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This work aims to get new insights into the “process monitoring tool” proposed by the authors for the online monitoring of the shear heating phenomenon during injection molding of technical rubber parts. The online monitoring is based on direct measurement of the surface rubber temperature (shear heating temperature, TSH) by an infrared thermal camera of the rubber as it leaves the extruder barrel of the injection molding machine. The measured rubber temperature is a process indicator giving the thermal history of the rubber compound injection and process safety. Therefore, this fast process control is applied to industrial applications to investigate the processing behavior of ethylene acrylate (AEM) rubber compounds. In particular, the relationships between TSH vs injection pressure, vs injection speed, vs screw speed rotation and vs screw length over diameter ratio (L/D ratio) and vs AEM rubber compound properties variation due to exceeding the shelf life are investigated. The results show that TSH is manly influenced by the screw L/D ratio, followed by injection pressure and screw speed rotation (especially if are set to higher levels), whereas the injection speed is the least effective parameter to reduce TSH. Furthermore, a previously found robust correlation between the shear heating parameter (ηSH) and the minimum torque measured in rheometric laboratory tests (ML) is used to show the noteworthy deviation from the proportional trend when the AEM rubber compound exceeded it shelf life. Therefore, the coefficient of determination of $${\text{log}}\eta_{{{\text{SH}}}}$$ log η SH vs ML curves provides a good indication of process stability, while it is running.

Background Endoscopic transnasal transclival intradural surgery is limited by a high postoperative cerebrospinal fluid leak rate. The aim of this study was to investigate the role of three-dimensional printing to create a personalized, rigid scaffold for clival reconstruction. Methods Two different types of clivectomy were performed in 5 specimens with the aid of neuronavigation, and 11 clival reconstructions were simulated. They were repaired with polylactide, three-dimensional–printed scaffolds that were manually designed in a computer-aided environment based either on the real or on the predicted defect. Scaffolds were printed with a fused filament fabrication technique and different offsets. They were positioned and fixed either following the gasket seal technique or with screws. Postdissection radiological evaluation of scaffold position was performed in all cases. In 3 specimens, the cerebrospinal fluid leak pressure point was measured immediately after reconstruction. Results The production process took approximately 30 hours. The designed scaffolds were satisfactory when no offset was added. Wings were added during the design to allow for screw positioning, but broke in 30% of cases. Radiological assessment documented maximal accuracy of scaffold positioning when the scaffold was created on the real defect; accuracy was satisfactory when the predicted clivectomy was performed under neuronavigation guidance. The cerebrospinal fluid leak pressure point was significantly higher when the scaffold was fixed with screws compared with the gasket technique. Conclusions In this preclinical setting, additive manufacturing allows the creation of customized scaffolds that are effective in reconstructing even large and geometrically complex clival defects.

Nowadays sustainability is a key topic and waste should be considered a resource. For this reason, a large body of literature is being developed on the management of the large quantity of post-cons...

Injection compression molding is an injection molding process with the addition of a compression stage after the injection. This process is useful for the injection molding of precision parts. A stable and controlled manufacturing process is needed to guarantee reliability of complex products, and usually process optimization is achieved by experimental and time consuming approaches. However, for being competitive a minimal market time is a very important requirement and computer simulations can help to optimize the process at the only expense of computational time. This paper reports and discusses for the first time the results of a 3D finite element simulation of reactive injection compression molding (RICM) by commercial software for the production of rubber diaphragms. In particular, the stages of mold filling dynamics and material curing are analyzed and the results verified with experimental tests. To get an accurate representation of the process, the rheological behavior, thermal properties, and kinetic behavior during curing of the real rubber compound were described by mathematical models. A differential scanning calorimeter (DSC) and a capillary rheometer are employed to characterize the rubber material in order to achieve an appropriate curing reaction and viscosity models, respectively. The computations are found to be in good agreement with the experimental results, indicating that reliable information on material viscosity and curing kinetics can play a key role in making well-founded predictions and avoiding trial and error methods.

