Search

In the next decade, we will witness the replacement of a majority of conventional light sources with light-emitting diodes (LEDs). Efficient LEDs other than phosphors can enhance their functionality and meet different lighting needs. Quantum dots (QDs) have high potential for future LED technology due to their sensitive band-gap tuning via the quantum confinement effect and compositional control, high photoluminescence quantum yield (PLQY), and mass-production capacity. Herein, we demonstrate white LEDs using QDs that reach over 150 lumens per electrical Watt. For that we synthesized green-and red-emitting ZnCdSe/ZnSe core/shell QDs by low-temperature nucleation, high-temperature shell formation, and postsynthetic trap-state removal. Their cadmium concentration is lower than 100 ppm, satisfying the current EU RoHS regulations, and their PLQY reaches a high level of 94%. The PLQY of QDs is maintained within the device on blue LED via liquid injection, and their integration at optimized optical densities leads to 129.6 and 170.4 lm/W for red-green-blue (RGB)-and green-blue (GB)-based white LEDs, respectively. Our simulations further showed that an efficiency level of over 230 lm/W is achievable using ultraefficient blue LED pumps. The simple fabrication and high performance of white LEDs using QD liquids show high promise for next-generation lighting devices., Scientific and Technological Research Council of Turkey (TÜBİTAK); Turkish Academy of Sciences (TUBA-GEBIP) The Young Scientist Award Program; Science Academy of Turkey (BAGEP) The Young Scientist Award Program; Bilim Kahramanlari Dernegi The Young Scientist Award

Polyurethanes are one of the most important classes of polymeric materials. This is mainly due to the availability of a very large number of inherently different starting materials that allows the design and synthesis of polyurethane based materials with a wide range of properties for numerous applications. In this short review, important physical and chemical factors and parameters that have a significant effect on the properties of polyurethanes are discussed. Critical contribution of hydrogen bonding on the structure-morphology-property behavior of these materials was emphasized by both experimental data and molecular simulation studies. Influence of the chemical structures, solubility parameters and molecular weights of the soft and hard segments on morphology and properties were discussed. Important issues regarding the reaction chemistry, synthetic method used and thermal history on structure and performance of polyurethanes were explained. We hope this article, which is prepared to celebrate the 100th anniversary of Polymer Science, will be useful to those who are newcomers to the field, but also to the experienced researchers to better understand the structure-property behavior of polyurethanes and tailor-design novel structures for various applications.

We developed quantum dot (QD) based color-conversion white LEDs that reach over 150 lumens per electrical Watt. For that we synthesized alloyed ZnCdSe/ZnSe QDs with 94% of quantum efficiency and injected QD-liquids on blue LEDs.

Effective skeletal muscle tissue engineering relies on control over the scaffold architecture for providing muscle cells with the required directionality, together with a mechanical property match with the surrounding tissue. Although recent advances in 3D printing fulfill the first requirement, the available synthetic polymers either are too rigid or show unfavorable surface and degradation profiles for the latter. In addition, natural polymers that are generally used as hydrogels lack the required mechanical stability to withstand the forces exerted during muscle contraction. Therefore, one of the most important challenges in the 3D printing of soft and elastic tissues such as skeletal muscle is the limitation of the availability of elastic, durable, and biodegradable biomaterials. Herein, we have synthesized novel, biocompatible and biodegradable, elastomeric, segmented polyurethane and polyurethaneurea (TPU) copolymers which are amenable for 3D printing and show high elasticity, low modulus, controlled biodegradability, and improved wettability, compared to conventional polycaprolactone (PCL) and PCL-based TPUs. The degradation profile of the 3D printed TPU scaffold was in line with the potential tissue integration and scaffold replacement process. Even though TPU attracts macrophages in 2D configuration, its 3D printed form showed limited activated macrophage adhesion and induced muscle-like structure formation by C2C12 mouse myoblasts in vitro, while resulting in a significant increase in muscle regeneration in vivo in a tibialis anterior defect in a rat model. Effective muscle regeneration was confirmed with immunohistochemical assessment as well as evaluation of electrical activity produced by regenerated muscle by EMG analysis and its force generation via a custom-made force transducer. Micro-CT evaluation also revealed production of more muscle-like structures in the case of implantation of cell-laden 3D printed scaffolds. These results demonstrate that matching the tissue properties for a given application via use of tailor-made polymers can substantially contribute to the regenerative outcomes of 3D printed tissue engineering scaffolds. Keywords: 3D printing; engineered muscle; polyurethane; polyurethaneurea; skeletal muscle; tibialis anterior defect.

The Dissipative Particle Dynamics (DPD) simulation technique was used to elucidate the composition-dependent equilibrium morphological behavior of three different symmetric ABA triblock copolymers, which were; poly(e-caprolactone)-poly(dimethylsiloxane)-poly(e-caprolactone) (PCL-PDMS-PCL), poly(e-caprolactone)-poly(ethylene oxide)-poly(e-caprolactone) (PCL-PEO-PCL) and poly(L-lactide)-poly(dimethylsiloxane)-poly(L-lactide) (PLLA-PDMS-PLLA). These polymers were chosen due to their biomedical and biotechnological importance. Polymeric A and B blocks were modeled as connected chain of beads with varying incompatibility. The impact of the block incompatibilities on the microphase separation as well as on the equilibrium phase behaviors were investigated at the mesoscopic scale. A detailed visual analysis of the DPD images and constructed phase diagram showed that quite different equilibrium morphologies were attainable by controlling the molecular weights of the blocks and the strength of the intermolecular interaction between them. More compatible A and B blocks underwent lamellar to cylindrical and cylindrical to spherical phase transitions at lower B block concentrations. Our results clearly showed that, Flory–Huggins interaction parameter (χ) and degree of polymerization (N) were the only control parameters, which determined the shape and size of the phase domains, as well as the extent of equilibrium nanophase separation. Our DPD simulated morphologies were compared with experimental images obtained by Atomic Force Microscopy (AFM).

