In vitro degradation and drug release from polymer blends based on poly(<Emphasis Type="SmallCaps">dl</Emphasis>-lactide), poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-glycolide) and poly(ε-caprolactone)

Bioresorbable materials are extensively used for a wide range of biomedical applications. Accurately modifying and evaluating the degradation rate of these materials is critical to their performance and the controlled release of bioactive agents. The aim of this work was to modify the physical properties, degradation rate and drug delivery characteristics of thin films for medical applications by blending poly(dl-lactic acid) (PDLLA), poly(l-lactide-co-glycolide) (PLGA) and poly(ε-caprolactone) (PCL). The thin films were prepared using solvent casting and compression moulding and the in vitro degradation study was performed by immersing the films in a phosphate-buffered saline at elevated temperature for a period of 4 weeks. The degradation rate of the materials was analysed by differential scanning calorimetry, tensile testing and weight loss studies. The thermal analysis of the blends indicated that the presence of PLGA or PDLLA in the film resulted in increased degradation of the amorphous regions of PCL. It was observed that the samples consisting of PDLLA with PCL demonstrated the greatest weight loss. The decrease in mechanical properties observed for both sets of polymer blends proved to be similar. The solvent cast technique was selected as the most appropriate for the formation of the polymer/drug matrices, due to the potentially adverse thermal processing effects associated with compression moulding. It was found that modulation of drug release was achievable by altering the ratio of PCL to PDLLA or PLGA in the thin film blends.     

Spectral study of interaction between poly(<Emphasis Type="SmallCaps">l</Emphasis>-lysine)–poly(ethylene glycol)–poly(<Emphasis Type="SmallCaps">l</Emphasis>-lysine) and nucleic acids

Polymer-DNA interactions have attracted considerable interests due to their important application in DNA transfection and cellular drug delivery technologies. In this work, a new detection assay for DNA is proposed with a tri-block copolymer poly(l-lysine)–poly(ethylene glycol)–poly(l-lysine) by resonance light scattering technique with the linear ranges from 0.0656 to 6.56 μg ml⁻¹. The detection limit for DNA is 0.42 ng ml⁻¹. Most coexisting substances do not interfere in the detection. UV-spectra and FTIR-spectra were employed to demonstrate the mechanisms of the interaction that the conformation of the DNA changes because the microenvironment of DNA changes.     

Evaluation of an injectable,photopolymerizable three-dimensional scaffold based on <Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide and ɛ-caprolactone in a tibial goat model

An in situ crosslinkable, biodegradable, methacrylate-encapped porous bone scaffold composed of D: ,L: -lactide, varepsilon-caprolactone, 1,6-hexanediol and poly(ortho-esters), in which crosslinkage is achieved by photoinitiators, was developed for bone tissue regeneration. Three different polymer mixtures (pure polymer and 30% bioactive glass or alpha-tricalcium phosphate added) were tested in a uni-cortical tibial defect model in eight goats. The polymers were randomly applicated in one of four (6.0 mm diameter) defects leaving a fourth defect unfilled. Biocompatibility and bone healing properties were evaluated by serial radiographies, histology and histomorphometry. The pure polymer clearly showed excellent biocompatibility and moderate osteoconductive properties. The addition of alpha-TCP increased the latter characteristics. This product offers potentials as a carrier for bone healing promoter substances.     

Emulsion electrospun vascular endothelial growth factor encapsulated poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid-<Emphasis Type="Italic">co</Emphasis>-ε-caprolactone) nanofibers for sustained release in cardiac tissue engineering

