The pH-induced thermosensitive poly (NIPAAm-<Emphasis Type="Italic">co</Emphasis>-AAc-<Emphasis Type="Italic">co</Emphasis>-HEMA)-<Emphasis Type="Italic">g</Emphasis>-PCL micelles used as a drug carrier

The macromonomer of 2-hydroxyethyl methyacrylate-caprolactone (HPCL) was synthesized by the ring-opening polymerization (ROP) of ε-caprolactone, which was initiated by 2-hydroxyethyl methyacrylate (HEMA). Then, the graft terpolymers of NIPAAm-co-AAc-co-HEMA-g-PCL (PHNA-CL) with varying mole ratios were subsequently synthesized by free radical polymerization of HEMA-PCL, N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc). PHNA-CL was further self-assembled in different types of solvent. All the as-prepared copolymers were characterized by ¹H NMR, FT-IR and GPC. Micellization behaviors of micelles were studied by TEM and DLS. The micelles exhibited a phase transition temperature which can be readily adjusted by changing pH value of the micellization system. Micelle loaded with doxorubicin (DOX) was used to evaluate the drug release behavior. The release of DOX from micelles could be controlled by changing pH value and temperature in buffer solutions. The micelles are potentially to be used as a new anticancer drug carrier for intracellular delivery.     

Body distribution of poly(<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-glycolide) copolymer degradation products in rats

Poly (d,l-lactide-co-glycolide) (PLGA) copolymers are among the few synthetic polymers approved for human use, but the biocompatibility of PLGA-derived oligomers and particles remains questionable. Here, high molecular weight PLGA (Mw = 32,000) was radiolabeled with ¹²⁵I in chloroform solution, and the body distribution of PLGA copolymer degradation products was examined following subcutaneous implantation of round ¹²⁵I-PLGA films on the back of Sprague Dawley rats. Autoradiographic images of the PLGA implant taken at 2, 4, 6, 8, 10, and 12 weeks revealed that the central portion of the film degraded much more rapidly than the marginal portions. Examination of the body compartment distribution at these time points revealed that over one-half of the radioactivity was recovered from skin. The remaining radioactivity was concentrated in the blood, liver, and kidneys. Radioactivity steadily appeared in the blood and remained elevated up to 12 weeks after implantation, while the liver to kidney distribution began to decrease after 6 weeks. Cumulatively, these results indicate that the clearance of degraded particles and fragments from the implantation site is extremely delayed. Moreover, the degraded particles and fragments were selectively concentrated in the liver and kidneys, following release of degraded products into the bloodstream from the implantation site.     

Elastomeric electrospun scaffolds of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-trimethylene carbonate) for myocardial tissue engineering

In myocardial tissue engineering the use of synthetically bioengineered flexible patches implanted in the infarcted area is considered one of the promising strategy for cardiac repair. In this work the potentialities of a biomimetic electrospun scaffold made of a commercial copolymer of (l)-lactic acid with trimethylene carbonate (P(l)LA-co-TMC) are investigated in comparison to electrospun poly(l)lactic acid. The P(l)LA-co-TMC scaffold used in this work is a glassy rigid material at room temperature while it is a rubbery soft material at 37°C. Mechanical characterization results (tensile stress–strain and creep-recovery measurements) show that at 37°C electrospun P(l)LA-co-TMC displays an elastic modulus of around 20 MPa and the ability to completely recover up to 10% of deformation. Cell culture experiments show that P(l)LA-co-TMC scaffold promotes cardiomyocyte proliferation and efficiently preserve cell morphology, without hampering expression of sarcomeric alpha actinin marker, thus demonstrating its potentialities as synthetic biomaterial for myocardial tissue engineering.     

Characterization of poly(ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate-<Emphasis Type="Italic">co</Emphasis>-carbon monoxide)/layered silicate clay hybrids obtained by melt mixing

In recent times, polymer-layered silicate nanocomposites have drawn a great deal of attention because they often exhibit tremendous improvements in material properties compared with virgin polymers or conventional micro- or macro-composites. In the present study, nanocomposites were developed from organically modified clay and poly(ethylene-co-vinyl acetate-co-carbon monoxide) by melt mixing. FTIR spectroscopy reveals that the interaction between the organoclay and EVACO is thermodynamically favored. High resolution wide angle X-ray diffraction and transmission electron microscopy were used to study the morphology of the nanocomposites. Elemental mapping by scanning electron microscopy indicates good dispersion and distribution of the nanoclay in EVACO matrix. The mechanical properties of the nanocomposites are optimum at a clay loading of 3%.     

