AtomicJ: an open source software for analysis of force curves

CellMAP: an open-source software tool to batch-process cell topography and stiffness maps collected with an atomic force microscope

Atomic force microscopy (AFM) is the gold-standard technique to simultaneously map the morphology and viscoelastic properties of living cells. Although existing software tools, both open-source and from AFM manufacturers, can analyze cells individually, there is a growing need for fast and accessible codes to compile data from multiple cells into a single dataset. To address this, we present CellMAP, a user-friendly software tool that streamlines the batch-processing of AFM-derived topography and stiffness maps of living cells. Our analysis pipeline includes but is not limited to: flattening of the underlying substrate surface, filtering of outlier values, measurement of the cell surface and volume, and measurement of height and stiffness distributions. CellMAP can also generate a composite cell that reflects the height and stiffness properties of an entire cell population.

Atomic force microscopy reveals the influence of substrate collagen concentration and TGF-β on lung fibroblast mechanics

Understanding how extracellular matrix (ECM) stiffness and biochemical factors such as TGF-β affect cell behaviour is critical for elucidating mechanisms underlying several pathologic conditions such as tissue fibrosis and cancer metastasis. This study investigates the effects of varying collagen substrate concentration and consequently varying stiffness conditions along with TGF-β treatment on the morphology, nanomechanical properties, and gene expression of normal human lung fibroblasts (NHLF). Our results reveal that increased substrate stiffness leads to more elongated cell morphology, decreased cellular stiffness, and significant alterations in gene expression related to cytoskeletal organization and myofibroblast activation genes. TGF-β treatment further induces myofibroblast differentiation, as evidenced by increased α-SMA and collagen expression, while also reducing cellular stiffness and promoting a more elongated, invasive phenotype. These findings highlight the critical role of both mechanical and biochemical cues in modulating fibroblast behaviour, with significant implications in fibrosis development and cancer progression.

Mechanical Properties of Eye Lens Cortical and Nuclear Membranes and the Whole Lens

Purpose

To elucidate the mechanical properties of the bovine lens cortical membrane (CM), the nuclear membrane (NM) containing cholesterol bilayer domains (CBDs), and whole bovine lenses.

Methods

The total lipids (lipids plus cholesterol) from the cortex and nucleus of a single bovine lens were isolated using the monophasic methanol extraction method. Supported CMs and NMs were prepared from total lipids extracted from the cortex and nucleus, respectively, using a rapid solvent exchange method and probe-tip sonication, followed by the fusion of unilamellar vesicles on a flat, freshly cleaved mica surface. Topographical images and force curves for the CMs and NMs were obtained via atomic force microscopy (AFM) in a fluid cell. Whole bovine lenses were affixed to custom-built glass Petri dishes, and an AFM was used to obtain force curves. Force curves were analyzed to estimate the breakthrough force, membrane stiffness (KA and Em), and lens stiffness (EL).

Results

The NMs containing CBDs exhibited significantly lower breakthrough force, KA, and Em than the CMs without CBDs. The Em values for CMs and NMs were significantly higher than the EL for the whole lens.

Conclusions

The significantly higher stiffness of the CM and NM compared to the stiffness of the whole lens suggests that slight modulation in CM and NM composition may play a crucial role in altering the overall lens stiffness. Furthermore, the NMs containing CBDs were less stiff than CMs without CBDs, suggesting that CBDs decrease lens membrane stiffness and possibly protect against lens hardening and presbyopia.

Chitosan/vanillin/polydimethylsiloxane scaffolds with tunable stiffness for muscle cell proliferation

The mechanical properties of scaffolds can significantly influence cell behavior. We propose a methodology for producing chitosan and vanillin-crosslinked chitosan films with tunable mechanical properties to be applied as scaffolds for C2C12 myoblasts. In this approach, aqueous polydimethylsiloxane (PDMS) elastomeric dispersions were prepared using polysorbate 20 as emulsifier. These dispersions were then cured and incorporated into chitosan or vanillin-crosslinked chitosan polymeric dispersions at two different volume fractions (1 % and 10 %), followed by casting into films. Atomic force microscopy in force spectroscopy mode was used to characterize the mechanical properties of the swollen systems in PBS buffer. The mechanical properties of the chitosan and vanillin-crosslinked chitosan scaffolds were modulated by the incorporation of the elastomer. The elastic modulus (E) of chitosan-based scaffolds varied from 60 to 200 kPa, while for vanillin-based scaffolds, it ranged from 200 to 600 kPa with the addition of PDMS elastomers. A general trend observed was that the softest scaffolds exhibited the highest swelling degree and the lowest gel content. After 24 h, good cell viability was observed for chitosan and chitosan-PDMS scaffolds, whereas vanillin-based scaffolds showed borderline cytotoxicity (∼70 %). C2C12 cells demonstrated good adhesion on scaffolds with E values ranging from 114 to 568 kPa.

Electric Field Cycling of Physisorbed Antibodies Reduces Biolayer Polarization Dispersion

The electric dipoles of proteins in a biolayer determine their dielectric properties through the polarization density P. Hence, its reproducibility is crucial for applications, particularly in bioelectronics. Biolayers encompassing capturing antibodies covalently bound at a biosensing interface are generally preferred for their assumed higher stability. However, surface physisorption is shown to offer advantages like easily scalable fabrication processes and high stability. The present study investigates the effects of electric-field (EF)-cycling of anti-Immunoglobulin M (anti-IgM) biolayers physisorbed on Au. The impact of EF-cycling on the dielectric, optical, and mechanical properties of anti-IgM biolayer is investigated. A reduction of the dispersion (standard deviation over a set of 31 samples) of the measured P values is observed, while the set median stays almost constant. Hence, physisorption combined with EF cycling, results in a biolayer with highly reproducible bioelectronic properties. Additionally, the study provides important insights into the mechanisms of dielectric rearrangement of dipole moments in capturing biolayers after EF-cycling. Notably, EF-cycling acts as an annealing process, driving the proteins in the biolayer into a statistically more probable and stable conformational state. Understanding these phenomena enhances the knowledge of the properties of physisorbed biolayers and can inform design strategies for bioelectronic devices.

Development of an accurate simplified approach for data processing in AFM indentation experiments

Atomic Force Microscopy (AFM) nanoindentation is the most effective method for determining the mechanical properties of soft biological materials and biomaterials at the nanoscale, with significant applications in many areas, including cancer diagnosis. However, a major drawback of this method is the complexity of the experimental procedure and data processing, which requires several calibration steps.To avoid this complexity, the AFM tip is usually approximated as a perfect cone. In this case, F=ch2, where F is the applied force, ℎ is the indentation depth, and c is a constant that depends on both the cone's half-angle and the material's properties. However, since AFM tips are pyramidal with a rounded tip apex (or similar to a truncated cone in some cases), the conical approximation may lead to non-negligible errors. Although equations exist that relate the applied force, indentation depth, and the sample's Young's modulus for real indenters, they are rarely used because they do not directly relate the applied force to the indentation depth (i.e., the fitting process is much more complicated compared to the conical approximation). In this paper, a new, accurate, simplified approach for data processing is proposed, based on fitting the force-indentation data to a quadratic equation of the form: F=c2h2+c1h. It is proven that the parameter c2 is independent of the tip apex properties. On the other hand, the parameter c1 depends on the material properties, the cone's half angle, and the shape and dimensions of the tip apex. Simulated force-indentation data from sphero-conical and blunted pyramidal indenters, along with real experimental data from lung tissues, are processed using the proposed approach. The key result is that Young's modulus can be accurately determined using only the c2 parameter; therefore, tip characterization can be avoided.