Emulsion electrospinning is a novel approach to fabricate core–shell nanofibers, and it is associated with several advantages such as the alleviation of initial burst release of drugs and it protects the bioactivity of incorporated drugs or proteins. Aiming to develop a sustained release scaffold which could be a promising substrate for cardiovascular tissue regeneration, we encapsulated vascular endothelial growth factor (VEGF) with either of the protective agents, dextran or bovine serum albumin (BSA) into the core of poly(l-lactic acid-co-ε-caprolactone) (PLCL) nanofibers by emulsion electrospinning. The morphologies and fiber diameters of the emulsion electrospun scaffolds were determined by scanning electron microscope, and the core–shell structure was evaluated by laser scanning confocal microscope. Uniform nanofibers of PLCL, PLCL–VEGF–BSA, and PLCL–VEGF–DEX with fiber diameters in the range of 572 ± 92, 460 ± 63, and 412 ± 61 nm, respectively were obtained by emulsion spinning. The release profile of VEGF in phosphate-buffered saline for up to 672 h (28 days) was evaluated, and the scaffold functionality was established by performing cell proliferations using human bone marrow derived mesenchymal stem cells. Results of our study demonstrated that the emulsion electrospun VEGF containing core–shell structured PLCL nanofibers offered controlled release of VEGF through the emulsion electrospun core–shell structured nanofibers and could be potential substrates for cardiac tissue regeneration.     

Fabrication and characterization of porous poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) scaffolds using solid–liquid phase separation

Freeze-extraction, which involves phase separation principle, gave highly porous scaffolds without the time and energy consuming freeze-drying process. The presented method eliminates the problem of formation of surface skin observed in freeze-drying methods. The effects of different freezing temperature (−80 and −24°C), medium (dry ice/ethanol bath and freezer) and polymer concentrations (1, 3, and 5 wt.%) on the scaffold properties were investigated in connection with the porous morphology and physicomechanical characteristics of the final scaffolds. The FESEM micrographs showed porous PLLA scaffolds with ladder-like architecture. The size of the longitudinal pores was in the range of 20–40 μm and the scaffolds had high porosity values ranging from 90% to 98%. Variation in porosity, mechanical resistance, and degree of regularity in the spatial organization of pores were observed when polymer concentration was changed. More open scaffold architecture with enhanced pore interconnectivity was achieved when a dry ice/ethanol bath of −80°C was used. Polymer concentration played an important role in fabricating highly porous scaffolds, with ladder-like architecture only appearing at polymer concentrations of above 3 wt.%. With the freeze-extraction method used here, highly porous and interconnected poly(l-lactide) scaffolds were successfully fabricated, holding great potential for tissue engineering applications.     

TiO<Subscript>2</Subscript> foams with poly-(<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) (PDLLA) and PDLLA/Bioglass<Superscript>®</Superscript> coatings for bone tissue engineering scaffolds

TiO₂ foam-like scaffolds with pore size ~300 μm and >95% porosity were fabricated by the foam replication method. A new approach to improve the structural integrity of the as-sintered foams, which exhibit extremely low compression strength, was explored by coating them with poly-(d,l-lactic acid) (PDLLA) or PDLLA/Bioglass^® layers. The PDLLA coating was shown to improve the mechanical properties of the scaffold: the compressive strength was increased by a factor of ~7. The composite coating involving Bioglass^® particles was shown to impart the rutile TiO₂ scaffold with the necessary bioactivity for the intended applications in bone tissue engineering. A dense hydroxyapatite layer formed on the surface of the foams upon immersion in simulated body fluid for 1 week.     

Fabrication of hydroxyapatite-poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) scaffolds by a combination of the extrusion and bi-axial lamination processes

Hydroxyapatite (HA)/poly(ε-caprolactone) (PCL) composite scaffolds were fabricated using a combination of the extrusion and bi-axial lamination processes. Firstly, HA/PCL composites with various HA contents (0, 50, 60, 70 wt%) were prepared by mixing the HA powders and the molten PCL at 100 °C and then extruded through an orifice with dimensions of 600 × 600 μm to produce HA/PCL composite fibers. Isobutyl methacrylate (IBMA) polymer fiber was also prepared in a similar manner for use as a fugitive material. The 3-D scaffold was then produced by the bi-axial lamination of the HA/PCL and IBMA fibers, followed by solvent leaching to remove the IBMA. It was observed that the HA/PCL composites had a superior elastic modulus and biological properties, as compared to the pure PCL. The fabricated HA/PCL scaffold showed a controlled pore structure (porosity of ∼49% and pore size of ∼512 μm) and excellent welding between the HA/PCL fibers, as well as a high compressive strength of ∼7.8 MPa.     

