S. Ramtani - Academia.edu (original) (raw)

Papers by S. Ramtani

Wound Repair and Regeneration

AbstactMyelomeningocele (MMC) is a congenital defect of the spine characterized by meningeal and ... more AbstactMyelomeningocele (MMC) is a congenital defect of the spine characterized by meningeal and spinal cord protrusion through the open vertebral arches. This defect causes progressive prenatal damage of the spinal cord, leading to lifelong handicap. Although midtrimester surgical repair may reduce part of the handicap, an earlier and less invasive approach would further improve the prognosis, possibly minimizing maternal and fetal risks. Several studies have proposed an alternative approach to surgical repair, by covering the defect with a patch and protect the exposed neural tissue. Our study aims to elaborate a waterproof and biodegradable bioactive patch for MMC prenatal fetal repair. We developed a double‐layer patch that can provide a waterproof coverage for the spinal cord, with a bioactive side, conducive to cell proliferation, and an anti‐adhesive side to avoid its attachment to the medulla.This article is protected by copyright. All rights reserved.

Lecture Notes in Mechanical Engineering, 2016

Trabecular fatigue fractures are observed as compressive stress fractures in the proximal femur, ... more Trabecular fatigue fractures are observed as compressive stress fractures in the proximal femur, vertebrae, calcaneus and tibia. These fractures are often preceded by buckling and bending of microstructural elements. But the etiology of these bone fractures is still poorly understood in biomechanical perspective. In the present work, it comes to predicting the buckling mechanism trabeculae in progress remodeling bone and in function of the boundary conditions without experimental data.

1 Abstract This work aims to construct a general framework of coupling tumor-bone remodeling proc... more 1 Abstract This work aims to construct a general framework of coupling tumor-bone remodeling processes for having plausible outcomes of the effects of tumors on the number of osteoclasts, osteoblasts, and the frequency of the bone turnover cycle. Here, Komarova’s model has been extended to include the effect of tumors on the bone remodeling processes. Thus, we explored three alternatives for coupling tumor presence into Komarova’s model: first, using a ”damage” parameter that depends on the tumor cell concentration. A second model follows the original structure of Komarova, including the tumor presence in those equations powered up to a new parameter, called the paracrine effect of the tumor on osteo-clasts and osteoblasts; the last model is replicated from Ayati and collaborators in which the impact of the tumor is included into the paracrine parameters. Through the models, we studied their stability and considered some examples that can reproduce the tumor effects seen in clinic a...

International Journal of Non-Linear Mechanics

IRBM, 2018

Highlights • Grafting of poly (sodium styrene sulfonate) onto PCL. • Direct grafting of bioactive... more Highlights • Grafting of poly (sodium styrene sulfonate) onto PCL. • Direct grafting of bioactive polymers by UV irradiation. • Different parameters such as polymerization time and lamp power were studied.

International Journal of Engineering Science, 2014

Metallic implants are routinely used in orthopedic and dental surgery where implant-bone loosenin... more Metallic implants are routinely used in orthopedic and dental surgery where implant-bone loosening is known as a major concern of failure, regardless of whether the implants are used in a temporary or permanent way (Cimerman et al., 2005; Goodacre et al., 2003; Herberts and Malchau, 2000). The problem of metallic pin fitted into medulla of a long bone as part of prosthetic device, previously studied by Cowin and van Buskirk (1978), is revisited in this contribution by considering bone material having cylindrical anisotropy. Indeed, the human femur exhibited statistically significant anatomic variation in elastic anisotropy, which may have important implications for whole bone numerical models and mechanobiology (Orias et al., 2009). This work offers improved results and new highlights with respect the original work, such as interfacial pressure evolution with respect to the degree of anisotropy a as well as stress-strain distributions during the remodeling process. Our results are quantitatively compared with those in the reference work dealing with homogenous long bone treated as a transversely isotropic material (Cowin and van Buskirk, 1978).