Degumming of Bombyx mori silk cocoons by a novel and mild process using aqueous ammonia and fabrication of electrospun polycaprolactone/silk fibroin (PCL/SF) nanofibrous scaffolds is reported. Cocoons were degummed in 0.3% w/w solutions of boiling ammonia (28–30%) for 45 min. Degummed SF fibers were dissolved in phosphoric and formic acid (7/3 v/v) mixture, coagulated in methanol, filtered and dried. PCL solutions containing different amounts of SF were electrospun in formic acid, a green solvent. Scaffolds were characterized to confirm the successful incorporation of SF and to demonstrate formation of nanofibrous webs with good biomechanical properties. Cell viability assay was performed by seeding Human BJ fibroblast cells on scaffolds. In vitro analysis showed that the scaffolds produced were non-toxic and incorporation of SF resulted in enhanced cell proliferation. Nanofibrous PCL/SF scaffolds with good biomechanical properties developed through dialysis free processing of silk fibroin can be promising substrates for tissue engineering applications.

There has been a considerable interest in developing stiff, strong, tough, and highly stretchable hydrogels in various fields of science and technology including biomedical and sensing applications. However, simultaneous optimization of stiffness, strength, toughness, and extensibility is a challenge for any material, and hydrogels are well-known to be mechanically weak materials. Here, we demonstrate that poly(ethylene oxide)-based dual stimuli-responsive semicrystalline poly(urethane-urea) (PU) copolymers with high hard segment contents (30 and 40%) can be utilized as stiff, strong, tough, and highly stretchable hydrogels with an elastic modulus (4-10 MPa) tens to hundreds of times higher than that of conventional hydrogels (0.01-0.1 MPa), strength (7-13 MPa) and toughness (53-74 m(-3) MJ. m(-3)) fairly comparable to those of the toughest hydrogels reported in the literature, and stretchability beyond 10 times their initial length (1000-1250%). In addition, the shape-memory program has been used to tune the room temperature stiffness and strength of the studied PU copolymers. Finally, the materials show fast shape recovery (less than 10 s) during both heat- and water-activated shape memory cycles, which can be adjusted by a simple modulation of the hard segment content and/or soft segment molecular weight. Our findings may be of interest in emerging biomedical and sensing applications.

An amorphous poly(urethane-urea) copolymer composed of 70 wt% poly(ethylene oxide) (PEO) soft segments (SS) (Mw = 2000 g mol-1) and 30 wt% cycloaliphatic hard segments (HS) was subjected to in-situ X-Rays during tensile deformation. Mechanical hardening at room temperature was attributed to strain induced crystallization (SIC) of the PEO SS through the multiplication of aligned crystallites. The permanent nature of these crystals after stress removal indicates a certain mechanical stability, which we related here to the concomitant effect of superstraining of the SS crystallites and the HS reorganization upon deformation. This is in marked contrast to previous studies which reported the crystalline phase to be temporary upon unloading. A manifestation of such enhanced stability is the memory effect evidenced by an increased crystallizability of PEO segments during incremental cyclic loading. These results offer a way to (i) tune the mechanical properties of TPUs via the formation of mechanically stable pre-oriented SS crystals and to (ii) tune the thermally/water activated shape memory properties of TPUs (shape fixity, kinetics of shape memory recovery).

Achieving a unique combination of stiffness, strength, extensibility, and toughness in sol-cast poly(urethane-urea) (PU) copolymer films is a challenge since these properties are-in general- mutually exclusive. Here we demonstrate that geometric confinement of the basic building blocks controls stiffness, strength, extensibility, and toughness in PU films. Our results suggest that the severity of geometric confinement can be tuned by adjusting (i) soft segment molecular weight (SSMW) and (ii) drying temperature (DT) thanks to their effects on the structure formation via microphase separation and/or (confined and/or bulk) crystallization. It is therefore possible to produce (i) soft (no notable confinement) and (ii) stiff, strong, extensible, and tough (severe confinement) materials without changing any other parameter except SSMW and DT. The former has a typical physically cross-linked network and shows a welldefined elastomeric behavior with an elastic modulus (E) of 5-20 MPa, a tensile strength (sigma(max)) of 30-35 MPa, an extensibility (epsilon) of 1000-1300%, and a toughness (W) of 90-180 MJ m(-3). The latter, on the other hand, possesses an elegant hierarchical structure containing tightly packed secondary structures (7(2)-helix, 4(1)-helix, and antiparallel beta-sheets) and displays an elastoplastic behavior with an E of 400-700 MPa, a sigma(max) of 45-55 MPa, an epsilon of 650-850%, and a W of 200-250 MJ m(-3). Hence, our findings may be of interest in designing advanced materials containing synthetic replica of the secondary structures found in protein-based materials. The structure formation in the materials with this structural hierarchy is driven by the confined crystallization of helical poly(ethylene oxide) (PEO) chains in subnanometer urea channels, which-to the best of our knowledge-is a phenomenon wellknown in host-guest systems but has not yet demonstrated in PU copolymers, and complemented by the "bulk" crystallization of PEO and/or the microphase separation.

