Heterogeneity Governs 3D-Cultures of Clinically Relevant Microbial Communities

The intrinsic heterogeneity of bacterial niches should be retained in in vitrocultures to represent the complex microbial ecology. As a case study,mucin-containing hydrogels -CF-Mu3Gel - are generated by diffusion-inducedgelation, bioinspired on cystic fibrosis (CF) mucus, and a microbial nichechallenging current therapeutic strategies. At breathing frequency, CF-Mu3Gelexhibits aG′andG′′equal to 24 and 3.2 Pa, respectively. Notably, CF-Mu3Gelexhibits structural gradients with a gradual reduction of oxygen tensionacross its thickness (280–194μmol L−1). Over the culture period, a steepdecline in oxygen concentration occurs just a few millimeters below theair–mucus interface in CF-Mu3Gel, similar to those of CF airway mucus.Importantly, the distinctive features of CF-Mu3Gel significantly influencebacterial organization and antimicrobial tolerance in mono- and co-cultures ofStaphylococcus aureusandPseudomonas aeruginosathat standard culturesare unable to emulate. The antimicrobial susceptibility determined inCF-Mu3Gel corroborates the mismatch on the efficacy of antimicrobialtreatment between planktonically cultured bacteria and those in patients.With this example-based research, new light is shed on the understanding ofhow the substrate influences microbial behavior, paving the way for improvedfundamental microbiology studies and more effective drug testing anddevelopment

Methyl methacrylate and respiratory sensitization: A Critical review

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants.The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer

Adesione di rivestimenti Ni-P su ABS mediante prova di frammentazione

Si è studiata l’adesione di uno strato di nichel ottenuto per deposizione autocatalitica su substrato polimerico (ABS, acrilonitrile butadiene stirene) mediante la prova di frammentazione. La prova di frammentazione -sviluppata per valutare l’adesione in compositi polimero/ceramico e successivamente estesa al caso di film ceramici su substrato polimerico- permette di caratterizzare l’adesione in termini di sforzo di taglio critico all’interfaccia substrato-rivestimento. La prova consiste nel sottoporre a trazione uniassiale un provino del materiale rivestito e nel rilevare il numero di frammenti che si formano nella direzione perpendicolare a quella di trazione. La lunghezza media dei frammenti da un certo punto della prova in poi si mantiene costante; da tale lunghezza si ricava la resistenza a taglio dell’interfaccia che è il parametro di adesione. Sono stati considerati campioni con quattro diverse combinazioni di tenore di polibutadiene e tempo di mordenzatura

Effect of chemical activity jumps on the viscoelastic behavior of an epoxy resin: Phyiscal aging response in carbon dioxide pressure jumps

We report the results fromtensile creep tests performed on an epoxy resin in the presence of carbon dioxide at different pressures (Pco2) and at a constant temperature below the glass-transition temperature. Time-Pco2 superposition was applied to the data to account for the plasticization effect because of the interaction between the carbon dioxide molecules and the polymer. In addition, physical aging of the epoxy films was investigated with sequential creep tests after carbon dioxide pressure down-jumps at constant temperature and after temperature down-jumps at constant carbon dioxide pressure. The isothermal pressure down-jump experiments showed physical aging responses similar to the isobaric temperature down-jump experiments. However, the aging rate for the CO2 jump was slightly lower than that for the temperature-jump (T-jump) experiments, and the retardation time for the Pco2-jump experiments was up to 6.3 times longer than for the T-jump conditions. The results are discussed in terms of classical physical aging and structural recovery frameworks, and speculation about the differences in the energy landscape resulting from the Pco2-jump and T-jump experiments is also made

