Natassa Pippa

DPPC:MPOx chimeric advanced Drug Delivery nano Systems (chi-aDDnSs): Physicochemical and structural characterization, stability and drug release studies

Chimeric advanced Drug Delivery nano Systems (chi-aDDnSs) could be defined as mixed nanosystems composed of different biomaterials that can be organized into new nanostructures that can offer advantages as drug carriers. In this work, we report on the self assembly behavior and on stability studies of chi-aDDnSs consisting of DPPC (dipalmitoylphosphatidylcholine) and poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline) (MPOx) gradient copolymer in Phosphate Buffer Saline (PBS). Light scattering techniques were used in order to extract information on their physicochemical and structural characteristics (i.e. ζ-potential, Polydispersity Index (PD.I.), size/shape and morphology), while their stability was also studied as a function of gradient block copolymer content, as well as temperature. The colloidal stability of the chimeric nanovectors and their thermoresponsive behavior indicates that these nanosystems could be considered as sterically stabilized nanocontainers. DPPC:MPOx chimeric advanced Drug Delivery nano Systems were found to be effective nanocontainers for the incorporation of indomethacin (IND). The combination of gradient block copolymers with phospholipids for the development of novel chimeric nanovectors is reported for the first time and appears very promising, mostly due to the fact that the MPOx acts as a modulator for the release rate of the IND.

PEO-b-PCL–DPPC chimeric nanocarriers: self-assembly aspects in aqueous and biological media and drug incorporation

In this work, we report on the self assembly behavior and stability studies of mixed amphiphilic nanosystems consisting of DPPC (dipalmitoylphosphatidylcholine) and poly(ethylene oxide)-b-poly(e-caprolactone) (PEO-b-PCL) block copolymer in HPLC-grade water, phosphate buffer saline (PBS) and fetal bovine serum (FBS). These nanosystems are sterically stabilized nanovectors and can be utilized as chimeric advanced Drug Delivery nano Systems (aDDnSs) with stealth properties. A gamut of light scattering techniques (static, dynamic and electrophoretic) and fluorescence spectroscopy were used in order to extract information on the structure, morphology, size, effective charge and internal nanostructure of the nanoassemblies formed, as a function of block copolymer content, as well as temperature and concentration. The incorporation of PEO-b-PCL leads to nanoassemblies of smaller size. All the mixed formulations were found to retain their original physicochemical characteristics for the course of two weeks. The hydrodynamic radii (Rh) of mixed nanosystems decreased in the process of heating up to 50 °C. Gradual degradation of the polymeric chain in an acidic dispersion medium, which leads to gradual structural changes of the chimeric nanovectors, was observed. The micropolarity of the hydrocarbon region of nanocarriers changed significantly in HPLC-grade water and PBS with increasing block copolymer content. The incorporation of indomethacin (IND) led to a decreased size of chimeric nanocarriers. The incorporation efficiency of mixed liposomal–block copolymer formulations for IND was increased in PBS in comparison with the HPLC-grade water, due to electrostatic interactions between the drug molecule and choline headgroups. PEO-b-PCL grafted DPPC liposomes are found to be effective nanocontainers for the encapsulation of IND, especially at the highest molar ratio of the block copolymer.

On the ubiquitous presence of fractals and fractal concepts in pharmaceutical sciences: a review.

Fractals have been very successful in quantifying natures geometrical complexity, and have captured the imagination of scientific community. The development of fractal dimension and its applications have produced significant results across a wide variety of biomedical applications. This review deals with the application of fractals in pharmaceutical sciences and attempts to account the most important developments in the fields of pharmaceutical technology, especially of advanced Drug Delivery nano Systems and of biopharmaceutics and pharmacokinetics. Additionally, fractal kinetics, which has been applied to enzyme kinetics, drug metabolism and absorption, pharmacokinetics and pharmacodynamics are presented. This review also considers the potential benefits of using fractal analysis along with considerations of nonlinearity, scaling, and chaos as calibration tools to obtain information and more realistic description on different parts of pharmaceutical sciences. As a conclusion, the purpose of the present work is to highlight the presence of fractal geometry in almost all fields of pharmaceutical research.

