Lorenza Gardella

PLA/POSS Nanofibers: A Novel System for the Immobilization of Metal Nanoparticles

In this work, a novel catalytic system is developed, consisting of palladium nanoclusters homogenously dispersed on the surface of nanostructured polymer nanofibers based on poly(L-lactic acid) (PLLA) and polyhedral oligomeric silsesquioxanes (POSS). Indeed, PLLA nanofibers containing amino-functionalized silsesquioxane molecules (POSS-NH2), potentially capable of interacting with the metal precursor, are prepared by means of electrospinning. Conversely to the polymer matrix, which does not show any tendency to retain the metal precursor, the submicrometric dispersion of POSS-NH2 in the PLLA nanofibers, as demonstrated by SEM-EDS analysis, turns out to promote the formation of metal nanoclusters. TEM measurements show a uniform distribution of Pd nanoparticles, characterized by an average dimension of ca. 4 nm, along the fibers. The prepared system proves a relevant catalytic activity toward the hydrogenation of stilbene under heterogeneous conditions. Moreover, as demonstrated by XPS measurements, the support is capable of retaining the catalyst during the hydrogenation reaction, thus preventing its leaching.

On the development of a facile approach based on the use of ionic liquids: preparation of PLLA (sc-PLA)/high surface area nano-graphite systems

In this work, a novel method to prepare composite systems based on polylactide (PLA) and high surface area nano-graphite (HSAG) has been developed, consisting of the application of ionic liquids (ILs) as dispersing/exfoliating agents for nanofillers. Indeed, the proposed approach is easy as well as with a low environmental impact, involving neither the use of co-solvents nor the preliminary oxidation of graphite. As a preparatory screening, systems based on either poly(L-lactide) (PLLA), or an equimolar mixture of poly(L-lactide) (PLLA) and poly(D-lactide) PDLA, and ionic liquids are prepared by melt-blending the polymer matrices with different kinds and amounts of imidazolium-type ILs. Among the tested ILs, 1-butyl-3-methylimidazoliumhexa-fluorophosphate ([bmim][PF6]) shows the highest solubility and the lowest tendency to decompose the polymer matrix during the processing. DSC and TGA measurements highlight that the above IL induces a slightly plasticizing effect on PLLA, with a limited decrease – of about 20 °C for the sample with the highest amount of [bmim][PF6] – of the onset degradation temperature. As evidenced by FE-SEM measurements, the chosen IL features a high sonication-assisted capability of dispersing/exfoliating the nano-graphite, thus allowing obtaining a system containing 2% by mass of the nanofiller, organized in aggregates with an average dimension of 300 nm and composed of few layers. Conversely to the direct insertion of the HSAG into the polymer matrix (which produces micrometer-sized aggregates) when the previously-prepared [bmim][PF6]/HSAG system is incorporated, a submicrometric dispersion of the nano-graphite is obtained. The presence of the finely dispersed nanofiller has a nucleating effect on PLLA crystallization, significantly increasing the crystal nucleation density. Moreover, it is of utmost relevance that, in the case of the stereocomplex-PLA-based systems, the HSAG promotes the exclusive formation of stereocomplex crystals over homo-crystals.

On stereocomplexed polylactide materials as support for PAMAM dendrimers: synthesis and properties

Stereocomplexed polylactide materials functionalized with poly(amido-amine) (PAMAM) dendrimer units were prepared by solution blending dendritic poly(D-lactide) (PDLA) star oligomers into a commercial poly(L-lactide) (PLLA), where the dendritic PDLA star oligomers were built up by ring-opening polymerization of D-lactide using a PAMAM dendrimer as macroinitiator. Whereas the synthesized poly(D-lactide)s (whose star-like architecture, comprising the PAMAM dendrimer as the core and a multi-arm PDLA shell, was demonstrated by means of 1H NMR spectroscopy) were observed to hardly structure/crystallize, their blended films, as revealed by DSC and WAXD measurements, proved capable of easy stereocomplexation in solution and melt crystallization alike. The stereocomplex, whose content and characteristics are greatly affected by the structure of the PDLA stars, affords improved thermal and chemical resistance, while simultaneously providing a strong link for the PAMAM units to the polymer matrix. The PAMAM dendrimers can thus manifest themselves, while being anchored onto a water/(solvent) insoluble, easy-processable polymeric support, which, in addition, is bio-based and bio-degradable and keeps the characteristics of biocompatibility. Indeed, thanks to the presence of the PAMAM functionalities, and unlike the neat polylactide, the resulting materials were shown to possess significant water-absorbency and Pd(II)-uptake-ability. This latter property was exploited for the removal of Pd catalyst from a homogeneous reaction system.

