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Jochen Guck - One of the best experts on this subject based on the ideXlab platform.

  • Mechanical deformation induces depolarization of neutrophils
    Science Advances, 2017
    Co-Authors: Andrew Ekpenyong, Jochen Guck, Gheorghe Cojoc, Christine Fiddler, Nicole Toepfner, Maik Herbig, Charlotte Summers, Edwin R. Chilvers
    Abstract:

    The transition of neutrophils from a resting state to a primed state is an essential requirement for their function as competent immune cells. This transition can be caused not only by chemical signals but also by mechanical perturbation. After cessation of either, these cells gradually revert to a quiescent state over 40 to 120 min. We use two biophysical tools, an Optical Stretcher and a novel microcirculation mimetic, to effect physiologically relevant mechanical deformations of single nonadherent human neutrophils. We establish quantitative morphological analysis and mechanical phenotyping as label-free markers of neutrophil priming. We show that continued mechanical deformation of primed cells can cause active depolarization, which occurs two orders of magnitude faster than by spontaneous depriming. This work provides a cellular-level mechanism that potentially explains recent clinical studies demonstrating the potential importance, and physiological role, of neutrophil depriming in vivo and the pathophysiological implications when this deactivation is impaired, especially in disorders such as acute lung injury.

  • Volume Transitions of Isolated Cell Nuclei Induced by Rapid Temperature Increase.
    Biophysical Journal, 2017
    Co-Authors: Chii J. Chan, Gheorghe Cojoc, Jochen Guck
    Abstract:

    Understanding the physical mechanisms governing nuclear mechanics is important as it can impact gene expression and development. However, how cell nuclei respond to external cues such as heat is not well understood. Here, we studied the material properties of isolated nuclei in suspension using an Optical Stretcher. We demonstrate that isolated nuclei regulate their volume in a highly temperature-sensitive manner. At constant temperature, isolated nuclei behaved like passive, elastic and incompressible objects, whose volume depended on the pH and ionic conditions. When the temperature was increased suddenly by even a few degrees Kelvin, nuclei displayed a repeatable and reversible temperature-induced volume transition, whose sign depended on the valency of the solvent. Such phenomenon is not observed for nuclei subjected to slow heating. The transition temperature could be shifted by adiabatic changes of the ambient temperature, and the magnitude of temperature-induced volume transition could be modulated by modifying the chromatin compaction state and remodeling processes. Our findings reveal that the cell nucleus can be viewed as a highly charged polymer gel with intriguing thermoresponsive properties, which might play a role in nuclear volume regulation and thermosensing in living cells.

  • Mechanical mismatch between Ras transformed and untransformed epithelial cells
    Soft Matter, 2017
    Co-Authors: Corinne Gullekson, Jochen Guck, Gheorghe Cojoc, Mirjam Schürmann, Andrew E. Pelling
    Abstract:

    The organization of the actin cytoskeleton plays a key role in regulating cell mechanics. It is fundamentally altered during transformation, affecting how cells interact with their environment. We investigated mechanical properties of cells expressing constitutively active, oncogenic Ras (RasV12) in adherent and suspended states. To do this, we utilized atomic force microscopy and a microfluidic Optical Stretcher. We found that adherent cells stiffen and suspended cells soften with the expression of constitutively active Ras. The effect on adherent cells was reversed when contractility was inhibited with the ROCK inhibitor Y-27632, resulting in softer RasV12 cells. Our findings suggest that increased ROCK activity as a result of Ras has opposite effects on suspended and adhered cells. Our results also establish the importance of the activation of ROCK by Ras and its effect on cell mechanics.