Effect of hydrophobic proteins in modulating the mechanical properties of lung surfactant membranes

Pulmonary surfactant is a membranous complex that enables breathing dynamics at the respiratory surface. Extremely low values of surface tension are achieved at end-expiration thanks to a unique mixture of lipids and proteins. In particular, the hydrophobic surfactant proteins, specially the protein SP-B, are crucial for surfactant biophysical function, in order to provide the surfactant lipid matrix with the ability to form membranous multi-layered interfacial films that sustain optimal mechanical properties. To analyse the contribution of the proteins to modulate the resistance to mechanical forces of surfactant membrane-based structures, atomic force microscopy of supported lipid bilayers has been used here to determine quantitative mechanical parameters defining the effect of the presence of proteins SP-B and/or SP-C on phospholipid membranes intended to model at least part of the structures integrated into pulmonary surfactant complexes. The results show clear differences introduced by proteins in membrane thickness, lateral packing and elasticity, providing evidence supporting protein-promoted modulating of the mechanical properties of surfactant membranes. These effects are found consistent with the behaviour of two relevant native materials: whole pulmonary surfactant isolated from porcine bronchoalveolar lavages and freshly produced human pulmonary surfactant isolated from amniotic fluid, where it is transferred from the foetal lung before the respiratory air-liquid interface has been established.

Nuclear deformability facilitates apical nuclear migration in the developing zebrafish retina

Nuclear positioning is a crucial aspect of cell and developmental biology. One example is the apical movement of nuclei in neuroepithelia before mitosis, which is essential for proper tissue formation. While the cytoskeletal mechanisms that drive nuclei to the apical side have been explored, the influence of nuclear properties on apical nuclear migration is less understood. Nuclear properties, such as deformability, can be linked to lamin A/C expression levels, as shown in various in vitro studies. Interestingly, many nuclei in early development, including neuroepithelial nuclei, express only low levels of lamin A/C. Therefore, we investigated whether increased lamin A expression in the densely packed zebrafish retinal neuroepithelium affects nuclear deformability and, consequently, migration phenomena. We found that overexpressing lamin A in retinal nuclei increases nuclear stiffness, which in turn indeed impairs apical nuclear migration. Interestingly, nuclei that do not overexpress lamin A but are embedded in a stiffer lamin A-overexpressing environment also exhibit impaired apical nuclear migration, indicating that these effects can be cell non-autonomous. Additionally, in the less crowded hindbrain neuroepithelium, only minor effects on apical nuclear migration are observed. Together, this suggests that the material properties of the nucleus influence nuclear movements in a tissue-dependent manner.

Mechanical investigation of a Tandem embolization-visualization system for minimally invasive procedures

Transcatheter arterial embolization is a minimally invasive intervention process in which the blood supply to a tumor or an abnormal area of tissue is blocked. One of the most commonly used embolic agents in clinics is microsphere (MS). In order to understand the flow behavior of microspheres in arteries, it is essential to study their mechanical properties systematically. In this work, calcium-alginate MSs with varying calcium concentrations were synthesized using a coaxial airflow method. Indocyanine green (ICG) was added as a fluorescent dye. The effect of ICG concentration change on microspheres was investigated by studying morphology, imageability, rheology, and swelling behavior. Then the effect of calcium chloride concentration change on microspheres was studied by conducting rheological tests, atomic force microscopy tests, hemolysis assay, and thrombogenicity assay. Results showed that microspheres with higher ICG concentrations have longer lasting fluorescence and lower storage modulus (G'). Higher concentrations of calcium chloride led to higher G', while the local Young's modulus obtained by AFM test was not significantly affected. The MSs with and without ICG showed good hemocompatibility and thrombogenicity.

Atomic force microscopy reveals morphological and mechanical properties of schistosoma mansoni tegument

Schistosoma mansoni, an intravascular parasitic worm and the causative agent of schistosomiasis, relies on its tegument (outer layer) for survival and host interaction. This study explored the morphology and mechanical properties of S. mansoni tegument using Atomic Force Microscopy (AFM). Notably, we employed the PeakForce Quantitative Nanomechanical Mapping (PF-QNM) mode in air, enabling simultaneous acquisition of 3D topography and mechanical property contrasts (adhesion, elastic modulus). Additionally, nanoindentation (AFM contact mode) was performed on female worm tegument for elastic modulus measurement. Both techniques revealed an elastic modulus range of fractions or units of GPa for the tegument. Interestingly, mechanical property maps, particularly adhesion contrast, displayed a recurring pattern of light and dark bands. We also measured the depth of annular furrows on the female tegument, finding an average of 128 ± 10 nm. These findings establish AFM, particularly PF-QNM, as a valuable tool to characterize S. mansoni tegument properties, offering insights for future investigations into parasite biology and its response to immunological or pharmacological challenges.

Substrate stiffness modulates extracellular vesicles' release in a triple-negative breast cancer model

Aim

The microenvironment effect on the tumoral-derived Extracellular Vesicle release, which is of significant interest for biomedical applications, still represents a rather unexplored field. The aim of the present work is to investigate the interrelation between extracellular matrix (ECM) stiffness and the release of small EVs from cancer cells. Here, we focus on the interrelation between the ECM and small extracellular vesicles (sEVs), specifically investigating the unexplored aspect of the influence of ECM stiffness on the release of sEVs.

Methods

We used a well-studied metastatic Triple-Negative Breast Cancer (TNBC) cell line, MDA-MB-231, as a model to study the release of sEVs by cells cultured on substrates of different stiffness. We have grown MDA-MB-231 cells on two collagen-coated polydimethylsiloxane (PDMS) substrates at different stiffness (0.2 and 3.6 MPa), comparing them with a hard glass substrate as control, and then we isolated the respective sEVs by differential ultracentrifugation. After checking the cell growth conditions [vitality, morphology by immunofluorescence microscopy, stiffness by atomic force microscopy (AFM)], we took advantage of a multi-parametric approach based on complementary techniques (AFM, Nanoparticle Tracking Analysis, and asymmetric flow field flow fractionation with a multi-angle light scattering detector) to characterize the TNBC-derived sEV obtained in the different substrate conditions.

Results

We observe that soft substrates induce TNBC cell softening and rounding. This effect promotes the release of a high number of larger sEVs.

Conclusion

Here, we show the role of ECM physical properties in the regulation of sEV release in a TNBC model. While the molecular mechanisms regulating this effect need further investigation, our report represents a step toward an improved understanding of ECM-cell-sEVs crosstalk.

Accurate Modelling of AFM Force-Indentation Curves with Blunted Indenters at Small Indentation Depths

When testing biological samples with atomic force microscopy (AFM) nanoindentation using pyramidal indenters, Sneddon's equation is commonly used for data processing, approximating the indenter as a perfect cone. While more accurate models treat the AFM tip as a blunted cone or pyramid, these are complex and lack a direct relationship between applied force and indentation depth, complicating data analysis. This paper proposes a new equation derived from simple mathematical processes and physics-based criteria. It is accurate for small indentation depths and serves as a viable alternative to complex classical approaches. The proposed equation has been validated for ℎ < 3R (where h is the indentation depth and R is the tip radius) and confirmed through simulations with blunted conical and pyramidal indenters, as well as experiments on prostate cancer cells. It is a reliable method for experiments where the tip radius cannot be ignored, such as in shallow indentations on thin samples to avoid substrate effects.

A Novel Nano-Spherical Tip for Improving Precision in Elastic Modulus Measurements of Polymer Materials via Atomic Force Microscopy

Micro-nano-scale mechanical properties are vital for engineering and biological materials. The elastic modulus is generally measured by processing the force-indentation curves obtained by atomic force microscopy (AFM). However, the measurement precision is largely affected by tip shape, tip wear, sample morphology, and the contact model. In such research, it has been found that the radius of the sharp tip increases due to wear during contact scanning, affecting elastic modulus calculations. For flat-ended tips, it is difficult to identify the contact condition, leading to inaccurate results. Our research team has invented a nano-spherical tip, obtained by implanting focused helium ions into a silicon microcantilever, causing it to expand into a silicon nanosphere. This nano-spherical tip has the advantages of sub-micro size and a smooth spherical surface. Comparative tests of the elastic modulus measurement were conducted on polytetrafluoroethylene (PTFE) and polypropylene (PP) using these three tips. Overall, the experimental results show that our nano-spherical tip with a consistent tip radius, symmetrical geometric shape, and resistance to wear and contamination can improve precision in elastic modulus measurements of polymer materials.

