Mechanical phenotyping of stem cells

Characterizing induced pluripotent stem cells and derived cardiomyocytes: insights from nano scale mass measurements and mechanical properties

Our study reveals that the nano-mechanical measures of elasticity and cell mass change significantly through induced pluripotent stem cell (iPSC) differentiation to cardiomyocytes, providing a reliable method to evaluate such processes. The findings support the importance of identifying these properties, and highlight the potential of AFM for comprehensive characterization of iPSC at the nanoscale.

Advances in Micropipette Aspiration: Applications in Cell Biomechanics, Models, and Extended Studies

With five decades of sustained application, micropipette aspiration has enabled a wide range of biomechanical studies in the field of cell mechanics. Here, we provide an update on the use of the technique, with a focus on recent developments in the analysis of the experiments, innovative microaspiration-based approaches, and applications in a broad variety of cell types. We first recapitulate experimental variations of the technique. We then discuss analysis models focusing on important limitations of widely used biomechanical models, which underpin the urge to adopt the appropriate ones to avoid misleading conclusions. The possibilities of performing different studies on the same cell are also considered.

Design and Validation of Equiaxial Mechanical Strain Platform, EQUicycler, for 3D Tissue Engineered Constructs

It is crucial to replicate the micromechanical milieu of native tissues to achieve efficacious tissue engineering and regenerative therapy. In this study, we introduced an innovative loading platform, EQUicycler, that utilizes a simple, yet effective, and well-controlled mechanism to apply physiologically relevant homogenous mechanical equiaxial strain on three-dimensional cell-embedded tissue scaffolds. The design of EQUicycler ensured elimination of gripping effects through the use of biologically compatible silicone posts for direct transfer of the mechanical load to the scaffolds. Finite Element Modeling (FEM) was created to understand and to quantify how much applied global strain was transferred from the loading mechanism to the tissue constructs. In vitro studies were conducted on various cell lines associated with tissues exposed to equiaxial mechanical loading in their native environment. In vitro results demonstrated that EQUicycler was effective in maintaining and promoting the viability of different musculoskeletal cell lines and upregulating early differentiation of osteoprogenitor cells. By utilizing EQUicycler, collagen fibers of the constructs were actively remodeled. Residing cells within the collagen construct elongated and aligned with strain direction upon mechanical loading. EQUicycler can provide an efficient and cost-effective tool to conduct mechanistic studies for tissue engineered constructs designed for tissue systems under mechanical loading in vivo.

Real-time deformability cytometry as a label-free indicator of cell function

The mechanical properties of cells are known to be a label-free, inherent marker of biological function in health and disease. Wide-spread utilization has so far been impeded by the lack of a convenient measurement technique with sufficient throughput. To address this unmet need, we have recently introduced real-time deformability cytometry (RT-DC) for continuous mechanical single-cell classification of heterogeneous cell populations at rates of several hundred cells per second. Cells are driven through the constriction zone of a microfluidic chip leading to cell deformations due to hydrodynamic stresses only. Our custom-built image processing software performs image acquisition, image analysis and data storage on the fly. The ensuing deformations can be quantified and an analytical model enables the derivation of cell material properties. Performing RT-DC we highlight its potential to identify rare objects in heterogeneous suspensions and to track drug-induced changes in cells. In summary, RT-DC enables marker-free, quantitative phenotyping of heterogeneous cell populations with a throughput comparable to standard flow cytometry.

Label-free and non-invasive monitoring of porcine trophoblast derived cells: differentiation in serum and serum-free media

Traditional approaches to characterize stem cell differentiation are time-consuming, lengthy and invasive. Here, Raman microspectroscopy (RM) and atomic force microscopy (AFM) - both considered as non-invasive techniques - are applied to detect the biochemical and biophysical properties of trophoblast derived stem-like cells incubated up to 10 days under conditions designed to induce differentiation. Significant biochemical and biophysical differences between control cells and differentiated cells were observed. Quantitative real time PCR was also applied to analyze gene expression. The relationship between cell differentiation and associated cellular biochemical and biomechanical changes were discussed. Monitoring trophoblast cells differentiation.

Temporal heterogeneity in single-cell gene expression and mechanical properties during adipogenic differentiation

Adipose-derived stem/stromal cells (ASCs) respond heterogeneously when exposed to lineage-specific induction medium. Variable responses at the single-cell level can be observed in the production of lineage-specific metabolites, expression of mRNA transcripts, and adoption of mechanical phenotypes. Understanding the relationship between the biological and mechanical characteristics for individual ASCs is crucial for interpreting how cellular heterogeneity affects the differentiation process. The goal of the current study was to monitor the gene expression of peroxisome proliferator receptor gamma (PPARG) in adipogenically differentiating ASC populations over two weeks, while also characterizing the expression-associated mechanical properties of individual cells using atomic force microscopy (AFM). Results showed that ASC mechanical properties did not change significantly over time in either adipogenic or control medium; however, cells expressing PPARG exhibited significantly greater compliance and fluidity compared to those lacking expression in both adipogenic and control media environments. The percent of PPARG+ cells in adipogenic samples increased over time but stayed relatively constant in controls. Previous reports of a slow, gradual change in cellular mechanical properties are explained by the increase in the number of positively differentiating cells in a sample rather than being reflective of actual, single-cell mechanical property changes. Cytoskeletal remodeling was more prevalent in adipogenic samples than controls, likely driving the adoption of a more compliant mechanical phenotype and upregulation of PPARG. The combined results reinforce the importance of understanding single-cell characteristics, in the context of heterogeneity, to provide more accurate interpretations of biological phenomena such as stem cell differentiation.