223mA h g-1 at 10 A g-1 and long-term stability with capacity retention of 97.5% over 1000 cycles. Such superior performances can be attributed to a good balance among active redox sites, charge transfer kinetics, and crystal structure stability, enabled by careful control of the interlayer space. Moreover, NH4 V4 O10 -C1.6 delivers NH4 + storage performances whose capacity reaches 296mA h g-1 at 0.1 A g-1 and lifespan lasts over 3000 cycles at 5 A g-1 . This study provides new insights into understand the limitation of interlayer space for ion storage in aqueous media and guides exploration of high-performance cathode materials.

Pillaring of a conductive polymer in layered V2O5 boosting ultra-fast Zn2+/H+ storage in aqueous media

Aqueous secondary zinc-ion batteries are promising candidates to replace lithium-ion batteries for large-scale energy storage, due to their high safety and low cost. However, the developed cathodes materials are facing low capacity or low cycle life due to sluggish diffusion kinetics. Therefore, the design of a cathode with ultrafast ion diffusion kinetics remains a great challenge. Here, we propose an in-situ intercalation strategy of polypyrrole to improve the cation diffusion kinetics of V2O5. The polypyrrole as a guest significantly enlarges the interlayer spacing, paving the ‘‘superhighway’’ for cation diffusion. In addition, thanks to the unique π-conjugated structure, polypyrrole can shield the electrostatic force of Zn2+ and the host oxygen-sublattice. The energy storage mechanism of the cathode was shown to be a stepwise H+/Zn2+co-intercalation by means of galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS) and ex situ X-ray diffraction (XRD). Based on the above advantages, the polypyrrole-intercalated V2O5 demonstrates high capacities and excellent cycling performance (220 mA h g−1 after 2000 cycles at 10 A g−1).

Design of Stimuli-Responsive Dynamic Covalent Delivery Systems for Volatile Compounds (Part 2): Fragrance-Releasing Cleavable Surfactants in Functional Perfumery Applications.

Amphiphilic imines prepared by condensation of a hydrophobic fragrance aldehyde with a hydrophilic amine derived from a poly(propylene oxide) and poly(ethylene oxide) diblock copolymer were investigated as cleavable surfactant profragrances in applications of functional perfumery. In water, the cleavable surfactants assemble into micelles that allow solubilization of perfume molecules that are not covalently attached to the surfactant. Dynamic headspace analysis on a glass surface showed that solubilized perfume molecules evaporated in a similar manner in the presence of the cleavable surfactant as compared with a non-cleavable reference surfactant. Under application conditions, the cleavable surfactant imine hydrolysed to release the covalently linked fragrance aldehyde. The profragrances were stable during storage in aqueous media, and upon dilution showed a blooming effect for the hydrolytical fragrance release and a more balanced performance of a solubilized perfume by retaining the more volatile fragrances and boosting the evaporation of the less volatile fragrances.

Green synthesis of time-stable palladium nanoparticles using microfluidic devices

A systematic comparison between batch and continuous systems was performed for the synthesis of palladium nanoparticles (PdNPs). An eco-friendly protocol was used in which glucose and starch were the reducer and capping agents, respectively. The material morphology, particle size distribution and catalytic activity for the reduction of 4-nitrophenol of both suspensions was studied in two states: (i) fresh and (ii) 7 months-stored. XRD, UV–vis, FTIR and TEM techniques were used for the material characterization. The catalytic results together with the characterization evidences lead to the conclusion that palladium nanoparticles obtained with the microreactor give rise to more stable suspensions with smaller size and narrower particle size distribution, as compared to the ones obtained with the batch system (continuous system: 4.40 ± 1.68 nm vs batch method: 7.18 ± 21.14 nm for the fresh samples). In addition, the TOF of the PdNPs prepared using the microfluidic system proved to be better than the resulted from the suspension prepared using the batch system (749 h-1 and 505 h−1, respectively). On the other hand, the higher stability of the material obtained in the microreactor could be confirmed, as the TOF value remained constant even after 7 months of storage in aqueous media (753 h−1 for the microreactor vs 336 h-1 for the batch set-up).

