Marija S. Nikolic

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).

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.

Synthesis and characterization of biodegradable poly(butylene succinate-co-butylene fumarate)s

Abstract A series of aliphatic biodegradable polyesters modified with fumaric residues was synthesized by transesterification in the melt of dimethyl succinate, dimethyl fumarate and 1,4-butanediol. The amount of unsaturation, originating from the fumaric acid residues in the polyesters chains was varied from 5 to 20 mol%. The molecular structure and composition of the polyesters were determined by 1H NMR spectroscopy. The effects of the content of fumaric residues on the thermal and thermo-oxidative properties of the synthesized polyesters were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. The degree of crystallinity was determined by DSC and wide angle X-ray scattering. The degrees of crystallinity of the unsaturated copolyesters were reduced, while the melting temperatures were higher in comparison to poly(butylene succinate). Biodegradation of the synthesized copolyesters was estimated in enzymatic degradation tests using a buffer solution with Rhizopus arrhizus lipase at 37 °C. Although the degree of crystallinity of the copolyesters decreases slightly with increasing unsaturation, the biodegradation is not enhanced suggesting that not only the chemical structure and molecular stiffness but also the morphology of the spherulites has an influence on the biodegradation properties. The highest biodegradability was observed for the copolyesters containing 5 and 10 mol% of fumarate units.

CdSe/CdS nanoparticles immobilized on pNIPAm-based microspheres

In this work, CdSe/CdS semiconductor ligand-exchanged nanoparticles have been immobilized on poly-(N-isopropylacrylamide) (pNIPAM)-based microspheres. The size and the shrinkage capacity of the spheres can be tuned by the ratio of NIPAM/styrene (pNIPAM-PS spheres) or NIPAM/BIS (N-N′-methylene-bis-acrylamide) and MA (maleic acid) (pNIPAM-BIS-MA spheres). A ligand-exchange procedure for the transfer of initially organic compatible nanoparticles into aqueous solution using amine-modified or thiol-modified poly(ethylene oxide)s (PEOs) has been carried out prior to their immobilization. We observed that the interaction of the nanoparticles with the pNIPAM-based system depends on the nature of the ligands and the chemical composition of the microspheres. Nanoparticles capped with amine- or mercapto- poly(ethylene oxide)s ligands interact with pNIPAM–PS beads while only amine-capped ones show a clear tendency to interact with pNIPAM containing acid groups which leads to a high nanoparticle coverage. Dynamic light scattering measurements, atomic force microscopy and optical spectroscopy hint that nanoparticles are placed on the surface of pNIPAM-BIS-MA beads while being partially incorporated into pNIPAM-PS network. Cell culture studies demonstrate that the fluorescent composites show non-specific binding to fibroblasts. These features may be very valuable to develop materials for drug delivery and specific targeting of cells combined with the outstanding optical properties of semiconductor nanoparticles as fluorescent labelers.

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.

Influence of a low content of PEO segment on the thermal, surface and morphological properties of triblock and diblock PCL copolymers

Two series, one of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers were prepared by ring-opening polymerization of ε-caprolactone catalized with tin(II) octoate and by using dihydroxy or monohydroxy poly(ethylene oxide) as the macroinitiator. The PEO block length was fixed (Mn 1,000 g/mol) and the PCL block lengths (Mn 10,000-40,000 g/mol) were tailored by changing weight ratio of ε-CL/PEO. The copolymers’ structure was confirmed by 1H and quantitative 13C NMR spectroscopy while their molecular weights were determined by GPC analysis. The thermal properties and the degree of crystallinity of the copolymers were investigated and compared by using DSC and WAXS. Both types of copolymers were semicrystalline with the orthorhombic PCL crystal lattice. The surface morphology of the copolymer films was investigated by using optical microscopy and AFM analysis, which confirmed the spherulitic lamellar structure with spherulites of different diameters. Data indicated that a low content of PEO segment had an influence on thermal degradation behavior, crystallinity and morphology of copolymers. Roughness of copolymer films was affected by the content of PEO and correlated with the spherulites’ diameter. The small changes in water and moisture absorption properties of copolymers compared to homopolymer PCL were observed.

Chapter 6:Biodegradable Polyesters: Synthesis and Physical Properties

This chapter summarizes the synthesis and physical properties of the main members of the biodegradable polyesters family, with special reference to their biodegradability behavior in different environments. Polyesters constitute a large group of biodegradable polymers intended for use in medicine and for the environment protection. Biodegradable polyesters are versatile group of polymers with a range of thermal, mechanical and degradation properties which can easily be tailored to suite a particular application. Biodegradable polyesters can be classified according to their origin as natural or synthetic, the later being further divided into those from renewable and those from petrochemical resources. The synthetic routes to most important polyesters from each of these groups and their physical properties are presented. The representative of polyesters from natural origin are poly(hydroxyalkanoate)s. Poly(lactic acid) is an example of a synthetic polyester obtained from renewable resources, while poly(e-caprolactone) and poly(butylene succinate) are the most important synthetic biodegradable polyesters obtained from petrochemicals. Although aromatic polyesters are not biodegradable, aliphatic-aromatic copolyesters with improved thermal properties and retained biodegradability have been developed. All of these polyesters, together with different copolyesters have been brought to full commercialization, however there is still room for further cost/performance improvements. The application potential of these materials is discussed and selected examples of commercially available polyesters are given. Future trends in the biodegradable polyester synthesis and material design are briefly discussed.

Triple notch UWB antenna controlled by three types of resonators

This paper discusses a microstrip fed UWB monopole antenna with a triple notch characteristic. The three notches are designed to occur at the WiMAX frequency range, the WLAN and at a third frequency in the higher end of the UWB range. Each of the three notches is controlled by a different type of resonators and each and every notch can be adjusted without affecting the position or the shape of the remaining two, thus allowing for an antenna design with adjustable, agile S11 response.

UWB antenna with a WiMAX frequency notch caused by a novel stepped U shaped slot that suppresses the parasitic notches

UWB antennas with embedded stubs or slots can create a notch in the frequency range. The frequency notch and therefore the reduced radiation intensity is confined to frequencies used by other applications in order to achieve reduced interference. However the use of such resonant elements causes additional notches at the fre quencies which equal to even or odd multiples of the design frequency. While the lowest odd multiple of the WLAN frequency (5.2–5.8 GHz) lays outside the UWB range (3.1–10.6 GHz) this is not the case for the WiMAX frequency. In this paper, a stepped slot is introduced in a UWB elliptical monopole that suppresses the unwanted higher order notch, and with the use of a linearly tapered feed line return loss better than −10dB is achieved throughout the UWB range with the exception of the WiMAX range.

Sparse localization of tumors inside an inhomogeneous breast

We discuss the application of the sparse processing techniques in the differential breast-cancer imaging. We derive the sparse model by assuming that the parameters of the inhomogeneous breast model are known from the previous measurements. In the linear model, we use the numerically computed three-dimensional Greens functions. We investigate the role of the regularization parameter and the number of sensors on the solution accuracy.