Evaluation of the influence of growth medium composition on cell elasticity

Nuclear deformation and dynamics of migrating cells in 3D confinement reveal adaptation of pulling and pushing forces

Eukaryotic cells show an astounding ability to remodel their shape and cytoskeleton and to migrate through pores and constrictions smaller than their nuclear diameter. However, the relation of nuclear deformation and migration dynamics in confinement remains unclear. Here, we study the mechanics and dynamics of mesenchymal cancer cell nuclei transitioning through three-dimensional compliant hydrogel channels. We find a biphasic dependence of migration speed and transition frequency on channel width, peaking at widths comparable to the nuclear diameter. Using confocal imaging and hydrogel bead displacement, we determine nuclear deformations and corresponding forces during confined migration. The nucleus deforms reversibly with a reduction in volume during confinement. With decreasing channel width, the nuclear shape during transmigration changes biphasically, concomitant with the transitioning dynamics. Our proposed physical model explains the observed nuclear shapes and transitioning dynamics in terms of the cytoskeletal force generation adapting from purely pulling-based to a combined pulling- and pushing-based mechanism with increasing nuclear confinement.

Cellular elasticity in cancer: a review of altered biomechanical features

A large number of studies have shown that changes in biomechanical characteristics are an important indicator of tumor transformation in normal cells. Elastic deformation is one of the more studied biomechanical features of tumor cells, which plays an important role in tumourigenesis and development. Altered cell elasticity often brings many indications. This manuscript reviews the effects of altered cellular elasticity on cell characteristics, including adhesion viscosity, migration, proliferation, and differentiation elasticity and stiffness. Also, the physical factors that may affect cell elasticity, such as temperature, cell height, cell-viscosity, and aging, are summarized. Then, the effects of cell-matrix, cytoskeleton, in vitro culture medium, and cell-substrate with different three-dimensional structures on cell elasticity during cell tumorigenesis are outlined. Importantly, we summarize the current signaling pathways that may affect cellular elasticity, as well as tests for cellular elastic deformation. Finally, we summarize current hybrid materials: polymer-polymer, protein-protein, and protein-polymer hybrids, also, nano-delivery strategies that target cellular resilience and cases that are at least in clinical phase 1 trials. Overall, the behavior of cancer cell elasticity is modulated by biological, chemical, and physical changes, which in turn have the potential to alter cellular elasticity, and this may be an encouraging prediction for the future discovery of cancer therapies.

Mechanical properties of human tumour tissues and their implications for cancer development

The mechanical properties of cells and tissues help determine their architecture, composition and function. Alterations to these properties are associated with many diseases, including cancer. Tensional, compressive, adhesive, elastic and viscous properties of individual cells and multicellular tissues are mostly regulated by reorganization of the actomyosin and microtubule cytoskeletons and extracellular glycocalyx, which in turn drive many pathophysiological processes, including cancer progression. This Review provides an in-depth collection of quantitative data on diverse mechanical properties of living human cancer cells and tissues. Additionally, the implications of mechanical property changes for cancer development are discussed. An increased knowledge of the mechanical properties of the tumour microenvironment, as collected using biomechanical approaches capable of multi-timescale and multiparametric analyses, will provide a better understanding of the complex mechanical determinants of cancer organization and progression. This information can lead to a further understanding of resistance mechanisms to chemotherapies and immunotherapies and the metastatic cascade.

"Patchiness" in mechanical stiffness across a tumor as an early-stage marker for malignancy

Mechanical phenotyping of tumors, either at an individual cell level or tumor cell population level is gaining traction as a diagnostic tool. However, the extent of diagnostic and prognostic information that can be gained through these measurements is still unclear. In this work, we focus on the heterogeneity in mechanical properties of cells obtained from a single source such as a tissue or tumor as a potential novel biomarker. We believe that this heterogeneity is a conventionally overlooked source of information in mechanical phenotyping data. We use mechanics-based in-silico models of cell-cell interactions and cell population dynamics within 3D environments to probe how heterogeneity in cell mechanics drives tissue and tumor dynamics. Our simulations show that the initial heterogeneity in the mechanical properties of individual cells and the arrangement of these heterogenous sub-populations within the environment can dictate overall cell population dynamics and cause a shift towards the growth of malignant cell phenotypes within healthy tissue environments. The overall heterogeneity in the cellular mechanotype and their spatial distributions is quantified by a "patchiness" index, which is the ratio of the global to local heterogeneity in cell populations. We observe that there exists a threshold value of the patchiness index beyond which an overall healthy population of cells will show a steady shift towards a more malignant phenotype. Based on these results, we propose that the "patchiness" of a tumor or tissue sample, can be an early indicator for malignant transformation and cancer occurrence in benign tumors or healthy tissues. Additionally, we suggest that tissue patchiness, measured either by biochemical or biophysical markers, can become an important metric in predicting tissue health and disease likelihood just as landscape patchiness is an important metric in ecology.

Engineered 3D ex vivo models to recapitulate the complex stromal and immune interactions within the tumor microenvironment

Cancer thrives in a complex environment where interactions between cellular and acellular components, surrounding the tumor, play a crucial role in disease development and progression. Despite significant progress in cancer research, the mechanism driving tumor growth and therapeutic outcomes remains elusive. Two-dimensional (2D) cell culture assays and in vivo animal models are commonly used in cancer research and therapeutic testing. However, these models suffer from numerous shortcomings including lack of key features of the tumor microenvironment (TME) & cellular composition, cost, and ethical clearance. To that end, there is an increased interest in incorporating and elucidating the influence of TME on cancer progression. Advancements in 3D-engineered ex vivo models, leveraging biomaterials and microengineering technologies, have provided an unprecedented ability to reconstruct native-like bioengineered cancer models to study the heterotypic interactions of TME with a spatiotemporal organization. These bioengineered cancer models have shown excellent capabilities to bridge the gap between oversimplified 2D systems and animal models. In this review article, we primarily provide an overview of the immune and stromal cellular components of the TME and then discuss the latest state-of-the-art 3D-engineered ex vivo platforms aiming to recapitulate the complex TME features. The engineered TME model, discussed herein, are categorized into three main sections according to the cellular interactions within TME: (i) Tumor-Stromal interactions, (ii) Tumor-Immune interactions, and (iii) Complex TME interactions. Finally, we will conclude the article with a perspective on how these models can be instrumental for cancer translational studies and therapeutic testing.

