STRATEGIES TO ENGINEER ELECTROSPUN SCAFFOLD ARCHITECTURE AND FUNCTION - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 298

electrospun around extruded microfibers. When the electrospun
fibers are deposited loosely to facilitate cell migration 41 ,the
microfibers serve to increase the mechanical properties of the scaf-
fold. In contrast, when the fibers are deposited densely (e.g., Fig.
15.2),themicrofibersmaybesubsequentlyremovedtoimprovecell
penetration into the scaffolds.
15.3.3 Incorporation of Porogens into Electospun Meshes
Researchers have endeavored to create pores by the incorporation
of soluble porogens into the electrospun scaffolds. For example, the
laboratories of Dr. Tae Gwan Park (KAIST, South Korea 42 )andDr.
Joseph Freeman (Virginia Tech, USA) have tried to incorporate salt
particles into the developing electrospun scaffolds. This approach
appears to increase cell density. 42 Recently Leong et al. 43 examined
theeffectofsimultaneouslygrowingicecrystalsonthemadrelwhile
electrospinning. By varying the humidity they could vary the size
of ice crystals and consequently the size of macropores. Both their
in vivo and in vitro data indicate cell infiltration throughout 50-
150-micron-thick scaffolds. However, the use of porogens to create
macropores decreases in the mechanical properties of the resultant
scaffolds. 43
15.3.4 Chemotaxis and other Considerations Regarding
Cell Infiltration into Electrospun Meshes
It is worth mentioning here that increasing the size of pores and
channels in electrospun meshes may not necessarily translate into
spontaneous cell infiltration. Chemical cues are often required to
induce cells to migrate (i.e., chemotaxis), and in the absence of
such stimuli cells may preferentially accumulate at the outer sur-
faces of biomaterials. It has been demonstrated previously that
cells seeded uniformly in foam scaffolds will—under static cul-
ture conditions—depopulate the scaffold interior and accumulate
at the scaffold surface, but will remain uniformly distributed when
culture medium is perfused through the scaffold. 44 , 45 These find-
ings suggest that cells prefer to grow on the external surfaces of