Mechanical characterization of Xenopus laevis oocytes using atomic force microscopy

Mechanical properties are essential for the biological activities of cells, and they have been shown to be affected by diseases. Therefore, accurate mechanical characterization is important for studying the cell lifecycle, cell-cell interactions, and disease diagnosis. While the cytoskeleton and actin cortex are typically the primary structural stiffness contributors in most live cells, oocytes possess an additional extracellular layer known as the vitelline membrane (VM), or envelope, which can significantly impact their overall mechanical properties. In this study, we utilized nanoindentation via an atomic force microscope to measure the Young's modulus of Xenopus laevis oocytes at different force setpoints and explored the influence of the VM by conducting measurements on oocytes with the membrane removed. The findings revealed that the removal of VM led to a significant decrease in the apparent Young's modulus of the oocytes, highlighting the pivotal role of the VM as the main structural component responsible for the oocyte's shape and stiffness. Furthermore, the mechanical behavior of VM was investigated through finite element (FE) simulations of the nanoindentation process. FE simulations with the VM Young's modulus in the range 20-60 MPa resulted in force-displacement curves that closely resemble experimental in terms of shape and maximum force for a given indentation depth.

A human pluripotent stem cell-based somitogenesis model using microfluidics

Emerging human pluripotent stem cell (hPSC)-based embryo models are useful for studying human embryogenesis. Particularly, there are hPSC-based somitogenesis models using free-floating culture that recapitulate somite formation. Somitogenesis in vivo involves intricately orchestrated biochemical and biomechanical events. However, none of the current somitogenesis models controls biochemical gradients or biomechanical signals in the culture, limiting their applicability to untangle complex biochemical-biomechanical interactions that drive somitogenesis. Herein, we develop a human somitogenesis model by confining hPSC-derived presomitic mesoderm (PSM) tissues in microfabricated trenches. Exogenous microfluidic morphogen gradients imposed on the PSM tissues cause axial patterning and trigger spontaneous rostral-to-caudal somite formation. A mechanical theory is developed to explain the size dependency between somites and the PSM. The microfluidic somitogenesis model is further exploited to reveal regulatory roles of cellular and tissue biomechanics in somite formation. This study presents a useful microengineered, hPSC-based model for understanding the biochemical and biomechanical events that guide somite formation.

PyFMLab: Open-source software for atomic force microscopy microrheology data analysis

Background

Atomic force microscopy (AFM) is one of the main techniques used to characterize the mechanical properties of soft biological samples and biomaterials at the nanoscale. Despite efforts made by the AFM community to promote open-source data analysis tools, standardization continues to be a significant concern in a field that requires common analysis procedures. AFM-based mechanical measurements involve applying a controlled force to the sample and measure the resulting deformation in the so-called force-distance curves. These may include simple approach and retract or oscillatory cycles at various frequencies (microrheology). To extract quantitative parameters, such as the elastic modulus, from these measurements, AFM measurements are processed using data analysis software. Although open tools exist and allow obtaining the mechanical properties of the sample, most of them only include standard elastic models and do not allow the processing of microrheology data. In this work, we have developed an open-source software package (called PyFMLab, as of python force microscopy laboratory) capable of determining the viscoelastic properties of samples from both conventional force-distance curves and microrheology measurements.

Methods

PyFMLab has been written in Python, which provides an accessible syntax and sufficient computational efficiency. The software features were divided into separate, self-contained libraries to enhance code organization and modularity and to improve readability, maintainability, testability, and reusability. To validate PyFMLab, two AFM datasets, one composed of simple force curves and another including oscillatory measurements, were collected on HeLa cells.

Results

The viscoelastic parameters obtained on the two datasets analysed using PyFMLab were validated against data processing proprietary software and against validated MATLAB routines developed before obtaining equivalent results.

Conclusions

Its open-source nature and versatility makes PyFMLab an open-source solution that paves the way for standardized viscoelastic characterization of biological samples from both force-distance curves and microrheology measurements.

Raman-AFM-fluorescence-guided impact of linoleic and eicosapentaenoic acids on subcellular structure and chemical composition of normal and cancer human colon cells

The regular overconsumption of high-energy food (rich in lipids and sugars) results in elevated nutrient absorption in intestine and consequently excessive accumulation of lipids in many organs e.g.: liver, adipose tissue, muscles. In the long term this can lead to obesity and obesity-associated diseases e.g. type 2 diabetes, non-alcoholic fatty liver disease, cardiovascular disease, inflammatory bowel disease (IBD). In the presented paper based on RI data we have proved that Raman maps can be used successfully for subcellular structures visualization and analysis of fatty acids impact on morphology and chemical composition of human colon single cells - normal and cancer. Based on Raman data we have investigated the changes related to endoplasmic reticulum, mitochondria, lipid droplets and nucleus. Analysis of ratios calculated based on Raman bands typical for proteins (1256, 1656 cm-1), lipids (1304, 1444 cm-1) and nucleic acids (750 cm-1) has confirmed for endoplasmic reticulum the increased activity of this organelle in lipoproteins synthesis upon FAs supplementation; for LDs the changes of desaturation of accumulated lipids with the highest unsaturation level for CaCo-2 cells upon EPA supplementation; for mitochondria the stronger effect of FAs supplementation was observed for CaCo-2 cells confirming the increased activity of this organelle responsible for energy production necessary for tumor development; the weakest impact of FAs supplementation was observed for nucleus for both types of cells and both types of acids. Fluorescence imaging was used for the investigations of changes in LDs/ER morphology. Our measurements have shown the increased area of LDs/ER for CaCo-2 cancer cells, and the strongest effect was noticed for CaCo-2 cells upon EPA supplementation. The increased participation of lipid structures for all types of cells upon FAs supplementation has been confirmed also by AFM studies. The lowest YM values have been observed for CaCo-2 cells including samples treated with FAs.

Fructose-1-kinase has pleiotropic roles in Escherichia coli

In Escherichia coli, the master transcription regulator catabolite repressor activator (Cra) regulates >100 genes in central metabolism. Cra binding to DNA is allosterically regulated by binding to fructose-1-phosphate (F-1-P), but the only documented source of F-1-P is from the concurrent import and phosphorylation of exogenous fructose. Thus, many have proposed that fructose-1,6-bisphosphate (F-1,6-BP) is also a physiological regulatory ligand. However, the role of F-1,6-BP has been widely debated. Here, we report that the E. coli enzyme fructose-1-kinase (FruK) can carry out its "reverse" reaction under physiological substrate concentrations to generate F-1-P from F-1,6-BP. We further show that FruK directly binds Cra with nanomolar affinity and forms higher order, heterocomplexes. Growth assays with a ΔfruK strain and fruK complementation show that FruK has a broader role in metabolism than fructose catabolism. Since fruK itself is repressed by Cra, these newly-reported events add layers to the dynamic regulation of E. coli's central metabolism that occur in response to changing nutrients. These findings might have wide-spread relevance to other γ-proteobacteria, which conserve both Cra and FruK.

Atomic Force Microscopy for the Study of Cell Mechanics in Pharmaceutics

Cell mechanics is gaining attraction in drug screening, but the applicable methods have not yet become part of the standardized norm. This review presents the current state of the art for atomic force microscopy, which is the most widely available method. The field is first motivated as a new way of tracking pharmaceutical effects, followed by a basic introduction targeted at pharmacists on how to measure cellular stiffness. The review then moves on to the current state of the knowledge in terms of experimental results and supplementary methods such as fluorescence microscopy that can give relevant additional information. Finally, rheological approaches as well as the theoretical interpretations are presented before ending on additional methods and outlooks.

