Focal cartilage defects
are a prevalent knee problem affecting
people of all ages. Articular cartilage (AC) possesses limited healing
potential, and osteochondral defects can lead to pain and long-term
complications such as osteoarthritis. Autologous chondrocyte implantation
(ACI) has been a successful surgical approach for repairing osteochondral
defects over the past two decades. However, a major drawback of ACI
is the dedifferentiation of chondrocytes during their in vitro expansion.
In this study, we isolated ovine chondrocytes and cultured them in
a two-dimensional environment for ACI procedures. We hypothesized
that 3D scaffolds would support the cells' redifferentiation
without
the need for growth factors so we encapsulated them into soft collagen
and alginate (col/alg) hydrogels. Chondrocytes embedded into the hydrogels
were viable and proliferated. After 7 days, they regained their original
rounded morphology (aspect ratio 1.08) and started to aggregate. Gene
expression studies showed an upregulation of COL2A1, FOXO3A, FOXO1,
ACAN, and COL6A1 (37, 1.13, 22, 1123, and 1.08-fold change expression,
respectively) as early as day one. At 21 days, chondrocytes had extensively
colonized the hydrogel, forming large cell clusters. They started
to replace the degrading scaffold by depositing collagen II and aggrecan,
but with limited collagen type I deposition. This approach allows
us to overcome the limitations of current approaches such as the dedifferentiation
occurring in 2D in vitro expansion and the necrotic formation in spheroids.
Further studies are warranted to assess long-term ECM deposition and
integration with native cartilage. Though limitations exist, this
study suggests a promising avenue for cartilage repair with col/alg
hydrogel scaffolds.