Evolution of nanocrystal size distribution in porous silicon nanoparticles during storage in aqueous media: X-ray diffraction analysis

X-ray diffraction studies of electrochemically prepared mesoporous and microporous silicon particles were carried out to monitor their dissolution in aqueous media. The dissolution process was found to result in either decreasing or an increasing of the mean size of silicon nanocrystallites in mesoporous and microporous samples, respectively. The evolution of nanocrystallite size was related by polydispersity of the initial size distribution and it was described by using a model of “shrinking spheres.” The proposed approach was used to confirm an effect of biopolymer surrounding of silicon nanocrystallites on their stability in aqueous medium. The obtained results and developed model can be useful for potential biomedical applications of porous silicon.

Carbon nanotube cloth for electrochemical charge storage in aqueous media

We report the study of recharging behavior of CNT cloth material, which allows a large-scale and relatively cheap fabrication, as well as rather simple electrode design. Oxidative chemical purification procedure is applied prior electrode preparation to decrease the content of iron, which served as the catalyst for CNT fabrication. We demonstrate that this procedure, as well as anodic oxidation, results in the increase of CNT specific capacity in both alkaline and acidic aqueous solutions. Recharging rate is less sensitive to oxidation and remains fast enough: at 1 V/s scan rate the capacities in both acidic and alkaline solutions are close to 25 F/g. These characteristics allow to consider CNT cloth as a future stable backbone for materials of aqueous supercapacitors.

Hydrogels with Modulated Ionic Load for Mammalian Cell Harvesting with Reduced Bacterial Adhesion.

In this manuscript, we describe the fabrication of hydrogel supports for mammalian cell handling that can simultaneously prevent materials from microbial contamination and therefore allow storage in aqueous media. For that purpose, hydrogels based on the antifouling polymer polyvinylpyrrolidone (PVP) were functionalized with different ionic groups (anionic, cationic, or two types of zwitterions). In order to prevent bacterial adhesion in the long-term, we took advantage of the synergistic effect of inherently antifouling PVP and additional antifouling moieties incorporated within the hydrogel structure. We evaluated, in a separated series of experiments, both the capability of the materials to act as supports for the growth of mammalian cell monolayers for transplantation (using C-166-GFP endothelial cell line), as well their antifouling properties against Staphylococcus aureus, were studied. All of the hydrogels are structurally pseudodouble networks with high swelling (around 90%) and similar mechanical properties (in the low range for hydrogel materials with Young modulus below 1250 kPa). With some differences, all the charged hydrogels were capable of hosting mouse endothelial cell line C166-GFP to confluence, as well as a monolayer detachment and transplantation through simple mechanical agitation. On the contrary, the uncharged hydrogel was not capable to detach a full monolayer for transplantation. Bacterial adhesion and proliferation was highly sensitive to the functionality (type of charge and density). In particular, we evidenced that monomers bearing zwitterionic sulfobetaine groups, those negatively charged as well as "electro neutral" hydrogels fabricated from stoichiometric amounts of positive and negative units, exhibit excellent antifouling properties both at initial adhesion times and during longer periods up to 72 h.

Biochemical piezoresistive sensors based on hydrogels for biotechnology and medical applications

Abstract. Many conventional analysis techniques achieve a high-detection sensitivity; however, they are equipment or time expensive due to a multi-step procedure. Sensor concepts, introduced in this work, using piezoresistive pressure sensor chips with integrated analyte-sensitive hydrogels enable inexpensive and robust biochemical sensors, which are miniaturized and in-line capable. For these sensor setups, it is important to optimize current established analyte-sensitive, reversible and biocompatible hydrogels for pH and glucose monitoring of chemical and biochemical processes. Therefore, low-viscous monomer mixtures based on hydroxypropyl methacrylate (HPMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), tetraethylene glycol dimethacrylate (TEGDMA) and ethylene glycol (EG) were prepared in molar ratios of 70∕30∕01∕20, 60∕40∕01∕20 and 60∕40∕02∕20, respectively. Redox-polymerization of these pre-gel solutions were realized with N,N,N′,N′-tetramethylethylenediamine and ammonium persulfate. The reversible pH-sensitive swelling behavior of hydrogels with compositions were compared. By using the photoinitiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, the free radical photopolymerization could be implemented leading to an increase of the swelling degree (SG). Glucose-sensitive hydrogels were prepared via immobilization of glucose oxidase in HPMA–DMAEMA–TEGDMA–EG hydrogel discs. These showed increasing swelling degrees with higher glucose concentrations in aqueous media and a reversible swelling behavior. The synthesized hydrogels were integrated in different piezoresistive sensors of different designs. The pH-depending course of the output voltage of a dip sensor with photopolymerized 60∕40∕02∕20 hydrogel was studied in detail. Besides the usage of a dip sensor, two implantable, parylene C-coated setups are presented. The implantable sensor with long isolated gold bond wires was proved to be functional even after storage in aqueous media for several days.

