Mapping the Mechanical Stiffness of Live Cells ... - Soft Matter World

Marquee goes hereDear soft matter colleagues,Long days, short nights and a packed conference schedule are a sign that the Summer season has officially started.This month's marquee image is taken from a recent edition of RSC's Soft Matter journal which you can read more aboutbelow. Also inluded is a feature on Colloidal Surfers and Surface Gravity Waves. Dont forget to friend us - see our socialicons on the bottom of page 2 and 3!Mapping the Mechanical Stiffness of Live Cells With The ScanningIon Conductance MicroscopeRheinlaender, J., & Schaffer, T.E. (2013). Soft Matter, 9, 3230-3236Figure 1: (A) A schematic of how the SICM is composed, depicting where the specimen would beplaced and where the voltage is applied. (B) Portrays both a stiffer cell on the left and a softer cell on theright. The softer cell leaves a larger indentation with a slower decline in ion current than the stiffer cell.(C) uses three different types of microscopes to view a cell after Cytochalasin D has been administeredand acts on the cytoskeleton. The top row being fluorescent actin, the middle being SICM height and thebottom row being SICM stiffness.Contact between a specimen andthe instrument used to observe thatspecimen has always been a hindrancewhen attempting to achievedetailed images. A new method toobserve the topography of cells thatimproves upon past procedures hasbeen developed. The Scanning IonConductive Microscope (SICM), developedby Johannes Rheinlaenderand Tilman E. Schaffer of the Universityof Tubingen, analyzes stiffness ofvarious points on the cell. This resultsin a detailed image that can determinethe shape of the cell, cytoskeletonfibers and even some organelleidentification.Comprised mostly of commercially-usedAFM parts, the SICM is easyto construct (Figure 1A). Where thismostly differs is the pipette at the tipof the microscope head, which emitsa pressure of 5-10 kPa. A constantvoltage is supplied to two electrodes,creating an ion current through thepipette. As the constant pressure isapplied, the pipette is slowly loweredtowards the specimen. A softer specimenreceives deeper indentation anda larger ion current is observed, whilea stiffer specimen does not indent onthe pipette’s closing position, leavinglittle room for the ion current to circulate(Figure 1B). Observing the ioncurrent on multiple pressurized locationson the specimen generates datato be analyzed using a ratio of Young’smodulus and the applied pressure.This data can then map out the entireimage of the specimen in great detail.As a way to test how accurately theSICM detects the indentation on thecell, cytochalasin D was applied to fibroblastcells. Cytochalasin D breaksdown the fibers within the cytoskeleton,resulting in the cell being muchsofter in the areas affected by the toxin.As expected, the SICM mappedout the path the toxin took, as seenin figure (1C), showing that the microscopecan be applied to live cellsthroughout structural changes.Read the full article at the RSC Publishingwebsite where you can seetheir image featured on the front coverof Soft Matter (see newsletter masthead).-Marcus Rice