  • Deformation of phospholipid vesicles in an Optical Stretcher
    Soft Matter, 2015
    Co-Authors: Ulysse Delabre, Kasper Feld, Eleonore Crespo, Graeme Whyte, Cecile Sykes, Udo Seifert, Jochen Guck
    Abstract:

    Phospholipid vesicles are common model systems for cell membranes. Important aspects of the membrane function relate to its mechanical properties. Here we have investigated the deformation behaviour of phospholipid vesicles in a dual-beam laser trap, also called an Optical Stretcher. This study explicitly makes use of the inherent heating present in such traps to investigate the dependence of vesicle deformation on temperature. By using lasers with different wavelengths, Optically induced mechanical stresses and temperature increase can be tuned fairly independently with a single setup. The phase transition temperature of vesicles can be clearly identified by an increase in deformation. In the case of no heating effects, a minimal model for drop deformation in an Optical Stretcher and a more specific model for vesicle deformation that takes explicitly into account the angular dependence of the Optical stress are presented to account for the experimental results. Elastic constants are extracted from the fitting procedures, which agree with literature data. This study demonstrates the utility of Optical stretching, which is easily combined with microfluidic delivery, for the future serial, high-throughput study of the mechanical and thermodynamic properties of phospholipid vesicles.

  • Unique Mechanical Properties of Cell Nuclei Regulated by Chromatin
    Biophysical Journal, 2015
    Co-Authors: Chii J. Chan, Mirjam Schürmann, Jana Scholze, Jochen Guck
    Abstract:

    Nuclear mechanics and structure could affect gene regulation and gene expression. Chromatin, a major component of cell nuclei, could play an important role in maintaining nuclear integrity and their mechanical properties. Previous studies on nuclear mechanical properties have focused largely on the role of the nuclear lamina, using techniques such as AFM and micropipette aspiration. In this work, we explicitly address the contributions of chromatin to nuclear rheology after isolation from the cell using a microfluidic Optical Stretcher. We find that isolated nuclei swell in volume under uni-axial stress and exhibit significant softening with increased nuclear size, which can be described by a filtration model for the nuclear membrane and a cortical chromatin model, respectively. In addition, changes to the state of chromatin condensation via histone modifications or chromatin remodeling processes (ATP, topoisomerase II) can strongly impact nuclear morphology and compliance. Moreover, isolated nuclear mechanics is also sensitive to ionic conditions: nuclei stiffen with increasing ionic strength of the buffer and exhibit a transition from stretch to contraction in the presence of multivalent ions (only). Finally, we find that in contrast to other studies suggesting a high refractive index of cell nuclei compared to the cytoplasm, the refractive index of isolated cell nuclei of a variety of cell types can be lower than the refractive index of the cells. The presented work establishes a quantitative link between nuclear mechanical properties and the compaction state of chromatin, which can be modulated by a change in nuclear volume, chromatin remodeling or electrochemical environment.

Josef A. Käs - One of the best experts on this subject based on the ideXlab platform.

  • Influence of Hyaluronic Acid Binding on the Actin Cortex measured by Optical Forces.
    Journal of Biophotonics, 2020
    Co-Authors: Jörg Schnauß, B. U. Sebastian Schmidt, Christina B. Brazel, Senol Dogan, Wolfgang Losert, Ulf Anderegg, Josef A. Käs
    Abstract:

    Melanoma cells are often surrounded by hyaluronic acid (HA) rich environments, which are considered to promote tumor progression and metastasis. Induced effects in compound materials consisting of cells embedded in an extracellular matrix have been studied, however, alterations of the single cells have never been addressed. Here, we explicitly addressed single cell properties and measured HA-induced biomechanical changes via deformations induced solely by Optical forces. With the Optical Stretcher setup, cells were deformed after culturing them in either the presence or absence of HA revealing the crucial interplay of HA with the CD44 receptor. To assess the role of CD44 in transducing effects of HA, we compared a CD44 expressing variant of the melanoma cell line RPM-MC to its natural CD44-negative counterpart. Our measurements revealed a significant stiffness change, which we attribute to changes of the actin cytoskeleton.

  • Detecting heterogeneity in and between breast cancer cell lines.
    Cancer Convergence, 2020
    Co-Authors: Yang Shen, Josef A. Käs, B. U. Sebastian Schmidt, Hans Kubitschke, Erik W. Morawetz, Benjamin Wolf, Wolfgang Losert
    Abstract:

