ORTHOPEDIC INTERFACE TISSUE ENGINEERING: BUILDING THE BRIDGE TO INTEGRATED MUSCULOSKELETAL TISSUE SYSTEMS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 591

Levine, and Lu 2006; Spalazzi, Dagher, Doty, Guo, Rodeo, and Lu 2006). Spalazzi
et al. (Spalazzi, Doty, Moffat, Levine, and Lu 2006) seeded fi broblasts and
osteoblasts onto Phase A and Phase C, respectively. Phase B was left unseeded.
After four weeks, the fi broblasts and osteoblasts each proliferated within
their respective phases and both cell types migrated into the interface phase
(Figure 17.4 B). The stratifi ed scaffold design enabled spatial control of cell distri-
bution, with both osteoblasts and fi broblasts localized in their respective regions,
while restricting their interaction to the interface region. This controlled cell
distribution also resulted in the formation of cell type-specifi c matrix on each
phase, with a mineralized matrix detected only in Phase C, and an extensive type
I collagen matrix found on both Phases A and B. When the tri-phasic scaffold
co-cultured with osteoblasts and fi broblasts was evaluated in a subcutaneous
athymic rat model, abundant tissue formation was observed on both Phase A and
Phase C. As shown in Figure 17.4C, extensive tissue infi ltration and vasculariza-
tion was observed in all three phases. Cells migrated into Phase B, and increased
matrix production was evident in this interface region. Extracellular matrix pro-
duction compensated for the temporal decrease in scaffold mechanical proper-
ties, and more importantly, controlled matrix heterogeneity was maintained
in vivo .
Similar to the fi ndings of the 2D co-culture model, while both anatomic
ligament- and bone-like regions were found on the tri-phasic scaffold in vitro and
in vivo , no fi brocartilage-like tissue was formed in the interface region. Recently,
Spalazzi et al. extended their in vivo evaluation by tri-culturing osteoblasts, chon-
drocytes and fi broblasts on the multi-phasic scaffold (Spalazzi, Dagher, Doty,
Guo, Rodeo, and Lu 2006). Specifi cally, articular chondrocytes were encapsulated
in a hydrogel matrix and loaded into Phase B of the scaffold, while ligament fi bro-
blasts and osteoblasts were pre-seeded onto Phase A and Phase C, respectively.
After two months in vivo , an extensive collagen-rich matrix was prevalent in all
three phases of the tri-cultured scaffolds, and the mineralized matrix was again
confi ned to the bone region (Phase C). In addition, a fi brocartilage - like region of
chondrocyte-like cells embedded in a matrix of collagen types I and II as well as
glycosaminoglycans was observed in the tri-cultured group.
These promising in vitro and in vivo results suggest that a fi brocartilage
region can indeed be formed in tri-culture, and demonstrate the potential of the
multi-phased scaffold for interface regeneration. Moreover, this scaffold can be
used as a model system to elucidate the mechanism for multi-tissue regeneration,
determining the role of heterotypic cellular interactions as well as the effects
of biochemical and biomechanical stimulation for interface tissue engineering.
Heterotypic cellular interactions are likely facilitated by physiological loading,
which can mediate cytokine transport between different cell types and tissue
regions. Additionally, nutrient transport (Botchwey et al. 2003; Botchwey et al.
2004; Cartmell et al. 2003; Mauck et al. 2003; Mauck, Hung, and Ateshian 2003;
Porter et al. 2005) through the scaffold and bioreactor cultures (Altman et al.
2002; Botchwey et al. 2001; Darling and Athanasiou 2003; Freed, Martin, and
Vunjak - Novakovic 1999 ; Freed, Vunjak - Novakovic, and Langer 1993 ; Yu et al.