Erlantz Lizundia

Crystallization, structural relaxation and thermal degradation in Poly(L-lactide)/cellulose nanocrystal renewable nanocomposites.

In this work, crystallization, structural relaxation and thermal degradation kinetics of neat Poly(L-lactide) (PLLA) and its nanocomposites with cellulose nanocrystals (CNC) and CNC-grafted-PLLA (CNC-g-PLLA) have been studied. Although crystallinity degree of nanocomposites remains similar to that of neat homopolymer, results reveal an increase on the crystallization rate by 1.7-5 times boosted by CNC, which act as nucleating agents during the crystallization process. In addition, structural relaxation kinetics of PLLA chains has been drastically reduced by 53% and 27% with the addition of neat and grafted CNC, respectively. The thermal degradation activation energy (E) has been determined from thermogravimetric analysis in the light of Kissingers and Ozawa-Flynn-Wall theoretical models. Results reveal a reduction on the thermal stability when in presence of CNC-g-PLLA, while raw CNC slightly increases the thermal stability of PLLA. Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy results confirm that the presence of residual catalyst in CNC-g-PLLA plays a pivotal role in the thermal degradation behavior of nanocomposites.

PLLA-grafted cellulose nanocrystals: Role of the CNC content and grafting on the PLA bionanocomposite film properties.

Cellulose nanocrystals (CNC), extracted from microcrystalline cellulose by acid hydrolysis, were grafted by ring opening polymerization of L-Lactide initiated from the hydroxyl groups available at their surface and two different CNC:L-lactide ratios (20:80 and 5:95) were obtained. The resulting CNC-g-PLLA nanohybrids were incorporated in poly(lactic acid) (PLA) matrix by an optimized extrusion process at two different content (1 wt.% and 3 wt.%) and obtained bionanocomposite films were characterized by thermal, mechanical, optical and morphological properties. Thermal analysis showed CNC grafted with the higher ratio of lactide play a significant role as a nucleating agent. Moreover, they contribute to a significant increase in the crystallization rate of PLA, and the best efficiency was revealed with 3 wt.% of CNC-g-PLLA. This effect was confirmed by the increased in Youngs modulus, suggesting the CNC graft ratio and content contribute significantly to the good dispersion in the matrix, positively affecting the final bionanocomposite properties.

Biocompatible Poly(L-lactide)/MWCNT Nanocomposites: Morphological Characterization, Electrical Properties, and Stem Cell Interaction

The promising perspectives of PLLA-based nanostructured biomaterials and their relevance in tissue engineering are reported. Nanocomposites based on PLLA and MWCNTs are developed with an MWCNT content ranging from 0 to 3 wt%. The electrical properties show a percolation threshold within a range of 0.21-0.33 wt% MWCNTs, and the conductivity increases by six orders of magnitude. The surface structure shows changes with the carbon nanotube concentration. The functional role of MWCNTs incorporation in terms of interactions with adult stem cells suggests that PLLA/MWCNT nanocomposites are suitable substrates for primary stem cell culture.

Increased functional properties and thermal stability of flexible cellulose nanocrystal/ZnO films

In this work we attempt to improve the functional properties and thermal stability of cellulose nanocrystal (CNC) films by means of eco-friendly materials and processes. Mechanically flexible films of closely packed CNCs with concentrations up to 5 wt.% of zinc oxide (ZnO) nanoparticles have been prepared by a simple, standard and environmentally friendly method using solely water. Results reveal that ultraviolet light is blocked by 98.5% at 1 wt.% ZnO while good transparency is maintained. A sharp hydrophobicity increase is observed with the addition of ZnO which would enhance the durability of films by decreasing the water diffusion through the material. The thermal degradation activation energy (E) presents an increase of 141%, denoting a high thermal stability of films, which would result beneficial for their potential application in the field of flexible electronics. Mechanical results demonstrate a high structural integrity of CNC/ZnO as a result of the occurring strong cellulosic inter- and intramolecular interactions within the closely packed CNC network. In overall, this work highlights the potential for environmentally friendly processing of sustainable nanostructured functional materials based on cellulose.

From implantation to degradation — are poly (l-lactide)/multiwall carbon nanotube composite materials really cytocompatible?

UNLABELLED Poly (l-lactide)s (PLLA) biodegradable properties are of special value in orthopaedic applications, but its mechanical strength limits its usage. To overcome this PLLA can be reinforced by multiwall carbon nanotubes (MWCNT). In this study the PLLA and MWCNT were combined to prepare nanostructured composites (nanocomposite) at 0, 0.1, 0.5 and 1wt.% reinforcement. The in vitro biocompatibility of these PLLA/MWCNT nanocomposites was evaluated taking into account the various stages of implantation including nanocomposite degradation. PLLA/MWCNT nanocomposites were highly biocompatible with human bone marrow stromal cells (HBMC). The potential surface degradation product, MWCNT, did not induce toxic responses on HBMC. However, the combination of MWCNT with lactic acid, resembling release after bulk degradation, significantly inhibited HBMC proliferation and activity. This study demonstrates the importance of comprehensive evaluations of novel materials for medical applications in predicting possible adverse effects during nanocomposite degradation. FROM THE CLINICAL EDITOR This study scrutinizes the cytocompatibility of poly-L-lactide reinforced by multiwall carbon nanotubes, and concludes that the combination of MWCNT with lactic acid significantly inhibited human bone marrow stromal cell proliferation and activity, highlighting the importance of comprehensive evaluations of novel materials.

Study of the chain microstructure effects on the resulting thermal properties of poly(L-lactide)/poly(N-isopropylacrylamide) biomedical materials.

