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Tissue and biomaterial microenvironments provide architectural cues that direct important cell behaviors including cell shape, alignment, migration, and resulting tissue formation. These architectural features may be presented to cells across multiple length scales, from nanometers to millimeters in size. In this study, we examined how architectural cues at two distinctly different length scales, “micro-scale” cues on the order of ∼1–2 μm, and “meso-scale” cues several orders of magnitude larger (>100 μm), interact to direct aligned neo-tissue formation. Utilizing a micro-photopatterning (μPP) model system to precisely arrange cell-adhesive patterns, we examined the effects of substrate architecture at these length scales on human mesenchymal stem cell (hMSC) organization, gene expression, and fibrillar collagen deposition. Both micro- and meso-scale architectures directed cell alignment and resulting tissue organization, and when combined, meso cues could enhance or compete against micro-scale cues. As meso boundary aspect ratios were increased, meso-scale cues overrode micro-scale cues and controlled tissue alignment, with a characteristic critical width (∼500 μm) similar to boundary dimensions that exist in vivo in highly aligned tissues. Meso-scale cues acted via both lateral confinement (in a cell-density-dependent manner) and by permitting end-to-end cell arrangements that yielded greater fibrillar collagen deposition. Despite large differences in fibrillar collagen content and organization between μPP architectural conditions, these changes did not correspond with changes in gene expression of key matrix or tendon-related genes. These findings highlight the complex interplay between geometric cues at multiple length scales and may have implications for tissue engineering strategies, where scaffold designs that incorporate cues at multiple length scales could improve neo-tissue organization and resulting functional outcomes. [ABSTRACT FROM AUTHOR]

In this paper, we outline a method for constructing nonnegative scaling vectors on the interval. Scaling vectors for the interval have been constructed in [1-3]. The approach here is different in that the we start with an existing scaling vector Φ that generates a multi-resolution analysis for L²(ℝ.) to create a scaling vector for the interval. If desired, the scaling vector can be constructed so that its components are nonnegative. Our construction uses ideas from [4,5] and we give results for scaling vectors satisfying certain support and continuity properties. These results also show that less edge functions are required to build multi-resolution analyses for L² ([a; b]) than the methods described in [5,6]. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers Gibbs'' phenomenon for scaling vectors in . We first show that a wide class of multiresolution analyses suffer from Gibbs'' phenomenon. To deal with this problem, in [Contemp. Math. 216 (1998) 63–79], Walter and Shen use an Abel summation technique to construct a positive scaling function , , from an orthonormal scaling function φ that generates . A reproducing kernel can in turn be constructed using . This kernel is also positive, has unit integral, and approximations utilizing it display no Gibbs'' phenomenon. These results were extended to scaling vectors and multiwavelets in [Proceedings of Wavelet Analysis and Multiresolution Methods, 2000, pp. 317–339]. In both cases, orthogonality and compact support were lost in the construction process. In this paper we modify the approach given in [Proceedings of Wavelet Analysis and Multiresolution Methods, 2000, pp. 317–339] to construct compactly supported positive scaling vectors. While the mapping into associated with this new positive scaling vector is not a projection, the scaling vector does produce a Riesz basis for and we conclude the paper by illustrating that expansions of functions via positive scaling vectors exhibit no Gibbs'' phenomenon. [Copyright &y& Elsevier]

Triple-shape polymers can memorize two independent shapes during a controlled recovery process. This work reports the 4D printing of electro-active triple-shape composites based on thermoplastic blends. Composite blends comprising polyester urethane (PEU), polylactic acid (PLA), and multiwall carbon nanotubes (MWCNTs) as conductive fillers were prepared by conventional melt processing methods. Morphological analysis of the composites revealed a phase separated morphology with aggregates of MWCNTs uniformly dispersed in the blend. Thermal analysis showed two different transition temperatures based on the melting point of the crystallizable switching domain of the PEU (Tm~50 ± 1 °C) and the glass transition temperature of amorphous PLA (Tg~61 ± 1 °C). The composites were suitable for 3D printing by fused filament fabrication (FFF). 3D models based on single or multiple materials were printed to demonstrate and quantify the triple-shape effect. The resulting parts were subjected to resistive heating by passing electric current at different voltages. The printed demonstrators were programmed by a thermo-mechanical programming procedure and the triple-shape effect was realized by increasing the voltage in a stepwise fashion. The 3D printing of such electroactive composites paves the way for more complex shapes with defined geometries and novel methods for triggering shape memory, with potential applications in space, robotics, and actuation technologies. [ABSTRACT FROM AUTHOR]