Tumor proliferation and invasion are intrinsically coupled and unraveled through tunable spheroid and physics-based models

Proliferation and invasion are two key drivers of tumor growth that are traditionally considered independent multicellular processes. However, these processes are intrinsically coupled through a maximum carrying capacity, i.e., the maximum spatial cell concentration supported by the tumor volume, total cell count, nutrient access, and mechanical properties of the tissue stroma. We explored this coupling of proliferation and invasion through in vitro and in silico methods where we modulated the mechanical properties of the tumor and the surrounding extracellular matrix. E-cadherin expression and stromal collagen concentration were manipulated in a tunable breast cancer spheroid to determine the overall impacts of these tumor variables on net tumor proliferation and continuum invasion. We integrated these results into a mixed-constitutive formulation to computationally delineate the influences of cellular and extracellular adhesion, stiffness, and mechanical properties of the extracellular matrix on net proliferation and continuum invasion. This framework integrates biological in vitro data into concise computational models of invasion and proliferation to provide more detailed physical insights into the coupling of these key tumor processes and tumor growth. STATEMENT OF SIGNIFICANCE: Tumor growth involves expansion into the collagen-rich stroma through intrinsic coupling of proliferation and invasion within the tumor continuum. These processes are regulated by a maximum carrying capacity that is determined by the total cell count, tumor volume, nutrient access, and mechanical properties of the surrounding stroma. The influences of biomechanical parameters (i.e., stiffness, cell elongation, net proliferation rate and cell-ECM friction) on tumor proliferation or invasion cannot be unraveled using experimental methods alone. By pairing a tunable spheroid system with computational modeling, we delineated the interdependencies of each system parameter on tumor proliferation and continuum invasion, and established a concise computational framework for studying tumor mechanobiology.

Ligand Binding-Induced Cellular Membrane Deformation is Correlated with the Changes in Membrane Stiffness

Study interaction between ligands and protein receptors is a key step for biomarker research and drug discovery. In situ measurement of cell surface membrane protein binding on whole cells eliminates the cost and pitfalls associated with membrane protein purification. Ligand binding to membrane protein was recently found to induce nanometer-scale cell membrane deformations, which can be monitored with real-time optical imaging to quantify ligand/protein binding kinetics. However, the insight into this phenomenon has still not been fully understood. We hypothesize that ligand binding can change membrane stiffness, which induces membrane deformation. To investigate this, cell height and membrane stiffness changes upon ligand binding are measured using atomic force microscopy (AFM). Wheat germ agglutinin (WGA) is used as a model ligand that binds to the cell surface glycoprotein. The changes in cell membrane stiffness and cell height upon ligand bindings are determined for three different cell lines (human A431, HeLa, and rat RBL-2H3) on two different substrates. AFM results show that cells become stiffer with increased height after WGA modification for all cases studied. The increase in cell membrane stiffness is further confirmed by plasmonic scattering microscopy, which shows an increased cell spring constant upon WGA binding. Therefore, this study provides direct experimental evidence that the membrane stiffness changes are directly correlated with ligand binding-induced cell membrane deformation.

Indentation of living cells by AFM tips may not be what we thought!

The models used to calculate Young's moduli from atomic force microscopy (AFM) force curves consider the shape of the indentation. It is then assumed that the geometry of the indentation is identical to the geometry of the indenter, which has been verified for hard materials (E > 1 MPa). Based on this assumption, the force curves calculated by these models, for the same object with a given Young's modulus, are different if the indenter geometry is different. On the contrary, we observe experimentally that the force curves recorded on soft living cells, with pyramidal, spherical, or tipless indenters, are almost similar. This indicates that this basic assumption on the indentation geometry does not work for soft materials (E of the order of 5 kPa or less). This means that, in this case, the shape of the indentation is therefore different from the shape of the indenter. Indentation of living cells by AFM is not what we thought!

Using Adhesive Micropatterns and AFM to Assess Cancer Cell Morphology and Mechanics

The mechanical properties of living cells reflect their physiological and pathological state. In particular, cancer cells undergo cytoskeletal modifications that typically make them softer than healthy cells, a property that could be used as a diagnostic tool. However, this is challenging because cells are complex structures displaying a broad range of morphologies when cultured in standard 2D culture dishes. Here, we use adhesive micropatterns to impose the cell geometry and thus standardize the mechanics and morphologies of cancer cells, which we measure by atomic force microscopy (AFM), mechanical nanomapping, and membrane nanotube pulling. We show that micropatterning cancer cells leads to distinct morphological and mechanical changes for different cell lines. Micropatterns did not systematically lower the variability in cell elastic modulus distribution. These effects emerge from a variable cell spreading rate associated with differences in the organization of the cytoskeleton, thus providing detailed insights into the structure-mechanics relationship of cancer cells cultured on micropatterns. Combining AFM with micropatterns reveals new mechanical and morphological observables applicable to cancer cells and possibly other cell types.

Mechanism of action and side effects of colchicine based on biomechanical properties of cells

Many diseases are related to changes in the biomechanical properties of cells; their study can provide a theoretical basis for drug screening and can explain the internal working of living cells. In this study, the biomechanical properties of nephrocytes (VERO cells), hepatocytes (HL-7702 cells), and hepatoma cells (SMCC-7721 cells) in culture were detected by atomic force microscopy (AFM) to analyse the side effects of colchicine at different concentrations (0.1 μg/mL (A) and 0.2 μg/mL (B)) at the nanoscale for 2, 4 and 6 h. Compared with the corresponding control cells, the damage to the treated cells increased in a dose-dependent manner. Among normal cells, the injury of nephrocytes (VERO cells) was markedly worse than that of hepatocytes (HL-7702 cells) in both colchicine solutions A and B. Based on the analyses of biomechanical properties, the colchicine solution reduced the rate of division and inhibited metastasis of SMCC-7721 cells. By comparing these two concentrations, we found that the anticancer effect of colchicine solution A was greater than that of solution B. Studying the mechanical properties of biological cells can help understand the mechanism of drug action at the molecular level and provide a theoretical basis for preventing the emergence and diagnosis of diseases at the nanoscale.

