Anisotropic run-and-tumble-turn dynamics

Run-and-tumble processes successfully model several living systems. While studies have typically focused on particles with isotropic tumbles, recent examples exhibit "tumble-turns", in which particles undergo 90° tumbles and so possess explicitly anisotropic dynamics. We study the consequences of such tumble-turn anisotropicity at both short and long-time scales. We model run-and-tumble-turn particles as self-propelled particles subjected to an angular potential that favors directions of movement parallel to Cartesian axes. Using agent-based simulations, we study the effects of the interplay between rotational diffusion and an aligning potential on the particles' trajectories, which leads to the right-angled turns. We demonstrate that the long-time effect is to alter the tumble-turn time, which governs the long-time dynamics. In particular, when normalized by this timescale, trajectories become independent of the underlying details of the potential. As such, we develop a simplified continuum theory, which quantitatively agrees with agent-based simulations. We find that the purely diffusive hydrodynamic limit still exhibits anisotropic features at intermediate times and conclude that the transition to diffusive dynamics precedes the transition to isotropic dynamics. By considering short-range repulsive and alignment particle-particle interactions, we show how the anisotropic features of a single particle are inherited by the global order of the system. We hope this work will shed light on how active systems can extend local anisotropic properties to macroscopic scales, which might be important in biological processes occurring in anisotropic environments.

Motility induced phase separation of deformable cells

Using a multi-phase field model, we examine how particle deformability, which is a proxy for cell stiffness, affects motility induced phase separation (MIPS). We show that purely repulsive deformable, i.e., squishy, cells phase separate more effectively than their rigid counterparts. This can be understood as due to the fact that deformability increases the effective duration of collisions. In addition, the dense regions become increasingly disordered as deformability increases. Our results contextualize the applicability of MIPS to biological systems and have implications for how cells in biological systems may self-organize.

The development of a regional network for health care research in Hamburg, Germany

Background

At the University Medical Center Hamburg-Eppendorf (UKE), health care research has been established as one of five research priorities recommended by the Research Council with the founding of the Center for Health Care Research (CHCR) in 2006. The CHCR was involved in numerous research projects with the focus on strengthening regional networking. Despite the numerous initiatives, there is still potential for improvement with regard to a systematic and sustainable exchange in the region of Hamburg, Germany.

Methods

These requirements led to the initiation of the ‘Hamburg Network Health Services Research (HAM-NET)'. The mission of HAM-NET is to build an open forum for all relevant institutions, to concentrate their interests and needs in health services research and to promote and conduct innovative, efficient, needs-based and patient-centred health services research projects in the metropolitan area of Hamburg. Three main tasks were appointed: 1) linking health care research to relevant regional institutions, 2) promoting research activities and new fields of research and 3) using methodological expertise to promote young scientists.

Results

By today 40 institutions from all sectors of health care joined HAM-NET. The regularly general meetings offer exchange and advice. Internal communication is promoted by mailing lists and newsletters. Also, HAM-NET presents itself with a website, logo and by organizing recurring events and participating in international and national congresses and networks. Within two funding phases a total of four overarching research projects were developed and implemented. Furthermore, a person with lived experience committee was established.

Conclusions

For the further development of health care research as one the core disciplines of public health a regional network with an efficient infrastructure is needed. HAM-NET promotes this with the implementation of an innovative, efficient and patient-oriented network.

Key messages

• Regional networks help to integrate multiple public health initiatives and community stakeholders.

• Public health networks can be established on multidisciplinary cooperations in different out- and inpatient sector levels.

Local Yield and Compliance in Active Cell Monolayers

The rheology of biological tissue plays an important role in many processes, from organ formation to cancer invasion. Here, we use a multiphase field model of motile cells to simulate active microrheology within a tissue monolayer. When unperturbed, the tissue exhibits a transition between a solidlike state and a fluidlike state tuned by cell motility and deformability-the ratio of the energetic costs of steric cell-cell repulsion and cell-edge tension. When perturbed, solid tissues exhibit local yield-stress behavior, with a threshold force for the onset of motion of a probe particle that vanishes upon approaching the solid-to-liquid transition. This onset of motion is qualitatively different in the low and high deformability regimes. At high deformability, the tissue is amorphous when solid, it responds compliantly to deformations, and the probe transition to motion is smooth. At low deformability, the monolayer is more ordered translationally and stiffer, and the onset of motion appears discontinuous. Our results suggest that cellular or nanoparticle transport in different types of tissues can be fundamentally different and point to ways in which it can be controlled.

