Biomedical Engineering Reference
In-Depth Information
and length of ~27 nm and then the nanorods were blended with poly(vinyl pyrolidone)
(PVP) to form composite nanofibers by electrospinning. The MSCs were well attached to the
HAp fabric substrates after culture for 24 h [70]. The same approach has been used to electro-
spin aligned nanofibrous PCL/PLLA/nHAp (nanohydroxyapatite) composites, and human
unrestricted somatic stem cells (USSCs) were seeded into the nanocomposites. Results
showed that stem cells were viable in the matrices [71]. However, higher HAp content in the
poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/HAp nanocomposites decreased the
MSC proliferation rate [72], while a blend of PLGA, collagen, and HAp nanoparticles was
electrospun for fabricating nanofibers, which supported MSC adhesion and spreading [73].
Composites consisting of nanoparticles of 20% Hap and 80% β-tricalcium phosphate (TCP)
and PCL were fabricated to demonstrate cell proliferation was inversely proportional to the
nanofiber roughness [74].
Multiwalled carbon nanotubes (MWNTs) have also been explored for their potential to
form nanocomposites. The MWNTs were encapsulated into PLLA nanofibers to provide
three specific enhancements to fibrous tissue matrices: modified fiber size, electrical conduc-
tivity, and increased mechanical strength. Adipose-derived human MSCs were integrated into
the PLA nanofibers with 1 wt% MWNT and were viable after day 14. The proliferation rate
of the hMSCs increased drastically by day 14 and MWNTs in the nanocomposites promoted
MSC proliferation [75].
As well as nanofibrous nanocomposites, nanocomposites can also be made from incorpo-
ration of nanoparticles or nanofibers into microporous hydrogels or macroporous sponges.
A thixotropic polyethylene glycol (PEG)-silica gel was prepared by combining multi-arm
PEG with hydrolyzed tetraethoxysilane (TEOS). The viscosity of thixotropic nanocompos-
ites decreases under stress and returns to its original situation after stress removal. Good
nutrient and gases delivery through the matrix improved proliferation and viability of MSCs
over 3 weeks [76].
Electronspun nanofibers can also serve as fillers in the macroporous structure to form a
new type of nanocomposite. Poly(glycolic acid) (PGA) nanofibers were formed as a sheet and
added as a layer within the collagen sponge. The sheets noticeably improved the compressive
strength of the collagen sponge. More cardiac stem cells (CSCs) were adhered to the collagen
sponge with PGA nanofibers than with the sponge alone. Nanofibers also promoted cell
proliferation [77].
Surface-Modified Nanostructures
Introducing nanofeatured elements such as nanotubes or ultrathin layers on the surfaces or
modifying their topography using nanopatterning techniques are other applications of
nanotechnology in stem cell three-dimensional culture (Table 14.2).
Nanopatterned surfaces with different topographies can be achieved through synthesis
methods or introduction of nanostructures to the surfaces. For example, di-block copoly-
mers of polystyrene and poly-2-vinylpyrindine or poly-4-vinylpyrindine formed dot-like
(6 nm) or worm-like (3 nm) surface nanotopography, respectively, via controlled microphase
separation. The worm-like surfaces supported greater human mesenchymal progenitor cell
proliferation. More elongated cells and thicker ECM deposits were found on the worm-like
surfaces [78].
Nanotopography of the surfaces can be changed by coating nanomaterials onto the
surfaces. Nanotubes on the matrix surface improved cellular tracking, sensing of microenvi-
ronments, delivering of transfection agents along with scaffold enhancement [79]. Carbon
nanotubes provided the needed structural reinforcement for tissue scaffolding [80-83] and
