195 research outputs found
Biofilm contamination in confined space stations: reduction, coexistence or an opportunity?
The prolonged human permanence in confined environments in space, such as in the case of the International Space Station, has inadvertently fostered conditions leading to uncontrolled microbial proliferation on surfaces, known as biofilm. Biofilm presence represents a challenge in critical spacecraft systems, that can lead to contamination issues and systems loss of function due to biofouling phenomena. This scenario is further complicated by microgravity that has a controversial role on biofilm growth and formation. Biocontamination can be a limiting factor in human long-term mission in outer Earth orbit and an economic and health issue on ISS. This study addresses the pressing need for effective antimicrobial strategies against such resilient biofilms in confined environments where the usage of biocidal chemical compounds is strictly controlled due to toxicity dangers. Traditional methods can be complemented by advanced antimicrobial coatings techniques. A promising approach is based on the oxygen plasma as coating platform. The technology can be potentially extended to a wide range of antibiofilm agents (e.g., peptides, bacteriophages, nanoparticles, quorum sensing disrupting agents, etc.) and substrates (e.g., metal, plastic, ceramic) showing an exceptional flexibility. An alternative vision of the biofilm challenge can be inspired by the dual nature of biofilms, addressed as “good” or “bad” depending on the specific application. Indeed, biofilm have a great potential in closed systems as small space habitat (e.g., ISS) that can be inspired by their role in “large space habitat” as planet Earth itself. The replication of such a complex biological equilibrium is an open challenge
Dynamic behaviour of Multilamellar Vesicles under Poiseuille flow
Surfactant solutions exhibit multilamellar surfactant vesicles (MLVs) under
flow conditions and in concentration ranges which are found in a large number
of industrial applications. MLVs are typically formed from a lamellar phase and
play an important role in determining the rheological properties of surfactant
solutions. Despite the wide literature on the collective dynamics of flowing
MLVs, investigations on the flow behavior of single MLVs are scarce. In this
work, we investigate a concentrated aqueous solution of linear alkylbenzene
sulfonic acid (HLAS), characterized by MLVs dispersed in an isotropic micellar
phase. Rheological tests show that the HLAS solution is a shear-thinning fluid
with a power law index dependent on the shear rate. Pressure-driven shear flow
of the HLAS solution in glass capillaries is investigated by high-speed video
microscopy and image analysis. The so obtained velocity profiles provide
evidence of a power-law fluid behaviour of the HLAS solution and images show a
flow-focusing effect of the lamellar phase in the central core of the
capillary. The flow behavior of individual MLVs shows analogies with that of
unilamellar vesicles and emulsion droplets. Deformed MLVs exhibit typical
shapes of unilamellar vesicles, such as parachute and bullet-like. Furthermore,
MLV velocity follows the classical Hetsroni theory for droplets provided that
the power law shear dependent viscosity of the HLAS solution is taken into
account. The results of this work are relevant for the processing of
surfactant-based systems in which the final properties depend on flow-induced
morphology, such as cosmetic formulations and food products.Comment: 11 pages, 7 figures. Accepted for publication in Soft Matte
Numerical Simulations of Vorticity Banding of Emulsions in Shear Flows
Multiphase shear flows often show banded structures that affect the global
behavior of complex fluids e.g. in microdevices. Here we investigate
numerically the banding of emulsions, i.e. the formation of regions of high and
low volume fraction, alternated in the vorticity direction and aligned with the
flow (shear bands). These bands are associated with a decrease of the effective
viscosity of the system. To understand the mechanism of banding experimentally
observed we have performed interface resolved simulations of the two-fluid
system. The experiments were perfomed starting with a random distribution of
droplets which, under the applied shear, evolves in time resulting in a phase
separation. To numerically reproduce this process, the banded structures are
initialized in a narrow channel confined by two walls moving in opposite
direction. We find that the initial banded distribution is stable when droplets
are free to merge and unstable when coalescence is prevented. In this case,
additionally, the effective viscosity of the system increases, resembling the
rheological behavior of suspensions of deformable particles. Droplets
coalescence, on the other hand, allows emulsions to reduce the total surface of
the system and hence the energy dissipation associated to the deformation,
which in turn reduces the effective viscosity
Impact of surfactant polydispersity on the phase and flow behavior in water: the case of Sodium Lauryl Ether Sulfate
