Stem Cell Differentiation Depending on Different Surfaces - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 273

They confirmed that the geometrical shape of the surface adhesion area affects the
cell differentiation behavior. A pattern array with various geometries, including
octagon, pentagon, right triangle, square, trapezoid, and triangle, has been
designed to cultivate hMSC. Analytical analysis of adipogenic differentiation was
performed on days 3, 5, 10, and 14. Striking differences were found in the rate of
differentiation depending on the geometrical shape. To exclude the possibility that
the surface area and therefore the population density influences the differentiation,
the area of each pattern was calculated for comparison. In summary, it could be
stated that only the pattern geometry has an influence on the adipogenic differ-
entiation rate, but not the pattern area. However, a too low pattern area and
therefore a decreasing cell population does not result in cell differentiation.
As shown earlier, differentiation requires a minimum cell density [ 69 ]. The results
of Luo et al. [ 23 ] presume that total differentiation within one pattern is elicited by
the cells on the periphery of the pattern, which seem to be able to sense the edges
of the pattern geometry [ 66 , 67 ]. Future work will use high-throughput screening
analysis tools to study the correlation between pattern geometry and various
differentiation directions.
4.5 Composite Materials
Composite materials combine synthetic inorganic materials with naturally derived
components [ 22 ] to construct a stable and bioactive matrix. The combination
of two components allows a precise adjustment of biomaterial properties. Four
different strategies to manufacture composite materials are well known (Fig. 3 ):
1. The mechanical mixture of a polymer and a ceramic component
2. The embedding of bioactive molecules
3. The application of microspheres
4. Surface functionalization
The most common method to fabricate composite materials is the mechanical
mixture of a polymer and a ceramic component. The interaction of an organic and
an inorganic component seems to be very attractive to regenerate hard tissues,
such as bone, because these composite matrices mimic natural bone. HAP and
b-tricalcium phosphate are often used as inorganic components since they are
considered to be osteoinductive. Mostly, they are mixed with the polymer as
nanoparticles or microparticles.
The embedding of bioactive molecules into a suitable matrix is another inter-
esting approach for stem cell differentiation. The goal is to control the release of
signal molecules, for example, growth and differentiation factors. The release
should be dose-dependent and exact in time and location. Different natural and
synthetic polymers, such as poly(lactic-co-glycolic acid) [ 70 , 71 ], gelatin [ 72 ],
alginate [ 73 ], and fibrin [ 74 ], have been investigated for this application. These
modified polymers can be combined with synthetic inorganic materials such as