Antibacterial Action of Nanoparticles by Lethal Stretching of Bacterial Cell Membranes.

It is commonly accepted that nanoparticles (NPs) can kill bacteria; however, the mechanism of antimicrobial action remains obscure for large NPs that cannot translocate the bacterial cell wall. It is demonstrated that the increase in membrane tension caused by the adsorption of NPs is responsible for mechanical deformation, leading to cell rupture and death. A biophysical model of the NP-membrane interactions is presented which suggests that adsorbed NPs cause membrane stretching and squeezing. This general phenomenon is demonstrated experimentally using both model membranes and Pseudomonas aeruginosa and Staphylococcus aureus, representing Gram-positive and Gram-negative bacteria. Hydrophilic and hydrophobic quasi-spherical and star-shaped gold (Au)NPs are synthesized to explore the antibacterial mechanism of non-translocating AuNPs. Direct observation of nanoparticle-induced membrane tension and squeezing is demonstrated using a custom-designed microfluidic device, which relieves contraction of the model membrane surface area and eventual lipid bilayer collapse. Quasi-spherical nanoparticles exhibit a greater bactericidal action due to a higher interactive affinity, resulting in greater membrane stretching and rupturing, corroborating the theoretical model. Electron microscopy techniques are used to characterize the NP-bacterial-membrane interactions. This combination of experimental and theoretical results confirm the proposed mechanism of membrane-tension-induced (mechanical) killing of bacterial cells by non-translocating NPs.

Model lipid systems and their use to evaluate the phase state of biomembranes, their mechanical properties and the effect of non-conventional antibiotics: the case of daptomycin.

The lipid bilayer is the basis of the structure and function of the cell membrane. The study of the molecular phenomena that affect biological membranes has a great impact on the understanding of cellular physiology. To understand these phenomena, it has become increasingly necessary to develop simple synthetic models that allow the most basic details of such processes to be reproduced. In this short communication, we took advantage of the properties of two well-established lipid model systems, GUVs and SLBs, with compositions mimicking the cell membrane present in mammals and bacteria, to study the thermotropic phase behavior of lipids as well as the effect of daptomycin, a cyclic lipopeptide used as an antibiotic. The study of mechanical and thermodynamical properties of these model systems could contribute to establish a theoretical framework to develop more efficient strategies for biological control.

Simulating the effect of sodium channel blockage on cardiac electromechanics.

There is growing interest to better understand drug-induced cardiovascular complications and to predict undesirable side effects at as early a stage in the drug development process as possible. The purpose of this paper is to investigate computationally the influence of sodium ion channel blockage on cardiac electromechanics. To do so, we implement a myofiber orientation dependent passive stress model (Holzapfel-Ogden) in the multiphysics solver Chaste to simulate an imaged physiological model of the human ventricles. A dosage of a sodium channel blocker was then applied and its inhibitory effects on the electrical propagation across ventricles were modeled. We employ the Kerckhoffs active stress model to generate electrically excited contractile behavior of myofibers. Our predictions indicate that a delay in the electrical activation of ventricular tissue caused by the sodium channel blockage translates to a delay in the mechanical biomarkers that were investigated. Moreover, sodium channel blockage was found to increase left ventricular twist. A multiphysics computational framework from the cell level to the organ level was thus used to predict the effect of sodium channel blocking drugs on cardiac electromechanics.

Computational investigation of the effect of water on the nanomechanical behavior of bone.

Previous experimental and computational studies have indicated that removing bound water in bone matrix makes bone stiffer, stronger, but more brittle at different length scales. However, a clear mechanistic explanation of the underlying mechanisms is lacking. Assuming that bound water mainly alters the mechanical behavior of collagen phase and the interfaces among bone constituents, this study investigated the effects of bound water on the mechanical properties of bone using a 2D cohesive finite element (FE) model representing the sub-lamellar hierarchy of the tissue. The model contained sufficient ultrastructural details of mineralized collagen fibrils (MCF), extrafibrillar matrix (EFM), and the interfaces among bone constituents. The mechanical behavior of the interfaces, and mineral/collagen phases, in the hydrated and dehydrated conditions was carefully selected based on the information available in the literature. The FE simulations indicated that hydration status induced changes at the interfaces played a key role in determining the mechanical behavior of bone. In tension, hydrated interfaces (weak but tough) in bone appeared to encourage multiple nanocrack formation, debonding between the MCF and EFM subunits, and crack bridging by MCFs. On the other hand, dehydrated (strong but brittle) interfaces made the tissue stiffer and stronger, but compromised the above energy dissipation mechanisms, thus leading to a brittle failure. In compression, hydrated interfaces resulted in sliding between the mineral crystals in EFM, debonding between EFM and MCF, and buckling of MCF, whereas dehydrated interfaces appeared to make the tissue stiffer and stronger and the energy dissipation mechanisms diminished. The outcome of this study provides new insights into the mechanisms underlying the effect of bound water on bone fragility at ultrastructural levels.

