A practical review on the measurement tools for cellular adhesion force

Cell cell and cell matrix adhesions are fundamental in all multicellular organisms. They play a key role in cellular growth, differentiation, pattern formation and migration. Cell-cell adhesion is substantial in the immune response, pathogen host interactions, and tumor development. The success of tissue engineering and stem cell implantations strongly depends on the fine control of live cell adhesion on the surface of natural or biomimetic scaffolds. Therefore, the quantitative and precise measurement of the adhesion strength of living cells is critical, not only in basic research but in modern technologies, too. Several techniques have been developed or are under development to quantify cell adhesion. All of them have their pros and cons, which has to be carefully considered before the experiments and interpretation of the recorded data. Current review provides a guide to choose the appropriate technique to answer a specific biological question or to complete a biomedical test by measuring cell adhesion

Recursive Least Squares Filtering Algorithms for On-Line Viscoelastic Characterization of Biosamples

The mechanical characterization of biological samples is a fundamental issue in biology and related fields, such as tissue and cell mechanics, regenerative medicine and diagnosis of diseases. In this paper, a novel approach for the identification of the stiffness and damping coefficients of biosamples is introduced. According to the proposed method, a MEMS-based microgripper in operational condition is used as a measurement tool. The mechanical model describing the dynamics of the gripper-sample system considers the pseudo-rigid body model for the microgripper, and the Kelvin–Voigt constitutive law of viscoelasticity for the sample. Then, two algorithms based on recursive least square (RLS) methods are implemented for the estimation of the mechanical coefficients, that are the forgetting factor based RLS and the normalised gradient based RLS algorithms. Numerical simulations are performed to verify the effectiveness of the proposed approach. Results confirm the feasibility of the method that enables the ability to perform simultaneously two tasks: sample manipulation and parameters identification

Biophysical implications of lipid bilayer rheometry for mechanosensitive channels

The lipid bilayer plays a crucial role in gating of mechanosensitive (MS) channels. Hence it is imperative to elucidate the rheological properties of lipid membranes. Herein we introduce a framework to characterize the mechanical properties of lipid bilayers by combining micropipette aspiration (MA) with theoretical modeling. Our results reveal that excised liposome patch fluorometry is superior to traditional cell-attached MA for measuring the intrinsic mechanical properties of lipid bilayers. The computational results also indicate that unlike the uniform bilayer tension estimated by Laplace's law, bilayer tension is not uniform across the membrane patch area. Instead, the highest tension is seen at the apex of the patch and the lowest tension is encountered near the pipette wall. More importantly, there is only a negligible difference between the stress profiles of the outer and inner monolayers in the cellattached configuration, whereas a substantial difference (~30%) is observed in the excised configuration. Our results have farreaching consequences for the biophysical studies of MS channels and ion channels in general, using the patch-clamp technique, and begin to unravel the difference in activity seen between MS channels in different experimental paradigms

Developing an Optomechanical Approach for Characterizing Mechanical Properties of Single Adherent Cells

Mechanical properties of a cell reflect its biological and pathological conditions including cellular disorders and fundamental cellular processes such as cell division and differentiation. There have been active research efforts to develop high-throughput platforms to mechanically characterize single cells. Yet, many of these research efforts are focused on suspended cells and use a flow-through configuration. Therefore, adherent cells are detached prior to the characterization, which seriously perturbs the cellular conditions. Also, methods for adherent cells are limited in their throughput. My study is aimed to fill the technical gap in the field of single cell analysis, which is a high-throughput and non-invasive mechanical characterization of single adherent cells. I developed a multi-modal platform to mechanically characterize single adherent cells. The platform is based on optomechanical principle, which induces least perturbation on the cells and does not require cell detachment. Besides, multiple measurements can be performed on a single cell to track its mechanical behavior over time. Proposed platform can expand our understanding on the relationship between mechanical properties and cellular status of adherent cells. Single adherent cells are characterized optomechanically using the vibration-induced phase shift (VIPS). VIPS is a phase shift of apparent velocity of a vertically vibrating substrate measured with laser Doppler vibrometer (LDV), when the measurement laser passes through an adherent cell or any transparent objects on the substrate. The VIPS and height oscillation of a single cell on a vibrating substrate have negative correlation with the cell stiffness. An analytical model is established which demonstrates relationship between cell’s mechanical properties and its VIPS. With the VIPS measurements, at multiple frequencies on large population of cells, the statistical significant difference in the cell stiffness is confirmed after exposure to various drugs affecting cytoskeleton network. Also, a 3-dimensional finite element model is developed to extract the cell stiffness from VIPS. VIPS technique is used to reconstruct the detailed oscillation pattern of transparent objects such as water microdroplets and intracellular lipid droplets on a vibrating substrate, which can give us better understanding of mechanical behavior of biological transparent objects. In addition, using VIPS measurement mechanical interaction between extracellular matrixes (ECMs) and adherent cells is studied. Statistical significant difference in bonding straight of single cells and different ECMs is demonstrated