Nuclear actin structure regulates chromatin accessibility

Polymerized β-actin may provide a structural basis for chromatin accessibility and actin transport into the nucleus can guide mesenchymal stem cell (MSC) differentiation. Using MSC, we show that using CK666 to inhibit Arp2/3 directed secondary actin branching results in decreased nuclear actin structure, and significantly alters chromatin access measured with ATACseq at 24 h. The ATAC-seq results due to CK666 are distinct from those caused by cytochalasin D (CytoD), which enhances nuclear actin structure. In addition, nuclear visualization shows Arp2/3 inhibition decreases pericentric H3K9me3 marks. CytoD, alternatively, induces redistribution of H3K27me3 marks centrally. Such alterations in chromatin landscape are consistent with differential gene expression associated with distinctive differentiation patterns. Further, knockdown of the non-enzymatic monomeric actin binding protein, Arp4, leads to extensive chromatin unpacking, but only a modest increase in transcription, indicating an active role for actin-Arp4 in transcription. These data indicate that dynamic actin remodeling can regulate chromatin interactions.

Characterization of the mechanical properties of the cortex region of human hair fibers by multiparametric atomic force microscopy mapping

We show the benefit of the use of atomic force microscopy (AFM) in spectroscopy force mode (FV: force volume) for evaluation of the cosmetic active effectiveness in improving the mechanical properties of human hair fibers cortex region. For this, we characterized human hair fibers without and with chemical damage caused by bleaching process. Fiber and resin (embedding material) data were obtained simultaneously in the mapping in order to have the resin data as a reference to ensure a coherent comparison between data from the different fiber groups. Our AFM results, which were evaluated using statistical tests, demonstrated the degradation of fibers after bleaching, corroborating the findings of transmission electron microscopy analysis and the effectiveness of a cosmetic active ingredient in improving the Young's modulus (elastic modulus) (E) of the damaged fibers. We also found a radial decrease in the natural logarithm of Young's modulus ln(E) along the cross-section of the active group fiber, which is compatible with confocal Raman spectroscopy analysis by other authors, demonstrating variation of the active permeation with depth. We note that Young's modulus was also determined by a tensile tester (macro-scale technique), in which it was not possible to obtain statistically significant differences between the groups, evidencing the advantage of the FV-AFM analysis. We also found an increase in ln(E) accompanied by a decrease in maximum adhesion force between tip and sample (negative Pearson correlation coefficient). This result can be explained by the fact that structures composed of hydrophobic components have a higher Young's modulus than structures composed of hydrophilic components.

Hyaluronic acid-based hydrogels with tunable mechanics improved structural and contractile properties of cells

Extracellular matrix (ECM) regulates cellular responses through mechanotransduction. The standard approach of in vitro culturing on plastic surfaces overlooks this phenomenon, so there is a need for biocompatible materials that exhibit adjustable mechanical and structural properties, promote cell adhesion and proliferation at low cost and for use in 2D or 3D cell cultures. This study presents a new tunable hydrogel system prepared from high-molecular hyaluronic acid (HA), Bovine serum albumin (BSA), and gelatin cross-linked using EDC/NHS. Hydrogels with Young's moduli (E) ranging from subunit to units of kilopascals were prepared by gradually increasing HA and BSA concentrations. Concentrated high-molecular HA network led to stiffer hydrogel with lower cluster size and swelling capacity. Medium and oxygen diffusion capability of all hydrogels showed they are suitable for 3D cell cultures. Mechanical and structural changes of mouse embryonic fibroblasts (MEFs) on hydrogels were compared with cells on standard cultivation surfaces. Experiments showed that hydrogels have suitable mechanical and cell adhesion capabilities, resulting in structural changes of actin filaments. Lastly, applying hydrogel for a more complex HL-1 cell line revealed improved mechanical and electrophysiological contractile properties.

Modeling Nonlinear Dynamics of Functionalization Layers: Enhancing Gas Sensor Sensitivity for Piezoelectrically Driven Microcantilever

This article presents a parametrized response model that enhances the limit of detection (LOD) of piezoelectrically driven microcantilever (PD-MC) based gas sensors by accounting for the adsorption-induced variations in elastic properties of the functionalization layer (binder) and the nonlinear motional dynamics of the PD-MC. The developed model is demonstrated for quantifying cadaverine, a volatile biogenic diamine whose concentration is used to assess the freshness of meat. At low concentrations of cadaverine, an increase in the resonance frequency is observed, contrary to the expected reduction due to mass added by adsorption. The study explores the variations in the elastic modulus vis-à-vis the adsorbed mass of cadaverine and derives the resonance frequency to the adsorbed mass response function. We advance a blended technique involving the analysis of atomic force microscopy (AFM) force-distance (f-d) curves and fitting of the quartz crystal microbalance (QCM) impedance response spectrum to deduce the adsorption-induced changes in the viscoelastic properties of the functionalization layer. The findings obtained are subsequently employed in modeling the response function for a structurally nonhomogenous PD-MC, highlighting the significance of the functionalization layer to the global elastic properties. The structural composition of the PD-MC beam adopted herein features a trapezoidal base hosting the actuating piezoelectric stratum and a rectangular free end with a functionalization layer. The Euler-Bernoulli beam theory coupled with Hamilton's principle is used to develop the equation of motion, which is subsequently discretized into a set of nonlinear ordinary differential equations via Galerkin expansion, and the solutions to the first fundamental mode of vibration are determined using the method of multiple scales. The obtained solutions provide a basis for deducing the nonlinear response function model to the adsorbed mass. The derived model is validated by recorded resonance frequency changes resulting from exposure to known concentrations of cadaverine. We demonstrate that the increase in resonance frequency for low concentrations of cadaverine is due to the dominance of the variation of the elastic modulus of the functionalization layer originating from the initial binder-analyte interactions over damping due to added mass. It is concluded that the developed nonlinear response function model can reliably be used to quantify the cadaverine concentration at low concentrations with an elevated Limit of Detection.

Short-Term l-arginine Treatment Mitigates Early Damage of Dermal Collagen Induced by Diabetes

Changes in the structural properties of the skin due to collagen alterations are an important factor in diabetic skin complications. Using a combination of photonic methods as an optic diagnostic tool, we investigated the structural alteration in rat dermal collagen I in diabetes, and after short-term l-arginine treatment. The multiplex approach shows that in the early phase of diabetes, collagen fibers are partially damaged, resulting in the heterogeneity of fibers, e.g., "patchy patterns" of highly ordered/disordered fibers, while l-arginine treatment counteracts to some extent the conformational changes in collagen-induced by diabetes and mitigates the damage. Raman spectroscopy shows intense collagen conformational changes via amides I and II in diabetes, suggesting that diabetes-induced structural changes in collagen originate predominantly from individual collagen molecules rather than supramolecular structures. There is a clear increase in the amounts of newly synthesized proline and hydroxyproline after treatment with l-arginine, reflecting the changed collagen content. This suggests that it might be useful for treating and stopping collagen damage early on in diabetic skin. Our results demonstrate that l-arginine attenuates the early collagen I alteration caused by diabetes and that it could be used to treat and prevent collagen damage in diabetic skin at a very early stage.

Identification and Measurement of Biomarkers at Single Microorganism Level for In Situ Monitoring Deep Ultraviolet Disinfection Process

Since the COVID-19 disease has been further aggravated, the prevention of pathogen transmission becomes a vital issue to restrain casualties. Recent research outcomes have shown the possibilities of the viruses existing on inanimate surfaces up to few days, which carry the risk of touch propagation of the disease. Deep ultraviolet germicide irradiation (UVGI) with the wavelength of 255-280nm has been verified to efficiently disinfect various types of bacteria and virus, which could prevent the aggravation of pandemic spread. Even though considerable experiments and approaches have been applied to evaluate the disinfection effects, there are only few reports about how the individual bio-organism behaves after ultraviolet C (UVC) irradiation, especially in the aspect of mechanical changes. Furthermore, since the standard pathway of virus transmission and reproduction requires the host cell to assemble and transport newly generated virus, the dynamic response of infectious cell is always the vital aspect of virology study. In this work, high power LEDs array has been established with 270nm UVC irradiation to evaluate disinfection capability on various types of bio-organism, and incubator embedded atomic force microscopy (AFM) is used to investigate the single bacterium and virus under UVGI. The real-time tracking of the living Vero cells infected with adenovirus has also been presented in this study. The results show that after sufficient UVGI, the outer shell of bacteria and viruses remain intact in structure, however the bio-organisms lost the capability of reproduction and normal metabolism. The experiment results also indicate that once the host cell is infected with adenovirus, the rapid production of newborn virus capsid will gradually destroy the cellular normal metabolism and lose mechanical integrity.

