Biomedical Engineering Reference
In-Depth Information
4
Mechanobiological Models for Bone Tissue. Applications to
Implant Design
Jose Manuel Garcıa-Aznar, Marıa Jos´eGomez-Benito, Marıa Angeles Perez, and
Manuel Doblare
4.1
Introduction
Bone is an evolving tissue that is active throughout the whole life. In spite of being
one of the hardest living tissues, it has an amazing capacity to adapt and self-heal.
In fact, bone changes its shape and mechanical properties as a response to the
mechanical environment. For instance, changes in bone mass could be observed
after long stance in bed, or changes in bone shape also appear in fracture healing
and after implantation of fixation devices.
Bone is a connective tissue formed by cells and extracellular matrix composed of
ground substance and fibers. In contrast to other connective tissues, its components
are calcified, making it a hard tissue. It has a high tensile strength due to the collagen
fibers and also a high compression strength due to the mineral components.
Moreover, bone is a light material whose structure is hierarchically organized
[1] both macroscopically and microscopically, in such a way that its strength is
maximized with the minimum weight.
In spite of these properties, bone injury is quite common, usually caused by a
sudden load that exceeds bone strength or the cyclic activity of loads (well below
bone strength) that gradually accumulates damage at a rate that cannot be repaired.
Depending on the type of injury, a prosthesis or fixation can be used. A prosthesis
is normally used to replace damaged or injured joints, while a fixator is used to treat
bone fractures, allowing a proper alignment of the fracture being removed after bone
healing. The performance of this kind of implant comprises two components, the
response of the bone to the implant and the behavior of the material in the host bone.
Therefore, it has to meet mechanical and biological requirements to fulfill the objec-
tives specified in its design. From a mechanical point of view, a prosthesis or implant
has to be capable of providing mechanical support as the original bone. For example,
in the case of a prosthesis, it has to present enough strength to resist overloads,
cyclic loads (fatigue), and wear. For fixations, it is necessary to get the appropriate
