Research Group

Group Publications

Research Activities

The research activities are mainly focused on the synthesis and physicochemical characterization of functional organized nanomaterials, mainly liposomes and dendritic polymers, giving emphasis on their applications as targeted and controlled release drug and gene delivery systems. The group is also involved in the synthesis of hybrid organic/inorganic nanoparticles based on functionalized dendritic polymers aiming at specific industrial applications. The group has been involved in EU and National research projects.

    Specifically, the research activity is focusing on:

 1. Functional Liposomes as Drug Delivery Systems

Liposomes, spherical vesicles whose lipid bilayers membranes are artificial analogs of cell membranes, can encapsulate lipophilic or hydrophilic drugs and are, therefore, widely employed as drug delivery systems (DDS). The interaction of liposomal DDS with various molecules or cells plays a crucial role in their design, development and efficiency. Therefore, liposomes bearing on their external surface recognizable groups have been developed that can interact through molecular recognition with simple molecules, linear and dendritic polymers or complementary liposomes in an attempt to simulate liposomal behavior in the biological environment, as well as interactions of drug delivery systems with cells.

The laboratory is involved in the development of efficient liposomal DDS that combine stability in the biological environment, cell specificity and membrane transporting properties, by appropriate modification of their external surfaces. Aiming at effective drug and gene delivery systems, multifunctional liposomes were developed bearing a variety of groups on their external surfaces to secure stability in the biological environment (by attaching polyethylene glycol chains), cell specificity (through the introduction of recognizable groups) and membrane transporting properties through cell membranes (through the introduction of guanidinium groups).

Liposomal formulations are characterized by atomic force and optical microscopy, dynamic light scattering, ζ-potential, and various spectroscopic methods while the thermodynamics of liposomal interactions are investigated by microcalorimetric methods. Drug encapsulation and release, membrane transport, subcellular localization and cell toxicity of the developed liposomal formulations are assessed employing a variety of cell lines. Factors affecting the release profiles of drugs such as temperature, and ionic strength are being studied.

Multifunctional Liposomal, Dendrimeric and Hyperbranched systems

 2. Functional Dendrimers and Hyperbranched Polymers as Drug and Gene Delivery Systems

Functionalized dendritic polymers, developed through the modification of a variety of commercially available dendrimers or hyperbranched polymers, have been studied as potential drug delivery systems. Multiple functionalization of dendrimers or hyperbranched polymers promote enhanced targeting properties, stability in the biological environment and cell membranes transport properties. Active drug ingredients, therapeutic proteins such as insulin, or MRI agents have been incorporated in multifunctional dendrimers or hyperbranched polymers. The transporting ability of active drug ingredients encapsulated in dendritic nanocarriers has been studied either physicochemically, employing multilamellar liposomes as cells model, or in vitro employing a variety of cell lines. Factors affecting the release profiles of drugs such as T, pH and ionic strength have been studied. The materials are characterized by a variety of physicochemical methods including spectroscopy (NMR, FTIR, UV-Vis), dynamic light scattering, multi-angle static light scattering and zeta-potential. Cell toxicity and sub-cellular localization have been studied on various cell lines.

Furthermore, appropriately designed positively charged dendrimers or hyperbranched polymers have been employed for complexation with DNA. The resulting polyplexes were physicochemically characterized, while transfection efficiency was validated in vitro employing several cell lines. The effect of macromolecular architecture and end group modifications on gene transfection efficiency has been investigated.

3. Dendrimeric and Hyperbranched Polymers: From Encapsulation properties to a water purification technology

Alkylated dendrimeric and hyperbranched polymers were used as novel "nanosponges" being able to encapsulate hydrophobic water impurities. Ultrapure water can thus be produced, with remaining organic impurities at the ppb level. In addition, cross-linked hydrophobic dendrimeric and hyperbranched polymers are also suitable for water purification. Finally, nanosponges’ impregnation into porous ceramic membranes affords filter modules with advanced retention characteristics that can be easily integrated in existing water purification units. Alternatively, work has been performed on the preparation of organosilicon dendrimers which were covalently attached to the pore surface of ceramic filters for the production of novel hybrid organic-inorganic water purification modules.

 SEM micrograph of Al₂O₃ porous filters impregnated with polymeric “nanosponges” and the developed filter module fo water purification.

4. Environmentally friendly biomimetic synthesis of hybrid organic/inorganic nanoparticles

 Dendrimers and hyperbranched polymers are able to control the growth and size of inorganic nanoparticles and therefore are being used for the efficient and environmentally benign synthesis of hybrid organic/inorganic nanoparticles that find various applications:

 4.1. Hybrid organic/inorganic nanoparticles for water remediation

Organic–inorganic hybrid silica nanospheres can be prepared through a biomimetic silicification process in water at ambient conditions by the interaction of low cost poly(ethylene imine) hyperbranched polymer with silicic acid. The so-produced hybrid nanoparticles were successfully employed for the removal of two completely different categories of pollutants, i.e. metal ions and polycyclic aromatic hydrocarbons.

