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Composite biopolymer/conducting polymer scaffolds, such as polylactic acid (PLA)/ polyaniline (PAni) nanofibers, have emerged as popular alternative scaffolds in the electrical-sensitive nerve tissue engineering (TE). Although mimicking the extracellular matrix geometry, such scaffolds are highly hydrophobic and usually present an inhomogeneous morphology with massive beads that impede nerve cell-material interactions. Therefore, the present study launches an exclusive combinatorial strategy merging successive pre- and post-electrospinning plasma treatments to cope with these issues. Firstly, an atmospheric pressure plasma jet (APPJ) treatment was applied on PLA and PLA/PAni solutions prior to electrospinning, enhancing their viscosity and conductivity. These liquid property changes largely eliminated the beaded structures on the nanofibers, leading to uniform and nicely elongated fibers having average diameters between 170 and 230 nm. After electrospinning, the conceived scaffolds were subjected to a N2 dielectric barrier discharge (DBD) treatment, which significantly increased their surface wettability as illustrated by large decreases in water contact angles for values above 125° to values below 25°. X-ray photoelectron spectroscopy (XPS) analyses revealed that 3.3% of nitrogen was implanted on the nanofibers surface in the form of C–N and N–C=O functionalities upon DBD treatment. Finally, after seeding pheochromocytoma (PC-12) cells on the scaffolds, a greatly enhanced cell adhesion and a more dispersive cell distribution were detected on the DBD-treated samples. Interestingly, when the APPJ treatment was additionally performed, the extension of a high number of long neurites was spotted leading to the formation of a neuronal network between PC-12 cell clusters. In addition, the presence of conducting PAni in the scaffolds further promoted the behavior of PC-12 cells as illustrated by more than a 40% increase in the neurite density without any external electrical stimulation. As such, this work presents a new strategy combining different plasma-assisted biofabrication techniques of conducting nanofibers to create promising scaffolds for electrical-sensitive TE applications.

Inorganic/organic sol–gel hybrids consist of co-networks of inorganic and organic components that can lead to unique properties, compared to conventional composites, especially when there is covalent bonding between the networks. The aim here was to develop new electrospun silica/gelatin sol–gel hybrids, with covalent coupling and unique 3D cotton–wool-like morphology for application as regenerative medicine scaffolds. Covalent coupling is critical for obtaining sustained dissolution of the fibres and we identified the sol–gel synthesis conditions needed for coupling within the electrospun fibres. Under carefully controlled conditions, such as constant humidity, we investigated the effect of the electrospinning process variables of sol viscosity (and aging time) and amount of coupling agent on the 3D morphology of the fibres, their structure (bonding) and dissolution, identifying a detailed optimised protocol for fibre scaffold production.

The interlayer stiffness of fused deposition modeled (FDM) parts is significantly impaired by the slow diffusion and re-entangling of polymer chains across filament interfacial welds in the build direction. To mechanically reinforce FDM interfaces, an approach based on timing and spatial direction of stereocomplexation across weld interfaces is introduced via alternating deposition of enantiomerically opposite poly(lactides). Fundamental insight into the kinetics and spatial distribution of homo- and stereocrystallization at FDM interfaces was successfully reconstructed in 2 and 3 dimensions by micrometer resolved Fourier transform infrared microscopy and synchrotron wide-angle X-ray diffraction tomography. The rate of isothermal stereocomplexation and consequential interfacial stiffening increases with decreased absolute and relative molar masses. The spatial distribution of stereocrystals is governed by the relative molar masses and the extent of interdiffusion, under not only isothermal but also nonisothermal FDM conditions. The net local heat dosage, which depends on print speed, governs the length scales of stereocomplexation and thus mechanical reinforcement. Interfacial stereocomplexation of poly(lactides) in FDM leads to a distinct 40% increase in stiffness and nucleation of bulk filaments, aiding in thermodynamic and geometrical stability.

Material Extrusion (ME), which is a type of Additive Manufacturing (AM), has become widely popular in the manufacturing world. However, the evolution of a material's temperature in this relatively new manufacturing method, which plays an important role in the polymer crystallinity, is not yet well researched. Next to voids, interlayer adhesion and surface roughness, the degree of crystallinity strongly determines the quality of printed products. Hence, a thorough and deep understanding of crystallinity in ME is essential for the improvement of the parts printed. In this paper, a primary generic model is proposed to predict the temperature evolution and crystal growth of printed polymer materials. The temperature evolution was developed based on the twodimensional domain discretisation method and the crystal growth was simulated via the Hoffman-Lauritzen theory. In the simulation, key parameters have been taken into consideration, such as the printing speed, thermal convection coefficient, thermal contact conductance with the platform, nozzle diameter and latent heat in crystallisation. Then, a single-line printing scenario was tested to verify the accuracy of the model. A comparison of the model predictions with the experimental results showed only of up to 3.8 degrees C deviations which is a 2% of maximum percentage mismatch from the full scale reading. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Underneath the unique and beautiful structures of biominerals there is always the presence of organic molecules that tightly interact with the developing inorganic nuclei/crystal directing its growth and assembly towards the final structure. This close interdigitation between organic and inorganic matter renders biominerals not only unique in their appearance but also with exceptional properties. A notable case of such combination is observed when combining double hydrophilic block copolymers (DHBCs) with different ions. In the particular case of calcium phosphate systems, the incorporation of DHBCs was found to induce the formation of unique and delicate neuron-like structures. The present article highlights that such structures are more common than probably expected and they can be created using much simpler organic molecules of a wider nature such as non-ionic surfactants (Tween 80 or Span 20), anionic polymers (sodium polyacrylate) and cationic polymers (polydiallyldimethylammonium chloride). The reaction conditions are however crucial in the stabilization of the structures.

