Study on hydrophilic 5-fluorouracil release from hydrophobic poly(ε-caprolactone) cylindrical implants

Hydrophilic 5-fluorouracil (5-FU) loaded cylindrical poly(ε-caprolactone) (PCL) implants with different implant diameters (2, 4 and 8 mm), different drug loadings (25% and 50%) and end-capping were fabricated and characterized. The implant structure, drug content and molecular weight of PCL after 120 days drug release were investigated. The in vitro release results showed that, when the drug loading was the same, drug release was fastest for the implant with a diameter of 2 mm and slowest for the implant with a diameter of 8 mm; for the implants with the same diameters, the release of drug from the implants with 50% drug loading was faster than that from the implants with 25% drug loading; however, this effect of drug loading decreased with the increase of implant diameter; in addition, 5-FU was released slightly slower from the end-capped implants than from the corresponding uncapped implants; the drug release data for all the uncapped implants were best fit with the Ritger-Peppas model. Drug release from the hydrophobic implants was found to be dominated by diffusion mechanism. Scanning electron microscopy images and drug content measurements revealed that 5-FU release took place gradually from the exterior region to the interior region of the implants.     

Precipitation and its effect on age-hardening behavior of as-cast Mg–Gd–Y alloy

Microstructures evolution of Mg–7Gd–3Y–0.4Zr (wt.%) alloy during aging at 200 °C was investigated by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the alloy could exhibit remarkable age-hardening response by optimum solid solution and aging conditions. Especially, the highest Vickers hardness (HV) of this alloy was obtained when it was aged at 200 °C for 120 h, which was mainly attributed to a dense distribution of β′ precipitation in the matrix.     

Review on microstructure evolution in Sn–Ag–Cu solders and its effect on mechanical integrity of solder joints

The use of Pb-bearing solders in electronic assemblies is avoided in many countries due to the inherent toxicity and environmental risks associated with lead. Although a number of “Pb-free” alloys have been invented, none of them meet all the standards generally satisfied by a conventional Pb–Sn alloy. A large number of reliability problems still exist with lead free solder joints. Solder joint reliability depends on mechanical strength, fatigue resistance, hardness, coefficient of thermal expansion which are influenced by the microstructure, type and morphology of inter metallic compounds (IMC). In recent years, Sn rich solders have been considered as suitable replacement for Pb bearing solders. The objective of this review is to study the evolution of microstructural phases in commonly used lead free xSn–yAg–zCu solders and the various factors such as substrate, minor alloying, mechanical and thermo-mechanical strains which affect the microstructure. A complete understanding of the mechanisms that determine the formation and growth of interfacial IMCs is essential for developing solder joints with high reliability. The data available in the open literature have been reviewed and discussed.     

Grain boundary character distribution and its effect on corrosion of Ni–23Cr–16Mo superalloy

Grain boundary character distribution (GBCD) of the Hastelloy C2000 alloy (Ni–23Cr–16Mo) and the effect of coincidence site lattice (CSL) grain boundaries on corrosion resistance were examined by electron backscattered diffraction and electrochemical experiments. Various deformation followed by annealing was applied to optimise the GBCD of the alloy. After grain boundary engineering (GBE) treatment, the proportion of CSL boundaries increased from 37.7% to 62.4% and the corrosion current density of the specimens decreased in NaCl solution. The results indicated that GBE treatment is responsible for preferable corrosion resistance due to the increase of the fraction of special low energy grain boundaries with perfect grain boundary atom arrangement after thermomechanical process.     

Fritless packed columns for capillary electrochromatography: separation of uncharged compounds on hydrophobic hydrogels