Effects of plasticizer type and concentration on rheological, physico-mechanical and structural properties of chitosan/zein film.

The purpose of this study was to evaluate the effect of plasticizer type (glycerol, PEG-400, and sorbitol) and concentration (0%, 15%, 30% and 45%, w/w dry polymer weight) on rheological and physico-mechanical and structural properties of chitosan/zein blend film. Based on the analysis of rheological properties of chitosan/zein film-forming solutions, all film-forming solutions exhibited non-Newtonian behavior. The flow index of film-forming solution increased and apparent viscosity decreased with the increase of plasticizer concentration. The storage modulus (G') and the loss modulus (G″) decreased when plasticizer was added. The permeability of films increased significantly with the increase of plasticizer concentration, but the C/Z-P film (plasticized chitosan/zein film with PEG-400) had better barrier performance compared with the other two. The C/Z-P film had better mechanical properties and light transmission. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed chitosan and zein had good compatibility due to the addition of the plasticizer, and crystallinity decreased with the increase of plasticizer concentration.

High Molecular Weight Mixed-Linkage Glucan as a Mechanical and Hydration Modulator of Bacterial Cellulose: Characterization by Advanced NMR Spectroscopy.

Bacterial cellulose (BC) consists of a complex three-dimensional organization of ultrafine fibers which provide unique material properties such as softness, biocompatibility, and water-retention ability, of key importance for biomedical applications. However, there is a poor understanding of the molecular features modulating the macroscopic properties of BC gels. We have examined chemically pure BC hydrogels and composites with arabinoxylan (BC-AX), xyloglucan (BC-XG), and high molecular weight mixed-linkage glucan (BC-MLG). Atomic force microscopy showed that MLG greatly reduced the mechanical stiffness of BC gels, while XG and AX did not exert a significant effect. A combination of advanced solid-state NMR methods allowed us to characterize the structure of BC ribbons at ultra-high resolution and to monitor local mobility and water interactions. This has enabled us to unravel the effect of AX, XG, and MLG on the short-range order, mobility, and hydration of BC fibers. Results show that BC-XG hydrogels present BC fibrils of increased surface area, which allows BC-XG gels to hold higher amounts of bound water. We report for the first time that the presence of high molecular weight MLG reduces the density of clusters of BC fibrils and dramatically increases water interactions with BC. Our data supports two key molecular features determining the reduced stiffness of BC-MLG hydrogels, that is, (i) the adsorption of MLG on the surface of BC fibrils precluding the formation of a dense network and (ii) the preorganization of bound water by MLG. Hence, we have produced and fully characterized BC-MLG hydrogels with novel properties which could be potentially employed as renewable materials for applications requiring high water retention capacity (e.g. personal hygiene products).

An Injectable Self-Healing Protein Hydrogel with Multiple Dissipation Modes and Tunable Dynamic Response.

Hydrogels with dynamic mechanical properties are of special interest in the field of tissue engineering and drug delivery. However, it remains challenging to tailor the dynamic mechanical response of hydrogels to simultaneously meet diverse application needs. Here, we report a hetero-coiled-coil complex cross-linked protein hydrogel exhibiting unusual multiple energy dissipation modes and tunable dynamic response. Such unique features confer on the hydrogel responsiveness to mechanical stimuli in a broad range of frequencies. Therefore, the hydrogels are injectable due to their shearing-thinning properties at low shear rates of 0.8 rad s-1 and can fully recover their mechanical properties within a few seconds due to the intrinsic fast dynamics of the cross-linkers. Moreover, the dynamic response of these hydrogels can be fine-tuned by the temperature and the hydrogel network structures. We anticipate that these hydrogels are promising candidates for delivering therapeutic drugs, biological molecules, and cells in a broad spectrum of biomedical applications.

Resveratrol-Induced Temporal Variation in the Mechanical Properties of MCF-7 Breast Cancer Cells Investigated by Atomic Force Microscopy.

