Life & Health Sciences

Dr Kathia Zaleta

Dr María-Cristina Del Rincon-Castro

Dr Barbara Reaves

Prof. Adrian Wolstenholme

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Size determination of microbubbles in optical microscopy: a best-case scenario


ABSTRACT

Microbubble-based ultrasound contrast agents are used in clinical settings to enhance backscattered ultrasound signals from blood during perfusion and blood flow measurements. The dynamics of microbubbles contained in ultrasound contrast agents are typically studied with a high-speed camera attached to a microscope. Such microbubbles, with resting diameters between 1 µm and 7 µm, are considered in optical focus if the bubble centers are in the focal plane of the objective lens. Nonetheless, when a three-dimensional object, a stack of infinitely thin two-dimensional layers, is imaged through a microscope, the image formed onto the charge coupled device element consists of contributions from all layers. If a bubble is larger than the depth of focus, the part of the bubble above the focal plane influences the image formation and therefore the bubble size measured. If a bubble is of a size in the order of the wavelengths of the light used, the system resolution and the segmentation method influence the bubble size measured. In this study, the projections of three dimensional microbubbles (hollow spheres) were computed with an ideal, weighted three-dimensional point spread function to find out under which circumstances the optical image formation leads to a significant deviation in measurement of the actual size. The artificial images were subjected to segmentation techniques for objectively comparing original microbubble sizes with measured microbubble sizes. Results showed that a systematic error was observed for objects in focus with radius ≤ 1.65µm. Also it was concluded that even though a three-dimensional object is in focus, there is discrepancy of up to 0.66% in size measurement. In addition, size measurement of an object for the same shift above and below focus could differ by up to 3.6%. Moreover, defocusing above 25% severely deviates size measurements while defocusing up to 90% could result in mean percentage error of up to 67.96.


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Harmonic response from microscopic antibubbles


ABSTRACT

An antibubble is a gas bubble containing a liquid droplet core. Both the droplet and the gas bubble are typically surrounded by stabilising shells. Owing to electrostatic forces exerted by these shells, core droplets of micrometer diameter do not readily coalesce with the surrounding liquid medium. Owing to the incompressibility of the liquid droplet core, antibubbles will oscillate asymmetrically, i.e., the radial excursion amplitude of the surface is greater during expansion than during contraction, when subjected to diagnostic ultrasound. Consequently, the harmonic content of the ultrasound signal radiated from antibubbles must be higher than that from identical bubbles without a liquid core. Whether the harmonic signal component generated by physical antibubbles is higher than the harmonic component of identical bubbles without a core has been studied here. We subjected prefabricated antibubbles and identical bubbles without core droplets to 1-MHz ultrasound and to a commercial ultrasound system, and recorded the spectra with a broadband transducer oriented perpendicularly to the transmitter. Normalised by the acoustic response from the medium, the antibubble signal shows stronger higher harmonics than the reference signal, and negligible fundamental response. In conclusion, antibubbles are suitable candidates for harmonic imaging. The generation of higher harmonics without fundamental has been attributed to asymmetric antibubble expansion.


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Ultrasonic identification technique in recycling of lithium ion batteries


ABSTRACT

The recycling of lithium ion batteries has been mentioned as one of the near-future waste management necessities. In order for recycling to be economically viable, straightforward and cost effective techniques need to be developed to separate the individual materials in a composite electrode. Ultrasonic separation might be such a technique, provided that lithium ion battery microparticles respond predictably to a sound field. Lithium ion battery cathodes contain hydrophobic carbon. Owing to the incompressibility of a solid, the thin gaseous layer surrounding these hydrophobic particles must oscillate asymmetrically, when subjected to ultrasound. Consequently, the harmonic content of the ultrasound signal radiated from hydrophobic microparticles must be higher than that from hydrophilic microparticles with the same size. The question of whether the harmonic signal response generated by physical hydrophobic microparticles present in lithium ion battery cathodes is higher than the harmonic response of other component materials in the cathode is the focus of this paper. The scattering response of cathode materials subjected to 1-MHz ultrasound was measured and compared. The cathode materials C65, PVDF, and NMC respond differently to 1-MHz ultrasound. The superharmonic response of C65 has been attributed to asymmetric oscillations owing to its hydrophobicity. In addition, C65 hydrophobic microparticles might be suitable candidates for harmonic imaging.