Automated estimation of cancer cell deformability with machine learning and acoustic trapping

Cell deformability is a useful feature for diagnosing various diseases (e.g., the invasiveness of cancer cells). Existing methods commonly inflict pressure on cells and observe changes in cell areas, diameters, or thickness according to the degree of pressure. Then, the Young’s moduli (i.e., a measure of deformability) of cells are estimated based on the assumption that the degrees of the changes are inversely proportional to Young’s moduli. However, manual measurements of the physical changes in cells are labor-intensive, and the subjectivity of the operators can intervene during this step, thereby causing considerable uncertainty. Further, because the shapes of cells are nonuniform, we cannot ensure the assumption for linear correlations of physical changes in cells with their deformability. Therefore, this study aims at measuring non-linear elastic moduli of live cells (degrees of cell deformability) automatically by employing conventional neural networks (CNN) and multilayer perceptrons (MLP) while preserving (or enhancing) the accuracy of the manual methods. First, we obtain photomicrographs of cells on multiple pressure levels using single-beam acoustic tweezers, and then, we suggest an image preprocessing method for emphasizing changes in cell areas on the photomicrographs. The CNN model is trained to measure the ratios of the cell area change at each pressure level. Then, we apply the multilayer perceptron (MLP) to learn the correlations of the cell area change ratios according to the pressure levels with cell deformability. The accuracy of the CNN was evaluated using two types of breast cancer cells: MDA-MB-231 (invasive) and MCF-7 (noninvasive). The MLP was assessed using five different beads (Young’s moduli from 0.214 to 9.235 kPa), which provides standardized reference data of the non-linear elastic moduli of live cells. Finally, we validated the practicality of the proposed system by examining whether the non-linear elastic moduli estimated by the proposed system can distinguish invasive breast cancer cells from noninvasive ones.

Atomic force microscopy reveals the mechanical properties of breast cancer bone metastases

Mechanically dependent processes are essential in cancer metastases. However, reliable mechanical characterization of metastatic cancer remains challenging whilst maintaining the tissue complexity and an intact sample. Using atomic force microscopy, we quantified the micro-mechanical properties of relatively intact metastatic breast tumours and their surrounding bone microenvironment isolated from mice, and compared with other breast cancer models both ex vivo and in vitro. A mechanical distribution of extremely low elastic modulus and viscosity was identified on metastatic tumours, which were significantly more compliant than both 2D in vitro cultured cancer cells and subcutaneous tumour explants. The presence of mechanically distinct metastatic tumour did not result in alterations of the mechanical properties of the surrounding microenvironment at meso-scale distances (>200 μm). These findings demonstrate the utility of atomic force microscopy in studies of complex tissues and provide new insights into the mechanical properties of cancer metastases in bone.

Molecular insights of metastasis and cancer progression derived using 3D cancer spheroid co-culture in vitro platform

The multistep metastasis process is carried out by the combinatorial effect of the stromal cells and the cancerous cells and plays vital role in the cancer progression. The scaffold/physical cues aided 3D cancer spheroid imitates the spatiotemporal organization and physiological properties of the tumor. Understanding the role of the key players in different stages of metastasis, the molecular cross-talk between the stromal cells and the cancer cells contributing in the advancement of the metastasis through 3D cancer spheroid co-culture in vitro platform is the center of discussion in the present review. This state-of-art in vitro platform utilized to study the cancer cell host defence and the role of exosomes in the cross talk leading to cancer progression has been critically examined here. 3D cancer spheroid co-culture technique is the promising next-generation in vitro approach for exploring potent treatments and personalized medicines to combat cancer metastasis leading to cancer progression.

Simultaneous 2D and 3D cell culture array for multicellular geometry, drug discovery and tumor microenvironment reconstruction

Cell culture systems are indispensablein vitrotools for biomedical research. Although conventional two-dimensional (2D) cell cultures are still used for most biomedical and biological studies, the three-dimensional (3D) cell culture technology attracts increasing attention from researchers, especially in cancer and stem cell research. Due to the different spatial structures, cells in 2D and 3D cultures exhibit different biochemical and biophysical phenotypes. Therefore, a new platform with both 2D and 3D cell cultures is needed to bridge the gap between 2D and 3D cell-based assays. Here, a simultaneous 2D and 3D cell culture array system was constructed by microprinting technology, in which cancer cells exhibited heterozygous geometry structures with both 2D monolayers and 3D spheroids. Cells grown in 3D spheroids showed higher proliferation ability and stronger cell-cell adhesion. Spheroids derived from various types of cancer cell lines exhibited distinct morphologies through a geometrical confinement stimulated biomechanical transduction. Z-projected images of cancer cell aggregates were used to analyze 3D multicellular architecture features. Notably, by using a support vector machine classifier, we distinguished tumor cells from normal cells with an accuracy greater than 95%, according to the geometrical features of multicellular spheroids in phase contrast microscopy images. Cancer cells in multicellular spheroid arrays exhibited higher drug resistance of anticancer drug cisplatin than cells grown in 2D cultures. Finally, we developed a co-culture system composed of tumor spheroid arrays, fibroblast cells and photo-crosslinkable gelatin methacryloyl hydrogel to mimic tumor microenvironment which consisted of solid tumor massed, surrounding stromal cells and extracellular matrix. Together, our newly developed simultaneous 2D and 3D cell culture array has great potential in comprehensive evaluation of cellular events in both 2D and 3D, rapid production of spheroid arrays and multicellular geometry-based tumor cell detection.

Dynamic cellular biomechanics in responses to chemotherapeutic drug in hypoxia probed by atomic force spectroscopy

The changes in cellular structure play an important role in cancer cell development, progression, and metastasis. By exploiting single-cell, force spectroscopy methods, we probed biophysical and biomechanical kinetics (stiffness, morphology, roughness, adhesion) of brain, breast, prostate, and pancreatic cancer cells with standard chemotherapeutic drugs in normoxia and hypoxia over 12–24 hours. After exposure to the drugs, we found that brain, breast, and pancreatic cancer cells became approximately 55–75% less stiff, while prostate cancer cells became more stiff, due to either drug-induced disruption or reinforcement of cytoskeletal structure. However, the rate of the stiffness change decreased up to 2-folds in hypoxia, suggesting a correlation between cellular stiffness and drug resistance of cancer cells in hypoxic tumor microenvironment. Also, we observed significant changes in the cell body height, surface roughness, and cytoadhesion of cancer cells after exposure to drugs, which followed the trend of stiffness. Our results show that a degree of chemotherapeutic drug effects on biomechanical and biophysical properties of cancer cells is distinguishable in normoxia and hypoxia, which are correlated with alteration of cytoskeletal structure and integrity during drug-induced apoptotic process.