IRBM, 2015

Abstract Objectives Our main goal is to improve, from theoretical point of view, the mechanistic ... more Abstract Objectives Our main goal is to improve, from theoretical point of view, the mechanistic understanding of bone buckling failure which is known as at the core of important clinical problems such as osteoporosis. Material and methods What is well argued is that in older bone, stability-initiated failure dominates because of the instability of the individual trabeculae which is prone to inelastic buckling at stresses far less than expected for strength-based failure. Taking advantage of our previous work, an improved original Euler's adaptive-beam buckling equation incorporating density gradient effect is investigated. Results For one, we indicate that resorption can leads to new elastic instabilities that can conduct to bone-buckling mechanism of fracture. For another, we demonstrate that bone density gradient play a key role in the initiation of the bone-column elastic buckling instability. Conclusion As a result, it is clearly stated here that firstly, the number of these elastic instabilities which are potentially implied in the mechanisms of bone fracture, localized at the trabecular element scale, depends strongly upon the material parameter η and secondly; the bone density gradient affect notably the stability of the bone-column deflection.

An attempt of modeling the behavior of concrete through a damage approach is presented. The pheno... more An attempt of modeling the behavior of concrete through a damage approach is presented. The phenomena which are studied are the elâstic anisotrbpy and the evolution of permanent strains induced by damage and i}re consequences of the closure of the cracks, i.e'. damage. Two damage variables are introduced in the free energy which is expanded in a Taylor series. The crack closure is desciibed via a partition of the elastic strain tensor. Some experimen-tal results are compared to the predictions given by our model.

Mechanics Research Communications, 1999

ABSTRACT The bone remodeling process is generally viewed as bone material response to functional ... more ABSTRACT The bone remodeling process is generally viewed as bone material response to functional demands and muscle attachments by continual process of growth, reinforcement and resorption which occur in living situation. Everyday activities damage bone, and this damage is normally repaired in a continuous process. When an imbalance in this remodeling process occurs, Bones may become more susceptible to fracture. An attempt to establish a relationship between induced microdamage and adaptive bone remodeling is proposed. A thermodynamic theoretical framework is provided as basis for a consistent formulation of bone remodeling involving a chemical reaction and mass transfer between two constituents in presence of microtracks.

Journal of Biomechanics, 1999

The aim of this paper is to illustrate the application of mathematical tools for the analysis of ... more The aim of this paper is to illustrate the application of mathematical tools for the analysis of non-linear dynamical systems to the study of global stability of one kind of bone remodeling scheme applied to n unit-elements model. The particular aspects analyzed here are the stationary states related to this theory and a condition of their stability. The non-linear equations governing the remodeling process are solved by finite-difference method and the well-known results on the heterogeneous spatial organizations have been retrieved and confirm the analytical study. This kind of remodeling theory is useful for investigating the effects of physiological parameters on the development, maintenance, and adaptation of bone under mechanical loading.

Carbon, 2008

Palladium-doped activated carbon fibers are being evaluated as candidate materials for enhanced h... more Palladium-doped activated carbon fibers are being evaluated as candidate materials for enhanced hydrogen storage at near ambient conditions. Pd-doped fibers were spun using a Pd salt mixed with an isotropic pitch precursor. Experimental techniques such as in situ X-ray analysis, thermogravimetric studies, scanning transmission electron microscopy and gas adsorption were employed to understand how processing conditions for the production of

Journal of Mechanics in Medicine and Biology, 2010

Bio-artificial tissues are being developed as replacements for damaged biologic tissues and their... more Bio-artificial tissues are being developed as replacements for damaged biologic tissues and their mechanical properties are critical for load-bearing applications. Reconstituted dense three-dimensional (3D) fibrillar collagen matrices are promising materials for tissue engineering, at the light of their interaction with fibroblasts.1,2 The mechanical properties of these fibrillar collagen matrices are now being characterized under unconfined compression loading for various strain rates and collagen concentrations. The data were compared to those obtained in the same conditions with a biological tissue, the rat dermis. The results show a very sensitive behavior to both the displacement rate, typical of biological soft tissues, and the collagen concentration varying between 5 and 40 mg/ml. The link between the mechanical properties and the microscopic structure of the collagen scaffolds show an increasing viscoelastic modulus with respect to the fibril density. It is found that the ma...