Cartilage tissue engineering remains problematic because no systems are able to induce signals that contribute to native cartilage structure formation. Therefore, we tested the potentiality of gelatin-polyethylene glycol scaffolds containing three different concentrations of chitosan (CH; 0%, 8%, and 16%) on chondrogenic differentiation of human platelet lysate-expanded human bone marrow mesenchymal stromal cells (hBM-MSCs). Typical chondrogenic (SOX9, collagen type 2, and aggrecan), hypertrophic (collagen type 10), and fibrotic (collagen type 1) markers were evaluated at gene and protein level at Days 1, 28, and 48. We demonstrated that 16% CH scaffold had the highest percentage of relaxation with the fastest relaxation rate. In particular, 16% CH scaffold, combined with chondrogenic factor TGFβ3, was more efficient in inducing hBM-MSCs chondrogenic differentiation compared with 0% or 8% scaffolds. Collagen type 2, SOX9, and aggrecan showed the same expression in all scaffolds, whereas collagen types 10 and 1 markers were efficiently down-modulated only in 16% CH. We demonstrated that using human platelet lysate chronically during hBM-MSCs chondrogenic differentiation, the chondrogenic, hypertrophic, and fibrotic markers were significantly decreased. Our data demonstrate that only a high concentration of CH, combined with TGFβ3, creates an environment capable of guiding in vitro hBM-MSCs towards a phenotypically stable chondrogenesis.

Recently, endoscopic transsphenoidal transclival approaches have been developed and their role is widely accepted for extradural pathologies. Their application to intradural pathologies is still debated, but is undoubtedly increasing. In the past five decades, different authors have reported various extracranial, anterior transclival approaches for intradural pathologies. The aim of this review is to provide a historical overview of transclival approaches applied to intradural pathologies. PubMed was searched in October 2018 using the terms transcliv*, cliv* intradural, transsphenoidal transcliv*, transoral transcliv*, transcervical transcliv*, transsphenoidal brainstem, and transoral brainstem. Exclusion criteria included not reporting reconstruction technique, anatomical studies, reviews without new data, and transcranial approaches. Ninety-one studies were included in the systematic review. Since 1966, transcervical, transoral, transsphenoidal microsurgical, and, recently, endoscopic routes have been used as a corridor for transclival approaches to treat intradural pathologies. Each approach presents a curve that follows Scott’s parabola, with evident phases of enthusiasm that quickly faded, possibly due to high post-operative CSF leak rates and other complications. It is evident that the introduction of the endoscope has led to a significant increase in reports of transclival approaches for intradural pathologies. Various reconstruction techniques and materials have been used, although rates of CSF leak remain relatively high. Transclival approaches for intradural pathologies have a long history. We are now in a new era of interest, but achieving effective dural and skull base reconstruction must still be definitively addressed, possibly with the use of newly available technologies.

The ultimate properties and resistance to fracture of nanocomposites based on poly(1,4-cis-isoprene) from Hevea Brasiliensis (natural rubber, NR) and a high surface area nanosized graphite (HSAG) were improved by using HSAG functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)propane-1,3-diol (serinol pyrrole) (HSAG-SP). The functionalization reaction occurred through a domino process, by simply mixing HSAG and serinol pyrrole and heating at 180 &deg, C. The polarity of HSAG-SP allowed its dispersion in NR latex and the isolation of NR/HSAG-SP masterbatches via coagulation. Nanocomposites, based either on pristine HSAG or on HSAG-SP, were prepared through traditional melt blending and cured with a sulphur-based system. The samples containing HSAG-SP revealed ultimate dispersion of the graphitic filler with smaller aggregates and higher amounts of few layers stacks and isolated layers, as revealed by transmission electron microscopy. With HSAG-SP, better stress and elongation at break and higher fracture resistance were obtained. Indeed, in the case of HSAG-SP-based composites, fracture occurred at larger deformation and with higher values of load and, at the highest filler content (24 phr), deviation of fracture propagation was observed. These results have been obtained with a moderate functionalization of the graphene layers (about 5%) and normal lab facilities. This work reveals a simple and scalable way to prepare tougher NR-based nanocomposites and indicates that the dispersion of a graphitic material in a rubber matrix can be improved without using an extra-amount of mechanical energy, just by modifying the chemical nature of the graphitic material through a sustainable process, avoiding the traditional complex approach, which implies oxidation to graphite oxide and subsequent partial reduction.

