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We demonstrate sodium pyruvate (NaPy) pre‐treatment as a successful approach for pressure ulcer (PU) prevention by averting their aetiological origin—cell‐level damage and death by large, sustained mechanical loads. We evaluated the NaPy pre‐treatment effect on permeability changes in the cell's plasma membrane (PM) following application of in vitro damaging‐level strains. Fibroblasts or myoblasts, respectively, models for superficial or deep‐tissue damage were grown in 0 or 1 mM NaPy, emulating typical physiological or cell culture conditions. Cells were pre‐treated for 4 hours with 0 to 5 mM NaPy prior to 3‐hour sustained, damaging‐level loads (12% strain). PM permeability was quantified by the cell uptake of small (4 kDa), fluorescent dextran compared with unstrained control using fluorescence‐activated cell sorting (FACS). Pre‐treatment with 1 mM, and especially 5 mM, NaPy significantly reduces damage to PM integrity. Long‐term NaPy pre‐exposure can improve protective treatment, affecting fibroblasts and myoblasts differently. Pre‐treating with NaPy, a natural cell metabolite, allows cells under damaging‐level mechanical loads to maintain their PM integrity, that is, to avoid loss of homeostasis and inevitable, eventual cell death, by preventing initial, microscale stages of PU formation. This pre‐treatment may be applied prior to planned periods of immobility, for example, planned surgery or transport, to prolong safe time in a position by preventing initial cell damage that can cascade and lead to PU formation. [ABSTRACT FROM AUTHOR]

Methods for tuning extracellular matrix (ECM) mechanics in 3D cell culture that rely on increasing the concentration of either protein or cross-linking molecules fail to control important parameters such as pore size, ligand density, and molecular diffusivity. Alternatively, ECM stiffness can be modulated independently from protein concentration by mechanically loading the ECM. We have developed a novel device for generating stiffness gradients in naturally derived ECMs, where stiffness is tuned by inducing strain, while local mechanical properties are directly determined by laser tweezers based active microrheology (AMR). Hydrogel substrates polymerized within 35 mm diameter Petri dishes are strained non-uniformly by the precise rotation of an embedded cylindrical post, and exhibit a position-dependent stiffness with little to no modulation of local mesh geometry. Here we present the device in the context of fibrin hydrogels. First AMR is used to directly measure local micromechanics in unstrained hydrogels of increasing fibrin concentration. Changes in stiffness are then mapped within our device, where fibrin concentration is held constant. Fluorescence confocal imaging and orbital particle tracking are used to quantify structural changes in fibrin on the micro and nano levels respectively. The micromechanical strain stiffening measured by microrheology is not accompanied by ECM microstructural changes under our applied loads, as measured by confocal microscopy. However, super-resolution orbital tracking reveals nanostructural straightening, lengthening, and reduced movement of fibrin fibers. Furthermore, we show that aortic smooth muscle cells cultured within our device are morphologically sensitive to the induced mechanical gradient. Our results demonstrate a powerful cell culture tool that can be used in the study of mechanical effects on cellular physiology in naturally derived 3D ECM tissues. [ABSTRACT FROM AUTHOR]

Small airway epithelial cells form a continuous sheet lining the conducting airways, which serves many functions including a physical barrier to protect the underlying tissue. In asthma, injury to epithelial cells can occur during bronchoconstriction, which may exacerbate airway hyperreactivity. To investigate the role of epithelial cell rupture in airway constriction, laser ablation was used to precisely rupture individual airway epithelial cells of small airways (<300-μm diameter) in rat lung slices (∼250-μm thick). Laser ablation of single epithelial cells using a femtosecond laser reproducibly induced airway contraction to ∼70% of the original cross-sectional area within several seconds, and the contraction lasted for up to 40 s. The airway constriction could be mimicked by mechanical rupture of a single epithelial cell using a sharp glass micropipette but not with a blunt glass pipette. These results suggest that soluble mediators released from the wounded epithelial cell induce global airway contraction. To confirm this hypothesis, the lysate of primary human small airway epithelial cells stimulated a similar airway contraction. Laser ablation of single epithelial cells triggered a single instantaneous Ca(2+) wave in the epithelium, and multiple Ca(2+) waves in smooth muscle cells, which were delayed by several seconds. Removal of extracellular Ca(2+) or decreasing intracellular Ca(2+) both blocked laser-induced airway contraction. We conclude that local epithelial cell rupture induces rapid and global airway constriction through release of soluble mediators and subsequent Ca(2+)-dependent smooth muscle shortening.

We report what is to our best knowledge the first observation of Mathieu-Gauss modes directly generated in an axicon-based stable resonator. By slightly breaking the symmetry of the cavity we were able to generate single lowest and high-order Mathieu-Gauss modes of high quality. The observed transverse modes have an inherent elliptic structure and exhibit remarkable agreement with theoretical predictions.