Search results for "Plastics"
showing 10 items of 2724 documents
α,β-Poly(N-Hydroxyethyl)-DL-Aspartamide Hydrogels as Drug Delivery Devices
1996
α,β-poly(N-hydroxyethyl)-DL-aspartamide (PHEA) was exposed to gamma radiation to obtain micromatrices able to swell in an aqueous medium. Crosslinked PHEA was loaded with an anti-inflammatory drug, 4-biphenylacetic acid (BPAA) and the drug dispersion in the network was investigated by X-ray analysis. The BPAA loaded PHEA microparticles were also characterized by dimensional analysis, which showed the presence of quasispherical shapes. The drug release from PHEA hydrogel was studied in vitro in a pH 1.1 (simulated gastric juice) and in a pH 7.4 buffer solution, respectively. The experimental data indicate that an anomalous delivery occurs, but Fickian diffusion through swollen PHEA hydrogel…
A bio-orthogonal functionalization strategy for site-specific coupling of antibodies on vesicle surfaces after self-assembly
2019
Attaching targeting ligands on the surface of self-assembled drug delivery systems is the key request for a controlled transport of the drug to a desired location. Most commonly, the amphiphilic molecules (blockcopolymers, lipids etc.) are therefore pre-functionalized before the self-assembly takes place. However, this strategy cannot be applied, if it interferes with the self-assembly process, if the introduced functional groups react with loaded cargo or if natural carriers like extracellular vesicles should be functionalized. Here, we present the site-specific coupling of antibodies to the surface of amino group-terminated liposomes via bio-orthogonal copper-free click chemistry after li…
Macromolecules in ordered media. II. A fluorescence study of the polymer-liposome association
1995
The interactions of poly (4-vinyl pyridine) with dimyristoylphosphatidic acid-based liposomes were studied in heterogeneous solution systems. The polymer was dispersed in aqueous buffer solutions of small unilamellar vesicles and after a suitable period of incubation to raise the equilibrium, the experiments has been conducted as a function of polymer concentration and temperature. According to the measurements of the steady-state fluorescence spectra, changes in the intensities as well as shifts in the emission peak wavelength, has served as raw data to accounting for the polymer-vesicle interactions. Quantitative evaluation of the interaction has been done using a simple associating model…
Time-resolved rheology as a tool to monitor the progress of polymer degradation in the melt state – Part II: Thermal and thermo-oxidative degradation…
2015
Abstract Thermal and thermo-oxidative degradation of nanocomposites based on polyamide 11 (PA11) and organo-modified clay (Cloisite® 30B) are studied in the melt state (T = 215 °C) via time-resolved mechanical spectroscopy (TRMS). The goal is assessing the potentiality of rheological analysis for studying polymer degradation in complex systems such as polymer nanocomposites, whose rheological response stems from the combination of the contributions of polymer and nanoparticles. We prove that a thorough analysis grounded on TRMS allows to isolate the effect of degradation of the polymer matrix, whose progress can be hence profitably monitored. Essentially the same degradation mechanisms as i…
A Deeper Insight into the Postpolymerization Modification of Polypenta Fluorophenyl Methacrylates to Poly(N -(2-Hydroxypropyl) Methacrylamide)
2014
This work provides a detailed insight into the synthesis of N-(2-hydroxypropyl)methacrylamide (HPMA) polymers employing the activated ester approach. In this approach, polypenta fluorophenyl methacrylate (PFPMA)-activated ester polymers are synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization and transferred into HPMA-based systems by the use of 2-hydroxypropylamine. To prove quantitative conversion in the absence of side reactions, special attention is devoted to investigate different reaction conditions by different analytical methods ((1) H, (19) F, inverse-gated (13) C NMR, and zeta potential measurements). Furthermore the influence of common solvent…
Degradable cationic nanohydrogel particles for stimuli-responsive release of siRNA.
2014
Well-defined nanogels have become quite attractive as safe and stable carriers for siRNA delivery. However, to avoid nanoparticle accumulation, they need to provide a stimuli-responsive degradation mechanism that can be activated at the payload's site of action. In this work, the synthetic concept for generating well-defined nanohydrogel particles is extended to incorporate disulfide cross-linkers into a cationic nanonetwork for redox-triggered release of oligonucleotide payload as well as nanoparticle degradation under reductive conditions of the cytoplasm. Therefore, a novel disulfide-modified spermine cross-linker is designed that both allows disassembly of the nanogel as well as removal…
Structural modifications in an irradiated ethylene-vinyl alcohol copolymer
1982
Extraction experiments and calorimetric measurements have been performed, on a commercial ethylene-vinyl alcohol copolymer irradiated in the dose range 0–20 Mrad.
Photodegradation of polyglycidol in aqueous solutions exposed to UV irradiation
2011
The photodegradation of polyglycidol in aqueous solution with UV wavelength of 254 nm was investigated. The experiments were carried out in air at a constant temperature and the photodegradation of polyglycidol (PGl) was compared to that of poly(ethylene oxide) (PEO), the most widely studied polyether. Size exclusion chromatography with multiangle light scattering detection (SEC-MALLS) was used to measure the changes in the molar masses and molar mass dispersities of polymers during degradation. The molar mass of PGl decreased dramatically during the first period of UV irradiation and then gradually approached a limiting value of 17,000 g/mol, regardless of the initial polymer concentration…
Effect of carboxymethyl cellulose concentration on rheological behavior of milk and aqueous systems. A creep and recovery study
2009
Carboxymethyl cellulose (CMC) is an anionic polysaccharide used mainly as stabilizer and thickener agent. The purpose of this study was to investigate the effect of CMC concentration on viscoelasticity of dairy and aqueous model systems through the analysis of creep and recovery tests. The viscoelastic properties of different concentrations of CMC (0.75, 1.00, 1.25, and 1.50% w/w) in two milk systems (skimmed milk and whole milk) were compared with those of the same concentration of biopolymer in aqueous solution. Creep curves were fitted to a six parameter mechanical model (Burger + Kelvin-Voigt), whereas an empirical equation was used for recovery. The creep and recovery properties of sam…
Photoswitchable Smectic Liquid-Crystalline Elastomers
2005
We succeeded in the synthesis of azo side chain containing polysioxanes with broad smectic C* and A phases. In these polymers the phase transition temperatures can be shifted reversibly by up to 17°C by irradiation with UV (cis) or VIS (trans) light. Thin films of these polymers in the smectie phase (both on substrates and as free-standing films) orient perfectly in a homeotropic manner. As a consequence, the aze chromophores do no longer absorb during a perpendicular illumination with light (dichroism). It is thus possible to crosslink these films photochemically to prepare photoswitchable smectic LC elastomers.