Introduction: Injectable scaffolds are emerging as a promising strategy in the field of myocardial tissue engineering. Among injectable scaffolds, microparticles have been poorly investigated. The goal of this study was the development of novel gelatin/gellan microparticles that could be used as an injectable scaffold to repair the infarcted myocardium. In particular, the effect of particle size on cardiac progenitor cell response was investigated. Methods: Particles were produced by a water-in-oil emulsion method. Phosphatidylcholine was used as a surfactant. Particles with different diameter ranges (125–300 µm and 350–450 µm) were fabricated using two different surfactant concentrations. Morphological, physicochemical, and functional characterizations were carried out. Cardiac progenitor cell adhesion and growth on microparticles were tested both in static and dynamic suspension culture conditions. Results: Morphological analysis of the produced particles showed a spherical shape and porous surface. The hydrophilicity of particle matrix and the presence of intermolecular interactions between gellan and gelatin were pointed out by the physicochemical characterization. A weight loss of 75 ± 5 % after 90 days of hydrolytic degradation was observed. Injectability through a narrow needle (26 G) and persistence of the microparticles at the injection site were preliminarily verified by ex vivo test. In vitro cell culture tests showed a preservation of rat cardiac progenitor biologic properties and indicated a preferential cell adherence to microparticles with a smaller size. Conclusion: Overall, the obtained results indicate that the produced gelatin/gellan microparticles could be potentially employed as injectable scaffolds for myocardial regeneration.

Electro-spinning is widely used in tissue-engineered applications mostly in form of non-woven structures. The development of e-spun yarn opens the door for textile fabrics which combine the micro to nanoscale dimension of electro-spun filaments with three-dimensional (3D) drapable textile fabrics. Therefore, the aim of the study was the implementation of a process for electro-spun yarns. Polylactic acid (PLA) and polyethylene glycol (PEG) were spun from chloroform solutions with varying PLA/PEG ratios (100:0, 90:10, 75:25 and 50:50). The yarn samples produced were analyzed regarding their morphology, tensile strength, water uptake and cytocompatibility. It was found that the yarn diameter decreased when the funnel collector rotation was increasd, however, the fiber diameter was not influenced. The tensile strength was also found to be dependent on the PEG content. While samples composed of 100% PLA showed a tensile strength of 2.5±0.7 cN/tex, the tensile strength increased with a decreasing PLA content (PLA 75%/PEG 25%) to 6.2±0.5 cN/tex. The variation of the PEG content also influenced the viscosity of the spinning solutions. The investigation of the cytocompatibility with endothelial cells was conducted for PLA/PEG 90:10 and 75:25 and indicated that the samples are cytocompatible.

International audience; The rheological properties of aqueous solutions of a hydrophobically modified poly(acrylic acid) were studied by diffusing-wave spectroscopy microrheology at various concentrations and temperatures and the formation of the transient network by hydrophobic association of the polymer chains was characterized. The Winter-Chambon power-law regime was found in a high frequency range accessible by microrheology, the physical gel point was successfully determined from the uniqueness of loss tangent, confirmed by the time-cure superposition of the mean-square displacement of the probe particles whose shift factors showed the critical power-law behaviors as a function of the relative distance from the gel point. The zero-shear viscosity as a function of the polymer concentration showed a plateau near the microrheologically determined gel point, indicating the presence of clusters which break before relaxing thus are rheologically undetectable. The largest relaxed cluster size was estimated to be 40 - 60 nm depending of the temperature. (C) 2017 Elsevier Ltd. All rights reserved.

The antibacterial features of natural pine/spruce rosin are well established, yet the functionality in various thermoplastics has not been surveyed. This work focuses on the processing of industrial grade purified rosin mixed with polyethylene (PE), polypropylene (PP), polylactic acid (PLA), polyamide (PA)and corn starch based biopolymer (CS). Homopolymer masterbatches were extrusion-compounded and melt-spun to form fibres for a wide range of products, such as filters, reinforcements, clothing and medical textiles. Due to the versatile chemical structure of rosin, it was observed compatible with all the selected polymers. In general, the rosin-blended systems were shear-thinning in a molten condition. The doped fibres spun of PE and PP indicated adequate melt-spinning capability and proper mechanical properties in terms of ultimate strength and Young's modulus. The antibacterial response was found dependent on the selected polymer. Especially PE with a 10 wt% rosin content showed significant antibacterial effects against Escherichia coli DH5α and Staphylococcus aureus ATCC 12598 when analysed in the Ringer's solution for 24 h. publishedVersion

