189 research outputs found
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
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
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
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
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 (
The MASSIMO system for the safeguarding of historic buildings in a seismic area: operationally-oriented platforms
In this paper, the non-invasive system MASSIMO is presented for the monitoring and the seismic vulnerability mitigation of the cultural heritage. It integrates ground-based, airborne and space-borne remote sensing tools with geophysical and in situ surveys to provide the multi-spatial (regional, urban and building scales) and multi-temporal (long-term, short-term, near-real-time and real-time scales) monitoring of test areas and buildings. The measurements are integrated through web-based GIS and 3D visual platforms to support decision-making stakeholders involved in urban planning and structural requalification. An application of this system is presented over the Calabria region for the town of Cosenza and a test historical complex
The Monitoring of Urban Environments and Built-Up Structures in a Seismic Area: Web-Based GIS Mapping and 3D Visualization Tools for the Assessment of the Urban Resources
In this paper, a non-invasive infrastructural system
called MASSIMO is presented for the monitoring and
the seismic vulnerability mitigation of cultural
heritages. It integrates ground-based, airborne and
space-borne remote sensing tools with geophysical and
in situ surveys to provide a multi-spatial (regional,
urban and building scales) and multi-temporal (longterm,
short-term and near-real-time scales) monitoring
of test areas and buildings. The measurements are
integrated through web-based Geographic Information
System (GIS) and 3-dimensional visual platforms to
support decision-making stakeholders involved in urban
and structural requalification planning. An application
of this system is presented over the Calabria region for
the town of Cosenza and a test historical complex.The present work is supported and funded by the Italian
Ministry of Education, University and Research
(MIUR) under the research project PON01-02710
"MASSIMO" - "Monitoraggio in Area Sismica di
SIstemi MOnumentali".Published9-134T. Sismologia, geofisica e geologia per l'ingegneria sismicaN/A or not JC
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