    Cellular heterogeneity in tumor cells is a well-established phenomenon. Genetic and phenotypic cell-to-cell variability have been observed in numerous studies both within the same type of cancer cells and across different types of cancers. Another known fact for metastatic tumor cells is that they tend to be softer than their normal or non-metastatic counterparts. However, the heterogeneity of mechanical properties in tumor cells are not widely studied. Here we analyzed single-cell Optical Stretcher data with machine learning algorithms on three different breast tumor cell lines and show that similar heterogeneity can also be seen in mechanical properties of cells both within and between breast tumor cell lines. We identified two clusters within MDA-MB-231 cells, with cells in one cluster being softer than in the other. In addition, we show that MDA-MB-231 cells and MDA-MB-436 cells which are both epithelial breast cancer cell lines with a mesenchymal-like phenotype derived from metastatic cancers are mechanically more different from each other than from non-malignant epithelial MCF-10A cells. Since stiffness of tumor cells can be an indicator of metastatic potential, this result suggests that metastatic abilities could vary within the same monoclonal tumor cell line.

  • Quantifying the mechanics and growth of cells and tissues in 3D using high resolution computational models.
    2018
    Co-Authors: Paul Van Liedekerke, Josef A. Käs, Johannes Neitsch, Tim Johann, Enrico Warmt, Ismael Gonzales Valverde, Stefan Höhme, Steffen Grosser, Dirk Drasdo
    Abstract:

    Abstract Mathematical models are increasingly designed to guide experiments in biology, biotechnology, as well as to assist in medical decision making. They are in particular important to understand emergent collective cell behavior. For this purpose, the models, despite still abstractions of reality, need to be quantitative in all aspects relevant for the question of interest. The focus in this paper is to study the regeneration of liver after drug-induced depletion of hepatocytes, in which surviving dividing and migrating hepatocytes must squeeze through a blood vessel network to fill the emerged lesions. Here, the cells’ response to mechanical stress might significantly impact on the regeneration process. We present a 3D high-resolution cell-based model integrating information from measurements in order to obtain a refined quantitative understanding of the cell-biomechanical impact on the closure of drug-induced lesions in liver. Our model represents each cell individually, constructed as a physically scalable network of viscoelastic elements, capable of mimicking realistic cell deformation and supplying information at subcellular scales. The cells have the capability to migrate, grow and divide, and infer the nature of their mechanical elements and their parameters from comparisons with Optical Stretcher experiments. Due to triangulation of the cell surface, interactions of cells with arbitrarily shaped (triangulated) structures such as blood vessels can be captured naturally. Comparing our simulations with those of so-called center-based models, in which cells have a rigid shape and forces are exerted between cell centers, we find that the migration forces a cell needs to exert on its environment to close a tissue lesion, is much smaller than predicted by center-based models. This effect is expected to be even more present in chronic liver disease, where tissue stiffens and excess collagen narrows pores for cells to squeeze through.

  • Changing cell mechanics—a precondition for malignant transformation of oral squamous carcinoma cells
    Convergent Science Physical Oncology, 2018
    Co-Authors: Felix Meinhövel, Josef A. Käs, Roland Stange, Jörg Schnauß, Michael Sauer, Torsten W. Remmerbach
    Abstract:

    Oral squamous cell carcinomas (OSCC) are the sixth most common cancer and the diagnosis is often belated for a curative treatment. The reliable and early differentiation between healthy and diseased cells is the main aim of this study in order to improve the quality of the treatment and to understand tumour pathogenesis. Here, the Optical Stretcher is used to analyse mechanical properties of cells and their potential to serve as a marker for malignancy. Stretching experiments revealed for the first time that cells of primary OSCCs were deformed by 2.9% rendering them softer than cells of healthy mucosa which were deformed only by 1.9%. Furthermore, the relaxation behaviour of the cells revealed that these malignant cells exhibit a faster contraction than their benign counterparts. This suggests that deformability as well as relaxation behaviour can be used as distinct parameters to evaluate emerging differences between these benign and malignant cells. Since many studies in cancer research are performed with cancer cell lines rather than primary cells, we have compared the deformability and relaxation of both types, showing that long time culturing leads to softening of cells. The higher degree of deformability and relaxation behaviour can enable cancer cells to traverse tissue emphasizing that changes in cell architecture may be a potential precondition for malignant transformation. Respecting the fact that even short culture times have an essential effect on the significance of the results, the use of primary cells for further research is recommended. The distinction between malignant and benign cells would enable an early confirmation of cancer diagnoses by testing cell samples of suspect oral lesions.