The fractal hologram and elucidation of the structure of liposomal carriers in aqueous and biological media

The present study deals with the physicochemical characterization (size, polydispersity, ζ-potential) of dipalmitoylphosphatidylcholine (DPPC) liposomes and DPPC:cholesterol (chol) (9:1 molar ratio) liposomes, and the determination of their fractal dimension (mass fractal (d(f)) and surface fractal (d(s))), in an aqueous (HPLC grade water) and in a biological (fetal bovine serum - FBS) medium. Dynamic, static and electrophoretic light scattering and fluorescence spectroscopy are used as experimental techniques to elucidate the structure and physicochemical parameters of liposomes in an ageing study in two different media, as well as their structural response in changes in concentration and temperature. The extended DLVO theory would be the tool to explain the phenomenology of the colloidal behavior in these systems and of their aggregation process. The fractal dimensionality of DPPC liposomes was decreased while for DPPC:cholesterol (9:1) it remained unaffected in the two dispersion media. The structure of the liposomal systems, the process kinetics, and the fractal dimension are consistent with the diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA) models. On the contrary, hydrodynamic radius (R(h)) was found to be stable during the variations of colloidal system conditions, especially due to concentration changes. Finally, we suggest that this study can be a rational road map to design advanced Drug Delivery nano Systems (aDDnSs) with improved pharmacokinetic profile which could be considered as crucial for their effectiveness.

Advanced drug delivery nanosystems (aDDnSs): a mini-review.

Abstract Significant progress has been made in nanoscale drugs and delivery systems employing diverse chemical formulations to facilitate the rate of drug delivery and to improve its pharmacokinetics. Biocompatible nanomaterials have been used as biological markers, contrast agents for imaging, healthcare products, pharmaceuticals, drug-delivery systems as well as in detection, diagnosis and treatment of various types of diseases. The classification of drug delivery nanosystems (DDnSs) is a crucial issue and fundamental efforts on this subject are missing from the literature. This article deals with the classification of DDnSs with a modulatory controlled release profile (MCR) denoted as modulatory controlled release nanosystems (MCRnSs). Conventional (c) and advanced (a) DDnSs are denoted by the acronyms cDDnSs and aDDnSs, and can be composed of a single or more than one biomaterials, respectively. The classification was based on their characteristics such as: surface functionality (f), the nature of biomaterials used and the kind of interactions between biomaterials. The aDDnSs can be classified as hybridic (Hy-) or chimeric (Chi-) based on the nature – same or different respectively – of biomaterials and inorganic materials used. The nature of the elements used for producing advanced biomaterials is of great importance and medicinal chemistry contributes effectively to the production of aDDnSs.

The delineation of the morphology of charged liposomal vectors via a fractal analysis in aqueous and biological media: Physicochemical and self-assembly studies

The present study deals with the physicochemical characterization of DPPC:DPPG (9:1 molar ratio) and DPPC:DODAP (9:1 molar ratio) liposomes, and the determination of their fractal dimension in HPLC-grade water, PBS and in FBS. Light scattering techniques were used in order to extract information on the structure, morphology, size and surface charge of liposomes in an ageing study and their structural response to changes in concentration and temperature. Fluorescence spectroscopy showed that the microviscosity of cationic liposomes changed by an increase of temperature. The fractal dimension, d(f), was found equal to 1.8 for reconstituted DPPC:DPPG (9:1) and DPPC:DODAP (9:1) liposomes in aqueous media. Aggregation of reconstituted DPPC:DPPG (9:1) and DPPC:DODAP (9:1) liposomes in FBS was observed. Their fractal dimensions were 1.46 and 2.45, respectively. The first order aggregation kinetics of DPPC:DODAP (9:1) liposomes in the presence of serum proteins was determined; the aggregates of cationic liposomes with serum components remained stable during 20 days with fractal dimension 2.5. The responsiveness of cationic liposomes to changes in temperature in the three dispersion media has revealed the self-assembly and the morphological complexity of cationic vectors. Finally, we suggest that these studies could be used for developing effective advanced drug delivery nano-systems (aDDnSs) based on their fractal characteristics which effectively draw their morphological profile.