The Technical Committee 4, “Polymers, Polymer Composites and Adhesives”, of the European Structural Integrity Society (ESIS TC4) developed a draft protocol based on the load separation criterion to determine two fracture parameters (an initiation parameter, JI,lim, and a crack growth parameter, ms) without the need to measure the crack growth (Δa). This is especially beneficial, since the measurement of Δa is prone to errors. The developed testing scheme displays promising results, as shown in a round-robin testing exercise. To further push this testing scheme, it is necessary to verify the specimen size scaling possibility. Hence, in this work, single edge notched in bending (SE(B)) specimens with different sizes, but geometrically similar, were manufactured. ESIS TC4 testing scheme was successfully applied to specimens with the different sizes, and data of JI,lim and ms were obtained. The observed effect of the specimen size on the aforementioned fracture parameters is presented and discussed.

Control of the injection molding process of rubber is made complex by the influence of many parameters. Shear heating, heat generation due to viscous dissipation, is a phenomenon largely exploited in rubber to lower compound viscosity, particularly in the extrusion phase, but it is impossible to predict it from laboratory tests. With the aim of providing useful tools for process control, a parameter for on-line monitoring of shear heating phenomenon is proposed. This parameter is based on direct measurement of rubber surface temperature by infrared thermal camera at the nozzle outlet of the injection molding machine extruder. The measured rubber temperature is a process indicator to give the thermal history of the rubber injection and process safety. Measured temperature increase is then converted into a parameter having dimensions of viscosity, the shear heating parameter, ηSH. Four different rubber compounds are investigated. The ηSH results are compared to minimum torque (ML) from routine rheometric laboratory measurement. The calculated ηSH values increase with increasing ML values. The ML value is a rough indication of the rubber compound viscosity, where its relevant variations affect the rubber processability. Meanwhile ηSH is more sensitive to small processability variations and more accurate because it takes into account the thermal history during the injection stage. The found relationship provides deeper insights into the behavior of rubber, compared to laboratory tests, and how it can be used in the industrial practice to improve the process control by monitoring the shear heating effect during the injection stage.

This work provides a direct comparison of several experimental approaches used in the literature to measure fracture toughness of rubber of rubber using single edge notched in tension (SENT) specimens, with the final aim to provide guidelines for an optimal testing procedure. Digital image correlation measurements were used to get new insights into the fracture process. SENT is experimentally advantageous because of the simple preparation from laboratory plates and the small amount of material required. The most common experimental approaches to measure fracture toughness of rubber rely on the energy release rate, measured by the tearing energy or the J-integral parameters. This work points out the importance of experimental conditions and test procedures: long specimens and short notches are preferred, identification of fracture initiation from the front view is necessary, strain energy density should not be evaluated from un-notched specimens at the critical stretch level, rather alternative strategies are shown in this work.

High performance gelatin-based biocompatible hybrid hydrogels are developed using functionalized polyethylene glycol as a cross-linker in presence of chitosan or hydroxyethyl cellulose. Tensile tes...

International audience; Material key curves are functions providing a relationship among load, displacement and crack size, and are used in fracture mechanics methods for ductile polymers. This work shows that the material key curves provide also a tool to distinguish among different deformational mechanisms involved in the fracture process and they reflect the constraint degree. Tests are carried out on an acrylonitrile-butadiene-styrene resin (ABS) as a model material, and different deformation mechanisms are induced by different temperatures and loading rates, up to impact conditions. Deformation mechanisms are investigated, for the first time on ABS, by tomography and the results are compared to more traditional imaging techniques as scanning and transmission electron microscopy.