Superhydrophobic PMMA surfaces were prepared by spin-coating and doctor blade coating of PMAA/hydrophobic silica (1/10 by weight) dispersions in toluene onto glass substrates. Influence of the number of coating layers applied and gauge thickness of the doctor blade used on surface properties were investigated. Formation of dual scale, micro/nano surface topographies were demonstrated by scanning electron microscopy, atomic force microscopy and white light interferometry studies. Roughness factor (r) and average surface roughness (Ra) values of the surfaces were determined. Wetting behavior of superhydrophobic PMMA surfaces obtained by introducing micro-nano, hierarchical roughness to inherently hydrophilic smooth PMMA films cannot be explained by Wenzel model. Therefore, wetting behavior of these surfaces were analyzed using Cassie-Baxter model and area fraction of surface protrusions were estimated.

Microporous poly(lactic acid) (PLA) coatings with fairly homogeneous pore size and distribution were obtained through spin-coating process. Critical effects of the thermal conductivity of the substrate (copper, glass, insulated glass), solvent type (dichloromethane, chloroform and tetrahydrofuran), polymer concentration (3–15% by weight) and relative humidity of the environment (0–85% relative humidity) on the formation and topography of microporous surfaces were investigated. Characterization of the surfaces was achieved via scanning electron microscopy, white light interferometry and static water contact angle measurements. By tuning the production parameters, PLA coatings displaying microporous surfaces with uniform pore sizes and distribution were obtained. Pore sizes varied from 1 to 7 μm depending on the experimental conditions.

Monolithic poly(lactic acid) (PLA) foams were produced by thermally induced phase separation. PLA solutions with concentrations 8-22 wt % were prepared in tetrahydrofuran/methanol (THF/MeOH) solvent/nonsolvent mixtures at 55 degrees C. Homogenous solutions were quenched at -20 degrees C to induce phase separation and gelation. Resulting gels were mechanically stabilized by solvent exchange. Subsequent supercritical CO2 drying yielded monolithic PLA foams. Crystal structure and degree of crystallinity of the foams were obtained by x-ray diffractometry and differential scanning calorimetry. Morphologies were determined by scanning electron microscopy. Tuning the PLA concentration and THF/MeOH ratio enabled preparation of monolithic PLA foams. Depending on the experimental conditions various morphologies, such as: interconnected networks, thin platelets, lamellar stacks, axialites, and spherulites were formed. Monoliths obtained were highly crystalline. By changing the PLA concentration monoliths with controlled average pore sizes (170-1440 nm) and porosities (80-90%) were produced. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 98-108

Smart surfaces with preferably reconfigurable wetting properties can lead to key applications in labon- a-chip analytical and preparative systems. In this paper, we present our recent results obtained using polymer surfaces whose wetting properties are modified in a permanent manner using laser ablation and in a reconfigurable manner using plasma oxidation. Polydimethylsiloxane (PDMS) diluted in solvent is used as the polymeric material coated over microscope glass slides in our studies. In the first part, the tracks of ~ 70 μm width are defined over the surface by surface oxidation using cold plasma exposure through a microfluidic channel. In the second part, femtosecond laser micromachining is used for selective removal of polymer coating and uncovering the hydrophilic glass substrate. We experimentally demonstrate guiding of water in the form of filaments and droplets over the obtained hydrophilic tracks of ~ 110 μm. We also discuss preliminary experiments to coat light sensitive azobenzene over a glass substrate with the help of a silane in order to achieve reversible isomerization upon periodic exposure to UV/vis radiation. Furthermore, we elaborate advantages, challenges and the significant role of such patterned surfaces in future applications.

Polymer surfaces reversibly switchable from superhydrophobic to superhydrophilic by exposure to oxygen plasma and subsequent thermal treatment are demonstrated. Two inherently different polymers, hydrophobic segmented polydimethylsiloxane-urea copolymer (TPSC) and hydrophilic poly(methyl methacrylate) (PMMA) are modified with fumed silica nanoparticles to prepare superhydrophobic surfaces with roughness on nanometer to micrometer scale. Smooth TPSC and PMMA surfaces are also used as control samples. Regardless of their chemical structure and surface topography, all surfaces display completely reversible wetting behavior changing from hydrophobic to hydrophilic and back for many cycles upon plasma oxidation followed by thermal annealing. Influence of plasma power, plasma exposure time, annealing temperature and annealing time on the wetting behavior of polymeric surfaces are investigated. Surface compositions, textures and topographies are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and white light interferometry (WLI), before and after oxidation and thermal annealing. Wetting properties of the surfaces are determined by measuring their static, advancing and receding water contact angle. We conclude that the chemical structure and surface topography of the polymers play a relatively minor role in reversible wetting behavior, where the essential factors are surface oxidation and migration of polymer molecules to the surface upon thermal annealing. Reconfigurable water channels on polymer surfaces are produced by plasma treatment using a mask and thermal annealing cycles. Such patterned reconfigurable hydrophilic regions can find use in surface microfluidics and optofluidics applications.

Polycaprolactone (PCL) foams were produced by thermally induced phase separation. Tetrahydrofuran/methanol (THF/MeOH) (solvent/non-solvent) mixture was used for the induction of liquid-liquid phase separation of PCL solutions at three different temperatures. Subsequent solvent exchange followed by vacuum drying yielded polymeric foams with different morphologies. Characterization of foams was obtained by scanning electron microscopy, x-ray diffractometry, mercury intrusion porosimetry and compression tests. Influence of polymer concentration (8, 10 and 12 wt%), quench temperature (4, -20 and -80 degrees C), and THF/MeOH ratio from (42/58) to (54/46) (wt/wt) on the foam formation, morphology and properties were investigated systematically. Lower PCL concentration, lower THF content and higher quench temperature lead to larger pore sizes in the foams obtained. Detailed discussions of the influence of processing parameters on foam structure and porosity, foam density, percent crystallinity and compressive properties are provided. By selectively tuning the process parameters, foams with controlled pore sizes (10-450 mu m), porosity (83-91%) and morphology (cellular, bead-like, micro-spherical) were obtained. (C) 2018 Elsevier Ltd. All rights reserved.

