Process study of the formation of biodegradable polymer microspheres for tissue engineering

A series of polymer microspheres was prepared via solvent evaporation by dispersing dichloromethane solutions of polylactic-co-glycolic acid (PLGA) in water. The dimensions of the final dry particles were measured by laser diffraction and correlated to the main fluid-dynamic parameters of the dispersion process, namely viscosity ratio, volume fraction of dispersed phase, intensity of stirring, and Weber number (We). Data analysis indicated that the system under study can be quantitatively well described by empirical models present in the literature and concerning the dispersion of liquid-liquid immiscible systems. The PLGA microspheres obtained in this way may be employed for fabrication of biodegradable scaffolds for tissue engineering

Development of a One-Dimensional Model for the Prediction of Leakage Flows in Regenerative Pumps

Regenerative pumps are characterized by a low specific speed that place them between rotary positive displacement pumps and purely radial centrifugal pumps. They are interesting for many industrial applications since, for a given flow rate and a specified head, they allow for a reduced size and can operate at a lower rotational speed with respect to purely radial pumps. The complexity of the flow within regenerative machines makes the theoretical performance estimation a challenging task. The prediction of the leakage flow rate between the rotating and the static disks is the one that more than others has an impact on the prediction of global performance. All the classical approaches to the disk clearance problem assume that there is no relevant circumferential pressure gradient. In the present case, the flow develops along the tangential direction and the pressure gradient is intrinsically non-zero. The aim of the present work is to develop a reliable approach for the prediction of leakage flows in regenerative pumps. The method assumes that the flow inside of the disk clearance can be decomposed into several stream-tubes. Energy balance is performed for each tube, thus generating a system that can be solved numerically. The new methodology has been tuned using data obtained from the numerical simulation of virtual prototypes of regenerative pumps where the disk clearance is part of the control volume. After that, the methodology has been integrated into an existing one-dimensional code called DART (developed at the University of Florence in cooperation with Pierburg Pump Technology Italy S.p.A.) and the new algorithm is verified using available experimental and numerical data. It is here demonstrated that an appropriate calibration of the leakage flow model allows for an improved reliability of the one-dimensional code

Thermoresponsive Host Polymer Matrix for Self-Healing Luminescent Solar Concentrators

© 2019 American Chemical Society. Luminescent solar concentrators (LSCs) are a promising solar energy technology for reducing architectural barriers to the integration of photovoltaic systems into the built environment. In this work, the first demonstration of thin-film LSCs based on a thermally reversible cross-linked host polymer is presented. This smart material is obtained via a dynamic-chemistry approach based on the Diels-Alder (DA) reaction between a furan-functionalized acrylic copolymer and an aliphatic bismaleimide to obtain optically clear, cross-linked systems capable of healing mechanical damage upon heat treatment. By carefully tuning the concentration of a perylene-based luminophore dopant, an optical efficiency as high as 4.9% can be achieved with this DA-based LSC. In addition, full recovery of device efficiency is demonstrated after complete thermal healing of mechanically induced surface damages as a result of the embedded DA functionality. The approach presented here paves the way to the development of highly efficient multifunctional thermoresponsive smart LSC systems.European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 818762

Long-term thermal stability of high-efficiency polymer solar cells based on photocrosslinkable donor-acceptor conjugated polymers

Highly efficient polymer solar cells based on novel photocrosslinkable donor–acceptor conjugated polymers are fabricated and their long-term thermal stability is reported. After 72 h of thermal annealing at 150 °C, a stable power conversion efficiency as high as 4.7% is maintained. The control of active layer morphology and device performance through annealing is correlated with the synthetic design of the photocrosslinkable polymer

Perylenetetracarboxy-3,4:9,10-diimide derivatives with large two-photon absorption activity

Three new perylenetetracarboxy-3,4:9,10-diimides, bearing 2,6-diisopropylphenyl groups at the imide positions and 4-(R-ethynyl)phenoxy moieties (R = 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole (P2), pyrene (P3) or pyrene-CH2OCH2 (P4)) at the four bay positions, were prepared, along with the known related derivative (R = phenyl (P1)), and well characterized. They have large two-photon absorption (TPA) cross-sections (sigma(2)), as determined by the Z-scan technique, the highest values being reached with P2 which bears a planar -delocalized donor moiety. P3 is characterized by higher sigma(2) values than both P1, as expected for the higher -conjugation of the donor pyrene moiety with respect to phenyl, and P4, due to the presence of the flexible and non-conjugated CH2OCH2 bridge between the pyrene and the ethynyl fragment in the latter compound. The molecular geometry of P1-P4 has been optimized by DFT modeling, showing that in P2 and P3 the bay substituents are stacked due to the - interactions of both pyrene and thiophene groups. The LUMO of P1-P4 lies at the same energy and is essentially delocalized on the perylene core whereas the HOMO and HOMO-1 of both P2 and P3 are degenerate and do not show contribution from the perylene core contrarily to that of P1 and P4. The HOMO-LUMO gap is therefore essentially influenced by the HOMO which reflects the electronic charge delocalization on the bay substituents, the lower gaps being observed for P2 and P3, which are characterized by the best TPA properties