This work provides a comprehensive investigation of the anisotropic mechanical and electrical properties of elastomeric nanocomposites based on natural rubber and sp2 carbon allotropes. They can be either nanometric and with high shape anisotropy like Carbon Nanotubes (CNT) and lamellar nanographite, or nanostructured and nearly isometric like carbon black. Studies were performed on calendered and compression molded plates. A complete mechanical characterization along all main directions could be performed by a non-standard testing approach. Composites with nanometric, high aspect ratio fillers gave rise to remarkable mechanical anisotropy, revealing an orthotropic and transversally isotropic response: modulus values were very similar in the sheet plane and much larger (almost twice as much) in the orthogonal direction. The electrical anisotropy achieved its maximum at lower CNT content. Composites with carbon black did not reveal mechanical anisotropy, while, quite strikingly, a very large electrical anisotropy was observed for carbon black content close to the percolation threshold. These results provide insights into the anisotropic behavior of nanofilled elastomers, and could pave the way to their exploitation in advanced engineering design and biomimicking biomedical applications.

Silica-based rubber composites have tremendous importance, as they allow the reduction in hysteresis in demanding dynamic-mechanical applications such as tire compounds and hence have a lower environmental impact. However, they also present drawbacks such as poor rheological behavior. In this work, an innovative silica-based hybrid filler system was developed, obtaining a rubber composite with an improved set of properties. A nanosized high surface area graphite (HSAG) was functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)propane-1,3-diol, serinol pyrrole (SP), through a simple process characterized by a high carbon efficiency. The HSAG-SP adduct, with about nine parts of SP per hundred parts of carbon filler, was used to form a hybrid filler system with silica. An elastomeric composite, with poly(styrene-co-butadiene) from anionic polymerization and poly(1,4-cis-isoprene) from Hevea brasiliensis was prepared with 50 parts of silica, which was replaced in a minor amount (15%) by either pristine HSAG or HSAG-SP. The best set of composite properties was obtained with HSAG-SP: the same dynamic rigidity and hysteresis and tensile properties of the silica-based material and appreciably better rheological properties, particularly in terms of flowability. This work paves the way for a new generation of silica-based composites, with improved properties, based on a hybrid filler system with a nanosized edge functionalized graphite.

In this work hydroxyethylcellulose (HEC) was employed to prepare macroporous polyacrylamide (PAAm) hydrogels with different porosities and degrees of interconnectivity. The porosity and the equilibrium mass swelling ratio of hydrogels equilibrated in 0.1 M NaCl increased with the amount of HEC employed in the reaction mixture. Tensile and fracture tests were performed to investigate the mechanical behavior of both as prepared hydrogels and of hydrogels equilibrated in 0.1 M NaCl. As prepared hydrogels displayed invariably better mechanical properties than the corresponding equilibrated hydrogels. The mechanical stiffness decreased regularly as the amount of HEC (and porosity) was increased. A more complex trend was observed for the ultimate properties (elongation and stress at break) and for the fracture resistance, which displayed a maximum at intermediate HEC contents. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Bone marrow and adipose tissue human mesenchymal stem cells were seeded in highly performing 3D gelatin–chitosan hybrid hydrogels of varying chitosan content in the presence of human platelet lysate and evaluated for their proliferation and osteogenic differentiation. Both bone marrow and adipose tissue human mesenchymal stem cells in gelatin–chitosan hybrid hydrogel 1 (chitosan content 8.1%) or gelatin–chitosan hybrid hydrogel 2 (chitosan 14.9%) showed high levels of viability (80%–90%), and their proliferation and osteogenic differentiation was significantly higher with human platelet lysate compared to fetal bovine serum, particularly in gelatin–chitosan hybrid hydrogel 1. Mineralization was detected early, after 21 days of culture, when human platelet lysate was used in the presence of osteogenic stimuli. Proteomic characterization of human platelet lysate highlighted 59 proteins mainly involved in functions related to cell adhesion, cellular repairing mechanisms, and regulation of cell differentiation. In conclusion, the combination of our gelatin–chitosan hybrid hydrogels with hPL represents a promising strategy for bone regenerative medicine using human mesenchymal stem cells.

