Biomedical Engineering Reference
In-Depth Information
Pore Size and Porosity
Small pore size in an electrospun scaffold is one of the known limitations of nanofiber
meshes, since it restricts cellular infiltration, nutrient delivery, waste removal, and tissue in-
growth [86]. Although the electrospinning parameters can affect the pore size [87], there are
numerous mechanisms for increasing the average pore size of electrospun scaffolds.
Combining electrospinning with a salt leaching technique is a promising way to control the
macroscopic porosity and pore size of delaminated structures through the amount and the
size of salt crystals embedded into the electrospun scaffold. Cryogenic electrospinning is
another method in which ice crystals are used as templates to create electrospun scaffolds
with large, three-dimensional interconnected pores. Another potentially useful approach
involves reducing the packing density of the electrospun scaffolds during the fabrication
process, or alternatively, decreasing the packing density post-electrospinning by employing
an ultrasonication method to mechanically separate the fibers, resulting in greater pore sizes
and enhanced cellular infiltration. Electrospinning of sacrificial fibers along with stable
fibers can also present larger pores after removal of the sacrificial fibers [86]. Thus these
simple modifications of electrospinning procedure help to overcome the limitation of small
pore size while maintaining the fibrous morphology of electrospun scaffolds.
Bioelectrospraying and Cell-Electrospinning
The processing of suspensions containing living cellular materials is an emerging field of
research that is rapidly and constantly evolving [88], and this has been performed by electro-
spraying or electrospinning [89] and are referred to as bioelectrospraying or cell-electrospinning,
respectively [90]. These techniques could be useful methods to deliver cells
in situ
into
three-dimensional scaffolds, so as to improve cell infiltration and distribution within the
scaffolds [91]. Both bioelectrospraying and cell-electrospinning have been investigated for
many different cell types, ranging from both immortalized and primary cells (including stem
cells) [92]. In order to maintain a high percentage of viable cells, it is essential that cells expe-
rience minimum or no stress/damage. Subsequently, these viable cells may be deposited for
the creation of a pre-organized cellular structure. The post-treated cells must demonstrate
complete absence of any cellular perturbations from a molecular level when compared to
respective native cells. Any aberrations that could lead to carcinogenic alterations in the cells
would be quite detrimental to the subsequently engineered tissue [93].
Assessing Cellular Viability
Recent studies have reported successful electrospraying of several mature cell types, including
smooth muscle cells, neuronal cells, kidney cells, lymphocytes, and even multicellular organ-
isms. While more than 70% of the electrosprayed mature cells have been shown to remain
viable in these studies during short-term culture over a period of 1 week, few studies have
attempted to bioelectrospray stem cells [91]. For the successful application of electrospraying
in stem-cell handling, it is essential that the viability and biofunctionality of stem cells are not
adversely affected. Preserving the viability, proliferative ability, and multilineage differenti-
ation potential of bioelectrosprayed bone-marrow-derived mesenchymal progenitor/stem cells
(BMSCs) indicated that bioelectrospraying could be safely used as a progenitor-/stem-cell
delivery technique for tissue engineering. Combined with the technology of electrospinning,
bioelectrospraying has the potential to create nanofibrous scaffolds with a uniform three-
dimensional distribution of multipotent BMSCs for applications in tissue engineering and
