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Adjustable Jig and Method for Targeting Interlocking Holes of an Intramedullary Nail
Get PDFA targeting jig apparatus for targeting interlocking holes of an intramedullary nail. The targeting jig includes a support-arm extending substantially parallel to the intramedullary nail. A targeting mechanism including a pair of targeting mechanism drill-guide orifices is adjustably disposed on the support arm for aligning the targeting mechanism drill-guide orifice with the interlocking holes of the intramedullary nail. The targeting mechanism includes a saddle having a U-shape including a base and parallel legs that are slidable along the support-arm. A connection mechanism includes a horizontal slot on the support-arm aligned with a vertical slot on the targeting mechanism and a pivot screw extending through the slots for facilitating adjustment of the targeting mechanism relative to the support arm
Cellular Hokey Pokey: A Coarse-Grained Model of Lamellipodia Protrusion Dynamics Driven by Fluctuations in Actin Polymerization
Get PDFAnimal cells that spread onto a surface often rely on actin-rich cell extensions called lamellipodia to execute cell protrusion. XTC cells on a two-dimensional substrate exhibit regular protrusion and retraction of their lamellipodium, even though the cell is not translating. Travelling waves of protrusion have also been observed, similar to those observed in crawling cells. These periodic fluctuations in leading edge position have been linked to excitable actin dynamics near the cell edge using a one dimensional model of actin dynamics, as a function of arc-length along the cell. In this work we extend this earlier model of actin dynamics into two-dimensions (along the arc-length and radial directions of the cell) and include a model membrane that protrudes and retracts in response to the changing number of free barbed ends of actin filaments near the membrane. We show that if the polymerization rate of these barbed ends changes depending on their local concentration at the leading edge and the opposing force from the cell membrane, the model can reproduce the patterns of membrane protrusion and retraction seen in experiment. We investigate both Brownian ratchet and switch-like force-velocity relationships between the membrane load forces and actin polymerization rate
A 3D Sparse Motion Field Filtering for Quantitative Analysis of Fascial Layers Mobility Based on 3D Ultrasound Scans
No full textIn the last few years, there has been an increasing interest in the role of deep fascia mobility in musculoskeletal dynamics and chronic pain mechanisms. In a previous paper we presented an innovative semiautomatic approach to evaluate the 3D motion of the fascia using ultrasound (US) imaging, generating a sparse deformation vector field. This paper presents an improvement of our original method, focusing on the filtering of the sparse vector field and its validation. Moreover, in order to evaluate the performance of the algorithm, a method is proposed to generate synthetic deformation vector fields, including: expansion, rotation, horizontal shear, and oblique shear components. Preliminary tests on the final synthetic deformation vector fields showed promising results. Further experiments are required in order to optimize the tuning of the algorithm
Measurement of Subcellular Force Generation in Neurons
No full textForces are important for neuronal outgrowth during the initial wiring of the nervous system and after trauma, yet subcellular force generation over the microtubule-rich region at the rear of the growth cone and along the axon has never, to our knowledge, been directly measured. Because previous studies have indicated microtubule polymerization and the microtubule-associated proteins Kinesin-1 and dynein all generate forces that push microtubules forward, a major question is whether the net forces in these regions are contractile or expansive. A challenge in addressing this is that measuring local subcellular force generation is difficult. Here we develop an analytical mathematical model that describes the relationship between unequal subcellular forces arranged in series within the neuron and the net overall tension measured externally. Using force-calibrated towing needles to measure and apply forces, in combination with docked mitochondria to monitor subcellular strain, we then directly measure force generation over the rear of the growth cone and along the axon of chick sensory neurons. We find the rear of the growth cone generates 2.0 nN of contractile force, the axon generates 0.6 nN of contractile force, and that the net overall tension generated by the neuron is 1.3 nN. This work suggests that the forward bulk flow of the cytoskeletal framework that occurs during axonal elongation and growth-cone pauses arises because strong contractile forces in the rear of the growth cone pull material forward
On-Demand Degrafting and the Study of Molecular Weight and Grafting Density of Poly(Methyl Methacrylate) Brushes on Flat Silica Substrates
No full textWe report on degrafting of surface-anchored poly(methyl methacrylate) (PMMA) brushes from flat silica-based substrates using tetrabutylammonium fluoride (TBAF) and determining their molecular weight distribution (MWD) using size exclusion chromatography (SEC). The grafted PMMA layer was synthesized using surface-initiated atom transfer radical polymerization (SI-ATRP) of MMA for polymerization times ranging from 6 to 24 h. X-ray photoelectron spectroscopy, ellipsometry, and time-of-flight secondary ion mass spectrometry were employed in tandem to characterize the degrafting process. The SEC eluograms were fit to various polymer distributions, namely Zimm–Schulz, ATRP in continuous stirred tank reactor, Wesslau, Schulz–Flory, and Smith et al. The ATRP model gives the best fit to the experimental data. The dry PMMA brush thickness and the number-average molecular weight (obtained from the MWD) suggest that the grafting density of the PMMA grafts is independent of polymerization time, indicating well-controlled/living growth of MMA. The observed polydispersity index (PDI) was higher than that generally observed in bulk grown polymers under similar conditions, indicating an effect due to chain confinement and crowding. We detect small but noticeable dependence of the polymer brush grafting density on the inhibitor/catalyst ratio. Higher inhibitor/catalyst ratio offers better control with lower early terminations, which results in a small increase in the apparent grafting density of the chains