Relaxation processes in a system with logarithmic growth

Precise Cancer Anti-acid Therapy Monitoring Using pH-Sensitive MnO2@BSA Nanoparticles by Magnetic Resonance Imaging

Microfluctuations in a pH gradient create a harsh microenvironment in tumors, leaving behind the most aggressive, invasive, and drug-resistant tumor cells. Directly visualizing the spatiotemporal distribution of pH variations and accurately quantifying the dynamic acid-base changes during cancer treatment are critical to estimate prognosis and to evaluate therapeutic efficacy. However, the quantification of subtle pH variations dynamically and noninvasively remains challenging. The purpose of this study is to determine and visualize dynamic acid-base changes in solid tumors during anti-acid treatments by magnetic resonance imaging (MRI) using pH-sensitive nanoparticles. We report the development of pH-sensitive nanoparticles, MnO₂@BSA, that rapidly and strongly amplify the MR contrast signal in response to the extracellular acidic environment of solid tumors. The spatiotemporal distribution and dynamic fluctuations of pH heterogeneity in NCI-H460 lung tumors were observed with MnO₂@BSA at different time points after an anti-acid treatment with esomeprazole, which directly interferes with the acidic microenvironment of the tumor. Imaging results were validated using a pH microsensor. MRI of pH-sensitive MnO₂@BSA nanoparticles provided direct readouts of the kinetics of pH gradient fluctuations during esomeprazole treatment. A significant MR signal reduction was observed at the 48 h time point after treatment. The manipulated extracellular pH changes detected noninvasively by MRI coincided with the extracellular pH fluctuations measured with a pH microsensor (pH 6.12-6.63). Immunofluorescence and Western blot analyses confirmed the expression of V-ATPase in NCI-H460 lung cancer cells, which could be inhibited by esomeprazole, as detected by ELISA assay. Overall, these results demonstrate that MnO₂@BSA MRI has great potential as a noninvasive tool to accurately monitor pH fluctuations, thereby paving the way for the dynamic detection of acidic microenvironments in vivo without the need for pH microsensors.

Dynamically generated hierarchies in games of competition

Spatial many-species predator-prey systems have been shown to yield very rich space-time patterns. This observation begs the question whether there exist universal mechanisms for generating this type of emerging complex patterns in nonequilibrium systems. In this work we investigate the possibility of dynamically generated hierarchies in predator-prey systems. We analyze a nine-species model with competing interactions and show that the studied situation results in the spontaneous formation of spirals within spirals. The parameter dependence of these intriguing nested spirals is elucidated. This is achieved through the numerical investigation of various quantities (correlation lengths, densities of empty sites, Fourier analysis of species densities, interface fluctuations) that allows us to gain a rather complete understanding of the spatial arrangements and the temporal evolution of the system. A possible generalization of the interaction scheme yielding dynamically generated hierarchies is discussed. As cyclic interactions occur spontaneously in systems with competing strategies, the mechanism discussed in this work should contribute to our understanding of various social and biological systems.

Coarsening with nontrivial in-domain dynamics: Correlations and interface fluctuations

Using numerical simulations we investigate the space-time properties of a system in which spirals emerge within coarsening domains, thus giving rise to nontrivial internal dynamics. Initially proposed in the context of population dynamics, the studied six-species model exhibits growing domains composed of three species in a rock-paper-scissors relationship. Through the investigation of different quantities, such as space-time correlations and the derived characteristic length, autocorrelation, density of empty sites, and interface width, we demonstrate that the nontrivial dynamics inside the domains affects the coarsening process as well as the properties of the interfaces separating different domains. Domain growth, aging, and interface fluctuations are shown to be governed by exponents whose values differ from those expected in systems with curvature driven coarsening.