Effect of ceramic filler content on the mechanical and thermal behaviour of poly-<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid and poly-<Emphasis Type="SmallCaps">l</Emphasis>-lactic-co-glycolic acid composites for medical applications

One main application of resorbable poly-l-lactic acid (PLLA) and poly-l-lactic-co-glycolic acid (PLGA) based materials is in medical implants. In this study composites were made from PLLA and PLGA with hydroxyapatite (HAp) respective β-tricalcium phosphate (β-TCP) fillers. The filler content and particle size were varied, and the thermal properties as well as the mechanical strength of the composites were investigated. The composites were made by an extrusion compounding process giving 2–2.5 mm diameter sized profiles. The results verified that the thermal stability of the composites was reasonable during the optimized compounding conditions. Scanning electron microscopy revealed that the fillers were well dispersed in the polymer matrices. The mechanical properties were improved by the addition of the fillers. The optimum mechanical properties for the extruded profiles were obtained with the HAp fillers. The E-modulus was increased from 3.3 to 4.6 GPa by addition of filler particles (30 wt%) whereas the flexural strength was reduced from 133 to 106 MPa.     

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.     

Histological study of surface modified three dimensional poly (<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps"> l</Emphasis>-lactic acid) scaffolds with chitosan in vivo

Biocompatibility and tissue regenerating capacity are essential for biomaterials that used in tissue engineering. The aim of this study was to histologically assess the tissue reactions and bone conductivities of surface modified three dimensional (3-D) poly (d, l-lactic acid) (PDLLA) scaffolds, which were coated with chitosan via a physical entrapment method. The native PDLLA scaffold was prepared via thermally induced phrase separation technique and was characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Osteocalcin assay, a method to evaluate the bone formation potential, has shown that the osteocalcin production in chitosan-modified 3-D PDLLA scaffold group was significantly higher (p < 0.05) than that of in control. The tissue reactions and bone conductivities between surface modified PDLLA and native PDLLA scaffolds were evaluated using a rabbit radialis defect model in vivo and compared at different implantation intervals (2, 4, 8 and 12 weeks). The histological results have shown a higher bone formation potential and better biocompatibility of chitosan-modified 3-D PDLLA scaffolds as compared with the control group scaffolds.     

Poly (<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide)/nano-hydroxyapatite composite scaffolds for bone tissue engineering and biocompatibility evaluation

Biodegradable polymer/bioceramic composite scaffolds can overcome the limitations of conventional ceramic bone substitutes such as brittleness and difficulty in shaping. However, conventional methods for fabricating polymer/bioceramic composite scaffolds often use organic solvents (e.g., the solvent casting and particulate leaching (SC/PL) method), which might be harmful to cells or tissues. In this study, Poly (d,l-lactide)/nano-hydroxyapatite (PDLLA/NHA) composites were prepared by in-situ polymerization, and highly porous scaffolds were fabricated using a novel method, supercritical CO₂/salt-leaching method (SC CO₂/SL). The materials and scaffolds were investigated by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and gel permeation chromatography (GPC). GPC showed that the molecular weight of composites decreased with increase of NHA content. However, the water absorption and compressive strength increased dramatically. The SEM micrographs showed that the scaffolds with pore size about 250 μm were obtained by controlling parameters of SC CO₂/SL. The biocompatibility of PDLLA/NHA porous scaffolds were evaluated in vitro and in vivo. The evaluation on the cytotoxicity were carried out by cell relative growth rate (RGR) method and cell direct contact method. The cytotoxicity of these scaffolds was in grade I according to ISO 10993-1. There was no toxicosis and death cases observed in acute systemic toxicity test. And histological observation of the tissue response (1 and 9 weeks after the implantation) showed that there are still some slight inflammation responses.     

