255,748 research outputs found
Thermal breakage of a semiflexible polymer: Breakage profile and rate
Understanding fluctuation-induced breakages in polymers has important
implications for basic and applied sciences. Here I present for the first time
an analytical treatment of the thermal breakage problem of a semi-flexible
polymer model that is asymptotically exact in the low temperature and high
friction limits. Specifically, I provide analytical expressions for the
breakage propensity and rate, and discuss the generalities of the results and
their relevance to biopolymers
Effects of process variables on micromeritic properties and drug release of non-degradable microparticles
Introduction: The purpose of this investigation was to evaluate microencapsulated controlled release preparation of theophylline using Eudragit RS 100 as the retardant material with high entrapment efficiency. Methods: Microspheres were prepared by the emulsion-solvent evaporation method. A mixed solvent system consisting of methanol and acetone and light liquid paraffin as oily phase were chosen. Sucrose stearate was used as the surfactant to stabilize the emulsification process. The prepared microspheres were characterized by drug loading, Fourier-transform infrared spectroscopy (FTIR), differential scanning colorimetry (DSC) and scanning electron microscopy (SEM). The in vitro release studies were performed at pH 1.2 and 7.4 aqueous medium. Results: Increasing the concentration of emulsifier, sucrose fatty acid ester F-70, decreased the particle size which contributed to increased drug release rate. The drug loading microparticle Eudragit RS100(1:6) showed 60-75% of entrapment and mean particle size 205.93-352.76 μm.The results showed that, an increase in the ratio of polymer: drug (F5, 6: 1) resulted in a reduction in the release rate of the drug which may be attributed to the hydrophobic nature of the polymer. Conclusion: The release of theophylline is influenced by the drug to polymer ratio and particle size. Drug release is controlled by diffusion and the best-fit release kinetic is Higuchi model. © 2011 by Tabriz University of Medical Sciences
Star polymers rupture induced by constant forces
In this work, we study the breakage process of an unknotted three-arm star-shaped polymer when it is pulled from its free ends by a constant force. The star polymer configuration is described through an array of monomers coupled by anharmonic bonds, while the rupture process is tracked in three-dimensional space by means of Langevin Molecular Dynamics simulations. The interaction between monomers is described by a Morse potential, while a Weeks-Chandler-Anderson energetic contribution accounts for the excluded volume interaction. We explore the effect of the molecular architecture on the distributions of rupture times over a broad interval of pulling forces and star configurations. It was found that the rupture time distribution of the individual star arms is strongly affected by the star configuration imposed by the pulling forces and the length of the arms. We also observed that for large pulling forces the rupture time distributions resemble the dominant features observed for linear polymer chains. The model introduced here provides the basic ingredients to describe the effects of tensile forces on stress-induced degradation of branched macromolecules and polymer networks.Fil: GarcĂa, Nicolás. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de FĂsica del Sur. Universidad Nacional del Sur. Departamento de FĂsica. Instituto de FĂsica del Sur; ArgentinaFil: Febbo, Mariano. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de FĂsica del Sur. Universidad Nacional del Sur. Departamento de FĂsica. Instituto de FĂsica del Sur; ArgentinaFil: Vega, Daniel Alberto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de FĂsica del Sur. Universidad Nacional del Sur. Departamento de FĂsica. Instituto de FĂsica del Sur; ArgentinaFil: Milchev, A.. Bulgarian Academy of Sciences; Bulgari
Oscillatory fracture path in thin elastic sheet
We report a novel mode of oscillatory crack propagation when a cutting tip is
driven through a thin brittle polymer film. The phenomenon is so robust that it
can easily be reproduced at hand (using CD packaging material for example).