Human mammary epithelial cells in a mature, stratified epithelial layer flatten and stiffen compared to single and confluent cells

BACKGROUND

The epithelium forms a protective barrier against external biological, chemical and physical insults. So far, AFM-based, micro-mechanical measurements have only been performed on single cells and confluent cells, but not yet on cells in mature layers.

METHODS

Using a combination of atomic force, fluorescence and confocal microscopy, we determined the changes in stiffness, morphology and actin distribution of human mammary epithelial cells (HMECs) as they transition from single cells to confluency to a mature layer.

RESULTS

Single HMECs have a tall, round (planoconvex) morphology, have actin stress fibers at the base, have diffuse cortical actin, and have a stiffness of 1 kPa. Confluent HMECs start to become flatter, basal actin stress fibers start to disappear, and actin accumulates laterally where cells abut. Overall stiffness is still 1 kPa with two-fold higher stiffness in the abutting regions. As HMECs mature and form multilayered structures, cells on apical surfaces become flatter (apically more level), wider, and seven times stiffer (mean, 7 kPa) than single and confluent cells. The main drivers of these changes are actin filaments, as cells show strong actin accumulation in the regions where cells adjoin, and in the apical regions.

CONCLUSIONS

HMECs stiffen, flatten and redistribute actin upon transiting from single cells to mature, confluent layers.

GENERAL SIGNIFICANCE

Our findings advance the understanding of breast ductal morphogenesis and mechanical homeostasis.

Evaluation of quasi-static and dynamic nanomechanical properties of bone-metastatic breast cancer cells using a nanoclay cancer testbed

In recent years, there has been increasing interest in investigating the mechanical properties of individual cells to delineate disease mechanisms. Reorganization of cytoskeleton facilitates the colonization of metastatic breast cancer at bone marrow space, leading to bone metastasis. Here, we report evaluation of mechanical properties of two breast cancer cells with different metastatic ability at the site of bone metastases, using quasi-static and dynamic nanoindentation methods. Our results showed that the significant reduction in elastic modulus along with increased liquid-like behavior of bone metastasized MCF-7 cells was induced by depolymerization and reorganization of F-actin to the adherens junctions, whereas bone metastasized MDA-MB-231 cells showed insignificant changes in elastic modulus and F-actin reorganization over time, compared to their respective as-received counterparts. Taken together, our data demonstrate evolution of breast cancer cell mechanics at bone metastases.

Estrogens Determine Adherens Junction Organization and E-Cadherin Clustering in Breast Cancer Cells via Amphiregulin

Estrogens play an important role in the development and progression of human cancers, particularly in breast cancer. Breast cancer progression depends on the malignant destabilization of adherens junctions (AJs) and disruption of tissue integrity. We found that estrogen receptor alpha (ERα) inhibition led to a striking spatial reorganization of AJs and microclustering of E-Cadherin (E-Cad) in the cell membrane of breast cancer cells. This resulted in increased stability of AJs and cell stiffness and a reduction of cell motility. These effects were actomyosin-dependent and reversible by estrogens. Detailed investigations showed that the ERα target gene and epidermal growth factor receptor (EGFR) ligand Amphiregulin (AREG) essentially regulates AJ reorganization and E-Cad microclustering. Our results not only describe a biological mechanism for the organization of AJs and the modulation of mechanical properties of cells but also provide a new perspective on how estrogens and anti-estrogens might influence the formation of breast tumors.

•

ERα inhibition causes adherens junction (AJ) reorganization through AREG and EGFR

•

AJ reorganization coincides with microclustering of E-Cadherin at cell membranes

•

AJ reorganization and microclustering of E-Cadherin are actomyosin dependent

•

AJ reorganization correlates with increased cell stiffness and reduced motility

Nanomechanics and Histopathology as Diagnostic Tools to Characterize Freshly Removed Human Brain Tumors

Background

The tissue-mechanics environment plays a crucial role in human brain physiological development and the pathogenesis of different diseases, especially cancer. Assessment of alterations in brain mechanical  properties during cancer progression might provide important information about possible tissue abnormalities with clinical relevance.

Methods

With atomic force microscopy (AFM), the stiffness of freshly removed human brain tumor tissue was determined on various regions of the sample and compared to the stiffness of healthy human brain tissue that was removed during neurosurgery to gain access to tumor mass. An advantage of indentation measurement using AFM is the small volume of tissue required and high resolution at the single-cell level.

Results

Our results showed great heterogeneity of stiffness within metastatic cancer or primary high-grade gliomas compared to healthy tissue. That effect was not clearly visible in lower-grade tumors like meningioma.

Conclusion

Collected data indicate that AFM might serve as a diagnostic tool in the assessment of human brain tissue stiffness in the process of recognizing tumors.

Applications of atomic force microscopy in immunology

Cellular mechanics, a major regulating factor of cellular architecture and biological functions, responds to intrinsic stresses and extrinsic forces exerted by other cells and the extracellular matrix in the microenvironment. Cellular mechanics also acts as a fundamental mediator in complicated immune responses, such as cell migration, immune cell activation, and pathogen clearance. The principle of atomic force microscopy (AFM) and its three running modes are introduced for the mechanical characterization of living cells. The peak force tapping mode provides the most delicate and desirable virtues to collect high-resolution images of morphology and force curves. For a concrete description of AFM capabilities, three AFM applications are discussed. These applications include the dynamic progress of a neutrophil-extracellular-trap release by neutrophils, the immunological functions of macrophages, and the membrane pore formation mediated by perforin, streptolysin O, gasdermin D, or membrane attack complex.

