Local tissue manipulation via a force- and pressure-controlled AFM micropipette for analysis of cellular processes

The Protective Effect of Aspirin Eugenol Ester on Paraquat-Induced Acute Liver Injury Rats

Aspirin eugenol ester (AEE) possesses anti-inflammatory and anti-oxidative effects. The study was conducted to evaluate the protective effect of AEE on paraquat-induced acute liver injury (ALI) in rats. AEE was against ALI by decreasing alanine transaminase and aspartate transaminase levels in blood, increasing superoxide dismutase, catalase, and glutathione peroxidase levels, and decreasing malondialdehyde levels in blood and liver. A total of 32 metabolites were identified as biomarkers by using metabolite analysis of liver homogenate based on ultra-performance liquid chromatography-tandem mass spectrometry, which belonged to purine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, glycerophospholipid metabolism, primary bile acid biosynthesis, aminoacyl-tRNA biosynthesis, phenylalanine metabolism, histidine metabolism, pantothenate, and CoA biosynthesis, ether lipid metabolism, beta-Alanine metabolism, lysine degradation, cysteine, and methionine metabolism. Western blotting analyses showed that Bax, cytochrome C, caspase-3, caspase-9, and apoptosis-inducing factor expression levels were obviously decreased, whereas Bcl-2 expression levels obviously increased after AEE treatment. AEE exhibited protective effects on PQ-induced ALI, and the underlying mechanism is correlated with antioxidants that regulate amino acid, phospholipid and energy metabolism metabolic pathway disorders and alleviate liver mitochondria apoptosis.

Electrokinetics in Micro-channeled Cantilevers: Extending the Toolbox for Reversible Colloidal Probes and AFM-Based Nanofluidics

The combination of atomic force microscopy (AFM) with nanofluidics, also referred to as FluidFM, has facilitated new applications in scanning ion conductance microscopy, direct force measurements, lithography, or controlled nanoparticle deposition. An essential element of this new type of AFMs is its cantilever, which bears an internal micro-channel with a defined aperture at the end. Here, we present a new approach for in-situ characterization of the internal micro-channels, which is non-destructive and based on electrochemical methods. It allows for probing the internal environment of a micro-channeled cantilever and the corresponding aperture, respectively. Acquiring the streaming current in the micro-channel allows to determine not only the state of the aperture over a wide range of ionic strengths but also the surface chemistry of the cantilever’s internal channel. The high practical applicability of this method is demonstrated by detecting the aspiration of polymeric, inorganic and hydrogel particles with diameters ranging from several µm down to 300 nm. By verifying in-situ the state of the aperture, i.e. open versus closed, electrophysiological or nano-deposition experiments will be significantly facilitated. Moreover, our approach is of high significance for direct force measurements by the FluidFM-technique and sub-micron colloidal probes.

In situ determination of exerted forces in magnetic pulling cytometry

Localized application of exogenous forces on soft biomaterials and cells is often essential for the study of their response to external mechanical stimuli. Magnetic means of applying forces, particularly those based on permanent magnets and magnetic beads coupled to substrates or cells provide an accessible means of exerting forces of appropriate magnitude. The amount of force exerted, however, is often inferred from calibration performed ex situ, with typically similar but different magnetic beads. Here, we construct a simple magnetic tweezer by coupling a pencil-shaped stainless-steel probe to permanent neodymium magnets using a 3D printed adapter. We then demonstrate the in situ determination of magnetic bead pulling forces on a super-paramagnetic micro-bead coupled to a soft substrate using traction force microscopy. We determine the force exerted on the magnetic bead by the magnet probe - and thus exerted by the magnetic bead on the soft polyacrylamide substrate - as a function of the distance between the probe tip and the magnetic bead. We also show that we can determine the force exerted on a magnetic bead coupled to a cell by the changes in the traction force exerted by the cell on the soft substrate beneath. We thus demonstrate that forces of nanonewton magnitude can be locally exerted on soft substrates or cells and simultaneously determined using traction force microscopy. Application of this method for the in situ measurement of localized exogenous forces exerted on cells can also enable dissection of cellular force transmission pathways.