Tissue engineers have explored a set of materials cues that can allow control of cell viability and guide cell fate and functions. Although the effect of substrate stiffness on cell fate has been extensively studied and established, the role of substrate stress relaxation, the ability of a substrate to dissipate cell-induced forces, is only emerging. Recently, several studies have demonstrated that substrate stress relaxation is an important mechanical cue for cell spreading, proliferation and differentiation in vitro. In this mini-review, we highlight the influence of substrate stress relaxation on cell behavior and function as well as provide future perspectives. Firstly, we describe the methods used for characterizing the stress relaxation/creep responses of hydrogels along with the molecular origin of viscoelastic properties. Then, we highlight the most recent studies elucidating the stress relaxation effect on cellular behavior using physically cross-linked hydrogels. Finally, we report on an emerging alternative design of tunable viscoelastic hydrogels: chemically cross-linked (reversible linkages) adaptable hydrogels that have been used as stable 3D cell culture platforms for a few years in the era of hydrogel systems.

International audience; Round-robin (RR) tests carried out under the direction of the Technical Committee 4, “Polymers, Polymer Composites and Adhesives,” of the European Structural Integrity Society (ESIS TC4) showed that the multispecimen methodology employed for the construction of the crack growth resistance curve (J vs crack extension, Δa) of polymers often does not provide reliable data because of the uncertainties associated with the measurement of Δa. With this in mind, the ESIS TC4 attention has been more recently focused on the analysis of a testing scheme based on the load separation criterion, which does not require the measurement of Δa. With the aim to employ this new approach into a standardized procedure, the degree of reproducibility of the results obtainable with the application of this testing scheme to ductile polymers has been assessed by means of multilaboratory RR testing exercises that started in 2011. An ESIS TC4 reference draft protocol was prepared and 10 laboratories participated in the RR activities. The present work describes the load separation criterion-based testing procedure recently examined by ESIS TC4 and gives a summary of the results obtained in the RR activities, which appear encouraging.

Composites of gelatin, chitosan and graphene layers functionalized with serinol pyrrole, containing hydroxyl groups, were prepared to create electrically conductive, mechanically robust and biodegradable hydrogels. The incorporation of hydrophilic graphene layers (up to 1% mass in wet condition) into the polymer matrix significantly improved mechanical and electrical properties. These composite hydrogels are promising candidates for use as conducting substrates for the growth of electro-responsive cells in tissue engineering.

This work presents high surface area sp2 carbon allotropes as important tools to design and prepare lightweight materials. Composites were prepared based on either carbon black (CB) or carbon nanotubes (CNT) or hybrid CB/CNT filler systems, with either poly(1,4-cis-isoprene) or poly(styrene-co-butadiene) as the polymer matrix. A correlation was established between the specific interfacial area (i.a.), i.e. the surface made available by the filler per unit volume of composite, and the initial modulus of the composite (G′γmin), determined through dynamic mechanical shear tests. Experimental points could be fitted with a common line, a sort of master curve, up to about 30.2 and 9.8 mass% as CB and CNT content, respectively. The equation of such master curve allowed to correlate modulus and density of the composite. Thanks to the master curve, composites with the same modulus and lower density could be designed by substituting part of CB with lower amount of the carbon allotrope with larger surface area, CNT. This work establishes a quantitative correlation as a tool to design lightweight materials and paves the way for large scale application in polymer matrices of innovative sp2 carbon allotropes.