Endosomal release has been identified as a rate-limiting step for intracellular delivery of therapeutic agents, in particular macromolecular drugs. Herein, we report a series of synthetic pH-responsive, membrane-anchoring polymers exhibiting dramatic endosomolytic activity for efficient intracellular delivery. The comb-like pseudopeptidic polymers were synthesized by grafting different amounts of decylamine (NDA), which act as hydrophobic membrane anchors, onto the pendant carboxylic acid groups of a pseudopeptide, poly(l-lysine iso-phthalamide). The effects of the hydrophobic relatively long alkyl side chains on aqueous solution properties, cell membrane destabilization activity, and in-vitro cytotoxicity were investigated. The optimal polymer containing 18 mol % NDA exhibited limited hemolysis at pH 7.4 but induced nearly complete membrane destabilization at endosomal pH within only 20 min. The mechanistic investigation of membrane destabilization suggests the polymer-mediated pore formation. It has been demonstrated that the polymer with hydrophobic side chains displayed a considerable endosomolytic ability to release endocytosed materials into the cytoplasm of various cell lines, which is of critical importance for intracellular drug delivery applications.

Environmentally degradable polyesters offer an interesting perspective for a vast number of applications. However, current front-runners like poly(lactide), poly(glycolide) and poly(e-caprolactone) are either semi-crystalline excluding applications for which optical transparency is desired, or exhibit low glass transition temperatures (Tg) resulting in poor dimensional stability at temperatures exceeding the Tg. In the present work, copolymers of lactide and mandelide are explored as a method to obtain amorphous, environmentally degradable polyesters with a glass transition temperature exceeding 50 °C. Mandelide and lactide can be successfully copolymerised and the resulting copolymers revealed rising Tg values upon increasing the mandelide content. The obtained molecular weights were superior to the molecular weights previously obtained via polycondensation, but were limited by the epimerisation of the mandelide monomer, which passes through an enolic intermediate that is able to initiate the polymerisation.

Block copolymers containing functionalized monomers, for example those containing charged groups, can be used for many purposes, one of which is the design of polymeric supramolecular materials based on electrostatic interactions. In this paper the synthesis of diblock copolymers and ABA-triblock copolymers containing poly(n-butyl acrylate) as a first or middle block and poly(2-(dimethylamino) ethyl acrylate), poly(1-ethoxyethyl acrylate) and poly(1-ethoxyethyl-2-carboxyethyl acrylate) as second or outer blocks, resulting in block copolymers that can contain positive or negative charges, is reported. The polymerizations were performed and optimized via one-pot sequential monomer addition reactions via Cu(0)-mediated polymerization using an automated parallel synthesizer. Different initiators, monomer concentrations and polymerization times were tested. While a bromide-containing initiator led to the best results for most monomers, when polymerizing 2-(dimethylamino) ethyl acrylate the use of a chloride-containing initiator was necessary. Due to the slower polymerization using this initiator, a longer polymerization time was needed before addition of the second monomer. Using the optimized conditions, the diblock and triblock copolymers could be synthesized with good control over molecular weight and dispersities around 1.1 were obtained.

International audience; Polyesters are polymers of choice in the design of drug delivery systems as a result of their good biocompatibility and their (bio) degradability. Such polyesters are mainly obtained by polymerization techniques using chemically based initiators whose presence in the final materials, even at trace levels, might induce toxic effects on in vivo uses. Therefore, lipases-catalyzed ring opening polymerization (ROP) of lactones might be considered as interesting solutions. In this context, we have studied the possibilities to use lipase-catalyzed ROP of the benzyl malolactonate (MLABe) to obtain the poly(benzyl malate), PMLABe. A Design of Experiment (DoE) approach has been elaborated to identify the important parameters having a significant influence on the polymerization reaction and on the characteristics of the obtained PMLABe. Such DoE technique allowed us to select conditions for lipase-catalyzed ROP of MLABe leading to PMLABe with a mass-average molar mass of around 10,000 g/mol with a dispersity of 1.4. (C) 2016 Wiley Periodicals, Inc.

Electrospun scaffolds are widely used for various biomedical applications. In this study, we prepared electrospun bioactive composite scaffolds combining hydroxyapatite, collagen (Col) and a synthetic polymer-PolyActive (TM)-to mimic naturally occurring extracellular matrix for in situ bone regeneration. Human mesenchymal stem cells (hMSCs) adhered and proliferated on these scaffolds. Cells on all scaffold types showed an increased metabolic activity with time. On day 4, the metabolic activity of cells cultured on PolyActive (TM) (PA)-hydroxyapatite (HA)-Col in 1,1,1,3,3,3-hexafluoro-2-propanolhexafluoro-2-propanol (HFIP) was significantly higher than that of cells grown on PA-Col samples. Furthermore, on day 6, cells on PA-HA-Col in HFIP showed significantly higher metabolic activity than those on PA and PA-Col scaffolds. Quantitative PCR analysis for a panel of osteogenic genes showed statistically significant differences between scaffolds. Cells cultured on PA-HA scaffolds had a significantly higher osteonectin and RunX2 expression compared to those on PA-HA-Col scaffolds. Cells on PA-HA-Col in HFIP scaffolds had significantly higher expression of alkaline phosphatase (ALP) and Col 1 compared to PA and PA-Col scaffolds respectively. The bone morphogenetic protein-2 and S100A4 expression of PA-Col and PA-HA-Col constructs was significantly lower than the basal level expression of cells on PA scaffolds. Although not statistically significant in all cases, cells cultured on PA-HA-Col in HFIP and PA-HA scaffolds had the highest expression for most of the genes analysed. The results of the study demonstrate that bioactive composite scaffolds prepared by electrospinning could find potential use in bone regeneration applications.