Preparation and characterization of chitosan/hydroxyapatite (CS/HA) nanocomposites displaying an intercalated structure is reported. Hydroxyapatite was synthesized through sol-gel process. Formic acid was introduced as a new solvent to obtain stable dispersions of nano-sized HA particles in polymer solution. CS/HA dispersions with HA contents of 5, 10 and 20% by weight were prepared. Self-assembling of HA nanoparticles during the drying of the solvent cast films led to the formation of homogeneous CS/HA nanocomposites. Composite films were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-rays (EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, X-rays diffraction (XRD) analysis and thermogravimetric analysis (TGA). SEM and AFM confirmed the presence of uniformly distributed HA nanoparticles on the chitosan matrix surface. XRD patterns and cross-sectional SEM images showed the formation of layered nanocomposites. Complete degradation of chitosan matrix in TGA experiments, led to the formation of nanoporous 3D scaffolds containing hydroxyapatite, β-tricalcium phosphate and calcium pyrophosphate. CS/HA composites can be considered as promising materials for bone tissue engineering applications.

Hydrogen bonding between hard segments has a critical effect on the morphology and properties of polyurethanes. Influence of temperature on hydrogen bonded urethane network and melting behavior of a model semicrystalline segmented polyurethane was investigated by experiments and simulations. Polyurethane was synthesized by the stoichiometric reaction between p-phenylene diisocyanate and poly(tetramethylene oxide) (PTMO) with a molecular weight of 1000 g/mol. Simulations were carried out using dissipative particle dynamics (DPD) and molecular dynamics (MD) approaches. Experimental melting behavior obtained by various techniques was compared with simulations. DPD simulations showed a room temperature microphase morphology consisting of a three-dimensional hydrogen-bonded urethane hard segment network in a continuous and amorphous PTMO matrix. The first-order melting transitions of crystalline urethane hard segments observed during the continuous isobaric heating in DPD and MD simulations (340–360 K) were in reasonably good agreement with those observed experimentally, such as AFM (320–340 K), WAXS (330–360 K), and FTIR (320–350 K) measurements. Quantitative verification of the melting of urethane hard segments was demonstrated by sharp discontinuities in energy versus temperature plots obtained by MD simulations due to substantial decrease in the number of hydrogen bonds above 340 K. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017.

Poly(ethylene oxide) (PEO) based polyurethaneurea-silica nanocomposites were prepared by solution blending and characterized by Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Differential Scanning Calorimetry and tensile testing. The colloidal silica nanoparticles with an average size of 50 nm were synthesized by modified Stober method in isopropanol. Silica particles were incorporated into three cycloaliphatic polyurethaneurea (PUs) copolymers based on PEO oligomers with molecular weights of 2,000, 4,600, and 8,000 g/mol. Hard segment content of PUs was constant at 30% by weight. Silica content of the PU nanocomposites varied between 1 and 20% by weight. Soft segment (SS) glass transition and melting temperatures slightly increased with increasing filler content for all the copolymers. Degree of SS crystallinity first increased with 1% silica incorporation and subsequently decreased by further silica addition. Elastic modulus and tensile strengths of PU copolymers gradually increased with increasing amount of the silica filler. Elongation at break values gradually decreased in PEO-2000 based PU copolymer with increasing silica content, whereas no significant change was observed in PUs based on PEO-4600 and PEO-8000. Enhancement in tensile properties of the materials was mainly attributed to the homogeneous distribution of silica filler in polymer matrices and strong polymer-filler interactions.

Colloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)-based polyurethane–urea copolymer matrix at a concentration of 10¿wt % (4.4¿vol %) in order to investigate the effect of their surface chemistry on the structure–property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30¿wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break.

When a liquid droplet (e.g., coffee, wine, etc.) is splattered on a surface, the droplet dries in a ring-shaped stain. This widely observed pattern in everyday life occurs due to the phenomenon known as a coffee stain (or coffee ring) effect. While the droplet dries, the capillary flow moves and deposits the particles toward the pinned edges, which shows a 2D ring-like structure. Here we demonstrate the transition from a 2D to a 3D coffee stain that has a well-defined and hollow sphere-like structure, when the substrate surface is switched from hydrophilic to superhydrophobic. The 3D stain formation starts with the evaporation of the pinned aqueous colloidal droplet placed on a superhydrophobic surface that facilitates the particle flow towards the liquid-air interface. This leads to spherical skin formation and a cavity in the droplet. Afterwards the water loss in the cavity due to pervaporation leads to bubble nucleation and growth, until complete evaporation of the solvent. In addition to the superhydrophobicity of the surface, the concentration of the solution also has a significant effect on 3D coffee stain formation. Advantageously, 3D coffee stain formation in a pendant droplet configuration enables the construction of all-protein lasers by integrating silk fibroin with fluorescent proteins. No tools, components and/or human intervention are needed after the construction process is initiated; therefore, 3D coffee-stains hold promise for building self-assembled and functional 3D constructs and devices from colloidal solutions.

Rigid poly(lactic acid) (PLA) foams were prepared by thermally induced phase separation followed by solvent exchange and vacuum drying. A novel tetrahydrofuran (THF)/water solvent system was used for the induction of liquid-liquid phase separation of PLA solution at three different temperatures; 24 degrees C, 4 degrees C and -20 degrees C. PLA gels obtained were mechanically stabilized by replacing THF/water solvent mixture with ethanol nonsolvent. Characterization of rigid PLA foams was obtained by scanning electron microscopy, mercury intrusion porosimetry, x-ray diffractometry, infrared spectroscopy and differential scanning calorimetry analyses. Effects of fabrication parameters on the morphology and pore structure were systematically examined. The parameters investigated included; (i) polymer concentration, (ii) THF/water ratio and (iii) quench temperature. Results showed that degree of porosity and the morphology of the pores, such as the pore size and shape could be controlled by tuning the fabrication parameters. By controlling the degree of phase separation of PLA solution, foams with dual micro and nano structures were obtained. (C) 2016 Elsevier Ltd. All rights reserved.