Correlation between plant cell wall stiffening and root extension arrest phenotype in the combined abiotic stress of Fe and Al

The plasticity and growth of plant cell walls (CWs) remain poorly understood at the molecular level. In this work, we used atomic force microscopy (AFM) to observe elastic responses of the root transition zone of 4-day-old Arabidopsis thaliana wild-type and almt1-mutant seedlings grown under Fe or Al stresses. Elastic parameters were deduced from force-distance curve measurements using the trimechanic-3PCS framework. The presence of single metal species Fe2+ or Al3+ at 10 µM exerts no noticeable effect on the root growth compared with the control conditions. On the contrary, a mix of both the metal ions produced a strong root-extension arrest concomitant with significant increase of CW stiffness. Raising the concentration of either Fe2+ or Al3+ to 20 µM, no root-extension arrest was observed; nevertheless, an increase in root stiffness occurred. In the presence of both the metal ions at 10 µM, root-extension arrest was not observed in the almt1 mutant, which substantially abolishes the ability to exude malate. Our results indicate that the combination of Fe2+ and Al3+ with exuded malate is crucial for both CW stiffening and root-extension arrest. However, stiffness increase induced by single Fe2+ or Al3+ is not sufficient for arresting root growth in our experimental conditions.

The interaction between titanium dioxide nanoparticles and light can have dualistic effects on the physiological responses of plants

The model plant Arabidopsis thaliana was exposed to combined stress factors, i.e., titanium dioxide nanoparticles (TiNPs) and high light. The concentrations of TiNPs used for irrigation were 250, 500, and 1000 μg/mL. This study shows that TiNPs alter the morphology and nanomechanical properties of chloroplasts in A. thaliana, which leads to a decrease in membrane elasticity. We found that TiNPs contributed to a delay in the thermal response of A. thaliana under dynamic light conditions, as revealed by non-invasive thermal imaging. The thermal time constants of TiNP-treated plants under excessive light are determined, showing a shortening in comparison to control plants. The results indicate that TiNPs may contribute to an alleviation of temperature stress experienced by plants under exposure to high light. In this research, we observed a decline in photosystem II photochemical efficiency accompanied by an increase in energy dissipation upon exposure to TiNPs. Interestingly, concentrations exceeding 250 µg/mL TiNPs appeared to mitigate the effects of high light, as shown by reduced differences in the values of specific OJIP parameters (FV/FM, ABS/RC, DI0/RC, and Pi_Abs) before and after light exposure.

The Potential of Congo Red Supplied Aggregates of Multitargeted Tyrosine Kinase Inhibitor (Sorafenib, BAY-43-9006) in Enhancing Therapeutic Impact on Bladder Cancer

Bladder cancer is a common malignancy associated with high recurrence rates and potential progression to invasive forms. Sorafenib, a multi-targeted tyrosine kinase inhibitor, has shown promise in anti-cancer therapy, but its cytotoxicity to normal cells and aggregation in solution limits its clinical application. To address these challenges, we investigated the formation of supramolecular aggregates of sorafenib with Congo red (CR), a bis-azo dye known for its supramolecular interaction. We analyzed different mole ratios of CR-sorafenib aggregates and evaluated their effects on bladder cancer cells of varying levels of malignancy. In addition, we also evaluated the effect of the test compounds on normal uroepithelial cells. Our results demonstrated that sorafenib inhibits the proliferation of bladder cancer cells and induces apoptosis in a dose-dependent manner. However, high concentrations of sorafenib also showed cytotoxicity to normal uroepithelial cells. In contrast, the CR-BAY aggregates exhibited reduced cytotoxicity to normal cells while maintaining anti-cancer activity. The aggregates inhibited cancer cell migration and invasion, suggesting their potential for metastasis prevention. Dynamic light scattering and UV-VIS measurements confirmed the formation of stable co-aggregates with distinctive spectral properties. These CR-sorafenib aggregates may provide a promising approach to targeted therapy with reduced cytotoxicity and improved stability for drug delivery in bladder cancer treatment. This work shows that the drug-excipient aggregates proposed and described so far, as Congo red-sorafenib, can be a real step forward in anti-cancer therapies.

Fructose-1-kinase has pleiotropic roles in Escherichia coli

In Escherichia coli, the master transcription regulator Catabolite Repressor Activator (Cra) regulates >100 genes in central metabolism. Cra binding to DNA is allosterically regulated by binding to fructose-1-phosphate (F-1-P), but the only documented source of F-1-P is from the concurrent import and phosphorylation of exogenous fructose. Thus, many have proposed that fructose-1,6-bisphosphate (F-1,6-BP) is also a physiological regulatory ligand. However, the role of F-1,6-BP has been widely debated. Here, we report that the E. coli enzyme fructose-1-kinase (FruK) can carry out its "reverse" reaction under physiological substrate concentrations to generate F-1-P from F-1,6-BP. We further show that FruK directly binds Cra with nanomolar affinity and forms higher order, heterocomplexes. Growth assays with a ΔfruK strain and fruK complementation show that FruK has a broader role in metabolism than fructose catabolism. The ΔfruK strain also alters biofilm formation. Since fruK itself is repressed by Cra, these newly-reported events add layers to the dynamic regulation of E. coli central metabolism that occur in response to changing nutrients. These findings might have wide-spread relevance to other γ-proteobacteria, which conserve both Cra and FruK.

Exoskeleton Partial-Coated Stem Cells for Infarcted Myocardium Restoring

The integration of abiotic materials with live cells has emerged as an exciting strategy for the control of cellular functions. Exoskeletons consisting ofmetal-organic frameworks are generated to produce partial-coated bone marrow stem cells (BMSCs) to overcome low cell survival leading to disappointing effects for cell-based cardiac therapy. Partially coated exoskeletons can promote the survival of suspended BMSCs by integrating the support of exoskeletons and unimpaired cellular properties. In addition, partial exoskeletons exhibit protective effects against detrimental environmental conditions, including reactive oxygen species, pH changes, and osmotic pressure. The partial-coated cells exhibit increased intercellular adhesion forces to aggregate and adhere, promoting cell survival and preventing cell escape during cell therapy. The exoskeletons interact with cell surface receptors integrin α5β1, leading to augmented biological functions with profitable gene expression alteration, such as Vegfa, Cxcl12, and Adm. The partial-coated BMSCs display enhanced cell retention in infarcted myocardium through non-invasive intravenous injections. The repair of myocardial infarction has been achieved with improved cardiac function, myocardial angiogenesis, proliferation, and inhibition of cell apoptosis. This discovery advances the elucidation of potential molecular and cellular mechanisms for cell-exoskeleton interactions and benefits the rational design and manufacture of next-generation nanobiohybrids.

