Biomedical Engineering Reference
In-Depth Information
in vivo. The other route is implanting the entirely in vitro developed construct into
the lesion site. When an appropriate bioreactor is used, cell metabolism and ECM
production could be controlled better in vitro than in vivo. Mostly, the first route is
preferred. It brings also the opportunity of non-destructive characterization of the
tissue prior to implantation. The main drawbacks of the second route are mostly
associated with tissue integration and mechanical fixation. Also, providing correct
mechanical loading is a challenge in vitro. In the first route, the tissue will adapt and
integrate better since it is formed in situ under physiological conditions as the result
of mechanical loading. However, on the long term, control of cellular activities is
more difficult.
Scaffolds may be used with or without cells, but cells are usually incorporated
into scaffolds. Various approaches can be used to design scaffolds for OC tissue
engineering [
17
]. These include using different scaffolds for bone and cartilage;
using a scaffold only for bone but not for cartilage; or using a single scaffold for both
bone and cartilage. Scaffolds can be homogenous or heterogeneous and can consist
of a single layer or more layers. In the study of Schaefer et al. [
94
], different scaffolds
were used for bone and cartilage parts. They developed in vitro engineered structures
composed of a cell-seeded scaffold and a SB support to be press-fitted into large
defects in OC tissue located in the rabbit knee joint. Allogeneic rabbit chondrocytes
were dynamically seeded onto a non-woven polyglycolic acid scaffold. SB support
was an osteoconductive spongemade of bovine collagen type. As controls, the defects
were either treated with cell-free scaffolds or kept empty. Their results showed that
the treatments done with composites were structurally superior to the ones done
with cell-free scaffolds or kept empty. Composites withstood the physiological loads
and showed remodelling into OC tissue with preserved cartilage at the articulating
surface and subchondral regeneration. However, the integration of the composites
with the host cartilage was not good, whereas a good integration was achieved with
the host bone.
In the study of Kandel et al. [
95
] a scaffold was used only for the bone part. They
developed biphasic constructs using cartilaginous tissues grown and fixed on top of
porous calcium polyphosphate substrates. Isolated chondrocytes were seeded on top
of the substrate and were grown with autologous serum for 8weeks to generate the
cartilaginous tissues. These in vitro-formed constructs were subsequently implanted
into OC defects in sheep and maintained up to 9months. The results supported the
suitability of the strategy to treat OCdefects. The constructs withstood in vivo loading
up to 9months with good integration to native cartilage and bone ingrowth into the
substrate. In another study, Oliveira et al. [
59
] developed HAp/chitosan bilayered
scaffolds through a combination of sintering and freeze-drying methods for OC
tissue engineering. Preliminary in vitro tests showed that goat marrow stromal cells
grew and differentiated into osteoblasts and chondrocytes, respectively in HAp and
chitosan layers. The physicochemical properties and biological performance of the
scaffolds revealed their great potential to be employed in the regenerative strategies
for treating OC lesions.
As mentioned previously, hydrogels are a group of scaffolding materials for tissue
engineering. The conventional hydrogel-based regenerative strategies for cartilage