Soluble hydrolysis-resistant composite formulation of curcumin containing α-glucosyl hesperidin and polyvinylpyrrolidone

We developed a formulation for increasing the water solubility of curcumin (CUR). The new formulation also protected CUR from hydrolytic degradation. A ternary system of CUR/α-glucosyl hesperidin (hesperidin-G)/polyvinylpyrrolidone (PVP) K-30 was prepared by the solvent evaporation method. Although the binary sample of CUR/hesperidin-G showed increased solubility, the effect disappeared within a few hours of storage in aqueous media. In contrast, the ternary system of CUR/hesperidin-G/PVP K-30 (1:10:5, weight ratio) exhibited a long-lasting solubility increase. This supersaturated CUR solution remained stable even after 24h, as shown by the 2600-fold increase in solubility compared with untreated CUR. The stability of CUR to hydrolytic degradation under alkaline conditions was improved dramatically by adding hesperidin-G and PVP K-30, whereas untreated CUR completely decomposed after a few minutes. The solubilizing effect may arise from the formation of an amorphous solid dispersion, including CUR, and from complex formation between CUR, hesperidin-G, and PVP K-30 in aqueous media. The complex may also protect CUR from hydrolytic degradation.

Multichannel 3D plotting for complex tissue equivalents and implants for defects at tissue interfaces

Event Abstract Back to Event Multichannel 3D plotting for complex tissue equivalents and implants for defects at tissue interfaces Michael Gelinsky1, Ashwini R. Akkineni1, Kathleen Schütz1, Tilman Ahlfeld1, Yvonne Förster1, Falko Doberenz1, Maja Brückner1 and Anja Lode1 1 TU Dresden, Centre for Translational Bone, Joint and Soft Tissue Research, Germany Introduction: Additive Manufacturing (AM) opens up fascinating possibilities for the generation of implants and tissue engineering (TE) constructs. 3D plotting, i. e. extrusion of pasty biomaterials at room or physiological temperature, allows utilization of a great variety of materials and incorporation of sensitive substances like drugs, growth factors or even living cells. Multichannel-3D plotting enables processing of more than one material within one construct and therefore manufacturing of complex specimens, e.g. for application at tissue interfaces and/or generation of improved tissue equivalents which closer mimic natural tissues than conventional TE strategies. We wanted to investigate whether we can load calcium phosphate cement (CPC) pastes with growth factors and combine them with biopolymer hydrogels for AM of complex scaffolds. Further questions were whether live cells can be included within the hydrogels and both materials combined in joint strands with core/shell morphology. Materials and Methods: For 3D plotting BioScaffolder 2.1 from GeSiM (Grosserkmannsdorf, Germany) was used. As CPC paste an hydroxyapatite (HA) forming α-tricalcium phosphate-based precursor mixture, suspended in a biocompatible oily phase[1], was utilized. Blends of alginate (3%) and methylcellulose (9%)[2] were used as hydrogel material. Before scaffold preparation, all materials were sterilized. After plotting of the scaffolds in air they were stabilized by immersion in 100 mM CaCl2 solution. As growth factor, VEGF (vascular endothelial GF) was used and human mesenchymal stroma cells (hMSC) for embedding experiments. For preparation of core/shell strands self-made double-nozzle extruders were applied, mounted onto the 3D plotter. The scaffolds were fully characterized including morphology, mechanical properties, VEGF release (ELISA and bioassay), cell survival (live/dead and MTT staining) and osteogenic differentiation. One type of scaffold was tested in a pilot animal study in a 5 mm femur defect in rat, stabilized with a metal plate. Results and Discussion: Combination of CPC and biopolymer hydrogel strands within one scaffold was possible. Immersion of the scaffolds after plotting in calcium ion containing media led to CPC setting and simultaneously to alginate crosslinking. Methylcellulose which improved viscosity and therefore plottability of the hydrogel paste slowly dissolves during further storage in aqueous media, creating an additional microporosity (besides the macropores = space between the strands). We could demonstrate that VEGF could be successfully incorporated in CPC as well as hydrogel strands; for mixing with CPC binding of the GF to chitosan microparticles was advantageous. GF release was much faster from hydrogel compared to CPC – and retained biological activity of released VEGF was proven with an bioassay using endothelial cells. Human MSC could be mixed into the biopolymer hydrogel blend and survived extrusion, scaffold crosslinking and additional 3 weeks of culture. Osteogenic differentiation could be induced by applying common supplements. In addition, the animal pilot study proved biocompatibility of the new type of scaffold and biological activity of the released VEGF in vivo. A novel type of core/shell strands with a stiff shell (CPC) and soft core (hydrogel) and 3D scaffolds made thereof could be manufactured using double-nozzle extruders. Such material combinations within one extruded strand open up new possibilities for dual drug loading and release. Conclusion: Multichannel 3D plotting is a versatile AM technology and allows combination of such different biomaterials like a calcium phosphate cement and a biopolymer hydrogel. Due to the mild processing conditions sensitive components like GF and living cells can be incorporated. Of special interest is the combination of different biomaterials in strands with core/shell morphology. This technology can be further developed towards more complex tissue and organ models. Saxon State Ministry for Higher Education, Research and the Arts (SMWK) for funding