Universal contact stiffness of elastic solids covered with tensed membranes and its application in indentation tests of biological materials

The inherent membrane tension of biological materials could vitally affect their responses to contact loading but is generally ignored in existing indentation analysis. In this paper, the authors theoretically investigate the contact stiffness of axisymmetric indentations of elastic solids covered with thin tensed membranes. When the indentation size decreases to the same order as the ratio of membrane tension to elastic modulus, the contact stiffness accounting for the effect of membrane tension becomes much higher than the prediction of conventional contact theory. An explicit expression is derived for the contact stiffness, which is universal for axisymmetric indentations using indenters of arbitrary convex profiles. On this basis, a simple method of analysis is proposed to estimate the membrane tension and elastic modulus of biological materials from the indentation load-depth data, which is successfully applied to analyze the indentation experiments of cells and lungs. This study might be helpful for the comprehensive assessment of the mechanical properties of soft biological systems. STATEMENT OF SIGNIFICANCE: This paper highlights the crucial effect of the inherent membrane tension on the indentation response of soft biomaterials, which has been generally ignored in existing analysis of experiments. For typical indentation tests on cells and organs, the contact stiffness can be twice or higher than the prediction of conventional contact model. A universal expression of the contact stiffness accounting for the membrane tension effect is derived. On this basis, a simple method of analysis is proposed to abstract the membrane tension of biomaterials from the experimentally recorded indentation load-depth data. With this method, the elasticity of soft biomaterials can be characterized more comprehensively.

A human pluripotent stem cell-based somitogenesis model using microfluidics

Emerging human pluripotent stem cell (hPSC)-based embryo models are useful for studying human embryogenesis. Particularly, there are hPSC-based somitogenesis models using free-floating culture that recapitulate somite formation. Somitogenesis in vivo involves intricately orchestrated bio-chemical and -mechanical events. However, none of the current somitogenesis models controls biochemical gradients or biomechanical signals in the culture, limiting their applicability to untangle complex biochemical-biomechanical interactions that drive somitogenesis. Here we report a new human somitogenesis model by confining hPSC-derived presomitic mesoderm (PSM) tissues in microfabricated trenches. Exogenous microfluidic morphogen gradients imposed on PSM cause axial patterning and trigger spontaneous rostral-to-caudal somite formation. A mechanical theory is developed to explain the size dependency between somites and PSM. The microfluidic somitogenesis model is further exploited to reveal regulatory roles of cellular and tissue biomechanics in somite formation. This study presents a useful microengineered, hPSC-based model for understanding the bio-chemical and -mechanical events that guide somite formation.

Hypoxia enhances anti-fibrotic properties of extracellular vesicles derived from hiPSCs via the miR302b-3p/TGFβ/SMAD2 axis

BACKGROUND

Cardiac fibrosis is one of the top killers among fibrotic diseases and continues to be a global unaddressed health problem. The lack of effective treatment combined with the considerable socioeconomic burden highlights the urgent need for innovative therapeutic options. Here, we evaluated the anti-fibrotic properties of extracellular vesicles (EVs) derived from human induced pluripotent stem cells (hiPSCs) that were cultured under various oxygen concentrations.

METHODS

EVs were isolated from three hiPSC lines cultured under normoxia (21% O2; EV-N) or reduced oxygen concentration (hypoxia): 3% O2 (EV-H3) or 5% O2 (EV-H5). The anti-fibrotic activity of EVs was tested in an in vitro model of cardiac fibrosis, followed by a detailed investigation of the underlying molecular mechanisms. Sequencing of EV miRNAs combined with bioinformatics analysis was conducted and a selected miRNA was validated using a miRNA mimic and inhibitor. Finally, EVs were tested in a mouse model of angiotensin II-induced cardiac fibrosis.

RESULTS

We provide evidence that an oxygen concentration of 5% enhances the anti-fibrotic effects of hiPS-EVs. These EVs were more effective in reducing pro-fibrotic markers in activated human cardiac fibroblasts, when compared to EV-N or EV-H3. We show that EV-H5 act through the canonical TGFβ/SMAD pathway, primarily via miR-302b-3p, which is the most abundant miRNA in EV-H5. Our results show that EV-H5 not only target transcripts of several profibrotic genes, including SMAD2 and TGFBR2, but also reduce the stiffness of activated fibroblasts. In a mouse model of heart fibrosis, EV-H5 outperformed EV-N in suppressing the inflammatory response in the host and by attenuating collagen deposition and reducing pro-fibrotic markers in cardiac tissue.

CONCLUSIONS

In this work, we provide evidence of superior anti-fibrotic properties of EV-H5 over EV-N or EV-H3. Our study uncovers that fine regulation of oxygen concentration in the cellular environment may enhance the anti-fibrotic effects of hiPS-EVs, which has great potential to be applied for heart regeneration.

A new modality for cholesterol impact tracking in colon cancer development - Raman imaging, fluorescence and AFM studies combined with chemometric analysis

Colorectal cancer (CRC) is the third most common cancer worldwide. Obesity, alcohol consumption, smoking, high consumption of red or processed meat and a diet with low fibre, fruit, and vegetable intake increase CRC risk. Despite advances in surgery (the basic treatment for recovery), chemotherapy, and radiotherapy, CRC remains the second leading cause of cancer-related deaths in the world. Therefore the social importance of this problem stimulates research aimed at developing new tools for rapid CRC diagnosis and analysis of CRC risk factors. Considering the association between the cholesterol level and CRC, we hypothesize that cholesterol spectroscopic and AFM (atomic force microscopy) studies combined with chemometric analysis can be new, powerful tools used to visualize the cholesterol distribution, estimate cholesterol content and determine its influence on the biochemical and nanomechanical properties of colon cells. Our paper presents the analysis of human colon tissues: normal and cancer and human colon single cells normal CCD18-Co and cancer CaCo-2 in the physiological state and CaCo-2 upon mevastatin supplementation. Based on vibrational features we have shown that Raman spectroscopy and imaging allow cholesterol content in human colon tissues and human colon single cells of both types to be tracked and allow the effectiveness of mevastatin in the mevalonate pathway modulation and disruption of the cholesterol level to be proven. All observations have been confirmed by chemometric analysis including principal component analysis (PCA) and partial least squares discriminant analysis (PLSDA). The positive impact of statins on cholesterol content has also been studied by using fluorescence microscopy and atomic force microscopy (AFM). A significant increase in Young modulus as a mechanomarker for CaCo-2 human cancer colon cells upon mevastatin supplementation compared to CCD18-Co human normal colon cells was observed. This paper is one of the first reports about the use of Raman spectroscopic techniques in cholesterol investigations and the first one about cholesterol investigation using Raman spectroscopy (RS) on human cells ex vivo in the context of colon cancer development.

Role of galectin-3 in the elastic response of radial growth phase melanoma cancer cells

Melanoma is originated from the malignant transformation of the melanocytes and is characterized by a high rate of invasion, the more serious stage compromising deeper layers of the skin and eventually leading to the metastasis. A high mortality due to melanoma lesion persists because most of melanoma lesions are detected in advanced stages, which decreases the chances of survival. The identification of the principal mechanics implicated in the development and progression of melanoma is essential to devise new early diagnosis strategies. Cell mechanics is related with a lot of cellular functions and processes, for instance motility, differentiation, migration and invasion. In particular, the elastic modulus (Young's modulus) is a very explored parameter to describe the cell mechanical properties; most cancer cells reported in the literature smaller elasticity modulus. In this work, we show that the elastic modulus of melanoma cells lacking galectin-3 is significantly lower than those of melanoma cells expressing galectin-3. More interestingly, the gradient of elastic modulus in cells from the nuclear region towards the cell periphery is more pronounced in shGal3 cells. RESEARCH HIGHLIGHTS: AFM imaging and force spectroscopy were used to investigate the morphology and elasticity properties of healthy HaCaT cells and melanoma cells WM1366, with (shSCR) and without (shGal3) expression of galectin-3. It is shown the effect of galectin-3 protein on the elastic properties of cells: the cells without expression of galectin-3 presents lower elastic modulus. By the results, we suggest here that galectin-3 could be used as an effective biomarker of malignancy in both melanoma diagnostic and prognosis.