Trends in characterizing single cell's stiffness properties

Biophysical properties of living cells such as mechanical and chemical have been proven to play important roles in regulations of various biological activities including disease progression both at the cellular and molecular levels. In the past decades, a number of research tools have been developed to provide better understanding towards cell¿s biophysical states. This growing interest was supported by the emergence of researches focusing on single cell analysis (SCA) which serves as a platform enabling various experimentation works to be carried out. In this context, various techniques have been developed for single cell¿s mechanical characterization to improve robustness, accuracy and operational flexibility. The generic solution varies from traditional approach, microelectromechanical system (MEMS) and microfluidic. This paper presents a review of progress and developments in the field of single cell mechanical properties specifically discussing on stiffness characterizations. An analytical comparison of the reviewed solutions is presented, and the advantages and disadvantages of different techniques are compared

Viscoelastic finite element modeling of deformation transients of single cells

The objective of this thesis is to use computational modeling to study the deformation of single cells subjected to mechanical stresses. Our motivation stems from experimental observations that cells are subjected to mechanical stresses arising from their environment throughout their lifetime, and that such stresses can regulate many important biological processes. While the exact mechanotransduction mechanisms involved are not well understood, quantitative models for cell deformation can yield important insights. In this thesis, we developed an axisymmetric finite element model to study the deformation of suspended fibroblasts in the optical stretcher and neutrophils in tapered micropipettes. The key feature of our model is the use of a viscoelastic constitutive equation whose parameters can be varied both spatially and temporally so as to mimic the experimentally-observed spatio-temporal heterogeneity of cellular material properties. Our model suggested that cellular remodeling, in the form of an increased cellular viscosity, occurred during optical stretching of fibroblasts. The increase would have to be approximately 20-fold to explain the experimental data for different loading time-scales. We also showed that cell size is a more important factor in determining the strain response of the optically-stretched fibroblasts compared to the thickness of the actin cortical region. This result can explain the higher optical deformability observed experimentally for malignant fibroblasts. In addition, our simulations showed that maximal stress propagates into the nuclear region for malignant fibroblasts whereas for normal fibroblasts, the maximal stress does not. Finally, results from modeling the tapered micropipette experiments also suggested that cellular remodeling, in the form of a decreased cellular elasticity and viscosity, occurred during the process of neutrophil aspiration. Taken together, our simulation results on optically-stretched fibroblasts and aspirated neutrophils suggested that cells in general are able to sense mechanical stresses and respond by varying their material properties during deformation

Assessing membrane material properties from the response of giant unilamellar vesicles to electric fields

Knowledge of the material properties of membranes is crucial to understanding cell viability and physiology. A number of methods have been developed to probe membranes in vitro, utilizing the response of minimal biomimetic membrane models to an external perturbation. In this review, we focus on techniques employing giant unilamellar vesicles (GUVs), model membrane systems, often referred to as minimal artificial cells because of the potential they offer to mimick certain cellular features. When exposed to electric fields, GUV deformation, dynamic response and poration can be used to deduce properties such as bending rigidity, pore edge tension, membrane capacitance, surface shear viscosity, excess area and membrane stability. We present a succinct overview of these techniques, which require only simple instrumentation, available in many labs, as well as reasonably facile experimental implementation and analysis