The elastic response of a living cell is affected by its physiological state. This property provides mechanical fingerprints of a cell’s dysfunctionality. The softness (kilopascal range) and ...thickness (2–15 μm) of mammalian cells imply that the force exerted by the probe might be affected by the stiffness of the solid support. This observation makes infinite sample thickness models unsuitable to describe quantitatively the forces and deformations on a cell. Here, we report a general theory to determine the true Young’s moduli of a single cell from a force-indentation curve. Analytical expressions are deduced for common geometries such as flat punches, paraboloids, cones, needles, and nanowires. For a given cell and indentation, the influence of the solid support on the measurements is reduced by using sharp and high aspect ratio tips. The theory is validated by finite element simulations.
Display omitted
•The atmospheric plasma treatment improves the wettability of PLA substrates.•Best wettability for a 10mm nozzle–substrate distance and a 100mms−1 advance rate.•PLA plasma surface ...energy gets values over 60mJm−2 twice the untreated sample value.•Polar contribution is important in surface wettability, increasing up to 32.8mJm−2.•Increase surface roughness and polar groups after treatment with atmospheric plasma.
The main objective of this experimental study is the validation of the technique of atmospheric plasma with the aim of improving the surface energy of the polylactic acid (PLA) for further adhesion uses. The wettability of PLA has been improved with the application of an atmospheric plasma surface treatment. This method provides good adhesion properties with the optimizing the process parameters in terms of the nozzle–substrate distance and sample advance rate. In order to achieve that goal, a new and environmentally friendly technology has been used which is based on the use of air atmospheric plasma. The effects of the surface treatment on this type of substrates have been analyzed. The macroscopic effects of the process parameters have been determined using contact angle measurements and subsequent surface free energy (SFE) calculation. In addition, the chemical changes at the topmost layers have been studied using X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared spectroscopy (FTIR). Surface topography changes due to the plasma-acting mechanisms have been evaluated with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The obtained results show a remarkable increase in surface free energy from 37.1mJm−2 up to values of 60mJm−2 thus indicating the effectiveness of the air plasma treatment. The main advantage of this technology is that the industrial process is continuous, it is easy to establish in current production systems and it does not generate wastes.
Free-living microorganisms may become suitable models for recovery of non-essential and essential heavy metals from wastewater bodies and soils by using and enhancing their accumulating and/or ...leaching abilities. This review analyzes the variety of different mechanisms developed mainly in bacteria, protists and microalgae to accumulate heavy metals, being the most relevant those involving phytochelatin and metallothionein biosyntheses; phosphate/polyphosphate metabolism; compartmentalization of heavy metal-complexes into vacuoles, chloroplasts and mitochondria; and secretion of malate and other organic acids. Cyanide biosynthesis for extra-cellular heavy metal bioleaching is also examined. These metabolic/cellular processes are herein analyzed at the transcriptional, kinetic and metabolic levels to provide mechanistic basis for developing genetically engineered microorganisms with greater capacities and efficiencies for heavy metal recovery, recycling of heavy metals, biosensing of metal ions, and engineering of metalloenzymes.
The influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNS N08031 stainless steel in a contaminated phosphoric acid solution were evaluated. ...Stabilisation of the passive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemical impedance spectroscopy (EIS) measurements, Mott–Schottky analysis and X-ray photoelectron spectroscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The film formed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed the presence of fluoride ions.
The influence of alloying elements on the electrochemical and semiconducting properties of thin passive films formed on several steels (carbon steel, ferritic and austenitic stainless steels) has ...been studied in a highly concentrated lithium bromide (LiBr) solution at 25°C, by means of potentiodynamic tests and Mott–Schottky analysis. The addition of Cr to carbon steel promoted the formation of a p-type semiconducting region in the passive film. A high Ni content modified the electronic behaviour of highly alloyed austenitic stainless steels. Mo did not modify the electronic structure of the passive films, but reduced the concentration of defects.
•The addition of Cr to carbon steel promotes p-type semiconductivity.•Passive films formed on stainless steels are made up of complex spinel oxides.•Ni modifies the electronic behaviour of highly alloyed austenitic stainless steels.
Understanding the relationship between the mechanical properties of living cells and physiology is a central issue in mechanobiology. Mechanical properties are used as fingerprints of the ...pathological state of a single cell. The force exerted on a cell is influenced by the stiffness of the solid support needed to culture it. This effect is a consequence of the cell's boundary conditions. It causes a cell to appear with mechanical properties different from their real values. Here we develop a bottom effect viscoelastic theory to determine the viscoelastic response of a cell. The theory transforms a force-distance curve into the cell's Young's modulus, loss modulus, relaxation time or viscosity coefficient with independence of the stiffness of the rigid support. The theory predicts that, for a given indentation, the force exerted on the cell's periphery will be larger than on a perinuclear region. Results based on the use of semi-infinite contact mechanics models introduce large numerical errors in the determination of the mechanical properties. Finite element simulations confirm the theory and define its range of applicability.
Understanding the relationship between the mechanical properties of living cells and physiology is a central issue in mechanobiology.
The passive and transpassive behaviour of Alloy 31, a highly alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine solution (400g/l) at 25°C using ...potentiostatic polarisation combined with electrochemical impedance spectroscopy and Mott–Schottky analysis. The passive film formed on Alloy 31 has been found to be p-type and/or n-type in electronic character, depending on the film formation potential. The thickness of the film formed at potentials within the passive region increases linearly with applied potential. The film formed at transpassive potentials is thinner and more conductive than the film formed within the passive region. These observations are consistent with the predictions of the Point Defect Model for passive and transpassive films on metals and alloys.
In this work, karanja oil has been epoxidized and further used as biobased plasticizer to improve some properties of poly (lactic acid) (PLA). The use of epoxidized karanja oil (EKO) has been studied ...because karanja oil is used in organic farming as an insecticide and generating an epoxidation of the oil can act as a PLA plasticizer. Melt extrusion was used to plasticize PLA with different EKO amounts in the 0–10 wt%. The formulations with EKO decrease the glass transition temperature as the EKO content increases and, in addition, generates an increase in elongation at break. Plasticizer saturation is observed by scanning electron microscopy (SEM) above 5% of EKO. PLA formulation with 5 wt% shows an optimal balance between the improvement of the fragility of the material, improving the elongation at breakage by 77%, using a relatively small concentration of plasticizer. Moreover, all materials were disintegrated under composting conditions at laboratory scale level.
•Karanja oil has been seccessfully epoxidized and use as PLA plasticizer.•Epoxidized karanja oil improved the ductility of PLA.•Epoxidized karanja oil improved thermar stability of PLA.•PLA with 5% EKO presents a balance between resistant and ductile properties.•All formulations were fully disintegrated under composting.
The development of high-resolution, label-free, noninvasive, and subsurface microscopy methods of living cells remains a formidable problem. Force-microscopy-based stiffness measurements contribute ...to our understanding of single-cell nanomechanics. The elastic properties of the cell’s outer structures, such as the plasma membrane and actin cytoskeleton, dominate stiffness measurements, which in turns prevents the imaging of intracellular structures. We propose that the above limitation could be overcome by combining 2D sections of the cell’s viscoelastic properties. We show the simultaneous imaging of the outer cell’s cytoskeleton and the organelles inside the nucleus. The elastic component of interaction force carries information on the cell’s outer elements as the cortex and the actin cytoskeleton. The inelastic component is sensitive to the hydrodynamic drag of the inner structures such the nucleoli.
PDF
