Application of micromixers - Micromixers Fundamentals Design and Fabrication - page 334

FIGURE 9.6
Parallel lamination gradient generator: (a) device concept; (b) generated concentration distribution; and (c) cell
spreading after subjecting to a nonlinear EGF gradient [55] .
Another important factor affecting axon guide is the mechanical stiffness of the substrate. Generating
a concentration gradient in gel matrices with controllable stiffness could open up new tools for
investigating axon guidance.
Stem cells are special types of cells that can grow into any specialized cell type in tissues and
organs. Several biochemical and biophysical factors control the differentiation of stem cells. A
gradient generator can be used to control the spatial and temporal distribution of cytokines and growth
factors. Chung et al. used a parallel lamination gradient generator to form a stable gradient of a growth
factor mixture of epidermal growth factor, fibroblast growth factor 2 (FGF2), and platelet-derived
growth factor (PDGF) [60] . Human neural stem cells (hNSCs) are grown into astrocytes in this
environment. The differentiation of hNSCs shows a clear dependence on the concentration gradient of
the growth factor mixture ( Fig. 9.7 ). Amadi et al. used a free-diffusion gradient generator to investigate
the differentiation of embryoid [61] . The cells were grown in a 3-D collagen matrix under a concen-
tration gradient of morphogen.
Angiogenesis is the growth process of new blood vessels from existing vessels. It is a vital
process in growth, development, and wound healing. However, angiogenesis is also a key step in
the transition of tumors from a dormant state to a malignant one. Controlled concentration gradient