Atomic force microscopy (AFM) combined with fluorescence microscopy has been used to quantify cytomechanical modifications induced by resveratrol (at a fixed concentration of 50 µM) in a breast cancer cell line (MCF-7) upon temporal variation. Cell indentation methodology has been utilized to determine simultaneous variations of Young's modulus, the maximum adhesion force, and tether formation, thereby determining cell motility and adhesiveness. Effects of treatment were measured at several time-points (0-6 h, 24 h, and 48 h); longer exposures resulted in cell death. Our results demonstrated that AFM can be efficiently used as a diagnostic tool to monitor irreversible morpho/nano-mechanical changes in cancer cells during the early steps of drug treatment.

Quasi-3D morphology and modulation of focal adhesions of human adult stem cells through combinatorial concave elastomeric surfaces with varied stiffness.

In vivo cell niches are complex architectures that provide a wide range of biochemical and mechanical stimuli to control cell behavior and fate. With the aim to provide in vitro microenvironments mimicking physiological niches, microstructured substrates have been exploited to support cell adhesion and to control cell shape as well as three dimensional morphology. At variance with previous methods, we propose a simple and rapid protein subtractive soft lithographic method to obtain microstructured polydimethylsiloxane substrates for studying stem cell adhesion and growth. The shape of adult renal stem cells and nuclei is found to depend predominantly on micropatterning of elastomeric surfaces and only weakly on the substrate mechanical properties. Differently, focal adhesions in their shape and density but not in their alignment mainly depend on the elastomer stiffness almost regardless of microscale topography. Local surface topography with concave microgeometry enhancing adhesion drives stem cells in a quasi-three dimensional configuration where stiffness might significantly steer mechanosensing as highlighted by focal adhesion properties.

PCL/EUG scaffolds with tunable stiffness can regulate macrophage secretion behavior.

Osteoarthritis (OA) is a prevalent joint disorder worldwide. Recent studies suggested that macrophages play an important role in the progression of OA. However, the detailed pathology related to macrophages is still ambiguous, especially where related to mechanotransduction. In this study, polycaprolactone (PCL) and Eucommia Ulmoides Gum (EUG) composite scaffolds were first fabricated by electrospinning. The stiffness of as-fabricated scaffolds was altered by adjusting the PCL-to-EUG ratio. The mechanical properties, structural characteristics and chemical composition of the scaffolds were investigated using various materials characterization techniques. The results show that stiffness of the scaffolds was in the same range as that of cartilage tissues with OA. Confocal microscopy and reverse transcription-polymerase chain reaction (RT-PCR) were performed to investigate the macrophages cultured on the scaffolds. Significant morphological changes of cells were observed on PCL/EUG scaffolds with different stiffness. The expression of inflammatory and fibrosis-related cytokines increases as scaffold stiffness decreases, similar to the trend observed in OA progression.

New generation bulk-fill resin composites: Effects on mechanical strength and fracture reliability.

PURPOSE: To investigate the mechanical performance and fracture reliability of new generation, bulk-fill resin composites of different viscosities. METHODS: Forty sound maxillary premolars were prepared into Class I cavities comprised of 5 mm width × 5 mm length × 5 mm thickness. The teeth were randomly allocated into four groups (n = 10) according to the restorative material: Negative control - without restoration; Positive control - conventional resin composite (Opallis; FGM) was applied using increments of up to 2.0 mm-thick; Bulk-Regular - bulk-fill resin composite of regular viscosity (Opus Bulk Fill; FGM) was applied using a single increment of 5 mm-thick; and Bulk-Flow - a low-viscosity bulk-fill resin composite (Opus Bulk Fill Flow; FGM) was applied as the first increment with ∼3.5 mm-thick, followed by two final increments of Opallis (∼1.5 mm-thick). The teeth were stored at 37 °C, for 24 h, and submitted to a mechanical testing machine (DL500; EMIC) under a compressive loading. Work of fracture (Wf) was also obtained. All data were analyzed using ANOVA and Tukey (α = 5%). Reliability of restorations and probability of failure were analyzed by Weibull analysis. RESULTS: The non-restored teeth showed the weakest behavior of the study. All the restored groups demonstrated similar mechanical properties to each other (p ≥ 0.242). The positive and negative controls failed exclusively within the cohesiveness of enamel/dentin, whereas the bulk-fill-based restorations showed a mixture of cohesive and mixed failures. The restored groups showed an overall similar reliability, although the Bulk-Regular group demonstrated greater characteristic strength than the positive control. CONCLUSION: The novel bulk-fill resin composites of low and regular viscosities show promising application in the restoration of Class I cavities in premolars, demonstrating similar mechanical performance and reliability as compared with restorations prepared using conventional resin composites. From the bulk-fill materials, the version with regular viscosity presented the greatest compliant behavior of the study.