Hyperbranched poly(ethylene imine)/silica hybrid microsphere formation process (left) and TEM micrograph of the resulting nanoparticles (right)

 4.2. Hybrid organic/inorganic nanoparticles for corrosion-resistant coatings

 Hybrid organic/inorganic nanoparticles were utilized for the development of novel organo-silicate corrosion resistant coatings of Al alloys. Corrosion protective sol–gel coatings were developed on Al AA2024-T3 through an aqueous sol–gel process which includes in-situ formation of a dense silica network from hydrolyzed 3-glycidoxy-propyltri-methoxysilane and tetraethoxysilane and hyperbranched poly(ethylene imine) as a cross-linking agent. Formulations that contain poly(ethylene imine) (PEI) demonstrate better corrosion barrier properties, especially when combined with the organic inhibitors. In fact, PEI deposited on Al surfaces is partially oxidized, and oxidation continues upon application of oxidative stresses, thus acting not only as a crosslinking agent for hybrid film formation, and as a solubilizer of organic corrosion inhibitors, but also as a corrosion inhibitor by itself, thus contributing in a variety of ways to the overall performance of the hybrid film.

4.3. Development of Hydroxyapatite nanoparticles and biopolymer- Hydroxyapatite 3D scaffolds.

Amine terminated dendritic polymers and synthetic polypeptides have been utilized for the formation of hydroxyapatite nanoparticles. The impact of hydroxyapatite nanoparticles on cellular function was studied by cell culture experiments monitoring the viability and morphology of osteogenic cells. It is thus possible to realize bioactive surfaces or 3D scaffolds based on hydoxyapatite nanoparticles and biopolymers such as chitosan or gelatin.

Hydroxyapatite nanoparticles (left) and Chitosan-Hydroxyapatite scaffold (right) (CT-scan image, in collaboration with the Dental School, UOA)

In addition, through the covalent attachment of hyperbranched poly(ethylene imine) on titanium surfaces it is possible to realize a bioactive surface that promotes the growth of a biocompatible hydroxyapatite coating from SBF which is firmly attached on the titanium surface thus improving biocompatibility, bioactivity and applicability of titanium based implants.

Cross section (SEM) of calcium phosphate layer developed on a Ti substrate

 5. Dendritic polymer/Carbon nanotubes or Graphene Oxide nanocomposites

 5.1. Functionalized Carbon-based Materials as antibacterial agents

 Cationic hydrophilic dendritic polymers induce, through appropriate interaction, the dispersion of carbon-based materials (carbon nanotubes, carbon nanodisks and graphene oxide) in water. The materials were physicochemically characterized by a variety of physicochemical methods including spectroscopy (XPS, Raman, NMR, FTIR), X-ray powder diffraction, TEM, SEM etc. Subsequently, these nanocomposites were evaluated as antibacterial agents in collaboration with K. Stamatakis, NCSRD, Institute of Biosciences & Applications, Biophysics and Biotechnology of Membranes Laboratory.

5.2. Dendritic Polymer-functionalized carbon-based nanostructured composites for fouling release

Novel polymer/carbon-based nanocomposites are being developed mainly for fouling release type paints for marine coating applications. Specifically lipophilic dendritic polymers were interacted with carbon-based materials (CBMs) as carbon nanotubes and graphene oxide, affording nanostructured composites able to be used as fillers into epoxy resin paints inducing their fouling release properties. CBMs/polymer nanocomposites facilitate the easy release of microorganisms responsible for biofouling. This is a critical property for hard fouling in the ship hull caused by higher organisms. These composites are expected to reduce the flow resistance leading to significant reduction in fuel consumption and carbon dioxide emissions. Concurrently, decrease in the maintenance costs will be attained due to the enhanced fouling release behavior of the system. This work is performed in collaboration with Dr F. K. Katsaros, NCSRD, IAMPPNM, Department of Physical Chemistry, MESL.

Novel fouling release marine coating containing functional dendritic polymers.

 5.3. Superhydrophobic nanostructured top coatings

 Superhydrophobic nanostructured top coatings based on silicon oxide and polymer functionalized carbon-based materials (carbon nanotubes or graphene) are being developed, aiming to improved aerodynamic efficiency and, at the same time, to prevent ice-formation on aircrafts. Therefore, these novel nanostructured top coatings with improved aerodynamic and de-icing behavior are foreseen to improve fuel efficiency and reduce carbon emissions. This work is performed in collaboration with Dr F. K. Katsaros, NCSRD, IAMPPNM, Department of Physical Chemistry, MESL.

6. Development of Novel Thermotropic Liquid Crystals

Novel amphiphilic compounds, whose liquid crystalline properties result from molecular recognition of complementary molecules through directed hydrogen bonding interactions, were synthesized. Research has been also focused on ionic low molecular weight or polymeric liquid crystals, on ionic compounds that also have the ability to form hydrogen-bonded networks, or on ionic compounds bearing moieties exhibiting dipole-dipole interactions. Standard mesophase characterization techniques employed in our laboratory include polarizing optical microscopy, thermal analysis and small-angle X-ray diffraction.  Supramolecular thermotropic liquid crystals derived from covalently or non-covalently functionalized dendritic polymers were also developed. Specifically, amphiphilic-type dendrimeric liquid crystals based on alkyl chain functionalized poly(propylene imine) dendrimers, and covalently, ionic or hydrogen bonded cholesterol-based dendrimeric or hyperbranched polymers were synthesized and the variety of mesomorphic phases obtained was characterized.

 Research Facilities