  • Pharmacological targeting of membrane rigidity: implications on cancer cell migration and invasion
    New Journal of Physics, 2015
    Co-Authors: Simone Braig, B. U. Sebastian Schmidt, Katharina Stoiber, Chris Händel, Till Möhn, Oliver Werz, Rolf Müller, Stefan Zahler, Andreas Koeberle, Josef A. Käs
    Abstract:

    The invasive potential of cancer cells strongly depends on cellular stiffness, a physical quantity that is not only regulated by the mechanical impact of the cytoskeleton but also influenced by the membrane rigidity. To analyze the specific role of membrane rigidity in cancer progression, we treated cancer cells with the Acetyl-CoA carboxylase inhibitor Soraphen A and revealed an alteration of the phospholipidome via mass spectrometry. Migration, invasion, and cell death assays were employed to relate this alteration to functional consequences, and a decrease of migration and invasion without significant impact on cell death has been recorded. Fourier fluctuation analysis of giant plasma membrane vesicles showed that Soraphen A increases membrane rigidity of carcinoma cell membranes. Mechanical measurements of the creep deformation response of whole intact cells were performed using the Optical Stretcher. The increase in membrane rigidity was observed in one cell line without changing the creep deformation response indicating no restructuring of the cytoskeleton. These data indicate that the increase of membrane rigidity alone is sufficient to inhibit invasiveness of cancer cells, thus disclosing the eminent role of membrane rigidity in migratory processes.

Mareike Zink - One of the best experts on this subject based on the ideXlab platform.

  • Active contractions in single suspended epithelial cells
    European Biophysics Journal, 2014
    Co-Authors: Markus Gyger, Roland Stange, Tobias R Kießling, Anatol Fritsch, Katja B. Kostelnik, Annette G. Beck-sickinger, Mareike Zink
    Abstract:

    Investigations of active contractions in tissue cells to date have been focused on cells that exert forces via adhesion sites to substrates or to other cells. In this study we show that also suspended epithelial cells exhibit contractility, revealing that contractions can occur independently of focal adhesions. We employ the Optical Stretcher to measure adhesion-independent mechanical properties of an epithelial cell line transfected with a heat-sensitive cation channel. During stretching the heat transferred to the ion channel causes a pronounced Ca^2+ influx through the plasma membrane that can be blocked by adequate drugs. This way the contractile forces in suspended cells are shown to be partially triggered by Ca^2+ signaling. A phenomenological mathematical model is presented, incorporating a term accounting for the active stress exerted by the cell, which is both necessary and sufficient to describe the observed increase in strain when the Ca^2+ influx is blocked. The median and the shape of the strain distributions depend on the activity of the cells. Hence, it is unlikely that they can be described by a simple Gaussian or log normal distribution, but depend on specific cellular properties such as active contractions. Our results underline the importance of considering activity when measuring cellular mechanical properties even in the absence of measurable contractions. Thus, the presented method to quantify active contractions of suspended cells offers new perspectives for a better understanding of cellular force generation with possible implications for medical diagnosis and therapy.

  • Der Optical Stretcher — kontaktfreie Messung der Zellmechanik
    BIOspektrum, 2012
    Co-Authors: Mareike Zink, Josef A. Käs
    Abstract:

    The Optical Stretcher, developed in our lab, is a technology to contact-free measure cellular mechanical properties with a through-put of several hundred cells per hour. Even without any biomolecular information, our approach clearly shows that the deformation of cells reflects enough information to distinguish different cell types and detect aging effects. Furthermore, three clinical studies on oral, breast and cervix carcinoma clearly show that tumor cells are softer and deform more than normal cells.

  • der Optical Stretcher kontaktfreie messung der zellmechanik
    Biospektrum, 2012
    Co-Authors: Mareike Zink, Josef A. Käs
    Abstract:

    The Optical Stretcher, developed in our lab, is a technology to contact-free measure cellular mechanical properties with a through-put of several hundred cells per hour. Even without any biomolecular information, our approach clearly shows that the deformation of cells reflects enough information to distinguish different cell types and detect aging effects. Furthermore, three clinical studies on oral, breast and cervix carcinoma clearly show that tumor cells are softer and deform more than normal cells.

