89 research outputs found
The people behind the papers - Yonit Maroudas-Sacks and Marko Popovic
No full textDuring Hydra regeneration, supracellular actomyosin fibres are disoriented at two distinct foci of the regenerating tissue. These sites of nematic topological defects eventually form the new head and foot of the regenerated animal. In a new study, Yonit MaroudasSacks, Marko Popovic, Kinneret Keren and colleagues propose a positive-feedback loop that incorporates fibre organisation, tissue strain and morphogen gradients to promote head organiser formation. To find out more about the work, we caught up with first author Yonit Maroudas-Sacks and co-corresponding author Marko Popovic, Group Leader at the Max Planck Institute for the Physics of Complex Systems, Germany
Contribution of postnatal collagen reorientation to depth-dependent mechanical properties of articular cartilage
No full textThe collagen fibril network is an important factor for the depth-dependent mechanical behaviour of adult articular cartilage (AC). Recent studies show that collagen orientation is parallel to the articular surface throughout the tissue depth in perinatal animals, and that the collagen orientations transform to a depth-dependent arcade-like structure in adult animals. Current understanding on the mechanobiology of postnatal AC development is incomplete. In the current paper, we investigate the contribution of collagen fibril orientation changes to the depth-dependent mechanical properties of AC. We use a composition-based finite element model to simulate in a 1-D confined compression geometry the effects of ten different collagen orientation patterns that were measured in developing sheep. In initial postnatal life, AC is mostly subject to growth and we observe only small changes in depth-dependent mechanical behaviour. Functional adaptation of depth-dependent mechanical behaviour of AC takes place in the second half of life before puberty. Changes in fibril orientation alone increase cartilage stiffness during development through the modulation of swelling strains and osmotic pressures. Changes in stiffness are most pronounced for small stresses and for cartilage adjacent to the bone. We hypothesize that postnatal changes in collagen fibril orientation induce mechanical effects that in turn promote these changes. We further hypothesize that a part of the depth-dependent postnatal increase in collagen content in literature is initiated by the depth-dependent postnatal increase in fibril strain due to collagen fibril reorientatio
Approximate Analytical Model for the Squeeze-Film Lubrication of the Human Ankle Joint with Synovial Fluid Filtrated by Articular Cartilage
No full textThe aim of this article is to propose an analytical approximate squeeze-film lubrication model of the human ankle joint for a quick assessment of the synovial pressure field and the load carrying due to the squeeze motion. The model starts from the theory of boosted lubrication for the human articular joints lubrication (Walker et al., Rheum Dis 27:512–520, 1968; Maroudas, Lubrication and wear in joints. Sector, London, 1969) and takes into account the fluid transport across the articular cartilage using Darcy’s equation to depict the synovial fluid motion through a porous cartilage matrix. The human ankle joint is assumed to be cylindrical enabling motion in the sagittal plane only. The proposed model is based on a modified Reynolds equation; its integration allows to obtain a quick assessment on the synovial pressure field showing a good agreement with those obtained numerically (Hlavacek, J Biomech 33:1415–1422, 2000). The analytical integration allows the closed form description of the synovial fluid film force and the calculation of the unsteady gap thickness
Ultra-high field magnetic resonance diffusion tensor imaging of the hyaline articular cartilage
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MARKET-CONSCIOUS STRATEGIES TO IMPROVE THE PERFORMANCE AND STABILITY OF PLANAR, p-i-n HYBRID ORGANIC-INORGANIC METAL HALIDE PEROVSKITE SOLAR CELLS
No full textPlanar, p-i-n (inverted) hybrid organic-inorganic perovskite solar cells that use low-temperature, solution-processable charge-transport layers have garnered much attention due to their direct compatibility with flexible substrates and cost-effective roll-to-roll manufacturing. Nevertheless, this architecture has failed to repeatedly achieve the superior power conversion efficiencies frequently attained by its n-i-p counterpart. Additionally, the perovskite active layer has poor stability in the presence of prolonged light exposure, high temperatures, and moisture. In this study, we propose commercially viable strategies to improve the performance and stability of inverted methylammonium lead iodide perovskite solar cells. First, we show that a simple two-step method comprising evaporation-induced self-assembly of a lead iodide intermediate film coupled with the intermolecular exchange of methylammonium iodide can yield high-quality methylammonium lead iodide perovskite films on non-ideal surfaces. Complete inverted devices with the perovskite active layer formed via this method outperformed those devices with a perovskite layer produced using a conventional method. Second, we successfully replace the commonly used but environmentally unstable calcium-aluminum electrode with a more stable silver electrode in inverted perovskite devices via interfacial engineering without compromising device performance. By introducing a solution-processable, thickness-tolerant n-doped zwitterionic fulleropyrrolidine interlayer between the phenyl-C61-butyric acid methyl ester electron-transporting layer and the silver electrode, we successfully lower the work function of the silver and improve charge transport, which led to an increase in device performance compared to those devices with a calcium-aluminum electrode. Third, we examine the use of copper-based hole-transport materials in inverted perovskite solar cells as a replacement for the more commonly used but less stable poly(3,4-ethylenedioxythiophene) polystyrene sulfonate hole-transport material. We show that in most cases devices with a copper-based hole-transport material outperform those with a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate hole-transport material due to the additive benefits from all relevant film/material properties (i.e. morphology, optics, crystallinity/charge transport potential, and electronic band level alignment). Finally, we present a procedure to effectively transfer monolayer CVD graphene onto a perovskite surface without damaging or degrading the perovskite. We show that the incorporation of graphene significantly improves perovskite film and inverted device stability in the presence of moisture and heat without sacrificing the overall device performance.Chemical EngineeringDoctor of Philosophy (Ph.D.
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