Bioactive Glass-Based Coatings and Modified Surfaces: Strategies for the Manufacture, Testing, and Clinical Applications for Regenerative Medicine - Biological and Biomedical Coatings: Processing and Characterization - page 422

and other topological features can be precisely controlled to encourage cellular adhesion,
migration, and proliferation. Research exploring this technique has focused on electro-
spinning of polymeric solutions to produce nonwoven fiber mats [65]. Over the past 5 years
there has been continued interest in producing bioactive nanofibers using sol-gel derived
glasses, where the charged sol is ejected onto a charged collection substrate (see Figure
9.20) [60-62, 64]. As the metal capillary is charged by the high voltage bias, the sol-gel solu-
tion is ejected from the tip, forming a Taylor cone. The sol-gel spirals downward, bending
and stretching to produce ultrathin fibers. Factors such as capillary/collection substrate
distance, voltage, and solution viscosity can be altered to produce fibers of various diam-
eters. Fiber orientation is changed by changing the orientation of the collection substrate
(e.g., dual rings or rotating drums).
Kim and coworkers [64] were the first to describe the production of potential sol-gel-
derived bioactive glass nanofibers using electrospinning. Limiting sol concentrations to
1 to 0.25 M, continuous and uniform fibers were produced. Thermal stabilization of the
fibers resulted in a reduction (by a factor of 2-3) in fiber diameter due to burnout of poly-
meric precursors. They were able to produce average fibers diameters of 630 to 84 nm (see
Figure 9.21).
Apatite formation was observed after 3 days of immersion in SBF coupled with dramatic
changes in surface morphology.
Interestingly, using fiber compaction followed by thermal treatment (700ºC), they were
able to bundle these fibers. Electrospinning coupled with warm stacking at 80ºC was used
to create a nanofibrous membrane and exposed to the same thermal treatment. In a carbon
mold, the membrane and bundles were stacked to produce 3-D constructs followed by the
same thermal treatment. To further stabilize the scaffold, it was impregnated with PLA
and pressed at 120ºC.
In 2009, a completely new method (laser spinning method) for producing bioactive glass
nanofibers was presented by Quintero and coworkers [65]. Using a laser spinning method,
a mesh of disordered intertwined fibers (glass fibers in diameters ranging from 200 to
300 nm) were produced from melt-derived bioactive glasses (45S5 composition and 52S4.6
composition). Laser spinning is an exciting, simple method because it does not rely on
chemical processing (e.g., sol-gel formation) and does not need any chemical additives.
It involves melting, via high powered CO 2 laser, a glass substrate, where the melt droplet
is blown off the substrate via a compressed airflow. During this stage, the droplet is elon-
gated and cooled producing the amorphous nanofibers (see Figure 9.22).

Sol-gel solution reservoir

High voltage power
supply

Metal capillary

Taylor cone

Bending instability region

Collection screen/substrate

FIGURE 9.20
Schematic of electrospinning method [63].