Upon some multi-membrane hydrogels based on poly(N,N-dimethyl-acrylamide-co-3,9-divinyl-2,4,8,10-tetraoxaspiro (5.5) Undecane): preparation,characterization and in vivo tests

The study presents the possibility of preparation of multi-membrane gel systems with different morphologies and properties, based on poly(N,N-dimethyl-acrylamide-co-3,9-divinyl-2,4,8,10-tetraoxaspiro (5.5) undecane) copolymer and crosslinked with N,N′-methylene-bis-acrylamide. The basic copolymer has dual thermo- and pH sensitive character. After the core hydrogel is realized, the preformed gel is immersed in the aqueous solutions of ammonia, sodium chloride and sodium citrate for further edge constructing of the supramolecular assemblies. Then, the new layers by adding new sets of gelifying components are realized. The new multi-membrane gel systems are intended to be used as matrix for bioactive substances embedding. In this context the systems were loaded with norfloxacin as drug model. The in vivo tests show good biocompatibility for the implants based on multi-membrane gel structures loaded with drug.     

Aspects regarding the grafting of some lignosulfonates with acrylamide under a magnetic field

The kinetics of the graft polymerization of acrylamide onto some lignosulfonate products in a continuous external magnetic field was studied. The registered magnetokinetic effects were correlated and associated with the conditions of the classic reaction. The grafting process of acrylamide onto the macromolecular chains depending on the cation (Ca²⁺, Cr²⁺, Fe²⁺, Fe³⁺ and NH₄⁺) present in the lignosulfonate structure and the magnetic field influence were corroborated and explained through the radical pairs mechanism. The augmentation of the graft polymerization rate in magnetic field and conversion was ascribed to the singlet-triplet transitions in the radical pairs as a result of the presence of the magnetic field.     

An in vitro release study of indomethacin from nanoparticles based on methyl methacrylate/glycidyl methacrylate copolymers

Indomethacin was coupled onto some macromolecular nanostructures based on methyl methacrylate copolymers with glycidyl methacrylate and tested as a model drug. The polymeric matrices were synthesized by radical emulsion copolymerization with and without the presence of a continuous external magnetic field of 1500 Gs intensity. Mathematical analysis of the release data was performed using Higuchi, Peppas–Korsmeyer equations. NIR chemical imaging (NIR-CI) was used to provide information about the spatial distribution of the components in the studied nanostructures. This opportunity was used to visualize the spatial distribution of bioactive substances (indomethacin) into the polymeric matrix, as well as to evaluate the degree of chemical and/or physical heterogeneity of the bioactive samples. The release rate dependence on the synthesis conditions as well as on the chemical compositions of the tested polymeric systems, it was also evidenced.     

A Simple Protocol for Sample Preparation for Scanning Electron Microscopic Imaging Allows Quick Screening of Nanomaterials Adhering to Cell Surface

Preparing biological specimens for scanning electron microscopy (SEM) can be difficult to implement, as it requires specialized equipment and materials as well as the training of dedicated personnel. Moreover, the procedure often results in damage to the samples to be analyzed. This work presents a protocol for the preparation of biological samples to evaluate the adherence of nanomaterials on the cell surface using SEM. To this end, we used silicon wafers as a substrate to grow cells and replaced difficult steps such as the critical point drying of the samples in order to make the method quicker and easier to perform. The new protocol was tested using two different types of cells, i.e., human osteosarcoma cells and adipose-derived mesenchymal stem cells, and it proved that it can grossly preserve cell integrity in order to be used to estimate nanomaterials’ interaction with cell surfaces.     

Room-temperature hydrogen release from activated carbon-confined ammonia borane

In chemical hydrogen storage, nanoconfinement (or nanoscaffolding) is an efficient approach to reduce the size of the particles of boron hydrides such as ammonia borane (AB, NH₃BH₃) at nanoscale while destabilizing its molecular network. It involves the dehydrogenation of AB at temperatures lower than 100 °C and hinders the formation of undesired gaseous by-products such as borazine. Herein, commercial activated carbon (AC) with a specific surface area of 716 m² g⁻¹ and a porous volume of 0.36 cm³ g⁻¹ was used as host material for AB nanoconfinement. A composite activated carbon-ammonia borane (AC@AB) was successfully prepared by infiltration in cold conditions (0 °C). Its dehydrogenation was followed by volumetric method, FTIR, XRD, TGA, DSC, GC–MS and ¹¹B MAS NMR. The most striking result is that the nanoconfined AB, being highly destabilized, dehydrogenates in ambient conditions, even at 3–4 °C. It is demonstrated that dihydrogen is formed according to two pathways that simultaneously take place. The first one is the dehydrogenation through inter- and/or intra-molecular reactions between protonic H and hydridic H of AB, and the second one is the acid-base reaction between protonic H of COO−H groups present on the AC surface and hydridic H of AB.     

