Multiscale Approach to Understand the Multiphysics Phenomena in Bone Adaptation

The ability of bone tissue to adapt itself to its physical environment is the research focus of several teams all over the world. If the physical stimuli playing a role in bone remodelling are often identified, how they act and are converted into a cellular response is still an open question. The aim of this paper is, in a first part, to propose an overview on the physical factors participating in the bone remodelling process. In a second part, we present some recent developments concerning the implications of hydro–electro-chemical couplings that could modify the bone adaptation process. Since the phenomena that are involved in this mechanism are related both to the mechanical solicitations of the tissue and the physical phenomena in the vicinity of bone cells, different scales, from the organ to the cell, should be considered to go deeper in its understanding. That is why a multiscale strategy based on periodic homogenization has been carried out to propagate the multiphysics description at the cellular scale toward the macroscopic scale of the tissue. This multi-level approach is so adapted to connect macroscopic physical information to microscopic phenomena, et vice versa. Thus, using convenient simulations, we have brought a new light on classical interrogations dealing with bone adaptation. These five questions are: i. Can the sole hydro-mechanical coupling describe the poro-mechanical behaviour of bone or should we consider a modified Biot model including electro-chemical effects?; ii. Similarly, is the classical Darcy law sufficient to describe the bone interstitial fluid flow?; iii. What is the nature of the stress-induced electric potentials that can be measured in vivo?; iv. What are the consequences of the electro-chemical couplings on the shear sensitivity of the osteocytes?; v. What are the consequences of the microscopic physico-chemical properties of the bone microstructure on the mass transport within the lacuno-canalicular system? Finally, from these simple model-driven observations, we propose a new perspective to alter the current bone adaptation paradigm.