This study delves into the impact of molecular polydispersity on the phase behavior of Sodium Lauryl Ether Sulfate (SLES) surfactant, aiming to deepen understanding of its implications for fundamental science and industrial applications. SLE3S is utilized as a model compound: a comprehensive characterization of molecular polydispersity is conducted using Gas Chromatography–Mass Spectrometry and Nuclear Magnetic Resonance spectroscopy, juxtaposing the findings with those for SLE1S. Our comprehensive investigative approach entails: (i) employing Time-Lapse dissolution experiments in microchannel geometries to observe the dissolution and phase transitions; (ii) utilizing polarized light microscopy, confocal microscopy, and Small Angle X-ray Scattering for microstructure identification assessments; (iii) conducting rheological evaluations at various concentrations and temperatures to determine their effects on the surfactant properties. The findings reveal that SLE3S, being more polydisperse, demonstrates complex phase behavior not observed in the less polydisperse SLE1S. Notably, SLE3S exhibits a unique concentration domain, corresponding to a concentration of about 60 %wt, where hexagonal (H), cubic, and lamellar (Lα) phases coexist, resulting in highly viscoelastic heterogeneous mixtures. This behavior is attributed to the local segregation of surfactant components with varying polarity, underscoring the crucial role of molecular polydispersity in the phase behavior of SLES surfactants
Diffusion induced anisotropic cancer invasion: A novel experimental method based on tumor spheroids
Tumour invasion is strongly influenced by microenvironment and, among other
parameters, chemical stimuli play an important role. An innovative methodology
for the quantitative investigation of chemotaxis in vitro by live imaging of
morphology of cell spheroids, in 3D collagen gel, is presented here. The assay
was performed by using a chemotactic chamber to impose a controlled gradients
of nutrients (glucose) on spheroids, mimicking the chemotactic stimuli
naturally occurring in the proximity of blood vessels. Different tumoral cell
lines (PANC-1 and HT-1080) are compared to non-tumoral ones (NIH/3T3).
Morphology response is observed by means a Time-lapse workstation equipped with
an incubating system and quantified by image analysis techniques. Description
of invasion phenomena was based on an engineering approach, based on transport
phenomena concepts. As expected, NIH/3T3 spheroids are characterized by a
limited tendency of cells to invade the surrounding tissue, unlike PANC-1 and
HT-1080 that show relatively stronger response to gradients.Comment: 14 pages, 9 figure
Compressional stress stiffening & softening of soft hydrogels - how to avoid artefacts in their rheological characterisation
Hydrogels have been successfully employed as analogues of the extracellular matrix to study biological processes such as cells' migration, growth, adhesion and differentiation. These are governed by many factors, including the mechanical properties of hydrogels; yet, a one-to-one correlation between the viscoelastic properties of gels and cell fate is still missing from literature. In this work we provide experimental evidence supporting a possible explanation for the persistence of this knowledge gap. In particular, we have employed common tissues' surrogates such as polyacrylamide and agarose gels to elucidate a potential pitfall occurring when performing rheological characterisations of soft-materials. The issue is related to (i) the normal force applied to the samples \textit{prior} to performing the rheological measurements, which may easily drive the outcomes of the investigation outside the materials' linear viscoelastic regime, especially when tests are performed with (ii) geometrical tools having unbefitting dimensions (i.e., too small). We corroborate that biomimetic hydrogels can show either compressional stress softening or stiffening, and we provide a simple solution to quench these undesired phenomena, which would likely lead to potentially misleading conclusions if they were not mitigated by a good practice in performing rheological measurements, as elucidated in this work
i-Rheo-optical assay: Measuring the viscoelastic properties of multicellular spheroids
This study introduces a novel mechanobiology assay, named “i-Rheo-optical assay”, that integrates rheology with optical microscopy for analysing the viscoelastic properties of multicellular spheroids. These spheroids serve as three-dimensional models resembling tissue structures. The innovative technique enables real-time observation and quantification of morphological responses to applied stress using a cost-effective microscope coverslip for constant compression force application. By bridging a knowledge gap in biophysical research, which has predominantly focused on the elastic properties while only minimally exploring the viscoelastic nature in multicellular systems, the i-Rheo-optical assay emerges as an effective tool. It facilitates the measurement of broadband viscoelastic compressional moduli in spheroids, here derived from cancer (PANC-1) and non-tumoral (NIH/3T3) cell lines during compression tests.