Multi-laminate annulus fibrosus repair scaffold with an interlamellar matrix enhances impact resistance, prevents herniation and assists in restoring spinal kinematics.

Focal defects in the annulus fibrosus (AF) of the intervertebral disc (IVD) arising from herniation have detrimental impacts on the IVD's mechanical function. Thus, biomimetic-based repair strategies must restore the mechanical integrity of the AF to help support and restore native spinal loading and motion. Accordingly, an annulus fibrosus repair patch (AFRP); a collagen-based multi-laminate scaffold with an angle-ply architecture has been previously developed, which demonstrates similar mechanical properties to native outer AF (oAF). To further enhance the mimetic nature of the AFRP, interlamellar (ILM) glycosaminoglycan (GAG) was incorporated into the scaffolds. The ability of the scaffolds to withstand simulated impact loading and resist herniation of native IVD tissue while contributing to the restoration of spinal kinematics were assessed separately. The results demonstrate that incorporation of a GAG-based ILM significantly increased (p < 0.001) the impact strength of the AFRP (2.57 ±â€¯0.04 MPa) compared to scaffolds without (1.51 ±â€¯0.13 MPa). Additionally, repair of injured functional spinal units (FSUs) with an AFRP in combination with sequestering native NP tissue and a full-thickness AF tissue plug enabled the restoration of creep displacement (p = 0.134), short-term viscous damping coefficient (p = 0.538), the long-term viscous (p = 0.058) and elastic (p = 0.751) damping coefficients, axial neutral zone (p = 0.908), and axial range of motion (p = 0.476) to an intact state. Lastly, the AFRP scaffolds were able to prevent native IVD tissue herniation upon application of supraphysiologic loads (5.28 ±â€¯1.24 MPa). Together, these results suggest that the AFRP has the strength to sequester native NP and AF tissue and/or implants, and thus, can be used in a composite repair strategy for IVDs with focal annular defects thereby assisting in the restoration of spinal kinematics.

Bioengineered analog of stromal cell-derived factor 1α preserves the biaxial mechanical properties of native myocardium after infarction.

Adverse remodeling of the left ventricle (LV) after myocardial infarction (MI) results in abnormal tissue biomechanics and impaired cardiac function, often leading to heart failure. We hypothesized that intramyocardial delivery of engineered stromal cell-derived factor 1α analog (ESA), our previously-developed supra-efficient pro-angiogenic chemokine, preserves biaxial LV mechanical properties after MI. Male Wistar rats (n = 45) underwent sham surgery (n = 15) or permanent left anterior descending coronary artery ligation. Rats sustaining MI were randomized for intramyocardial injections of either saline (100 µL, n = 15) or ESA (6 µg/kg, n = 15), delivered at four standardized borderzone sites. After 4 weeks, echocardiography was performed, and the hearts were explanted. Tensile testing of the anterolateral LV wall was performed using a displacement-controlled biaxial load frame, and modulus was determined after constitutive modeling. At 4 weeks post-MI, compared to saline controls, ESA-treated hearts had greater wall thickness (1.68 ±â€¯0.05 mm vs 1.42 ±â€¯0.08 mm, p = 0.008), smaller end-diastolic LV internal dimension (6.88 ±â€¯0.29 mm vs 7.69 ±â€¯0.22 mm, p = 0.044), and improved ejection fraction (62.8 ±â€¯3.0% vs 49.4 ±â€¯4.5%, p = 0.014). Histologic analysis revealed significantly reduced infarct size for ESA-treated hearts compared to saline controls (29.4 ±â€¯2.9% vs 41.6 ±â€¯3.1%, p = 0.021). Infarcted hearts treated with ESA exhibited decreased modulus compared to those treated with saline in both the circumferential (211.5 ±â€¯6.9 kPa vs 264.3 ±â€¯12.5 kPa, p = 0.001) and longitudinal axes (194.5 ±â€¯6.5 kPa vs 258.1 ±â€¯14.4 kPa, p < 0.001). In both principal directions, ESA-treated infarcted hearts possessed similar tissue compliance as sham non-infarcted hearts. Overall, intramyocardial ESA therapy improves post-MI ventricular remodeling and function, reduces infarct size, and preserves native LV biaxial mechanical properties.

