Biomedical Engineering Reference
In-Depth Information
Polymer solution reservoir
(b)
(a)
High-voltage power supply
Syringe pump
Nozzle
Charged fiber jet
(c)
Grounded plate collector
FIGURE 20.5
A schematic illustration of a typical electrospinning instrument. Parameters that affect the
electrospinning process include (a) polymer concentration, viscosity, fl ow rate; (b) accelerating voltage; and
(c) distance between nozzle and spinning atmosphere.
the electrostatic forces in the solution overcome the surface tension of the solution, and a thin jet of
charged solution is ejected toward the oppositely charged target (Figure 20.5). The high surface
area to volume ratio of the jet allows effi cient solvent evaporation and further thinning of the jet.
Processing parameters have a direct effect on the electrospun polymer fi bers. These include solution
concentration and viscosity, polymer fl ow/feed rate, spinning atmosphere, accelerating voltage, and
tip-to-target distance [60].
Unmodifi ed poly(lactic-
co
-glycolic acid) nonwoven nanofi brous membranes did not produce
a signifi cant reduction in adhesions compared with control groups. The ineffectiveness of the
poly(lactic-
co
-glycolic acid) meshes was attributed to the substantial shrinkage of the nanofi ber
scaffold caused by the hydrophobic nature of poly(lactic-
co
-glycolic acid) when exposed to body
fl uids. The shrinkage reduced the tissue surface area effectively covered by the membrane, allowing
an increased frequency of adhesions to form in the animal model studied. To overcome this problem,
poly(ethylene glycol)/poly(d,l-lactide) was blended with poly(lactic-
co
-glycolic acid) to modify the
hydrophobicity of the electrospun membrane. The hydrophilic PEG-PLA diblock copolymer main-
tained good membrane dimensional stability, resulting in effective coverage of the injured tissue
surfaces and a signifi cant reduction in the frequency of adhesions observed.
The barrier properties of the nonwoven nanofi brous membranes were further improved by
incorporating antibiotics into the membranes. The antibiotic (cefoxitin sodium) was slowly mixed
into the polymer solution before electrospinning. Although the role of antibiotics used in preventing
adhesions remains uncertain, medicated barriers that locally delivered cefoxitin sodium exhibited
excellent results for the prevention of adhesions [59].