Mechanical properties of human glioma

Brain gliomas represent some of the most aggressive tumors encountered by modern medicine and, despite major efforts to optimize early diagnosis and treatment, the prognosis remains poor. Due to the complex structure of the brain and the unique mechanical properties of the extracellular matrix, gliomas invade and expand into the brain parenchyma, along white matter tracts and within perivascular spaces, usually sparing normal vessels. Different methods have been developed to study the mechanical properties of gliomas in a wide range of scales, from cells and the microscale to tissues and the macroscale. In this review, the current view on glioma mechanics is presented and the methods used to determine glioma mechanical properties are outlined. Their principles and current state of affairs are discussed.

An AFM-Based Nanomechanical Study of Ovarian Tissues with Pathological Conditions

BACKGROUND

Different diseases affect both mechanical and chemical features of the involved tissue, enhancing the symptoms.

METHODS

In this study, using atomic force microscopy, we mechanically characterized human ovarian tissues with four distinct pathological conditions: mucinous, serous, and mature teratoma tumors, and non-tumorous endometriosis. Mechanical elasticity profiles were quantified and the resultant data were categorized using K-means clustering method, as well as fuzzy C-means, to evaluate elastic moduli of cellular and non-cellular parts of diseased tissues and compare them among four disease conditions. Samples were stained by hematoxylin-eosin staining to further study the content of different locations of tissues.

RESULTS

Pathological state vastly influenced the mechanical properties of the ovarian tissues. Significant alterations among elastic moduli of both cellular and non-cellular parts were observed. Mature teratoma tumors commonly composed of multiple cell types and heterogeneous ECM structure showed the widest range of elasticity profile and the stiffest average elastic modulus of 14 kPa. Samples of serous tumors were the softest tissues with elastic modulus of only 400 Pa for the cellular part and 5 kPa for the ECM. Tissues of other two diseases were closer in mechanical properties as mucinous tumors were insignificantly stiffer than endometriosis in cellular part, 1300 Pa compared to 1000 Pa, with the ECM average elastic modulus of 8 kPa for both.

CONCLUSION

The higher incidence of carcinoma out of teratoma and serous tumors may be related to the intense alteration of mechanical features of the cellular and the ECM, serving as a potential risk factor which necessitates further investigation.

Investigation of cell mechanics using single-beam acoustic tweezers as a versatile tool for the diagnosis and treatment of highly invasive breast cancer cell lines: an in vitro study

Advancements in diagnostic systems for metastatic cancer over the last few decades have played a significant role in providing patients with effective treatment by evaluating the characteristics of cancer cells. Despite the progress made in cancer prognosis, we still rely on the visual analysis of tissues or cells from histopathologists, where the subjectivity of traditional manual interpretation persists. This paper presents the development of a dual diagnosis and treatment tool using an in vitro acoustic tweezers platform with a 50 MHz ultrasonic transducer for label-free trapping and bursting of human breast cancer cells. For cancer cell detection and classification, the mechanical properties of a single cancer cell were quantified by single-beam acoustic tweezers (SBAT), a noncontact assessment tool using a focused acoustic beam. Cell-mimicking phantoms and agarose hydrogel spheres (AHSs) served to standardize the biomechanical characteristics of the cells. Based on the analytical comparison of deformability levels between the cells and the AHSs, the mechanical properties of the cells could be indirectly measured by interpolating the Young's moduli of the AHSs. As a result, the calculated Young's moduli, i.e., 1.527 kPa for MDA-MB-231 (highly invasive breast cancer cells), 2.650 kPa for MCF-7 (weakly invasive breast cancer cells), and 2.772 kPa for SKBR-3 (weakly invasive breast cancer cells), indicate that highly invasive cancer cells exhibited a lower Young's moduli than weakly invasive cells, which indicates a higher deformability of highly invasive cancer cells, leading to a higher metastasis rate. Single-cell treatment may also be carried out by bursting a highly invasive cell with high-intensity, focused ultrasound.

Classification of Breast Cancer Cells Using the Integration of High-Frequency Single-Beam Acoustic Tweezers and Convolutional Neural Networks

Single-beam acoustic tweezers (SBAT) is a widely used trapping technique to manipulate microscopic particles or cells. Recently, the characterization of a single cancer cell using high-frequency (>30 MHz) SBAT has been reported to determine its invasiveness and metastatic potential. Investigation of cell elasticity and invasiveness is based on the deformability of cells under SBAT’s radiation forces, and in general, more physically deformed cells exhibit higher levels of invasiveness and therefore higher metastatic potential. However, previous imaging analysis to determine substantial differences in cell deformation, where the SBAT is turned ON or OFF, relies on the subjective observation that may vary and requires follow-up evaluations from experts. In this study, we propose an automatic and reliable cancer cell classification method based on SBAT and a convolutional neural network (CNN), which provides objective and accurate quantitative measurement results. We used a custom-designed 50 MHz SBAT transducer to obtain a series of images of deformed human breast cancer cells. CNN-based classification methods with data augmentation applied to collected images determined and validated the metastatic potential of cancer cells. As a result, with the selected optimizers, precision, and recall of the model were found to be greater than 0.95, which highly validates the classification performance of our integrated method. CNN-guided cancer cell deformation analysis using SBAT may be a promising alternative to current histological image analysis, and this pretrained model will significantly reduce the evaluation time for a larger population of cells.

The mechanical responses of advecting cells in confined flow

Fluid dynamics have long influenced cells in suspension. Red blood cells and white blood cells are advected through biological microchannels in both the cardiovascular and lymphatic systems and, as a result, are subject to a wide variety of complex fluidic forces as they pass through. In vivo, microfluidic forces influence different biological processes such as the spreading of infection, cancer metastasis, and cell viability, highlighting the importance of fluid dynamics in the blood and lymphatic vessels. This suggests that in vitro devices carrying cell suspensions may influence the viability and functionality of cells. Lab-on-a-chip, flow cytometry, and cell therapies involve cell suspensions flowing through microchannels of approximately 100-800  μ m. This review begins by examining the current fundamental theories and techniques behind the fluidic forces and inertial focusing acting on cells in suspension, before exploring studies that have investigated how these fluidic forces affect the reactions of suspended cells. In light of these studies' findings, both in vivo and in vitro fluidic cell microenvironments shall also be discussed before concluding with recommendations for the field.