Helical flow states in active nematics

We show that confining extensile nematics in three-dimensional (3D) channels leads to the emergence of two self-organized flow states with nonzero helicity. The first is a pair of braided antiparallel streams-this double helix occurs when the activity is moderate, anchoring negligible, and reduced temperature high. The second consists of axially aligned counter-rotating vortices-this grinder train arises between spontaneous axial streaming and the vortex lattice. These two unanticipated helical flow states illustrate the potential of active fluids to break symmetries and form complex but organized spatiotemporal structures in 3D fluidic devices.

Solid-Liquid Transition of Deformable and Overlapping Active Particles

Experiments and theory have shown that cell monolayers and epithelial tissues exhibit solid-liquid and glass-liquid transitions. These transitions are biologically relevant to our understanding of embryonic development, wound healing, and cancer. Current models of confluent epithelia have focused on the role of cell shape, with less attention paid to cell extrusion, which is key for maintaining homeostasis in biological tissue. Here, we use a multiphase field model to study the solid-liquid transition in a confluent monolayer of deformable cells. Cell overlap is allowed and provides a way for modeling the precursor for extrusion. When cells overlap rather than deform, we find that the melting transition changes from continuous to first order like, and that there is an intermittent regime close to the transition, where solid and liquid states alternate over time. By studying the dynamics of five- and sevenfold disclinations in the hexagonal lattice formed by the cell centers, we observe that these correlate with spatial fluctuations in the cellular overlap, and that cell extrusion tends to initiate near fivefold disclinations.

Shape and size changes of adherent elastic epithelia

Epithelial tissues play a fundamental role in various morphogenetic events during development and early embryogenesis. Although epithelial monolayers are often modeled as two-dimensional (2D) elastic surfaces, they distinguish themselves from conventional thin elastic plates in three important ways- the presence of an apical-basal polarity, spatial variability of cellular thickness, and their nonequilibrium active nature. Here, we develop a minimal continuum model of a planar epithelial tissue as an active elastic material that incorporates all these features. We start from a full three-dimensional (3D) description of the tissue and derive an effective 2D model that captures, through the curvature of the apical surface, both the apical-basal asymmetry and the spatial geometry of the tissue. Crucially, variations of active stresses across the apical-basal axis lead to active torques that can drive curvature transitions. By identifying four distinct sources of activity, we find that bulk active stresses arising from actomyosin contractility and growth compete with boundary active tensions due to localized actomyosin cables and lamellipodial activity to generate the various states spanning the morphospace of a planar epithelium. Our treatment hence unifies 3D shape deformations through the coupled mechanics of apical curvature change and in-plane expansion/contraction of substrate-adhered tissues. Finally, we discuss the implications of our results for some biologically relevant processes such as tissue folding at the onset of lumen formation.

How do patients with anorexia nervosa "process" psychotherapy between sessions? A comparison of cognitive-behavioral and psychodynamic interventions

OBJECTIVE

Patients' processing of psychotherapy between sessions ("inter-session process" (ISP)) has been repeatedly shown to be related to outcome. The aim of this study was to compare ISP characteristics of cognitive-behavioral vs. psychodynamic psychotherapy in the treatment of anorexia nervosa (AN) and their relation to outcome.

METHODS

Data of 106 patients participating in a randomized-controlled trial who received either 40 sessions of enhanced cognitive-behavioral therapy (CBT-E) or focal psychodynamic therapy (FPT) were analyzed. The ISP was measured with the Inter-session Experience Questionnaire (IEQ). Three outcome classes were distinguished: full recovery, partial recovery, and still fulfilling all AN criteria.

RESULTS

Patients receiving CBT-E reported more on "applying therapy" in the initial and the final treatment phase compared to FPT patients. In terms of process-outcome relations, higher levels of "recreating the therapeutic dialogue between sessions," "recreating the therapeutic dialogue with negative emotions" as well as "applying therapy with negative emotions" in the final phase of treatment predicted negative outcome in FPT, whereas overall higher levels of negative emotions predicted negative outcome in CBT-E.

CONCLUSIONS

In outpatient treatment in AN, the processing of therapy as measured by the IEQ showed surprisingly few differences between CBT-E and FPT. However, different ISP patterns were predictive of outcome, pointing to different mechanisms of change.

Emergent tilt order in Dirac polymer liquids

We study a liquid of zigzagging two-dimensional directed polymers with bending rigidity, i.e., polymers whose conformations follow checkerboard paths. In the continuum limit the statistics of such polymers obey the Dirac equation for particles of imaginary mass. We exploit this observation to investigate a liquid of these polymers via a quantum many-fermion analogy. A self-consistent approximation predicts a phase of tilted order, in which the polymers may develop a preference to zig rather than zag. We compute the phase diagram and key response functions for the polymer liquid, and comment on the role played by fluctuations.