Electrospun poly(<Emphasis Type="SmallCaps">d</Emphasis>/<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="SmallCaps">l</Emphasis>-lactide) hybrid matrix: a novel scaffold material for soft tissue engineering

Electrospinning is a long-known polymer processing technique that has received more interest and attention in recent years due to its versatility and potential use in the field of biomedical research. The fabrication of three-dimensional (3D) electrospun matrices for drug delivery and tissue engineering is of particular interest. In the present study, we identified optimal conditions to generate novel electrospun polymeric scaffolds composed of poly-d/l-lactide and poly-l-lactide in the ratio 50:50. Scanning electron microscopic analyses revealed that the generated poly(d/l-lactide-co-l-lactide) electrospun hybrid microfibers possessed a unique porous high surface area mimicking native extracellular matrix (ECM). To assess cytocompatibility, we isolated dermal fibroblasts from human skin biopsies. After 5 days of in vitro culture, the fibroblasts adhered, migrated and proliferated on the newly created 3D scaffolds. Our data demonstrate the applicability of electrospun poly(d/l-lactide-co-l-lactide) scaffolds to serve as substrates for regenerative medicine applications with special focus on skin tissue engineering.     

Fabrication and characterization of porous poly(lactic-<Emphasis Type="Italic">co</Emphasis>-glycolic acid) (PLGA) microspheres for use as a drug delivery system

In this work, Simvastatin (SIM) loaded porous poly(lactic-co-glycolic acid) (PLGA) microspheres were fabricated using the W/O/W1/W2 double emulsion and solvent evaporation method. The optimal conditions for fabricating porous PLGA microspheres were determined to be 20% distilled water (v/v), 10% PLGA (m/v), and a 4:1 ratio of internal polyvinyl alcohol (PVA) to dichloromethane (DCM). The pores size distribution of porous PLGA microspheres was varied from 0.01 to 40 μm, while their particle displayed a bimodal size distribution that had two diameter peaks at around 100 μm and 500 μm. The SIM encapsulation efficacy was found to be very high with a yield near 80% and the porous PLGA microspheres showed the excellent biocompatibility. In addition, the drug release profile was found to be significantly different from a temporal basis. Base on the combined results of this study, SIM loaded PLGA microspheres holds great promise for use in biomedical applications, especially in drug delivery system or tissue regeneration.     

Adsorptive features of poly(glycidyl methacrylate-<Emphasis Type="Italic">co</Emphasis>-hydroxyethyl methacrylate): effect of porogen formulation on heavy metal ion adsorption

Preparation of crosslinked copolymer beads based on glycidyl methacrylate (GMA), 2-hydroxyethyl methacrylate (HEMA), and divinyl benzene for the use of heavy metal adsorption has been investigated. In our study, a series of porous copolymer beads were synthesized by suspension polymerization in the presence of porogens, 1-dodecanol, toluene, and heptane at different dilutions. The effect of the porogens on the surface appearance and the porous structure of copolymer beads was studied by scanning electron microscopy and BET method. Diethylene triamine chelating copolymers were obtained through a reaction between amine groups of diethylene triamine and epoxide pendant groups of GMA. Adsorption isotherm and quantitative analysis for adsorption capacity involving copper, chromium, manganese, cadmium, iron, and zinc ions were investigated using atomic absorption spectrophotometer. The adsorption was a function of types of metal ions, adsorption time, and solution properties including pH and metal concentration. Adsorption equilibrium was achieved in approximately 50 min with a maximum adsorption capacity at pH 5.0. The Langmuir isotherm was found to be well fitted on the adsorption behavior. The maximum metal adsorption capacities in single ion solution in mole basis were in the order Cu(II) > Cr(VI) > Mn(II) > Zn(II) > Cd (II) > Fe(II). It was found that introducing porogen in the polymerization mixture produced the copolymer beads with better adsorption capacity. The maximum Cu(II) adsorption capacity of chelating poly(GMA-co-HEMA) beads were 1.35 mmol/g (85.79 mg/g) measured from the beads prepared in the presence of 1-heptane with 50% dilution. Consecutive adsorption–desorption experiments showed that crosslinked poly(GMA-co-HEMA) micro-beads can be reused almost without any change in the adsorption capacity.     

Mechanical properties and density of BC<Emphasis Type="Italic">x</Emphasis>N<Emphasis Type="Italic">y</Emphasis> films grown by low-pressure chemical vapor deposition from triethylamine borane

Boron carbonitride (BC _x N _y ) films of different compositions have been grown by low-pressure chemical vapor deposition using triethylamine borane as a single-source precursor and ammonia as an additional nitrogen source. Experiments were performed at various initial vapor compositions. The resultant films have been characterized by ellipsometry, IR spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, nanoindentation, and surface acoustic wave spectroscopy. The mechanical properties of the films are shown to correlate with their density and chemical composition. With increasing initial ammonia partial pressure in the vapor phase, the elemental composition of the films moves away from boron carbide, approaching boron nitride, which is accompanied by a reduction in the Young’s modulus, hardness, and density of the films.     