The modification of solid-liquid interfaces with polyelectrolyte multilayer films appears as a versatile tool to confer new functionalities to surfaces in environmentally friendly conditions. Indeed such films are deposited by alternate dipping of the substrates in aqueous solutions containing the interacting species or spraying these solutions on the surface of the substrate. Spin coating is more and more used to produce similar films. The aim of this short review article is to provide an unifying picture about the deposition mechanisms of polyelectrolyte multilayer films. Often those films are described as growing either in a linear or in a supralinear growth regime with the number of deposited "layer pairs". The growth regime of PEM films can be controlled by operational parameters like the temperature or the ionic strength of the used solutions. The control over the growth regime of the films as a function of the number of deposition steps allows to control their functional properties: either hard and impermeable films in the case of linear growth or soft and permeable films in the case of supralinear growth. Such different properties can be obtained with a given combination of interacting species by changing the operational parameters during the film deposition. [ABSTRACT FROM AUTHOR]

Background: Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear resistance than conventional UHMWPE but lower strength and toughness. To produce crosslinked UHMWPE with improved mechanical properties, the material can be treated before crosslinking by tension to induce molecular alignment (texture). Questions/purposes: We asked how (1) the microstructure of UHMWPE evolves when subjected to tension and (2) whether the new microstructure (texture) increases strength and toughness. Methods: We analyzed microstructure evolution of UHMWPE by small- and wide-angle xray scattering and scanning electron microscopy. We then developed a method to characterize the local strength and toughness of undeformed and textured UHMWPEs by means of nanoscratch tests along and perpendicular to the specimen axis. In three samples we determined the scratch characteristics in terms of deformation mode, coefficient of friction (μ), and viscoelastic recovery (r). Results: Before the tensile process, the scratch behavior of UHMWPE was characterized by a μ ranging from 0.64 to 0.68, no cracking, and r ranging from 0.58 to 0.60. Microfibrillar morphologic features resulted from the tensile process. The new microstructure had an increased strength (r = 0.78) and decreased toughness (cracking + μ = 0.77) perpendicular to the fibril axis and decreased strength (r = 0.53) and increased toughness (no cracking + μ = 0.55) parallel to the fibril axis. Conclusions: Textured UHMWPE behaves like a fiber composite with high strength and toughness in well-defined directions. However, the effect of crosslinking on these specific properties is unknown and therefore it is important to verify that the properties are retained. If wear resistance of crosslinked-textured UHMWPE is at least as high as that of crosslinked UHMWPE, novel medical devices made of crosslinked-textured UHMWPE could be developed and clinically tested. [ABSTRACT FROM AUTHOR]

The mechanics of structure genome has been extended to heat conduction problem of composite materials with a general linear thermal imperfect interface model. This full field micromechanics approach is applied to predict the effective thermal conductivity of composite materials containing thermal imperfect contact between the matrix and the reinforcements. Examples of spheroidal particles reinforced composites are used to demonstrate the robustness and accuracy of this micromechanics theory. The size-dependency of the overall thermal conductivity shows the importance of imperfect interfaces in modeling the thermal behavior of composite materials. The proposed micromechanics method is versatile and can be applied for estimating the effective thermal conductivity of nanocomposite materials. [ABSTRACT FROM AUTHOR]

