Multiscale Approach to Understand the Multiphysics Phenomena in Bone Adaptation - Multiscale Computer Modeling in Biomechanics and Biomedical Engineering - page 33

Notwithstanding the nature of these triggering signals, it appears that it is
correlated to the local hydro-mechanical state of the tissue and/or the cells vicinity.
The great difficulty in carrying out experimental investigations of in situ bone
poro-mechanical behaviour renders theoretical investigations crucial. In most of
the representations of bone remodelling, the mechanical stimuli acting on cells
(pressure, shear stress, drag forces, etc.) are calculated from the poro-elasticity
theory [ 15 ], which adopts intrinsically a macroscopic point of view [ 24 ]. These
mechanical inputs are then somehow downscaled and converted into biochemical
microscopic signals regulating the remodelling activity [ 1 ]. In this manner, the
nature of the incoming signals is thought to be purely mechanical. Moreover, the
microscopic phenomena are not directly involved since the fluid flow is quantified
by a macroscopic textural parameter, the hydraulic permeability. In other words,
even if involving microscopic biochemical signals, these modelling strategies
remain purely macroscopic.
In this contribution, we would like to emphasize recent developments that may
strongly modify the current bone mechano-sensation paradigm. Using a multiscale
strategy, we propose to investigate the multiphysics effects due to the physico-
chemical phenomena that occur at the microstructural scale of bone tissue. In
particular, we trace how the fluid-flow and mass transport models for mechano-
transduction should be changed by considering additional effects related to electro-
chemical couplings that characterize the cellular vicinity. Our strategy consists in
discussing, at both the macroscale and the microscale, the importance of the
multiphysical phenomena featuring in bone behaviour using physiologically-based
simulations. That is why, after having described the bone structure and the dif-
ferent physical stimuli that may affect its behaviour, the ingredients of our model
are introduced. Grounded on several former studies [ 57 , 74 - 76 , 84 - 86 ] invoking
the periodic homogenization method, a multiscale description linking the macro-
scopic and microscopic features is proposed. Then, some numerical examples are
presented to investigate the real implications of underlying electro-chemical
couplings in the bone remodelling signals expression. Even if their consequences
are not visible at the macroscale, these multiphysical effects could be significant at
the cellular scale and thus should be taken into account in new scenarios of bone
adaptation. To illustrate this, the discussion provides five model-driven examples
proving the necessity of creating a new paradigm in bone remodelling including
multiphysics considerations.
2 Some Basic Aspects in Bone Physiology
When aiming at understanding the complex mechanisms governing biological
systems, the in vivo insuperable problems quickly arise and make it very difficult
to progress without tremendous efforts. In the bone biology field, you have to be
prepared to move mountains when carrying out experiments intending at analyzing
the remodelling process. An alternative avenue of research could be the in silico