A novel column is described that does not require frits to keep packing material within a capillary. A continuous bed is prepared in situ in aqueous solution by radical copolymerization of N-isopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid (the resultant gel is denoted poly(AMPS-co-IPAAm). N,N'-Methylenebisacrylamide is used for cross-linking. On the application of an electrical field, electroosmotic flow (EOF) is developed in the bed along the capillary, where fluid propulsion would be otherwise difficult to achieve. The resultant EOF transports neutral compounds through the column without forcing the gel out of the capillary. Examination of the fluid motion in the continuous bed using a video microscope system and an image processor shows a relatively flat flow profile of EOF. The bed functions as the stationary phase for reversed-phase capillary electrochromatography (CEC). This new approach is an alternative to packed capillary columns which have been used previously in CEC. A high efficiency is obtained for a steroid which is separated on a 4.0% total monomer concentration (T), 10.0% degree of cross-linking (C), and 10.0% mole fraction of AMPS in the total monomer (S), poly(AMPS-co-IPAAm) column. A mixture of polyaromatic hydrocarbons is separated on a 6.9% T, 5.8% C, and 5.5% S poly(AMPS-co-IPAAm) column. The capacity factor of benzo[a]pyrene increases from 0.63 to 1.91 as the acetonitrile content in a Tris-boric acid buffer is decreased from 45 to 30% (v/v). The run-to-run RSD of analyte migration time is less than 0.73%, and the day-to-day RSD is acceptable. Potential benefits of this approach are also mentioned.     

Co-delivery of hydrophilic and hydrophobic drugs by micelles: a new approach using drug conjugated PEG–PCLNanoparticles

Co-delivery strategy has been proposed to minimize the amount of each drug and to achieve the synergistic effect for cancer therapies. A conjugate of the antitumor drug, doxorubicin, with diblock methoxy poly (ethylene glycol)-poly caprolactone (mPEG-PCL) copolymer was synthesized by the reaction of mPEG–PCL copolymer with doxorubicin in the presence of p-nitrophenylchloroformate. The conjugated copolymer was characterized in vitro by ¹H-NMR, FTIR, DSC and GPC techniques. Then, the doxorubicin conjugated mPEG–PCL(DOX–mPEG-PCL) was self-assembled into micelles in the presence of curcumin in aqueous solution. The resulting micelles were characterized further by various techniques such as dynamic light scattering (DLS) and atomic force microscopy (AFM).The encapsulation efficiency of doxorubicin and curcumin were 82.31?±?3.32 and 78.15?±?3.14%, respectively. The results revealed that the micelles formed by the DOX–mPEG-PCL with and without curcumin have spherical structure with average size of 116 and 134?nm respectively. The release behavior of curcumin and doxorubicin loaded to micelles were investigated in a different media. The release rate of micelles consisted of the conjugated copolymer was pH dependent as it was higher at lower pH than in neutral condition. Another feature of the conjugated micelles was a sustained release profile. The cytotoxicity of micelles were evaluated by MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, atetrazole) assay on lung cancer A549 cell lines. In vitro cytotoxicity assay showed that the mPEG–PCL copolymer did not affect the growth of A549 cells. The cytotoxic activity of the micelles against A549 cells was greater than free doxorubicin and free curcumin.     

Drug absorption and release properties of crosslinked hydrogels based on diepoxy-terminated poly(ethylene glycol)s and aliphatic polyamines — a study on the effect of the gel molecular structure

Crosslinked hydrogels with well-defined chemical structures and characteristics were prepared through the reaction between diepoxy-terminated poly(ethylene glycol)s of various molecular weights and aliphatic polyamines of different hydrocarbon chain length and functionalities, and the influence of some network parameters (molecular weight between crosslinking points, crosslinking degree, hydrophobic character) upon the absorption and release of drugs of different capacity to interact with the polymer chains was comparatively investigated. Diclofenac sodium (DCFNa) and 5-fluorouracil (5FU) were used as model drugs, based on their dissimilar hydrophobic character and ability of DCFNa to form crown ether-like complexes with PEG chains through the sodium cation. The experiments showed that the most important interactions occurring in these systems were mainly the hydrophobic ones and to a lesser extent the complexation of the Na⁺ ion by the PEG chains. Both of them were in favor of DCFNa, resulting in a larger incorporation and a slower release of this one in comparison with 5FU. For both drugs, loading was larger for hydrogels with shorter PEG chains and/or crosslinked with amines with longer hydrocarbon chain or higher functionality. Drug release tests showed a lower rate for stronger drug–network interactions in agreement with the absorption experiments.     

