The Effect of Glycol Derivatives on the Properties of Bio-Based Unsaturated Polyesters.

The scope of the present study was to prepare fully bio-based unsaturated polyester resins (UPRs) with comparable properties to the commercial formulations. The focus was set on the determination of the optimal prepolymer formulation using the same set of diacids (itaconic and succinic acid) and different diols (propylene glycol, isosorbide and neopentyl glycol) or its equimolar mixtures, keeping the fixed molar ratio of 1:1:2.1 in all feed compositions. Instead of commonly used styrene, bio-based dimethyl itaconate was used as a reactive diluent (RD). The rheology of the obtained resins was studied in detail. The effect of the used diol on structural (FTIR), thermal (DSC), thermomechanical (DMA), and mechanical (tensile) properties was explained. The properties of UPRs were found to be highly dependent on the diol used in the prepolymer formulation. The UPR with an equimolar ratio of propylene glycol and neopentyl glycol was shown to be the most promising candidate to compete with the commercial petroleum-based resins.

Release behaviour of carbamazepine-loaded poly(ε-caprolactone)/poly(ethylene oxide) microspheres.

Poly(ε-caprolactone) (PCL), a biodegradable and biocompatible aliphatic polyester has a great potential as a drug carrying material in controlled drug delivery/release systems. The most simple and economical way to tailor the release profile of active substances from biodegradable polymer matrix is by the addition of the second polymeric component in the polymer matrix, i.e. by blending. This study describes the preparation and characterization of a carbamazepine-loaded microspheres by the use of PCL blended with poly(ethylene oxide) as a drug carrying material. By the use of two-component hydrophilic/hydrophobic polymer blend as a microspheres' matrix material, release profile of the drug can be modified and dictated. The microspheres prepared by classical oil-in-water emulsion solvent evaporation technique were characterized with respect to particle size and morphology, polymer matrix composition, encapsulation efficiency, physical state of the drug and in vitro release behaviour. It was presented that the release profile can be modified by the presence and the amount of hydrophilic component in the starting formulation of microspheres.

Fluorescence properties of hydrophilic semiconductor nanoparticles with tridentate polyethylene oxide ligands.

In this contribution a facile, one-step synthesis of tridentate thiol-functionalized PEO ligands and their ability to stabilize CdSe/CdS/ZnS core-shell-shell nanoparticles in aqueous media are described. The PEO-coated quantum dots show colloidal stability as well as preserved fluorescence even at very low concentrations of a few nM. For improved ligand attachment and enhanced fluorescence properties a method for ligand exchange was developed, which includes formation of a ligand zinc complex before the actual exchange reaction. The stability and fluorescence properties in various aqueous buffers and cell media and at pH values down to pH 3 were investigated. The firm binding of the tridentate ligands to the particle surface makes this ligand-particle system a promising tool for biological applications. In addition, activation of the ligands' terminal hydroxyl group for covalent biofunctionalization by esterification with succinic acid is reported.

Real-time magnetic resonance imaging and quantification of lipoprotein metabolism in vivo using nanocrystals.

Semiconductor quantum dots and superparamagnetic iron oxide nanocrystals have physical properties that are well suited for biomedical imaging. Previously, we have shown that iron oxide nanocrystals embedded within the lipid core of micelles show optimized characteristics for quantitative imaging. Here, we embed quantum dots and superparamagnetic iron oxide nanocrystals in the core of lipoproteins--micelles that transport lipids and other hydrophobic substances in the blood--and show that it is possible to image and quantify the kinetics of lipoprotein metabolism in vivo using fluorescence and dynamic magnetic resonance imaging. The lipoproteins were taken up by liver cells in wild-type mice and displayed defective clearance in knock-out mice lacking a lipoprotein receptor or its ligand, indicating that the nanocrystals did not influence the specificity of the metabolic process. Using this strategy it is possible to study the clearance of lipoproteins in metabolic disorders and to improve the contrast in clinical imaging.

Micelle and vesicle formation of amphiphilic nanoparticles.

Nanoparticle brushes: Complex nanostructures can be formed by self assembly of amphiphilic CdSe/CdS core-shell nanoparticles that bear a brushlike layer of poly(ethylene oxide) chains. This route is based on controlling the volume fractions of hydrophilic and hydrophobic moieties within the particles and allows the formation of micellar, cylindrical, or vesicular nanoobjects (see picture).

Size and surface effects on the MRI relaxivity of manganese ferrite nanoparticle contrast agents.

Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches. First, we applied a ligand exchange in order to form a water soluble polymer shell. Second, the particles were embedded into an amphiphilic polymer shell. Third, the nanoparticles were embedded into large micelles formed by lipids. Although all approaches lead to effective negative contrast enhancement, we observed significant differences concerning the magnitude of this effect. The transverse relaxivity, in particular r2*, is greatly higher for the micellar system compared to the polymer-coated particles using same-sized nanoparticles. We also observed an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystals. The results are qualitatively compared with theoretical models describing the dependence of relaxivity on the size of magnetic spheres.