Biomedical Engineering Reference
In-Depth Information
of many body systems (e.g., musculo-skeletal, cardiovascular) [
1
]. Collagen,
elastin and ground substance are the main constituents of the extracellular matrix
in soft tissues, and their arrangement significantly affect the tissue mechanical
response. For instance, stiffness and strength features in soft tissues mainly depend
on the arrangement and the amount of collagen, which is organized in agreement
with a precise hierarchical multiscale scheme [
2
]. Since the fundamental
mechanical role of collagen, soft tissues are usually referred to as collagenous
tissues.
The structured organization of soft tissues, and thereby their mechanical
behavior, is highly related to the biochemical processes occurring within them [
2
].
In fact, altered tissue response in disease (e.g., aneurism, keratoconus, arthofibrosis)
arises from pathological tissue remodeling, inducing unphysiological histology and
biochemical composition. Typical disorders, such as tissue hyper-extensibility or
weakness, can be associated with alterations at different scales [
3
-
7
]: in content of
tissue constituents, in shape of collagen fibers, in collagen genetic pattern, in density
of inter-molecular cross-links. Nevertheless, available non-invasive techniques do
not allow to measure directly a number of important histological, mechanical, and
biochemical properties of collagenous tissues such as, for instance but not exclu-
sively, collagen content and fiber waviness, collagen cross-linking, elastin amount
and stiffness of elastin networks.
In this context, the biomechanical analysis and modeling of collagen-rich
tissues can be retained a frontier challenge aiming to understand many physio-
pathological processes occurring at very different length scales, as well as to
identify relationships among alterations and diseases. Accordingly, dominant
mechanisms occurring at different scales should be accounted for and consistently
coupled in a unique modeling approach. Moreover, in order to enhance model
reliability for diagnostic and clinical practice, model parameters should be few and
associated with clear physical properties of the tissue, avoiding to introduce
phenomenological descriptions. These requirements can be satisfied if the tissue
structured hierarchical arrangement is explicitly described, possibly reducing
model complexity by means of multiscale homogenization techniques. Such an
approach, employed for example in [
8
], will be referred to as a structural multi-
scale method, and consists in developing mechanical models at very different
length scales, which are coupled each other by means of consistent inter-scale
relationships. In some way, the structural multiscale approach exploits the ratio-
nale followed by nature in ''designing'' tissues and ''building'' organs.
Structural multiscale models open to the possibility of developing virtual
simulation tools, that are patient-specific not only for the geometric description of
the tissue domains, but also for the accurate representation of the tissue mechanical
properties. As a result, the effects of changes in histological arrangement or bio-
chemical processes on the overall macroscopic functionality of tissues and organs
could be predicted. Thereby, really customized pharmacological treatments and
therapeutic strategies could be conveniently designed and applied. Finally, para-
metric biomechanical simulations of tissues and organs based on a multiscale
structural framework might be coupled with non-invasive in vivo histological and
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