Biomedical Engineering Reference
In-Depth Information
produce growth factors [
610
]. Others have genetically modified MSCs to express key signaling
and transcription factors of cartilage to investigate their ability to help regenerate cartilage [
612
,
613
]. Recently, mechanical stimulation has also been used in directing MSCs to a chondrogenic
linage [
475
,
513
]. Despite this progress, it remains to be seen whether the pursuits with MSCs will
demonstrate the generation of tissue that has the biomechanical wherewithal of native cartilage, or
that MSC-derived cartilage can provide long-term solutions to cartilage pathology [
614
].
Knowledge gleaned from the differentiation of MSCs has been applied to other adult stem
cells. Similar chondrogenic differentiation of adipose derived stem cells [
615
] have been performed
with TGF-
β
1 and BMP-2 [
616
], and, recently, the role of hydrostatic pressure has also been im-
plicated [
506
]. Hydrostatic pressure applied at 0-0.5 MPa and 0.5 Hz resulted in a higher rate of
matrix accumulation than controls. Adipose stem cells are attractive because they are relatively easier
to obtain than MSCs. An even less invasive cell source would be the derivation of multipotent der-
mal precursors [
617
,
618
]. Chondrodifferentiation of dermis-derived cells has been seen by seeding
these cells onto demineralized bone matrix [
619
] and in combination with growth factors [
620
], as
well as using a surface coated with aggrecan [
582
]. Subsequent purification of the starting skin cell
population has yielded tissue engineered constructs that stain throughout for collagen type II with
absence of collagen type I staining [
301
] and improved collagen type II expression over un-purified
cells.
5.1.3 CHONDROGENICDIFFERENTIATIONOF ESC
The evidence remains scarce regarding the use of ESC for cartilage tissue engineering strategies.
Much of the evidence supporting the use of ESC for cartilage tissue engineering comes from work
with mouse ESC [
608
]. The chondrogenic differentiation of these cells has been demonstrated
in
vitro
using BMP-2 (2 ng/ml; 10 ng/ml) and BMP-4 (10 ng/ml) [
591
]. Their phenotypic stability
in a differentiated state has also been investigated [
591
,
593
]. Others have also been able to differ-
entiate ESC into a chondrogenic lineage with the use of special culture conditions with growth fac-
tors [
588
,
590
], without growth factors [
592
], and in co-culture with limb bud progenitor cells [
589
].
An example is the use of hydrogels with mouse ESC that were chondrogenically differentiated with
TGF-
β
1 or BMP-2 [
621
]. Recently, hESCs were differentiated into mesenchymal precursors, which
can be subsequently chondrogenically differentiated with TGF-
β
3 (10 ng/ml) [
599
]. For instance,
ESC can be exposed to TGF-
β
3 (10 ng/ml) to form hyaline-like cartilage through a mesodermal
lineage [
588
]. Recently, the use of differentiated hESCs for tissue engineering has been pursued in
a modular approach. That is, cells are differentiated as a first step and then, after dissociation and/or
purification, assembled into tissue engineered constructs [
308
]. Since past studies have shown that
culturing stem cells under serum-free conditions may result in a lower mitotic index for cells, apop-
tosis, and poor adhesion [
622
,
623
], these studies are particularly notable since the differentiation
is performed in serum-free conditions. Another study has demonstrated the musculoskeletal differ-
entiation of human embryonic germ cells; here, a chemically defined chondrogenic differentiation
medium with 1% serum and with one of two differentiation factors, BMP-2 and TGF-
β
3, was
