Integrated Biomaterials Science

Soft Tissue Replacement 447
friction (Turner et al., 1990; Durselen et al., 1996). Improved mechanical and
biological properties are therefore necessary to reduce the number of
implant failures due to either foreign body reactions or to poor biomechanical
properties. The aggressive in vivo environment and the effects of cyclic
loading conditions can act synergistically, resulting in a decrease of the
mechanical performances which dramatically affects the life of the prosthesis
(Ambrosio et al., 1996). As a consequence, except for augmentation or in
cases where no autologous tissue is available, these devices are no longer
used clinically to repair tendon and ligament failure.
The primary purpose of the prosthetic replacement of ligaments and
tendons is to replace a damaged tissue with an artificial device that will
mimic the function of the original tendon and ligament as well as possible.
New prostheses’ designs, that more effectively emulate the complex
aspects of these systems, may improve the success rate of the replacement
surgery (O’Connor et al., 1993). The reproduction of the mechanical and
viscoelastic features of the natural systems is therefore necessary. This can
be done by imitating the composite structure of natural tendons and
ligaments. Good functional reproduction of these properties is impossible to
obtain with a single material, as a consequence of the many functions of the
tissue which affect mechanical behavior, and may therefore only be achieved
using composite prosthesis (Pradas et al., 1991; Migliaresi et al., 1981).
A development of a semibiodegradable composite artificial tendon
prosthesis, composed of water-swollen poly(2-hydroxyethylmethacrylate)/
poly(caprolactone) blend hydrogel matrix reinforced with poly(glycolic
acid) fibers, was presented by Davis et al. (1991). The latter is constituted
by fibers wound in a matrix of hydrogel and oriented in such a way as to
obtain the desired mechanical behavior. The nonlinear behavior of the
mechanical response of such a system has been correlated with the deformation
mechanism associated with the geometrical variations of the composite
structure during a loading process. The mechanical behavior of such soft
composite structures have been shown to resemble closely the natural tissue
(Ambrosio et al., 1998). Recently, the advanced technique of tissue engineering
has been applied to design scaffolds and cellular devices which may lead
to the ultimate production of nature-like ligaments and tendons (Goulet et
al., 1997).
14.4.5. Intervertebral Disc Prostheses
Low back pain is one of the most common medical conditions in the
world. Disc degeneration, an inevitable process of aging, is one of the major
causes of low back pain. Currently, there are two major surgical interventions
for treating conditions related to the degenerative disc: discectomy and