CONSIDERATIONS ON THE STRUCTURE OF BIOMATERIALS FOR SOFT- AND HARD-TISSUE ENGINEERING - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 531

have been combined with BMSCs, which enhanced vascularization
of the regenerated tissue. 48
26.3.5.2 Growth factor incorporation into scaffolds
Results from clinical studies have shown that the process of bone
regeneration is relatively long and may continue more than one
year after cell transplantation. The time for cell transplantation is
not a goal but the beginning of more complex phenomena taking
place in the body, including cell-to-cell and/or cell-to-biomaterial
interactions. Unfortunately, the fates of the transplanted cells and
the detailed regenerating process have not been well documented,
especially in humans. Transplanted cells play an important role
initially, but there are likely many other factors playing roles in
laterstages.Thetransplants(transplantedcellsandscaffolds)inter-
act with host-derived cells, which affect degradation of the scaf-
fold. The process could also be regulated by local growth factors/
cytokines.
Anexcitingapproachfornovelbiomaterialsforbonetissueengi-
neering is the generation of slow-release drug delivery systems
for growth factors/cytokines. 49 These are released from the scaf-
fold to establish a favorable environment for bone regeneration,
rather than a permissive effect of the location. Growth factors can
be directly immersed in ceramic-based scaffolds. When the scaffold
is a composite of synthetic polymers, the polymer can function as
a slow-release device by controlling the rate of degradation of the
polymer. The factors are expected to coordinate with transplanted
cells to regenerate bone. Investigations into the mechanism should
facilitate this approach in the future.
26.4 Conclusions and Outlook
This article has focused on scaffold design almost exclusively from
a clinical point of view, and we selected small-caliber blood vessels
and alveolar bone as examples of tissue engineering. It is one of our
aims to emphasize the importance of effective discussions between
material scientists andclinical teams.