During the past decade, synthesizing silver nanoparticles (Ag NPs) by liquid phase-pulsed laser ablation (LP-PLA) has attracted a lot of attention. Basically, this technique allows producing various metallic nanoparticles with controlled size, shape, composition, or surroundings in several liquids (i.e., water, ethanol, acetone, toluene, and so forth). Recently, such processes have been studied in liquid organic monomer such as methyl methacrylate (MMA). However, the influence of the laser parameters on the materials synthesized in such reactive liquid and their features were not fully investigated so far. Here we investigate the LP-PLA of silver in two different but rather similar acrylate monomers: dodecyl acrylate (DOCA) and 1H,1H,2H,2H perfluorodecyl acrylate (PFDA). The influence of the fluence and the number of pulses on the production, size, and morphology of the materials has been examined. First, factorial design experiments have been achieved in order to determine the weight of the laser parameters in each precursor. This study shows two highly different behaviors in function of the monomer where the process took place. This has been explained by the plasma plume confinement and/or the "interpulses" self-absorption of the particles by the laser beam. The formation of graphite around the synthesized AgNPs has been highlighted by Raman spectroscopy at low number of pulses. Nevertheless, increasing the number of pulses could lead to three phenomenon depending on the fluence and the used monomer: degradation of the matrix, conservation of the matrix with changes in AgNPs size and distribution, or sustainment of the matrix with any changes in the particles properties. So the surrounding, the size, and stability could be triggered by adjusting these parameters. This paper does highlight that LP-PLA is a powerful technique to provide AgNPs in acrylate monomer with a good control of their features. [ABSTRACT FROM AUTHOR]

New intumescent flame retardant coating made from poly(allylamine) (PAH), sodium polyphosphates (PSP) and TiO 2 nanoparticles was designed using layer-by-layer assembly. The (PAH-PSP-PAH-TiO 2 ) n (where “ n ” denotes the number of quadralayers) assembly has been deposited on silicon wafers in order to evaluate its thickness as well as its topography by ellipsometry and by atomic force microscopy (AFM), respectively. According to AFM measurements, the coating appears smooth and continuous. The film exhibits a linear growth regime with a thickness of approximately 500 nm for 15 quadralayers (QL). However, when deposited on polyamide or polyester fabrics, this coating displays different morphologies as it was shown by scanning electron microscopy (SEM) analysis. The thermo-oxidative degradation and flammability properties of the coatings and their effect on polyamide and polyester fabrics have been evaluated by thermogravimetric analyses (TGA) and pyrolysis combustion flow calorimeter (PCFC) respectively. We have found that the coating acts efficiently in reducing the peak of the heat release rate (pHRR) value for polyamide fabric while very limited effect was observed on polyester fabric. [ABSTRACT FROM AUTHOR]

Background: Surgical treatment for terrible triad injuries of the elbow (defined as elbow dislocations with concomitant fractures of the radial head and coronoid) remains a challenging clinical problem. Specifically, the question of whether to repair or replace the radial head remains controversial. Questions/purposes: We compared patients with terrible triad injuries of the elbow whose radial head fracture was treated with either internal fixation and internal fixation (ORIF) or radial head arthroplasty in terms of (1) clinical outcome measures (DASH and Broberg-Morrey scores, ROM), (2) elbow stability and radiographic signs of arthrosis, and (3) complications and reoperation rates. Methods: Retrospective review identified 39 patients with terrible triad injuries and minimum 18-month complete clinical and radiographic followup (mean, 24 months; range, 18-53 months). Patients were managed with a standard algorithm consisting of (1) repair (n = 9) or replacement (n = 30) of the radial head, (2) repair of the lateral ulnar collateral ligament, and (3) repair of the coronoid fracture. During the study period, the radial head generally was internally fixed when there were fewer than four articular fragments; otherwise, it was replaced. Evaluation included the DASH score, the Broberg-Morrey index, measurements of elbow stability and motion, and radiographic assessment for signs of arthrosis; chart review was performed for complications and reoperations. Complete followup was available on 87% (39 of 45 patients). Results: There were no differences between groups in terms of ROM or elbow scores. All patients who underwent radial head arthroplasty at the index procedure had a stable elbow at final followup whereas three of nine patients who underwent ORIF were unstable (p = 0.009). However, 11 patients who underwent arthroplasty demonstrated radiographic signs of arthrosis compared to none in the ORIF group (p = 0.04). Eleven patients (28%) underwent reoperation (seven arthroplasty, four ORIF) for various reasons. With the numbers available, there was no difference in reoperation rate between groups (p = 0.45). Conclusions: For terrible triad injuries, radial head arthroplasty afforded the ability to obtain elbow stability with comparable overall outcomes when compared to ORIF. As these injuries commonly occur in younger patients, longer-term studies will be required to ascertain whether the apparent benefits of radial head arthroplasty are offset by late complications of arthroplasty, such as loosening. Level of Evidence: Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence. [ABSTRACT FROM AUTHOR]

