Mineralization-driven bone tissue evolution follows from fluid-to-solid phase transformations in closed thermodynamic systems

AbstractThe fundamental mechanisms that govern bone mineralization have been fairly well evidenced by means of experimental research. However, rules for the evolution of the volume and composition of the bone tissue compartments (such as the mineralized collagen fibrils and the extrafibrillar space in between) have not been provided yet. As an original contribution to this open question, we here test whether mineralizing bone tissue can be represented as a thermodynamically closed system, where crystals precipitate from an ionic solution, while the masses of the fibrillar and extrafibrillar bone tissue compartments are preserved. When translating, based on various experimental and theoretical findings, this mass conservation proposition into diffraction–mass density relations, the latter are remarkably well confirmed by independent experimental data from various sources. Resulting shrinkage and composition rules are deemed beneficial for further progress in bone materials science and biomedical engineering

Ductile sliding between mineral crystals followed by rupture of collagen crosslinks: Experimentally supported micromechanical explanation of bone strength

International audienceThere is an ongoing discussion on how bone strength could be explained from its internal structure and composition. Reviewing recent experimental and molecular dynamics studies, we here propose a new vision on bone material failure: mutual ductile sliding of hydroxyapatite mineral crystals along layered water films is followed by rupture of collagen crosslinks. In order to cast this vision into a mathematical form, a multiscale continuum micromechanics theory for upscaling of elastoplastic properties is developed, based on the concept of concentration and influence tensors for eigenstressed microheterogeneous materials. The model reflects bone's hierarchical organization, in terms of representative volume elements for cortical bone, for extravascular and extracellular bone material, for mineralized fibrils and the extrafibrillar space, and for wet collagen. In order to get access to the stress states at the interfaces between crystals, the extrafibrillar mineral is resolved into an infinite amount of cylindrical material phases oriented in all directions in space. The multiscale micromechanics model is shown to be able to satisfactorily predict the strength characteristics of different bones from different species, on the basis of their mineral/collagen content, their intercrystalline, intermolecular, lacunar, and vascular porosities, and the elastic and strength properties of hydroxyapatite and (molecular) collagen

A micro-macro evaluation of the vertebral bony endplate permeability based on computational fluid dynamics

The intrinsic permeability is an important parameter that describes the resistance of a porous structure to fluid flo w. It has a key role in poroelastic finite element models of spinal segments, especially at the vertebral endplate, i.e. the interface between intervertebral disc and vertebra. In the understanding of the properties of the complex endplate system, an expli cit evaluation for permeability of subchondral bone is missing. Thus, a new method wa s proposed to evaluate the intrinsic permeability of the bony endplate. CT - based reconstruction s of the bony endplate from a lumbar vertebra were analyzed using computational fluid dynamics , and the i ntrinsic permeability and porosity of the structure were calculated. Results showed that the permeability did not depend on the fluid flow direction, and was statistically similar for both the superior and inferior endplates . Permeability values varied within the range of trabecular bone, while porosity values w ere lower than trabecular bone characteristic values. Finally, i ntrins ic permeability correlated well with porosity through the Kozeny - Karman model, which offer s perspectives for parametric studies involving degenerative or age - related changes at the disc - bone interface.Postprint (published version

Platynereis dumerilii chaetae: mechanical loading estimation from kinematics in larva stage

This work was supported by grant Bio3DPrint from the Austrian Academy of Sciences (OeAW)

Coupling systems biology with multiscale mechanics, for computer simulations of bone remodeling

