Thursday, March 29, 2007

Soft tissue mechanics

Soft tissues are inhomogeneous, anisotropic materials which show viscoelastic and nonlinear properties. Morover, even under physiological conditions they undergo large deformations. For instance, in arteries, the in vivo longitudinal stretch ratio may pass more than 1.6. ( in vivo length/ unloaded length=1.6)

These properties make the continuum approach suitable for the purpose of analyzing material properties of soft tissue. Therefore, knowledge of nonlinear solid mechanics by a continuum approach seems essential.

Identification of an appropriate strain energy function (SEF) is the preferred method to describe the complex nonlinear elastic properties of vascular tissues. Once the strain energy function is known, the constitutive stress-strain relationships can be directly obtained from the SEF.

Early formulations of SEFs were purely phenomenological, in the sense that parameters involved in the mathematical expression of SEF bared little physiological meaning. Lately, significant effort has been put into developing structure-based or constituent-based SEF, where the parameters of the strain energy function represent some identifiable physical or structural characteristics of the different components of the vessel wall, such as elastic constants of elastin and collagen, fiber structural characteristics of the collagen network, volume fraction of elastin, collagen and vascular smooth muscle cells, etc.

An example of a constituent -based SEF which considers some structural properties, i.e. the orientation of the collagen fibers relative to the arterial wall’s circumferential direction is the model by Holzapfel and colleagues. The Holzapfel et al. model has been subsequently modified and extended by Zulliger et al. take the waviness of collagen fibers into the account and later to include vascular tone.

The structure-based SEFs did provide a significant improvement over the previous phenomenological SEFs. Furthermore, they supplied scientists more powerful tools to relate morpholoy with mechanical properties of soft tissue. Pa

Thursday, March 22, 2007

CISM : international center for mechanical sciences

CISM, International Centre For Mechanical Sciences, offers different specialized courses in in interdisciplinary fields like robotics, biomechanics, environmental engineering and so on. I participated in the following summer course last year 2006 :

Biomechanical Modelling at the Molecular, Cellular and Tissue Levels

The course was really interesting and the organisation was very well-done. That was a really fantastic opportunity to encounter people working in this field and to discuss with the professors as well as the students and research people. Furthermore, Udine,the city in which the organisation is situated, is a really cute small Italian town close to Venice. If you have a chance to participate in one of the courses offered by CISM, don't hesitate to go.
P.S. The picture shows the classroom.

Friday, March 16, 2007

Mechanobiology versus Biomechanics

I heard once these definitions from Prof. J.Humphrey and I find them quite nice :

Mechanobiology – the study of altered cellularactivity (gene expression or function) in response to changes in mechanical stimuli.

Biomechanics – the development, extension,and application of mechanics for purposes of understanding better biology, physiology, and pathophysiology as well as the treatment of disease and injury.(must invoke the 5 basic postulates of mechanics)

what I really like about the latter, is that mechanic laws should be extended and developed in order to be used in living tissue. We can not always use the existing rules. We should look for new ones, new relationships and discover new horizons. For sure, we have to remain in the framework of principle of mechanics.

up coming conferences (2)

European Symposium of Vascular Biomaterials(ESVB2007)

Tuesday, March 13, 2007

Upcoming conferences (1)

summer bioengineering conference, keystone,colorado,USA June 20-24 2007