Biomedical Engineering Reference
In-Depth Information
the pluripotent nature and self-renewal capability of hematopoietic stem
cells (HSCs) has also been considered as a potential stem cell source for
tissue engineering. However, their potential as a source for cell-based therapy
has not yet been fulfilled because these cells are difficult to expand
in vitro
in clinically relevant numbers. One of the reasons for this poor yield is the
absence of a single cell surface antigen which may allow their identification
and optimal culturing conditions. However, studies in this direction are
now providing important information for their use in clinics (Hines
et al
.,
2008).
in a different approach, human dental germ pulp has also been used as a
source of haematopoietic CD34
+
stem cell population capable of differentiating
into pre-osteoblasts (Graziano
et al
., 2008). these cells were allowed to
adhere to PLa/PGa scaffolds without pre-expansion in culture and then
transplanted into immunocompromised rats, subcutaneously. Histology
showed ectopic bone noduli formation after 60 days. in addition, the presence
of platelet endothelial cell adhesion molecules and von Willebrand factor
immunoreactivity suggested neo-angiogenesis within nodules. importantly,
these vessels were HLa-1
+
and, thus, clearly human in origin. this study
suggests that CD34
+
cells obtained from dental pulp may be used for
engineering bone without the need for prior culture expanding procedures,
offering the advantage of angiogenesis, a key factor in the long-term survival
of newly formed bone.
indeed, the vascularisation of bone tissue engineering constructs is a
key factor in ensuring their integration in large bone defects with no risk of
ischaemia. angiogenesis could be promoted by seeding tissue engineering
scaffolds with a co-culture of osteoblasts and endothelial cells. However,
as discussed for osteoblasts, the use of differentiated endothelial cells
suffers from limitations such as their limited availability and proliferation
capability. advances in stem cell technology have enabled researchers to
derive endothelial or endothelial-like cells from stem cells or other precursor
populations (Kim and Von Recum, 2008).
From the analysis of all these aspects linked to the use of stem cells,
it emerges that the future of bone tissue engineering may depend on the
ability to regulate the pathways of cell proliferation and differentiation in a
biochemically, spatially and chronologically tuned manner. this tuning may
include technological strategies for:
∑
homing circulating connective tissue progenitor cells by stimulation with
growth factors, drugs and other bioactive molecules
∑
modifying the biological performance of connective tissue progenitor
cells by means of genetic modifications.
Cell engineering is therefore likely to become a fundamental tool in
delivering clinically performing tissue engineering constructs. in addition to