Robustness issues for <Emphasis Type="SmallCaps">cub</Emphasis> models

The present paper deals with a parametric class of models implemented for ordered categorical data, denoted as cub  model, which is defined as a discrete mixture of a shifted binomial and a uniform random variable. For these models, robustness issues are considered. In particular, the influence function is introduced and subsequently used to define the robustness measures for categorical data. By exploiting the peculiar parametrization of the cub  models, diagnostic plots are proposed which allow to display the effect of a contamination in the data, simultaneously for all categories. The breakdown point is also considered and a computational procedure is suggested to determine an upper bound. The paper provides evidence that, despite the limited range of the support, contaminations in the data can heavily affect the inferential procedures and hence robustness topics are indeed relevant for ordinal data.     

Extraction of U(VI) and Th(IV) ions from nitric acid solutions with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-tetra-2-ethylhexylglutaramide

N,N,N′,N′-Tetra-2-ethylhexylglutaramide (TEHGA) was used as a new extractant for the extraction of U(VI) and Th(IV) from nitric acid solutions. Toluene was found to be the most suitable diluent for TEHGA. The extraction of nitric acid was also studied. The influence exerted on the distribution ratio (D) of U(VI) and Th(IV) by the concentrations of HNO₃, TEHGA, and LiNO₃ as salting-out agent, and also by the equilibration time, temperature, and kind of diluent was examined. Good U–Th separation can be achieved using 2–3 M HNO₃. The results obtained show that U(VI) and Th(IV) are mainly extracted as UO₂(NO₃)₂·2TEHGA and Th(NO₃)₄·TEHGA, respectively. The IR spectra of the extracted species were analyzed. The thermodynamic functions of the process were calculated. Back-extraction of U(VI) and Th(IV) from the organic phases was also studied.     

Biofunctionalized poly(ethylene glycol)-<Emphasis Type="Italic">block</Emphasis>-poly(ε-caprolactone) nanofibers for tissue engineering

Electrospun fibers with contrasting cell adhesion properties provided non-woven substrates with enhanced in vitro acceptance and controllable cell interactions. Poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL) block copolymers with varying segment lengths were synthesized in two steps and characterized by NMR and GPC. A cell adhesive peptide sequence, GRGDS, was covalently coupled to the PEG segment of the copolymer in an additional step. The suitability of polymers with molecular weights ranging from 10 to 30 kDa for electrospinning and the influences of molecular weight, solvent, and concentration on the resulting morphologies were investigated. Generally, electrospun fibers were obtained by electrospinning polymers with molecular weight larger than 25 kDa and concentrations of 10 wt%. Methanol/chloroform (25/75, v/v) mixtures proved to be good solvent systems for electrospinning the PEG-b-PCL and resulted in hydrophilic, non-woven fiber meshes (contact angle 30°). The mesh without cell adhesive GRGDS ligands showed no attachment of human dermal fibroblasts after 24 h cell culture demonstrating that the particular combination of the material and electrospinnig conditions yielded protein and cell repellent properties. The GRGDS immobilized mesh showed excellent cellular attachment with fibroblasts viable after 24 h with spread morphology. Electrospun nanofibers based on block copolymers have been produced which are capable of specifically targeting cell receptor binding and are a promising material for tissue engineering and controlling cell material interactions.     

Effect of high-pressure high-temperature processing on the phase composition of Mn<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sb (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1) alloys

High-pressure high-temperature processing (p = 7 GPa, T = 2300 K) has been shown to alter the phase composition of Mn_2?x Cr _x Sb alloys, resulting in a two-phase state: Mn₃Sb (sp. gr. Pm3m, no. 221) and a hexagonal phase of variable composition (sp. gr. P6₃/mmc, no. 194). With increasing chromium concentration, the content of the hexagonal phase increases, while that of the cubic phase drops. In addition, the occupancy of the bipyramidal interstitial sites in the hexagonal phase increases, reaching a maximum in the single-phase alloy MnCrSb (Ni₂In structure).     