Role of metal ions of Langmuir–Blodgett film in hydrophobic to hydrophilic transition of HF-treated Si surface

Hydrophobic to hydrophilic transition of HF-treated Si surface strongly depends upon the metal ions, which are present in the headgroups of the deposited Langmuir–Blodgett (LB) film. Structure of LB films studied by X-ray reflectivity technique and chemical analysis of LB film–substrate interfaces studied by X-ray photoelectron spectroscopy combinedly suggest that the partial transition or partial oxidation of the HF-treated Si surface takes place under the subphase water but further transition or oxidation is possible only in the presence of metal ions. Electrovalent and covalent natures of the metal ions tune this transition or oxidation. Ni ions, for which bonding with headgroups are electrovalent in nature, are favorable for such transition/oxidation and as a result, complete transition/oxidation takes place when nickel arachidate LB film is deposited. On the other hand, Cd ions, for which bonding with headgroups show covalent nature, is not favorable for such transition and can not oxidize the underlying H-passivated Si substrate totally when cadmium arachidate LB film is deposited on such HF-treated Si surface. This ion-specific hydrophobic to hydrophilic transition is visualized by X-ray reflectivity, contact angle and X-ray photoelectron spectroscopy measurements.     

The effect of process parameters on volatile release for a benzoxazine–epoxy RTM resin

Volatile release during cure is a potential cause of void formation during the resin transfer molding of complex thermosetting resins. In this study, a blended benzoxazine–epoxy resin system is analyzed to determine the rate at which volatiles are evolved, as well as the dependence of that rate on process parameters. The evolution of thermophysical and thermochemical resin properties is characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The identity and rate of evolution of the gaseous byproducts released during cure are determined at ambient pressure using a Fourier transform infrared spectrometer (FTIR) linked to a reaction cell. The results show that gas release during cure can be reduced but not eliminated by degassing at elevated temperature. Furthermore, the results indicate that the nature and rate of volatile release can be modified by judicious selection of cure cycle, as shown by a preliminary analysis of manufactured neat resin panels.     

Temper-treatment development to decompose detrimental martensite–austenite and its effect on linepipe welds

A tempering cycle was developed via heat treatment to study the decomposition of detrimental martensite–austenite (MA). The heat treatment cycle was found to preferentially decompose hard MA with a critical size of ≥1?µm, which decreases the hardness of these microconstituents after tempering at 300°C for 10?min. The dislocation density inside the MA and in the surrounding matrix was also decreased. Tempering of the X80 weldments containing MA reveals a similar decomposition behaviour. During transverse weld tensile testing of welds, a fracture occurred in the heat-affected zone due to void formation at the MA/ferrite interfaces. However, a fracture occurred in base metal with improved strength and ductility after tempering, in comparison to the fracture in the heat-affected zone of as-welded samples.     

pH-independent dissolution enhancement for multiple poorly water-soluble drugs by nano-sized solid dispersions based on hydrophobic–hydrophilic conjugates

The objective of this study was to achieve an optimal formulation of hydrophilic–hydrophobic conjugates for nano-sized solid dispersions (SDs) with enhanced dissolution of multiple drugs in different gastrointestinal (GI) tract environments. A new conjugate powder with an optimized process was used to fabricate SDs that contained three poorly water-soluble drugs that were also poorly soluble in different dissolution media. The self-assembled nanoparticle formation, drug crystallinity and SD molecular interactions were investigated by measuring the particle size during dissolution testing and physicochemical property analysis (powder X-ray diffraction and Fourier transform infrared spectroscopy). Drug release studies indicated that SD containing conjugated powder significantly improved the dissolution rates of these poorly water-soluble drugs in the GI tract. In addition, particle size analysis showed nano-sized particles in the dissolution media in the early stage with a tendency to reduce smaller particles over time. Physicochemical characterizations demonstrated almost amorphous drug states and hydrogen bonding interactions between the drugs and conjugates in the SD. This study optimized a promising material for SD, and the material was shown to have a promising performance under various pH medium conditions with poorly water-soluble drugs.     

