A minimal physical model for curvotaxis driven by curved protein complexes at the cell's leading edge.

Cells often migrate on curved surfaces inside the body, such as curved tissues, blood vessels, or highly curved protrusions of other cells. Recent in vitro experiments provide clear evidence that motile cells are affected by the curvature of the substrate on which they migrate, preferring certain curvatures to others, termed "curvotaxis." The origin and underlying mechanism that gives rise to this curvature sensitivity are not well understood. Here, we employ a "minimal cell" model which is composed of a vesicle that contains curved membrane protein complexes, that exert protrusive forces on the membrane (representing the pressure due to actin polymerization). This minimal-cell model gives rise to spontaneous emergence of a motile phenotype, driven by a lamellipodia-like leading edge. By systematically screening the behavior of this model on different types of curved substrates (sinusoidal, cylinder, and tube), we show that minimal ingredients and energy terms capture the experimental data. The model recovers the observed migration on the sinusoidal substrate, where cells move along the grooves (minima), while avoiding motion along the ridges. In addition, the model predicts the tendency of cells to migrate circumferentially on convex substrates and axially on concave ones. Both of these predictions are verified experimentally, on several cell types. Altogether, our results identify the minimization of membrane-substrate adhesion energy and binding energy between the membrane protein complexes as key players of curvotaxis in cell migration.

Design organization and clinical processes around patient characteristics: Evidence from a multiple case study of Hemophilia.

Background: There is growing evidence of the relevance of designing organization of care around patient characteristics; this is especially true in the case of complex chronic diseases.Purpose: The goal of the paper - that focuses on the analysis of the clinical condition hemophilia in three different centers - is to address two different research questions:1. How can we define, within the same clinical condition, different patient profiles homogeneous in terms of intensity of service required (e.g. number of visits or diagnostics)? 2. What are the conditions to re-organize care around these patient profiles in a multidisciplinary and coordinated manner?Research design: The authors have used a multiple case study approach combining both qualitative and quantitative methodologies; in particularly the semi-structured interviews and the direct observation were aimed to map the process in order to come up with an estimate of the cost of the full cycle of care.Study sample: The research methodology has been applied consistently in three different centers. The selection of the structures has been based on two main different criteria: (i) high standards regarding both organizational and clinical aspects and (ii) willingness from management, nurses and physicians to provide data.Results: The study clearly shows that different patient profiles - within the same clinical condition - trigger a different set of diagnostic and therapeutic activities. It is, thus, important considering patient characteristics in the development and implementation of clinical pathways and this will imply relevant differences in terms of organizational and economic impact.Conclusions: These process-based analyses are very much critical especially if we want to move to a bundled and integrated payment system but, as shown by this study itself, require a lot of time and efforts since our healthcare information systems are still fragmented and vertically designed.