Antireflection properties of diamond-like carbon films on Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> ∼ 0.04) single crystals

The optical properties of diamond-like carbon (DLC) films obtained by plasmachemical deposition on Cd_{1 − x} Zn _x Te (x ∼ 0.04) single crystals have been studied by ellipsometry. The ellipsometric data have been interpreted within the framework of a three-layer model of the DLC film-semiconductor crystal refractory system with transition layers between the film and substrate. It is found that DLC films exhibit antireflection properties in this refractory system in the IR spectral range. It is established that the proposed antireflection film-substrate structure is stable with respect to thermal cycling and ultrasonic treatment.     

<Emphasis Type="Italic">T</Emphasis>–<Emphasis Type="Italic">P</Emphasis> Phase Diagram of Nitrogen at High Pressures

By employing a mean field model, calculation of the T–P phase diagram of molecular nitrogen is performed at high pressures up to 200 GPa. Experimental data from the literature are used to fit a quadratic function in T and P, describing the phase line equations which have been derived using the mean field model studied here for N₂, and the fitted parameters are determined. Our model study gives that the observed T–P phase diagram can be described satisfactorily for the first-order transitions between the phases at low as well as high pressures in nitrogen. Some thermodynamic quantities can also be predicted as functions of temperature and pressure from the mean field model studied here and they can be compared with the experimental data.     

Thermal conductivity of Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> ≤ 0.025) solid solutions

The thermal conductivity of Er _x Sn_{1 ? x} Se solid solutions has been measured at temperatures from 80 to 360 K. The results have been used to evaluate the electronic and lattice components of thermal conductivity for elastic carrier scattering, parabolic bands, and arbitrary degeneracy. With increasing erbium content and temperature, both the electronic and lattice components decrease considerably. Long-term annealing increases both components. It follows from the present experimental data that heat conduction in Er _x Sn_{1 ? x} Se is mainly due to phonons and that the observed rise in thermal resistance with Er content is due to phonon-phonon and paramagnetic-ion scattering.     

Growth and properties of single crystals of Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (0 < <Emphasis Type="Italic">x</Emphasis> < 0.35) solid solutions

Single-crystalline Si_{1 − x} Ge _x ingots with a germanium content of up to 35 at. %, a diameter of 10mm, and a length of up to 10 cm were grown using the crucibleless float-zone melting technique. The ingots had a homogeneous distribution of germanium and a low density of dislocations. The material was characterized with respect to the structure and electrical properties. The resistivity and the carrier lifetime, mobility, and concentration in Si_{1 − x} Ge _x single crystals have been studied as functions of the germanium content.     

Synthesis and characterization of arginine–glycine–aspartic peptides conjugated poly(lactic acid-co-<Emphasis Type="SmallCaps">l</Emphasis>-lysine) diblock copolymer

A biodegradable Copolymer of poly(lactic acid-co-lysine)(PLA–PLL) was synthesized by a modified method and novel Arginine–Glycine–Aspartic (RGD) peptides were chemical conjugated to the primary ε-amine groups of lysine components in four steps: I to prepare the monomer of 3-(N^ε-benzoxycarbonyl-l-lysine)-6-l-methyl-2,5-morpholinedione; II to prepare diblock copolymer poly(lactic acid-co-(Z)-l-lysine) (PLA–PLL(Z)) by ring-opening polymerization of monomer and l,l-lactide with stannous octoate as initiator; III to prepare diblock copolymer PLA–PLL by deprotected the copolymer PLA–PLL(Z) in HBr/HoAc solution; IV the reaction between RGD and the primary ε-amine groups of the PLA–PLL. The structure of PLA–PLL–RGD and its precursors were conformed by FTIR-Raman and ¹H NMR. Low weight average molecular weight (9,200 g/mol) of the PLA–PLL was obtained and its PDI is 1.33 determined by GPC. The PLA–PLL contained 2.1 mol% lysine groups as determined by ¹H NMR using the lysine protecting group’s phenyl protons. Therefore, the novel RGD-grafted diblock copolymer is expected to find application in drug carriers for tumor therapy or non-viral DNA carriers for gene therapy.     