This approach plays a crucial role in elucidating the mechanical properties of spheroids and holds potential for identifying biomarkers to discriminate between healthy tissues and their pathological counterparts. Offering comprehensive insights into the biomechanical behaviour of biological systems, i-Rheo-optical assay marks a significant advancement in tissue engineering, cancer research, and therapeutic development
Collective rotational motion of freely expanding T84 epithelial cell colonies
Coordinated rotational motion is an intriguing, yet still elusive mode of collective cell migration, which is relevant in pathological and morphogenetic processes. Most of the studies on this topic have been carried out on epithelial cells plated on micropatterned substrates, where cell motion is confined in regions of well-defined shapes coated with extracellular matrix adhesive proteins. The driver of collective rotation in such conditions has not been clearly elucidated, although it has been speculated that spatial confinement can play an essential role in triggering cell rotation. Here, we study the growth of epithelial cell colonies freely expanding (i.e. with no physical constraints) on the surface of cell culture plates and focus on collective cell rotation in such conditions, a case which has received scarce attention in the literature. One of the main findings of our work is that coordinated cell rotation spontaneously occurs in cell clusters in the free growth regime, thus implying that cell confinement is not necessary to elicit collective rotation as previously suggested. The extent of collective rotation was size and shape dependent: a highly coordinated disc-like rotation was found in small cell clusters with a round shape, while collective rotation was suppressed in large irregular cell clusters generated by merging of different clusters in the course of their growth. The angular motion was persistent in the same direction, although clockwise and anticlockwise rotations were equally likely to occur among different cell clusters. Radial cell velocity was quite low as compared to the angular velocity, in agreement with the free expansion regime where cluster growth is essentially governed by cell proliferation. A clear difference in morphology was observed between cells at the periphery and the ones in the core of the clusters, the former being more elongated and spread out as compared to the latter. Overall, our results, to our knowledge, provide the first quantitative and systematic evidence that coordinated cell rotation does not require a spatial confinement and occurs spontaneously in freely expanding epithelial cell colonies, possibly as a mechanism for the system
Amputação do reto convencional x laparoscópica no tratamento do câncer do reto distal após quimioirradiação neoadjuvante: resultados de estudo prospectivo e randomizado
OBJECTIVE: The aims of this study were to evaluate the safety and efficacy of laparoscopic abdominoperineal resection compared to conventional approach for surgical treatment of patients with distal rectal cancer presenting with incomplete response after chemoradiation. METHOD: Twenty eight patients with distal rectal adenocarcinoma were randomized to undergo surgical treatment by laparoscopic abdominoperineal resection or conventional approach and evaluated prospectively. Thirteen underwent laparoscopic abdominoperineal resection and 15 conventional approach. RESULTS: There was no significant difference (pOBJETIVO: Comparar os resultados de eficácia e segurança do emprego da operação de amputação do reto por via laparoscópica e por via convencional no tratamento cirúrgico de pacientes com câncer do reto distal que apresentaram resposta incompleta a quimioirradiação pré-operatória. MÉTODO: Vinte e oito pacientes com adenocarcinoma de reto distal foram randomizados para se submeter à amputação do reto por via laparoscópica ou à amputação do reto por via convencional. Treze pacientes submeteram-se à amputação do reto por via laparoscópica e 15 à amputação do reto por via convencional. RESULTADOS: Não houve diferença significativa (
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