  • ERBB2 overexpression triggers transient high mechanoactivity of breast tumor cells.
    Cytoskeleton, 2012
    Co-Authors: Mireille Martin, Mareike Zink, Karla Müller, Cristina Cadenas, Matthias Hermes, Jan G. Hengstler, Josef A. Käs
    Abstract:

    Biomechanical properties of tumor cells play an important role for the metastatic capacity of cancer. Cellular changes of viscoelastic features are prerequisite for cancer progression since they are essential for proliferation and metastasis. However, only little is known about the way how expression of oncogenes influences these biomechanical properties. To address this aspect we used a breast cancer cell line with inducible expression of an oncogenic version of ERBB2. ERBB2 is known to be correlated with bad prognosis in breast cancer. Cell elasticity was determined by the Optical Stretcher, where suspended cells are deformed by two slightly divergent laser beams. We found that induction of ERBB2 caused remarkable biomechanical alterations of the MCF-7 cells after 24 h: the cells actively contracted in response to mechanical stimuli, a phenomenon known as mechanoactivation. After this period, as the cells became senescent, the mechanoactivity returned to control levels. Time-resolved gene array analysis revealed that mechanoactivation was accompanied by temporal upregulation of 46 cytoskeletal genes. A possible role of these genes in tumor progression was investigated by expression analyses of 766 breast cancer patients. This showed an association of 12 out of these 46 genes with increased risk of metastasis. Our results demonstrate that overexpression of ERBB2 causes mechanoactivation of tumor cells, which may enhance tumor cell motility fostering distant metastasis.

  • Calcium imaging in the Optical Stretcher
    Optics Express, 2011
    Co-Authors: Markus Gyger, Mareike Zink, Daniel Rose, Roland Stange, Tobias R Kießling, Ben Fabry, Josef A. Käs
    Abstract:

    The Microfluidic Optical Stretcher (MOS) has previously been shown to be a versatile tool to measure mechanical properties of single suspended cells. In this study we combine Optical stretching and fluorescent calcium imaging. A cell line transfected with a heat sensitive cation channel was used as a model system to show the versatility of the setup. The cells were loaded with the Ca(2+) dye Fluo-4 and imaged with confocal laser scanning microscopy while being stretched. During Optical stretching heat is transferred to the cell causing a pronounced Ca(2+) influx through the cation channel. The technique opens new perspectives for investigating the role of Ca(2+) in regulating cell mechanical behavior.

Graeme Whyte - One of the best experts on this subject based on the ideXlab platform.

  • Optomechanical measurement of the role of lamins in whole cell deformability.
    Journal of Biophotonics, 2017
    Co-Authors: Thorsten Kolb, Julia Kraxner, Kai Skodzek, Michael Haug, Dean Crawford, Kendra K. Maaß, Katerina E. Aifantis, Graeme Whyte
    Abstract:

    There is mounting evidence that the nuclear envelope, and particularly the lamina, plays a critical role in the mechanical and regulation properties of the cell and changes to the lamina can have implications for the physical properties of the whole cell. In this study we demonstrate that the Optical Stretcher can measure changes in the time-dependent mechanical properties of living cells with different levels of A-type lamin expression. Results from the Optical Stretcher shows a decrease in the deformability of cells as the levels of lamin A increases, for cells which grow both adherently and in suspension. Further detail can be probed by combining the Optical Stretcher with fluorescence microscopy to investigate the nuclear mechanical properties which show a larger decrease in deformability than for the whole cell.

  • Deformation of phospholipid vesicles in an Optical Stretcher
    Soft Matter, 2015
    Co-Authors: Ulysse Delabre, Kasper Feld, Eleonore Crespo, Graeme Whyte, Cecile Sykes, Udo Seifert, Jochen Guck
    Abstract:

    Phospholipid vesicles are common model systems for cell membranes. Important aspects of the membrane function relate to its mechanical properties. Here we have investigated the deformation behaviour of phospholipid vesicles in a dual-beam laser trap, also called an Optical Stretcher. This study explicitly makes use of the inherent heating present in such traps to investigate the dependence of vesicle deformation on temperature. By using lasers with different wavelengths, Optically induced mechanical stresses and temperature increase can be tuned fairly independently with a single setup. The phase transition temperature of vesicles can be clearly identified by an increase in deformation. In the case of no heating effects, a minimal model for drop deformation in an Optical Stretcher and a more specific model for vesicle deformation that takes explicitly into account the angular dependence of the Optical stress are presented to account for the experimental results. Elastic constants are extracted from the fitting procedures, which agree with literature data. This study demonstrates the utility of Optical stretching, which is easily combined with microfluidic delivery, for the future serial, high-throughput study of the mechanical and thermodynamic properties of phospholipid vesicles.