Star poly(ε-caprolactone)-based electrospun fibers as biocompatible scaffold for doxorubicin with prolonged drug release activity

In this work, a novel drug delivery system consisting of poly(ε-caprolactone) (PCL) electrospun fibers containing an ad-hoc-synthesized star polymer made up of a poly(amido-amine) (PAMAM) core and PCL branches (PAMAM-PCL) was developed. The latter system which was synthesized via the ring opening polymerization of ε-caprolactone, starting from a hydroxyl-terminated PAMAM dendrimer and characterized by means of 1H NMR, IR and DSC, was found to be compatible with both the polymer matrix and a hydrophilic chemotherapeutic drug, doxorubicin (DOXO), the model drug used in this work. The preparation of the dendritic PCL star product with an average arm length of 2000g/mol was characterized using IR and 1H NMR measurements. The prepared star polymer possessed a higher crystallinity and a lower melting temperature than that of the used linear PCL. Electrospun fibers were prepared starting from solutions containing the neat PCL as well as the PCL/PAMAM-PCL mixture. Electrospinning conditions were optimized in order to obtain defect free fibers, which was proven by the structural FE-SEM study. PAMAM moieties enhanced the hydrophilicity of the fibers, as proved by comparing the water absorption for the PCL/PAMAM-PCL fibers to that neat PCL fibers. The drug-loaded system PCL/PAMAM-PCL was prepared by directly introducing DOXO into the electrospinning solutions. The DOXO-loaded PCL/PAMAM-PCL showed a prolonged release of the drug with respect to the DOXO-loaded PCL fibers and elicited effective controlled toxicity over A431 epidermoid carcinoma, HeLa cervical cancer cells and drug resistant MCF-7 breast cancer cells. On the contrary, the drug-free PCL/PAMAM-PCL scaffold demonstrated no toxic effects on human dermal fibroblasts, suggesting the biocompatibility of the proposed system which can be used in cellular scaffold applications.

A Novel Electrostimulated Drug Delivery System Based on PLLA Composites Exploiting the Multiple Functions of Graphite Nanoplatelets

A novel drug delivery system based on poly(l-lactide) (PLLA), graphite, and porphyrin was developed. In particular, 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (THPP) was chosen because, besides its potential as codispersing agent of graphite, it is a pharmacologically active molecule. Graphite nanoplatelets, homogeneously dispersed in both the neat PLLA and the PLLA/porphyrin films, which were prepared by solution casting, turned out to improve the crystallinity of the polymer. Moreover, IR measurements demonstrated that unlike PLLA/porphyrin film, where the porphyrin was prone to aggregate causing variable concentration throughout the sample, the system containing also GNP was characterized by a homogeneous dispersion of the above molecule. The effect of graphite nanoplatelets on the thermal stabilization, electrical conductivity, and improvement of mechanical properties of the polymer resulted to be increased by the addition of the porphyrin to the system, thus demonstrating the role of the molecule in ameliorating the filler dispersion in PLLA. The porphyrin release from the composite film, occurring both naturally and with the application of an electrical field, was measured using an UV–vis spectrophotometer. Indeed, voltage application turned out to improve significantly the kinetic of drug release. The biocompatibility of the polymer matrix as well as the mechanical and thermal properties of the composite together with its electrical response makes the developed material extremely promising in biological applications, particularly in the drug delivery field.

Preparation and characterization of novel electrospinnable PBT/POSS hybrid systems starting from c-PBT

Novel hybrid systems based on poly(butyleneterephthalate) (PBT) and polyhedral oligomeric silsesquioxanes (POSS) have been prepared by applying the ring-opening polymerization of cyclic poly(butyleneterephthalate) oligomers. Two types of POSS have been used: one characterized by hydroxyl functionalities (named POSS-OH) and another without specific reactive groups (named oib-POSS). It was demonstrated that POSS-OH acts as an initiator for the polymerization reaction, leading to the direct insertion of the silsesquioxane into the polymer backbone. Among the possible applications of the PBT/POSS hybrid system, the possibility to obtain nanofibers has been assessed in this work.