Granulocyte–macrophage colony-stimulating factor (GM-CSF) is a cytokine used in the treatment of serious conditions resulting from chemotherapy and bone marrow transplantation such as neutropenia and aplastic anemia. Despite these effects, GM-CSF has a very short biological half-life, and it requires frequent injection during the treatment. Therefore, the cytokine production is possible in the body with plasmid-encoded GM-CSF (pGM-CSF) coding for cytokine administered to the body. However, the selection of the proper delivery system for the plasmid is important. In this study, two different delivery systems, encapsulated plasmid such as fucoidan–chitosan (fucosphere) and chitosan microspheres, were prepared and the particle physicochemical properties evaluated. Fucospheres and chitosan microspheres size ranges are 151–401 and 376–681 nm. The zeta potential values of the microspheres were changed between 8.3–17.1 mV (fucosphere) and +21.9–28.9 mV (chitosan microspheres). The encapsulation capacity of fucospheres changed between 84.2% and 94.7% depending on the chitosan molecular weight used in the formulation. In vitro plasmid DNA release from both delivery systems exhibited slower profiles of approximately 90–140 days. Integrity of released samples was checked by agarose gel electrophoresis, and any additional band was not seen. All formulations were analyzed kinetically. The calculated regression coefficients showed a higher r 2 value with zero-order kinetics. In conclusion, the characterizations of the microspheres can be modulated by changing the formulation variables, and it can be concluded that fucospheres might be a potential carrier system for the controlled delivery of GM-CSF encoding plasmid DNA.

A novel biocompatible and biodegradable microgel system has been developed for controlled uptake and release of especially proteins. It contains TEMPO-oxidized potato starch polymers, which are chemically cross-linked by sodium trimetaphosphate (STMP). Physical chemical properties have been determined for microgels of different weight ratios of cross-linker to polymer (0.10, 0.15, 0.20, 0.30, and 0.40) and degrees of oxidation (30, 50, 70, and 100%). The charge density of the microgels as determined by proton titration is found to be in good agreement with the expected degree of oxidation (DO). The electrophoretic mobility of the microgel particles is used as a qualitative indicator of the pore size and scales with microgel swelling capacity as expected. The swelling capacity increases with increasing pH and decreasing salt concentration. Preliminary data for the uptake of the globular protein lysozyme by the microgels show it increases with increasing DO and decreasing cross-linker to polymer ratio. Highly charged microgels with intermediate cross-linker to polymer ratios (0.15 and 0.2) are found to be optimal for encapsulating lysozyme. © 2009 American Chemical Society. Chemicals / CAS: lysozyme, 9001-63-2; oxidoreductase, 9035-73-8, 9035-82-9, 9037-80-3, 9055-15-6; proton, 12408-02-5, 12586-59-3; sodium chloride, 7647-14-5; trimetaphosphoric acid, 13566-25-1, 7785-84-4

We investigated the hierarchical structure of complex coacervate core micelles formed by mixing a supramolecular coordination polymer and a diblock copolymer. Cryogenic transmission electron microscopy (cryo-TEM) on those systems was only possible for very dilute samples and suggested the existence of wormlike micelles or strings of spherical micelles (Y. Yan, N. A. M. Besseling, A. de Keizer, R. Fokkink, M. Drechsler and M. A. Cohen Stuart, J. Phys. Chem. B 2007, 111, 11662). Using small-angle X-ray scattering (SAXS) we investigated those mixtures with a concentration of up to 0.6 vol%. Depending on the charge ratio and the concentration the above mixtures was proven to build spherocylindrical objects of different sizes. In the case of charge neutrality spherical micelles are found. Thus, we confirmed by SAXS experiments that the structures seen by cryo-TEM indeed exist in solution.

Functionalised nanomaterials are gaining popularity for use as drug delivery vehicles and, in particular, mucus penetrating nanoparticles may improve drug bioavailability via the oral route. To date, few polymers have been investigated for their muco-penetration, and the effects of systematic structural changes to polymer architectures on the penetration and diffusion of functionalised nanomaterials through mucosal tissue have not been reported. We investigated the influence of poly(2-oxazoline) alkyl side chain length on nanoparticle diffusion; poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline), and poly (2-n-propyl-2-oxazoline) were grafted onto the surface of thiolated silica nanoparticles and characterised by FT-IR, Raman and NMR spectroscopy, thermogravimetric analysis, and small angle neutron scattering. Diffusion coefficients were determined in water and in a mucin dispersion (using Nanoparticle Tracking Analysis), and penetration through a mucosal barrier was assessed using an ex vivo fluorescence technique. The addition of a single methylene group in the side chain significantly altered the penetration and diffusion of the materials in both mucin dispersions and mucosal tissue. Nanoparticles functionalised with poly(2-methyl-2-oxazoline) were significantly more diffusive than particles with poly(2-ethyl-2-oxazoline) while particles with poly(2-n-propyl-2-oxazoline) showed no significant increase compared to the unfunctionalised particles. These data show that variations in the polymer structure can radically alter their diffusive properties with clear implications for the future design of mucus penetrating systems.

