Open PhD Position at Institut National des Sciences Appliquées (INSA) of Lyon, France

Description
of the position:

This
PhD position is potentially available at the doctoral school MEGA of
INSA Lyon.

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The
funding will be assigned only after a competition and consists of a
net monthly salary of almost 1450 Euros for three years. This
competition will take place in Lyon during the month of june 2012.
Eventual travel expenses could be reimbursed to the pre-selected
candidate if coming from abroad.

Subject:

Bone
adaptation and remodeling is an amazing subject which has stimulated
the minds of biologists and mechanicians ever since 1892 when Wolff
observed that “internal architecture and external conformation of
bones changes in accordance with mathematical laws”. The twentieth
century has then seen an explosion of the research in the field and
different mathematical models have been proposed to describe
functional adaptation and bone remodeling. The model on which the
thesis will be based follows the idea of adopting the strain energy
density (SED) as the principal trigger of bone remodeling. More
precisely, we assume that the osteocytes are well placed within bone
porosity to function as ‘strain gauges’, and to emit a signal
(stimulus) the intensity of which is proportional to the measured
strain energy and to bone apparent density. Moreover, we assume that
a threshold value of the stimulus exists such that osteoblasts (bone
synthesis) are activated if the value of stimulus is higher than this
threshold, while osteoclasts (bone resorption) are activated if the
value of stimulus is lower than the threshold itself. The hypothesis
of existence of such a threshold value is based on the idea that a
high value of the deformation energy is associated to a need of a
more compact bone, while a low value of strain energy may be
associated to a “surplus” of material at a given location which
can then be resorbed and re-used in other locations subjected to
higher mechanical solicitations. The idea of using SED as the
principal trigger of bone remodeling is very well known in the
scientific literature and has been validated by several experimental
observations.As far as the long-term behavior of bio-resorbable
prostheses is concerned, rigorous theoretical studies become rarer
and effective models allowing for the description of resorption of
bio-materials and their gradual substitution with natural tissues are
not available. Indeed, several works exist on systematic experimental
studies on animals aiming to produce indications on which material
shows the better compromise between optimal initial mechanical
properties and maximum final percentage of replacement. Nevertheless,
reliable models allowing for the prediction of resorption of
bio-materials and of their gradual replacement with natural bone
still need to be found and therefore represent an open challenge. The
basic idea which will be developed within this research project is to
use a second gradient, continuum, two-solids, mixture model to
predict resorption of both natural bone and bio-material and
synthesis of natural bone. Some preliminary results in this sense
have been obtained in [1]: the candidate is strongly recommended to
read this paper in order to have a clearer idea of the proposed
subject.The proposed continuum model will be enhanced by means of the
use of a second gradient theory in order to account for the
possibility of describing the effect of microstructure on the
macroscopic behavior of the considered
natural-bone/bio-resorbable-material system. It is indeed very well
established in scientific literature that classical Cauchy-type
continuum theories do not allow for the correct prediction of the
mechanical behavior of bone, when considering sufficiently small
scales. This scale-effect is related to the fact that bone is a
hierarchically heterogeneous material, i.e. it can be considered as
homogeneous at the scale of the millimeter, but it starts presenting
heterogeneities at the scale of the micron. [1] Madeo A., Lekszycki
T., dell'Isola F. : 'A continuum model for the bio-mechanical
interactions between living tissue and bio-resorbable graft after
bone reconstructive surgery'. CRAS Mécanique, 339, 625–640 (2011).

Candidate's
Profile:

The
candidate must have well grounded knowledges in the field of
continuum mechanics in order to be able to capture the basic features
of the second gradient, continuum, two-solids mixture model which is
proposed to describe phenomena of resorption of bio-material and its
gradual replacement with natural bone tissue as the result of
mechanical loading. He/she will be asked to implement the governing
equations of the bio-mechanical system
natural-bone/artificial-material in a numerical code and to perform
FEM numerical simulations. This will be done by implementing the
proposed model in a suitable commercial software like e.g. COMSOL
Multiphysics starting with simple 1D cases. Later on, he/she will
conceive and perform more complex simulations which are closer to
real 3D cases.A bio-resorbable material initially in contact with
natural bone tissue will be considered and its gradual resorption and
replacement with newly created natural bone tissue will be analyzed
as a function of the external applied load. The preliminary task of
this study is to investigate the effect of all the numerous
mechanical (such as external force) and biological (such as density
of actor and sensor cells) on the final percentage of replacement of
the artificial material with natural bone tissue.

Particular
attention will be paid to the study of the effect of the second
gradient parameters on the final percentage of replacement of
artificial bio-material. This will allow for investigating the effect
of bone and bio-material microstructure on the process of
reconstructed bone remodeling.

Contact
& Documents to Provide

Please,
send a CV, a record of transcripts and a motivation letter to:

angela.madeo [at] insa-lyon.fr (angela[dot]madeo[at]insa-lyon[dot]fr)

Tel.
+33 (0)4 72438463