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Permeation of probe molecules into alginate microbeads: Effect of salt and processing


ABSTRACT

The ability to exclude harmful factors from a hydrogel microbead is important for the degree of protection the beads offers to what is encapsulated within. The permeability of alginate microbeads, prepared by water-in-oil emulsification, was investigated by their ability to exclude FITC-labelled protein probes. The influence of alginate concentration, calcium concentration and method of addition, and salt content of the environment was investigated. The permeability was also compared to the permeability of beads made by the traditional method of dripping an alginate solution into a CaCl2 solution. Beads produced with low amounts of CaCl2 show a significant degree of swelling and are therefore very permeable (C/C0 (BSA) = 0.62, where C is the final concentration of BSA-FITC in the bead, and C0 the concentration of BSA-FITC in the continuous phase). With additional calcium, either by adding more calcium crystals after the emulsification step or by washing with a CaCl2 solution, beads swell less and are less permeable (C/C0 (BSA) = 0.13 and 0.12). Beads made by dripping are very permeable (C/C0 (BSA) ∼ 0.60). Because in this process the droplets of alginate are not constrained by a water-oil boundary, the beads can swell during gelation. The salt concentration in the continuous phase influences the strength of the electrostatic repulsion between the probes and the alginate network and hence affects the permeation of the probes into the beads. In the absence of salt, even FITC (389Da) is mostly excluded from the interior of the beads (C/C0 (FITC) ∼ 0.09).


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Species-specific patterns of shelter exploitation in Chagas disease vectors of the genus Rhodnius


ABSTRACT

Triatomines are insect vectors of Trypanosoma cruzi¸ the etiological agent of Chagas disease. Several species belonging to the genus Rhodnius (Hemiptera: Reduviidae) have been reported inhabiting domestic and peridomestic environments in different regions of Latin America. However, behavioral and sensory ecology aspects related to their use of shelters have been poorly studied. The objective of the present study was to characterize how bug density, illumination and thigmotactic information affect the use of shelters by three species belonging to the Rhodnius prolixus species complex. We evaluated whether exposure to different insect densities affects the proportion of R. prolixus, Rhodnius robustus and Rhodnius neglectus that choose to stay inside a refuge. Besides, we evaluated whether absence of an illumination regime affects their tendency to hide in shelters. Our results showed that the proportion of individuals that remained outside the shelter increased with rising insect densities. Nevertheless, while R. prolixus only reacted by augmenting this proportion with the highest density tested, the other species showed significant increases already at lower densities. On the other hand, a significantly higher number of R. robustus stayed outside the shelter in the absence of a light cycle, while no change was induced for the other species. Thus, this study determined species-specific profiles of refuge exploitation defined by factors such as thigmotaxis and negative phototaxis. The differences observed among these Rhodnius species may impact their house colonization abilities, which seem to be critically affected by bug hiding performance during health service detection processes.


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Attraction of Rhodnius prolixus males to a synthetic female-pheromone blend


ABSTRACT

Background
The triatomine bug Rhodnius prolixus Stål, 1859 (Heteroptera: Reduviidae) is the primary vector of Chagas disease in Colombia and Venezuela. An important step in controlling Chagas disease is monitoring the growth and spread of bug populations to inform effective management. Such monitoring could be carried out using pheromone traps. To develop effective pheromone traps, it is vital to understand the pheromone chemistry of R. prolixus. Previous studies have found that female R. prolixus metasternal gland secretions induce males to: leave shelters, take off, orientate during walking, aggregate around mating pairs, and mate. This study aims to identify a synthetic blend of female metasternal gland compounds that could be used to attract R. prolixus.

Results
We investigated the electrophysiological activity of the ten most abundant compounds in female R. prolixus metasternal glands using single sensillum recordings. In total we obtained 60 recordings from basiconic sensilla in male R. prolixus. In 31 of these recordings, responses to individual compounds were observed. Each of the ten tested compounds elicited neuron responses in a minimum of eight recordings. Having confirmed their electrophysiological activity, we tested these ten compounds by presenting them to male Rhodnius prolixus in a “T” olfactometer. Male bugs showed a significant preference for the blend of metasternal gland compounds compared to the clean air control.

Conclusions
A simple blend of ten compounds found in female R. prolixus metasternal glands is attractive to conspecific males. All compounds in the blend are either commercially available at low cost, or easily synthetically prepared from simple precursors. We hope that this blend will be evaluated as a lure for pheromone traps in field bioassays.