Amylose-block-polystyrenes with various block copolymer compositions were investigated in water and in THF solution. Fluorescence correlation spectroscopy, dynamic light, scattering (DLS), and asymmetric flow field-flow fractionation with multiangle light scattering detection indicate the presence of unimers, oligomers, and large micellar species in THF. Up to four different species: were detectable by DLS with hydrodynamic radii ranging from a few nanometers to > 10 mum, indicating that the system is not in a thermodynamic equilibrium state. Collapsed aggregrates were monitored on a Silicon surface by scanning force microscopy and transmission electron microscopy. In water. crew-cut micelles were obtained from the same block copolymers by a single solvent approach, using elevated temperature and pressure. These crew-cut aggregates are much more uniform than the respective star aggregates in THF, and their radii scale with R-h proportional to N-core(1/4), R-h proportional to N-corona(1/6) in solution and with R proportional to N-core(1/4), R proportional to N-corona(1/2) on a silicon surface.

The miscibility and phase behavior of poly(4-vinylphenol) (PVPh) with poly(vinyl methyl ketone) (PVMK) was investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was shown that all blends of PVPh/PVMK are totally miscible. A DSC study showed the apparition of a single glass transition (T-g) over their entire composition range. When the amount of PVPh exceeds 50% in blends, the obtained T(g)s are found to be significantly higher than those observed for each individual component of the mixture, indicating that these blends are capable of forming interpolymer complexes. FTIR analysis revealed the existence of preferential specific interactions via hydrogen bonding between the hydroxyl and carbonyl groups, which intensified when the amount of PVPh was increased in blends. Furthermore, the quantitative FTIR study carried out for PVPh/PVMK blends was also performed for the vinylphenol (VPh) and vinyl methyl ketone (VMK) functional groups. These results were also established by scanning electron microscopy study (SEM). The authors would like to acknowledge the financial support from the Basque Government (IT618-13) and Basque Country University (UFI 11/56).

Ultrasound micro-molding technology has been tested as a new method to get polymer/clay nanocomposites. Biodegradable polylactide (PLA) and poly (nona-methylene azelate) (PE99) have been used as polymer matrices, whereas different silicate clays have been assayed. The new technology is able to get specimens without evidences of degradation during processing. Only the use of organo-modified clays could give rise to a slight molecular weight decrease when the poly (alkylene dicarboxylate) sample was considered. Ultrasonic micro-molding has revealed effective to get directly nanocomposites with the final form required for a selected application, a homogeneous clay distribution up to a load of 6 wt-% and more interestingly exfoliated structures without being necessary the use of a compatibilizer agent between the organic polymer and the inorganic silicate clay. Transmission electron micrographs and X-ray diffraction profiles revealed exfoliated structure when N757, C20A, C25A, and N848 clays were employed.; Crystallization behavior of exfoliated PLA nanocomposites was highly peculiar since clay particles had an antinucleating effect that decreased the overall crystallization rate respect to the neat polymer. In addition, the incorporation of layers into growing spherulites increased the crystal growth rate. A typical crystallization effect was on the contrary observed for nanocomposites derived from the poly (alkylene dicarboxylate) sample.

Hybrid materials constituted by peptides and synthetic polymers have nowadays a great interest since they can combine the properties and functions of each constitutive block, being also possible to modify the final characteristics by using different topologies. Poly(L-lactide-b-L-phenylalanine) copolymers with various block lengths were synthesized by sequential ring-opening polymerization of L-lactide and the N-carboxyanhydride of L-phenylalanine. The resulting block copolymers were characterized by NMR spectrometry, IR spectroscopy, gel permeation chromatography, MALDI-TOF and UV-vis, revealing the successful incorporation of the polyphenylalanine (PPhe) peptide into the previously formed poly(L-lactide) (PLLA) polymer chain. X-ray diffraction and DSC data also suggested that the copolymers were phase-separated in domains containing either crystalline PLLA or PPhe phases. A peculiar thermal behavior was also found by thermogravimetric analysis when polyphenylalanine blocks were incorporated into polylactide.

We present here the measurement of the single-polymer entropic elasticity and the single covalent bond force profile, probed with two types of atomic force microscopes (AFM) on a synthetic polymer molecule: polymethacrylic acid in water. The conventional AFM allowed us to distinguish two types of interactions present in this system when doing force spectroscopic measurements: the first interaction is associated with adsorption sites of the polymer chains onto a bare gold surface, the second interaction is directly correlated to the rupture process of a single covalent bond. All these bridging interactions allowed us to stretch the single polymer chain and to determine the various factors playing a role in the elasticity of these molecules. To obtain a closer insight into the bond rupture process, we moved to a force sensor stable in position when measuring attractive forces. By optimizing the polymer length so as to fulfill the elastic stability conditions, we were able for the first time to map out the entire force profile associated with the cleavage of a single covalent bond. Experimental data coupled with molecular quantum mechanical calculations strongly suggest that the breaking bond is located at one end of the polymer chain.