Titanium dioxide (TiO<Subscript>2</Subscript>) nanoparticles filled poly(<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis> lactid acid) (PDLLA) matrix composites for bone tissue engineering

Titanium dioxide (TiO₂) nanoparticles were investigated for bone tissue engineering applications with regard to bioactivity and particle cytotoxicity. Composite films on the basis of poly(d,l lactid acid) (PDLLA) filled with 0, 5 and 30 wt% TiO₂ nanoparticles were processed by solvent casting. Bioactivity, characterised by formation of hydroxyapatite (HA) on the materials surface, was investigated for both the free TiO₂ nanoparticles and PDLLA/TiO₂ composite films upon immersion in supersaturated simulated body fluid (1.5 SBF) for up to 3 weeks. Non-stoichiometric HA nanocrystals (ns-HA) with an average diameter of 40 nm were formed on the high content (30 wt% TiO₂) composite films after 2 weeks of immersion in 1.5 SBF. For the pure PDLLA film and the low content composite films (5 wt% TiO₂) trace amounts of ns-HA nanocrystals were apparent after 3 weeks. The TiO₂ nanopowder alone showed no bioactivity. The effect of TiO₂ nanoparticles (0.5–10,000 μg/mL) on MG-63 osteoblast-like cell metabolic activity was assessed by the MTT assay. TiO₂ particle concentrations of up to 100 μg/mL had no significant effect on MG-63 cell viability.     

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.     

Programmed water-induced shape-memory of bioabsorbable poly(<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide): activation and properties in physiological temperature

This study reports of the novel water-induced shape-memory of bioabsorbable poly(d,l-lactide). We have developed an orientation-based programming process that generates an ability for poly(d,l-lactide) to transform its shape at 37°C in an aqueous environment without external energy and to adapt to a predefined stress level by stress generation or relaxation. In this orientation-programming process, polymer material is deformed and oriented at an elevated temperature and subsequently cooled down while retaining its deformed shape, tension, and polymer chain entanglements. At body temperature and in an aqueous environment, the shape-memory is activated by the plasticizing effect of water molecules diffused into the polymer matrix causing an entropy-driven directed relaxation of oriented and preloaded polymer chains. This plasticizing effect is clearly seen as a decrease of the onset glass transition temperature by 10–13°C. We found that γ-irradiation used for sterilizing the orientation-programmed materials strongly affected the shape-recovery rate, but not the recovery ratio. Both non-γ-irradiated and γ-irradiated sample materials showed excellent shape-recovery ratios during a ten-week test period: 94 and 97%, respectively. The orientation-programmed materials generated a predefined load in a 37°C aqueous environment when their shape-recovery was restricted, but when external tension was applied to them, they adapted to the predefined level by stress relaxation. Our results show that functionality in terms of shape-memory can be generated in bioabsorbable polymers without tailoring the polymer chain structure thus shortening the time from development of technology to its utilization in medical devices.     

Computational and electrochemical studies on the inhibition of corrosion of mild steel by <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine and its derivatives

This article presents the investigation of l-Cysteine (CYS) and its derivatives including N-Acetyl-l-Cysteine (NACYS), N-Acetyl-S-Benzyl-l-Cysteine (NASBCYS), and N-Acetyl-S-Hexyl-l-Cysteine (NASHCYS) as green chemical corrosion inhibitors for mild steel in 1 M HCl solutions. Weight loss method and Tafel polarization measurement were performed to determine the corrosion parameters and inhibition efficiencies. Experimental results showed that these compounds suppressed both anodic and cathodic reactions, and the inhibition efficiency of the four inhibitors followed the order NASBCYS > NASHCYS > NACYS > CYS. In order to further study the corrosion mechanisms, quantum chemical calculation and molecular dynamics method were applied. The relationships between quantum chemical parameters and corrosion inhibition efficiency were discussed. Molecular dynamics method was used to simulate the adsorption behavior of each inhibitor in solvent. The results showed that these four inhibitors can adsorb on mild steel surface by donor acceptor interactions between lone-pair electrons of heteroatoms/π-electrons of aromatic ring and vacant d-orbital of iron.     

<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.     

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.      

How hybridization with zinc oxide whiskers and carbon fibers affects the thermal diffusivity and mechanical properties of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) nanocomposites

The enhanced thermal diffusivity and mechanical properties of poly(l-lactic acid) (PLLA) nanocomposites reported here are based on the percolation network formed when PLLA is hybridized with short carbon fibers (CFs) and functionalized zinc oxide whiskers. The PLLA nanocomposite containing 30 wt% (≈9.5 vol%) ZnO whiskers and 10 wt% (≈8.1 vol%) CFs had a thermal diffusivity almost as high as that of stainless steel and an insulator-level electrical resistivity (>10¹⁰ Ωm). Modifying the surface of the ZnO whiskers by esterifying them using specific alcohols with long linear alkyl chains improved the elastic strength and toughness of the nanocomposites significantly. These results suggest that hybridizing PLLA with short CFs and functionalized ZnO whiskers yields nanocomposites with high thermal diffusivity as well as high electrical resistivity and excellent mechanical properties.     