Bone remodeling is a process involving removal of mature bone tissue and subsequent formation of new bone tissue. This process is driven by complex actions of biological cells and biochemical factors, and it is sensitive to the loads applied onto the skeleton. Herein, we develop a mathematical framework describing this process at the (macroscopic) level of cortical bone, by combining, for the first time, bone cell population kinetics with multiscale bone mechanics. Key variables are concentrations of biological cells (osteoclasts, osteoblasts and their progenitors) and biochemical factors (RANK, RANKL, OPG, PTH, and TGF-beta), as well as mechanical strains, both at the ("macroscopic") level of cortical bone and at the ("microscopic") level of the extravascular bone matrix. Multiscale bone mechanics delivers, as a function of the vascular porosity, the relation between the macroscopic strains resulting from the loads, and the microscopic strains, which are known to modulate, either directly, or via poromechanical couplings such as hydrostatic pressure or fluid flow, the expression or proliferation behavior of the biological cells residing in, or attached to the extravascular bone matrix. Hence, these microscopic strains enter the biochemical kinetics laws governing cell expression, proliferation, differentiation, and apoptosis. Without any additional phenomenologically motivated paradigm, this novel approach is able to explain the experimentally observed evolutions of bone mass in postmenopausal osteoporosis and under microgravity conditions: namely, a decrease of bone loss over time

Seeds of Change: Corn Seed Mixtures for Resistance Management and Integrated Pest Management

The use of mixtures of transgenic insecticidal seed and nontransgenic seed to provide an in-field refuge for susceptible insects in insect-resistance-management (IRM) plans has been considered for at least two decades. However, the U.S. Environmental Protection Agency has only recently authorized the practice. This commentary explores issues that regulators, industry, and other stakeholders should consider as the use of biotechnology increases and seed mixtures are implemented as a major tactic for IRM. We discuss how block refuges and seed mixtures in transgenic insecticidal corn, Zea mays L., production will influence integrated pest management (IPM) and the evolution of pest resistance. We conclude that seed mixtures will make pest monitoring more difficult and that seed mixtures may make IRM riskier because of larval behavior and greater adoption of insecticidal corn. Conversely, block refuges present a different suite of risks because of adult pest behavior and the lower compliance with IRM rules expected from farmers. It is likely that secondary pests not targeted by the insecticidal corn as well as natural enemies will respond differently to block refuges and seed mixtures

The concept of frozen elastic energy as a consequence of change in microstructure morphology

Une approche micromécanique et multi-échelle pour la modélisation des tissus mous explique la non-linéarité de leur réponse au chargement mécanique, la dépendance de leur réponse mécanique vis-à-vis de la trajectoire de déformation ainsi que l'éventuelle énergie stockée, comme conséquences du changement de morphologie de la microstructure

Systematic literature review informing the 2018 update of the EULAR recommendation for the management of large vessel vasculitis : focus on giant cell arteritis

© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ. This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.Objectives: To analyse the current evidence for the management of large vessel vasculitis (LVV) to inform the 2018 update of the EULAR recommendations. Methods: Two systematic literature reviews (SLRs) dealing with diagnosis/monitoring and treatment strategies for LVV, respectively, were performed. Medline, Embase and Cochrane databases were searched from inception to 31 December 2017. Evidence on imaging was excluded as recently published in dedicated EULAR recommendations. This paper focuses on the data relevant to giant cell arteritis (GCA). Results: We identified 287 eligible articles (122 studies focused on diagnosis/monitoring, 165 on treatment). The implementation of a fast-track approach to diagnosis significantly lowers the risk of permanent visual loss compared with historical cohorts (level of evidence, LoE 2b). Reliable diagnostic or prognostic biomarkers for GCA are still not available (LoE 3b).The SLR confirms the efficacy of prompt initiation of glucocorticoids (GC). There is no high-quality evidence on the most appropriate starting dose, route of administration, tapering and duration of GC (LoE 4). Patients with GCA are at increased risk of dose-dependent GC-related adverse events (LoE 3b). The addition of methotrexate or tocilizumab reduces relapse rates and GC requirements (LoE 1b). There is no consistent evidence that initiating antiplatelet agents at diagnosis would prevent future ischaemic events (LoE 2a). There is little evidence to guide monitoring of patients with GCA. Conclusions: Results from two SLRs identified novel evidence on the management of GCA to guide the 2018 update of the EULAR recommendations on the management of LVV.info:eu-repo/semantics/publishedVersio