45 research outputs found
Three-dimensional jamming and flows of soft glassy materials
Various disordered dense systems such as foams, gels, emulsions and colloidal
suspensions, exhibit a jamming transition from a liquid state (they flow) to a
solid state below a yield stress. Their structure, thoroughly studied with
powerful means of 3D characterization, exhibits some analogy with that of
glasses which led to call them soft glassy materials. However, despite its
importance for geophysical and industrial applications, their rheological
behavior, and its microscopic origin, is still poorly known, in particular
because of its nonlinear nature. Here we show from two original experiments
that a simple 3D continuum description of the behaviour of soft glassy
materials can be built. We first show that when a flow is imposed in some
direction there is no yield resistance to a secondary flow: these systems are
always unjammed simultaneously in all directions of space. The 3D jamming
criterion appears to be the plasticity criterion encountered in most solids. We
also find that they behave as simple liquids in the direction orthogonal to
that of the main flow; their viscosity is inversely proportional to the main
flow shear rate, as a signature of shear-induced structural relaxation, in
close similarity with the structural relaxations driven by temperature and
density in other glassy systems.Comment: http://www.nature.com/nmat/journal/v9/n2/abs/nmat2615.htm
Seaweed polysaccharide-based hydrogels used for the regeneration of articular cartilage
This manuscript provides an overview of the in vitro and in vivo studies reported in the
literature focusing on seaweed polysaccharides based hydrogels that have been proposed for
applications in regenerative medicine, particularly, in the field of cartilage tissue engineering.
For a better understanding of the main requisites for these specific applications, the main
aspects of the native cartilage structure, as well as recognized diseases that affect this tissue are
briefly described. Current available treatments are also presented to emphasize the need for
alternative techniques. The following part of this review is centered on the description of the
general characteristics of algae polysaccharides, as well as relevant properties required for
designing hydrogels for cartilage tissue engineering purposes. An in-depth overview of the
most well known seaweed polysaccharide, namely agarose, alginate, carrageenan and ulvan
biopolymeric gels, that have been proposed for engineering cartilage is also provided. Finally,
this review describes and summarizes the translational aspect for the clinical application of
alternative systems emphasizing the importance of cryopreservation and the commercial
products currently available for cartilage treatment.Authors report no declarations of interest. Authors thank the Portuguese Foundation for Science and Technology (FCT) for the PhD fellowship of Elena G. Popa (SFRH/BD/64070/2009) and research project (MIT/ECE/0047/2009). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no REGPOT-CT2012-316331-POLARIS
Large Colloids in Cholesteric Liquid Crystals
International audienceno abstrac
A constitutive equation for entangled linear polymers inspired by reptation theory and consistent with non-equilibrium thermodynamics
Using the single generator bracket formalism of non-equilibrium thermodynamics, we build a thermodynamically consistent constitutive equation of the differential type for linear entangled polymers. The starting point of our developments is the MGI rheological model proposed recently by Marrucci et al. [Rheol. Acta 40 (2) (2001) 98], which can be viewed as a modification of the classical Doi-Edwards reptation theory that includes convective constraint release and a modified strain measure. The proposed constitutive equation has an additional parameter which governs the dissipative part of the model. The MGI model is recovered as a particular case, but with a stress-conformation relationship which contains an additional term suggested by non-equilibrium thermodynamics. Predictions of the proposed model in steady and transient shear flows are shown to be in qualitative agreement with experimental observations. (C) 2001 Elsevier Science B.V. All rights reserved
Bracket formulation as a source for the development of dynamic equations in continuum mechanics
The bracket formulation of the dynamic equations in nonequilibrium thermodynamics is examined here. After a short review of the early historical development of the subject, we present an introduction to the theoretical foundations of the one-generator bracket formalism, where the one generator is the Hamiltonian. The Hamiltonian represents the system's total (extended) internal energy but, through a Legendre transform similar to that used in equilibrium thermodynamics, its derivatives can also be calculated from the available expression for the system's extended free energy. First, the conservative component of the bracket is recognized as the Poisson bracket of Hamiltonian mechanics. Its properties are briefly reviewed and justified based on its connection to Hamiltonian mechanics. The Poisson structure of the conservative bracket is also manifested in a variety of other formalisms of the dynamic equations of nonequilibrium thermodynamics, thus providing a unilying connection. Next, the nonconservative, dissipative component is presented in the one-generator formalism, a more extensive treatment of which can be found in the research monograph by Beris and Edwards [A.N. Beris, B.J. Edwards, Thermodynamics of Flowing Systems with Internal Microstructure, Oxford University Press, New York, 1994]. We further address here some of the more recent developments that have taken place since the publication of the above-mentioned work. Hence, the two-generator form of the bracket equations that corresponds to the GENERIC framework of description is considered next. The two generators are the Hamiltonian (or total energy), which drives the conservative part of the dynamics, and the entropy, which drives the dissipative part. Differences and similarities between the two-and the one-generator formalisms are pointed out. Finally, the advantage of the use of the bracket formulation is illustrated, as a number of recent applications are reviewed. (C) 2001 Elsevier Science B.V. All rights reserved
Non-union of femoral neck fractures with osteonecrosis of the femoral head: treatment with combined free vascularized fibular grafting and subtrochanteric valgus osteotomy
Femoral neck fractures, frequently complicated by non-union and femoral
head osteonecrosis, present a difficult clinical situation, especially
when young patients are concerned. Existing treatment options are valgus
osteotomy to address the biomechanical factors or bone grafting to
address the biologic factor. The authors describe the operative
technique and results of combined subtrochanteric valgus osteotomy and
free vascularized fibular grafting in management of five young patients
with both non-union and avascular necrosis