Vilalta Alonso , G.; Soudah, E.; Vilalta , J.; Nieto, F.; Bordone, M.; Pérez, M.; Vaquero, C. Journal of biomechanics Vol. 45, p. S37- DOI: 10.1016/S0021-9290(12)70038-6 Data de publicació: 2012-07-01 Article en revista
Because bone marrow-derived stromal cells (BMSCs) are able to generate many cell types, they are
envisioned as source of regenerative cells to repair numerous tissues, including bone, cartilage, and
ligaments. Success of BMSC-based therapies, however, relies on a number of methodological
improvements, among which better understanding and control of the BMSC differentiation pathways.
Since many years, the biochemical environment is known to govern BMSC differentiation, but more
recent evidences show that the biomechanical environment is also directing cell functions. Using in
vitro systems that aim to reproduce selected components of the in vivo mechanical environment, it was
demonstrated that mechanical loadings can affect BMSC proliferation and improve the osteogenic,
chondrogenic, or myogenic phenotype of BMSCs. These effects, however, seem to be modulated by
parameters other than mechanics, such as substrate nature or soluble biochemical environment. This
paper reviews and discusses recent experimental data showing that despite some knowledge
limitation, mechanical stimulation already constitutes an additional and efficient tool to drive BMSC
A statistical factorial analysis approach was conducted on a poroelastic finite element model of a lumbar intervertebral disc to analyse the influence of six material parameters (permeabilities of annulus, nucleus, trabecular vertebral bone, cartilage endplate and Young’s moduli of annulus and nucleus) on the displacement, fluid pore pressure and velocity fields. Three different loading modes were investigated: compression, flexion and axial rotation. Parameters were varied considering low and high levels in agreement with values found in the literature for both healthy and degenerated lumbar discs. Results indicated that annulus stiffness and cartilage endplate permeability have a strong effect on the overall fluid- and solid-phase responses in all loading conditions studied. Nucleus stiffness showed its main relevance in compression while annulus permeability influenced mainly the annular pressure field. This study confirms the permeability’s central role in biphasic modelling and highlights for the lumbar disc which experiments of material property characterization should be performed. Moreover, such sensitivity study gives important guidelines in poroelastic material modelling and finite element disc validation.
Simulating the muscular system has many applications in biomechanics, biomedicine and the study of
movement in general. We are interested in studying the genesis of a very common pathology: human
inguinal hernia. We study the effects that some biomechanical parameters have on the dynamic
simulation of the region, and their involvement in the genesis of inguinal hernias. We use the finite element method(FEM) and current models for the muscular contraction to determine the deformed fascia transversalis for the estimation of the maximum strain. We analysed the effect of muscular tissue
density,Young’smodulus, Poisson’s coefficient and calcium concentration in the genesis of human inguinal hernia. The results are the estimated maximum strain in our simulations,has a close correlation with experimental data and the accepted commonly models by the medical community.Our
model is the first study of the effect of various biological parameters with repercussions on the genesis of heinguinal hernias.
The mechanical induction of specific cell phenotypes can only be properly controlled if the local stimuli
applied to the cells are known as a function of the external applied loads. Finite element analysis of the
cell carriers would be one method to calculate these local conditions. Furthermore, the constitutive
model of the construct material should be able to describe mechanical events known to be responsible
for cell stimulation, such as interstitial fluid flow. The aim of this study was to define a biphasic
constitutive model for fibrin, a natural hydrogel often used for tissue engineering but not yet thoroughly
characterized. Large strain poroelastic and poroviscoelastic constitutive equations were implemented
into a finite element model of a fibrin gel. The parameter values for both formulations were found by
either analytically solving equivalent low strain equations, or by optimizing directly the large strain
equations based on experimental stress relaxation data. No poroelastic parameters that satisfactorily
described the fibrin carrier behaviour could be found, suggesting that network viscoelasticity and fluid-
flow time-dependent behaviour must be separately accounted for. It was demonstrated that fibrin can
be described as a poroviscoelastic material, but a large strain characterization of the parameter values
was necessary. The analytical resolution of the low strain poroviscoelastic equations was, however,
accurate enough to serve as a reliable initial condition for further optimization of the parameter values
with the large strain formulation.
A new finite element model is proposed for the analysis of the mechanical aspects of morphogenesis and tested on the biologically well studied gastrulation phenomenon, in particular ventral furrow invagination of the Drosophila melanogaster embryo. A set of mechanisms are introduced in the numerical model, which lead to the observed deformed shapes. We split the total deformation into two parts: an imposed active deformation, and an elastic deformation superimposed onto the latter. The active deformation simulates the effects of apical constriction and apico-basal elongation. These mechanisms are associated with known gene expressions and so in this way we attempt to bridge the well explored signalling pathways, and their associated phenotypes in a mechanical model. While the former have been studied in depth, much less can be said about the forces they produce and the mechanisms involved. From the numerical results, we are able to test different plausible mechanical hypotheses that generate the necessary folding observed in the invagination process. In particular, we conclude that only certain ratios between both modes (apical constriction and apico-basal elongation) can successfully reproduce the invagination process. The model also supports the idea that this invagination requires the contribution of several mechanisms, and that their redundancy provides the necessary robustness.