  • A monolithic glass chip for active single-cell sorting based on mechanical phenotyping
    Lab on a Chip, 2015
    Co-Authors: Christoph Faigle, Graeme Whyte, Franziska Lautenschläger, Philip Homewood, Estela Martín-badosa, Jochen Guck
    Abstract:

    The mechanical properties of biological cells have long been considered as inherent markers of biological function and disease. However, the screening and active sorting of heterogeneous populations based on serial single-cell mechanical measurements has not been demonstrated. Here we present a novel monolithic glass chip for combined fluorescence detection and mechanical phenotyping using an Optical Stretcher. A new design and manufacturing process, involving the bonding of two asymmetrically etched glass plates, combines exact Optical fiber alignment, low laser damage threshold and high imaging quality with the possibility of several microfluidic inlet and outlet channels. We show the utility of such a custom-built Optical Stretcher glass chip by measuring and sorting single cells in a heterogeneous population based on their different mechanical properties and verify sorting accuracy by simultaneous fluorescence detection. This offers new possibilities of exact characterization and sorting of small populations based on rheological properties for biological and biomedical applications.

  • impact of heating on passive and active biomechanics of suspended cells
    Interface Focus, 2014
    Co-Authors: Jochen Guck, Graeme Whyte, Lars Boyde, Chii J. Chan, Guillaume Salbreux
    Abstract:

    A cell is a complex material whose mechanical properties are essential for its normal functions. Heating can have a dramatic effect on these mechanical properties, similar to its impact on the dynamics of artificial polymer networks. We investigated such mechanical changes by the use of a microfluidic Optical Stretcher, which allowed us to probe cell mechanics when the cells were subjected to different heating conditions at different time scales. We find that HL60/S4 myeloid precursor cells become mechanically more compliant and fluid-like when subjected to either a sudden laser-induced temperature increase or prolonged exposure to higher ambient temperature. Above a critical temperature of 52 ± 1°C, we observed active cell contraction, which was strongly correlated with calcium influx through temperature-sensitive transient receptor potential vanilloid 2 (TRPV2) ion channels, followed by a subsequent expansion in cell volume. The change from passive to active cellular response can be effectively described by a mechanical model incorporating both active stress and viscoelastic components. Our work highlights the role of TRPV2 in regulating the thermomechanical response of cells. It also offers insights into how cortical tension and osmotic pressure govern cell mechanics and regulate cell-shape changes in response to heat and mechanical stress.

  • Elastic theory for the deformation of a solid or layered spheroid under axisymmetric loading
    Acta Mechanica, 2013
    Co-Authors: Lars Boyde, Andrew Ekpenyong, Graeme Whyte, Jochen Guck
    Abstract:

    The theory for the deformations of a spheroidal particle is of great scientific interest in numerous physical and biological problems ranging from fracture analysis of plain solids to the compression of biological cells in an atomic force microscope or during micropipette aspiration. Using a formulation in terms of Papkovich–Neuber potentials, we derive the deformations of a prolate, elastic spheroid under known axisymmetric loading. The internal stresses to which the object is subjected are deduced from Hooke’s law of elasticity in prolate spheroidal coordinates. The generalisation to layered spheroids with viscoelastic properties is also discussed. Since for isotropic objects the surface displacements and stresses are directly related by the elastic modulus and Poisson’s ratio alone, the presented, closed-form, analytical solutions may be applied to deduce these important elastic constants from standard stress-deformation experiments. We illustrate the versatility of the findings by analysing the surface displacements and stress states of spheroids with small and large aspect ratios in the presence of both normal and shear surface tractions. Of particular interest in this study is the influence of Poisson’s ratio on the deformation of a near-spherical particle, for instance a soft cancer cell, which is subjected to surface stresses of the kind that can be found in Optical traps, like the Optical Stretcher.