Investigation of mechanical and superconducting properties of iron diffusion-doped <Emphasis Type="Italic">Bi</Emphasis>-<Emphasis Type="Italic">2223</Emphasis> superconductors

The mechanical and superconducting properties of the Fe diffusion-doped (Bi-Pb)-2223 superconductor have been investigated. First, iron was evaporated on Bi-2223 superconductor and then the Fe layered superconductor was annealed at 830 °C for 10, 30 and 60 h. Static Vickers hardness, dc electrical resistivity, X-ray diffraction and scanning electron microcopy have been carried out to assess the effects of Fe doping. These measurements indicates that Fe doping, in comparison with the undoped samples, increased the critical transition temperature, and improved formation of high T _c phase, while decreasing the number and size of voids. Moreover, both microhardness and grain size were also enhanced by increasing the amount of diffusion. The values of microhardness were found to be load dependent. In addition, we have investigated the indentation size effect (ISE) behavior using some models such as the Kick’s law, modified proportional specimen resistance (MPRS) model and the Hays- Kendall (HK) approach. Among them, both HK and MPRS models are successful. In this study, the possible reasons of noticed improvement on mechanical and physical properties due to iron diffusion are discussed.     

反应性乳化剂作用下的醋酸乙烯酯乳液聚合

对反应性乳化剂作用下的醋酸乙烯酯(VAC)乳液聚合动力学体系进行了研究,实验结果发现,聚合速率随乳化剂、引发剂浓度、温度的增大而加快,乳胶粒平均直径较传统的的乳液聚合乳胶粒子大得多,且成核期结束较早。     

Ductile-<Emphasis Type="Italic">to</Emphasis>-brittle transition in cenosphere-filled polypropylene composites

Cenosphere-filled polypropylene (PP) composites were fabricated and characterized for their structural/morphological and fracture mechanical behaviour. The fracture properties were studied following the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. The structural attributes and its consequent effects on the dynamic mechanical properties were characterized by wide angle X-ray diffraction (WAXD), hot-stage polarized light optical microscopy (PLOM) and dynamic mechanical analysis (DMA). The WAXD studies have revealed a decrease in crystallinity of the composites with increase in cenosphere content. PLOM studies reveals a threefold reduction in the diameter of the spherulite in case of composite with 10 wt% of cenosphere compared to that of PP followed by an increase of ~50% in the composite with 20 wt% of cenosphere compared to that of the composite with 10 wt% cenosphere. DMA revealed an enhancement in the energy dissipation ability of the composite with 10 wt% of cenosphere and an increase in the storage modulus up to ~30% in the composites relative to the soft PP phase. The non-essential work of fracture (NEWF: βw _p) as the resistance to stable crack propagation has shown a maximum at 10 wt% of cenosphere followed by a sharp drop at higher cenosphere content indicating a cenosphere-induced ductile-to-brittle transition (DBT). Fractured surface morphology investigations revealed that the failure mode of the composites undergo a systematic transition from matrix-controlled shear deformation to filler-controlled quasi-brittle modes above a cenosphere loading of 10 wt% in the composites reiterating the possibility of filler-induced semiductile-to-DBT transition.     

<Emphasis Type="Italic">Streptococcus sanguinis</Emphasis> adhesion on titanium rough surfaces: effect of shot-blasting particles

Dental implant failure is commonly associated to dental plaque formation. This problem starts with bacterial colonization on implant surface upon implantation. Early colonizers (such as Streptococcus sanguinis) play a key role on that process, because they attach directly to the surface and facilitate adhesion of later colonizers. Surface treatments have been focused to improve osseointegration, where shot-blasting is one of the most used. However the effects on bacterial adhesion on that sort of surfaces have not been elucidated at all. A methodological procedure to test bacterial adherence to titanium shot-blasted surfaces (alumina and silicon carbide) by quantifying bacterial detached cells per area unit, was performed. In parallel, the surface properties of samples (i.e., roughness and surface energy), were analyzed in order to assess the relationship between surface treatment and bacterial adhesion. Rather than roughness, surface energy correlated to physicochemical properties of shot-blasted particles appears as critical factors for S. sanguinis adherence to titanium surfaces.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

Photoacoustic Studies of Cd<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Be<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se Mixed Crystals

This paper reports the results of photoacoustic measurements of Cd_1-xBe_xSe mixed crystals grown by the high pressure Bridgman method with varying concentrations of Be (0.1 < x < 0.2). For examining continuous wave photoacoustic spectra, a piezoelectric transducer (PZT) and an open cell were used. An increase of the energy gap with increasing x has been observed. The thermal diffusivity values were estimated using the dependence of the amplitude and phase of the PA signal on the light modulation frequency.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions in ZnO implanted with group V ions

n-Type ZnO〈Ga〉 films were implanted with 150-keV N⁺ (As⁺) ions to a dose of 7 × 10¹⁵ cm⁻² and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm²/(V s), and carrier concentration of ∼10¹⁸ cm⁻³. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.     