ABSTRACT To show the effect of the sign of stress on the behaviour of the material, a new procedu... more ABSTRACT To show the effect of the sign of stress on the behaviour of the material, a new procedure is proposed . First it consists in creating distributed damage by a tensile loading, and subsequently âppiying a compressive loading on the same specimen. Distributed damaqg is-obtained ttrough aiùniinum Uars -gtued on the laieral surfaces ofthe concrete specimen, the load is applied on the bars which impàse an uniform strain state to the concrete, so that nolocalization appears in spite of large strain values. The results obtained show that a strain-softening behaviour in the context of coitinuum media is possible for concrete. The subsequent compressive loading shows that the behaviour is not considerably modified by tensile damage (stiffness and ultimate stress values), that exhibits ùe unilateral character of concrete behaviour.

Materials Science & Engineering: A, 2010

Near fully dense polycrystalline nickel with a random crystallographic texture was consolidated b... more Near fully dense polycrystalline nickel with a random crystallographic texture was consolidated by hot isostatic pressing of blends of nanocrystalline and conventional microcrystalline powders with different volume fractions. The transformation process resulted in a composite-like microstructure constituted by clusters of soft coarse grains regularly distributed in a hard ultrafine-grained matrix. It was found that the ultrafine-grained matrix hinders the coalescence of the coarse grains component during sintering resulting in a smaller grain size than in the fully coarse-grained counterpart in a sort of "barrier effect". This effect was found to depend on the volume fraction of the ultrafine-grained matrix. Conversely, during the hot isostatic pressing, the plastic deformation of the coarse-grained fraction is preferred to that of the ultrafine-grained fraction, because of greater dislocation activity in the former type of grains, resulting in lower defect densities in the ultrafine-grained matrix ("shielding effect"). It is shown that as a result of the interplay between the coarse-grained and ultrafine-grained components during sintering, the mechanical behavior of the composite materials cannot be obtained by a linear interpolation between the characteristics of fully ultrafine-grained and coarse-grained counterparts.

Le beton en tant que materiau heterogene a matrice fragile possede un comportement mecanique part... more Le beton en tant que materiau heterogene a matrice fragile possede un comportement mecanique particulier. Au fur et a mesure que se developpe la microfissuration, une forte anisotropie elastique induite accompagnee de deformations anelastiques apparait. De plus, lors du changement de signe des sollicitations exterieures, les microfissures creees peuvent se refermer ce qui est la cause de restaurations partielles ou totales des proprietes elastiques macroscopiques (effet unilateral). Une modelisation elaboree dans le cadre de la thermodynamique dans laquelle s'inscrit naturellement la theorie de l'endommagement est proposee pour decrire ces trois phenomenes. Des identifications basees sur des essais simples sont proposees pour rendre compte des performances et des lacunes de notre modele

Journal of Adhesion Science and Technology, 2012

For the aim of fixing and stabilizing the Total Knee Arthroplasty (TKA) tibial component, pull-ou... more For the aim of fixing and stabilizing the Total Knee Arthroplasty (TKA) tibial component, pull-out strength of the post is one of the most important factors to be considered. The material properties of bone, coupled with the principal dimensions of bone/post assembly such as diameter, interference fit and implantation length, may affect the pull-out strength of the post fixation. In

Mechanics Research Communications, 2018

A metal rod forced into the medullary cavity of a bone, known as an intramedullary pinning, is co... more A metal rod forced into the medullary cavity of a bone, known as an intramedullary pinning, is considered as the quickest and cheapest form of oblique fracture repair available for use in the femur, tibia, metatarsal bones, humerus, ulna and metacarpal bones. Implants endurance as well as a good clinical tolerance depends on the recovery of a physiological stress/strain distribution within bone after implantation. What is well known is that the human femur, along the entire femoral diaphysis, exhibited statistically significant anatomic variation in elastic magnitude and anisotropy and the main question treated here is: does bone's inhomogeneity, expressed here by the proportionality to some power of the hollow bone cylinder radius r with respect to the elastic tensor components, affects substantially the implantbone interfacial pressure as well as the implant-bone interfacial strains and stresses both immediately and a longtime after insertion?