Two simple processes; (i) spin-coating, and (ii) doctor blade coating of silica/polymer dispersions are described for the preparation of superhydrophobic polymer surfaces. To demonstrate the versatility and broad applicability of the processes, polymeric surfaces modified included a thermoplastic resin, polystyrene (PS) and a thermoset, crosslinked epoxy resin (ER). Micro/nano hierarchical nature of the surface topographies obtained were demonstrated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and white light interferometry (WLI) studies. Roughness factor (r) and average surface roughness (Ra) values, which are critical in obtaining superhydrophobic surfaces were determined for each polymeric system. It was clearly demonstrated that increased (r) and (Ra) values resulted in superhydrophobic behavior with very high static, advancing and receding water contact angles, well above 150° and contact angle hysteresis values of less than 10°. Incorporation of small amounts (1.0% by weight) of a silicone copolymer or a perfluoroether glycol oligomer reduced the contact angle hysteresis in the epoxy resin system well below 10° and produced truly superhydrophobic surfaces.

I materiali alloplastici vengono frequentemente utilizzati negli interventi di chirurgia plastica sul volto, quali la rinoplastica e la chirurgia ricostruttiva del naso. Ad oggi non è stato ancora individuato un materiale alloplastico con caratteristiche ottimali. Il presente studio sperimentale si propone di valutare la risposta tissutale e la resistenza nel tempo di cinque nuovi polimeri proposti come materiali alloplastici. Il presente studio è stato condotto presso un ospedale universitario di terzo livello. Sono state ricavate sei tasche sottocutanee sul dorso di 10 conigli che sono state usate per l’impianto di ciascuno dei polimeri testati più una tasca di controllo. Ciascuna delle tasche è stata escissa congiuntamente al tessuto circostante dopo tre mesi, ed è stata sottoposta ad un esame istopatologico. È stata quindi condotta una valutazione semi quantitativa con focus su neo angiogenesi, infiammazione, fibrosi, formazione di ascessi, presenza di cellule giganti multinucleate contenenti corpi estranei e stato dei polimeri testati. E’ stata inoltre effettuata una valutazione statistica, che per quanto riguarda la comparazione diretta fra la tasca di controllo e i polimeri II, III e IV non ha mostrato differenze significative in merito alla neo vascolarizzazione, all’infiammazione, alla fibrosi, alla presenza di ascessi ed alla presenza di cellule giganti multinucleate. Il polimero I ha invece mostrato un grado di fibrosi inferiore rispetto alla tasca di controllo (p = .027) and V (p = .018), benché le altre variabili prese in considerazione fossero sostanzialmente uguali. L’integrità nel tempo dei polimeri III (9 intatti, uno frammentato) e IV (8 intatti, 2 assenti) è stata migliore di quella ottenuta con gli altri polimeri testati. Questo gruppo di nuovi polimeri può essere considerato interessante per future applicazioni cliniche. Tutti i polimeri hanno mostrato risultati accettabili in termini di risposta dei tessuti, tuttavia i fenomeni di integrazione fibrovascolare sono stati maggiori nel caso dei polimeri II, III e IV. Inoltre la durata nel tempo dei polimeri III e IV è stata la migliore in assoluto.

Catalytic conversion of carbon dioxide to liquid fuels and basic chemicals by using solar-derived hydrogen at, or near, ambient pressure is a highly desirable goal in heterogeneous catalysis. If realized, this technology could lead to a more sustainable society together with decentralized power generation. A novel class of holmium-containing multi-metal oxide Cu catalysts, discovered through the application of high-throughput methods, is reported. In particular, ternary systems of Cu-GaOx-HoOy>Cu-CeOx-HoOy approximate to Cu-LaOx-HoOy supported on -Al2O3 exhibited superior methanol production (10x) with less CO formation than previously reported catalysts at 1atm pressure. Holmium was shown to be highly dispersed as few-atom clusters, suggesting that the formation of trimetallic sites could be the key for the promotion of methanol synthesis by Ho.

Poly(e-caprolactone)–polydimethylsiloxane–poly(e-caprolactone) (PCL-PDMS-PCL) triblock copolymers with a wide range of block lengths (1000–32,000 g/mol) were synthesized by the ring-opening polymerization of e-caprolactone using aminopropyl terminated PDMS oligomers as the initiator. Reactions were carried out in bulk or solution at 125 ± 5 °C under the catalytic action of tin octoate. Products obtained in high yields were characterized by FTIR spectroscopy, gel permeation chromatography, X-ray diffraction, temperature-dependent optical microscopy, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy and static water contact angle measurements. Effect of the polymer composition and the molecular weight of the PDMS and PCL blocks on; (i) copolymer morphology and the extent of microphase separation, (ii) crystallization of PCL segments and (iii) surface properties of copolymers were investigated. Regardless of the block lengths, all PCL-PDMS-PCL copolymers displayed well microphase separated morphologies. The extent of microphase separation, resultant morphology and sizes of the microphases were strongly dependent on the copolymer composition and the block lengths of both PCL and PDMS segments. Crystalline PCL microphase was observed in all copolymers, which increased as a function of PCL content and molecular weight. Hydrophobicity of the copolymer surfaces was improved with increasing PDMS molecular weight, as determined by static water contact angle measurements.