To tune the toughness of PLA, a novel pathway to chemically modify PLA via reactive extrusion in the presence of 'reactive' PEG derivatives is proposed. PEG methyl ether methacrylate (MAPEG) and PEG methyl ether acrylate (AcrylPEG) are melt-mixed and extruded with PLA in the presence of 2,5-dimethyl-2,5-di( tert-butylperoxy)hexane (L101) as a free-radical initiator. Molecular characterization reveals that about 20 and 65%, respectively, of the initially introduced MAPEG and AcrylPEG can be grafted onto the PLA backbone. The plasticization effect is demonstrated by a significant decrease of the glass transition temperature and storage modulus together with a significant increase of the elongation at break as compared to neat PLA. [ABSTRACT FROM AUTHOR]

The risk of anterior cruciate ligament (ACL) injury and re-injury is greater for women than men. Among other factors, compositional differences may play a role in this differential risk. Patellar tendon (PT) autografts are commonly used during reconstruction. The aim of the study was to compare protein expression in male and female ACL and PT. We hypothesized that there would be differences in key structural components between PT and ACL, and that components of the proteome critical for response to mechanical loading and response to injury would demonstrate significant differences between male and female. Two-dimensional liquid chromatography-tandem mass spectrometry and a label-free quantitative approach was used to identify proteomic differences between male and female PT and ACL. ACL contained less type I and more type III collagen than PT. There were tissue-specific differences in expression of proteoglycans, and ACL was enriched in elastin, tenascin C and X, cartilage oligomeric matrix protein, thrombospondin 4 and periostin. Between male and female donors, alcohol dehydrogenase 1B and complement component 9 were enriched in female compared to male. Myocilin was the major protein enriched in males compared to females. Important compositional differences between PT and ACL were identified, and we identified differences in pathways related to extracellular matrix regulation, complement, apoptosis, metabolism of advanced glycation end-products and response to mechanical loading between males and females. Identification of proteomic differences between male and female PT and ACL has identified novel pathways which may lead to improved understanding of differential ACL injury and re-injury risk between males and females. [ABSTRACT FROM AUTHOR]

X-ray micro-computed tomography (μCT) is used to generate 3D- and 2D-imaging reconstruction of the meso-structure of high-density polyethylene (HDPE)/short hemp fibre composites subjected to in situ tensile testing. These composites exhibit marked fibre/matrix debonding mechanisms starting at low strain level that are carefully analysed. In particular, debonding causes the formation of micro-cracks that first starts at the tip of fibres oriented parallel to the tensile direction and along fibres oriented perpendicular to the tensile direction. With increasing strain level, the thickness of these micro-cracks increases and coalescence mechanisms between adjacent micro-cracks are noted. The coalescence mechanism of some micro-cracks is believed to be at the origin of the material rupture. [ABSTRACT FROM AUTHOR]