This work aims at investigating the fracture behaviour of polyacrylamide hydrogels, which have been chosen for their ideal hyperelastic response and their widespread engineering and biomedical applications. The applicability of the energy separation principle to this class of hydrogels is analysed. This principle allows identifying the fracture initiation without visual monitoring of the specimen and to calibrate the geometry factor required to estimate the fracture toughness. Such innovative approach is compared to established methods: (i) single specimen methods, based on the determination of the energy release rate, for the calculation of fracture toughness; (ii) a multi-specimen methodology for the calibration of the geometry factor. Results show that the energy separation principle is valid for this class of hydrogels, and it can provide a toughness parameter corresponding to a small crack advancement.

Hydrogel has been bourgeoning in recent years as a scaffold in the tissue engineering thanks to its excellent ability to mimic natural extracellular matrix (ECM). Driven by enormous potential of hydrogels, we have developed a green, facile and simple synthesis approach to fabricate gelatin/polyethylene glycol (G/PEG) macroporous hydrogels by three steps process consist of gelation, lyophilization and post curing. Poly(ethylene glycol) diglycydyl ether (PEGDGE) was used as a crosslinking agent. The effect of altering the composition on hydrogel structure, mechanical properties, swelling and degradation resistance was evaluated by adding hydroxyethyl cellulose (HEC) into G/PEG system. Structural features and crosslinking interaction of the hydrogels were confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The morphology of the porous hydrogels was studied by scanning electron microscopy. Mechanical properties were measured by uniaxial tensile tests, and the characterization revealed non-linear and J-shaped stress-strain curves for all hydrogels, similar to those found for native ECM. The mechanical integrity of the hydrogels was monitored during hydrolytic degradation over time.

In this work, conductive polyurethane (PU) foam is developed to be used as skin electrode for long term use medical devices. Water based polyurethane and other eco-friendly substances are selected ...

Melt blending of hybrid nanofillers with rubber matrices could make rubber nanocomposites more attractive for industrial applications. In this work, the low-amplitude dynamic shear modulus of polyisoprene rubber filled with carbon nanotubes or nano-graphite, individually or in combination with carbon black, was measured. A rationalisation of the results highlighted interactive effects of carbon allotropes on the mechanical reinforcement of rubber nanocomposites. The filler–matrix interfacial area was identified as a parameter able to correlate the moduli values of different fillers, by reducing them to a common master curve.

Nonwoven fibrous mats based on semicrystalline networks are prepared starting from poly(ε-caprolactone) and properly combining electrospinning and sol–gel reactions. The mats are obtained as continuous, randomly oriented micrometric fibers with different network densities. The systems are subjected to thermomechanical cycles to investigate their one-way and two-way shape memory behavior. One-way tests aim at exploring the effects of the deformation temperature on the materials response, with particular interest to the less investigated cold-working conditions (i.e., deformation temperature below Tm). The materials display two-way shape memory capabilities (i.e., the ability to change between two distinguished shapes upon heating and cooling under a fixed nonzero stress) and the effect of the applied stress is explored. The shape memory characterization is accompanied by an ex situ SEM analysis, to describe the concurrent microstructural evolution during the macroscopic shape variation, and by the assessment of their biocompatibility, to explore the suitability of the nonwovens for biomedical applications. (Figure presented.).

Rational design and development of tailorable simple synthesis process remains a centerpiece of investigational efforts toward engineering advanced hydrogels. In this study, a green and scalable synthesis approach is developed to formulate a set of gelatin-based macroporous hybrid hydrogels. This approach consists of four sequential steps starting from liquid-phase pre-crosslinking/grafting, unidirectional freezing, freeze-drying, and finally post-curing process. The chemical crosslinking mainly involves between epoxy groups of functionalized polyethylene glycol and functional groups of gelatin both in liquid and solid state. Importantly, this approach allows to accommodate different polymers, chitosan or hydroxyethyl cellulose, under identical benign condition. Structural and mechanical anisotropy can be tuned by the selection of polymer constituents. Overall, all hydrogels show suitable structural stability, good swellability, high porosity and pore interconnectivity, and maintenance of mechanical integrity during 3-week-long hydrolytic degradation. Under compression, hydrogels exhibit robust mechanical properties with nonlinear elasticity and stress-relaxation behavior and show no sign of mechanical failure under repeated compression at 50% deformation. Biological experiment with human bone marrow mesenchymal stromal cells (hMSCs) reveals that hydrogels are biocompatible, and their physicomechanical properties are suitable to support cells growth, and osteogenic/chondrogenic differentiation, demonstrating their potential application for bone and cartilage regenerative medicine toward clinically relevant endpoints.