The development of thermally-sensitive poly(N-isopropylacrylamide) (PNIPAAm) and biocompatible/biodegradable poly(L-lactide) (PLLA) blends offers us an efficient strategy in order to obtain materials with improved functional properties to be used in the emerging field of biomedicine. In this sense, thermal properties of PLLA and PNIPAAm have been investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD) were conducted to shed more light on the obtained results. For a better understanding of PLLA/PNIPAAm system, both low and high molecular weight PLLA and PNIPAAm have been synthesized by ring opening polymerization and aqueous redox polymerization respectively. Obtained results are interpreted from the viewpoint of chain microstructure of each homopolymer and the ratio between two constituent materials. DSC, SEM and WAXD results show a phase separation over the entire composition range irrespectively of the molecular weight of both homopolymers. Additionally, it was found a nucleating agent behavior of low molecular weight PNIPAAm, while high molecular weight PNIPAAm hinders the crystallization of PLLA. FTIR results suggest that the strong autoassociation present in PNIPAAm plays a key role impairing the miscibility of the whole system. Thermogravimetric analysis reveals that thermodegradation process of PLLA could be continuously delayed with the addition of PNIPAAm due to the increased thermal stability of N-isopropylacrylamide in regard to L-lactide sequences.

Construction of antibacterial poly(ethylene terephthalate) films via layer by layer assembly of chitosan and hyaluronic acid

Polyelectrolytic multilayers (PEMs) with enhanced antibacterial properties were built up onto commercial poly(ethylene terephthalate) (PET) films based on the layer by layer assembling of bacterial contact killing chitosan and bacterial repelling highly hydrated hyaluronic acid. The optimization of the aminolysis modification reaction of PET was carried out by the study of the mechanical properties and the surface characterization of the modified polymers. The layer by layer assembly was successfully monitored by TEM microscopy, surface zeta-potential, contact angle measurements and, after labeling with fluorescein isothiocyanate (FTIC) by absorption spectroscopy and confocal fluorescent microscopy. Beside, the stability of the PEMs was studied at physiological conditions in absence and in the presence of lysozyme and hyaluronidase enzymes. Antibacterial properties of the obtained PEMs against Escherichia coli were compared with original commercial PET.

Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) based polyurethanes: thermal, shape-memory and mechanical behavior

Shape memory polymers (SMPs) have attracted extensive attention from basic and fundamental research to industrial and practical applications. Among them, shape memory polyurethanes (SMPUs) have different applications such as in textile finishings, adhesives, coatings, automotive parts, furniture, construction materials, thermal insulation materials and footwear industries because they can be synthesized with different types of molecular architectures by manipulating their composition and properly choosing the chemical structure of their individual components. In this work, the synthesis and characterization of SMPUs, based on two-step polymerization, are reported. The hard segment of SMPU was composed of diisocyanate (toluene 2,4-diisocyanate (TDI) or 4,4′-methylene diphenyl diisocyanate (MDI)) and a chain extender, 1,4-butanediol (BD). On the other hand, the soft segment was prepared by a polyol, poly(oxytetramethylene) glycol (PTMG). By selectively choosing the hard-to-soft segment content, the glass transition temperature of SMPUs could be varied from −52.1 °C to 8.6 °C, while the proper combination of both segments imparts combined ductility and strength to our materials. Furthermore, the shape memory effect was found to depend on hydrogen bonding molecular interactions, making TDI-based SMPUs more appropriate for their commercial use.

Three-dimensional orientation of poly(L-lactide) crystals under uniaxial drawing

In this work the effects of three-dimensional crystal development upon polymer stretching are investigated. Poly(L-lactide) has been selected as a model semicrystalline polymer owing to its high chain stereoregularity which enables its crystallization by strain-induced mechanism. Specimens containing a bulk crystal volume fraction up to 55.5% have been obtained. Fourier transform infrared spectroscopy (FTIR) proves the development of more densely packed domains with strong dipole–dipole interactions for the more stretched PLLA. X-ray diffraction (XRD) has been implemented to obtain insights about the occurring micro-structural changes. Additionally, to determine macromolecular orientations texture analysis using XRD has been performed via pole figure measurements, which demonstrate that crystalline domains are transformed from fibrils into planar spherulites as stretching evolves. It is proposed that the strain-induced crystallization mechanism upon stretching is governed by the decrease of the number of degrees of freedom for the crystallization process when the compression is enough to limit one of the possible orientations. Obtained morphological evidences for the suggested crystal transformations by field emission scanning electron microscopy (FE-SEM) further confirm our hypothesis. In future, the analysis of three-dimensional strain-induced crystal orientation would be of prime interest for other commonly used semicrystalline polymers such as isotactic polypropylene (iPP), polyethylene (PE), polyethylene terephthalate (PET) and polyamide 66 (nylon).

PLLA/ZnO nanocomposites: Dynamic surfaces to harness cell differentiation

This work investigates the effect of the sequential availability of ZnO nanoparticles, (nanorods of ∼40nm) loaded within a degradable poly(lactic acid) (PLLA) matrix, in cell differentiation. The system constitutes a dynamic surface, in which nanoparticles are exposed as the polymer matrix degrades. ZnO nanoparticles were loaded into PLLA and the system was measured at different time points to characterise the time evolution of the physicochemical properties, including wettability and thermal properties. The micro and nanostructure were also investigated using AFM, SEM and TEM images. Cellular experiments with C2C12 myoblasts show that cell differentiation was significantly enhanced on ZnO nanoparticles-loaded PLLA, as the polymer degrades and the availability of nanoparticles become more apparent, whereas the release of zinc within the culture medium was negligible. Our results suggest PLLA/ZnO nanocomposites can be used as a dynamic system where nanoparticles are exposed during degradation, activating the material surface and driving cell differentiation.