Abstract: A new ammonium-based surfactant (PkH+), synthesized from a 3-alkyl phenol glycidyl ether issued from renewable cashew nutshell liquid (CNSL), has been used to modify the surface of sepiolite clay. This surfactant is especially designed to enhance the compatibility of the needle-like clays with epoxy networks (e.g. DGEBA): ionic PkH+–sepiolite interactions are provided by the ammonium groups, and covalent grafting of DGEBA onto the surfactant is enabled by NH and OH reactive groups. MALDI-ToF-MS was used with success to evidence the grafting of DGEBA units onto the modified clay. Morphological analyses by SEM highlighted the promoted compatibilization and dispersion of sepiolite in DGEBA networks. The properties of the filled networks were characterized by DSC, DMA and evidenced a strong shift of 20°C of the Tg of the network to higher temperatures and an enhancement of the storage modulus below the Tg. Interestingly, the thermal stability of the network was not affected by the modification of sepiolite by the ammonium. In conclusion, the intercalation of PkH+ onto sepiolite subserves its compatibilization into epoxy networks with a remarkable thermal and thermomechanical properties improvement. [Copyright &y& Elsevier]

Abstract: The present article focuses on the influence of the salt concentration as well as on the influence of the nature of the salt on the deposition of (PAH-PSP) n films in the case where PSP is made from only 24 monomer units on average. The two main messages of this article are that: (i) for salt concentrations lower than about 0.2M, the film thickness increases linearly with the number of adsorption cycles after the deposition of a coating with a critical thickness necessary to prime the deposition of the film. In addition, for salt concentrations lower than 0.2M, there is no effect of the influence of the supporting electrolyte on the film thickness but a marked influence on the film composition as revealed from XPS measurements. (ii) For salt concentrations higher than about 0.2M, the films are extremely rough, and we demonstrate that the use of a homogeneous and isotropic model is not suited anymore to calculate the film thickness and its refractive index from the measured ellipsometric angles. Finally we try to rationalize all the data obtained so far on the (PAH-PSP) n films on the basis of counterion condensation of Na+ cations on the PSP chains. [Copyright &y& Elsevier]

Abstract: The deposition of polyelectrolyte multilayer films consists of the sequential adsorption of polycationic and polyanionic species at solid–liquid interfaces. The adsorption process can be performed either by alternated dipping of the substrate to be coated in the polyelectrolyte containing solutions, by alternated spin coating of these solutions or by alternated spraying of them. Different coating technologies can lead to different properties of the obtained coatings even for the same combination of polycations and polyanions. The aim of this article is to show that by playing on the concentration of the supporting electrolyte, NaCl, the films obtained by alternated spraying and alternated dipping grow differently and display different properties, in terms of refractive index, surface morphology, wettability for water and surface composition. [Copyright &y& Elsevier]

Abstract: The formation of “polydopamine” thin films becomes a popular method to confer multifunctionality to solid–liquid interfaces through the available catechol groups of such films. The mechanism of film formation is, however, not well elucidated, and most investigators use the protocol developed by Messersmith et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.) using a dopamine solution at a constant concentration of 2gL−1 in the presence of Tris(hydroxymethyl aminomethane) at pH 8.5. A particular finding of this initial study was that the film thickness reaches a constant value (almost substrate independent) of about 40nm. Herein, we investigate the change in the polydopamine film thickness, morphology, surface energy and electrochemical properties as a function of the concentration of the dopamine solution put in the presence of silicon substrates. As a surprising finding, we observe a constant increase in the maximal film thickness with an increase in the dopamine solution between 0.1 and 5gL−1. The surface morphology is also markedly affected by the concentration of the dopamine solution, whereas the different components of the surface energy stay unaffected by the dopamine solution concentration. In addition, electrochemical impedance spectroscopy shows that the higher the initial dopamine concentration, the more rapidly compact and impermeable films are formed. Finally, we propose a model for the deposition of polydopamine films taking all our findings into account. This model relies on a rate equation taking into account both attractive and repulsive interactions between small polydopamine aggregates on the surface and in solution. [Copyright &y& Elsevier]

