29 research outputs found

    Stimuli-responsive behavior of PNiPAm microgels under interfacial confinement

    Get PDF
    The volume phase transition of microgels is one of the most paradigmatic examples of stimuli-responsiveness, enabling a collapse from a highly swollen microgel state into a densely coiled state by an external stimulus. Although well characterized in bulk, it remains unclear how the phase transition is affected by the presence of a confining interface. Here, we demonstrate that the temperature-induced volume phase transition of poly(N-isopropylacrylamide) microgels, conventionally considered an intrinsic molecular property of the polymer, is in fact largely suppressed when the microgel is adsorbed to an air/liquid interface. We further observe a hysteresis in core morphology and interfacial pressure between heating and cooling cycles. Our results, supported by molecular dynamics simulations, reveal that the dangling polymer chains of microgel particles, spread at the interface under the influence of surface tension, do not undergo any volume phase transition, demonstrating that the balance in free energy responsible for the volume phase transition is fundamentally altered by interfacial confinement. These results imply that important technological properties of such systems, including the temperature-induced destabilization of emulsions does not occur via a decrease in interfacial coverage of the microgels

    Soft particles at liquid interfaces: From molecular particle architecture to collective phase behavior

    Get PDF
    Soft particles such as microgels and core-shell particles can undergo significant and anisotropic deformations when adsorbed to a liquid interface. This, in turn, leads to a complex phase behavior upon compression. Here we develop a multiscale framework to rationally link the molecular particle architecture to the resulting interfacial morphology and, ultimately, to the collective interfacial phase behavior, enabling us to identify the key single-particle properties underlying two-dimensional continuous, heterostructural, and isostructural solid-solid transitions. Our approach resolves existing discrepancies between experiments and simulations and thus provides a unifying framework to describe phase transitions in interfacial soft-particle systems. We establish proof-of-principle for our rational approach by synthesizing three different poly(N-isopropylacrylamide) soft-particle architectures, each of which corresponds to a different targeted phase behavior. In parallel, we introduce a versatile and highly efficient coarse-grained simulation method that adequately captures the qualitative key features of each soft-particle system; the novel ingredient in our simulation model is the use of auxiliary degrees of freedom to explicitly account for the swelling and collapse of the particles as a function of surface pressure. Notably, these combined efforts allow us to establish the first experimental demonstration of a heterostructural transition to a chain phase in a single-component system, as well as the first accurate in silico account of the two-dimensional isostructural transition. Overall, our multiscale framework provides a bridge between physicochemical soft-particle characteristics at the molecular- and nanoscale and the collective self-assembly phenomenology at the macroscale, paving the way towards novel materials with on-demand interfacial behavior

    Interface-induced hysteretic volume phase transition of microgels: simulation and experiment

    Get PDF
    Thermo-responsive microgel particles can exhibit a drastic volume shrinkage upon increasing the solvent temperature. Recently we found that the spreading of poly(N-isopropylacrylamide)(PNiPAm) microgels at a liquid interface under the influence of surface tension hinders the temperature-induced volume phase transition. In addition, we observed a hysteresis behavior upon temperature cycling, i.e. a different evolution in microgel size and shape depending on whether the microgel was initially adsorbed to the interface in expanded or collapsed state. Here, we model the volume phase transition of such microgels at an air/water interface by monomer-resolved Brownian dynamics simulations and compare the observed behavior with experiments. We reproduce the experimentally observed hysteresis in the microgel dimensions upon temperature variation. Our simulations did not observe any hysteresis for microgels dispersed in the bulk liquid, suggesting that it results from the distinct interfacial morphology of the microgel adsorbed at the liquid interface. An initially collapsed microgel brought to the interface and subjected to subsequent swelling and collapsing (resp. cooling and heating) will end up in a larger size than it had in the original collapsed state. Further temperature cycling, however, only shows a much reduced hysteresis, in agreement with our experimental observations. We attribute the hysteretic behavior to a kinetically trapped initial collapsed configuration, which relaxes upon expanding in the swollen state. We find a similar behavior for linear PNiPAm chains adsorbed to an interface. Our combined experimental - simulation investigation provides new insights into the volume phase transition of PNiPAm materials adsorbed to liquid interfaces