Crack nucleation and propagation in microcrystalline-cellulose based granules subject to uniaxial and triaxial load.

Cracking patterns in four kinds of granules, based on the common pharmaceutical excipient microcrystalline cellulose (MCC) and subject to compressive load, were examined. The initial pore structure and the location of initial failure under uniaxial compression were assessed using X-ray micro-computed tomography, whereas contact force development and onset of cracking under more complex compressive load were examined using a triaxial testing apparatus. Smoothed particle hydrodynamics (SPH) simulations were employed for numerical analysis of the stress distributions prior to cracking. For granules subject to uniaxial compression, initial cracking always occurred along the meridian and the precise location of the crack depended on the pore structure. Likewise, for granules subject to triaxial compression, the fracture plane of the primary crack was generally parallel to the dominant loading direction. The occurrence of cracking was highly dependent on the triaxiality ratio, i.e. the ratio between the punch displacements in the secondary and dominant loading directions. Compressive stresses in the lateral directions, induced by triaxial compression, prevented crack opening and fragmentation of the granule, something that could be verified by simulations. These results provide corroboration as well as further insights into previously observed differences between confined and unconfined compression of granular media.

Sustainable restoration: the contribution of algae.

The application of algae to the most meaningful fields of our life, such as food, environment and energy, finds a further confirmation in the extension of this application to cultural heritage protection. In this letter, we present the results of a preliminary study testing how a polysaccharide extracted from algal matrix can restore degraded paper giving back it mechanical strength and chemical structure.

Photoactivatable Hydrogel Interfaces for Resolving the Interplay of Chemical, Mechanical, and Geometrical Regulation of Collective Cell Migration.

Collective migration is the mechanobiological interplay within migrating cell clusters and against extracellular matrixes (ECMs) underneath, mediating various physiological and pathological processes. Therefore, it is crucial to develop a robust platform on which collective migration can be studied under standardized conditions to understand how cells migrate differently between normal and disease states. We herein demonstrated phtotoactivatable hydrogel interfaces as suitable candidates for such applications. The substrate was composed of a poly(acrylamide) (PAAm) hydrogel whose surface was sequentially functionalized with poly-d-lysine (PDL) and photocleavable poly(ethylene glycol) (PEG). On the surface of the gel substrates, cell clusters with any given geometries can be prepared by controlling the irradiation patterns (geometrical cue), and their collective migration can be induced by the subsequent irradiation of the surrounding regions. Moreover, the substrate mechanical properties can be controlled by changing the composition of the PAAm hydrogel (mechanical cue), and the chemical properties were controlled by changing the amount of immobilized PDL, thereby altering the adsorbed amount of ECM proteins (chemical cue). The photoactivatable gel substrates were characterized by fluorescence microscopy, ζ-potential measurements, and the protein adsorption test. Through the study of the interplay of chemical, mechanical, and geometrical cues in the regulation of collective characteristics, we found additive effects of chemical and mechanical cues on the suppression of circular expansion by up-regulating the epithelial morphology. Also, the impact of geometrical cues became more significant by decreasing the chemical cue. We believe the present platform will be a useful research tool for the comprehensive mechanobiological analysis of collective cell migration.

Mechanoregulation of Cancer-Associated Fibroblast Phenotype in Three-Dimensional Interpenetrating Hydrogel Networks.

Tumor stromal residing cancer-associated fibroblasts (CAFs) are significant accomplices in the growth and development of malignant neoplasms. As cancer progresses, the stroma undergoes a dramatic remodeling and stiffening of its extracellular matrix (ECM). However, exactly how these biomechanical changes influence the CAF behavior and the functional paracrine crosstalk with the neighboring tumor cells in a 3-dimensional (3D) microenvironment remains elusive. Herein, a collagen and alginate interpenetrating network (CoAl-IPN) hydrogel system was employed as a 3D in vitro surrogate of the cancerous breast tissue stromal niche. In this study, the mechanical properties of CoAl-IPN were precisely fine-tuned with Young's modulus ( E) values of ∼108 and 898 Pa. The results revealed that the 3D polymeric network mechanics and microstructure are critical biophysical determinants of the human breast CAF (b-CAF) morphology, phenotype, and paracrine dialogue with MDA-MB-231 tumoroids. A compliant hydrogel network favors b-CAF spreading, nuclear translocation of the YAP/TAZ mechanosignaling protein, and upregulation of CAF hallmark transcripts. Conversely, a rigid and highly cross-linked hydrogel network imposed a physical entrapment effect on the b-CAFs that limited their spreading and phenotype in a manner that effectively muted their pro-tumorigenic paracrine activity. Collectively, the CoAl-IPN 3D culture system has proven to be a versatile platform in defining the 3D biophysical parameters that could either promote or restrain the protumorigenic activity of b-CAFs and sheds critical mechano-mediated light onto the phenotypic plasticity and corresponding specific bioactivity of b-CAFs in the 3D microenvironment.