Details on the Formation of Ti<Subscript>2</Subscript>Cu<Subscript>3</Subscript> in the Ag-Cu-Ti System in the Temperature Range 790 to 860 °C

Silver-copper-titanium (Ag-Cu-Ti) ternary alloys are often used as active braze alloys for joining ceramics to metals at temperatures ranging from 780 °C (the melting point of the Ag-Cu eutectic) up to 900 °C. When Ti/Ag-Cu joints are brazed at low temperature (near 800 °C), the intermetallic compound Ti₂Cu₃ (tetragonal, P4/nmm, a = 0.313 nm, c = 1.395 nm) is systematically missing from the interface reaction layer sequence. An experimental investigation based on isothermal diffusion experiments in the Ag-Cu-Ti ternary system has then been undertaken to clarify the issues of thermal stability and formation kinetics of this compound. Evidence has been found for the stability of Ti₂Cu₃ at temperatures ranging from 790 to at least 860 °C. By heat treating Ag-Cu-Ti powder mixtures at 790 °C for increasing times, it has moreover been shown that Ti₂Cu₃ forms at a much slower rate than the two adjacent Ti-Cu compounds: TiCu₄, the first phase to form, and Ti₃Cu₄. This explains why although thermodynamically stable, Ti₂Cu₃ is not obtained when temperature is too low or reaction time too short.     

Helical sorbent microtrap for continuous sampling by a membrane and trap interface for on-line gas chromatographic monitoring of volatile organic compounds

A helical sorbent microtrap consisting of a helical sorbent fixed inside a silicosteel capillary tube is presented. The main parameters that affect the safe sampling time of the helical sorbent microtrap in continuous sampling by a membrane and trap interface for on-line gas chromatographic monitoring of organic volatiles in gaseous samples are examined, taking into account the helical configuration of the sorbent, the presence of the membrane in system, and the properties of the analytes. Thermal desorption of analytes from the helical sorbent trap was also examined having regard to the influence of the turbulent flow generated by the helical sorbent in the heat transfer and the effect of thermal backward flow on the peak shape. The practical application of the helical sorbent microtrap in a membrane and trap interface was demonstrated by on-line gas chromatographic monitoring of four volatile organic compounds in the fume hood air and of volatile organic compounds from a diesel engine exhaust. The limit of detection was in the picogram per milliliter range, depending on the time of trapping and the parameters that affect the permeation through the membrane.     

Hydrogen release by thermolysis of ammonia borane NH3BH3 and then hydrolysis of its by-product [BNHx]

Ammonia borane (AB) is one of the most attractive hydrides owing to its high hydrogen density (19.5 wt%). Stored hydrogen can be released by thermolysis or catalyzed hydrolysis, both routes having advantages and issues. The present study has envisaged for the first time the combination of thermolysis and hydrolysis, AB being first thermolyzed and then the solid by-product believed to be polyaminoborane [NH₂BH₂]_n (PAB) being hydrolyzed. Herein we report that: (i) the combination is feasible, (ii) PAB hydrolyzes in the presence of a metal catalyst (Ru) at 40 °C, (iii) a total of 3 equiv. H₂ is released from AB and PAB-H₂O, (iv) high hydrogen generation rates can be obtained through hydrolysis, and (v) the by-products stemming from the PAB hydrolysis are ammonium borates. The following reactions may be proposed: AB → PAB + H₂ and PAB + xH₂O → 2H₂ + ammonium borates. All of these aspects as well as the advantages and issues of the combination of AB thermolysis and PAB hydrolysis are discussed.     

Current and future miniature refrigeration cooling technologies for high power microelectronics

Utilizing refrigeration may provide the only means by which future high-performance electronic chips can be maintained below predicted maximum temperature limits. Widespread application of refrigeration in electronic packaging will remain limited, until the refrigerators can be made sufficiently small so that they can be easily incorporated within the packaging. A review of existing microscale and mesoscale refrigeration systems revealed that only thermoelectric coolers (TECs) are now commercially available in small sizes. However, existing TECs are limited by their maximum cooling power and low efficiencies. A simple model was constructed to analyze the performance of both existing and predicted future TECs, in an electronic packaging environment. Comparison with the cooling provided by an existing high-performance fan shows that they are most effective for heat loads less than approximately 100 W, but that for higher heat loads, fan air cooling actually yields a lower junction temperature. Thermal resistance between the refrigerator and the chip is not as critical as the thermal resistance between the refrigerator and the ambient air.