Effects of Backpacks on Ground Reaction Forces in Children of Different Ages When Walking, Running, and Jumping

Backpacks for transporting school loads are heavily utilized by children, and their mechanical advantages have been allowing children to transport heavy loads. These heavy loads may increase ground reaction forces (GRFs), which can have a negative effect on joints and bone health. The aim of this study was to investigate the effect of backpacks on the GRFs generated by children during walking, running, and jumping. Twenty-one children from the fifth (G-5, n = 9) and ninth (G-9, n = 12) grades walked, ran, and jumped over a force plate. When walking, the G-5 had GRF increments in the first (17.3%; p 0.05), unlike the G-5 (p = 0.001). When running, total stance time increased 15% (p < 0.001) and 8.5% (p < 0.001) proportionally to the relative load carried, in the G-5 and G-9, respectively. Peak GRF did not increase in any group when running or landing from a jump over an obstacle. It was found that GRF was affected by the backpack load when walking and running. However, when landing from a jump with the backpack, schoolchildren smoothed the landing by prolonging the reception time and thus avoiding GRF peak magnitudes.info:eu-repo/semantics/publishedVersio

Mitochondrial Na+ controls oxidative phosphorylation and hypoxic redox signalling

All metazoans depend on O2 delivery and consumption by the mitochondrial oxidative phosphorylation (OXPHOS) system to produce energy. A decrease in O2 availability (hypoxia) leads to profound metabolic rewiring. In addition, OXPHOS uses O2 to produce reactive oxygen species (ROS) that can drive cell adaptations through redox signalling, but also trigger cell damage1–4, and both phenomena occur in hypoxia4–8. However, the precise mechanism by which acute hypoxia triggers mitochondrial ROS production is still unknown. Ca2+ is one of the best known examples of an ion acting as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential and collaborating in ion transport10. Here we show that Na+ acts as a second messenger regulating OXPHOS function and ROS production by modulating fluidity of the inner mitochondrial membrane (IMM). We found that a conformational shift in mitochondrial complex I during acute hypoxia11 drives the acidification of the matrix and solubilization of calcium phosphate precipitates. The concomitant increase in matrix free-Ca2+ activates the mitochondrial Na+/Ca2+ exchanger (NCLX), which imports Na+ into the matrix. Na+ interacts with phospholipids reducing IMM fluidity and mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III, generating a redox signal. Inhibition of mitochondrial Na+ import through NCLX is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ import into the mitochondrial matrix controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences in cellular metabolism

4to. Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad. Memoria académica

Este volumen acoge la memoria académica de la Cuarta edición del Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad, CITIS 2017, desarrollado entre el 29 de noviembre y el 1 de diciembre de 2017 y organizado por la Universidad Politécnica Salesiana (UPS) en su sede de Guayaquil. El Congreso ofreció un espacio para la presentación, difusión e intercambio de importantes investigaciones nacionales e internacionales ante la comunidad universitaria que se dio cita en el encuentro. El uso de herramientas tecnológicas para la gestión de los trabajos de investigación como la plataforma Open Conference Systems y la web de presentación del Congreso http://citis.blog.ups.edu.ec/, hicieron de CITIS 2017 un verdadero referente entre los congresos que se desarrollaron en el país. La preocupación de nuestra Universidad, de presentar espacios que ayuden a generar nuevos y mejores cambios en la dimensión humana y social de nuestro entorno, hace que se persiga en cada edición del evento la presentación de trabajos con calidad creciente en cuanto a su producción científica. Quienes estuvimos al frente de la organización, dejamos plasmado en estas memorias académicas el intenso y prolífico trabajo de los días de realización del Congreso Internacional de Ciencia, Tecnología e Innovación para la Sociedad al alcance de todos y todas

Efficient Recovery of 3D Forces exerted by Cells on Thin Substrates

status: accepte

Spatiotemporal analyses of cellular tractions characterize the effect of substrate stiffness and adhesion molecule at subcellular scale

Poster presentationstatus: accepte

Analysis of local traction dynamics as a function of substrate mechanical properties in endothelial cells