Dielectric relaxation behaviour of Sr<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>SbMnO<Subscript><Emphasis Type="Bold">6</Emphasis></Subscript> ceramics fabricated from nanocrystalline powders prepared by molten salt synthesis

Double perovskite polycrystalline single phase and dense Sr ₂ SbMnO ₆ (SSM) ceramics, fabricated using the nanocrystalline powders synthesized by molten salt method, exhibited high dielectric constant with low dielectric loss as compared to that of SSM ceramics obtained from the powders prepared by solid-state synthesis method. The dielectric data obtained over a wide frequency (100 Hz–1 MHz) and temperature (190 K–300 K) ranges exhibited distinct relaxations owing to both the grain and grain boundary. The dielectric dispersion was modeled using the Cole–Cole equation consisting of two separate relaxation terms corresponding to the grain and grain boundary. The grain and grain boundary relaxations observed in the Nyquist plots (Z ^′ and Z ^″) were modeled by an equivalent circuit consisting of two parallel RC circuits connected in series with each other. A careful analysis of both the impedance (Z ^″ vs ω) and modulus (M ^″ vs ω) behaviour corroborated the conclusions drawn from the dielectric data.     

Chemical synthesis and characterization of hydrous tin oxide (SnO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>:H<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>O) thin films

In the present investigation, we report chemical synthesis of hydrous tin oxide (SnO ₂ :H ₂ O) thin films by successive ionic layer adsorption and reaction (SILAR) method at room temperature ( \thicksim \thicksim 300 K). The films are characterized for their structural and surface morphological properties. The formation of nanocrystalline SnO ₂ with porous and agglomerated particle morphology is revealed from X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies, respectively. The Fourier transform infrared spectroscopy (FTIR) study confirmed the formation of Sn–O phase and hydrous nature of the deposited film. Static water contact angle studies showed the hydrophilic nature of SnO ₂ :H ₂ O thin film. Electrical resistivity showed the semiconducting behaviour with room temperature electrical resistivity of 10 ⁵  W\boldsymbol\Omega cm. The electrochemical properties studied in 0·5 M Na ₂ SO ₄ electrolyte showed a specific capacitance of 25 F g ^− 1 at 5 mVs ^− 1 scan rate.     

Use of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine amino acid as biomodifier of Cloisite Na<Superscript>+</Superscript> for preparation of novel poly(vinyl alcohol)/organoclay bionanocomposites film

Cloisite Na⁺ was modified via cation exchange reaction using natural l-tyrosine amino acid. This novel chiral organo-modified Cloisite Na⁺ was characterized using fourier transform infrared spectroscopy (FT–IR), X-ray diffraction (XRD), and thermogravimetric analysis/derivative thermal gravimetric (TGA/DTG). Then, polymer bionanocomposites were prepared by dispersing chiral organo-modified Cloisite Na⁺ in poly(vinyl alcohol) (PVA) via ultrasonic irradiation. The novel bionanocomposites were characterized by FT–IR, UV–Visible, TGA, and XRD. Scanning electron microscopy and transmission electron microscopy were used to obtain the information about morphological structure of PVA/Cloisite Na⁺/Tyr bionanocomposites. The results showed that a mixture of intercalated and exfoliated Cloisite Na⁺ dispersion in PVA matrix. The TGA data was compared with the pure PVA and the results showed that the introduction of a small amount of Cloisite Na⁺/Tyr led to improvement in thermal stability of the obtained new bionanocomposites. UV–Visible transmission spectra of pure PVA and new bionanocomposites film in the visible light region (400–800 nm) showed that they are rather transparent.     

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.     

