A uniaxial cell stretching technique to measure time-resolved local substrate strain while simultaneously imaging adherent cells is presented. The experimental setup comprises a uniaxial stretcher platform compatible with inverted microscopy and transparent elastomer samples with embedded fluorescent beads. This integration enables the acquisition of real-time spatiotemporal data, which is then processed using a single-particle tracking algorithm to track the positions of fluorescent beads for the subsequent computation of local strain. The present local strain tracking method is demonstrated using polydimethylsiloxane (PDMS) samples of rectangular and dogbone geometries. The comparison of experimental results and finite element simulations for the two sample geometries illustrates the capability of the present system to accurately quantify local deformation even when the strain distribution is non-uniform over the sample. For a regular dogbone sample, the experimentally obtained value of local strain at the center of the sample is 77%, while the average strain calculated using the applied cross-head displacement is 48%. This observation indicates that considerable errors may arise when cross-head measurement is utilized to estimate strain in the case of non-uniform sample geometry. Finally, the compatibility of the proposed platform with biological samples is tested using a unibody PDMS sample with a well to contain cells and culture media. HeLa S3 cells are plated on collagen-coated samples and cell adhesion and proliferation are observed. Samples with adherent cells are then stretched to demonstrate simultaneous cell imaging and tracking of embedded fluorescent beads.

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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.