status: accepte

TRACTIONS, MORPHOLOGY AND MOTILITY DYNAMICS IN ENDOTHELIAL CELLS ON COMPLIANT SUBSTRATES

“TRACTIONS, MORPHOLOGY AND MOTILITY DYNAMICS IN ENDOTHELIAL CELLS ON COMPLIANT SUBSTRATES” A. Izquierdo-Álvarez1, A. Jorge Peñas1, D.A. Vargas1, S. Ragunathan1, R. Subramani2 and H. Van Oosterwyck1,3. 1 Biomechanics Section, KU Leuven Celestijnenlaan 300C box 2419, 3001 Leuven. 2 Division of Mechatronics, Biostatistics and Sensors, KU Leuven, Kasteelpark Arenberg 30 box 2456, 3001 Leuven. 3 Prometheus, div. Skeletal Tissue Engineering, KU Leuven, Belgium A number of studies have shed light on the biochemical regulation of angiogenesis, but how mechanical properties modulate this process is still poorly understood. We have focused our attention on how substrate stiffness and adhesion proteins affect the morphology, traction and motility of human umbilical vein endothelial cells (HUVECs) and how they correlate to each other, both at the whole cell population as well as at single cell level. HUVECs were cultured on top of polyacrylamide surfaces of different stiffness, functionalized with fibronectin or collagen. For traction force microscopy (TFM), fluorescent beads contained in the substrate were used as fiducial markers. Time lapse TFM experiments were performed and displacement calculations were made using Free Form Deformation (FFD)-based image registration. We have previously demonstrated that this method calculates displacements more accurately and, consequently, leads to more reliable tractions [1]. In order to calculate migration parameters we have applied the Persistence Random Walk model previously described in Pei-Hsun et al. [2]. A series of morphological features and the minimal distance between cells where measured from the images of HUVECs. To test whether there is a relation between condition and behavior, we performed an analysis using the software SAPHIRE [3]. This analysis uses principal component analysis (PCA) and hidden Markov models (HMM) to define a series of cellular states for each cell incorporating temporal dependencies during model inference. This analysis provides a transition probability matrix that can be used to compare across conditions. Preliminary results show a direct correlation between the total force exerted by the cell and the stiffness of the substrate, being collagen the adhesion protein promoting higher tractions. Also, tracking of the local ‘hot spots’ of traction force with time, points to forces that are more persistent for cells on collagen than on fibronectin, especially in softer substrates. Furthermore, the PCA analysis revealed the length of cells’ minor axis as the morphological parameter that describes most variability within a cell population. Surprisingly, distance to other cells showed no correlation with cellular state. Finally, hierarchical clustering of transition probability matrices shows potential to distinguish among cellular responses to different substrate stiffness. In summary, the resulting data will shed light on the relation between the cell and its physical environment and how the mechanical cues modulate cell fate in angiogenesis. Acknowledgements: FP7/2007-2013)/ ERC StG n° 308223, FWO G.0821.13, KU Leuven internal funding (IDO 13/016) [1] Jorge-Peñas A et al. (2015) PLoS ONE 10(12): e0144184. [2] Pei-Hsun W et al. (2015) Nature Protocols 10, 517–527. [3] Gordonov et al. (2016) Integrative Biology 8(1):73-90.status: publishe

Correlation between cell morphology, tractions and motility of endothelial cells on compliant substrates

“Correlation between cell morphology, tractions and motility of endothelial cells on compliant substrates” Alicia Izquierdo-Álvarez, Álvaro Jorge Peñas, Diego Vargas, Srilakshmi Ragunathan, Ramesh Subramani and Hans Van Oosterwyck. Biomechanics Section, KU Leuven Celestijnenlaan 300C box 2419, 3001 Leuven. Angiogenesis is the formation of new vessels from the preexisting vasculature. It is an essential process not only in tissue regeneration but also in cardiovascular disease and cancer. Chemical regulation of this process has been studied for many years but how physical cues regulate angiogenesis is still poorly understood. We are investigating how substrate stiffness and adhesion properties affect cell morphology, tractions and motility of human umbilical vein endothelial cells (HUVECs) and how they correlate at the single cell level. HUVECs were cultured on polyacrylamide substrates with different stiffness, functionalized with fibronectin or collagen and containing fluorescent beads for traction force microscopy (TFM). Time lapse TFM experiments were performed, using Free Form Deformation (FFD)-based image registration for substrate displacement calculation. We have previously demonstrated that this method leads to more accurate displacements and recovered tractions [2]. The migration parameters, speed and persistence time, were calculated from a fit of the MSD in accordance to the persistent random walk model described by Pei-Hsun et al [3]. A series of cell morphological features (18 in total) and the minimal distance between cells were measured from time lapse confocal fluorescence microscopy images. Correlation analyses are being performed by means of the software SAPHIRE [1], which uses principal component analysis (PCA) and hidden Markov models (HMM) to define a series of cellular states for each cell, incorporating temporal dependencies during model inference. This analysis provides a transition probability matrix that can be used to compare across conditions. Our preliminary results showed that the total force exerted by cells increases with the substrate stiffness and its magnitude depends on the adhesion protein, being collagen the one promoting higher cellular tractions. Furthermore, the PCA analysis revealed the length of cells’ minor axis as the morphological parameter that describes most variability within a cell population. Surprisingly, distance to other cells showed no correlation with cellular state. Finally, hierarchical clustering of transition probability matrices shows potential to distinguish among cellular responses to different substrate stiffness. In summary, the resulting information is expected to provide a quantitative view of the cell-matrix mechanical interaction of HUVECs and leads to a better comprehension of cell mechanobiology in angiogenesis. Acknowledgements: The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ ERC Grant Agreement n° 308223) and from the Research Foundation-Flanders (FWO – project number G.0821.13) [1] Gordonov et al. (2016) Time series modeling of live-cell shape dynamics for image-based phenotypic profiling. Integrative Biology 8(1):73-90 [2] Jorge-Peñas A et al. (2015) Free Form Deformation–Based Image Registration Improves Accuracy of Traction Force Microscopy. PLoS ONE 10(12): e0144184. [3] Pei-Hsun W et al. (2015) Statistical analysis of cell migration in 3D using the anisotropic persistent random walk model. Nature Protocols 10, 517–527status: publishe

The influence of swelling on local elastic properties of polyacrylamide hydrogels

The influence of swelling on local elastic properties of polyacrylamide hydrogel

Capturing spatial and temporal dynamics of traction exertion to guide computational modeling: How endothelial cells react to substrate mechanical and chemical properties

Oral presentationstatus: accepte