NANOFIBER TECHNOLOGY FOR CONTROLLING STEM CELL FUNCTIONS AND TISSUE ENGINEERING - Micro and Nanotechnologies in Engineering Stem Cells and Tissues - page 42

surface of scaffolds to increase cell-surface interactions, eventually increasing the
rate of mineralization. 91,92 Human ESC-derived embryoid body cells were cultured
in the presence of osteogenic supplements such as ascorbic acid and beta-
glycerophosphate (BGP) for 14 days, and dexamethasone was added to this medium
for another 24 h. The stimulated cells were further seeded onto poly(lactic acid)
(PLA) scaffolds and implanted subcutaneously to the back of immunodeficient mice
for 5 weeks. Discrete areas of mineralization were observed, and osteocalcin was
expressed by the implanted cells. 93 The cell-cell interactions and bone morphogenic
proteins secreted by primary bone-derived cells stimulated human embryonic stem
cells (hESCs) into osteogenic lineages in a direct coculture system. 94 Cell extracts
derived from hESC-derived osteogenic cultures induced undifferentiated hESCs into
osteogenic lineage. 95 Electrospun nanofibrous scaffolds have been successful in
supporting the maintenance of chondrocyte phenotype and chondrogenic induction
of stem cells. 96 These nanofibrous scaffolds have given hope for cartilage tissue-
engineering applications. Chondrocytes seeded on electrospun scaffolds have shown
increased proliferation within 3 weeks of culture than the controls. Increased
chondrocytes proliferation, differentiation, and attachment have been studied in
nanofibrous scaffold by Li et al. 97 The differentiation of stem cells to chondrocytes
on nanofibrous scaffold was comparable to an established cell pellet culture. It was
advantageous to use nanofibers rather than a cell pellet system, owing to their better
mechanical properties, oxygen-nutrient exchange, and ease of fabrication. Cheng
et al. reported that human cartilage cells attached and proliferated on hyaluronic
acid nanocrystals homogeneously dispersed in PLA and that collagen fibers of
110-1.8mm diameter supported chondrocyte growth and infiltration. 98 Chondro-
genesis of MSCs was supported on 3D porous aqueous-derived silk scaffolds,
forming cartilage-like tissue with spatial distribution of cells and ECM, with
expression of chondrogenic genes, and zonal architecture resembling the native
FIGURE 2.7 Confocal microscopy image of PLLA nanofibers (a) and PLLA/PBLG/Col/
n-HA nanofibers (b) showing dual expression of both ADSC specific marker protein CD 105
and osteoblasts specific marker protein osteocalcin. Arrows indicate the characteristic
cuboidal morphology of osteoblasts shown by the ADSCs that have undergone osteogenic
differentiation on the PLLA/PBLG/Col/n-HA nanofibers at 60 magnification. Reproduced
with permission from Ref. [102].