A New Elementary Method for Determining the Tip Radius and Young's Modulus in AFM Spherical Indentations

Atomic force microscopy (AFM) is a powerful tool for characterizing biological materials at the nanoscale utilizing the AFM nanoindentation method. When testing biological materials, spherical indenters are typically employed to reduce the possibility of damaging the sample. The accuracy of determining Young's modulus depends, among other factors, on the calibration of the indenter, i.e., the determination of the tip radius. This paper demonstrates that the tip radius can be approximately calculated using a single force-indentation curve on an unknown, soft sample without performing any additional experimental calibration process. The proposed method is based on plotting a tangent line on the force indentation curve at the maximum indentation depth. Subsequently, using equations that relate the applied force, maximum indentation depth, and the tip radius, the calculation of the tip radius becomes trivial. It is significant to note that the method requires only a single force-indentation curve and does not necessitate knowledge of the sample's Young's modulus. Consequently, the determination of both the sample's Young's modulus and the tip radius can be performed simultaneously. Thus, the experimental effort is significantly reduced. The method was tested on 80 force-indentation curves obtained on an agarose gel, and the results were accurate.

Multilevel Assessment of Stent-Induced Inflammation in the Adjacent Vascular Tissue

A recent U.S. Food and Drug Administration report presented the currently available scientific information related to biological response to metal implants. In this work, a multilevel approach was employed to assess the implant-induced and biocorrosion-related inflammation in the adjacent vascular tissue using a mouse stent implantation model. The implications of biocorrosion on peri-implant tissue were assessed at the macroscopic level via in vivo imaging and histomorphology. Elevated matrix metalloproteinase activity, colocalized with the site of implantation, and histological staining indicated that stent surface condition and implantation time affect the inflammatory response and subsequent formation and extent of neointima. Hematological measurements also demonstrated that accumulated metal particle contamination in blood samples from corroded-stetted mice causes a stronger immune response. At the cellular level, the stent-induced alterations in the nanostructure, cytoskeleton, and mechanical properties of circulating lymphocytes were investigated. It was found that cells from corroded-stented samples exhibited higher stiffness, in terms of Young's modulus values, compared to noncorroded and sham-stented samples. Nanomechanical modifications were also accompanied by cellular remodeling, through alterations in cell morphology and stress (F-actin) fiber characteristics. Our analysis indicates that surface wear and elevated metal particle contamination, prompted by corroded stents, may contribute to the inflammatory response and the multifactorial process of in-stent restenosis. The results also suggest that circulating lymphocytes could be a novel nanomechanical biomarker for peri-implant tissue inflammation and possibly the early stage of in-stent restenosis. Large-scale studies are warranted to further investigate these findings.

Acute brain slice elastic modulus decreases over time

A common benchmark in the brain tissue mechanics literature is that the properties of acute brain slices should be measured within 8 h of the experimental animal being sacrificed. The core assumption is that-since there is no substantial protein degradation during this time-there will be no change to elastic modulus. This assumption overlooks the possibility of other effects (such as osmotic swelling) that may influence the mechanical properties of the tissue. To achieve consistent and accurate analysis of brain mechanics, it is important to account for or mitigate these effects. Using atomic force microscopy (AFM), tissue hydration and volume measurements, we find that acute brain slices in oxygenated artificial cerebrospinal fluid (aCSF) with a standard osmolarity of 300 mOsm/l experience rapid swelling, softening, and increases in hydration within the first 2 hours after slicing. Reductions in elastic modulus can be partly mitigated by addition of chondroitinase ABC enzyme (CHABC). Increasing aCSF osmolarity to 400 mOsm/l does not prevent softening but may hasten equilibration of samples to a point where measurements of relative elastic modulus are consistent across experiments.

Enzymatic polymerization of enantiomeric L-3,4-dihydroxyphenylalanine into films with enhanced rigidity and stability

_L-3,4-dihydroxyphenylalanine is an important molecule in the adhesion of mussels, and as an oxidative precursor of natural melanin, it plays an important role in living system. Here, we investigate the effect of the molecular chirality of 3,4-dihydroxyphenylalanine on the properties of the self-assembled films by tyrosinase-induced oxidative polymerization. The kinetics and morphology of pure enantiomers are completely altered upon their co-assembly, allowing the fabrication of layer-to-layer stacked nanostructures and films with improved structural and thermal stability. The different molecular arrangements and self-assembly mechanisms of the _L+D-racemic mixtures, whose oxidation products have increased binding energy, resulting in stronger intermolecular forces, which significantly increases the elastic modulus. This study provides a simple pathway for the fabrication of biomimetic polymeric materials with enhanced physicochemical properties by controlling the chirality of monomers.

Measuring external primary cell wall elasticity of seedling roots using atomic force microscopy

Stiffness plays a central action in plant cell extension. Here, we present a protocol to detect changes in stiffness on the external epidermal cell wall of living plant roots using atomic force microscopy (AFM). We provide generalized instructions for collecting force-distance curves and analysis of stiffness using contact-based mechanical model. With this protocol, and some initial training in AFM, a user is able to perform indentation experiments on 4- and 5-day-old Arabidopsis thaliana and determine stiffness properties. For complete details on the use and execution of this protocol, please refer to Godon et al.¹.

Pancreatic Cancer Presents Distinct Nanomechanical Properties During Progression

Cancer progression is closely related to changes in the structure and mechanical properties of the tumor microenvironment (TME). In many solid tumors, including pancreatic cancer, the interplay among the different components of the TME leads to a desmoplastic reaction mainly due to collagen overproduction. Desmoplasia is responsible for the stiffening of the tumor, poses a major barrier to effective drug delivery and has been associated with poor prognosis. The understanding of the involved mechanisms in desmoplasia and the identification of nanomechanical and collagen-based properties that characterize the state of a particular tumor can lead to the development of novel diagnostic and prognostic biomarkers. In this study, in vitro experiments were conducted using two human pancreatic cell lines. Morphological and cytoskeleton characteristics, cells' stiffness and invasive properties were assessed using optical and atomic force microscopy techniques and cell spheroid invasion assay. Subsequently, the two cell lines were used to develop orthotopic pancreatic tumor models. Tissue biopsies were collected at different times of tumor growth for the study of the nanomechanical and collagen-based optical properties of the tissue using Atomic Force Microscopy (AFM) and picrosirius red polarization microscopy, respectively. The results from the in vitro experiments demonstrated that the more invasive cells are softer and present a more elongated shape with more oriented F-actin stress fibers. Furthermore, ex vivo studies of orthotopic tumor biopsies on MIAPaCa-2 and BxPC-3 murine tumor models highlighted that pancreatic cancer presents distinct nanomechanical and collagen-based optical properties relevant to cancer progression. The stiffness spectrums (in terms of Young's modulus values) showed that the higher elasticity distributions were increasing during cancer progression mainly due desmoplasia (collagen overproduction), while a lower elasticity peak was evident - due to cancer cells softening - on both tumor models. Optical microscopy studies highlighted that collagen content increases while collagen fibers tend to form align patterns. Consequently, during cancer progression nanomechanical and collagen-based optical properties alter in relation to changes in collagen content. Therefore, they have the potential to be used as novel biomarkers for assessing and monitoring tumor progression and treatment outcomes.

Cholesterol and Sphingomyelin Polarize at the Leading Edge of Migrating Myoblasts and Involve Their Clustering in Submicrometric Domains

Myoblast migration is crucial for myogenesis and muscular tissue homeostasis. However, its spatiotemporal control remains elusive. Here, we explored the involvement of plasma membrane cholesterol and sphingolipids in this process. In resting C2C12 mouse myoblasts, those lipids clustered in sphingomyelin/cholesterol/GM1 ganglioside (SM/chol/GM1)- and cholesterol (chol)-enriched domains, which presented a lower stiffness than the bulk membrane. Upon migration, cholesterol and sphingomyelin polarized at the front, forming cholesterol (chol)- and sphingomyelin/cholesterol (SM/chol)-enriched domains, while GM1-enriched domains polarized at the rear. A comparison of domain proportion suggested that SM/chol- and GM1-enriched domains originated from the SM/chol/GM1-coenriched domains found at resting state. Modulation of domain proportion (through cholesterol depletion, combined or not with actin polymerization inhibition, or sphingolipid synthesis inhibition) revealed that the higher the chol- and SM/chol-enriched domains, the higher the myoblast migration. At the front, chol- and SM/chol-enriched domains were found in proximity with F-actin fibers and the lateral mobility of sphingomyelin in domains was specifically restricted in a cholesterol- and cytoskeleton-dependent manner while domain abrogation impaired F-actin and focal adhesion polarization. Altogether, we showed the polarization of cholesterol and sphingomyelin and their clustering in chol- and SM/chol-enriched domains with differential properties and roles, providing a mechanism for the spatial and functional control of myoblast migration.