Rapid tooling for injection molding inserts

Injection molding is a widespread manufacturing technology for mass production of polymeric parts. Conventionally, fused polymers are injected at high pressure in a metallic mold. This tool is typically characterized by high manufacturing costs and times, making the injection molding process not affordable for small batches or prototypal applications. Additive Manufacturing represents a practical solution to cut down tooling costs and times of molds and inserts. In this work, FDM (Fused Deposition Technology) has been considered as candidate technology to produce polymeric inserts for injection molding. Considering the commercially available filaments for FDM, a PEI (Polyetherimide) grade has been selected as tooling material for the injection of a part made of Polypropylene. The PEI grade represents a good compromise between manufacturing costs and thermo-mechanical properties required for the application. The PEI grade has been characterized with DSC (Differential Scanning Calorimetry), DMA (Dynamical Mechanical Analysis) and compression tests. The data gathered were used to set up 2D simplified thermo-mechanical finite element analyses, simulating the response of the PEI inserts subjected to repeated injection molding cycles. The simulations confirmed that the PEI grade is a good candidate tooling material but the progressive tool heating could lead to prolonged cooling time of the Polypropylene part. Finally, some PEI inserts were 3D printed with FDM and tested in a real injection molding machine injecting POM. In total, 20 POM parts have been injected correctly without relevant damaging of the PEI inserts

Development of empirical hepatic biomechanical models through experimental characterization of porcine and bovine livers

INTRODUCTION Complex models of the liver are envisioned to support drug development with high-throughput experimental platforms. The chemo-mechanical niche, the set of biochemical and mechanical characteristics of a physiological or a pathological organ, greatly influences the fate and the behavior of cultured cells for the in vitro reproduction in vivo-like responses. The studies of the mechanical properties of liver are few, and empirical hepatic biomechanical models, dataset obtained through direct analyses of the organ, are widely dispersed. The differences between experimental techniques, conditions, or organ sources2 limits the possibility to compare them. Pioneering studies rely on indirect methods (i.e., magnetic resonance elastography) 3,4. Moreover, the intra-and inter-species variability and anisotropy of these tissues are not addressed. In this study we focus on the development of a methodology to experimentally evaluate the mechanical properties of the liver, in response to small shear deformations in oscillatory regime and to axial deformation applied in compression in quasi-static tests, to reproduce the physiological stresses on the organ by blood perfusion and surrounding organs. EXPERIMENTAL METHODS Porcine and bovine livers were kindly provided by a local butcher less than to 12 hours after the slaughter. Organs were sectioned along three spatial planes (Figure 1). From each slice, cylindrical specimens ( 25 mm) were cut. To prevent dehydration and coagulation, each specimen was injected from the top face, the bottom face, and from the side with 10 ml of isotonic (4% w/v) Na-citrate, in H2O, then immersed in the same solution, and finally stored at 4 °C until the measurements. Preliminary analyses were performed with a rheometer (MCR 502e, Anton-Paar, AT) mounting a 25 mm parallel plate geometry, and imposing different preload forces in the range 0.1 N – 5 N. The mechanical properties of the organs were then measured at small deformations in oscillatory regime in response to shear stresses and quasi-static compressions. Different livers were obtained and analyzed to evaluate the variability within the same species. Porcine and bovine livers were evaluated with the same test protocols, to compare interspecies variability. The effect of different preservation techniques was investigated on samples that were previously frozen at different temperatures up to -120°C. RESULTS AND DISCUSSION The study of relation between the gap among plates and the normal force indicates that preloads greater than 1 N progressively produced structural changes on specimens, as the response significantly varied with the higher preloads. The set preload was therefore considered for the following tests. Shear analyses highlighted that the liver tissues, both porcine and bovine, are characterized by a gel-like behavior, with a conservative modulus (G’) higher than the dissipative ones (G’’) at all the analyzed frequencies. Only sectioning the livers in the XZ plane (Fig. 1) resulted in reproducibility of G’, G’’, and loss factor (tan δ) data, with G’ and G’’ always ranging between 300-400 Pa and 70-100 Pa respectively, indicating the anisotropy of the tissues. Compressive modulus of organs did not display a significant variability between species and highlighted a similar anisotropy to the one observed with rheological analyses. The evaluated G’, G’’, and tan δ fall within the range of data from magnetic resonance elastography (MRE) 4. Up to now, the cryopreservation of samples seems appropriate. Thawed samples displayed mechanical properties that are aligned with the ones of fresh samples. CONCLUSION The developed procedure can be implemented to build an empirical model of the hepatic biomechanics as a reference when engineering a three-dimensional matrix to produce in vitro models of the liver. The protocol is proposed to characterize the hepatic biomechanics, even if, in principle, the same methodology can be applied to other types of biological soft tissue. The gel-like behavior of the hepatic tissues suggests the feasibility of producing hydrogels-based 3D models of the liver