Finite Element Modelling of Single Cell Based on Atomic Force Microscope Indentation Method

The stiffness of cells, especially cancer cells, is a key mechanical property that is closely associated with their biomechanical functions, such as the mechanotransduction and the metastasis mechanisms of cancer cells. In light of the low survival rate of single cells and measurement uncertainty, the finite element method (FEM) was used to quantify the deformations and predict the stiffness of single cells. To study the effect of the cell components on overall stiffness, two new FEM models were proposed based on the atomic force microscopy (AFM) indentation method. The geometric sizes of the FEM models were determined by AFM topography images, and the validity of the FEM models was verified by comparison with experimental data. The effect of the intermediate filaments (IFs) and material properties of the cellular continuum components on the overall stiffness were investigated. The experimental results showed that the stiffness of cancer cells has apparent positional differences. The FEM simulation results show that IFs contribute only slightly to the overall stiffness within 10% strain, although they can transfer forces directly from the membrane to the nucleus. The cytoskeleton (CSK) is the major mechanical component of a cell. Furthermore, parameter studies revealed that the material properties (thickness and elasticity) of the continuum have a significant influence on the overall cellular stiffness while Poisson's ratio has less of an influence on the overall cellular stiffness. The proposed FEM models can determine the contribution of the major components of the cells to the overall cellular stiffness and provide insights for understanding the response of cells to the external mechanical stimuli and studying the corresponding mechanical mechanisms and cell biomechanics.

Enhanced osteoinduction of electrospun scaffolds with assemblies of hematite nanoparticles as a bioactive interface

Purpose

Electrospun scaffolds have been studied extensively for their potential use in bone tissue engineering. However, their hydrophobicity and relatively low matrix stiffness constrain their osteoinduction capacities. In the present study, we studied polymer electrospun scaffolds coated with hydrophilic hematite nanoparticles (αFeNPs) constructed using layer-by-layer (LbL) assembly to construct a bioactive interface between the scaffolds and cells, to improve the osteoinduction capacities of the scaffolds.

Materials and methods

The morphology of the αFeNPs was assessed. Surface properties of the scaffolds were tested by X-ray photoelectron spectroscopy (XPS), surface water contact angle, and in vitro protein adsorption test. The stiffness of the coating was tested using an atomic force microscope (AFM). In vitro cell assays were performed using rat adipose-derived stem cells (ADSCs).

Results

Morphology characterizations showed that αFeNPs assembled on the surface of the scaffold, where the nano assemblies improved hydrophilicity and increased surface roughness, with increased surface stiffness. Enhanced initial ADSC cell spread was found in the nano assembled groups. Significant enhancements in osteogenic differentiation, represented by enhanced alkaline phosphatase (ALP) activities, elevated expression of osteogenic marker genes, and increased mineral synthesis by the seeded ADSCs, were detected. The influencing factors were attributed to the better hydrophilicity, rougher surface topography, and harder interface stiffness. In addition, the presence of nanoparticles was believed to provide better cell adhesion sites.

Conclusion

The results suggested that the construction of a bioactive interface by LbL assembly using αFeNPs on traditional scaffolds should be a promising method for bone tissue engineering.

Measuring Elastic Properties of Single Cancer Cells by AFM

Atomic force microscopy (AFM) enables the measurements of the elastic properties of individual cells in liquids that mimic natural conditions. The single-cell deformability, quantitatively described through the Young's (elastic) modulus, can be used as a marker of pathological alterations, particularly those observed in cancer progression. Here, the AFM-based measurements and data analysis of mechanical properties of single cancerous cells are presented.

Magnetic Cell-Scaffold Interface Constructed by Superparamagnetic IONP Enhanced Osteogenesis of Adipose-Derived Stem Cells

One of the key factors in tissue engineering and regenerative medicine is to optimize the interaction between seed cells and scaffolds such that the cells can grow in naturally biomimetic conditions. Their similarity to macromolecules and many unique properties mean that functional nanoparticles have promising potential for the modification and improvement of traditional scaffolds to obtain excellent biocompatibility, tunable stiffness, physical sensing, and stimulus-response capabilities. In the present study, we report magnetic poly(lactic- co-glycolic acid)/polycaprolactone (PLGA/PCL) scaffolds that were fabricated using a combination of the electrospinning technique and layer-by-layer assembly of superparamagnetic iron oxide nanoparticles (IONPs). PLGA/PCL scaffolds assembled with gold nanoparticles were prepared using the same method for comparison. The results showed that the assembled film of nanoparticles on the surface greatly enhanced the hydrophilicity and increased the elastic modulus of the scaffold, which subsequently improved the osteogenesis of the stem cells. Furthermore, the magnetic property of the IONPs proved to be the key factor in enhancing osteogenic differentiation, which explained the superior osteogenic capacity of the magnetic scaffolds compared with that of the gold nanoparticle-assembled scaffold. These results demonstrated the importance of magnetic nanomaterials as a bioactive interface between cells and scaffolds and will promote the design of biomaterials to improve tissue engineering and regenerative medicine efficacy.

Development of a novel optogenetic indicator based on cellular deformations for mapping optogenetic activities

Optogenetic techniques have changed the landscape of neuroscience by offering high temporal and spatial mapping of the activities of genetically defined population of cells with optical controlling tools. The mapping of optogenetic activities demands optogenetic indicators whose optical properties change in response to cellular activities, but the existing optogenetic indicators only specifically characterize limited optogenetic activities. Here, we propose a novel optogenetic indicator based on cellular deformation to characterize the activities of optogenetically engineered cells. The cellular activities triggered by light stimulation lead to changes in the cell membrane structure and result in cellular deformation, which is measured by atomic force microscopy. The deformation recordings of the cells expressing channelrhodopsin-2 (ChR2) and the corresponding control experiments together confirm that the deformation is generated generally when the cells are exposed to light, which is also validated indirectly via the change in the Young's modulus of the cells before and after absorption of photons. The activities of cells expressing different subtypes of opsins were also recorded using the optogenetic indicator of cellular deformation. This study provides a novel and general optogenetic indicator based on cellular deformation for monitoring the activities of optogenetically engineered cells. Moreover, this new optogenetic indicator offers ever-better tools for the applications of optogenetic activity mapping and neural and brain imaging.

