Michelina Soccio

Influence of chemical and architectural modifications on the enzymatic hydrolysis of poly(butylene succinate)

Copolymers of poly(butylene succinate) (PBS) containing diethylene succinate sequences (PBSPDGS) with different molecular architectures were prepared via reactive blending in the presence of a Ti-based catalyst. In particular, a block copolymer with long sequences and a random one with very short sequences were synthesized, characterized and investigated in terms of enzymatic biodegradability. For comparison, the parent homopolymer PBS has been also prepared by the usual two-stage melt polycondensation. Preliminary biodegradation tests based on the highly sensitive film opacity assay indicated that lipase from Candida cylindracea was the most effective among four different commercially available lipases (e.g., those from Candida rugosa, Candida cylindracea, Aspergillus niveus and hog pancreas) and a serine protease (α-chymotrypsin from bovine pancreas), and that optimal test conditions were 50 enzyme U mL−1, 30 °C and pH 7.0. Under such conditions, copolymers degraded to a much higher extent as compared to PBS. Moreover, the random copolymer degraded 100 times faster than the block one. ATRIR analysis and DSC measurements indicated that the enzyme attacked the amorphous phase first. Further, NMR analysis indicated that enzyme hydrolysis involved preferentially ester groups of DGS sequences, more hydrophilic than the others. These findings confirm previous evidence on the correlation between polymers biodegradation rate and their hydrophilic and amorphous degree. More importantly, they indicate (i) that dramatic increases in polyesters biodegradability can be obtained by introducing ether-oxygen atoms into the polymer chain and (ii) that biodegradability of oxygen etheroatom-containing copolyesters might be tuned within a wide range of rates through the modification of their molecular architecture.

Grazing-incidence small-angle X-ray scattering of soft and hard nanofabricated gratings

Grazing-incidence small-angle X-ray scattering (GISAXS) has been used to structurally characterize model hard and soft gratings of nanotechnological interest. The different gratings exhibit GISAXS patterns with characteristic features that can be associated with their level of order along the direction of periodicity and the length of the lines. Highly ordered gratings, made out of silicon by electron beam lithography, and those nanofabricated on spin-coated polymer films by nanoimprint lithography, exhibit characteristic semicircle-like GISAXS patterns with intensity spots periodically distributed on a semicircle whose radius is related to the incidence angle used. These gratings can be considered as one-dimensional crystalline lattices as provided by computer simulations. Less ordered polymer gratings prepared by the laser-induced periodic surface structuring method exhibit a GISAXS pattern characterized by periodic rod-like scattering maxima whose intensity decreases with increasing horizontal scattering angle. In this case the gratings can be considered as one-dimensional paracrystals. The transition from a rod-like to a semicircle-like GISAXS pattern has been simulated and attributed to the contribution of the form factor by changing the length of the line (ripple). A critical length value for the transition is located at around a few micrometres.

Poly(butylene/diethylene glycol succinate) multiblock copolyester as a candidate biomaterial for soft tissue engineering: Solid-state properties, degradability, and biocompatibility

A multiblock bioresorbable copolyester, poly(butylene/diethylene glycol succinate), was synthesized by reactive blending, and it was used, together with the corresponding poly(butylene succinate) homopolymer, to form films and to fabricate biomimetic electrospun scaffolds. The poly(butylene/diethylene glycol succinate) scaffold had a more pronounced elastomeric behavior than poly(butylene succinate). It also underwent hydrolytic degradation faster than poly(butylene succinate) since the incorporated diethylene glycol succinate units rendered the copolymer more hydrophilic than poly(butylene succinate). The films degraded faster than electrospun samples due to the autocatalytic effect of carboxylic end-groups. The biodegradable poly(butylene/diethylene glycol succinate) scaffold supported the growth and preserved the cardiac phenotype markers of H9c2 cells, demonstrating its potential utility in soft tissue engineering applications.

Structure and Morphology of Thin Films of Linear Aliphatic Polyesters Prepared by Spin-Coating

Thin films, with thicknesses from 10 to 400 nm of linear aliphatic polyesters (X, Y), based on propylenediol (X = 3) and on dicarboxylic acid of different chain length (Y = 2, 3, and 4 CH(2) units) were prepared by spin coating of CHCl(3) polymer solutions with different polymer concentrations. Morphology and structure of the spin coated thin films were investigated by atomic force microscopy (AFM) and by grazing incidence X-ray scattering techniques at small, (GISAXS) and wide angles (GIWAXS). AFM revealed a strong dewetting for all three polymers for coatings thinner than 100 nm. The polymer films are clearly semicrystalline for thicknesses higher than 50 nm. GIWAXS of the thicker films revealed their oriented crystalline nature. An edge-on-lamellae morphology is clearly shown by the AFM-phase images even for relatively thin films. SAXS with the beam parallel to the sample plane also support the presence of lamellae perpendicular to the substrate. The use of a mu-beam helped to interpret the GIWAXS patterns and allowed to obtain oriented WAXS patterns from melt solidified filaments. Thus, a crystal chain packing is proposed for the three polymers and consequently the indexing of the observed reflections. Accordingly, the polymer chains lie parallel to the substrate being the bc plane of the monoclinic crystal unit cell parallel to the substrate.