Effect of the coating method on the formation of superhydrophobic polydimethylsiloxane–urea copolymer (TPSC) surfaces, modified by the incorporation of hydrophobic fumed silica nanoparticles was investigated. Four different coating methods employed were: (i) layer-by-layer spin-coating of hydrophobic fumed silica dispersed in an organic solvent onto TPSC films, (ii) spin-coating of silica–polymer mixture onto a glass substrate, (iii) spray coating of silica/polymer mixture by an air-brush onto a glass substrate, and (iv) direct coating of silica–polymer mixture by a doctor blade onto a glass substrate. Influence of the coating method, composition of the polymer/silica mixture and the number of silica layers applied on the topography and wetting behavior of the surfaces were determined. Surfaces obtained were characterized by scanning electron microscopy (SEM), white light interferometry (WLI) and advancing and receding water contact angle measurements. It was demonstrated that superhydrophobic surfaces could be obtained by all methods. Surfaces obtained displayed hierarchical micro-nano structures and superhydrophobic behavior with static and advancing water contact angles well above 150° and fairly low contact angle hysteresis values.

Formation of superhydrophobic polymer surfaces were investigated through successive spin-coating of hydrophobic fumed silica dispersed in an organic solvent onto polymer films. Two different polymers, a hydrophobic segmented silicone-urea copolymer (TPSC) and hydrophilic poly(methyl methacrylate) (PMMA) were used as model substrates. Influence of the polymer type and structure, silica concentration and the number of silica layers applied on the topography, average roughness and the wetting behavior of the surfaces were determined. Polymer surfaces obtained were characterized by scanning electron microscopy, white light interferometry, atomic force microscopy and advancing and receding water contact angle measurements. It was possible to obtain superhydrophobic surfaces displaying hierarchical micro/nano features both for TPSC and PMMA. A close correlation was observed between the number of silica layers applied and average surface roughness obtained. It was demonstrated that an average surface roughness value of 125–150 nm was necessary for the formation of superhydrophobic surfaces, both for TPSC and PMMA. Chemical structure and nature of the polymeric substrate seem to play a significant role on the topography and average roughness of the silica coated surfaces formed. Superhydrophobic surfaces displayed static and advancing water contact angles well above 150° and fairly small contact angle hysteresis.

The transition from a 2D to a 3D coffee stain that has a well-defined and hollow sphere-like structure is demonstrated. Self-assembled all-protein lasers are constructed by 3D coffee stains.

In this study, silk fibroin in hydrogel form is analyzed as an eco-friendly alternative to conventional polymers for lens applications in light-emitting diodes. The intensity profile was controlled via dome- and crater-type lenses.

A comprehensive discussion is provided of the critical physical, chemical and structural parameters, such as soft and hard segment structures and their molecular weights, polymer composition, solubility parameters, competitive intermolecular interactions and others, which strongly affect the morphology and bulk and surface properties of segmented thermoplastic polyurethanes, polyureas and polyurethaneureas (TPUs). Important developments related to the design, synthesis and structure-property behavior of segmented polyurethanes are discussed. Although the main emphasis is placed on linear materials, some brief comments are also given on the effect of chemical crosslinking on the structure–property behavior of segmented polyurethanes.

Today the high demand for electronics leads to massive production of waste, thus green materials based electronic devices are becoming more important for environmental protection and sustainability. The biomaterial based hydrogels are widely used in tissue engineering, but their uses in photonics are limited. In this study, silk fibroin protein in hydrogel form is explored as a bio-friendly alternative to conventional polymers for lens applications in light-emitting diodes. The concentration of silk fibroin protein and crosslinking agent had direct effects on optical properties of silk hydrogel. The spatial radiation intensity distribution was controlled via dome- and crater-type silk-hydrogel lenses. The hydrogel lens showed a light extraction efficiency over 0.95 on a warm white LED. The stability of silk hydrogel lens is enhanced approximately three-folds by using a biocompatible/biodegradable poly(ester-urethane) coating and more than three orders of magnitude by using an edible paraffin wax coating. Therefore, biomaterial lenses show promise for green optoelectronic applications., Marie Curie Career Integration Grant (PROTEINLED); Turkish Academy of Sciences; Scientific and Technological Research Council of Turkey (TÜBİTAK)

Quantum mechanical calculations (QMC) and dissipative particle dynamics (DPD) simulations were utilized to understand the nature of the short and long-range hydrogen bonding and its influence on the microphase morphology in segmented polyurethanes and segmented polyureas prepared without chain extenders through the stoichiometric reactions of hydroxy or amine terminated poly(tetramethylene oxide) (PTMO-1000) with 1,4-phenylene diisocyanate (PPDI) and 1,3-phenylene diisocyanate (MPDI). The possibility of long-range connectivity due to a network of well-ordered hydrogen bonds between symmetrical PPDI and kinked MPDI based model urethane and urea compounds were also investigated. Special emphasis was given on the understanding of the influence of diisocyanate symmetry and nature of the hydrogen bonding between hard segments on the morphology development. QMC results obtained clearly indicated the possibility of long-range ordering of hydrogen bonds between PPDI based urethane and urea groups, while MPDI based systems did not display such a behavior. DPD results strongly supported the QMC studies and clearly demonstrated the possibility of long-range connectivity of hydrogen bonds between urethane and urea groups in PPDI based segmented copolymers, leading to the formation of microphase separated morphologies in these systems, which was not observed in the kinked MPDI based segmented urethane and urea copolymers. Computational results obtained strongly supported the experimental observations reported on the morphology and thermal and mechanical properties of these segmented polyurethanes and polyureas based on PPDI and MPDI.

