Biomedical Engineering Reference
In-Depth Information
management. The basic cell biology of tendons is still not fully understood, and the
management of tendon injury poses a considerable challenge for clinicians.
Clinical approaches to tendons rupture often involve surgical repair, which frequently
implies working with degenerative, frayed tendon tissue, unable to sustain the rigors of
normal activities, and may fail again.
After an injury, the healing process in tendons results in the formation of a fibrotic scar and
it is accompanied by an increased risk of further damage. (Longo UG et al. 2010)
The structural, organizational, and mechanical properties of this healed tissue are
insufficient as tendons possess a limited capacity to regenerate.(Wong JK et al. 2009) (Woo
SL et al.2006)
Adhesion formation after intrasynovial tendon injury poses a major clinical problem.
Disruption of the synovial sheath at the time of the injury or surgery allows granulation
tissue and fibroblasts from the surrounding tissue to invade the repair site. Exogenous cells
predominate over endogenous tenocytes, allowing the surrounding tissue to attach to the
repair site, resulting in adhesion formation. (Wong JK et al. 2009) (Woo SL et al.2006)
Despite remodeling, the biochemical and mechanical properties of healed tendon tissue
never match those of intact tendon. It is well demonstrated that mechanical loading plays a
central role in tenocyte proliferation and differentiation, and that the absence of mechanical
stimuli leads to a leak of cellular phenotype. (Wang JH 2006) (Woo SL et al.2006)
While certain tendons can be repaired by suturing the injured tissue back together, some
heal poorly in response to this type of surgery, necessitating the use of grafts.(Kim CW &
Pedowitz RA 2003)
Unfortunately, finding suitable graft material can be problematic and biological grafts have
several drawbacks. Autografts from the patient are only available in limited amounts, they
can induce donor site morbidity, while allografts from cadavers may cause a harmful
response from the immune system besides also being limited in supply. In both cases, the
graft often does not match the strength of the undamaged tissue.(Goulet F et al. 2000)
For this reason, obtaining tendinous tissue through tissue engineering approaches becomes
a clinical necessity.
Tissue engineering is a multidisciplinary field that involves the application of the principles
and methods of engineering and life sciences towards i) the fundamental understanding of
structure-function relationships in normal and pathological mammalian tissues and ii) the
development of biological substitutes that restore, maintain or improve tissue function.
The goal of tissue engineering is to surpass the limitations of conventional treatments based
on organ transplantation and biomaterial implantation. It has the potential to produce a
supply of immunologically tolerant, 'artificial' organs and tissue substitutes that can grow
within the patient. This should lead to a permanent solution to the damage caused to the
organ or tissue without the need for supplementary therapies, thus making it a cost-
effective, long-term treatment.
The tissue-engineering approach involves the combination of cells, a support biomaterial
construct, and micro-environmental factors to induce differentiation signals into surgically
transplantable formats and promote tissue repair, functional restoration, or both.
The earliest clinical application of human cells in tissue engineering, started around 1980,
was for skin tissue using fibroblasts, and keratinocytes, on a scaffold. During the last 30
years, many innovative approaches have been proposed to reconstruct different tissues:
skin, bone, and cartilage. The field of tendon tissue engineering is relatively unexplored due
to the difficulty in
in vitro
preservation of tenocyte phenotype, and only recently has
