Artificial Scaffolds and Mesenchymal Stem Cells for Hard Tissues - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 156

help for patients with diseased organs. The increased demand for organs caused by
a variety of different reasons, for instance cancer, infectious and metabolic dis-
eases, or degeneration due to old age, cannot be covered by donation. Regenerative
medicine, a new research field dedicated to rebuilding damaged organs and tissues,
may provide alternatives in the future.
An interesting and rather new approach in regenerative medicine is the use of
stem cells (SC), promising with their capacity for self-renewal and organ repair an
unlimited source of material. But cells in vitro do not grow in three dimensions,
but in a monolayer, and an organ with its highly regulated structures and various
cell types cannot easily be constructed. Even simple tissues such as bone still
provide obstacles which have to be overcome before tissue or organ replacement
with SCs can be successfully applied in patients.
Musculoskeletal disorders such as osteoporosis, osteoarthritis, and bone
defects represent major health problems worldwide with increasing incidence
due to extended life expectancy and new recreational behavior. Critical-size
bone defects, such as conditions after limb-preserving tumor surgeries and
trauma-based osseous defects, still remain a huge challenge for reconstructive
orthopedic surgery. Due to lack of alternatives, autologous bone transplantation
is still the gold standard for treatment of osseous defects but, on the other hand,
the sources of supply for autografts are limited and associated with several
problems including infection risks, severe additional pain and donor site mor-
bidity. Guided tissue regeneration with undifferentiated or differentiated SCs
might be an alternative.
The necessity for tooth replacement is another widespread problem in industrial
nations. The combination of tooth decay, formerly known as dental caries, and
periodontal diseases has led to ten million lost teeth per year in Germany alone.
To produce a stable implant often requires bone reconstruction and to achieve
regeneration of the periodontium, the formation of the soft and mineralized con-
nective tissues (root cementum, connective tissue fibers, bone) is required. Several
therapies, such as implantation of autografts, allografts, alloplastic materials, or
guided tissue regeneration, have been evaluated. However, results vary widely and
are largely unpredictable [ 1 ].
For both approaches, cells and scaffold materials with specific characteris-
tics are indispensable. The cells should be available in abundance, preferably
from the actual patient, to avoid undesired immune reactions. For this, SCs
seem to present the best source. A functionalized scaffold with appropriate
design to provide skeletal mechanotransduction for increased proliferation and/
or enhance site-specific differentiation for the SCs used, thus leading to
osteogenesis and bone remodeling, is the aim which must be met for the three-
dimensional (3D) cell support material. And finally the interaction mechanisms
between the biological organism and the cell-loaded scaffold must be explored
to produce a customized tissue replacement with good potential for clinical
implementation. The status quo for SCs and scaffold materials is discussed in
the following.