Tissue Engineering: Focus on the Musculoskeletal System - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 215

Electrospun nanofibers
Electrospinning is a method of fabricating unlimitedly long nanofibers (100-
200 nm in diameter) from a viscous polymer [103]. An electrospinning plat-
form consists of a syringe, a direct current (DC) power source connected to the
needle of the syringe, a syringe pump to extrude polymers, and a grounded
plate to collect polymers. During fabrication, the polymer extruded from the
syringe needle is highly charged (10-100 kV) by the DC power and is stretched
by electrostatic repulsion between the polymer molecules; the electrostatic
force induces a jet of polymer toward the grounded plate. Before reaching the
grounded plate, as a result of charge repulsion the polymer jet performs a
whipping motion, which leads to elongated, thin polymer fibers of submicron
diameters. For most applications, the fibrous polymer should be solidified
after being deposited onto the grounded plate; this can be achieved by using
either a molten polymer that turns solid at room temperature, a dissolved
polymer that rapidly dries, or a pre-polymer that solidifies in a post-crosslink-
ing. Compared to other scaffolding materials, electrospun nanofibers have an
advantage of higher mechanical strength; the electrospinning process allows
creating nanofibers from organic or inorganic materials of high Young's mod-
ulus. Nanofibers woven from strong, synthetic materials, such as poly(lactic-
co-glycolic acid) (PLGA) and polycaprolactone (PCL), have been intensively
used to create electrospun scaffolds for bone regeneration [103].
In addition to synthetic polymers, electrospinning has also been applied
to fabricate scaffolds from natural materials. Rnjak and coworkers [104] cre-
ated a synthetic elastin scaffold from human tropoelastin and tropocollagen.
Human dermal fibroblasts adhered to and proliferated across the electro-
spun nanofibers and deposited extracellular matrix proteins, such as type
I collagen and fibronectin. The mechanical modulus of the created elastin
scaffold was 0.3-1 MPa, which is comparable to the strength of human skin.
The application of electrospun nanofibers is normally for 2-dimensional cell
cultures; sheets of nanofibers could be applied to suturing surface tissues,
such as at artery walls. To explore the application of electrospun sheets in
3D, Panseri and coworkers [105] created a cylindrical grounded collector
to weave PLGA/PCL nanofibers into tubular sheets or tubes. Their report
shows that the electrospun tubes effectively induced nervous regeneration
of the severed nerve tracts in a rat model.
Conclusions
While significant progress has been made in musculoskeletal tissue engineer-
ing research, translating these technologies into tissue engineering products
has been slow, and a huge lag remains between research findings and commer-
cially available products. Further research is needed to address the challenges,