Background: Osteonecrosis of the femoral head (ONFH) is a debilitating condition affecting primarily young patients. Free vascularized fibular grafting (FVFG) may provide a durable means to preserve the femoral head. When used in the precollapse stages of ONFH, this treatment may alter the course of disease. Questions/purposes: We asked: (1) In what percentage of patients does FVFG preserve the femoral head beyond 10 years? (2) When long-term preservation is not achieved, what is the duration of femoral head preservation? (3) Do demographic or etiologic factors predict FVFG survivorship? (4) What long-term improvements in function and activity can be anticipated? Methods: We retrospectively reviewed 61 patients (65 hips) who underwent FVFG for precollapse ONFH. We calculated graft survivorship, SF-12 scores, activity levels, and Harris hip scores. Minimum followup was 10.5 years (mean, 14.4 years; range, 10.5-26 years). Results Forty-nine of 65 hips (75%) had surviving FVFG for at least 10 years. At last followup, 39 of 65 hips (60%) had surviving FVFG, with a mean graft survival time of 15 years (range, 10.5-26.1 years). Twenty-six of the 65 hips with FVFG (40%) underwent conversion to THA at a mean of 8 years postoperatively. Demographic factors, lesion size, additional procedures, and low preoperative function were not associated with changes in graft survivorship. Pain and function were similar in patients with surviving FVFG and patients who had conversion to THA. Patients with surviving FVFG were more likely to engage in impact sports or active events than were patients who had conversion to THA. Conclusions: When patients with precollapse ONFH undergo FVFG, the majority have preservation of the hip lasting for greater than 10 years with low levels of pain and reasonable function. In patients who ultimately undergo conversion surgery to THA, the mean duration of hip preservation before conversion is 8 years. We continue to use FVFG for treating patients younger than 50 years with symptomatic, precollapse ONFH. Level of Evidence: Level IV, therapeutic study. See Instructions to Authors for a complete description of levels of evidence. [ABSTRACT FROM AUTHOR]

Abstract: Compact and linearly growing polyelectrolyte multilayer films have been used to suppress desorption of drugs, nanoparticles or proteins from underlying polyelectrolyte multilayer films as well as to significantly change their mechanical properties. The polyelectrolyte based capping layers are however cumbersome to deposit and alternative barrier layers offering enzymatic retention in the films as well as permeability to small molecules, for example the substrates of the embedded enzymes, are highly desired. In this article we show that barrier layers made through atmospheric pressure dielectric barrier discharge polymerization of ethylene glycol dimethacrylate offer the opportunity to simultaneously suppress enzyme desorption from the underlying polyelectrolyte multilayer film and to ensure accessibility of the enzymatic substrate. This holds true when the barrier film totally covers the underlying film and as long is not too thick. When the plasma deposited barrier becomes 300nm thick, the hydrolysis curve of the enzyme presents a lag phase typical of a diffusion-limited process. [Copyright &y& Elsevier]

The article discusses the treatment for triad elbow fracture-dislocation with a systematic approach includes its fixation on the coronoid using the lasso technique. It notes on the three critical aspects which describes the fracture-dislocations of the elbow includes coronoid fracture, posterior elbow dislocation and radial head fracture. It also mentions that elbows treated with coronoid suture lasso technique has lower rate of complications including malunion, hardware failure and nounion.

Abstract: Electrospray tandem mass spectrometry was used here to study the soluble part of a thin film prepared by plasma polymerization of octamethylcyclotetrasiloxane (D4). Accurate mass measurements and 29Si nuclear magnetic resonance (NMR) spectroscopy, as well as synthesis of authentic compounds used as models to understand the MS/MS behavior of plasma polymers, were combined to structurally investigate oligomers present in this extract. All precursor ions were protonated or ammoniated molecules, known to provide more useful information for dimethylsiloxane (DMS)-based polymers as compared to alkali adducts. Apart from a major compound consisting of two D4 units connected via an oxygen bridge, it was found that the soluble part of this plasma polymer was mainly composed of cyclolinear polysiloxanes, in which cyclic units composed of four DMS were covalently connected by linear DMS segments. As the size of precursor ions increases, discrepancies observed between MS/MS data of synthesized molecules and of plasma oligomers would reveal the presence of branched isomers in the soluble part of the film, consistently with the expected propensity of the plasma polymerization process to favor random branching. [Copyright &y& Elsevier]

