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<p>Articular cartilage is the thin, load-bearing connective tissue that lines the
ends of long bones in diarthroidal joints, providing predominantly a mechanical function.
Because cartilage is avascular and aneural, it has little capacity for self-repair
if damaged. One repair strategy is through a functional tissue engineering approach
using adipose-derived stem cells (ASCs). ASCs are an abundant progenitor cell source
easily obtained through a minimally invasive liposuction procedure. When appropriately
stimulated, ASCs have demonstrated significant potential for chondrogenic differentiation.
Though studies have demonstrated the ability of ASCs to synthesize cartilage-specific
macromolecules, a more thorough understanding of factors that modulate ASC chondrogenesis
is required. Accordingly, the central aim of this dissertation was to study the chondrogenic
response of ASCs to biochemical, biomechanical, and biomaterial factors.</p><p>We
hypothesized that factors, other than TGF-beta and dexamethasone, would improve ASC
chondrogenesis. BMP-6 emerged as a potent regulator of ASC chondrogenesis, particularly
in early culture, as noted by significant upregulation of cartilage-specific extracellular
matrix (ECM) genes and downregulation of cartilage hypertrophy markers.</p><p>Hypothesizing
that biomechanical factors would accelerate the formation of cartilage-specific macromolecules,
we designed and manufactured an instrument to apply dynamic deformational loading
to ASC seeded constructs. Dynamic loading significantly inhibited ASC metabolism
and downregulated cartilage-specific ECM genes. However, 21 days of dynamic loading
induced the production of type II collagen, a principal component of articular cartilage.</p><p>We
hypothesized that a biomaterial derived from cartilage would serve as a bioactive
scaffold and induce chondrogenic differentiation. The novel, ECM-derived scaffold
promoted the most robust differentiation of ASCs relative to both biochemical and
biomechanical factors, particularly noted by a type II collagen-rich matrix after
28 days of culture. After 42 days of culture, biphasic mechanical testing revealed
an aggregate modulus of 150 kPa, approaching that of native cartilage. These data
suggest that the ECM-derived scaffold may retain important signaling molecules to
drive differentiation or that ASC differentiation is dependent on proper cell anchorage.</p><p>In
summary, we have shown that biochemical, biomechanical, and biomaterial factors have
strong influences on the chondrogenic potential of ASCs. Optimization of these factors
will ultimately be required to successfully engineer a functional tissue.</p>
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