Fibre crosslinking drives the emergence of order in a three-dimensional dynamical network model.

The extracellular-matrix (ECM) is a complex interconnected three-dimensional network that provides structural support for the cells and tissues and defines organ architecture as key for their healthy functioning. However, the intimate mechanisms by which ECM acquire their three-dimensional architecture are still largely unknown. In this paper, we study this question by means of a simple three-dimensional individual based model of interacting fibres able to spontaneously crosslink or unlink to each other and align at the crosslinks. We show that such systems are able to spontaneously generate different types of architectures. We provide a thorough analysis of the emerging structures by an exhaustive parametric analysis and the use of appropriate visualization tools and quantifiers in three dimensions. The most striking result is that the emergence of ordered structures can be fully explained by a single emerging variable: the number of links per fibre in the network. If validated on real tissues, this simple variable could become an important putative target to control and predict the structuring of biological tissues, to suggest possible new therapeutic strategies to restore tissue functions after disruption, and to help in the development of collagen-based scaffolds for tissue engineering. Moreover, the model reveals that the emergence of architecture is a spatially homogeneous process following a unique evolutionary path, and highlights the essential role of dynamical crosslinking in tissue structuring.

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!

Nanobiomechanical behavior of Fe3O4@SiO2and Fe3O4@SiO2-NH2nanoparticles over HeLa cells interfaces.

In this work, we studied the impact of magnetic nanoparticles (MNPs) interactions with HeLa cells when they are exposed to high frequency alternating magnetic field (AMF). Specifically, we measured the nanobiomechanical properties of cell interfaces by using atomic force microscopy (AFM). Magnetite (Fe3O4) MNPs were synthesized by coprecipitation and encapsulated with silica (SiO2): Fe3O4@SiO2and functionalized with amino groups (-NH2): Fe3O4@SiO2-NH2, by sonochemical processing. HeLa cells were incubated with or without MNPs, and then exposed to AMF at 37 °C. A biomechanical analysis was then performed through AFM, providing the Young's modulus and stiffness of the cells. The statistical analysis (p < 0.001) showed that AMF application or MNPs interaction modified the biomechanical behavior of the cell interfaces. Interestingly, the most significant difference was found for HeLa cells incubated with Fe3O4@SiO2-NH2and exposed to AMF, showing that the local heat of these MNPs modified their elasticity and stiffness.

Automation of Bio-Atomic Force Microscope Measurements on Hundreds of C. albicans Cells.

The method presented in this paper aims to automate Bio-AFM experiments and the recording of force curves. Using this method, it is possible to record forces curves on 1000 cells in 4 hours automatically. To maintain a 4 hour analysis time, the number of force curves per cell is reduced to 9 or 16. The method combines a Jython based program and a strategy for assembling cells on defined patterns. The program, implemented on a commercial Bio-AFM, can center the tip on the first cell of the array and then move, automatically, from cell to cell while recording force curves on each cell. Using this methodology, it is possible to access the biophysical parameters of the cells such as their rigidity, their adhesive properties, etc. With the automation and the large number of cells analyzed, one can access the behavior of the cell population. This is a breakthrough in the Bio-AFM field where data have, so far, been recorded on only a few tens of cells.

Characterization of the physical properties of tumor-derived spheroids reveals critical insights for pre-clinical studies.

Three-dimensional spheroids are widely used as cancer models to study tumor cell proliferation and to evaluate new anticancer drugs. Growth-induced stress (i.e., stress that persists in tumors after external loads removal) influences tumor growth and resistance to treatment. However, it is not clear whether spheroids recapitulate the tumor physical properties. Here, we demonstrated experimentally and with the support of mathematical models that, like tumors, spheroids accumulate growth-induced stress. Moreover, we found that this stress is lower in spheroids made of 5,000 cancer cells and grown for 2 days than in spheroids made of 500 cancer cells and grown for 6 days. These two culture conditions associated with different growth-induced stress levels also had different effects on the spheroid shape (using light sheet microscopy) and surface topography and stiffness (using scanning electron microscopy and atomic force microscopy). Finally, the response to irinotecan was different in the two spheroid types. Taken together, our findings bring new insights into the relationship between the spheroid physical properties and their resistance to antitumor treatment that should be taken into account by the experimenters when assessing new therapeutic agents using in vitro 3D models or when comparing studies from different laboratories.

