Abstract
Cell-stretching is a key method to regulate deformation magnitude, cyclic strain levels, and frequencies, therefore elucidating the biological processes involved in activation of mechanosensitive pathways, cell patterning and morphological changes at physiologically relevant mechanical loads. Although several approaches and methods such as uniaxial or biaxial devices have been demonstrated to deform cells and usually compute ration cross-head displacement to original length of sample as an indicator of percentage stretch, however in-plane strain components may have a non-uniform spatial distribution due to heterogeneous extracellular matrix of connective tissue around cells. Therefore, the average value of the applied cross-head strain is expected to be different than local strain in the vicinity of cells. This limitation has prompted us to develop an alternative approaches.
Here, we present a novel uniaxial cell-stretching device integrated into inverted fluorescence microscope that provides a high spatial resolution to determine the local strain changes around fluorescent and non-fluorescent cells (RSI, 2016, 87, 023905). Transparent and biocompatible polydimethylsiloxane PDMS elastomer modified with small fluorescent beads are used to deliver uniform strain at the physiologically relevant magnitude and cycles. The design of our device for acquisition of real-time spatiotemporal data and single-particle tracking methods to determine bead positions that was used for computation of strain fields at various sample geometries will be described (Fig. 1). Briefly, trajectory of beads is computed by comparing each registered location in consecutive frames and minimizing the square displacement of centroids. Displacement vector is obtained from displacements and later used to calculate longitudinal normal, traverse normal and shear components of strain with relevant deformation tensor (Fig. 2). Lastly, we will discuss that HeLa S3 cells adhered to biocompatible and flexible collagen coated surface are stretched to determine simultaneously detection of morphological changes and local strains around the cells by tracking embedded fluorescent beads (Fig. 3). The method enables to measure local strain field and image adherent cells simultaneously, therefore provides accurate and time-resolved correlation between applied mechanical deformation and cell response.
Acknowledgements
This work is financially supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grants 112E580 and 112T823. O.B.A. is supported by 2210 national scholarship predoctoral training program.
Figures:
Fig. 1. (a) Assembly of designed uniaxial cell stretcher and integration into inverted fluorescent microscope. (b) Schematic representation of device setup that provides synchronization to control the stage and the stretcher, therefore samples are kept in the field during the stretching and imaging.
Fig. 2. (a) Comparison of mean displacement of beads with and without stage control. (b) Movement of beads during the stretching recorded under fluorescence (top) and white light (bottom) illumination. (c) Time evolution of local strain components computed from position and displacement of beads.
Fig. 3. Thin and biocompatible PDMS elastomer used for seeding cells. (a) Unibody PDMS sample prepared for cell attachment and stretching, that is also coated with collagen fibers to enhance cell adhesion. (b) Trajectories of fluorescent beads are overlaid onto the brightfield image of adherent cells for a sample that is stretched without motion compensation to better illustrate the bead trajectories. (c, d, e) Close-up brightfield, fluorescence, and overlaid images showing beads embedded in the sample with adherent cells.
To cite this abstract:
Halil Bayraktar, Onur Aydin, Bekir Aksoy, Ozge Begum Akalin, B. Erdem Alaca; Temporally and spatially resolved local strain tracking microscopy. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/temporally-and-spatially-resolved-local-strain-tracking-microscopy/. Accessed: December 2, 2023« Back to The 16th European Microscopy Congress 2016
EMC Abstracts - https://emc-proceedings.com/abstract/temporally-and-spatially-resolved-local-strain-tracking-microscopy/