Design of polymer-based antimicrobial hydrogels through physico-chemical transition

The antimicrobial activity represents a cornerstone in the development of biomaterials: it is a leading request in many areas, including biology, medicine, environment and industry. Over the years, different polymeric scaffolds are proposed as solutions, based on the encapsulation of metal ions/particles, antibacterial agents or antibiotics. However, the compliance with the biocompatibility criteria and the concentration of the active principles to avoid under- and over-dosing are being debated. In this work, we propose the synthesis of a versatile hydrogel using branched polyacrylic acid (carbomer 974P) and aliphatic polyetherdiamine (elastamine\uae) through physico-chemical transition, able to show its ability to counteract the bacterial growth and infections thanks to the polymers used, that are not subjected to further chemical modifications. In particular, the antimicrobial activity is clearly demonstrated against Staphyloccoccus aureus and Candida albicans, two well-known opportunistic pathogens. Moreover, we discuss the hydrogel use as drug carrier to design a unique device able to combine the antibacterial/antimicrobial properties to the controlled drug delivery, as a promising tool for a wide range of biomedical applications

Fluorescent probes based on chemically-stable core/shell microcapsules for visual microcrack detection

Core/shell microcapsule-based fluorescent probes are presented in this work for potential use as early visual detection tool of microcracks in structural materials. A new microcapsule-based system is developed consisting of a UV-screening polyurea shell containing a fluorescent liquid core. The UV-screening functionality allows to prevent unwanted fluorescence emission from intact microcapsules upon UV-light exposure and yields excellent visibility contrast of the locally damaged region where fluorescent liquid core released from ruptured microcapsules is present. In addition, by carefully tuning the chemical composition of the shell material, microcapsules with enhanced chemical stability can be formed, as demonstrated by their superior solvent resistance over dwell time originating from the highly crosslinked shell structure that prevents core extraction from the microcapsules. A thorough chemical, thermal, morphological and optical characterization combined with a functional demonstration of the damage visualization capabilities of this new microcapsule-based system highlights its potential as a highly chemically-stable damage sensor for microcrack detection in structural materials

Lignin-Based Polymer Electrolyte Membranes for Sustainable Aqueous Dye-Sensitized Solar Cells

In the quest for sustainable materials for quasi-solid-state (QS) electrolytes in aqueous dye-sensitized solar cells (DSSCs), novel bioderived polymeric membranes were prepared in this work by reaction of preoxidized kraft lignin with poly(ethylene glycol)diglycidylether (PEGDGE). The effect of the PEGDGE/lignin relative proportions on the characteristics of the obtained membranes was thoroughly investigated, and clear structure–property correlations were highlighted. In particular, the glass transition temperature of the materials was found to decrease by increasing the amount of PEGDGE in the formulation, indicating that polyethylene glycol chains act as flexible segments that increase the molecular mobility of the three-dimensional polymeric network. Concurrently, their swelling ability in liquid electrolyte was found to increase with the concentration of PEGDGE, which was also shown to influence the ionic transport efficiency within the membrane. The incorporation of these lignin-based cross-linked systems as QS electrolyte frameworks in aqueous DSSCs allowed the preparation of devices with excellent long-term stability under UV–vis light, which were found to be superior to benchmark QS-DSSCs incorporating state-of-the-art carboxymethylcellulose membranes. This study provides the first demonstration of lignin-based QS electrolytes for stable aqueous DSSCs, establishing a straightforward strategy to exploit the potential of lignin as a functional polymer precursor for the field of sustainable photovoltaic devices

Lignin as polymer electrolyte precursor for stable and sustainable potassium batteries

Potassium batteries show interesting peculiarities as large-scale energy storage systems and, in this scenario, the formulation of polymer electrolytes obtained from sustainable resources or waste-derived products represents a milestone activity. In this study, a lignin-based membrane is designed by crosslinking a pre-oxidized Kraft lignin matrix with an ethoxylated difunctional oligomer, leading to self-standing membranes that are able to incorporate solvated potassium salts. The in-depth electrochemical characterization highlights a wide stability window (up to 4 V) and an ionic conductivity exceeding 10−3 S cm−1 at ambient temperature. When potassium metal cell prototypes are assembled, the lignin-based electrolyte attains significant electrochemical performances, with an initial specific capacity of 168 mAh g−1 at 0.05 A g−1 and an excellent operation for more than 200 cycles, which is an unprecedented outcome for biosourced systems in potassium batteries