Falk Wottawah - One of the best experts on this subject based on the ideXlab platform.

  • Oral Cancer Diagnosis by Mechanical Phenotyping
    Cancer Research, 2009
    Co-Authors: Torsten W. Remmerbach, Bryan Lincoln, Falk Wottawah, Julia Dietrich, Christian Wittekind, Jochen Guck
    Abstract:

    Oral squamous cell carcinomas are among the 10 most common cancers and have a 50% lethality rate after 5 years. Despite easy access to the oral cavity for cancer screening, the main limitations to successful treatment are uncertain prognostic criteria for (pre-)malignant lesions. Identifying a functional cellular marker may represent a significant improvement for diagnosis and treatment. Toward this goal, mechanical phenotyping of individual cells is a novel approach to detect cytoskeletal changes, which are diagnostic for malignant change. The compliance of cells from cell lines and primary samples of healthy donors and cancer patients was measured using a microfluidic Optical Stretcher. Cancer cells showed significantly different mechanical behavior, with a higher mean deformability and increased variance. Cancer cells (n approximately 30 cells measured from each patient) were on average 3.5 times more compliant than those of healthy donors [D(normal) = (4.43 +/- 0.68) 10(-3) Pa(-1); D(cancer) = (15.8 +/- 1.5) 10(-3) Pa(-1); P < 0.01]. The diagnosis results of the patient samples were confirmed by standard histopathology. The generality of these findings was supported by measurements of two normal and four cancer oral epithelial cell lines. Our results indicate that mechanical phenotyping is a sensible, label-free approach for classifying cancer cells to enable broad screening of suspicious lesions in the oral cavity. It could in principle be applied to any cancer to aid conventional diagnostic procedures.

  • Reconfigurable microfluidic integration of a dual-beam laser trap with biomedical applications
    Biomedical Microdevices, 2007
    Co-Authors: Bryan Lincoln, Falk Wottawah, Stefan Schinkinger, Susanne Ebert, Kort Travis, Frank Sauer, Jochen Guck
    Abstract:

    A dual-beam fiber laser trap, termed the Optical Stretcher when used to deform objects, has been combined with a capillary-based microfluidic system in order to serially trap and deform biological cells. The design allows for control over the size and position of the trap relative to the flow channel. Data is recorded using video phase contrast microscopy and is subsequently analyzed using a custom edge fitting routine. This setup has been regularly used with measuring rates of 50–100 cells/h. One such experiment is presented to compare the distribution of deformability found within a normal epithelial cell line to that of a cancerous one. In general, this microfluidic Optical Stretcher can be used for the characterization of cells by their viscoelastic signature. Possible applications include the cytological diagnosis of cancer and the gentle and marker-free sorting of stem cells from heterogeneous populations for therapeutic cell-based approaches in regenerative medicine.

  • High-throughput rheological measurements with an Optical Stretcher
    Methods in Cell Biology, 2007
    Co-Authors: Bryan Lincoln, Falk Wottawah, Stefan Schinkinger, Susanne Ebert, Jochen Guck
    Abstract:

    The cytoskeleton is a major determinant of the mechanical strength and morphology of most cells. The composition and assembly state of this intracellular polymer network evolve during the differentiation of cells, and the structure is involved in many cellular functions and is characteristically altered in many diseases, including cancer. Here we exploit the deformability of the cytoskeleton as a link between molecular structure and biological function, to distinguish between cells in different states by using a laser-based Optical Stretcher (OS) coupled with microfluidic handling of cells. An OS is a cell-sized, dual-beam laser trap designed to nondestructively test the deformability of single suspended cells. Combined with microfluidic delivery, many cells can be measured serially in a short amount of time. With this tool it could be shown that Optical deformability is sensitive enough to monitor subtle changes during the progression of cells from normal to cancerous and even a metastatic state. Stem cells can also be distinguished from more differentiated cells. The surprisingly low number of cells required for this assay reflects the tight regulation of the cytoskeleton by the cell. This suggests the possibility of using Optical deformability as an inherent cell marker for basic cell biological investigation, diagnosis of disease, and sorting of stem cells from heterogeneous populations, obviating the need for external markers or special preparation. Many additional biological assays can be easily adapted to utilize this innovative physical method. This chapter details the setup and use of the microfluidic OS, the analysis and interpretation of data, and the results of a typical experiment.