Microsphere-Based Nanoindentation for the Monitoring of Cellular Cortical Stiffness Regulated by MT1-MMP

Biophysical properties are intimately connected to metastatic functions and aggressiveness in cancers. Especially, cellular stiffness is regarded as a biomarker for the understanding of metastatic potential and drug sensitivity. Here, protease-mediated changes of cortical stiffness are identified due to the deformation of cytoskeleton alignment at a cortex. For the past few decades, membrane type 1-matrix metalloproteinase (MT1-MMP) has been well known as a kernel protease enriched in podosomes during metastasis for extracellular matrix degradation. However, the biophysical significance of MT1-MMP expressing cancer cells is still unknown. Therefore, the nanomechanics of cancer cells is analyzed by a nanoindentation using a microsphere-attached cantilever of atomic force microscopy (AFM). In conclusion, the results suggest that MT1-MMP has contributed as a key regulator in cytoskeletal deformation related with cancer metastasis. Particularly, the AFM-based nanoindentation system for the monitoring of cortical nanomechanics will be crucial to understand molecular networks in cancers.

Nanoparticle-Cell Interaction: A Cell Mechanics Perspective

Progress in the field of nanoparticles has enabled the rapid development of multiple products and technologies; however, some nanoparticles can pose both a threat to the environment and human health. To enable their safe implementation, a comprehensive knowledge of nanoparticles and their biological interactions is needed. In vitro and in vivo toxicity tests have been considered the gold standard to evaluate nanoparticle safety, but it is becoming necessary to understand the impact of nanosystems on cell mechanics. Here, the interaction between particles and cells, from the point of view of cell mechanics (i.e., bionanomechanics), is highlighted and put in perspective. Specifically, the ability of intracellular and extracellular nanoparticles to impair cell adhesion, cytoskeletal organization, stiffness, and migration are discussed. Furthermore, the development of cutting-edge, nanotechnology-driven tools based on the use of particles allowing the determination of cell mechanics is emphasized. These include traction force microscopy, colloidal probe atomic force microscopy, optical tweezers, magnetic manipulation, and particle tracking microrheology.

Stereochemical Structure Activity Relationship Studies (S-SAR) of Tetrahydrolipstatin

Tetrahydrolipstatin (THL), its enantiomer, and an additional six diastereomers were evaluated as inhibitors of the hydrolysis of p-nitrophenyl butyrate by porcine pancreatic lipase. IC₅₀s were found for all eight stereoisomers ranging from a low of 4.0 nM for THL to a high of 930 nM for the diastereomer with the inverted stereocenters at the 2,3,2'-positions. While the enantiomer of THL was also significantly less active (77 nM) the remaining five stereoisomers retained significant inhibitory activities (IC₅₀s = 8.0 to 20 nM). All eight compounds were also evaluated against three human cancer cell lines (human breast cancers MCF-7 and MDA-MB-231, human large-cell lung carcinoma H460). No appreciable cytotoxicity was observed for THL and its seven diastereomers, as their IC₅₀s in a MTT cytotoxicity assay were all greater than 3 orders of magnitude of camptothecin.

Biomechanical measurement and analysis of colchicine-induced effects on cells by nanoindentation using an atomic force microscope

Colchicine is a drug commonly used for the treatment of gout, however, patients may sometimes encounter side-effects induced by taking colchicine, such as nausea, vomiting, diarrhea and kidney failure. In this regard, it is imperative to investigate the mechanism effects of colchicine on biological cells. In this paper, we present a method for the detection of mechanical properties of nephrocytes (VERO cells), hepatocytes (HL-7702 cells) and hepatoma cells (SMCC-7721 cells) in culture by atomic force microscope (AFM) to analyze the 0.1 μg/mL colchicine-induced effects on the nanoscale for two, four and six hours. Compared to the corresponding control cells, the biomechanical properties of the VERO and SMCC-7721 cells changed significantly and the HL-7702 cells did not considerably change after the treatment when considering the same time period. Based on biomechanical property analyses, the colchicine solution made the VERO and SMCC-7721 cells harder. We conclude that it is possible to reduce the division rate of the VERO cells and inhibit the metastasis of the SMCC-7721 cells. The method described here can be applied to study biomechanics of many other types of cells with different drugs. Therefore, this work provides an accurate and rapid method for drug screening and mechanical analysis of cells in medical research.

A combined experimental and theoretical approach towards mechanophenotyping of biological cells using a constricted microchannel

We report a combined experimental and theoretical technique that enables the characterization of various mechanical properties of biological cells. The cells were infused into a microfluidic device that comprises multiple parallel micro-constrictions to eliminate device clogging and facilitate characterization of cells of different sizes and types on a single device. The extension ratio λ and transit velocity U_c of the cells were measured using high-speed and high-resolution imaging which were then used in a theoretical model to predict the Young's modulus E_c = f(λ, U_c) of the cells. The predicted Young's modulus E_c values for three different cell lines (182 ± 34.74 Pa for MDA MB 231, 360 ± 75 Pa for MCF 10A and, 763 ± 93 Pa for HeLa) compare well with those reported in the literature from micropipette measurements and atomic force microscopy measurement within 10% and 15%, respectively. Also, the Young's modulus of MDA-MB-231 cells treated with 50 μM 4-hyrdroxyacetophenone (for localization of myosin II) for 30 min was found out to be 260 ± 52 Pa. The entry time t_e of cells into the micro-constrictions was predicted using the model and validated using experimentally measured data. The entry and transit behaviors of cells in the micro-constriction including cell deformation (extension ratio λ) and velocity U_c were experimentally measured and used to predict various cell properties such as the Young's modulus, cytoplasmic viscosity and induced hydrodynamic resistance of different types of cells. The proposed combined experimental and theoretical approach leads to a new paradigm for mechanophenotyping of biological cells.

Atomic Force Microscopy in Characterizing Cell Mechanics for Biomedical Applications: A Review

Cell mechanics is a novel label-free biomarker for indicating cell states and pathological changes. The advent of atomic force microscopy (AFM) provides a powerful tool for quantifying the mechanical properties of single living cells in aqueous conditions. The wide use of AFM in characterizing cell mechanics in the past two decades has yielded remarkable novel insights in understanding the development and progression of certain diseases, such as cancer, showing the huge potential of cell mechanics for practical applications in the field of biomedicine. In this paper, we reviewed the utilization of AFM to characterize cell mechanics. First, the principle and method of AFM single-cell mechanical analysis was presented, along with the mechanical responses of cells to representative external stimuli measured by AFM. Next, the unique changes of cell mechanics in two types of physiological processes (stem cell differentiation, cancer metastasis) revealed by AFM were summarized. After that, the molecular mechanisms guiding cell mechanics were analyzed. Finally the challenges and future directions were discussed.