    Pathogenic characteristics of persistent feline enteric coronavirus infection in cats

    Get PDF
    Feline coronaviruses (FCoV) comprise two biotypes: feline enteric coronaviruses (FECV) and feline infectious peritonitis viruses (FIPV). FECV is associated with asymptomatic persistent enteric infections, while FIPV causes feline infectious peritonitis (FIP), a usually fatal systemic disease in domestic cats and some wild Felidae. FIPV arises from FECV by mutation. FCoV also occur in two serotypes, I and II, of which the serotype I viruses are by far the most prevalent in the field. Yet, most of our knowledge about FCoV infections relates to serotype II viruses, particularly about the FIPV, mainly because type I viruses grow poorly in cell culture. Hence, the aim of the present work was the detailed study of the epidemiologically most relevant viruses, the avirulent serotype I viruses. Kittens were inoculated oronasally with different doses of two independent FECV field strains, UCD and RM. Persistent infection could be reproducibly established. The patterns of clinical symptoms, faecal virus shedding and seroconversion were monitored for up to 10 weeks revealing subtle but reproducible differences between the two viruses. Faecal virus, i.e. genomic RNA, was detected during persistent FECV infection only in the large intestine, downstream of the appendix, and could occasionally be observed also in the blood. The implications of our results, particularly our insights into the persistently infected state, are discussed

    Steering self-organisation through confinement

    Get PDF
    Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement occurs through interactions with boundaries, and can function as either a catalyst or inhibitor of self-organisation. It can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework for future research, we examine the role of confinement in self-organisation and identify overarching scientific challenges across disciplines that need to be addressed to harness its full scientific and technological potential. This framework will not only accelerate the generation of a common deeper understanding of self-organisation but also trigger the development of innovative strategies to steer it through confinement, with impact, e.g., on the design of smarter materials, tissue engineering for biomedicine and crowd management

    Steering self-organisation through confinement

    Get PDF
    Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self-organisation of soft-matter systems and identify overarching scientific challenges that need to be addressed to harness its full scientific and technological potential in soft matter and related fields. By drawing analogies with other disciplines, this framework will accelerate a common deeper understanding of self-organisation and trigger the development of innovative strategies to steer it using confinement, with impact on, e.g., the design of smarter materials, tissue engineering for biomedicine and in guiding active matter

    RAPD typing of Klebsiella pneumoniae, Klebsiella oxytoca, Serratia marcescens and Pseudomonas aeruginosa isolates using standardized reagents

    Get PDF
    ObjectiveTo perform quality assessment of standardized random amplified polymorphic DNA (RAPD) analysis for epidemiologic typing of Klebsiella pneumoniae, K. oxytoca, Serratia marcescens and Pseudomonas aeruginosa.MethodsThirty K. pneumoniae, 15 K. oxytoca, 30 S. marcescens and 33 P. aeruginosa epidemiologically unrelated isolates and four collections of clinically related isolates of each species were included in the study. RAPD analysis was performed using Ready-To-Go RAPD Analysis beads with primer ERIC-1R and Ready-To-Go primer 2 for K. pneumoniae and K. oxytoca, primer set ERIC-2/1026 and Ready-To-Go primer 2 for S. marcescens, and primers D-10514 and D-14306 for P. aeruginosa.ResultsAll epidemiologically unrelated K. pneumoniae and K. oxytoca isolates were distinguished. Twenty-nine types were distinguished among the 30 unrelated S. marcescens isolates and 32 types among the 33 unrelated P. aeruginosa isolates. Indistinguishable banding patterns were obtained in repeated analyses of two isolates and from 11 serial subcultures of three isolates of each species included in the study. The RAPD data from the clinically related isolates correlated with the epidemiologic origin of the isolates.ConclusionsThe use of Ready-To-Go RAPD Analysis beads resulted in reproducible and stable banding patterns with a high discriminatory capacity, and the RAPD typing results corresponded with the epidemiologic origin of the isolates

