Biomedical Engineering Reference
In-Depth Information
distance, and the physical properties of the solution. The unique characteristics of electrospraying
for atomizing a liquid offer several advantages over other techniques. These characteristics include
[3,45-47] (1) the relatively easy instrumental setup; (2) ability to perform in an open atmosphere
without the need of a sophisticated chamber; (3) the generation of controllable particle sizes in a
narrow distribution; (4) high production effi ciency due to the direct ejection of charged particles
onto the collector under an electric fi eld; and (5) well-dispersed particles due to the self-repellence
resulting from the electric charges on the particles.
11.2.8 F
ABRICATION
OF
B
IOLOGICAL
M
ATERIALS
11.2.8.1
Drug Deliver y Carriers
Signifi cant effort has recently been devoted to the development of novel technologies for prepar-
ing drug delivery carriers by either localized or targeted delivery in a cost-effective, versatile way.
These technologies offer suitable means for delivering small molecular weight drugs as well as
macromolecules such as proteins, peptides, or genes [48-50]. Traditional drug-delivery carriers
are not the most effi cient formulations for a given product and novel delivery carriers are required
to optimize effi ciency and minimize side effects of the delivered agents to the tissues [51]. Bio-
degradable micro- and nanoparticles have attracted signifi cant attention as carriers for delivering
low-molecular mass drugs and macromolecule proteins. These particles in a micrometer or nanom-
eter size range can be prepared by using solvent-evaporation emulsion and spray-drying methods
[52,53]. The methods using ultrasound and air pressure can result in the agglomeration of the biode-
gradable polymer particle, making it diffi cult to control bead size and uniformity. Electrospraying
has been considered as a promising technique for preparing drug-delivery carriers. It is a simple
and cost-effective method for preparing polymer particles with controllable microstructures in a
desired particle size. The biodegradable particles prepared using electrospraying have a fairly nar-
row size distribution and are well-dispersed because of the electrical repellence. Compared with
conventional methods for preparing drug-delivery carriers, electrospraying is capable of preparing
micro- and nanoparticulate drug-delivery systems such as microsphere and microcapsules in which
the biological agents are encapsulated into biodegradable polymer particles.
11.2.8.1.1
Drug Delivery
Drug delivery remains an important challenge in medicine and various fabrication techniques have
been used to develop novel processing to generate size-controllable and well-dispersed delivery
carriers with high encapsulation effi ciency in the last decade. The micro- and nanometer deliver-
ies through novel technologies for small molecules, proteins, and DNA, among other things, have
advanced the development of new and effi cient therapeutic treatment.
Ding et al. prepared poly(ε-caprolactone) (PCL) particles encapsulated with the anticancer
drug Taxol using the electrospraying technique [7]. PCL has been used as the polymer matrix of
controlled drug-release devices because of its biodegradable, biocompatible, and highly crystalline
properties. The solution was prepared by dissolving PCL in dichloromethane solvent. The mixed
precursor containing PCL solution and Taxol was injected into a chamber through a spraying
nozzle using a syringe pump at a constant fl ow rate. A schematic diagram of the setup is shown in
Figure 11.9. High voltages were applied to the spray nozzle (
V
n
) and the copper ring (
V
r
) around the
nozzle to generate a high electric fi eld to electrospray the precursor for generating fi ne droplets. The
function of the grounded corona needle was to supply the ions to discharge the droplets or particles.
The electrosprayed droplets were transported to the collection fi lter by a cross fl ow of nitrogen.
PCL particles prepared using electrospraying have a smooth surface and uniform morphology with
a uniform size distribution, as shown in Figures 11.10a and 11.10b. Particles collected from the
side wall of the chamber, grounded needle, or spraying nozzle usually have a similar morphology
and microstructure as those collected from the fi lter, as shown in Figures 11.10e and 11.10f. The
morphology of particles became comparatively smoother with an increase in concentration of the