A key property of rubbers for sealing applications is their ability to rapidly recover the deformation during a fast movement of the counterparts, occurring in a transient deformation phase. In this work, a simple experimental test method (recovery test) is put forward to mimic the transient phase and to get insight into the behavior of the material during such phase. The effect of the addition of small quantities of carbon nanotubes (CNT) to a carbon black filled nitrile butadiene rubber on the sealing ability of the material was studied. The recovery tests show that the overall recovery behavior is related mostly to the material stress relaxation behavior, while the recovery behavior at very short times, which is indicative of the performance during a transient deformation phase, is strongly influenced by the material elastic modulus and, therefore, it is improved by the presence of CNT in the elastomeric composite. (C) 2016 Elsevier Ltd. All rights reserved.

Non-woven fibrous mats based on semicrystalline networks were prepared starting from poly(ε-caprolactone) and by combining electrospinning process and sol-gel crosslinking reaction. The mats were subjected to proper thermo-mechanical cycles to investigate their two-way shape memory capabilities (i.e. the possibility to change between two distinguished shapes upon heating and cooling), and an improvement of the two-way behaviour was researched through the application of a training cycle. An ex-situ SEM analysis described the microstructural evolution accompanying the two-way shape memory cyclic response.

This work shows the remarkable anisotropic nonlinear mechanical behavior of nanocomposites based on carbon nanotubes and poly(1,4-cis-isoprene), prepared by mechanical mixing, calendering, and compression molding. The dynamic-mechanical moduli were measured as a function of the applied strain and along specific directions. The specimens revealed, at all filler contents, an orthotropic and transversally isotropic response, which means properties very similar inside the sheet plane and very different from those in the orthogonal direction. This response was correlated to the material structure by means of bright field transmission electron microscopy analysis, coupled with electron diffraction measurements, so to observe the nanofiller structuring through the specimen thickness. Preferential orientation of nanotubes and alternate areas containing large or low CNT amount were revealed. This work shows that energy dissipation is not isotropic in CNT-filled polymer nanocomposites and aims at giving a contribut...

In this work it is shown that hydroxyethylcellulose (HEC) can be employed for preparing macroporous polyacrylamide (PAAm) hydrogels with tailored morphology and mechanical properties. By changing the HEC content in the reaction mixture hydrogels with different pore sizes and degrees of interconnectivity can be synthesized. The equilibrium swelling ratio in 0.1 M NaCl increases with the amount of HEC employed. Tensile tests run on equilibrated hydrogels show that these materials behave as rubber-like materials. Their mechanical stiffness decreases regularly as the amount of HEC, and therefore their porosity, is increased. A more complex trend is observed for elongation and stress at break, which display a maximum at intermediate contents of HEC.