Investigating the nanomechanical properties and reversible color change properties of the beetle <Emphasis Type="Italic">Dynastes</Emphasis> <Emphasis Type="Italic">tityus</Emphasis>

The wing cases (elytra) of Dynastes tityus are able to change coloration from yellow-green in a dry state to deep brown in a wet state due to different degrees of water absorption. An environmental scanning electron microscope was used to investigate the elytra’s reversible color change properties. Because the elytra cuticle has a spongy structure that is composed of laminated chitin and protein, a UV–Vis–NIR spectrophotometer was used to investigate the elytra’s optical properties. The width of the curve peak gradually decreased from 60 to 10 nm when the color of the elytra varied from deep brown to yellow-green. In a humid environment, air between the voids was replaced by water with a higher refractive index that induced an elytra color changed from yellow-green to deep brown. Interestingly, when both humidity and elytra color changed, the elytra’s mechanical properties varied too. When the humidity of the environment changed from 100 to 34%, the reduced modulus (E _r) and hardness (H) of the elytra increased 230 and 440%, respectively. The storage modulus (E′) of the elytra is 1.98 ± 0.65 and 1.17 ± 0.22 GPa in yellow-green and deep brown color at 10 Hz, respectively, while their loss modulus (E″) is similar. tan δ of deep brown elytra is 0.072 ± 0.017, which is nearly two times higher than that of yellow-green. It can be demonstrated that when the elytra’s color turns to yellow-green, they are more elastic with less energy loss. The relationship between the elytra’s mechanical properties and structure color will not only help us gain insight into the biological functionality of the color change but also inspire the designs of artificial biomimetic devices.     

Influence of the Trapped Field on the Levitation Performance of the Magnetized Bulk High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductor

A magnetized bulk high-T _c superconductor (HTSC) magnet is a good candidate to improve the levitation performance of the high-T _c superconducting (HTS) maglev system. Compared with the unmagnetized bulk HTSC, the magnetized bulk HTSC magnet can supply stronger levitation or guidance force above a permanent magnet guideway (PMG). Different from the permanent magnet, the magnetic field of a magnetized bulk HTSC magnet is sustained by the induced superconducting current produced during the magnetizing process. Given that the induced superconducting current within the magnetized bulk HTSC magnet is very sensitive to the magnetic field, the levitation performance of the magnetized bulk HTSC magnet is directly related to its own trapped field and the magnetic field of the PMG. This article discusses the influence of trapped and external magnetic fields on the levitation performance of a magnetized bulk HTSC magnet by experiments, and the Critical State Model is used to analyze the test results. The analyses and conclusions of this article are useful for the application of magnetized bulk HTSC magnet in practical HTS maglev systems.     

In vitro degradation of poly-<Emphasis Type="SmallCaps">l</Emphasis>-<Emphasis Type="SmallCaps">d</Emphasis>-lactic acid (PLDLA) pellets and powder used as synthetic alloplasts for bone grafting

The objective of this study was to evaluate the in vitro degradation of pellet and powder forms of a poly-L: -D: -lactic acid material used to produce plates and screws for orthopedic, oral, and maxillofacial applications. Materials and methods In order to produce the powder form the as-received pellets were milled in a cryogenic chamber. Particles size distribution (PSD) histograms were developed for both forms. The materials were then characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) before and after immersion in simulated body fluid for 30, 60, and 90 days. Results SEM showed that for both forms material degradation started after 30 days of immersion in SBF and evolved until 90 days. Degradation started at the amorphous zones of the polymer and exposed of deeper crystalline layers. The pellet and powder samples PSD showed polydispersed patterns with mean diameters of 673.98 mum and 259.55 mum. Thermal onset degradation temperatures were 365.64 degrees C and 360.30 degrees C, and of 363.49 degrees C and 359.83 degrees C before immersion and after 90 days in SBF for the pellet and powder forms, respectively. The Tg's of the pellets and the powder were approximately 61.5 degrees C and 66 degrees C, and their respective endothermic peaks were observed at approximately 125 degrees C and 120 degrees C. The specific heat (c) was approximately 8.5 J/g and 6.2 J/g for the pellet and powder material, respectively. Conclusion According to the results obtained, cryogenic milling resulted in particle plastic deformation, and alterations in glass transition temperature, melting temperature, and specific heat of the material.