CELL - BASED NANOCOMPOSITES AND BIOMOLECULES FOR BONE TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 556

Laser-treated coral materials showed a signifi cant level of ALP activity
on day two of culture but at later culture stages (days 21 and 28), ALP activity
was signifi cantly reduced as compared to control samples. These results implied
that low level laser irradiation quickens the differentiation of MSC into an
osteoblastic phenotype during bone formation processes in early culture periods,
whilst at later stages, cellular response and bone maintenance by osteocytes are
predominant 99 .
Mygind and co-workers studied the effect of different pore size of the coral-
line hydroxyapatite scaffolds and found out that scaffolds with an average pore
size of 200

m showed a greater rate of osteogenic differentiation based on
increased ALP and enhanced expression of osteogenic markers such as osteocal-
cin, BMP-2, BSP-I (bone sialoprotein-I) and so on than a 500

μ

m pore - sized scaf-
fold 100 . In this study, they had also showed that slightly fewer but more
differentiated cells were found in the 200

μ

m pore - sized scaffold. These scaffolds
reached full confl uency more quickly than bigger pore-sized scaffolds, owing to a
higher degree of cell-to-cell communication, resulting in a higher rate of osteo-
blastic differentiation.
On the other hand, a signifi cant number of less-differentiated cells, that is,
higher proliferation was associated with the bigger pore-sized scaffold, possibly
due to its higher surface area to volume ratio, which could have facilitated cellu-
lar adhesion on day one of culture. Other probable reasons were that more cells
are needed to fi ll up the voids in these bigger pore-sized scaffolds for 3D confl u-
ency, and that stimulated fl uid fl ow aided in the proliferation process. By subject-
ing the constructs in a dynamic spinner fl ask as compared to a static cultivation,
superior proliferation and differentiation of the cells within the scaffolds were
observed, as seen in Figure 16.5. Osteoblast matrix production was more promi-
nent in constructs that underwent dynamic cultivation 100 .
Chastain et al. showed that MSCs isolated from adult bone marrow
in 3D PLGA scaffolds expressed and maintained greater osteocalcin gene
expression than in PCL over a period of fi ve weeks. They hypothesized that
the differential adsorption of certain ECM proteins in the serum- containing
culture media and integrin-mediated attachment may be the reason of this dif-
ference. Type I collagen seemed to favor MSC adhesion to PLGA. However,
vitronectin enhanced the attachment of MSC to PCL. Greater ALP activity
was observed for the PLGA group after two weeks, suggesting osteogenesis
was more predominant in the Type I collagen-mediated attachment of MSC
to PLGA (more osteoconductive) than in vitronectin-mediated MSC attachment
to PCL.
Chastain et al. acknowledged that the conformation and specifi c integrin-
binding motifs in the ECM proteins and not just the identity of the ECM protein
were some factors that modulated osteogenesis 101 . Other reasons for the prefer-
ential adsorption of the ECM proteins could be the wettability of the polymer,
surface chemistry, nanotopography, and so on 102 - 105 .
The MSCs fate to an osteogenic lineage was said to be dependent on
certain cues, such as cell shape, which could be regulated by, for example, Rho A

μ