The physicochemical/thermodynamic balance of advanced drug liposomal delivery systems

The aim of this work is to study the morphological characteristics via fractal analysis and the alterations of the thermotropic behavior of dipalmitoylphosphatidylcholine (DPPC) liposomes, caused by the incorporation of cholesterol, poly(amidoamine) (PAMAM) dendrimer, and MPOx (poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline)) gradient block copolymer (9:1 molar ratio). A gamut of light scattering techniques and differential scanning calorimetry were used in order to extract information on the morphological (in different dispersion media) and thermodynamic characteristics of liposomal drug nanocarriers, respectively. The vesicles’ structure of liposomes has a different thermodynamic content, which corresponds to a different thermotropic behavior, in comparison to pure lipid bilayers. The observed metastable phase only for DPPC liposomes has been considered as a “physical impurity”, which leads to “physical incompatibility” and consequently promotes the aggregation of DPPC liposomes in aqueous media. The incorporation of biomaterials such as PAMAM G4 and MPOx, caused alterations in the thermotropic behavior of DPPC liposomes affecting only the main transition specific enthalpy ΔH. All the other calorimetric parameters remained unaltered. These findings supported the hypothesis that the exceptional stability and transition cooperativity of the chimeric liposomal membrane might be due to the reduction of the vesicle size with the smaller membrane curvature that is indicated by the fractal dimensionality of the system. In conclusion, the results from the thermal analysis of the liposomal systems were in line with the picture of their structural characteristics, as indicated by the interplay between physicochemical and thermodynamical parameters, which determines their fractal morphology.

Incorporation of dimethoxycurcumin into charged liposomes and the formation kinetics of fractal aggregates of uncharged vectors

Abstract Dimethoxycurcumin (DMC) is a lipophilic analog of curcumin found in Curcuma longa Linn., which is known to possess significant activity against various cancer cell lines. The purpose of this study was to develop suitable liposomal formulations in order to overcome DMC’s poor water solubility and to study the aggregation kinetic profile using the fractal analysis. DMC was incorporated into liposomal formulations composed of DPPC, DPPC:DPPG:chol (9:1:1 molar ratio) and DPPC:DODAP:chol (9:1:1 molar ratio) liposomes. Light scattering techniques were used to elucidate the physicochemical parameters of the liposomal formulations with and without DMC. The structural characteristics of the incorporated molecule were found to be crucial and promote the aggregation mechanism depending also on the liposomes’ composition. The results of our study contribute to the overall scientific efforts to prepare efficient carriers for DMC and could be a useful tool in order to study more efficiently the kinetics of the aggregation process of the liposomal carriers.

Insulin/poly(ethylene glycol)-block-poly(L-lysine) Complexes: Physicochemical Properties and Protein Encapsulation.

Insulin (INS) was encapsulated into complexes with poly(ethylene glycol)-block-poly(L-lysine) (PEG-b-PLys), which is a polypeptide-based block copolymer (a neutral-cationic block polyelectrolyte). The particular cationic-neutral block copolymer can complex INS molecules in aqueous media via electrostatic interactions. Light-scattering techniques are used to study the complexation process and structure of the hybrid nanoparticles in a series of buffers, as a function of protein concentration. The physicochemical and structural characteristics of the complexes depend on the ionic strength of the aqueous medium, while the concentration of PEG-b-PLys was constant through the series of solutions. As INS concentration increased the size distribution of the complexes decreased, especially at the highest ionic strength. The size/structure of complexes diluted in biological medium indicated that the copolymer imparts stealth properties and colloidal and biological stability to the complexes, features that could in turn affect the clearance properties in vivo. Therefore, these studies could be a rational roadmap for designing the optimum complexes/effective nanocarriers for proteins and peptides.

The interplay between the rate of release from polymer grafted liposomes and their fractal morphology

The purposes of this study were to investigate the indomethacin (IND) release profile from dipalmytolphosphatidylcholine:poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline (DPPC:MPOx) (in different molar ratios) mixed liposomal nanovectors, to examine the relevance of power law using these experimental release data, and to detect the relationship of the fractal dimension (df) of nanovectors with the fraction of the IND release. The df of the mixed liposomes was determined by Static Light Scattering during the release of IND from the nanocontainers. It is observed that the in vitro release of the drug from the prepared nanostructures is quite fast especially for the nanovectors prepared with the lower ratio of MPOx. The release kinetics was studied by regression analysis of drug concentrations in fractal matrices with respect to time. A power law, a piece-wise power law functions and Weibull distribution were fitted to the release data and the model parameters were estimated. Good fits were observed in all datasets analyzed, while distinct regions of different release rates corresponding to different df values were described. The authors proposed that the fractal morphology of the mixed liposomes affects the drug release and must be taken into account to develop liposomal drug with complete knowledge of their structural properties.