  • Feeling with light for cancer
    Advanced Biomedical and Clinical Diagnostic Systems IV, 2006
    Co-Authors: Mireille Martin, Bryan Lincoln, Falk Wottawah, Stefan Schinkinger, Maren Romeyke, Karla Mueller, Josef A. Käs
    Abstract:

    Even minute alterations in a cell's intracellular scaffolds, i.e. the cytoskeleton, which organize a cell, result in significant changes in a cell's elastic strength since the cytoskeletal mechanics nonlinearly amplify these alterations. Light has been used to observe cells since Leeuwenhoek's times and novel techniques in Optical microscopy are frequently developed in biological physics. In contrast, with the Optical Stretcher we use the forces caused by light described by Maxwell's surface tensor to feel cells. Thus, the Stretcher exemplifies the other type of biophotonic devices that do not image but manipulate cells. The Optical Stretcher uses Optical surface forces to stretch cells between two opposing laser beams, while Optical gradient forces, which are used in Optical tweezers, play a minor role and only contribute to a stable trapping configuration. The combination of the Optical Stretcher's sensitivity and high throughput capacity make a cell's "Optical stretchiness" an extremely precise parameter to distinguish different cell types. This avoids the use of expensive, often unspecific molecular cell markers. This technique applies particularly well to cells with dissimilar degrees of differentiation, as a cell's maturation correlates with an increase in cytoskeletal strength. Because malignant cells gradually dedifferentiate during the progression of cancer, the Optical Stretcher should allow, the direct staging from early dysplasia to metastasis of a tumor sample obtained by MRI-guided fine needle aspirations or cytobrushes. With two prototypes of a microfluidic Optical Stretcher at our hands, we prepare preclinical trials to study its potential in resolving breast tumors' progression towards metastasis. Since the Optical Stretcher represents a basic technology for cell recognition and sorting, an abundance of further biomedical applications can be envisioned.

  • Quantifying the contribution of actin networks to the elastic strength of fibroblasts
    Journal of Theoretical Biology, 2006
    Co-Authors: Revathi Ananthakrishnan, Jochen Guck, Bryan Lincoln, Falk Wottawah, Stefan Schinkinger, Maren Romeyke, Tessie J Moon, Josef A. Käs
    Abstract:

    The structural models created to understand the cytoskeletal mechanics of cells in suspension are described here. Suspended cells can be deformed by well-defined surface stresses in an Optical Stretcher [Guck, J., Ananthakrishnan, R., Mahmood, H., Moon, T.J., Cunningham, C.C., Kas, J., 2001. The Optical Stretcher: a novel laser tool to micromanipulate cells. Biophys. J. 81(2), 767-784], a two-beam Optical trap designed for the contact-free deformation of cells. Suspended cells have a well-defined cytoskeleton, displaying a radially symmetric actin cortical network underlying the cell membrane with no actin stress fibers, and microtubules and intermediate filaments in the interior. Based on experimental data using suspended fibroblasts, we create two structural models: a thick shell actin cortex model that describes cell deformation for a localized stress distribution on these cells and a three-layered model that considers the entire cytoskeleton when a broad stress distribution is applied. Applying the models to data, we obtain a (actin) cortical shear moduli G of approximately 220 Pa for normal fibroblasts and approximately 185 Pa for malignantly transformed fibroblasts. Additionally, modeling the cortex as a transiently crosslinked isotropic actin network, we show that actin and its crosslinkers must be co-localized into a tight shell to achieve these cortical strengths. The similar moduli values and cortical actin and crosslinker densities but different deformabilities of the normal and cancerous cells suggest that a cell's structural strength is not solely determined by cytoskeletal composition but equally importantly by (actin) cytoskeletal architecture via differing cortical thicknesses. We also find that although the interior structural elements (microtubules, nucleus) contribute to the deformed cell's exact shape via their loose coupling to the cortex, it is the outer actin cortical shell (and its thickness) that mainly determines the cell's structural response.