Hot deformation behavior of an antibacterial Co–29Cr–6Mo–1.8Cu alloy and its effect on mechanical property and corrosion resistance

In order to optimize the deformation processing, the hot deformation behavior of Co–Cr–Mo–Cu(hereafter named as Co–Cu) alloy was studied in this paper at a deformation temperature range of 950–1150°C and a strain rate range of 0.008–5 s~(-1). Based on the true stress–true strain curves, a constitutive equation in hyperbolic sin function was established and a hot processing map was drawn. It was found that the flow stress of the Co–Cu alloy increased with the increase of the strain rate and decreased with the increase of the deforming temperature. The hot processing map indicated that there were two unstable regions and one well-processing region. The microstructure, the hardness distribution and the electrochemical properties of the hot deformed sample were investigated in order to reveal the influence of the hot deformation. Microstructure observation indicated that the grain size increased with the increase of the deformation temperature but decreased with the increase of the strain rate. High temperature and low strain rate promoted the crystallization process but increased the grain size, which results in a reduction in the hardness. The hot deformation at high temperature(1100–1150°C) would reduce the corrosion resistance slightly. The final optimized deformation process was: a deformation temperature from 1050 to 1100°C, and a strain rate from 0.008 to 0.2 s~(-1), where a completely recrystallized and homogeneously distributed microstructure would be obtained.     

Microcrack nucleation and its effect on the plastic deformation of FL γ-TiAl alloy

Microcracks and their effect on the plastic deformation of -TiAl alloy with fully lamellar microstructure (FL) at relatively low strain rate (1 × 10^–5/s) has been investigated. It is found that a large number of microcracks nucleate within the grains. The microcrack density increases with the increase of grain size. Most of the microcracks nucleate at the /₂ interfaces and gather at grains with soft-orientations. Based on the observation and analysis, a model of microcrack nucleation in FL -TiAl alloy is built up. The plastic elongation of -based TiAl alloys with FL microstructure changes non-monotonously with the increase of grain size, which results from cooperation of micro-deformations and microcracks.     

Ion and molecular recognition effects on the crystallisation of bovine serum albumin–salt mixtures

The effects of various bio-medically important salts Na, K, Li, Mg, Ca, Ni, Co, Cr, Fe and Cl on the dendritic or simple crystallisation of aqueous solutions of Bovine Serum Albumin have been investigated by contact or non-contact mode Atomic Force Microscopy. Four classes of structure are observed depending on the nature of the cation; a) unstructured protein–salt aggregates, b) large scale protein–salt meso-composites, c) mixed salt–protein gels, and d) microscopically phase separated systems.     

Cationic poly(VCL–AETA) hydrogels and ovalbumin (OVA) release in vitro

The objective of this research is to explore the synthesis of a new family of water soluble polycationic copolymeric precursors that could be photo-crosslinked into hydrogels. The in vitro control release of ovalbumin protein (OVA) from this family of hydrogels was also studied to assess the biomedical potential of this new family polycationic hydrogels. A series of novel poly(VCL–AETA) copolymer hydrogels was fabricated in an aqueous medium via photo-induced polymerization and crosslinking of hydrophobic N-vinylcaprolactam (VCL) and hydrophilic [2-(acryloxy)ethyl]trimethylammonium chloride (AETA) monomers over a wide range of VCL to AETA feed molar ratios of 2:1, 1:1, 1:2, 1:5. N,N′-methylene bisacrylamide (MBA) was used as a crosslinker. Ovalbumin (OVA), a model antigen, was preloaded into poly(VCL–AETA) hydrogel precursors and its release profiles in pH 7.4 PBS at 37°C were investigated as a function of VCL to AETA monomer feed ratios over a period of 4 weeks. The in vitro results showed that OVA initial burst and subsequent sustained releases could be controlled by 3 material parameters: the hydrophobic VCL to hydrophilic AETA monomer feed ratios, crosslinking density and hydrogel degradation rate. Thus, the hydrophobic-hydrophilic VCL–AETA hydrogel network for controlled OVA release could offer advantages over organic solvent-based single component polymer system. However, these in vitro OVA release profiles may change in an in vivo environment.     