Observation of Star-ShapedSurface Gravity WavesRajchenbach, J., Clamond, D., & Leroux, A. (2013). Physical Review Letters,110(9), 094502-1 Ð 094502-5.Figure 2: A shows the standing wave for a vibrational amplitude of 1.95mm alternating between a star (A) and a pentagon (B). Figures 2C and 2Dshow that the wave pattern is independent of container size and shapeMany types of waves occur in different physical systems.One particularly interesting example, standing gravitywaves, occur due to nonlinearity and dispersive effects inliquids. A collaborative research team from the Universitede Nice has discovered a new type of standing gravitywave formed in silicon oil that transitions between star andpolygon shapes.The experiment involved placing oil filled containers ofvarying size and shape onto a shaking apparatus. Oncemounted, the containers experienced a vertical sinusoidalmotion resulting in surface waves that were dependenton frequency and vibrational amplitude. After reaching aspecific vibrational amplitude, the oil waves alternated betweena star shape and polygon shape.When a cylindrical container vibrated at a frequency of8 Hz and vibrational amplitude of 1.55 mm, the oil wouldcreate two axisymmetric gravity waves that moved towardthe center of the container. Once the wave reached thecenter, the silicon oil would jet up and fall down back intothe container as a droplet. Increasing the vibrational amplitudeto 1.85 mm caused the crest line of the waves toform five corners, the tips of the corners representing thebreak of rotational symmetry. At an amplitude of 1.95 mmthe wave geometry alternated between a star shape andpolygon shape (Figure 2 A-B). The shape alteration wasdue to a phase shift between the waves.The forming gravity waves were independent of containersize and shape. Alternating star and polygon shapeswere observed when a cylindrical container was used; thesquare container resulted in similar shapes adjacent toone another (Figure 2 C-D).The research group attempted to derive a theoreticalexplanation for the results based on previous theories inquasicrystals and the formation of quasipatterns in capillarywaves. The proposed model explained the formationof the gravity waves, but could not predict the final symmetriesof the waves as they relate to the forcing parametersof the experiment. Future studies may focus on thedesign of a theory to explain steep cnoidal standing wavesin shallow water.Visit PRL to read the full text and to see some of thesupplemental material included with the text.-Amanda BaijnauthLiving Crystals of Light-ActivatedColloidal SurfersJeremie Palacci, Stefano Sacanna, Asher Preska Steinberg, David J. Pine, Paul M. Chaikin. 2013.Science 339, 936 DOI: 10.1126/science.1230020In order to study self-organizationof colloids, U.S. researchers have createda planar system of self-propelledparticles, the motility of which canbe turned on and off with blue light.The colloidal particles consisted of acubic hematite core mostly enclosedin a polymer sphere, and they can beJune | 2013 | Issue #53steered by a magnetic field within thecontaining basic solution.When subjected to blue light, theparticles moved randomly, collidingand creating dynamic crystallinestructures while continuously breakingapart and reforming (Figure 3A-C). When a magnetic field was applied,the particles aligned with thefield and the break up of the crystalswas suppressed. In effect, they moveden masse in a single direction. Alternatively,when the magnetic field wasapplied before the blue light was activated,the particles again aligned.When the blue light was applied, theymoved en masse with no collisions,and therefore no crystal formation occurred.The researchers tested each part ofthe system individually to better un-2

derstand the mechanism behind the motility. When subjectedto blue light, an uncovered hematite cube catalyzeddecomposition of hydrogen peroxide present in the surroundingbasic solution, producing thermal and chemicalgradients. Through the chemical diffusion gradient, the silicatracers were attracted to the cube via a process calleddiffusiophoresis. The converse was also true – hematitecubes were attracted to a fixed silica surface.The effect of surface area fraction ϕ Swas also analyzed.Above 7%, crystallites began forming after 25 seconds ofexposure to blue light. Cluster size, averaging 35 particles,was not dependent on ϕ Swhen above 10%. Fluctuationsin the number of local particles followed a power law ΔN~ N α .The researchers suggest this demonstration of self-assemblythrough non-equilibrium driving forces may beFigure 3: The false colors show the time evolution of different clusters.The clusters rearrange, exchange particles, merge (A), break apart (B),becomeunstable and explode (blue cluster, C).applied to directed self assembly, opening a new area fordesign and the creation of novel motile structures.Visit ScienceMag to read the full article.- Michael LaneSITE UPDATESConferencesWe have released a seperate bulletin pertaining to allthe upcoming conference deadlines and features. It isnever too late to have your conference, featured freeof charge.postings@softmatterworld.orgGalleryFor any of our readers who missed out on a chance toreceive a hard copy of the 2013 Soft Matter World Calendarit is now available for download in the Gallerysection in high resolution PDF format.Feel free to print them out for yourselfand remember that the Soft MatterWorld 2014 Calendar is not far away.We hope you enjoy browsing and come back soonLinda S. Hirst & Adam P. OssowskiJoin the Mailing List!June | 2013 | Issue #533