Adsorption of Proteins on m-CPPD and Urate Crystals Inhibits Crystal-induced Cell Responses: Study on Albumin-crystal Interaction.

The biological effects and cellular activations triggered by monosodium urate (MSU) and calcium pyrophosphate dihydrate (monoclinic: m-CPPD) crystals might be modulated by protein coating on the crystal surface. This study is aimed at: (i) Identifying proteins adsorbed on m-CPPD crystals, and the underlying mechanisms of protein adsorption, and (ii) to understand how protein coating did modulate the inflammatory properties of m-CPPD crystals. The effects of protein coating were assessed in vitro using primary macrophages and THP1 monocytes. Physico-chemical studies on the adsorption of bovine serum albumin (BSA) upon m-CPPD crystals were performed. Adsorption of serum proteins, and BSA on MSU, as well as upon m-CPPD crystals, inhibited their capacity to induce interleukin-1-ß secretions, along with a decreased ATP secretion, and a disturbance of mitochondrial membrane depolarization, suggesting an alteration of NLRP3 inflammasome activation. Proteomic analysis identified numerous m-CPPD-associated proteins including hemoglobin, complement, albumin, apolipoproteins and coagulation factors. BSA adsorption on m-CPPD crystals followed a Langmuir-Freundlich isotherm, suggesting that it could modulate m-CPPD crystal-induced cell responses through crystal/cell-membrane interaction. BSA is adsorbed on m-CPPD crystals with weak interactions, confirmed by the preliminary AFM study, but strong interactions of BSA molecules with each other occurred favoring crystal agglomeration, which might contribute to a decrease in the inflammatory properties of m-CPPD crystals. These findings give new insights into the pathogenesis of crystal-related rheumatic diseases and subsequently may open the way for new therapeutic approaches.

Biophysical properties of cardiomyocyte surface explored by multiparametric AFM.

PeakForce Quantitative Nanomechanical Mapping (PeakForce QNM) multiparametric AFM mode was adapted to qualitative and quantitative study of the lateral membrane of cardiomyocytes (CMs), extending this powerful mode to the study of soft cells. On living CM, PeakForce QNM depicted the crests and hollows periodic alternation of cell surface architecture previously described using AFM Force Volume (FV) mode. PeakForce QNM analysis provided better resolution in terms of pixel number compared to FV mode and reduced acquisition time, thus limiting the consequences of spontaneous living adult CM dedifferentiation once isolated from the cardiac tissue. PeakForce QNM mode on fixed CMs clearly visualized subsarcolemmal mitochondria (SSM) and their loss following formamide treatment, concomitant with the interfibrillar mitochondria climbing up and forming heaps at the cell surface. Interestingly, formamide-promoted SSM loss allowed visualization of the sarcomeric apparatus ultrastructure below the plasma membrane. High PeakForce QNM resolution led to better contrasted mechanical maps than FV mode and provided correlation between adhesion, dissipation, mechanical and topographical maps. Modified hydrophobic AFM tip enhanced contrast on adhesion and dissipation maps and suggested that CM surface crests and hollows exhibit distinct chemical properties. Finally, two-dimensional Fast Fourier Transform to objectively quantify AFM maps allowed characterization of periodicity of both sarcomeric Z-line and M-band. Overall, this study validated PeakForce QNM as a valuable and innovative mode for the exploration of living and fixed CMs. In the future, it could be applied to depict cell membrane architectural, mechanical and chemical defects as well as sarcomeric abnormalities associated with cardiac diseases.

Methods of Micropatterning and Manipulation of Cells for Biomedical Applications.

Micropatterning and manipulation of mammalian and bacterial cells are important in biomedical studies to perform in vitro assays and to evaluate biochemical processes accurately, establishing the basis for implementing biomedical microelectromechanical systems (bioMEMS), point-of-care (POC) devices, or organs-on-chips (OOC), which impact on neurological, oncological, dermatologic, or tissue engineering issues as part of personalized medicine. Cell patterning represents a crucial step in fundamental and applied biological studies in vitro, hence today there are a myriad of materials and techniques that allow one to immobilize and manipulate cells, imitating the 3D in vivo milieu. This review focuses on current physical cell patterning, plus chemical and a combination of them both that utilizes different materials and cutting-edge micro-nanofabrication methodologies.