Poly(lactic acid)/poly(butylene succinate) (PLA/PBS) blends, containing a small amount of 4,4′-bis(2-benzoxazolyl)stilbene (BBS) dye, showed a chromogenic response after heating above 80 °C, due to the formation of BBS aggregates. This smart behaviour can be useful for many different applications, such as for the realization of time–temperature optical indicators, and the understanding of the processes lying behind the aggregation of chromophores is fundamental for improving their performances. In this work, the phase transitions occurring in the PLA/PBS polymeric matrix under heating were investigated in detail by combining spectrofluorimetric, DSC, and variable-temperature solid state NMR (SSNMR) measurements on both PLA- (in pellets and film) and PLA/PBS-BBS films. A detailed characterization of the phase behaviour of both PLA and PBS domains was achieved. More specifically, the SSNMR analysis of 1H FID at different temperatures was found to be a very powerful and useful approach to investigate the phase transitions of PLA, complementary to DSC. Different phase and dynamic processes, PBS and PLA cold crystallization and PLA glass transition, seem to concur, at different levels, to promote BBS aggregation. A possible mechanism for the formation of BBS aggregates under heating was proposed.

Super absorbent polymers of acrylic acid-graphene oxide (PAA-GO) were synthesized with different percentage of chemical neutralization (0, 10, and 20%) of the acrylic acid monomer before its polymerization. The influence of their swelling and adsorption/desorption capacity of cadmium ions in aqueous solutions were studied and revealed that the GO enables greater mechanical stability in the materials. The PAA hydrogels, with the same degrees of neutralization, were also prepared without GO to compare with the composites. Additionally, carbon paste electrodes (CPE) modified with the composites PAA-GO were used to asses and compare their adsorption properties with cadmium(II). The anodic stripping voltammetry (ASV) peak, in the differential pulse voltammetry mode, for cadmium oxidation was found to be influenced by the presence of GO into the polymer, and also by their percentage of neutralization. The accumulation of cadmium(II) on the surface of the modified CPEs was performed under open-circuit conditions taking an account the preconcentration time of the metal cation. The presence of GO enhances the electrical signal of the electrodes in short times of immersion in cadmium(II) solutions. This property contributed to get linear responses of the CPEs modified with the composites, which were influenced by their degrees of neutralization. The PAA-GO 10N electrode with 10% of neutralization combined the influence of GO and the degree of neutralization in the same matrix, and also showed good performance in terms of its mechanical stability, it was chosen for preliminary studies on the selectivity of the electrode toward Zn(II) and Cu(II).

Calcium phosphate cements (CPCs) are extensively used as synthetic bone grafts, but their poor mechanical properties limit their applicability to non-stress-bearing applications. The aim of the present work is to evaluate the potential of plasma surface modification of polylactide (PLA) fibers for reinforcement of CPCs. Oxygen low-pressure plasma was employed at different treatment times and the surface properties of the untreated and plasma-treated PLA were evaluated. Plasma treatment on the PLA fibers reduced the setting times of the PLA-CPC composites and improved their flexural properties.

Several methods of introducing crosslinks into poly(L-lactide) (PLLA) were studied. Electron beam irradiation was not effective in crosslinking PLLA, and, moreover, caused severe polymer degradation and embrittlement of the material. Peroxide crosslinking of PLLA with dicumyl peroxide (DCP), however, resulted in gelation. At high peroxide concentrations (13-25 wt%) and high curing temperatures (192 degrees C), a gel fraction equal to 1 could be determined gravimetrically. Peroxide crosslinking with DCP caused chemical modification of the PLLA polymer chain, with the decomposition products having a plasticizing effect on the resulting network. For the in situ crosslinking, a tetrafunctional monomer, 5,5'-bis(oxepane-2-one) (5,5'-BO), was synthesized and used in the copolymerization with epsilon-caprolactone and L-lactide. Differential scanning calorimetry (d.s.c.) and swelling experiments showed that network formation did take place. A pronounced difference in reactivity between the L-lactide and the 5,5'-BO crosslinker was observed, with this difference in reactivity being found to be comparable to the difference between L-lactide and epsilon-caprolactone. Swelling experiments carried out with crosslinked PLLA showed that incorporation of this crosslinker into the polymer network increased at higher polymerization temperatures and longer polymerization times. When 1 mol% of crosslinker was used in the copolymerization with L-lactide, a significant increase in the impact and tensile strength was obtained when compared to uncrosslinked PLLA. Copyright (C) 1996 Elsevier Science Ltd.

In this study for the first time, we compared physico-chemical and biological properties of polycaprolactone-gelatin-hydroxyapatite scaffolds of two types: one in which the nano-hydroxyapatite (n-HA) was deposited on the surface of electrospun polycaprolactone-gelatin (PCG) fibers via alternate soaking process (PCG-HA(AS)) and other in which hydroxyapatite (HA) powders were blended in electrospinning solution of PCG (PCG-HA(B)). The microstructure of fibers was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which showed n-HA particles on the surface of the PCG-HA(AS) scaffold and embedded HA particles in the interior of the PCG-HA(B) fibers. PCG-HA(AS) fibers exhibited the better Young's moduli and tensile strength as compared to PCG-HA(B) fibers. Biological properties such as cell proliferation, cell attachment and alkaline phosphatase activity (ALP) were determined by growing human osteosarcoma cells (MG-63) over the scaffolds. Cell proliferation and confocal results clearly indicated that the presence of hydroxyapatite on the surface of the PCG-HA(AS) scaffold promoted better cellular adhesion and proliferation as compared to PCG-HA(B) scaffold. ALP activity was also observed better in alternate soaked PCG scaffold as compared to PCG-HA(B) scaffold. Mechanical strength and biological properties clearly demonstrate that surface deposited HA scaffold prepared by alternate soaking method may find application in bone tissue engineering. (C) 2013 Elsevier B.V. All rights reserved.

