Manipulating Cardiovascular Cellular Interactions and Mechanics: A Multidimensional and Multimodal Approach

The goal of this dissertation is to better understand cellular mechanics across length scales for the development of computational models of tissue behavior. To this end, we had two major approaches, multidimensional and multimodal. Firstly, to use a model that better mimics in vivo like cellular environment, microtissue (spheroid) cell culture system was used to study cell mechanics. Secondly, a novel technique was designed to study single cell mechanics in multiple dimensions. Cell mechanical properties are directly related to the composition and organization of the cytoskeleton, which is physically coupled to neighboring cells through adherens junctions and to extracellular matrix through focal adhesion complexes. As such, we hypothesize that the variations in cellular interactions affects cell mechanics. To test our hypothesis, cardiomyocytes and vascular smooth muscle microtissues were cultured under several conditions that limited the cell-cell and cell-matrix interactions. Cell interactions facilitated by integrin β1, connexin 43, and N-cadherin was inhibited and their effect on cell stiffness was characterized by atomic force microscopy (AFM). Currently, there does not exist a single technique that can measure mechanics of a single cell in two different dimensions. To address this gap, we designed a novel set up that combines two different single cell mechanics measurement techniques, AFM and carbon fiber. This combination allows for characterization of mechanical properties of single cells in multiple dimensions. The results of these studies provide insights from a basic science perspective. The results provide information regarding cell mechanics in multiple dimensions at both single cell as well microtissue level. The ultimate fulfillment of this work would be its incorporation into a multiscale model, leading to the ability to tie macro- scale behaviors to nano- scale phenomenon. Such models may help to better understand tissue behavior and further our understanding of the etiology of many diseases

Supplementary material from Simultaneous assessment of radial and axial myocyte mechanics by combining atomic force microscopy and carbon fibre techniques

Cardiomyocytes sense and shape their mechanical environment, contributing to its dynamics by their passive and active mechanical properties. While axial forces generated by contracting cardiomyocytes have been amply investigated, the corresponding radial mechanics remain poorly characterized. Our aim is to simultaneously monitor passive and active forces, both axially and radially, in cardiomyocytes freshly isolated from adult mouse ventricles. To characterize axial and radial forces, we combine a carbon fibre (CF) set-up with a custom-made atomic force microscope (AFM). CF allows us to apply stretch and to record passive and active forces in the axial direction. The AFM, modified for frontal access to fit in CF, is used to characterize radial cell mechanics. We show that stretch increases the radial elastic modulus of cardiomyocytes. We further find that during contraction, cardiomyocytes generate radial forces that are reduced, but not abolished, when cells are forced to contract near isometrically. Radial forces may contribute to ventricular wall thickening during contraction, together with the dynamic re-orientation of cells and sheetlets in the myocardium. This new approach for characterizing cell mechanics allows one to obtain a more detailed picture of the balance of axial and radial mechanics in cardiomyocytes at rest, during stretch and during contraction.This article is part of the theme issue ‘The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health and disease’

Deconvolution of subcellular protrusion heterogeneity and the underlying actin regulator dynamics from live cell imaging

Cell protrusion dynamics are heterogeneous at the subcellular level, but current analyses operate at the cellular or ensemble level. Here the authors develop a computational framework to quantify subcellular protrusion phenotypes and reveal the underlying actin regulator dynamics at the leading edge

Analysis of Light Propagation on Physiological Properties of Neurons for Nanoscale Optogenetics

Miniaturization of implantable devices is an important challenge for future brain-computer interface applications, and in particular for achieving precise neuron stimulation. For stimulation that utilizes light, i.e., optogenetics, the light propagation behavior and interaction at the nanoscale with elements within the neuron is an important factor that needs to be considered when designing the device. This paper analyzes the effect of light behavior for a single neuron stimulation and focuses on the impact from different cell shapes. Based on the Mie scattering theory, the paper analyzes how the shape of the soma and the nucleus contributes to the focusing effect resulting in an intensity increase, which ensures that neurons can assist in transferring light through the tissue toward the target cells. At the same time, this intensity increase can in turn also stimulate neighboring cells leading to interference within the neural circuits. This paper also analyzes the ideal placements of the device with respect to the angle and position within the cortex that can enable axonal biophoton communications, which can contain light within the cell to avoid the interference.acceptedVersionPeer reviewe