Abstract: New plasticization ways based on low molecular plasticizers from citrates family were investigated to improve the ductility of poly(lactide) (PLA). Grafting reactions between anhydride-grafted PLA (MAG-PLA) copolymer with hydroxyl-functionalized citrate plasticizer, i.e. tributyl citrate (TbC), were so-carried out through reactive extrusion. TributylO-acetylcitrate (ATbC) was used as a non-functionalized reference. Both plasticizers drastically decreased the T g of PLA. However, the grafting reaction of TbC into MAG-PLA revealed a shift of PLA T g toward higher values. After 6months of aging, no phase separation was observed. However, plasticizer leaching was noticed in the case of PLA/ATbC materials, leading to the shift of T g toward lower temperatures. In contrast, no major leaching phenomenon was noticed in PLA/TbC and PLA/MAG-PLA/TbC blends, indicating that the mobility restriction derived from the hydrogen bonding that can occur between PLA and TbC as well as the grafting reaction of TbC into MAG-PLA enabled to reduce leaching phenomena. [Copyright &y& Elsevier]

Abstract: The deposition of polyelectrolyte multilayer films (PEMs) appears more and more as a versatile tool to functionalize a broad range of materials with coatings having controlled thicknesses and properties. To increase the control over the properties of such coatings, a good knowledge of their deposition mechanism is required. Since Cohen Stuart et al. (Langmuir 18 (2002) 5607–5612) showed that the adsorption of one polyelectrolyte could induce desorption of polyelectrolyte complexes instead of regular deposition, more and more findings highlight peculiarities in the deposition of such films. Herein we demonstrate that the association of sodium polyphosphate (PSP) as the polyanion and either poly(-L-lysine hydrobromide) (PLL) or poly(allylamine chloride) (PAH) as the polycations may lead to non-monotonous film deposition as a function of time. Complementary, films containing PSP and PLL can be obtained from a (PLL–HA) n template films after the exchange of HA (hyaluronic acid) from the sacrificial template by PSP from the solution. This exchange is accompanied by pronounced film erosion. However, when starting from a (PAH–HA) n template, the film erosion and exchange due to the contact with PSP is by far less pronounced, nevertheless the film morphology changes. These findings show that the nature of the polycation used to deposit the PEM film may have a profound influence of the film’s response to a competing polyanion. [Copyright &y& Elsevier]

Abstract: Dopamine–melanin films produced through the oxidation of dopamine in the presence of oxygen as an oxidant allow to reduce silver ions onto silver particles as already described in the paper by Lee et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.). This reduction process has to occur through the oxidation of moieties present in the melanin film. This investigation shows that the free radicals present in the pseudomelanin film, quantified by means of electron spin resonance spectroscopy (ESR) for the first time, are not used in the transformation of Ag+ cations to deposit silver. The ESR signal is hardly affected by the deposition of silver particles. On the other hand, X-ray photoelectron spectroscopy shows a small increase in the density of quinone groups and a small decrease of catechol groups on the surface of the film during the deposition of silver. This suggests that the deposited pseudomelanin films contain a significant fraction of catechol groups able to trigger reduction processes of metallic cations. These silver nanoparticles remain adherent to the melanin films and allow for a quantitative killing of Escherichia coli over a broad range of bacterial dilutions. However, the presence of the bacteria induces a release of the nanoparticles. The pseudomelanin films cannot be reused again for a silver ion reduction step. Nevertheless, the easy preparation of the pseudomelanin–silver composite and its effective one shot bacterial killing activity renders the strategy presented in this paper attractive. Some fundamental questions about redox process allowed by the pseudomelanin films will also be asked. [Copyright &y& Elsevier]