Elasticity, Adhesion, and Tether Extrusion on Breast Cancer Cells Provide a Signature of Their Invasive Potential.

We use single-cell force spectroscopy to compare elasticity, adhesion, and tether extrusion on four breast cancer cell lines with an increasing invasive potential. We perform cell attachment/detachment experiments either on fibronectin or on another cell using an atomic force microscope. Our study on the membrane tether formation from cancer cells show that they are easier to extrude from aggressive invasive cells. Measured elastic modulus values confirm that more invasive cells are softer. Moreover, the adhesion force increases with the invasive potential. Our results provide a mechanical signature of breast cancer cells that correlates with their invasivity.

Automated and Multiplexed Soft Lithography for the Production of Low-Density DNA Microarrays.

Microarrays are established research tools for genotyping, expression profiling, or molecular diagnostics in which DNA molecules are precisely addressed to the surface of a solid support. This study assesses the fabrication of low-density oligonucleotide arrays using an automated microcontact printing device, the InnoStamp 40(®). This automate allows a multiplexed deposition of oligoprobes on a functionalized surface by the use of a MacroStamp(TM) bearing 64 individual pillars each mounted with 50 circular micropatterns (spots) of 160 µm diameter at 320 µm pitch. Reliability and reuse of the MacroStamp(TM) were shown to be fast and robust by a simple washing step in 96% ethanol. The low-density microarrays printed on either epoxysilane or dendrimer-functionalized slides (DendriSlides) showed excellent hybridization response with complementary sequences at unusual low probe and target concentrations, since the actual probe density immobilized by this technology was at least 10-fold lower than with the conventional mechanical spotting. In addition, we found a comparable hybridization response in terms of fluorescence intensity between spotted and printed oligoarrays with a 1 nM complementary target by using a 50-fold lower probe concentration to produce the oligoarrays by the microcontact printing method. Taken together, our results lend support to the potential development of this multiplexed microcontact printing technology employing soft lithography as an alternative, cost-competitive tool for fabrication of low-density DNA microarrays.

Essential role of class II PI3K-C2α in platelet membrane morphology.

The physiologic roles of the class II phosphoinositide 3-kinases (PI3Ks) and their contributions to phosphatidylinositol 3-monophosphate (PI3P) and PI(3,4)P2 production remain elusive. Here we report that mice heterozygous for a constitutively kinase-dead PI3K-C2α display aberrant platelet morphology with an elevated number of barbell-shaped proplatelets, a recently discovered intermediate stage in the final process of platelet production. Platelets with heterozygous PI3K-C2α inactivation have critical defects in α-granules and membrane structure that are associated with modifications in megakaryocytes. These platelets are more rigid and unable to form filopodia after stimulation. Heterozygous PI3K-C2α inactivation in platelets led to a significant reduction in the basal pool of PI3P and a mislocalization of several membrane skeleton proteins known to control the interactions between the plasma membrane and cytoskeleton. These alterations had repercussions on the performance of platelet responses with delay in the time of arterial occlusion in an in vivo model of thrombosis and defect in thrombus formation in an ex vivo blood flow system. These data uncover a key role for PI3K-C2α activity in the generation of a basal housekeeping PI3P pool and in the control of membrane remodeling, critical for megakaryocytopoiesis and normal platelet production and function.

Atomic force and electron microscopic-based study of sarcolemmal surface of living cardiomyocytes unveils unexpected mitochondrial shift in heart failure.