The development of macroporous biodegradable polymeric materials with three-dimensional pore structure is an important research field in tissue engineering. Structural scaffolds not only provide the cells with a mechanical support, but also perform an interactive physico-chemical role in tissue regeneration, thus it becomes important to be able to tune their mechanical properties to deliver appropriate mechanical signals to adhered cells for proper tissue regeneration. This work presents two series of poly(L-lactic acid) (PLLA) scaffolds in which we modulated the mechanical properties by systematically changing two synthesis parameters: polymer/solvent ratio and polymer-solution/porogen percentage. The peculiarity of the constructs is the presence of a double porosity: micropores generated by dioxane solvent using a freeze extraction technique and macropores produced by the leaching of macroporogen spheres. An increase in the PLLA/dioxane ratio decreases the micropores size and also influences to some extent the macropores size, due to the ability of dioxane to swell macroporogen particles. On the other hand, an increase in the amount of macroporogen increases the porosity by increasing the dimension of pore the throats connecting the macropores. Consequently, the increase in the PLLA/dioxane ratio produces a significant decrease in the permeability, and an increase in the apparent compression Young's modulus and aggregate modulus. When increasing the amount of macroporogen the permeability significantly increases and a decrease in the mechanical properties of the scaffolds is observed. Summarizing, with a systematic change of two fabrication parameters (amount of dioxane and macroporogen) the structural characteristics of the scaffolds were modulated and thereby their mechanical and transport properties were controlled., The authors gratefully acknowledge research support from the Spanish Ministry of Science and Innovation through research project DPI2010-20399-C04-00. CIBER-BBN is an initiative funded by the VI National R&D&D&i Plan 2008-2011, Iniciativa Ingenio 2010, and Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.

The observed brittle fracture behavior of amorphous polylactides seems to be contradicted by the low value of C(infinity) = 2 determined for poly(L-lactide) by Flory and coworkers. Such very flexible polymer chains deform by shear yielding, and fracture in a ductile manner. In this study, C(infinity) was estimated in a number of ways, resulting in much higher values of C(infinity) = 11.7 and C(infinity) = 9.1 for poly(L-lactide) and L- and D-lactide copolymers, respectively. These high values of C(infinity) and the low entanglement density account for the brittle fracture behavior of amorphous poly(lactide), as well as for the maximum attainable draw ratios of poly(L-lactide) networks and melt spun fibers. Bulk polymerized poly(L-lactide) networks, where crystallization during polymerization impedes severe entangling, could be hot-drawn most effectively to draw ratios of 8-16, resulting in very strong materials with tensile strengths of 550-805 MPa. By comparison, amorphous, non-crystallizable L/D lactide networks, which do not crystallize during polymerization, could be drawn less, to lambda = 7. These materials with strengths up to 460 MPa could, nevertheless, be oriented much more effectively than linear, amorphous L/D lactide copolymers.

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (M(w): 167-553 kg mol(-1)) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (D(g)) as well as gel sol analysis and swelling tests for doses above D(g) indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials. (C) 2011 Elsevier Ltd. All rights reserved.

Absorbable fibres have been prepared from various copolymers Of L-lactide with either D-lactide or epsilon-caprolactone. The lower crystallinity of these copolymers, compared with the homopolymer, is desirable in the light of their potential use as an absorbable suture material and has a pronounced effect on both preparation procedure and mechanical properties of these fibres. Due to the low crystallinity of the fibres, their mechanical properties are related to the structure of the amorphous phase, as is reflected by the effect of the glass transition temperature and molecular weight on tensile properties. By means of a dry spinning/hot drawing process, low crystalline fibres having strengths of 1 GPa could be prepared, whereas fibres prepared by melt spinning/hot drawing have strengths ranging from 0.19 for a completely amorphous copolymer to 0.53 GPa for the poly(L-lactide) homopolymer.

In this work, a new thermal stimuli sensitive multiphase polymer system consisting of a bio-related mixture of poly(lactic acid) (PLA, 85 wt%) and poly(1,4-butylene succinate) (PBS, 15 wt%) was prepared by the controlled incorporation of moderate amounts (60 to 70 C) leading to a clear change of the emission properties due to the occurrence of dye aggregation. Thermal analysis by DSC showed an evident connection between blend morphology features and luminescence response. The results are here discussed with reference to the transition temperatures of the two polymer phases and their effect on aggregation/disaggregation of dispersed BBS.

Biodegradable elastomeric poly(trimethylene carbonate) (PTMC) networks were efficiently formed by gamma irradiating the linear polymer in the presence of pentaerythritol triacrylate (PETA). The properties of networks formed upon irradiation of PTMC films containing (0.1.5 wt %.) PETA as cross-linking aid were evaluated. The gel contents and network densities increased with increasing PETA contents, irradiation dose, and initial polymer molecular weight. At a dose of 25 kGy, networks with gel fractions up to 0.96 could be obtained. The networks were noncytotoxic had elastic moduli below 10.7 MPa and high tensile strengths of up to 37.7 MPa. The incorporation of PETA also improved the resistance to creep and to tear propagation significantly, resulting in permanent set values that were as low as 0.9% strain and tear strengths up to 9.3 +/- 2.0 N/mm. Furthermore, the enzymatic erosion rates of the networks could be decreased from 12.0 +/- 2.9 to 3.0 +/- 1.6 mu m/day. These biodegradable elostomeric PTMC networks may be utilized in a broad range of medical applications.