Careful experiments show that the amplitude and wavelength of the oscillatory
crack path scale lineraly with the width of the cutting tip over a wide range
of lenghtscales but are independant of the width of thje sheet and the cutting
speed. A simple geometric model is presented, which provides a simple but
thorough interpretation of the oscillations.Comment: 6 pages, submitted to Comptes Rendus Academie des Sciences. Movies
available at http://www.lmm.jussieu.fr/platefractur
Label-free Raman hyperspectral imaging of single cells cultured on polymer substrates
While Raman hyper-spectral imaging has been widely used for label-free mapping of biomolecules in cells, these measurements require the cells to be cultured on weakly Raman scattering substrates. However, many applications in biological sciences and engineering require the cells to be cultured on polymer substrates that often generate large Raman scattering signals. Here, we discuss the theoretical limits of the signal-to-noise ratio in the Raman spectra of cells in the presence of polymer signals and how optical aberrations may affect these measurements. We show that Raman spectra of cells cultured on polymer substrates can be obtained using automatic subtraction of the polymer signals and demonstrate the capabilities of these methods in two important applications: tissue engineering and in-vitro toxicology screening of drugs. Apart from their scientific and technological importance, these applications are examples of the two most common measurement configurations: 1) cells cultured on an optically thick polymer substrate measured using an immersion/dipping objective; 2) cells cultured on a transparent polymer substrate and measured using an inverted optical microscope. In these examples we show that Raman hyperspectral datasets with sufficient quality can be successfully acquired to map the distribution of common biomolecules in cells, such as nucleic acids, proteins and lipids, as well as detecting the early stages of apoptosis. We also discuss strategies for further improvements that could expand the application of Raman hyperspectral imaging on polymer substrates even further in biomedical sciences and engineering
A Convergent Synthetic Platform for Single-Nanoparticle Combination Cancer Therapy: Ratiometric Loading and Controlled Release of Cisplatin, Doxorubicin, and Camptothecin
The synthesis of polymer therapeutics capable of controlled loading and synchronized release of multiple therapeutic agents remains a formidable challenge in drug delivery and synthetic polymer chemistry. Herein, we report the synthesis of polymer nanoparticles (NPs) that carry precise molar ratios of doxorubicin, camptothecin, and cisplatin. To our knowledge, this work provides the first example of orthogonally triggered release of three drugs from single NPs. The highly convergent synthetic approach opens the door to new NP-based combination therapies for cancer.MIT Research Support CommitteeLincoln Laboratory. Advanced Concepts CommitteeUnited States. Dept. of Defense (Ovarian Cancer Research Program Teal Innovator Award)National Institutes of Health (U.S.) (Ruth L. Kirschstein National Research Service Award 1F32EB017614-01)Natural Sciences and Engineering Research Council of Canada (Postdoctoral Fellowship)Natural Sciences and Engineering Research Council of Canada (Graduate Fellowship)National Cancer Institute (U.S.) (Koch Institute Support (Core) Grant P30-CA14051
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Poly(acrylic acid) interpolymer complexation: use of a fluorescence time resolved anisotropy as a poly(acrylamide) probe
YesA low concentration poly(acrylamide) sensor has been developed
which uses the segmental mobility of another polymer probe with a
covalently attached fluorescent marker. Interpolymer complexation
with poly(acrylic acid) leads to reduced segmental mobility which can
be used to determine the concentration of polymer in solution. This
technique could be useful in detecting the runoff of polymer dispersants
and flocculants in fresh water supplies following water purification
processes.Funding for the research was kindly provided by the Engineering and Physical Sciences Research Council (EPSRC)
Chemically specifi C multiscale modeling of clay-polymer nanocomposites reveals intercalation dynamics, tactoid self-assembly and emergent materials properties
A quantitative description is presented of the dynamical process of polymer intercalation into clay tactoids and the ensuing aggregation of polymerentangled tactoids into larger structures, obtaining various characteristics of these nanocomposites, including clay-layer spacings, out-of-plane clay-sheet bending energies, X-ray diffractograms, and materials properties. This model of clay-polymer interactions is based on a three-level approach, which uses quantum mechanical and atomistic descriptions to derive a coarse-grained yet chemically specifi c representation that can resolve processes on hitherto inaccessible length and time scales. The approach is applied to study collections of clay mineral tactoids interacting with two synthetic polymers, poly(ethylene glycol) and poly(vinyl alcohol). The controlled behavior of layered materials in a polymer matrix is centrally important for many engineering and manufacturing applications. This approach opens up a route to computing the properties of complex soft materials based on knowledge of their chemical composition, molecular structure, and processing conditions.This work was funded in part by the EU FP7 MAPPER project (grant number RI-261507) and the Qatar National Research Fund (grant number 09–260–1–048). Supercomputing time was provided by PRACE on JUGENE (project PRA044), the Hartree Centre (Daresbury Laboratory) on BlueJoule and BlueWonder via the CGCLAY project, and on HECToR and ARCHER, the UK national supercomputing facility at the University of Edinburgh, via EPSRC through grants EP/F00521/1, EP/E045111/1, EP/I017763/1 and the UK Consortium on Mesoscopic Engineering Sciences (EP/L00030X/1). The authors are grateful to Professor Julian Evans for stimulating discussions during the course of this project. Data-storage and management services were provided by EUDAT (grant number 283304)
TransPolymer: a Transformer-based language model for polymer property predictions
Accurate and efficient prediction of polymer properties is of great
significance in polymer design. Conventionally, expensive and time-consuming
experiments or simulations are required to evaluate polymer functions.
Recently, Transformer models, equipped with self-attention mechanisms, have
exhibited superior performance in natural language processing. However, such
methods have not been investigated in polymer sciences. Herein, we report
TransPolymer, a Transformer-based language model for polymer property
prediction. Our proposed polymer tokenizer with chemical awareness enables
learning representations from polymer sequences. Rigorous experiments on ten
polymer property prediction benchmarks demonstrate the superior performance of
TransPolymer. Moreover, we show that TransPolymer benefits from pretraining on
large unlabeled dataset via Masked Language Modeling. Experimental results
further manifest the important role of self-attention in modeling polymer
sequences. We highlight this model as a promising computational tool for
promoting rational polymer design and understanding structure-property
relationships from a data science view
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