Characterization of Self-Assembled Polyelectrolyte Complex Nanoparticles Formed from Chitosan and Pectin

Chronic wounds continue to be a global healthcare concern. Thus, the development of new nanoparticle-based therapies that treat multiple symptoms of these "non-healing" wounds without encouraging antibiotic resistance is imperative. One potential solution is to use chitosan, a naturally antimicrobial polycation, which can spontaneously form polyelectrolyte complexes when mixed with a polyanion in appropriate aqueous conditions. The requirement of at least two different polymers opens up the opportunity for us to form chitosan complexes with an additional functional polyanion. In this study, chitosan:pectin (CS:Pec) nanoparticles were synthesized using an aqueous spontaneous ionic gelation method. Systematically, a number of parameters, polymer concentration, addition order, mass ratio, and solution pH, were explored and their effect on nanoparticle formation was determined. The size and surface charge of the particles were characterized, as well as their morphology using transmission electron microscopy. The effect of polymer concentration and addition order on the nanoparticles was found to be similar to that of other chitosan:polyanion complexes. The mass ratio was tuned to create nanoparticles with a chitosan shell and a controllable positive zeta potential. The particles were stable in a pH range from 3.5 to 6.0 and lost stability after 14 days of storage in aqueous media. Due to the high positive surface charge of the particles, the innate properties of the polysaccharides used, and the harmless disassociation of the polyelectrolytes, we suggest that the development of these CS:Pec nanoparticles offers great promise as a chronic wound healing platform.

Gum Arabic-Coated Magnetic Nanoparticles for Potential Application in Simultaneous Magnetic Targeting and Tumor Imaging