Effect of surface functionalization and loading on the mechanical properties of soft polymeric nanoparticles prepared by nano-emulsion templating

Drug and gene delivery systems based on polymeric nanoparticles offer a greater efficacy and a reduced toxicity compared to traditional formulations. Recent studies have evidenced that their internalization, biodistribution and efficacy can be affected, among other factors, by their mechanical properties. Here, we analyze by means of Atomic Force Microscopy force spectroscopy how composition, surface functionalization and loading affect the mechanics of nanoparticles. For this purpose, nanoparticles made of Poly(lactic-co-glycolic) (PLGA) and Ethyl cellulose (EC) with different functionalizations and loading were prepared by nano-emulsion templating using the Phase Inversion Composition method (PIC) to form the nano-emulsions. A multiparametric nanomechanical study involving the determination of the Young's modulus, maximum deformation and breakthrough force was carried out. The obtained results showed that composition, surface functionalization and loading affect the nanomechanical properties in a different way, thus requiring, in general, to consider the overall mechanical properties after the addition of a functionalization or loading. A graphical representation method has been proposed enabling to easily identify mechanically equivalent formulations, which is expected to be useful in the development of soft polymeric nanoparticles for pre-clinical and clinical use.

3D AFM Nanomechanical Characterization of Biological Materials

Atomic Force Microscopy (AFM) is a powerful tool enabling the mechanical characterization of biological materials at the nanoscale. Since biological materials are highly heterogeneous, their mechanical characterization is still considered to be a challenging procedure. In this paper, a new approach that leads to a 3-dimensional (3D) nanomechanical characterization is presented based on the average Young's modulus and the AFM indentation method. The proposed method can contribute to the clarification of the variability of the mechanical properties of biological samples in the 3-dimensional space (variability at the x-y plane and depth-dependent behavior). The method was applied to agarose gels, fibroblasts, and breast cancer cells. Moreover, new mathematical methods towards a quantitative mechanical characterization are also proposed. The presented approach is a step forward to a more accurate and complete characterization of biological materials and could contribute to an accurate user-independent diagnosis of various diseases such as cancer in the future.

Determining Spatial Variability of Elastic Properties for Biological Samples Using AFM

Measuring the mechanical properties (i.e., elasticity in terms of Young's modulus) of biological samples using Atomic Force Microscopy (AFM) indentation at the nanoscale has opened new horizons in studying and detecting various pathological conditions at early stages, including cancer and osteoarthritis. It is expected that AFM techniques will play a key role in the future in disease diagnosis and modeling using rigorous mathematical criteria (i.e., automated user-independent diagnosis). In this review, AFM techniques and mathematical models for determining the spatial variability of elastic properties of biological materials at the nanoscale are presented and discussed. Significant issues concerning the rationality of the elastic half-space assumption, the possibility of monitoring the depth-dependent mechanical properties, and the construction of 3D Young's modulus maps are also presented.

In Situ Measurements of Cell Mechanical Properties Using Force Spectroscopy

Mechanobiology focuses on how physical forces and the mechanical properties of cells and whole tissues affect their function. The mechanical properties of cells are of particular interest to developmental biology and stem cell differentiation, lymphocyte activation and phagocytic action in phagocytes, and development of malignant tumors and metastases. These properties can be measured on whole tissue and cell culture. Advances in instrument sensitivity and design, as well as improved techniques and scientific know-how achieved over the past few decades, allow researchers to study the mechanical properties of single cells and even at the subcellular level. Particularly, nanoindentation measurements using atomic force microscopy (AFM) mechanically probes single cells and even allows mapping of these traits. This chapter discusses these measurements from the experimental design to the analysis.

Effect of surface stiffness in initial adhesion of oral microorganisms under various environmental conditions

Biofilms are three-dimensional structures formed as a result of microorganism's adhesion on a biotic or abiotic surface. Once a biofilm is established, it is onerous to eradicate it or kill the pathogens therein. Thus, targeting the microbial adhesion process, the initial stage of biofilm formation, is a reasonable approach to avoid challenges associated with subsequently formed biofilms. While many properties of interacting material that play significant roles in initial bacterial adhesion have been widely studied, the effect of surface stiffness on bacterial adhesion was relatively underexplored. In this study, we aimed to investigate the effect of surface stiffness on the adhesion of microbial species found in the oral cavity by employing representative oral bacteria, Streptococcus mutans and Streptococcus oralis, and the fungus, Candida albicans. We compared the adhesion behavior of these species alone or in combination toward various surface stiffness (0.06 - 3.01 MPa) by assessing the adhered and planktonic cell numbers at an early (4 h) adhesion stage under various carbon sources and the presence of conditioning film. Our data revealed that in general, a higher amount of microbial cells adhered to softer PDMS surfaces than stiffer ones, which indicates that surface stiffness plays a role in the adhesion of tested species (either single or co-cultured). This pattern was more obvious under sucrose conditions than glucose + fructose conditions. Interestingly, in monospecies, saliva coating did not alter the effect of surface stiffness on S. mutans adhesion while it diminished S. oralis and C. albicans adhesion. However, in the multispecies model, saliva coating rendered the percentage of all adhered microbes to varied PDMS not distinct. The data provide new insights into the role of surface stiffness on microbial mechanosensing and their initial adhesion behavior which may set a scientific foundation for future anti-adhesion strategies.

Nano-structural stiffness measure for soft biomaterials of heterogeneous elasticity

Measuring the structural stiffness aims to reveal the impact of nanostructured components or various physiological circumstances on the elastic response of material to an external indentation. With a pyramidal tip at a nano-scale, we employed the atomic force microscopy (AFM) to indent the surfaces of two compositions of polyacrylamide gels with different softness and seedling roots of Arabidopsis thaliana. We found that the stiffness-depth curve derived from the measured force exhibits a heterogeneous character in elasticity. According to the tendency of stiffness-depth curve, we decomposed the responding force into depth-impact (F_C), Hookean (F_H) and tip-shape (F_S) components, called trimechanic, where F_S and its gradient should be offset at the surface or subsurfaces of the indented material. Thereby, trimechnic theory allows us to observe how the three restoring nanomechanics change with varied depth. Their strengths are represented by the respective spring constants (k_C, k_H, k_S) of three parallel-connected spring (3PCS) analogs to differentiate restoring nanomechansims of indented materials. The effective Young's modulus Ê and the total stiffness k_T (= k_H + k_S) globally unambiguously distinguish the softness between the two gel categories. Data fluctuations were observed in the elasticity parameters of individual samples, reflecting nanostructural variations in the gel matrix. Similar tendencies were found in the results from growing plant roots, though the data fluctuations are expectedly much more dramatic. The zone-wise representation of stiffness by the trimechanic-3PCS framework demonstrates a stiffness measure that reflects beneath nanostructures encountered by deepened depth. The trimechanic-3PCS framework can apply any mechanical model of power-law based force-depth relationship and is compatible with thin layer corrections. It provides a new paradigm for analyzing restoring nanomechanics of soft biomaterials in response to indenting forces.

Measuring ventral nerve cord stiffness in live flat-dissected Drosophila embryos by atomic force microscopy

Drosophila is an amenable system for addressing the mechanics of morphogenesis. We describe a workflow for characterizing the mechanical properties of its ventral nerve cord (VNC), at different developmental stages, in live, flat-dissected embryos employing atomic force microscopy (AFM). AFM is performed with spherical probes, and stiffness (Young's modulus) is calculated by fitting force curves with Hertz's contact model. For complete details on the use and execution of this protocol, please refer to Karkali et al. (2022).