Loss of T-tubules (TT), sarcolemmal invaginations of cardiomyocytes (CMs), was recently identified as a general heart failure (HF) hallmark. However, whether TT per se or the overall sarcolemma is altered during HF process is still unknown. In this study, we directly examined sarcolemmal surface topography and physical properties using Atomic Force Microscopy (AFM) in living CMs from healthy and failing mice hearts. We confirmed the presence of highly organized crests and hollows along myofilaments in isolated healthy CMs. Sarcolemma topography was tightly correlated with elasticity, with crests stiffer than hollows and related to the presence of few packed subsarcolemmal mitochondria (SSM) as evidenced by electron microscopy. Three days after myocardial infarction (MI), CMs already exhibit an overall sarcolemma disorganization with general loss of crests topography thus becoming smooth and correlating with a decreased elasticity while interfibrillar mitochondria (IFM), myofilaments alignment and TT network were unaltered. End-stage post-ischemic condition (15days post-MI) exacerbates overall sarcolemma disorganization with, in addition to general loss of crest/hollow periodicity, a significant increase of cell surface stiffness. Strikingly, electron microscopy revealed the total depletion of SSM while some IFM heaps could be visualized beneath the membrane. Accordingly, mitochondrial Ca(2+) studies showed a heterogeneous pattern between SSM and IFM in healthy CMs which disappeared in HF. In vitro, formamide-induced sarcolemmal stress on healthy CMs phenocopied post-ischemic kinetics abnormalities and revealed initial SSM death and crest/hollow disorganization followed by IFM later disarray which moved toward the cell surface and structured heaps correlating with TT loss. This study demonstrates that the loss of crest/hollow organization of CM surface in HF occurs early and precedes disruption of the TT network. It also highlights a general stiffness increased of the CM surface most likely related to atypical IFM heaps while SSM died during HF process. Overall, these results indicate that initial sarcolemmal stress leading to SSM death could underlie subsequent TT disarray and HF setting.

Detection of label-free cancer biomarkers using nickel nanoislands and quartz crystal microbalance.

We present a technique for the label-free detection and recognition of cancer biomarkers using metal nanoislands intended to be integrated in a novel type of nanobiosensor. His-tagged (scFv)-F7N1N2 is the antibody fragment which is directly immobilized, by coordinative bonds, onto ~5 nm nickel islands, then deposited on the surface of a quartz crystal of a quartz crystal microbalance (QCM) to validate the technique. Biomarker GTPase RhoA was investigated because it has been found to be overexpressed in various tumors and because we have recently isolated and characterized a new conformational scFv which selectively recognizes the active form of RhoA. We implemented a surface chemistry involving an antibiofouling coating of polyethylene glycol silane (PEG-silane) (<2 nm thick) and Ni nanoislands to reach a label-free detection of the active antigen conformation of RhoA, at various concentrations. The methodology proposed here proves the viability of the concept by using Ni nanoislands as an anchoring surface layer enabling the detection of a specific conformation of a protein, identified as a potential cancer biomarker. Hence, this novel methodology can be transferred to a nanobiosensor to detect, at lower time consumption and with high sensitivity, specific biomolecules.

Poly(dimethylsiloxane) contamination in microcontact printing and its influence on patterning oligonucleotides.

It is well-established that, during microcontact printing (muCP) using poly(dimethylsiloxane) (PDMS)-based stamps, some unexpected siloxane fragments can be transferred from the stamp to the surface of the sample. This so-called contamination effect coexists with the delivery of the molecules constituting the ink and by this way influences the printing process. The real impact of this contamination for the muCP technique is still partially unknown. In this work, we investigate the kinetics of this contamination process through the surface characterization of both the sample and the stamp after imprinting. The way both the curing conditions of the PDMS material and the contact time influence the degree of contamination of the surface is investigated on silicon and glass substrates. We propose a cleaning process of the stamp during several hours which eliminates any trace of contamination during printing. We show that hydrophobicity recovery of PDMS surfaces after hydrophilic treatment using oxygen plasma is considerably slowed down when the PDMS material is cleaned using our procedure. Finally, by comparing cleaned and uncleaned PDMS stamps, we show the influence of contamination on the quality of muCP using fluorescent DNA molecules as an ink. Surprisingly, we observe that the amount of DNA molecules transferred during muCP is higher for the uncleaned stamp, highlighting the positive impact of the presence of low molecular weight siloxane fragments on the muCP process. This result is attributed to the better adsorption of oligonucleotides on the stamp surface in presence of these contaminating molecules.