Porous polylactide constructs were prepared by stereolithography, for the first time without the use of reactive diluents. Star-shaped poly(D,L-lactide) oligomers with 2, 3 and 6 arms were synthesised, end-functionalised with methacryloyl chloride and photo-crosslinked in the presence of ethyl lactate as a non-reactive diluent. The molecular weights of the arms of the macromers were 0.2, 0.6, 1.1 and 5 kg/mol, allowing variation of the crosslink density of the resulting networks. Networks prepared from macromers of which the molecular weight per arm was 0.6 kg/mol or higher had good mechanical properties, similar to linear high-molecular weight poly(D,L-lactide). A resin based on a 2-armed poly(D,L-lactide) macromer with a molecular weight of 0.6 kg/mol per arm (75 wt%), ethyl lactate (19 wt%), photo-initiator (6 wt%), inhibitor and dye was prepared. Using this resin, films and computer-designed porous constructs were accurately fabricated by stereolithography. Pre-osteoblasts showed good adherence to these photo-crosslinked networks. The proliferation rate on these materials was comparable to that on high-molecular weight poly(D,L-lactide) and tissue culture polystyrene. (C) 2009 Elsevier Ltd. All rights reserved.

International audience; We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.

Microtubule sensors for glucose, urea, and triglyceride were fabricated based on poly(styrene sulfonate)-polyaniline (PSS-PANI) composites synthesized within the pores of track-etched polycarbonate membranes. The synthesis of a sufficiently thick and conducting PSS-PANI film at pH 5 provided the advantage of immobilizing enzymes during polymerization. This resulted in the improvement of sensor response for urea and triglyceride by a factor of approximately 10(2) with a significant increase in the linear region of response compared to polyaniline-based sensors, where the enzymes were immobilized by physical adsorption after the polymerization. The sensors based on urea and triglyceride were found to have a higher linear range of response, better sensitivity, improved multiple use capability, and faster response time compared to the potentiometric and amperometric sensors based on polyaniline. A microtubule sensor array for glucose, urea, and triglyceride based on PSS-PANI was fabricated by immobilization of three different sets of enzymes on three closely spaced devices and its response was found to be free from cross-interference when a sample containing a mixture of the above analytes was analyzed in a single measurement.

Polylactides (PLAs) are a family of degradable plastics having a component of the dipole moment both perpendicular and parallel to the polymer backbone (i.e. is a type-A polymer). We have studied the sub-glass. segmental and global chain dynamics in a series of fully amorphous samples having an L:D ratio of 80:20, with molecular weights in the range: 3.8 x 10(3) < M-n < 4.7 x 10(4). Finite size effects have been observed for both the segmental and the sub-glass process. The segmental mode was found to have a steeper temperature and pressure dependence compared to the longest normal mode in accord with findings from other type-A polymers. The molecular weight dependence of the longest normal mode relaxation times (tau similar to M-n(3.1)) reflects on the intermediate molecular weight regime (M-c similar to 6 x 10(3)) from Rouse to entangled chains. These findings are compared with the viscoelastic results on the same system. Agreement in the c, value of the WLF equation is found but the scaling of the normalized longest relaxation time derived from the rheological measurements shows a stronger than expected dependence on the molecular weight. (C) 2002 Elsevier Science B.V. All rights reserved. Journal of Non-Crystalline Solids

Several methods of introducing crosslinks into poly(L-lactide) (PLLA) were studied. Electron beam irradiation was not effective in crosslinking PLLA, and, moreover, caused severe polymer degradation and embrittlement of the material. Peroxide crosslinking of PLLA with dicumyl peroxide (DCP), however, resulted in gelation. At high peroxide concentrations (13-25 wt%) and high curing temperatures (192 degrees C), a gel fraction equal to 1 could be determined gravimetrically. Peroxide crosslinking with DCP caused chemical modification of the PLLA polymer chain, with the decomposition products having a plasticizing effect on the resulting network. For the in situ crosslinking, a tetrafunctional monomer, 5,5'-bis(oxepane-2-one) (5,5'-BO), was synthesized and used in the copolymerization with epsilon-caprolactone and L-lactide. Differential scanning calorimetry (d.s.c.) and swelling experiments showed that network formation did take place. A pronounced difference in reactivity between the L-lactide and the 5,5'-BO crosslinker was observed, with this difference in reactivity being found to be comparable to the difference between L-lactide and epsilon-caprolactone. Swelling experiments carried out with crosslinked PLLA showed that incorporation of this crosslinker into the polymer network increased at higher polymerization temperatures and longer polymerization times. When 1 mol% of crosslinker was used in the copolymerization with L-lactide, a significant increase in the impact and tensile strength was obtained when compared to uncrosslinked PLLA. Copyright (C) 1996 Elsevier Science Ltd.