Magnetic iron oxide nanoparticles (MNP) coated with gum arabic (GA), a biocompatible phytochemical glycoprotein widely used in the food industry, were successfully synthesized and characterized. GA-coated MNP (GA-MNP) displayed a narrow hydrodynamic particle size distribution averaging about 100 nm; a GA content of 15.6% by dry weight; a saturation magnetization of 93.1 emu/g Fe; and a superparamagnetic behavior essential for most magnetic-mediated applications. The GA coating offers two major benefits: it both enhances colloidal stability and provides reactive functional groups suitable for coupling of bioactive compounds. In vitro results showed that GA-MNP possessed a superior stability upon storage in aqueous media when compared to commercial MNP products currently used in magnetic resonance imaging (MRI). In addition, significant cellular uptake of GA-MNP was evaluated in 9L glioma cells by electron spin resonance (ESR) spectroscopy, fluorescence microscopy, and MRI analyses. Based on these findings, it was hypothesized that GA-MNP might be utilized as a MRI-visible drug carrier in achieving both magnetic tumor targeting and intracellular drug delivery. Indeed, preliminary in vivo investigations validate this clinical potential. MRI visually confirmed the accumulation of GA-MNP at the tumor site following intravenous administration to rats harboring 9L glioma tumors under the application of an external magnetic field. ESR spectroscopy quantitatively revealed a 12-fold increase in GA-MNP accumulation in excised tumors when compared to contralateral normal brain. Overall, the results presented show promise that GA-MNP could potentially be employed to achieve simultaneous tumor imaging and targeted intra-tumoral drug delivery.

Surface-modified polymeric pads for enhanced performance during chemical mechanical planarization

The chemical mechanical planarization (CMP) process occurs at an atomic level at the slurry/wafer interface and hence slurries and polishing pads play a critical role in their successful implementation. Polyurethane is a commonly used polymer in the manufacturing of CMP pads. These pads are incompatible with some chemicals present in the CMP slurries, such as hydrogen peroxide. To overcome these problems, Psiloquest has developed new Application Specific Pads (ASP). Surface of such pads has been modified by depositing a thin film of tetraethyl orthosilicate using plasma-enhanced chemical vapor deposition (PECVD) process. In the present study, mechanical properties of such coated pads have been investigated using nanoindentation. The surface morphology and the chemistry of the ASP were studied using scanning electron microcopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy techniques. It was observed that mechanical and chemical properties of the pad top surface are a function of the PECVD coating time. Such PECVD-treated pads are found to be hydrophilic and do not require storage in aqueous media during the not-in-use period. The metal removal rate using such surface-modified polishing pads was found to increase linearly with the PECVD coating time.

A preliminary study of experimental polyacid-modified composite resins (‘compomers’) containing vinyl phosphonic acid

The aim of this investigation was to determine the properties of two novel compomers formulated with the monomer vinyl phosphonic acid (VPA). The setting properties, mechanical strength, wear characteristics and fluoride release of two experimental unshaded compomers containing VPA were determined, and compared with the commercial compomer Dyract A (shade C3). Two novel compomers were prepared, containing, respectively, 0.24% (A) and 2.31% (B) by mass of VPA, and an appropriate amount of reactive glass filler. Their properties were compared with those of Dyract AP (shade A3). Depth of cure was determined according to the method of ISO 4049. Polymerization of model mixtures of bisGMA, TEGDMA and VPA was studied using FT Raman spectroscopy, by comparing the absorption at 1608cm(-1) (aromatic C-C bond) with that at 1313cm(-1) (CC aliphatic). Compressive and biaxial flexure strengths were determined for sets of 6 specimens stored either wet or dry. Wear was determined using a toothbrushing machine and an abrasive slurry, and fluoride release was determined following up to 6 weeks storage in aqueous media, using a fluoride-selective electrode. Of the model monomer mixtures, the one with the greater quantities of VPA showed lowest degrees of polymerization after irradiation for 40s. Compomer A had an acceptable depth of cure, and similar properties to Dyract AP in terms of compressive and biaxial flexure strength, and also fluoride release. Resistance to toothbrush abrasion of both of the experimental compomers was superior to that of Dyract AP. These studies demonstrate that VPA can be used as the active monomer in experimental compomers, and is capable of yielding materials with properties equivalent to a commercial material, but with improved resistance to toothpaste abrasion. The level of VPA in the formulation is critical, because this monomer inhibits addition polymerization, hence must be used only in small amounts.