A comprehensive survey of the recent developments on the synthesis, properties and applications of silicone containing copolymers is provided. Influence of (-R2Si-O-) backbone composition on the physicochemical properties of silicone copolymers, such as thermal transitions, solubility parameter and surface tension is discussed. Preparation and properties of well-defined am-reactive organofunctionally terminated (telechelic) silicone oligomers and their utilization in the preparation of a wide range of block and segmented copolymers through step-growth, anionic, ring-opening and living free-radical polymerization techniques are provided. Use of silicone oligomers in the modification of polymeric network structures is also discussed. Special emphasis is given to the discussion of the effect of silicone oligomer and organic segment structure and molecular weight on the morphology and surface and bulk properties of the resultant silicone containing copolymers and networks., NA

Hydrophilization of polydimethylsiloxane–urea copolymer (PSU) surfaces and the extent of hydrophobic recovery were investigated as a function of; (i) UV/ozone (UV/O) exposure time, (ii) the aging period after UV/O exposure, (iii) sample preparation method, and (iv) polydimethylsiloxane (PDMS) soft segment molecular weight of the copolymer (1500, 3000 and 11,000 g/mol). All copolymers had a constant urea hard segment content of 15% by weight. Samples were prepared by three different methods, which were; solution casting, spin-coating and electrospinning. XPS spectra clearly showed transformation of PDMS into SiO 2 and sub-oxides, which increased gradually with increasing UV/O exposure time. XPS and ATR-FTIR measurements also revealed that the copolymer based on PDMS-11000 displayed the highest amount of SiO 2 formation and overall surface modification. Static water contact angle values of the spincoated silicone–urea copolymer films decreased significantly from 110° to 43° after 3 h of UV/O exposure. Interestingly, the hydrophobicity of the electrospun fibers was retained under similar UV/O exposure conditions, most probably due to the preserved surface roughness. Hydrophobic recovery was evaluated after 2 months of storage at ambient conditions. The slowest recovery was observed for spin-coated copolymer film based on PDMS-11000, due to higher amount of surface oxidation and formation of a thicker SiO 2 barrier layer.

Objectives: This study was performed to evaluate the biocompatibility and tensile strength of two new polymeric materials — A polyfluoro ether-modified thermoplastic polyurethane urea and a polydimethyl silicone elastomer — In an experimental rabbit model. Methods: The two polymers were implanted inside separate subperichondrial pockets created over the auricular cartilages of 12 rabbits. A control pocket received no implant. After 3 months, the animals were painlessly sacrificed, and each site was analyzed histologically for vascular congestion, acute and chronic inflammation, and fibrosis in the tissue surrounding the implant materials. Results: There were no statistically significant differences in vascular congestion, fibrosis, or acute or chronic inflammation between the control sites and either implant site. Conclusions: These results suggest that the polymers are well accepted by the tissue and remain stable during the entire study period, and that they could be very suitable materials for use in nasal reconstruction.

In-situ liquid-state Si-29 nuclear magnetic resonance was used to investigate the temporal concentration changes during ammonia-catalyzed initial hydrolysis of tetraethyl orthosilicate in different solvents (methanol, ethanol, n-propanol, iso-propanol and n-butanol). Dynamic light scattering was employed to monitor simultaneous changes in the average diameter of silica particles and atomic force microscopy was used to image the particles within this time frame. Solvent effects on initial hydrolysis kinetics, size and polydispersity of silica particles were discussed in terms of polarity and hydrogen-bonding characteristics of the solvents. Initial hydrolysis rate and average particle size increased with molecular weight of the primary alcohols. In comparison, lower hydrolysis rate and larger particle size were obtained in the secondary alcohol. Exceptionally, reactions in methanol exhibited the highest hydrolysis rate and the smallest particle size. Ultimately, our investigation elaborated, and hence confirmed, the influences of chemical structure and nature of the solvent on the formation and growth of the silica particles under applied conditions.

The effect of poly(ethylene oxide) (PEO) soft segment molecular weight (M-n = 2000, 4600 and 8000 g mol(-1)) on the glass transition, crystallinity, molecular mobility and segmental dynamics of a series of aliphatic polyurethaneurea copolymers (PUU) with a constant hard segment content of 30% by weight was investigated using differential scanning calorimetry and dielectric relaxation spectroscopy. The soft segment (PEO) glass transition temperature increased with increasing molecular weight. Furthermore, five different relaxations were observed in dielectric analyses of all copolymers. These included local glassy state motions (gamma) and (beta), segmental motion of the soft phase (alpha), conductivity relaxation, and interfacial Maxwell-Wagner-Sillars (MWS) polarization. Local relaxations follow Arrhenius behavior and their time scale is not affected by the soft segment molecular weight. alpha-Relaxation follows Vogel-Tammann-Fulcher (VTF) behavior and is slower for the copolymer based on PEO-4600. Conductivity relaxation and the interfacial MWS polarization also follow VTF behavior and have quite similar slopes since both are related to the same phenomena. Unexpectedly, the interfacial MWS polarization is not affected by the soft segment molecular weight. Although this result suggests that the soft segment molecular weight does not affect the microphase separation in these copolymers, we believe that no safe conclusions can be extracted for this system due to the high complexity and the presence of many phases with different conductivity. However, significant differences were observed in the conductivity relaxation, which is much faster for the copolymer based on PEO-2000, due to its lower crystallinity when compared with others.

A simple method was developed for the preparation of polymeric materials with controlled surface wettability or tunable surface wetting. The method is applicable to a large number of polymers, thermoplastic or thermoset. With this method, it is possible to prepare polymer surfaces with static water contact angles ranging from 0° (superhydrophilic) to greater than 170° (superhydrophobic). The method developed is based on spin-coating of a hydrophilic/hydrophobic silica mixture dispersed in an organic solvent or solvent mixture onto the polymer surface. Depending on the hydrophilic/hydrophobic silica ratio in the coating mixture, it is possible to obtain polymer surfaces displaying gradually changing wettability from superhydrophilic to superhydrophobic. In this article, preparation and surface characteristics of polystyrene (PS) and cross-linked epoxy resin (ER) films are provided as general examples. Polymer surfaces obtained were characterized by scanning electron microscopy, white light interferometry, atomic force microscopy, X-ray photoelectron spectroscopy, and static water contact angle measurements. Effects of the type of polymeric substrate and composition of the silica mixture on the surface behavior of the composite systems were investigated.