Study of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) microparticles based on supercritical CO<Subscript>2</Subscript>

Poly(l-lactide) (PLLA) microparticles were prepared in supercritical anti-solvent process. The effects of several key factors on surface morphology, and particle size and particle size distribution were investigated. These factors included initial drops size, saturation ratio of PLLA solution, pressure, temperature, concentration of the organic solution, the flow rate of the solution and molecular weight of PLLA. The results indicated that the saturation ratio of PLLA solution, concentration of the organic solution and flow rate of the solution played important roles on the properties of products. Various microparticles with the mean particle size ranging from 0.64 to 6.64 μm, could be prepared by adjusting the operational parameters. Fine microparticles were obtained in a process namely solution-enhanced dispersion by supercritical fluids (SEDS) process with dichloromethane/acetone mixture as solution.     

<Emphasis Type="SmallCaps">l</Emphasis>-Tryptophan as green corrosion inhibitor for low carbon steel in hydrochloric acid solution

The inhibition behavior of low carbon steel in 1 M HCl by l-tryptophan was investigated with weight loss experiment and Tafel polarization curve in the used temperature range (298–328 K). All the experimental results show that l-tryptophan has excellent corrosion inhibition performance and the most effective concentration of inhibitor is 1 × 10⁻² mol L⁻¹. The Tafel polarization curve results indicate that l-tryptophan acts more as a cathodic than anodic inhibitor. The adsorption of l-tryptophan on the surface of low carbon steel obeys the Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The adsorption behavior of l-tryptophan at Fe surface (1 1 0) was also investigated by the molecule dynamics simulation method and density functional theory. The results indicated that the l-tryptophan could adsorb firmly on the Fe surface through the indole ring with π-electrons and nitrogen/oxygen atom with lone-pair electrons in its molecule.     

Influence of specimen geometry and size-effect on the <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">R</Emphasis></Subscript>-curve based on the cohesive stress in concrete

Comparative study for determining the K _R -curves associated with the cohesive stress distribution for complete fracture process for two standard specimen geometries i.e., three-point bending test and compact tension test specimen geometries of concrete using analytical method and weight function approach is reported in the paper. The laboratory size specimen (100 ≤  D  ≤  400 mm) with initial-notch length/depth ratios 0.3 and 0.5 are considered in the investigation. The load-crack opening displacement curves for these specimens are obtained using well known version of Fictitious Crack Model (FCM). It is found from the numerical results that the weight function method improves computational efficiency without any appreciable error. The stability analysis on the K _R -curves and the influence of specimen geometry and the size-effect on the K _R -curves, the CTOD-curves and the process zone length during crack propagation of complete fracture process are also described.     

Synthesis,growth, optical,mechanical and electrical properties of <Emphasis Type="Italic">L</Emphasis>-lysine <Emphasis Type="Italic">L</Emphasis>-lysinium dichloride nitrate (<Emphasis Type="Italic">L</Emphasis>-LLDN) single crystal

Semi-organic nonlinear optical material, L-lysine L-lysinium dichloride nitrate (2C₆H₁₅N₂O₂⁺_{2}^{+} · H⁺ · NO₃^-_{3}^{-} · 2Cl⁻) was synthesized at room temperature. Single crystals of L-LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (ε _r), dielectric loss (tan δ) and a.c. conductivity (σ _ac) were also measured.     

Carbonization behavior of <Emphasis Type="SmallCaps">l</Emphasis>-tryptophan and gluten

Carbonization behavior of l-tryptophan and gluten has been investigated in comparison with that of acenaphthylene using CHN elemental analysis, wide angle X-ray diffractometry, laser Raman spectroscopy and polarizing light microscopy. The carbon derived from l-tryptophan by the heat-treatment at 3,000 °C showed almost the same degree of graphitization as that from acenaphthylene and the average interlayer spacings of both these carbons approached to 0.3354 nm. The average interlayer spacing of the carbon from gluten, on the other hand, did not approach to this value at 3,000 °C. The crystallites in the carbon from l-tryptophan were smaller than those in the carbon from acenaphthylene but larger than those in the carbon from gluten. The ratio, R, of the intensity of the Raman band at 1,360 cm⁻¹ against that at 1,580 cm⁻¹ and the half width, Δλ, of the Raman band at 1,580 cm⁻¹ were measured. The R and Δλ are the measures for the degree of graphitization. Those values for the carbon from l-tryptophan were nearly equal to those for the carbon from acenaphthylene and smaller than those for the carbon from gluten. The thin film of l-tryptophan heat-treated at 500 °C for 2 h showed a texture consisting of a fine mosaic mesophase structure and an anisotropic flow-type texture of mesophase.