Biomedical Engineering Reference
In-Depth Information
both in vivo and in vitro (Sharma et al, 2005, personal communication) [22].
Our studies and others demonstrate the great potential of MSCs as an al-
ternative cell source for cartilage tissue engineering, given the limitations of
chondrocytes. In the case of in vivo studies, Sharma et al. used high mo-
lecular weight hyaluronan along with PEGDA oligomer solution to create
a semi-interpenetrating network for the scaffold. In addition to increasing the
viscosity of the starting solution for easy handling, the presence of HA also fa-
cilitates the differentiation of MSCs to chondrocytes. Moreover, the presence
of HA in the hydrogel downregulates collagen type I expression indicating
that HA plays a crucial role in modulating chondrocyte phenotype. These
observations may be attributed to known biological functions of HA such
as ligand-specific interactions with the cells. Hegewald et al. also observed
a beneficial effect of HA on chondrogenic differentiation of equine MSCs [316].
In addition to their chondrogenic potential, MSCs have also been investi-
gated for their ability to regenerate bone with the aid of three-dimensional
hydrogel scaffolds. Recently, Meinel et al. investigated the effect of scaffold
properties on differentiation of human bone marrow-derived mesenchymal
stem cells (hMSC) into bone tissues by analyzing scaffolds made out of vari-
ous materials such as collagen, crosslinked collagen, and silk [230]. According
to these investigators, silk scaffolds outweigh the others in terms of per-
formance. The authors attributed these observations to silk's high porosity,
slow biodegradation, and structural integrity. These findings indicate that
the differentiation of MSCs into the osteogenic lineage can be modulated
by scaffold chemistry of the hydrogel systems. Temeoff et al. used hydrogels
based on OPF for osteogenesis of MSCs. They observed enhanced osteogene-
sis within OPF hydrogels with higher swelling ability [31]. Wang et al. applied
phosphoester-polyethylene glycol-based hydrogels for the encapsulation of
MSCs and their subsequent osteogenic differentiation [311]. This hydrogel is
hydrolytically degradable. The presence of phosphate groups in the hydro-
gel promotes the osteogenic differentiation of MSCs and autocalcification in
addition to responding to the cell-secreted osteogenesis-related enzymes. The
above studies demonstrate the requirement of suitable material properties
and chemistry of scaffolds along with suitable growth factors and adequate
degradation kinetics for the proper differentiation of MSCs.
Another cell line that could potentially be used for musculoskeletal tis-
sue engineering is the embryonic stem (ES) cells. Embryonic stem cells are
termed as pluripotent due to their versatile differentiation potential. How-
ever, controlled differentiation of ES cells into a particular lineage poses
a grand challenge. Recently it has been reported that the encapsulation of
ES cells within a scaffold system could increase its differentiation efficiency
and allow formation of three-dimensional tissues (Hwang et al, 2005, per-
sonal communication) [72, 317, 318]. Guiding the differentiation of ES cells
using a biomaterial scaffold is currently a relatively unexplored area, which
has great potential in tissue engineering.