Thermoplastic segmented polyurethanes which are based on poly(tetramethylene oxide) (PTMO) soft segment, linear symmetric para-phenylene diisocyanate (pPDI), and chain extended with 1,4-butanediol (BD) are discussed. The effect of variation of the soft and hard segment molecular weights as well as the overall hard segment content on structure–property behavior is investigated. Together, atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) clearly establish the presence of a unique ordered thread-like microphase separated structure that displays considerable order. This thread-like microphase structure is similar to that of the “single molecule” hard segment systems reported earlier from our laboratory [1] , [2] , [3] , [4] . In addition, small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and ambient temperature tensile testing results help to better define the nature of the hard and soft domains.

A simple and general method has been developed for the preparation of polymeric materials with superhydrophobic surfaces. The process is applicable to a large number of polymers, thermoplastic or thermoset. In this manuscript preparation and characteristics of superhydrophobic surfaces prepared from a segmented polydimethylsiloxane–urea copolymer (TPSU), a polyether based polyurethaneurea (TPU), poly(methyl methacrylate) (PMMA), polystyrene (PS), polycarbonate (PC) and a crosslinked epoxy resin (EPOXY) are discussed. All samples were prepared onto glass surfaces by using a simple, multi-step spin-coating procedure. In the first step a thin film of the desired polymer was coated onto the glass slide. This was followed by spin-coating of two layers of hydrophobic fumed silica using a dispersion in tetrahydrofuran. Finally to obtain a durable surface, a very thin film of the parent polymer was spin-coated from a very dilute solution containing 2.5% by weight hydrophobic silica and 0.25% by weight matrix polymer in tetrahydrofuran. Surfaces were characterized by scanning electron microscopy (SEM), which clearly showed the formation of rough surfaces with homogeneously distributed silica particles in 1–10 μm range. Static water contact angle and contact angle hysteresis measurements proved the formation of superhydrophobic surfaces. Samples displayed static water contact angles larger than 170° and very low contact angle hysteresis of less than 3°.

Highly hydrophobic surfaces of silicone–urea copolymers were transformed into hydrophilic ones upon UV/ozone treatment. The extent of surface modification was strongly dependent on the sample preparation method and the exposure time. The physical and chemical changes at the copolymer surfaces were analyzed by spectroscopic (XPS, ATR-FTIR), microscopic (SEM) techniques and static water contact angle measurements. ATR-FTIR spectra clearly showed the dramatic change in the strongly hydrogen bonded urea hard segments and the degradation of dimethylsiloxane units in silicone–urea copolymers. XPS results revealed the formation of SiO x on the surface, which gradually increased with exposure time. After 3 h of UV/ozone exposure, Si(2p) binding energy shifted from 101.9 to 102.85 eV, which is a clear indication of an increase in the oxidation state of silicon. The deterioration of microroughness of the electrospun webs upon UV/ozone exposure, which was revealed by SEM, resulted in a dramatic decrease in the static water contact angle values from 129 to 62°. These results clearly show that UV/ozone process is a very simple and facile method to transform hydrophobic silicone–urea copolymer surfaces into fairly hydrophilic ones.

Effect of polydimethylsiloxane (PDMS) soft segment molecular weight (Mn = 3200, 10,800 and 31,500 g/mol) and urea hard segment content (2.0–11.4% by weight) on the hysteresis and permanent set behavior of segmented silicone-urea (TPSU) copolymers were investigated. In spite of very low hard segment contents, all copolymers formed self-supporting films and displayed good mechanical properties. When the mechanical hysteresis and set behavior of the silicone-urea copolymers with similar hard segment contents (around 7.5% by weight) but based on PDMS-3K, PDMS-11K and PDMS-32K were compared, it was very clear that as the PDMS molecular weight increased, hysteresis and instantaneous set values decreased significantly. Copolymers based on the same silicone soft segment (PDMS-11K or PDMS-32K) but with different hard segment contents showed a linear increase in hysteresis and a slight decrease in the instantaneous set as a function of hard segment content. Constant initial stress creep experiments also showed lower creep as the PDMS segment molecular weight increased for copolymers with similar urea contents. Since the critical entanglement molecular weight (Me) of PDMS is stated to be 24,500 g/mol, our results tend to suggest important contribution of chain entanglements on the hysteresis and instantaneous set of these silicone-urea copolymers.

Novel segmented poly(urethaneurea) elastomers (TPUU) were prepared through the reaction of poly(tetramethylene oxide)glycols (PTMO-1000 and PTMO-2000) with excess aromatic diisocyanates (TDI and MDI), followed by in situ chain extension with water, through the formation of urea linkages. High molecular weight TPUU polymers with high urea hard segment (HS) contents of up to 44% by weight were obtained. FTIR analysis of the carbonyl region clearly showed the presence of strongly hydrogen bonded urethane and urea groups in the system. Dynamic mechanical analysis indicated the formation of microphase separated morphologies with well-defined PTMO glass transitions, followed by a composition dependent rubbery plateau extending well beyond 200 °C. Tapping mode AFM studies clearly indicated the formation of microphase morphology with hard urea domains dispersed or percolated through soft polyether matrix. Stress−strain tests demonstrated the formation of very strong elastomers with tensile strengths of up to 50 M...