Under high-energy diets, amino acid N is difficult to dispose of, as a consequence of the availability of alternative substrates. We found, recently, that WAT contains a complete functional urea cycle, we analyzed the possible overall changes in the WAT urea cycle (and other-related amino acid metabolism gene expressions) in rats subjected to a cafeteria diet. Adult female Wistar rats were fed control or simplified cafeteria diets. Samples of WAT sites: mesenteric, periovaric, retroperitoneal and subcutaneous, were used for the estimation of all urea cycle enzyme activities and gene expressions. Other key amino acid metabolism gene expressions, and lactate dehydrogenase were also measured. Subcutaneous WAT showed a differentiated amino acid metabolism profile, since its cumulative (whole site) activity for most enzymes was higher than the activities of the other sites studied. After one month of eating an energy-rich cafeteria diet, and in spite of doubling the size of WAT, the transforming capacity of most amino acid metabolism enzymes remained practically unchanged in the tissue. This was not only due to limited changes in the overall enzyme activity, but also a consequence of a relative decrease in the expression of the corresponding genes. Overall, the results of this study support the consideration of WAT as an organ, disperse but under uniform control. The metabolic peculiarities between its different sites, and their ability to adapt to different energy availability conditions only add to the variable nature of adipose tissue. We have presented additional evidence of the significant role of WAT in amino acid metabolism.

Micro-injection moulding is one of the key manufacturing technologies for the mass production of high value polymeric miniaturized-components.However, this process is not just a straightforward down scaling of the conventional injection moulding technique. Indeed, during the micro-injection the polymer melt is forced to flow at high strain rates through very small channels in non-isothermal conditions, and this can lead to complex microstructures and to parts with unexpected performances.In this work, the relationships among the processing conditions, the mechanical properties and the microstructural characteristics of miniaturized specimens obtained by injection moulding were investigated. Two model systems were considered with the same filler content of 15% wt. (HDPE-talc and HDPE-glass beads), representative of two different types of micro-composites: containing lamellar and spherical micro-particles, respectively.The attention was focused on the influence of the filler type and the process conditions ...

High-energy (hyperlipidic) cafeteria diets induce insulin resistance limiting glucose oxidation, and lower amino acid catabolism. Despite high amino-N intake, amino acids are preserved, lowering urea excretion. We analysed how energy partition induced by cafeteria diet affects liver ammonium handling and urea cycle. Female and male rats were fed control or cafeteria diets for 30 days. There was a remarkable constancy on enzyme activities and expressions of urea cycle and ammonium metabolism. The key enzymes controlling urea cycle: carbamoyl-P synthase 1, arginino-succinate synthase and arginase expressions were decreased by diet (albeit more markedly in males), and their activities were correlated with the gene expressions. The effects observed, in ammonium handling enzyme activities and expressions behaved in a way similar to that of the urea cycle, showing a generalized downregulation of liver amino acid catabolism. This process was affected by sex. The different strategies of amino-N handling by females and males further modulated the preservation of 2-amino N under sufficient available energy. The effects of sex were more marked than those of diet were, since different metabolism survival strategies changed substrate partition and fate. The data presented suggest a lower than expected N flow to the liver, which overall importance for amino acid metabolism tends to decrease with both cafeteria diet and female sex. Under standard conditions, liver availability of ammonium was low and controlled. The situation was unchanged (or even lowered) in cafeteria-fed rats, ultimately depending on intestinal amino acid catabolism.

Poly(e-caprolactone)-based non-woven fibrous mats showing excellent one-way shape memory properties were obtained through a straightforward approach by combining electrospinning process and sol–gel reaction. A solution of partially crosslinked α,ω-triethoxysilane-terminated poly(e-caprolactone) was used to obtain bead-free fibers through electrospinning. Non-woven mats with different crosslinking degrees have been prepared and the effect of the different crosslinking extent and of the microfibrous structure were correlated to the mechanical and shape memory properties of the material. The evolution of fiber architecture within the non-woven mat following deformation and shape memory cycles was also investigated.

In this work an innovative fracture mechanics experimental methodology for J testing of rubbers was investigated and tentatively applied. This single-specimen approach, based on the energy separation principle, would allow to identify the point of fracture initiation without any visual observation of the test, and to evaluate the material resistance to crack initiation (JIc). For comparison, fracture initiation was detected also by a methodology based on the visual observation of the crack growth by a camera. Although both methodologies evidenced that fracture initiation in rubbers is a progressive process, the energy separation based approach results to be a promising methodology.