Biomedical Engineering Reference
In-Depth Information
5.4.6 Multi-tissue systems
A multi-tissue system is required for correction of certain orthopaedic
defects. Extensive individual studies have been conducted on regeneration
of bone, ligaments, tendons and cartilage. However, an important aspect of
successful implantation and integration of the tissues is interface between
bone and the other soft tissues. The interfaces between these tissues expe-
rience complex load distributions and are mechanically the least stable
components of reconstructive surgery. Tissue engineering solutions to these
types of injuries need to include scaffolds that are able to restore mechan-
ical properties and functionality of the interface. However, the material
properties of the injury site vary across the site as the interface connects
two mechanically different tissues with different functionality. This poses a
tremendous challenge to culturing models of these constructs, especially in
bioreactors. The delivery of morphological cues and mechanical stimulation
needs to be appropriate to stimulate the interface tissue. This is evident in
terms of osteochondral interface regeneration.
Articular cartilage lesions are diffi cult to regenerate due to avascular
physiology of the osteochondral region. This presents a great challenge in
terms of recruiting new cells as well as the delivery of growth factors to
the site of injury. The main approaches taken in regeneration of the osteo-
chondral region have been culture of both tissues individually and simulta-
neous implantation into the defect, culture of both cells on different sides
of an individual scaffold in separated chambers and seeding progenitor cells
with different differentiation cues on each side of the scaffold in separate
chambers. Mahmoudifar and Doran (2005) have conducted a study using
chondrocytes dynamically seeded on PGA scaffolds. The composite scaf-
folds were constructed out of two thin PGA fi lms and cultured in a recir-
culation column bioreactor. The results have shown similar GAG content
to ones tested
ex vivo
. However, total collagen and collagen type II con-
tent did not match its natural counterpart. Chang
et al.
(2004) have used a
double-chamber stirred bioreactor to regenerate the osteochondral region.
The system included two separate chambers designed to circulate media
specifi c to each culture in the chambers. After four weeks of culture the
biphasic scaffold had signifi cant collagen II content, indicating retention
of the phenotype. There have been many studies that attempted to regen-
erate bone and cartilage alone. However, few studies have been reported
combining the mechanical and morphological stimuli of both tissues into a
single bioreactor. Similarly, the co-cultures of osteoblasts and chondrocytes
conditioned in a bioreactor or its chambers have not been proper investi-
gated. Mano and Reis (2007) suggested the use of current bioreactor tech-
nology for osteochondral constructs with the aid of appropriate co-culture
conditions.