    Insect resistance to dietary protease inhibitors

    No full text
    Protease inhibitors (PIs) are plant defensive com-pounds that are considered as candidates for future genetic modification of crop plants. They target the digestive proteolytic enzymes in the gut of insects. However, insect resistance to these antinutritional PIs is frequently observed. The general aim of this research was to identify PI induced compensatory responses in the gut of the African migratory locust, Locusta migratoria, an infamous pest insect, capable of forming huge swarms. Using microarray analysis we studied transcriptional changes after oral uptake of plant protease inhibitors by the locust.status: publishe

    Collapse-induced phase transitions in binary interfacial microgel monolayers

    Get PDF
    Microgels, consisting of a swollen polymer network, exhibit a more complex self-assembly behavior compared to incompressible colloidal particles, because of their ability to deform at a liquid interface or collapse upon compression. Here, we investigate the collective phase behavior of two-dimensional binary mixtures of microgels confined at the air/water interface. We use stimuli-responsive poly(N-isopropylacrylamide) microgels with different crosslinking densities, and therefore different morphologies at the interface. We find that the minority microgel population introduces lattice defects in the ordered phase of the majority population, which, in contrast to bulk studies, do not heal out by partial deswelling to accommodate in the lattice. We subsequently investigate the interfacial phase behavior of these binary interfacial assemblies under compression. The binary system exhibits three distinct isostructural solid-solid phase transitions, during which the coronae between two small particles collapse first, followed by the collapse between small-large and large-large microgel pairs. A similar hierarchy of phase transitions is found for mixtures of microgels and core-shell particles. Simulations based on augmented potentials qualitatively reproduce the experimentally observed phase transitions. We rationalize the presence of this hierarchy in phase transitions from differences in the interfacial morphology between the species: the larger coronae of softer (and therefore larger) microgels provide a higher resistance to phase transitions compared to the smaller coronae of the more crosslinked microgels and core-shell particles. The control of phase transitions via the molecular architecture further allows the formation of characteristic, flower-like defects by introducing particles with "weaker"coronae that are more prone to collapse with their neighboring particles. Our findings underline the dominating role of the corona for interfacial microgel assemblies, which acts as an energy barrier, shifting the collapse to higher surface pressures

    Transcriptional Analysis of The Adaptive Digestive System of The Migratory Locust in Response to Plant Defensive Protease Inhibitors

    No full text
    Herbivorous insects evolved adaptive mechanisms to compensate for the presence of plant defensive protease inhibitors (PI) in their food. The underlying regulatory mechanisms of these compensatory responses remain largely elusive. In the current study, we investigated the initiation of this adaptive response in the migratory locust, Locusta migratoria, via microarray analysis of gut tissues. Four hours after dietary uptake of PIs, 114 and 150 transcripts were respectively found up- or downregulated. The results suggest a quick trade-off between compensating for potential loss of digestive activity on the one hand, and stress tolerance, defense, and structural integrity of the gut on the other hand. We additionally addressed the role of a group of related upregulated hexamerin-like proteins in the PI-induced response. Simultaneous knockdown of corresponding transcripts by means of RNA interference resulted in a reduced capacity of the locust nymphs to cope with the effects of PI. Moreover, since insect hexamerins have been shown to bind Juvenile Hormone (JH), we also investigated the effect of JH on the proteolytic digestion in L. migratoria. Our results indicate that JH has a stimulatory effect on the expression of three homologous chymotrypsin genes, while knocking down the JH receptor (methoprene tolerant) led to opposite effects.status: publishe
    corecore