Biomedical Engineering Reference
In-Depth Information
individual ages, but their ability to proliferate
remains the same [
only stem cells or one factor alone were
used [
]. Therefore, for
repairs in the elderly, more stem cells have to
be harvested; alternatively, allogenic cells can
be used.
Although the effects of aging on the ability
of human stem cells to form tendon and liga-
ment are unknown, an intradonor rabbit study
utilizing BM-MSCs extracted from animals
1
39
,
110
].
An exciting use of adult stem cells in mesen-
chymal tissue engineering is to take advantage
of subtle differences found among cells from
different body sites [
44
]. Shi and colleagues
recently described the isolation, characteriza-
tion, and propagation of stem cells from dif-
ferent regions of adult human dental tissues
that, when combined with appropriate scaf-
folds, developed into tissues resembling bone,
dentin pulp, and cementum [
95
,
101
years of age found no statistically
signifi cant differences in the mechanical pro-
perties of tendon regenerated by cells from
the younger and the older animals. The stem
cells from the older animals, however, exhib-
ited reduced mechanical properties. Therefore,
banking stem cells early in life for later use may
lead to a better outcome. When the clinical
and biomechanical factors involved in tendon
and ligament differentiation are understood,
tendons and ligaments grown from adipose
or bone marrow cells are likely to become
commonplace.
and
4
]. From an
industry perspective, multiorigin stem-cell-
engineered tissue poses signifi cant intellectual
property and regulatory hurdles for those who
are brave enough to attempt to bring such
tissue to the medical community. Ultimately,
however, this approach may provide the regen-
erative capacity needed fully to restore or
replace a damaged organ.
These considerations lead to what is perhaps
an obvious conclusion: as tissue engineers
identify and implement the essential multi-
factorial requirements for growing new or
fi xing old mesenchymal tissues, the full thera-
peutic potential of stem cells may ultimately be
realized.
105
1.8 The Answers Are on
the Horizon
Bone, cartilage, tendon, and ligament engi-
neered from stem cells hold great promise to
reduce suffering resulting from orthopedic
injury and disease. With proper selection of
stem cells and an appropriate supply of envi-
ronmental signals, outcomes approaching
100
References
1
. Abdel-Hamid M, Hussein MR, Ahmad AF, Elgezawi
EM (
) Enhancement of the repair of meniscal
wounds in the red-white zone (middle third) by the
injection of bone marrow cells in canine animal
model. Int J Exp Pathol
2005
% recovery may become possible. Indeed,
mesenchymal tissue-engineered therapies that
use novel combinations of scaffolds, stem cells,
and differentiation factors are being reported
almost monthly.
These novel approaches represent attempts
to overcome the limitations of conventional
stem-cell delivery systems. For example, replac-
ing collagen with silk fi bers generates porous
silk fi broin scaffolds that are biodegradable
and stronger than collagen scaffolds and that
can support higher rates of human stem-cell
differentiation than can conventional scaffolds
[
86
:
117
-
123
.
2
. Aggarwal S, Pittenger MF (
) Human mesen-
chymal stem cells modulate allogenic immune cell
responses. Blood
2005
105
:
1815
-
1822
.
3
. Alhadlaq A, Elisseeff JH, Hong L, Williams CG,
Caplan AI, Sharma B, Kopher RA, Tomkoria S,
Lennon DP, Lopez A, Mao JJ (
) Adult stem cell
driven genesis of human-shaped articular condyle.
Ann Biomed Eng
2004
32
:
911
-
923
.
4
. Altman GH, Horan RL, Lu HH, Moreau J, Martin
I, et al (
) Silk matrix for tissue engineered
anterior cruciate ligaments. Biomaterials
2002
23
:
4131
-
4141
.
5
. Asakura A, Komaki M, Rudnicki M (
) Muscle
satellite cells are multipotential stem cells that
exhibit myogenic, osteogenic, and adipogenic differ-
entiation. Differentiation
2001
]. When BM-MSCs were loaded onto a
biodegradable scaffold embedded with DNA
that encodes an osteodifferentiation factor
(BMP-
75
,
76
68
:
245
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253
.
6
. Aust L, Devlin B, Foster SJ, Halvorsen YD, Hicok K,
du Laney T, Sen A, Willingmyre GD, Gimble JM
(
) and a proangiogenic factor (VEGF),
greater amounts of properly vascularized bone
were formed than when scaffolds containing
4
) Yield of human adipose-derived adult stem
cells from liposuction aspirates. Cytotherapy
6
2004
:
7
-
14
.