Regulation of Endothelial Cell Adherence and Elastic Modulus by Substrate Stiffness

Although substrate stiffness has been previously reported to affect various cellular aspects, such as morphology, migration, viability, growth, and cytoskeletal structure, its influence on cell adherence has not been well examined. Here, we prepared three soft, medium, and hard polyacrylamide (PAAM) substrates and utilized AFM to study substrate elasticity and also the adhesion and mechanical properties of endothelial cells in response to changing substrate stiffness. Maximum detachment force and cell stiffness were increased with increasing substrate stiffness. Maximum detachment force values were 0.28 ± 0.14, 0.94 ± 0.27, and 1.99 ± 0.59 nN while Young's moduli of cells were 218.85 ± 38.73, 385.58 ± 131.67, and 933.20 ± 428.92 Pa for soft, medium, and hard substrates, respectively. Human umbilical vein endothelial cells (HUVECs) showed round to more spread shapes on soft to hard substrates, with the most organized and elongated actin structure on the hard hydrogel. Our results confirm the importance of substrate stiffness in regulating cell mechanics and adhesion for a successful cell therapy.

Nano-mechanical signature of brain tumours

Glioblastoma (GBM) and meningothelial meningioma (MM) are the most frequent malignant and benign brain lesions, respectively. Mechanical cues play a major role in the progression of both malignancies that is modulated by the occurrence of aberrant physical interactions between neoplastic cells and the extracellular matrix (ECM). Here we investigate the nano-mechanical properties of human GBM and MM tissues by atomic force microscopy. Our measures unveil the mechanical fingerprint of the main hallmark features of both lesions, such as necrosis in GBM and dural infiltration in MM. These findings have the potential to positively impact on the development of novel AFM-based diagnostic methods to assess the tumour grade. Most importantly, they provide a quantitative description of the tumour-induced mechanical modifications in the brain ECM, thus being of potential help in the search for novel ECM targets for brain tumours and especially for GBM that, despite years of intense research, has still very limited therapeutic options.

Remote Actuation of Magnetic Nanoparticles For Cancer Cell Selective Treatment Through Cytoskeletal Disruption

Motion of micron and sub-micron size magnetic particles in alternating magnetic fields can activate mechanosensitive cellular functions or physically destruct cancer cells. However, such effects are usually observed with relatively large magnetic particles (>250 nm) that would be difficult if at all possible to deliver to remote sites in the body to treat disease. Here we show a completely new mechanism of selective toxicity of superparamagnetic nanoparticles (SMNP) of 7 to 8 nm in diameter to cancer cells. These particles are coated by block copolymers, which facilitates their entry into the cells and clustering in the lysosomes, where they are then magneto-mechanically actuated by remotely applied alternating current (AC) magnetic fields of very low frequency (50 Hz). Such fields and treatments are safe for surrounding tissues but produce cytoskeletal disruption and subsequent death of cancer cells while leaving healthy cells intact.

Current status and perspectives in atomic force microscopy-based identification of cellular transformation

Understanding the complex interplay between cells and their biomechanics and how the interplay is influenced by the extracellular microenvironment, as well as how the transforming potential of a tissue from a benign to a cancerous one is related to the dynamics of both the cell and its surroundings, holds promise for the development of targeted translational therapies. This review provides a comprehensive overview of atomic force microscopy-based technology and its applications for identification of cellular progression to a cancerous phenotype. The review also offers insights into the advancements that are required for the next user-controlled tool to allow for the identification of early cell transformation and thus potentially lead to improved therapeutic outcomes.

Discrimination Between Normal and Cancerous Cells Using AFM

Currently, biomechanics of living cells is in the focus of interest due to noticeable capability of such techniques like atomic force microscopy (AFM) to probe cellular properties at the single cell level directly on living cells. The research carried out, so far, delivered data showing, on the one hand, the use of cellular mechanics as a biomarker of various pathological changes, which, on the other hand, reveal relative nature of biomechanics. In the AFM, the elastic properties of living cells are delivered from indentation experiments and described quantitatively by Young's modulus defined here as a measure of cellular deformability. Here, the AFM studies directly comparing the mechanical properties of normal and cancerous cells are summarized and presented together with a few important issues related to the relativeness of Young's modulus.

Characterization and sorting of cells based on stiffness contrast in a microfluidic channel

This paper reports the characterization and sorting of cells based on stiffness contrast. A microfluidic device with focusing and spacing control for stiffness based sorting of cells is designed, fabricated and demonstrated.

Lovastatin enhances adenovirus-mediated TRAIL induced apoptosis by depleting cholesterol of lipid rafts and affecting CAR and death receptor expression of prostate cancer cells

Oncolytic adenovirus and apoptosis inducer TRAIL are promising cancer therapies. Their antitumor efficacy, when used as single agents, is limited. Oncolytic adenoviruses have low infection activity, and cancer cells develop resistance to TRAIL-induced apoptosis. Here, we explored combining prostate-restricted replication competent adenovirus-mediated TRAIL (PRRA-TRAIL) with lovastatin, a commonly used cholesterol-lowering drug, as a potential therapy for advanced prostate cancer (PCa). Lovastatin significantly enhanced the efficacy of PRRA-TRAIL by promoting the in vivo tumor suppression, and the in vitro cell killing and apoptosis induction, via integration of multiple molecular mechanisms. Lovastatin enhanced PRRA replication and virus-delivered transgene expression by increasing the expression levels of CAR and integrins, which are critical for adenovirus 5 binding and internalization. Lovastatin enhanced TRAIL-induced apoptosis by increasing death receptor DR4 expression. These multiple effects of lovastatin on CAR, integrins and DR4 expression were closely associated with cholesterol-depletion in lipid rafts. These studies, for the first time, show correlations between cholesterol/lipid rafts, oncolytic adenovirus infection efficiency and the antitumor efficacy of TRAIL at the cellular level. This work enhances our understanding of the molecular mechanisms that support use of lovastatin, in combination with PRRA-TRAIL, as a candidate strategy to treat human refractory prostate cancer in the future.