Changes in the volatile components of virgin olive oil during fruit storage in aqueous media

Storage of olives in sea water is a traditional way of fruit storage in olive oil production in Croatia that is still in frequent use. The changes of volatile compounds of olive oil, responsible for positive and negative odor properties that occur during this kind of fruit storage, were investigated. The influence of sea water was compared to brine and drinking water and with storage in the open air. The composition and content of volatile compounds were determined by dynamic headspace analysis with direct connection to gas chromatography and mass spectrometry. No significant differences were found among aqueous media. The olive oils from aqueous media had an essentially different composition and content of positive as well of negative volatile compounds in comparison to the reference sample and the samples stored in the air. The analytical method can give useful information about fruit storage before olive oil extraction.

Durability of APC2/Polyurethane adhesive joints for biomedical applications

Thermoplastic polyurethane elastomer was thermally bonded to carbon fibre-reinforced polyetheretherketone (APC2) in the development of a biomedical device. Argon plasma treatment of the APC2 substrate was investigated as a means of enhancing bonding. Contact angle measurements were used to optimise the surface treatment and, it was observed that the wettability decreased on ageing. Kinetic analysis gave an activation energy of 25 kJ/mol, which was consistent with a bond rotation mechanism. Optimally treated substrates were bonded to polyurethane and bond stability at 37°C was evaluated. While the bond was stable in air for over 1 year, storage in aqueous media lead to rapid deterioration of bond strength. This phenomenon was observed both in distilled water and in Ringer's solution. Measured diffusion rates for both environments were very similar and it is suggested that the observed faster rate of loss of bond strength in Ringer's solution is by the interaction of buffered components from the Ringers or solubilisation of low molecular weight material by the Ringers.

Long-term flexural strength of three direct aesthetic restorative materials

Objectives: This investigation evaluates the long-term flexural strength behaviour of three different glass-ionomer cement (GIC) based materials. Methods: The materials under investigation were a conventional GIC (Opusfil), a metal-reinforced GIC (Opus Silver) and a resin-modified GIC (Fuji II LC). Flexural strength specimens of the materials were prepared according to the relevant manufacturers' instructions for clinical use. After 10-min maturation at 37 °C, the specimens were placed in water, also at 37 °C, until required for testing. Specimens were tested under four-point bend at intervals between 7 and 130 days after manufacture. Results: Opusfil increased in strength up to day 56, but was significantly weaker after this time. Opus Silver was strongest on day 7, although there was no further decline in strength after day 14. Fuji II LC increased in strength up to day 14, but there was deterioration in strength after day 100. Opus Silver had the highest early strength of the three materials, but after day 7 there was no significant difference in strength between the three materials under test. Conclusions: The three cements tested did not exhibit the continued increase in strength with time that has been attributed to glass-ionomer cements. Each material behaved differently, but they all appeared to be adversely affected by storage in aqueous media. Materials formed by the inclusion of metal or the incorporation of resins into the glass-ionomer cement formulation should be regarded as separate sub-classes of materials in their own rights.

Stability of poly (ε caprolacton) nanospheres in sterile aqueous media

Polyester nanoparticles have shown promising results in the ophthalmic area for optimization of the bioavailability of drugs. However, polyesters can undergo hydrolysis during storage in aqueous media and their degradation can be enhanced by micro-organisms. Poly (ε caprolacton) (PEC) nanospheres were formulated for an ophthalmic application, i.e. sterile, isotonic and containing a preservative. Their physical and chemical stabilities were studied during a 6-month storage at 25 and 40°C. The influence of temperature, surfactant, viscosifiant addition, and buffered or non-buffered pH was evaluated. The physical stability of nanospheres was followed by the study of visual appearance and mean particle size. The pH and tonicity of the suspensions, and the molecular weight and crystallinity of PEC were additionally analyzed to evaluate their chemical stability. The influence of surfactants was observed only on the nanosphere physical stability. Better results were obtained with Pluronic F127. The degradation of PEC was especially affected by pH and temperature. At 25°C and pH 7, the variation of polymer molecular weight was negligible. At 40°C, the hydrolysis rate increased with a loss of 50% of the initial molecular weight after 6 months in pH 7 buffer, and 60% in non-buffered pH 7 medium. Finally, the mean particle size of all nanospheres remained unchanged throughout this study.