Luminescent rhenium and ruthenium complexes of an amphoteric poly(amidoamine) functionalized with 1,10-phenanthroline.

A new amphoteric copolymer, PhenISA, has been obtained by copolymerization of 4-(4'-aminobutyl)-1,10-phenanthroline (BAP) with 2-methylpiperazine and bis(acrylamido)acetic acid (BAC) (6% of phenanthroline-containing repeating units). The copolymer showed excellent solubility in water, where it self-aggregated to give clear nanoparticle suspensions (hydrodynamic diameter = 21 ± 2 nm, by dynamic light scattering (DLS) analysis). The phenanthroline pendants of the polymer stably coordinated either Re(CO)(3)(+) or Ru(phen)(2)(2+) fragments, affording luminescent Re-PhenISA, Re-Py-PhenISA, and Ru-PhenISA polymer complexes, emitting from triplet metal-to-ligand charge transfer ((3)MLCT) excited states (with λ(em) = 608, 571, and 614 nm, respectively, and photoluminescence quantum yields Φ(em) = 0.7%, 4.8%, and 4.1%, in aerated water solution, respectively). DLS analyses indicated that the polymer complexes maintained the nanosize of PhenISA. All the complexes were stable under physiological conditions (pH 7.4, 0.15 M NaCl) in the presence of an excess of the ubiquitous competitor cysteine. In vitro viability assays showed no toxicity of Re-Py-PhenISA and Ru-PhenISA complexes, at concentrations in the range of 0.5-50 µM (calculated on the metal-containing unit), toward HEK-293 (human embryonic kidney) cells. A preliminary investigation of internalization in HEK-293 cells, by means of fluorescence confocal microscopy, showed that Ru-PhenISA enters cells via an endocytic pathway and, subsequently, homogeneously diffuse within the cytoplasm across the vesicle membranes.

Biological performance of a novel biodegradable polyamidoamine hydrogel as guide for peripheral nerve regeneration.

Polyamidoamines (PAAs) are a well-known family of synthetic biocompatible and biodegradable polymers, which can be prepared as soft hydrogels characterized by low interfacial tension and tunable elasticity. For the first time we report here on the in vivo performance of a PAA hydrogel implant as scaffold for tissue engineering. In particular, an amphoteric agmatine-deriving PAA hydrogel shaped as small tubing was obtained by radical polymerization of a soluble functional oligomeric precursor and used as conduit for nerve regeneration in a rat sciatic nerve cut model. The animals were analyzed at 30, 90, and 180 days post-surgery. PAA tubing proved to facilitate nerve regeneration. Good surgical outcomes were achieved with no signs of inflammation or neuroma. Moreover, nerve regeneration was morphologically sound and the quality of functional recovery satisfactory. In conclusion, PAA hydrogel scaffolds may represent a novel and promising material for peripheral nerve regeneration.

Amphoteric agmatine containing polyamidoamines as carriers for plasmid DNA in vitro and in vivo delivery.

In this paper we report on the investigation, as DNA nonviral carriers, of three samples of an amphoteric polyamidoamine bearing 4-aminobutylguanidine deriving units, AGMA5, AGMA10, and AGMA20, characterized by different molecular weights (M(w) 5100, 10100, and 20500, respectively). All samples condensed DNA in spherical, positively charged nanoparticles and protected it against enzymatic degradation. AGMA10 and AGMA20 polyplexes had average diameters lower than 100 nm. AGMA5 polyplexes were larger. All polyplexes showed negligible cytotoxicity and were internalized in cells. AGMA10 and AGMA20 performed differently from AGMA5 as nucleic acid carriers in vitro. AGMA10 and AGMA20 effectively promoted transfection, whereas AGMA5 was ineffective. FITC-labeled AGMA10 was prepared and the intracellular trafficking of its DNA polyplex was studied. DNA/AGMA10 polyplex was largely localized inside the nucleus, while AGMA10 concentrated in the perinuclear region. DNA/AGMA10 polyplex intravenously administered to mice promoted gene expression in liver but not in other organs without detectable toxic side effects.

Direct microfabrication of topographical and chemical cues for the guided growth of neural cell networks on polyamidoamine hydrogels.

Cell patterning is an important tool for organizing cells in surfaces and to reproduce in a simple way the tissue hierarchy and complexity of pluri-cellular life. The control of cell growth, proliferation and differentiation on solid surfaces is consequently important for prosthetics, biosensors, cell-based arrays, stem cell therapy and cell-based drug discovery concepts. We present a new electron beam lithography method for the direct and simultaneous fabrication of sub-micron topographical and chemical patterns, on a biocompatible and biodegradable PAA hydrogel. The localized e-beam modification of a hydrogel surface makes the pattern able to adsorb proteins in contrast with the anti-fouling surface. By also exploiting the selective attachment, growth and differentiation of PC12 cells, we fabricated a neural network of single cells connected by neuritis extending along microchannels. E-beam microlithography on PAA hydrogels opens up the opportunity of producing multifunctional microdevices incorporating complex topographies, allowing precise control of the growth and organization of individual cells.

Tricarbonyl-rhenium complexes of a thiol-functionalized amphoteric poly(amidoamine).

An amphoteric thiol-functionalized poly(amidoamine) nicknamed ISA23SH(10%) was synthesized. Rhenium complexes 1 and 2, containing 0.5 and 0.8 equiv of rhenium, respectively, were easily obtained by reacting ISA23SH(10%) with [Re(CO)(3)(H(2)O)(3)](CF(3)SO(3)) in aqueous solution at pH 5.5. Both ISA23SH(10%), and its rhenium complexes were soluble in water under physiological conditions. The resultant solutions were stable, even in the presence of cysteine. Rhenium chelation occurred through the S and N atoms of the cysteamine moiety, as demonstrated by (1)H, (13)C, and (15)N NMR spectroscopy. The diffusion coefficients and the hydrodynamic radii of ISA23SH(10%) and complex 1 were determined by pulsed gradient spin echo (PGSE) NMR experiments. The radius of the rhenium complexes 1 and 2 was always slightly larger than that of the parent polymer. TEM analysis showed that both complexes form spherical nanoparticles with narrow size distributions. Consistent results were obtained by dynamic light scattering. The observed sizes were in good agreement with those evaluated by PGSE. Preliminary in vitro and in vivo biological studies have been performed on complexes 1 and 2 as well as on the parent ISA23SH(10%). Neither hemolytic activity of the two rhenium complexes and the parent polymer, up to a concentration of 5 mg/mL, nor cytotoxic effects were observed on Hela cell after 48 h at a concentration of 100 ng/mL. In vivo toxicological tests showed that ISA23SH(10%) is highly biocompatible, with a maximum tolerated dose (MTD) of 500 mg/kg. No toxic side effects were apparent after the intravenous injection in mice of the two rhenium complexes in doses up to 20 mg/kg.