Abstract: In this work, new ways of plasticizing polylactide (PLA) with low molecular poly(ethylene glycol) (PEG) were developed to improve the ductility of PLA while maintaining the plasticizer content at maximum 20wt.% PLA. To this end, a reactive blending of anhydride-grafted PLA (MAG-PLA) copolymer with PEG, with chains terminated with hydroxyl groups, was performed. During the melt-processing, a fraction of PEG was grafted into the anhydride-functionalized PLA chains. The role of the grafted fraction was to improve the compatibility between PLA and PEG. Reactive extrusion and melt-blending of neat and modified PLA with PEG did not induce any dramatic drop of PLA molecular weight. The in situ reactive grafting of PEG into the modified PLA in PLA/PEG blends showed a clear effect on the thermal properties of PLA. It was demonstrated by DSC that the mobility gained by PLA chains in the plasticized blends yielded crystallization. The grafting of a fraction of PEG into PLA did not affect this process. However, DSC results obtained after the second heating showed an interesting effect on the T g when 20wt.% PEG were melt blended with neat PLA or 10wt.% MAG-PLA. In the latter case, the T g displayed by the reactive blend was shifted to even lower temperatures at around 14°C, while the T g of neat PLA and PLA blended with 20wt.% PEG was around 60 and 23°C, respectively. Regarding viscoelastic and viscoplastic properties, the presence of MAG-PLA does not significantly influence the behavior of plasticized PLA. Indeed, with or without MAG-PLA, elastic modulus and yield stress decrease, while ultimate strain increases with the addition of PEG into PLA. [Copyright &y& Elsevier]

Abstract: The yield behaviour of dimer acid-based polyamides (DAPA) and DAPA reinforced with cellulose fibres (CF) was examined in this study. Both dynamic mechanical analysis (DMA) and tensile tests were used to follow the effect of strain rate or frequency, temperature and filler content on the transitions temperatures, the storage modulus and the yield stresses. The DMA results show that the storage modulus increases with increasing CF concentration. The tensile tests reveal that the yield stress is strain rate, temperature and CF concentration sensitive. Both activation enthalpy and activation volume calculated by the Eyring’s model reveal a slight increase of activation energy with increasing filler content and a decrease of the activation volume. A micromechanically-model was used to predict the yield stress of both DAPA and DAPA/cellulose composites. The model predictions of the yield stress are in good agreement with the experimental data. [Copyright &y& Elsevier]

Compositional images from a SEM (scanning electron microscope) are sometimes complemented by quantitative topographical data from devices such as an AFM (atomic force microscope) or WLI (white light interferometer). Indeed, even if a SEM could provide both kinds of information (composition and topography), the topographical data are incomplete because the SEM does not allow measuring the vertical dimension (i.e., perpendicular to the measurement plane). Thus these two kinds of information are usually measured using two different techniques, and at different locations on the sample. Mean values of surface composition are then linked to mean values of topography, and as a consequence this approach does not allow precisely linking a local topographical peak to its corresponding composition. The present work deals with a SEM/WLI combination methodology, based on the characterization, at the same location, of a nanocomposite (nanoparticles of AlCeO3 dispersed in a plasma-polymerized hexamethyldisiloxane ppHMDSO matrix and deposited by atmospheric plasma on a glass substrate) developed for improving anticorrosion properties. SEM images allow the supposition that the protuberances (peaks) observed on the surface of a specimen are linked to the nanoparticles dispersed in the polymer coating, but this link is not fully convincing. Thanks to a precise localization method, SEM compositional data and WLI topographical data are here measured at the same location. The recombination of both signals to form a 4D image (3D geometry and 1D composition) allows linking protuberances to nanoparticles aggregates without ambiguity. This composite image appears to be an interesting new tool (at the scale of observation, i.e., hundreds of micrometers) for the study of nanostructured coatings. [ABSTRACT FROM AUTHOR]

In this work, the use of Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was explored as a technique for monitoring the interfacial retro Diels–Alder (retro DA) reaction occurring on well-controlled self-assembled monolayers (SAMs). A molecule containing a Diels–Alder (DA) adduct was grafted on to the monolayers, then the surface was heated at different temperatures to follow the reaction conversion. A TOF-SIMS analysis of the surface allowed the detection of a fragment from the molecule, which is released from the surface when retro DA reaction occurs. Hence, by monitoring the decay of this fragment's peak integral, the reaction conversion could be determined in function of the time and for different temperatures. The viability of this method was then discussed in comparison with the results obtained by 1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]