Stochastic numerical models of oscillatory phenomena

The use of time series for integrating ordinary differential equations to model oscillatory chemical phenomena has shown benefits in terms of accuracy and stability. In this work, we suggest to adapt also the model in order to improve the matching of the numerical solution with the time series of experimental data. The resulting model is a system of stochastic differential equations. The stochastic nature depends on physical considerations and the noise relies on an arbitrary function which is empirically chosen. The integration is carried out through stochastic methods which integrate the deterministic part by using one-step methods and approximate the stochastic term by employing Monte Carlo simulations. Some numerical experiments will be provided to show the effectiveness of this approach

Signal transduction and communication through model membranes in networks of coupled chemical oscillators

In nature, an important example of chemical communication and synchronicity can be found in cell populations where long-range chemical communication takes place over micrometer distance. In vitro laboratory systems can be useful to understand and control such complex biological mechanisms and, in a biomimetic approach, we present in this paper a model based on three basic features, namely (i) the compartmentalization of chemical information (using microfluidics), (ii) a stable emitter of periodic chemical signals inside compartments (Belousov-Zhabotinsky oscillating reaction) and (iii) a suitable spatio-temporal monitoring of the emitted chemical signal. In particular, starting from our recent work on the communication among oscillators via chemical intermediates in networks of lipid-stabilised droplets, we discuss here the role of compartments and of the geometry of the system. We present 3 different experimental configurations, namely liposomes (water-in-water dispersions), double emulsions (water-in-oil-in-water dispersions) and simple emulsions (water-in-oil dispersions) and we show that the global behaviour of networks can be influenced and controlled by several experimental parameters, like the nature of the collecting solvent, the presence of dopants and the network geometry. Numerical models supporting and explaining the experimental findings are also discussed

The relevance of inorganic nonlinear chemical reactions for the origin of life studies

We discuss the fundamental role played by nonlinear inorganic chemical reactions to understand the minimal conditions for the origin of life. In particular, we propose a focus on the chemo-physical processes that modulate the interplay between self-organisation and self-assembly at the basis of important life-like functionalities. We present results about two proofs-of-concept that support this view. The first pertains the collective behaviours and patterns obtained from networks of autonomous inorganic oscillators confined in self-assembled structures and coupled via chemical communication. The second shows how a specific autocatalytic reaction can trigger conformational changes of self-assembled structures, giving rise to membrane self-division processes

Microwave ablation in a hepatic porcine model: correlation of CT and histopathologic findings

Background. Thermal ablative techniques have gained increasing popularity in recent years as safe and effective options for patients with unresectable solid malignancies. Microwave ablation has emerged as a relatively new technique with the promise of larger and faster burns without some of the limitations of radiofrequency ablation (RFA). Here we study a new microwave ablation device in a living porcine model using gross, histologic, and radiographic analysis. Materials and methods. The size and shape of ablated lesions were assessed using six pigs in a non-survival study. Liver tissue was ablated using 2, 4, and 8 min burns, in both peripheral and central locations, with and without vascular inflow occlusion. To characterize the post-ablation appearance, three additional pigs underwent several 4 min ablations each followed by serial computed tomography (CT) imaging at 7, 14, and 28 days postoperatively. Results. The 2 and 4 min ablations resulted in lesions that were similar in size, 33.5 cm3 and 37.5 cm3, respectively. Ablations lasting 8 min produced lesions that were significantly larger, 92.0 cm3 on average. Proximity to hepatic vasculature and inflow occlusion did not significantly change lesion size or shape. In follow-up studies, CT imaging showed a gradual reduction in lesion volume over 28 days to 25–50% of the original volume. Discussion. Microwave ablation with a novel device results in consistently sized and shaped lesions. Importantly, we did not observe any significant heat-sink effect using this device, a major difference from RFA techniques. This system offers a viable alternative for creating fast, large ablation volumes for treatment in liver cancer

Modelling Approach to Enzymatic pH Oscillators in Giant Lipid Vesicles

The urease-catalyzed hydrolysis of urea can display feedback driven by base production (NH 3 ) resulting in a switch from acidic to basic pH under non-buffered conditions. Thus, this enzymatic reaction is a good candidate for investigation of chemical oscillations or bistability. In order to determine the best conditions for oscillations, a two-variable model was initially derived in which acid and urea were supplied at rates k H and k S from an external medium to an enzyme-containing compartment. Oscillations were theoretically observed providing the necessary condition that k H > k S was met. To apply this model, we devised an experimental system able to ensure the fast transport of acid compared to that of urea. In particular, by means of the droplet transfer method, we encapsulated the enzyme, together with a proper pH probe, in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) based liposomes, where differential diffusion of H + and urea is ensured by the different permeability (P m ) of the membrane to the two species. Here we present an improved theoretical model that accounts for the products transport and for the probe hydrolysis, to obtain a better guidance for the experiments

Modelling Approach to Enzymatic pH Oscillators in Giant Lipid Vesicles

The urease-catalyzed hydrolysis of urea can display feedback driven by base production (NH 3 ) resulting in a switch from acidic to basic pH under non-buffered conditions. Thus, this enzymatic reaction is a good candidate for investigation of chemical oscillations or bistability. In order to determine the best conditions for oscillations, a two-variable model was initially derived in which acid and urea were supplied at rates k H and k S from an external medium to an enzyme-containing compartment. Oscillations were theoretically observed providing the necessary condition that k H > k S was met. To apply this model, we devised an experimental system able to ensure the fast transport of acid compared to that of urea. In particular, by means of the droplet transfer method, we encapsulated the enzyme, together with a proper pH probe, in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) based liposomes, where differential diffusion of H + and urea is ensured by the different permeability (P m ) of the membrane to the two species. Here we present an improved theoretical model that accounts for the products transport and for the probe hydrolysis, to obtain a better guidance for the experiments