Crystallization behavior of poly(hydroxybytyrate-<Emphasis Type="Italic">co</Emphasis>-valerate) in model and bulk PHBV/kenaf fiber composites

The kinetics of non-isothermal crystallization and melting behavior of poly(hydrohybutyrate-co-valerate) (PHBV) in model, bulk and compatibilized (PHBV)/kenaf fiber composites were investigated using differential scanning calorimetry (DSC). Analysis of the non-isothermal crystallization data was carried out based on the Avrami and Mo’s models. Activation energies of the crystallization process were determined by the Kissinger approach, and were in the range between 41 and 48 kJ/mol for all investigated samples. It was shown that the kenaf fibers, as well as their content, do not affect significantly the crystallization kinetics of PHBV matrix. The results indicate that crystallization behavior of polymer resin in bulk composites is not affected by the melt processing, thus suggesting absence of degradation processes.     

The Temperature Evolution of the Inhomogeneous Magnetic Response of Cuprate Superconductors Above <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>

Many different experiments and probes have displayed some form of anomalous behavior that may be related to charge inhomogeneity in different families of cuprate superconductors. In some materials, it appears to be associated with charge density waves and in others as local static domains of varying densities. The doping and temperature evolution of such charge instability is a matter of current intense research. We present here a model based on a phase separation transition to the temperature evolution of transverse field muon spin relaxation (TF- μSR) magnetic inhomogeneous response of cuprates above T _c recently measured.     

Thermal Transport Properties of Cd<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se Mixed Crystals Measured by Means of the Photopyroelectric Method

The concentration dependence of the thermal conductivity and thermal diffusivity were determined for Cd_1-x Mg _x Se mixed crystals in the temperature range between 20 ^◦C and 40 ^◦C. To determine the thermal transport properties, the photopyroelectric setup in the back detection configuration was constructed. In the concentration range 0< x <0.36, both thermal conductivity and thermal diffusivity were found to decrease with increasing magnesium concentration as well as with increasing temperature. The observed concentration dependence is discussed in the framework of the Adachi model.     

Specific features of technology of electron irradiation of large-area <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> silicon structures

We have studied the influence of irradiation by 4-MeV electrons via flat metal screens on the main electrical characteristics of high-power silicon diodes intended to operate at currents up to 600 A. The electron irradiation was performed via metal masks, which led to the formation of enhanced recombination zones (ERZs) in the base region of p ⁺-n-n ⁺ silicon structures. It is shown that the local irradiation of a large-area diode structure improves (as compared to the total irradiation) the relationship been the reverse recovery time (t _rr ) and energy loss in the conducting state (U _f ), while decreasing the temperature sensitivity of the reverse current (I _R ). It is established that the relationships between t _rr , U _F , and I _R in locally irradiated structures depends on the experimental conditions (ERZ size).     

Porous-conductive chitosan scaffolds for tissue engineering II. <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> degradation

Porous-conductive chitosan scaffolds were fabricated by blending conductive polypyrrole (PPy) particles with chitosan solution and employing an improved phase separation method. In vitro and in vivo degradation behaviors of these scaffolds were investigated. In the case of in vitro degradation, an enzymatic degradation system was employed and lysozyme was used as a working enzyme. Meanwhile, the degradation products of scaffolds, glucosamine and N-acetyl-glucosamine, were also analyzed with a HPLC method. In vivo degradation of scaffolds was performed by subcutaneously implanting these scaffolds in rat for prescheduled time intervals. In the both cases, the weight-loss of scaffolds was monitored during the whole degradation process for evaluating the degradation of scaffolds. The changes in conductivity of scaffolds afterin vitro or in vivo degradation were also measured using a four-point technique. It was observed that the pore parameters of scaffolds themselves could significantly influence the degradation behaviors of scaffolds but the PPy content in the scaffolds seemed not to impart its effect to the degradation of scaffolds. Degradation dynamics of scaffolds and conductivity measurements indicated that these scaffolds shown fairly different behaviors in their in vitro and in vivo degradation process. According to the results obtained from in vitro and in vivo degradation of scaffolds and based on some requirements of practical tissue engineering application, it was suggested that the PPy content in the scaffold should be slightly higher than 3 wt.% but lower than 6 wt.%.