Linking particle dynamics to local connectivity in colloidal gels

Colloidal gels are a prototypical example of a heterogeneous network solid whose complex properties are governed by thermally-activated dynamics. In this Letter we experimentally establish the connection between the intermittent dynamics of individual particles and their local connectivity. We interpret our experiments with a model that describes single-particle dynamics based on highly cooperative thermal debonding. The model, in quantitative agreement with experiments, provides a microscopic picture for the structural origin of dynamical heterogeneity in colloidal gels and sheds new light on the link between structure and the complex mechanics of these heterogeneous solids.Comment: 5 pages, 5 figure

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Data underlying the publication: Phytophthora pathogens exploit slicing action for host invasion

Host entry requires plant pathogens to breach the protective surface of the plant. Phytophthora species, classified as oomycetes, are among the most destructive filamentous plant pathogens worldwide and pose a substantial threat to food security. Little is known about the biomechanics of host invasion in oomycetes, yet this understanding is crucial to combat these pathogens more effectively. Here we unveil how Phytophthora spp. invade elastic surfaces by pressure application at an oblique angle without appressorium formation. This ‘slicing’ action, coined the naifu-mechanism, facilitates crack initiation by concentrating stresses towards the surface enabling host entry through the crack void. This contrasts the ‘brute’ force approach found in fungal filamentous plant pathogens capable of producing a melanized appressorium that generates tremendous turgor pressures. Measurements of surface deformations during invasion reveal an asymmetric geometry of decoupled adherence and indentation sites that is quantitatively described with a mathematical model. Moreover, we establish how polarized growth, surface adherence and turgor generation are each essential to accomplish host entry by this approach. The naifu-mechanism enables Phytophthora pathogens to penetrate their hosts without necessitating specialized pressure organs and vast turgor pressures

Data from the paper An actin mechanostat ensures hyphal tip sharpness in Phytophthora infestans to facilitate host entry.

Filamentous plant pathogens apply mechanical forces to pierce their hosts surface and penetrate its tissues. Devastating Phytophthora pathogens harness a specialized form of invasive tip growth to slice through the plant surface, wielding their hypha as a microscopic knife. Slicing requires a sharp hyphal tip that is not blunted at the site of the mechanical interaction. How tip shape is controlled, however, is unknown. We uncover an actin-based mechanostat in P. infestans that controls tip sharpness during penetration. Mechanical stimulation of the hypha leads to the emergence of an aster-like actin structure, which shows fast, local and quantitative feedback to the local stress. We evidence that this functions as an adaptive mechanical scaffold that sharpens the invasive weapon and prevents it from blunting. The hyphal tip mechanostat enables the efficient conversion of turgor into localized invasive pressures that are required to achieve host penetration