50 CHAPTER 4. T ISSUE ENGINEERING OF THE DISC
enhance biosynthesis and improve matrix homogeneity in articular chondrocyte-seeded constructs.
The results of this study did not support its future use with these cells, however, as statically cultured
constructs generally outperformed the rotating groups.
The stability of the TMJ disc cell phenotype during in vitro culture was examined in three
studies [17, 328, 330]. Gene expression did not vary depending on the region of the disc from which
cells were isolated, though cells were found to rapidly down-regulate aggrecan, collagen type I, and
collagen type II expression with passage [17].Expansion of cells would be necessary to obtain enough
cells for creation of a full-sized autologous construct; therefore attempts were made to recover the lost
phenotype. Cells passaged up to five times were exposed to the growth factors IGF-I,TGF-β1, and
TGF-β3 for 24 hours in monolayer or pellet culture and analyzed using real time RT-PCR [328].
The growth factors did not have a positive effect on cells cultured using either method, and pellet
culture had a negative effect on expression relative to monolayer. Recovery of phenotype was then
attempted through culture on ECM coated surfaces [330]. Passage 0, 1, and 2 cells were plated on
surfaces coated with aggrecan, collagen type I, collagen type II, or decorin, though no treatment had
a significantly positive effect.
More recently, a series of studies were published that suggested that costal cartilage could
serve as an autologous cell source for disc tissue engineering [1], [332]–[334]. This tissue would be
particularly appealing as many craniofacial surgeons have experience replacing the mandible with
a rib graft. In one study [333], scaffoldless constructs (see scaffolds section below) were created
from primary and passaged goat costal chondrocytes (CCs), and compared to control TMJ disc
cells. Cellularity and GAG content of primary and passaged CCs constructs were nearly an order
of magnitude higher than disc-cell constructs after 6 weeks of culture, and most importantly, CC
constructs retained their size and shape throughout the culture period (3 mm dia.), while disc-cell
constructs contracted severely (0.84 mm dia.). Immunostaining revealed the presence of collagen
types I and II throughout primary CC constructs, though constructs from passaged cells only stained
around the periphery and in the middle where a large, fluid-filled core had formed. This sphere did
not form in primary CC or disc-cell constructs. Not surprisingly, similar results were observed
when mandibular condylar cartilage cells were compared directly to hyaline cartilage cells from the
ankle [302, 335], with hyaline cartilage cells outperforming the TMJ cells (see Chapter 5).
4.3 SCAFFOLDS
The purpose of a scaffold is to provide a vehicle upon which cells may grow and deposit matrix.
A suitable scaffold must be biocompatible, sterilizable, and biodegradable. It must be sufficiently
porous and allow unrestricted cell growth and diffusion of nutrients through large, interconnected
pores [336]. The physical properties of the scaffold should support matrix deposition, and the
degradation profile should allow newly deposited matrix to gradually assume mechanical loads.
Additionally, there should be a method for which the size and shape of the scaffold can be modified
to fit the specific dimensions of the target tissue. It may also be advantageous for a scaffold to direct

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