Structure,swelling, and drug release of thermoresponsive poly(amidoamine) dendrimer–poly(N-isopropylacrylamide) hydrogels

Functional drug delivery systems are important for improved pharmacotherapy. The aim of this work was to describe how the introduction of varying amounts of the dendrimer polyamidoamine (PAMAM) into a chemically cross-linked thermoresponsive poly(N-isopropylacrylamide) (PNIPAAM) gel affects the structure, swelling properties, and drug release characteristics. The structure of the gel system was characterized by small-angle X-ray scattering (SAXS), while the drug delivery system was characterized by measuring the swelling, loading, and release of the model drug. The SAXS results suggest that the PNIPAAM gel is heterogeneous on a local length scale, whereas more homogeneous gels are formed in the presence of PAMAM. Increased swelling and loading capacity were observed for higher fractions of PAMAM dendrimer. This was explained by the enhanced hydrophilicity obtained by inclusion of the dendrimers. The swelling process was observed to be very slow taking place over several days, indicating other mechanisms than diffusion to be the rate-limiting step. The temperature-induced deswelling was more pronounced for the dendrimer-containing formulations. This process was observed to be very fast and complete within a couple of hours. Similarly the release rate was quite fast without being affected by inclusion of the dendrimer. Retention of a significant portion of the loaded drug at specific conditions was shown to be due to the hydrogen bonding ability of PNIPAAM. Improved conditions for drug delivery were achieved in several respects by incorporation of PAMAM dendrimer molecules in the PNIPAAM hydrogel. Our results indicate that the PAMAM entities expand the PNIPAAM gel and that the gel becomes more homogeneous.     

Aging at 400–600°C of submerged arc welds of 22Cr–3Mo–8Ni duplex stainless steel and its effect on toughness and microstructure

Abstract

Submerged arc welds of a 22Cr–3Mo–8Ni (wt-%) duplex stainless steel were aged in the temperature range 400–600°C to simulate stress relieving conditions of mild steel. Particular attention was paid to the relationship between toughness and microstructure. It was concluded that sufficient toughness could be obtained on aging in the range 500–550°C provided that the aging time did not exceed 10 h. At temperatures >550°C, rather rapid embrittlement occurred as a result of the precipitation of essentially R phase and to some extent π phase. At ~≤500°C, spinodal decomposition of ferrite caused embrittlement, albeit more slowly than the precipitate induced embrittlement. Precipitation of the Mo rich phases Rand π was found to cause depletion of Mo in solid solution in ferrite. This offers a possible explanation for the decrease in pitting corrosion resistance observed in previous work.

MST/1426     

Preparation of non-spherical silica composite abrasives by lanthanum ion-induced effect and its chemical–mechanical polishing properties on sapphire substrates

Chemical–mechanical polishing is the only technology that can provide a global planarization, and has become widely accepted. Abrasives are one of the important factors influencing chemical–mechanical polishing. In order to improve surface planarization and increase material removal rate of sapphire substrates, non-spherical silica composite abrasives were synthesized by lanthanum ion-induced effect-assisted growth method. Scanning electron microscopy showed the morphologies of non-spherical silica composite abrasives were peanut-shaped, chemical–mechanical polishing tests displayed the material removal rate of the non-spherical silica composite abrasives increased by 32.6% compared with spherical silica composite abrasives, Ambios Xi-100 surface profiler indicated the best surface roughness of sapphire substrate was 1.540 nm, and the element compositions of solids after polishing were analyzed by X-ray photoelectron spectroscopy, which investigated the interactions between abrasives and sapphire substrates. Non-spherical silica composite abrasives may lead to more solid-chemical reactions with sapphire substrates, and higher material removal rate may be also attributed to the mechanical grinding effect enhanced owing to the unique shape to achieve the purpose of material removal.     

Precipitation characteristics of μ-phase in wrought nickel-base alloys and its effect on their properties

Thermal exposures consisting of 1–16000 h at 540, 650, 760, and 870°C were used to study the susceptibility of selected nickel-base alloys to precipitation of -phase and its effect on mechanical strength and corrosion resistance. Analytical electron microscopy and X-ray diffraction were used to characterize the -phase. A -phase of the type Mo₆Ni₇ in nickel-base alloys was found to be stabilized by critical concentrations of iron in an excess of about 3 wt%. Generally, the -phase had a characteristic defect structure consisting of twins and stacking faults, and it exhibited a preferential tendency for precipitation at existing molybdenum-rich carbide particles within the alloy matrix and at grain boundaries. Precipitation of -phase was found to produce a moderate loss of room-temperature tensile ductility; however, it resulted in a considerable degradation of impact toughness and corrosion resistance. In contrast, it had no significant effect on elevated temperature tensile properties. A correlation was found to exist between the Ni/Fe + Co ratio as well as the Mo + W content of the alloy and susceptibility to precipitation of -phase.