Understanding crystallization features of P(VDF-TrFE) copolymers under confinement to optimize ferroelectricity in nanostructures

The successful development of ferroelectric polymer devices depends on the effective fabrication of polar ferroelectric crystalline nanostructures. We demonstrate, by scanning X-ray microdiffraction using synchrotron light, the heterogeneous character of high aspect ratio one-dimensional nanoarrays of poly(vinylidene fluoride-co-trifluoroethylene) copolymers supported by a residual polymer film. They were prepared by melt and solution template wetting, using porous anodic aluminum oxide as a template. The spatial evolution of different polymorphs from the mixture of paraelectric and ferroelectric crystal forms (residual film) to the pure ferroelectric form (nanoarray) is evidenced for the samples prepared by solution wetting. However, for samples prepared by melt wetting the ferroelectric phase is exclusively obtained in both the residual film and nanoarray. The crystal nuclei formed in the polymer film connected to the nanoarray play a key role in determining the formation of a crystallinity distribution gradient, where the crystallinity decreases along the first 5-10 microns in the nanorods reaching a steady value afterwards. The minimum decrease in crystallinity is revealed for samples prepared by melt wetting. The results reported in this work endeavour to enhance the understanding of crystallization under confinement for ferroelectric copolymers and reveal the parameters for improving the ferroelectric character of polymer nanostructures.

Easily synthesized novel biodegradable copolyesters with adjustable properties for biomedical applications

Current compositions of biodegradable aliphatic polyesters experience a number of limitations associated with the difficulty of customizing mechanical, physicochemical, and biological properties for different biomedical applications. In this study, we propose a new class of multiblock copolyesters made using butylene succinate (BS) and triethylene succinate (TES). In particular, four copolyesters with the same chemical composition but different block lengths – P(BS18TES18), P(BS9TES9), P(BS4TES4), and P(BS2TES2) – were synthesized by reactive blending. Physicochemical characterization (DSC, WAXS, tensile tests, WCA, hydrolysis experiments) demonstrated that, by simply varying block length, it is possible to control polymer crystallinity, thermal and mechanical properties, wettability, and degradation rate. Copolymers displayed different stiffness, depending on the crystallinity degree, a tunable range of degradation rates, and different surface hydrophilicity. In vitro drug release and cell culture experiments were performed to evaluate the potential of these new copolyesters in the biomedical field. In particular, fluorescein isothiocyanate (FITC) was used as a model molecule to study the release profile of small molecules, and polymer cytocompatibility and fibronectin absorption capability were assessed. Depending on comonomer distribution, the polyesters are capable of releasing FITC in a tailorable manner. Moreover, the newly developed biomaterials are not cytotoxic and they are able to absorb proteins and, consequently, to tailor cell adhesion according to their surface hydrophilicity.

Nanofabrication of tailored surface structures in dielectrics using temporally shaped femtosecond-laser pulses

We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses for producing nanostructures in two dielectric materials (sapphire and phosphate glass) with different characteristics in their response to pulsed laser radiation. For this purpose, laser pulses shaped by third-order dispersion (TOD) were used to generate temporally asymmetric excitation pulses, leading to the single-step production of subwavelength ablative and subablative surface structures. When compared to previous works on the interaction of tightly focused TOD-shaped pulses with fused silica, we show here that this approach leads to very different nanostructure morphologies, namely, clean nanopits without debris surrounding the crater in sapphire and well-outlined nanobumps and nanovolcanoes in phosphate glass. Although in sapphire the debris-free processing is associated with the much lower viscosity of the melt compared to fused silica, nanobump formation in phosphate glass is caused by material network expansion (swelling) upon resolidification below the ablation threshold. The formation of nanovolcanoes is a consequence of the combined effect of material network expansion and ablation occurring in the periphery and central part of the irradiated region, respectively. It is shown that the induced morphologies can be efficiently controlled by modulating the TOD coefficient of the temporally shaped pulses.

Improving information density in ferroelectric polymer films by using nanoimprinted gratings

In this work, well-defined low aspect ratio nanostructures based on nanogratings on thin films of poly(vinylidene fluoride–trifluoroethylene) copolymers were prepared. By using these nanogratings, an improved management of writing and reading information of about 500 Gbit/in.2 (0.01 bit/nm2) can be reached as revealed by Piezoresponse Force Microscopy. Structural investigation by means of X-ray diffraction techniques indicates that the physical confinement generated by nanoimprint promotes the development of smaller and edge-on oriented crystals. Our results evidence that one-dimensional nanostructuring can be a straightforward approach to improve the control of the polarization in ferroelectric polymer thin films.

Novel Random PBS-Based Copolymers Containing Aliphatic Side Chains for Sustainable Flexible Food Packaging

In the last decade, there has been an increased interest from the food packaging industry toward the development and application of biodegradable and biobased plastics, to contribute to the sustainable economy and to reduce the huge environmental problem afflicting the planet. In this framework, the present paper describes the synthesis of novel PBS (poly(butylene succinate))-based random copolymers with different composition containing glycol sub-units characterized by alkyl pendant groups of different length. The prepared samples were subjected to molecular, thermal, diffractometric and mechanical characterization. The barrier performances to O2, CO2 and N2 gases were also evaluated, envisioning for these new materials an application in food packaging. The presence of the side alkyl groups did not alter the thermal stability, whereas it significantly reduced the sample crystallinity degree, making these materials more flexible. The barrier properties were found to be worse than PBS; however, some of them were comparable to, or even better than, those of Low Density Polyethylene (LDPE), widely employed for flexible food packaging. The entity of variations in the final properties due to copolymerization were more modest in the case of the co-unit with short side methyl groups, which, when included in the PBS crystal lattice, causes a more modest decrement of crystallinity degree.

Non‐Radial Growth of Helical Homopolymer Crystals: Breaking the Paradigm of the Polymer Spherulite Microstructure

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X-ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat-on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.