Mechanical and morphological response of confluent epithelial cell layers to reinforcement and dissolution of the F-actin cytoskeleton.

The F-actin cytoskeleton and its connection to the plasma membrane provide structure and shape of epithelial cells. In this study we focus on the impact of the F-actin cytoskeleton on the morphology and mechanical behaviour of confluent epithelial cells. F-actin depolymerisation was fostered by Latrunculin A, while depolymerisation was allayed by Jasplakinolide. The impact of drug treatment on cellular mechanics was measured using atomic force microscopy based active microrheology and force-indentation curves, while morphology was monitored by AFM imaging, electric cell-substrate impedance sensing (ECIS) experiments and fluorescence microscopy. A softening and fluidisation of the cells upon dissolution of F-actin was observed, accompanied by reduction of cell-substrate and cell-cell contacts and an altered topography. The strengthening of actin filaments upon Jasplakinolide treatment was mirrored in several mechanical properties. The largest impact was on the cellular viscosity. The cells were, however, capable of restoring their initial phenotypes, e.g., amount of actin, intercellular and cell-substrate interactions.

Novel adhesives for distal radius fixation: A biomechanical analysis.

Wrist fractures can be difficult to treat due to advanced age of the patient, medical co-morbidities, and comminution of the bone. This study examines the effectiveness of two injectable glass polyalkenoate cements (GPCs), derived from two different glasses (A and B), as minimally invasive treatments for distal radius fractures. Twenty-seven fresh cadaveric radial pairs were tested either in compressive fatigue or to quasi-static compressive failure. The radii tested to failure had one pair fixated with a GPC while the other was left intact. The radii tested under fatigue had one pair fixated with a GPC and the other with a volar locking plate. A wedge osteotomy was used to simulate a severely comminuted fracture. When loaded to failure, the radii fixated with a GPC made from glass A or B were found to be, respectively, at least 57% and 62% as strong as their intact biological pair (95% Confidence Interval, Lower). Using a paired t-test, the radii fixated with either adhesive were found to be significantly stiffer than their biological pairs fixated with a volar locking plate for all cycles of fatigue loading. The adhesives under investigation demonstrate promise as treatment for distal radius fractures. In vivo investigations are warranted to determine the effect that the adhesives have on the bone remodelling process.

Escherichia coli lipopolysaccharide induces alveolar epithelial cell stiffening.

INTRODUCTION: Application of lipopolysaccharide (LPS) is a widely employed model to mimic acute respiratory distress syndrome (ARDS). Available data regarding LPS-induced biomechanical changes on pulmonary epithelial cells are limited only to P. aeruginosa LPS. Considering that LPS from different bacteria could promote a specific mechanical response in epithelial cells, we aim to assess the effect of E. coli LPS, widely employed as a model of ARDS, in the biomechanics of alveolar epithelial cells. METHODS: Young's modulus (E) of alveolar epithelial cells (A549) was measured by atomic force microscopy every 5 min throughout 60 min of experiment after treatment with LPS from E. coli (100 µg/mL). The percentage of cells presenting actin stress fibers (F-actin staining) was also evaluated. Control cells were treated with culture medium and the values obtained were compared with LPS-treated cells for each time-point. RESULTS: Application of LPS induced significant increase in E after 20 min (77%) till 60 min (104%) in comparison to controls. Increase in lung epithelial cell stiffness induced by LPS was associated with a higher number of cells presenting cytoskeletal remodeling. CONCLUSIONS: The observed effects of E. coli LPS on alveolar epithelial cells suggest that this widely-used LPS is able to promote a quick formation of actin stress fibers and stiffening cells, thereby facilitating the disruption of the pulmonary epithelial barrier.